Conference unifix::sailing

    I don't have any RADAR tricks but I am very interested in your comments
    since I am considering purchasing a RADAR this spring. I absolutely
    agree with the three element strategy for navigation. I use dead
    reckoning and LORAN most of the time and rarely miss ATN by more than a
    quarter mile. I want to put a RADAR on beccause I spend most of my time
    in Maine and sometimes dealing with the fog becomes tedious. I want the
    RADAR to get that extra level of confidence while navigating in fog and
    to eliminate the search time for ATN's when its really thick.
    
    I have a 30 ft. sail and I've pretty much narrowed my coice down to the
    APELCO 9910 and the Raytheon R10. Since the R10 is about $400 more than
    the 9910 I am wondering if the increased resolution is worth the cost.
    I can't believe that there is much difference between the two units
    other than target resolution. I am not expecting to see a vivid coast
    line at eight miles out, I just want to see a RADAR reflecting nun at a
    half a mile. 
    
    Considering your experience with the 9900 (and anyone elses experience
    with smaller sets) how valuable is increased resolution? Are ther any
    other sinificant differences in usability between LCD and CRT RADAR
    displays?  

    Ref .1 and others considering purchasing radar:
    Does it make any sense to consider three or four of us purchasing a
    good radar unit?  My only problem is that I would only use it for 
    infrequent trips to Maine, Nantucket, etc.  For most of the season, my
    Loran keeps me happy as a clam in, well, mud.
    Sure, we would probably want to duplicate wiring, possibly the antennna
    stand, etc., but I would be much more willing to pay out $300 - $400
    than $1200 & up, for the use I would get out of the unit. However, I
    agree, when you do Maine, life gets thrilling after four or five hours
    of dead-reckoning.  (I didn't even have my Loran when we last did our
    Maine trip. Also, I plan to remember Alan's comments about Loran
    offsets when we do again venture down East.)
    

	This note is very timely.  I have decided to get the Furuno 1720
because of:
	1) the dealer resides in the marina
	2) the professionals seem to like the Furuno gear
	3) I like the quality and design of my Furuno LC90 loran
	4) I sail out of Ebenecook Harbor (Boothbay Maine)
	5) it takes 3 amps when not in standby

	I figure that the loran and dead reckoning will be my main navigation
strategy, and the radar will be mainly for collision detection, and ATN
locating, but then I'm new to the game.

	Thanks for the experienced comments.  I will keep them in mind
as I learn use the hardware.  I like the idea of the grease pencils.

	Could an instant camera be used to capture approach specifics?
The sketch would probably be just as effective and a lot cheaper.  HMmm,
I guess I'll have to get a binder for a radar 'log'

	Question for those with experience:

Are you under sail power or auxilary power when using the radar.  If its that
foggy, is it usually that windy to sail, or do you feel more comforable to
run under power to keep course lines between specific buoys?

	Dave

	I have been looking at RADAR sets off and on for a few years now...  The
one difference between the APELCO, Raytheon and Foruno that I am trying to
nail down (maybe at the NE Boat Show) is target resolution...  I learned to use
RADAR on military sets, and remember the 'strength of signal' on a target as a
useful peice of information...  My understanding is that on digital sets, the
strength of the return may be lost...  APELCO makes no reference to this that I
remember...  Raytheon says they have 'target expansion' whatever that is, and
Foruno states they will report 4 different return strengths, indicated by
brightness I believe...  This can be a useful feature when approaching a coast
that has beach with a high bluff behind it...  You should get different strength
returns, which with a chart, will give you a better range off the beach (the
range you want)...  Personally, my thinking has been to avoid the APELCO, as the
$400 ($300 stays in my mind) diff for the Raytheon, or even the $600 for the
Foruno would be money well spent...

    re .3 I am fascinated that in fog someone would be using an electronic
    aide and Dead Reckoning (DR) and not Estimated Position (EP) Just
    to ensure it is not the "two nations divided by one language" syndrome.
    DR = distance run at course steered, EP=DR with tide and leeway
    applied. In fog surely it is critical to be plotting the tidal vector
    and leeway vector. In terms of sail or power in sea fog there is
    potentially enough wind thus it can be safer as the hearing is enhanced
   ?????? Last season we were followed out of Treguir in Brittany by
    a Halberg Rassy with Radar fitted and because of the large number
    of rocks and bouys around the entrance channel had difficulty in
    establishing what was what, for their home port of Lymington and
    varios other regular ports they had some 35mm photo's taken and
    then enlarged, seemed impressive anyway. 
    
    Confused of Reading ......(UK that is not Pennsyslvania!)
    
    Pete
     

    RE .5  Pete, I think that it may be just semantics;  that the
    references to DR are really shorthand for "piloting", which is ploting
    your DR course, DR positions, EP positions, fixes, running fixes and
    all that.  
    
    I practice I have seen everything used from simply ignoring current, to
    "plug in 10 deg to the left for current and leeway", to a formal plot
    that includes the current vector. 
    
    As to the topic at hand, I've sailed a couple of times on boats with
    radar, and even it situations where radar would have given the answer
    (such as finding an unlit bouy at night) we didn't turn it on.  Don't
    know why, but it probably has something to do with lack of familiarity. 
    If you don't use it all the time, you won't be ABLE to use it when
    you really need it.
    
    Travis Belton
    really need it.

re .4:

Target resolution, as I understand it, refers to two related concepts: 

First, the size of the image on the radar screen should, ideally, be 
proportional to the size of the target. That is, a VLCC should have a 
huge image and a buoy a very small one. My impression is that the images 
for most targets are more or less the same size. Obviously, radar 
reflectors confude the radar -- a good reflector will make a small 
sailboat look like a 100' steel fishing trawler. 

Second, resolution refers to how far apart two targets must be before 
the radar will display them as separate targets. Far apart means the 
distance perpendicular to the line of sight from the radar to the 
targets. 

I don't think that signal strength, per se, has anything to do with 
this.

>First, the size of the image on the radar screen should, ideally, be 
>proportional to the size of the target. That is, a VLCC should have a 
>huge image and a buoy a very small one. My impression is that the images 
>for most targets are more or less the same size. Obviously, radar 
>reflectors confude the radar -- a good reflector will make a small 
>sailboat look like a 100' steel fishing trawler. 

	I think the Furuno and 4 levels of display intensity in attempt to 
reflect received signal strength on a raster scan display.

	Dave

RE: .7,

>>>  My impression is that the images for most targets are more or less 
>>>  the same size. 

I've spent only a few dozen hours peering into a radar screen, but 
remember how useful it was to think of signal reflection as analagous to 
one with light.  A long low island viewed end-on may show the same target 
display as a 50' fishing boat beam-on, for instance.  The key feature here 
is arc of view.  Fortunately all buoys are narrow (small arc) and thus 
necessarily show up as points on the screen.

The other useful thing to remember in distinguishing some boats from 
islands, or more usually one island from another, is that a high bluff 
island face will tend to present a bright line on the screen whereas an 
island that starts low and gradually gains the same altitude over a mile 
away from shore will tend to have a less bright but deeper (bigger)
display image. I found the topo features on charts to be extremely useful
when using radar in Maine for this very reason.  It's one instance where
radar can actually give you information you can't easily get on even the
sunniest of days. 

>>>  ...a good reflector will make a small sailboat look like a 100' 
>>>  steel fishing trawler. 

Isn't it wonderful?!  

>>>  I don't think that signal strength, per se, has anything to do with 
>>>  [resolution].

Only to the extent that a stronger signal produces more return (if the 
receiver is commensurately sensitive), which may display features sooner.  
The most important factor in resolution probably isn't signal strength or
even reception sensitivity as much as it is antenna size.  Does anyone
know how much resolution theoretically improves if one goes from a 24" to
a 36" antenna width (all else being equal)? 

J.

	Re Target resolution...  As I recall, and this is going back a ways, so
correct me if I'm wrong, but on the perfect infinite resolution screen the
accuracy of the size of the image and the ability to seperate two close targets
is a function of the range and the wavelength of the transmitted pulse...  Of
course the non-perfect reolution 10" digital screen will then present the target in
discrete sizes, thus 'losing' some info re size and seperation...  I now
suspect that this is what Raytheon deals with as target expansion...  If you
zoom the target, you get an image where screen resolution is less of a
limiting factor...  Anyone know if this is what they are doing???


	The return strenght issue is a bit different...  On an analog screen
the bouy, being metal and perhaps having a radar relector, will show as a
small bright image...  The 25' fiberglass sport fisherman anchored in the
channel will show as a weak spot pretty close to the same size, simply because
not enough of the radar transmisions bounced back...  Looking at the display,
you can tell which is which (assuming you use it often enough to recognize
the situation)...  This is the type of info I would hate to lose in a digital
display...  Hence the view that the money for the Foruno, assuming the raytheon
and apelco don't have any return strength differentiation, would be well spent..


	Still investigating that perfect function zero cost RADAR set....


The Wanderer

	For the sake of comparison, can you give us the screen size and
resolution on the 1830???  Also a rough quess as to the range when shapes
become distinquishable for say a 50' boat???  Any other info of like sort,
maybe hieght of your antenna, what you see as a real usable max range, stuff
like that???


Thanks...

    re: resolution and range
    
    Everything I am about to say is with regard to the signal quality,
    INDEPENDENT of the display quality.
    
    Resolution comes in two flavors with RADAR.   Azimuth resolution is
    mostly a function of beam width of the antenna.  Range resolution is
    mostly a function of pulse duration.   
    
    To get narrower beam width you need a larger antenna array.   So if
    a vendor is claiming better azimuth resolution look for increased
    antenna size.  This is a function of physics so don't let a salesman
    BS you.
    
    To get shorter pulse duration you need higher bandwidth in the system.
    This won't neccesarily show up as anything physical, only in the price.
    Look for a set with a good low range (like 1/4 mile range).  This will
    have ( by default ) good bandwidth built in.
    
    I wouldn't buy based on long range specs.  This is only required for
    warships.   Anything over 16 miles is a waste of money (your horizon
    will be more like 15 anyway) and batteries.   This is a rare case when
    more is worse!
    
    re: Display
    
    More is Better!  Buy the largest practical display.   It will help with
    resolution (relative to a small display) and generate far less fatigue.

	The Furnuo 1720 is a 16 mile radar with minimun transmit power.  The
effective range is a lot less than 16 miles.  This is the reason I'm putting
the radome on a 10' mast on the transom.  This gives me about the same height
above the waves as a lot of power boats.  The added height of a mainmast
installation would be useless with this radar, plus worring about those 50
fine wire connections every time the mast is stepped.

	The beamwidth is 5.7 degrees horizontal.  This isn't great, but
then the radome is 40cm with a weight of 10 pounds.

	Around display resolution:  The display is a 7" diagonal crt.
This size display is compensated for by moving the center of the display
down from the center of the display, and not displaying the entire sweep.
The results are that you see the entire range of the sweep at the top of
the display.  The sides and bottom are squared off.  This gives more detail
on the screen at the cost of not seeing all the way out on the sides and
astern.  Seems like the right compromise

	time will tell

	Dave

    I have had a Furuno 1830 since last April. This was the first model
    year for the 1830 targeted at the Raytheon models in the 3K range. Like
    many of my purchases I opted for the higher costing unit because my
    long range plans include more than just N.England coastal cruising.
   
    Antenna is mounted on Mast 35-40ft above waterline. 1830 has a 10' inch
    screen and claims 24m range. I can't really comment on actual range..I 
     mostly use it from 1/4 to 6 miles and am never too interested in any-
    thing beyond that yet. I can say that I could spot the significant 
    features of Nanktucket at the edge of the 12 mile range this summer.
    Ferry targets were easily visible at various distances on this range.I
    really haven't done any rigorous testing of range, target size and 
    discrimination, etc. Perhaps a fun experiment for this Spring!
    
    This unit has many features including:
    
    1. as opposed to the Raytheon 2nd set of range & bearing markers, this
    system has a Track ball which moves a cursor on the screen and displays
    range and relative bearing(mag bearing with optional fluxgate) of
    target at cursor position.
    2. Loran interface, if your loran has nema180/183 output it will
    display current waypoint as dotted circle at the end of a dotted line
    emanating from centyer of screen.
    3. Echo mode which leaves a low intensity trace of moving targets over
    time, this supplements, but should not be considered a replacement for
    collision avoidance plotting.
    
    - On quantitization
    
    The relative signal strength of the returning signal is a function of
    the target's absorption/reflectivity of radar signals and to some
    extent the target's size. Shore areas which rise slowly from sea level
    will usually return weaker signals than more vertical shore profiles,
    etc.In older analog sets this was evident in the brightness of the trace.
    The 1830 has four level quantitization which basically means it will
    display a target with four different levels of brightness based on an
    algorithm which is primarily a function of return signal strength.
    
    There are various opinions about this...some say the quantitization
    causes some weaker, but perhaps important targets, to drop in and out on
    successive antenna passes because of low level and varying return
    signal strength.....some say the variation in target brightness helps
    distinguish target differences, particularly shore areas may show up
    more like chart representations of them. I know that on a foggy return
    to Boston Harbor both Long Island and Spectacle Island almost mirrored
    their chart representation on the display of the 1830.
    
    I have heard that better algorithms and 8-level quantization are on the
    way and may resolve the disadvantages presented.
    
    - Using Radar/Knowing how to use radar(re: reply #6)
    
      I followed the advice of a friend and every time I go for a sail (and
    sometimes just when I sitting in the harbor), I turn on the radar for
    a while and look at the screen and then visually observe the targets to 
    see how different types of targets present themselves on the screen.
    Consequently the first time I needed it I was very comfortable with my
    ability to interpret the display. The old adage of practice, practice,
    practice....
    
    - Target shapes
    
    On the 1830 I have found different types of targets to be very
    distinguishable. Buoys show a very distinctive radial dash with crisp
    edges and corners whereas vessels are usually more oval shaped.
    Sailboats with radar reflectors don't show up as the 'size' of larger
    vessels but show more brightly than boats without reflectors. Perhaps
     this is due to quantization which prevents 'blooming' of the target.
    
    While sailing in Cape Cod bay I have been also able to monitor the
    approach and directions of rain squalls. A nice bonus!
    
    
    
    regards
    
    Tom
      

    	I use an Apelco 9900 on my 22' power boat. Admittedly I puchased it
    because of its price ($659), but I also liked its small size,
    ruggedness, resistance to the elements and relatively low power 
    consumption. I would think these virtues would be welcomed in a sailboat 
    as well. 
    	I don't run the unit long when I'm not under power because of the
    battery drain and I would imagine that the CRT or Analog units would draw 
    a lot more.  
    	I primarily use the unit to keep me off the rocks and out of the way 
    of others in the fog, which is a constant feature of Maine boating. Even 
    though the image resolution is poor it serves these purposes very well.
    	The 9910 has three times the pixel density and offers a few of the 
    more standard features so I would think that it would be something
    worth considering. 
    	I guess if the price wasn't so good I wouldn't have considered the
    unit but in my case a low end RADAR in the boat is better than a high end 
    unit on the shelf in a chandlery.
    Regards,
    Paul  
    	 

    Powerboat Reports did a write-up in their June 1, 1989, Vol.2, #11
    issue on low cost radar set, under $1800.00. They compared the 
    Apelco 9910, Furuno 1720, Goldstar 930 and 951, Raytheon r10 and
    Ray Jefferson m-12c. Its been awhile since I read the article but
    I believe they didn't really feel any of them were very good because
    of the range resolution and horizonal beanwidth restrictions. 
    I tend to disagree with their conclusion, I've been using a Raytheon
    R20 for three years and wouldn't be without a radar. 
    
    Steve

    Hi all - The token Power Boat here,
    
    	I have a Raytheon R20 on my 34' mounted on the fly bridge and
    am VERY PLEASED with this unit.
    
    	It has a 16 mile range ---
    	So what my horizon is about 3.5 miles so the normal display
    	is from around 3.5 to 12+ miles depending upon the height of
    	the target.  Also I never use it for more than about 3 miles
   	as it really serves no purpose good navigation techniques haven't
    	covered.   Use it for close in navigation and collision avoidance.
    
    	It felt to me in reading some of he above comments that there
    is often a confusion between "resolution" and it's "presentation".
    As commented (in.13 I think) the resolution is dependent upon the
    beam width & therefore the antenna length.  If the beam is too wide
    targets will run together.  Narrow is better.
    
    	The presentation is dependent upon - the screen size (to make
    it easy for us older types to read - & the pixcel array/raster/etc..
    depending uopn the type of display (to differentiate the targets
    to the same level to beam reported.   
    
    	Now for Raytheons "Expansion" -- a reasonable beam has reported
    a reasonable signal, digitized it, and put it on a reasonable display; 
    however, the lonely bouy your looking for is very small and not
    readily perceptible by your old eyes -- so some random programer
    said "hey if they want lets light up a few more pixcels around the
    target - easy to do since it's all digitized"  so all the targets
    look a bit bolder.  Simple as that.
    
    re: Al's comment in .7 regarding a radar reflecter making a small
    boat appear bigger -- not really true (in all cases)
    The reflecter will return a stronger signal - but remember now days
    it's digitized and (given the beam width thing) is still a "small"
    return -- i.e. it definitly there; but, no larger.
    Indeed a big boat with areflecter might look like a dot if not much
    of the hull reflected (just the reflector) or like a big boat(island?)
    if the hull does reflect - and the digitizing will hide the variance
    in signal return strength.  (this is where some units play the
    brightness game.)
    
    	One last comment I really agree with -- Use it! Use it! ---
    It is hard to read a display well at all; but, there are two catches
    First - you had better seen a display before, under a range of
    conditions, etc..   i.e. Use it!
    Second - All unit are very dependent upon how they are tuned  -
    and this is every time the unit is turned on and different from
    day to day.   Use it!
    
    Well - I made it between the jetties in Kennebunkport last Aug.
    before I could see them with the naked eye -- I like my Radar 8>)
    
    			Think Spring,
                                      Lou

    For anyone considering the Furuno 1720 and/or 1830. Be aware that
    Furuno is supposed to be producing a new unit called the 1730. If I
    remember right, it's got some of the additional 1830 features at or
    near the 1720, price. 
    
    Possibly this will show up in some of the 1990 catalogs which should be
    on the way.
    
    J_R

	I just talked with my Furuno dealer, and the 1730 uses 4 amps of
power in transmit, has a bigger radome, and he thought that the display
was the same as the 1720 with no additional feature, but then he hadn't
really studied the liturature either.

	If its just a bigger radome and more signal, I'll stick with the
1720.
	Oh yes, my price for the 1730 is $650 more than the 1720.


	Dave

p.s.	 The comments from radar users is great!! Thanks for the info

    
RE: .1

Hi Ken,
There may be a number of differences between the R10 and 9910 that might
be worth considering.

	Range on the R10 might be greater than on the 9910. If this is so,
then I believe this really translates into more reliable operation in bad
weather at the one mile range. In very heavy rain, I am not optimistic about the
capabilities of the 9900 in picking out buoys. I haven't had a whole
lot of experience with it, but moderate rain sure did slow it down.
I don't remember the exact usable range, but use for collision avoidance
would certainly be limited even with the gain and clutter control
adjusted properly.

	My display is mounted so that the helmsman can see the display
while steering. I believe the CRT would provide a brighter image 
that would be more visible to the helmsman if you chose the R10.

	Installation considerations are another area to investigate.
I believe that the maximum cable length specified for the 9900 
and most likely 9910 was 12.5 meters. If you choose to mount your dome
on the mast, it might exceed this limit. It would be worth checking
the R10 for the cable length limit.
	 Also while on this topic, most likely you will need to provide
additional cable beyond the cable supplied  with the unit.  This cable
is very costly, and should be factored into the overall installation price.
	There was also a warning about placing the dome cable near any
VHF or LORAN cables with the 9900, might be wise to check that limitation on
both units as well if you're considering the mast mount.

	Resolution has been thoroughly discussed by many of the replies
to the base note, I don't have much to add other than describe one situation
where I would have found better resolution to be of great value.
	I was approaching Damariscove Island off the Maine coast in very
heavy fog. The entrance to the anchorage is quite narrow, with submerged
shoals on both sides of the entrance. Even though there is a buoy a half
mile off the entrance, it is nice to have some verification from radar.
The radar was of minimal value in this instance because of its low resolution.

	If you're prime concern is cost, the 9910 can provide some peace of
mind in normal foggy conditions.

	I'm quite happy with the 9900 because I had realistic expectations
of what it would and wouldn't do prior to purchase. If I was making the
choice between the 9910 and the R10 I would go for the R10 (or one of
the other CRT based, higher power radars for the $400 cost difference.

	Hope this is of some help..............Rich


RE .2  Radar Sharing
	A few thoughts on this topic. Perhaps you might be better off
purchasing one of the hand held radars (formerly called Whistlers)
This would meet your price goals, plus you would avoid the multiple
installation issues such as extra cables, protection of exposed connectors
to the elements, etc.

RE .3

Greetings Dave,

	I think your instant camera idea is a good one. perhaps an
old oscilloscope camera could do the trick. I wonder how hard it would
be to adapt a low cost dot matrix printer for this purpose. I was considering
doing a book of radar images of harbor entrances along the coast.
I contacted several radar manufactures about their involvement in the project,
in terms of loaning equipment for the project,there was little interest.

Buoy to buoy?
	In general, my experience with radar and loran is that running buoy
to buoy is not always the safest approach. Often, when going buoy to
buoy this, there have been numerous other boats all doing the same thing,
and it seems like the chances for collision are increased in heavy fog as the
density of boats increases.
	I remember one trip between Scituate and Newport where it seemed
like there was a parade of boats when the fog lifted a bit. It would seem
to make more sense to go out a mile or so further, watch the parade on radar
and provide visual confirmation prior to approaching critical areas such
as the Cape Cod Canal or harbor entrances.

Motoring vs. Sailing
 	On the question of motoring versus sailing in fog, I believe there
are a number of dimensions to consider: 
size of the crew, experience of the skipper and crew, level of familiarity with the area, currents, schedule and morale.
     If you're singlehanding the boat or have one inexperienced crew, motoring
might make more sense. This would minimize the number of tasks to be done.
You can then run straight line courses between buoys (assuming wind is on
the nose), eliminate the jobs of sheet and  sail handling.
     I realize that some folks will strongly disagree with this opinion,
I'm just stating what works for me, on my boat as it is presently set up
when I'm short or singlehanding.
  Sure there are those macho folks who have an autohelm, sail through pea soup
fog alone, and can handle sails, lines,navigation, VHF communication with tugs,
keep a good watch while sounding their horn regularly and keep an eye on radar
and depth sounder simultaneously. This may work offshore, or on very long tacks
but in crowded coastal conditions it is extremely difficult.

	My perspective is that I would prefer to sail if there is decent wind
(many times wind and fog do not seem to coexist, other times watch out!)
and have an adequate crew.  Sail offers the bonus of another dimension, SOUND,
which could be of major help in hearing other boat's engines, fog horns,
or breakers that might not be heard if the engine is on. Keeping a proper
log will also help determine position while beating. In heavy fog while 
cruising in hazardous waters, log entries are made at a minimum of every 
half hour. If you tack, log it. A good log book combined with loran, radar,
depth sounder, up to date charts, light list and current tables will minimize
the navigation hassle associated with sailing in fog.

RE .5
	Sorry Pete for being so lax with the language, indeed as .6 states
our differences are only semantic.


RE .13  "anything over 16 miles is a waste of money"
	It would seem that the radar power issue is:
 Will it work when the weather is bad? As you state, the range issue itself
 doesn't mean much.

RE .15 Tom, thanks for the information on quantitization, good stuff!

Re .13 and others

The specs for Radar can be tricky to understand even when they are given.
The following may be help when you are trying to select a Radar best suited
for your expected use. Sorry for duplicate info; it's included for completeness.

Beam Width 
	Determines horizontal resolution, so narrower is better. However, at
	high ranges it may cause very small targets to be missed because the
	target is not illuminated long enough. This can be offset by increasing
	the transmitted power (sometimes called peak power or pulse power) or
	increasing the pulse repetition rate (see the limitation below).

Pulse Length
	Determines range (radial) resolution, so shorter is better. However, at
	high ranges may cause weaker reflective targets to be missed because
	the target is not illuminated long enough. Once again more power will 
	help. At very short ranges the pulse must be short in order to insure 
	that close in targets can be detected.

Pulse Repetition Rate
	High repetition rate can help improve target detection by 1) improving
	total target illumination, 2) insuring multiple hits on a small targets
	or multiple hits along the length of larger objects without gaps.
	However, the repetition rate must be slower for working at high ranges 
	to allow time for the earlier pulses to return before the next one is 
	transmitted. This is also related with pulse length.

Transmitted Power
	Determines maximum range at which weaker reflective objects to be 
	detected. In reality your maximum range is effected greatly by antenna
	height (radar is line of sight) and by the sensitivity of the 
	Radar's receiver. 

Other considerations
	Display resolution and quantization (signal strength) should be matched
	to the rest of the Radar sets capabilities (see above). Too much 
	display is wasted money and too little is lost target info.

	Many better Radars automatically swift pulse length and pulse power as
	you change ranges. Once in awhile the pulse repetition rate will also
	be changed. This can improve the overall performance and ease of use
	greatly.

	One of the effects of high pulse rates and of course pulse power will
	be to increase DC power consumed. Some manufacturer will put more 
	design effort into the receiver and keep the pulse power down. 

	Beam height (not height of the antenna) may also be important when 
	your vessel is subject to extreme rolling and pitching (or heel for 
	the sailors). This can cause the beam to be too far above or below the
	horizon to yield a useful return signal.

	As all ready mentioned in reply .13, other performance factors may be
	important to your use. For heavy weather (rain, snow or fog), your
	tradeoffs will vary from those with more routine needs. 

It is easy to see where the added expense of better Radars comes from.
  
Regards,
Jerry

    One more comment on resolution.  
    
    The basic limiting factor is the antenna length.  Short antennas,
    eg 18" radomes put out wide beams, specifically 5.7 degrees.  Long
    antennas such as professional 8 footers have a beamwidth of 0.95
    degrees.  My calculator says that at 3000 feet (about .5nm) the
    5.7 degree beam is 300 feet wide.  Or the pulse power is spread
    out over that distance.  This means not much energy is hitting that
    bouy you are trying to find and thus less energy is reflected back
    to receive.  Then there is even more bad news - the power gain of
    the antenna when it is receiving is lower because of the wide beam-
    width.
    
    So let's assume the receiver circuitry did "hear" the echo.  Because
    of the wide beam width there is a large position uncertainty, or
    you see a big "blob" on the display.
    
    So much for theory.  My experience after 6 years with a trusty Raytheon
    1200 (24 or 30 inch radome, I forgot) leads me to recommend:
    
    1. buy a radar.  At night offshore tracking bigger ships it's
    wonderful.  And, why bother with Maine without one?
    
    2. Buy the biggest antenna you can fit and afford.
    
    3. Next get the most output power.
    
    4. Finally, worry about pixels, colors, quantization, VRM's, EBL's
    etc.  (Opinion - lot's of marketing here!).
    
    Someday (soon) we'll see real time digital signal processing like
    the military has had for a while.  Then, the functionality, ease
    of use, and accuracy should make a big leap forward.
    

At the recent Boston Boat Show I spent some time looking at the Furuno 
1730 radar. It certainly appears to be an impressive unit. But .....

The 1730 draws 4 amperes when transmitting. Using it continuously would 
more than triple our daily electrical consumption. This would require a 
substantial and expensive upgrade of our boat's electrical system 
(easily over $1000 done right). Even non-continuous use would be a 
problem since today we can go about three days without running the 
engine. 

Now some questions:

The antenna rotates about, what, 20 rpm? Thus there is about a 3 second 
period between successive (groups of) pulses hitting a target. In rough 
weather, a boat can easily change heading many degrees (20 or more) in 3 
seconds. Does this cause blurring or visible shifting in the position of 
targets on the screen? Do continual heading changes make using the 
electronic bearing line (or whatever Furuno calls it) difficult? At the 
very least I would think that it would make determining if you're on a 
collision course with a target somewhat difficult and problematic.

Does anyone have any idea how the detection probability varies with 
target distance, sea state, weather, target reflectivity, etc? I'm sure 
that the radar makers would like us to think that the radar will see all 
targets, but I'm quite sure this is not so. I'd like to have a radar to
make overnight or longer singlehanded passages safer. The Furuno has a
guard zone, and any target within that guard zone sounds an alarm.
Targets inside the guard zone don't cause an alarm. The guard zone
appears to be rather narrow. So, what is is probability of detecting a
target while it is within the guard zone? The farther out the guard zone
is, the less likely a target is to be detected. The closer the guard
zone, the less time to react to a dangerous situation. What is the
tradeoff? How much assurance does the guard zone really provide? After
all, a Furuno 1730 is likely to be about $3000 installed (plus another
$1000 for electrical system improvements). While I don't much like to,
I've so far been successful at navigating in fog without radar and with
loran and dead reckoning. Is radar really worth $4000? (I'm not
convinced that the less expensive radars would meet my needs.) After
all, I could go cruising for six months on $4000. This question of
detection probability is especially important given what has been said
regarding reduction in range in fog, rain, etc. If one has radar, the
tendency may be to depend upon it too much, or to believe that it
provides more safety than it really does. After all, big ships with
radar run into each other with some regularity. 

You raise good practical questions. My Comments follow >>>>>


           <<< MSCSSE::SYS$SYSDEVICE:[NOTES$LIBRARY]SAILING.NOTE;1 >>>
                                  -< SAILING >-
================================================================================
Note 1438.24                    Radar Experiences                       24 of 24
MSCSSE::BERENS "Alan Berens"                         44 lines  27-FEB-1990 17:41
                                 -< questions >-
--------------------------------------------------------------------------------
At the recent Boston Boat Show I spent some time looking at the Furuno 
1730 radar. It certainly appears to be an impressive unit. But .....

The 1730 draws 4 amperes when transmitting. Using it continuously would 
more than triple our daily electrical consumption. This would require a 
substantial and expensive upgrade of our boat's electrical system 
(easily over $1000 done right). Even non-continuous use would be a 
problem since today we can go about three days without running the 
engine. 

Now some questions:

The antenna rotates about, what, 20 rpm? Thus there is about a 3 second 
period between successive (groups of) pulses hitting a target. In rough 
weather, a boat can easily change heading many degrees (20 or more) in 3 
seconds. Does this cause blurring or visible shifting in the position of 
targets on the screen? 

>>>> It surely does cause blurring and/or visible shifting. The display is
relative to your vessel heading. There are (for a price) features which can
help to overcome this. One is an external compass input (usually a gyro on 
large vessels) which can give you a display which has any selected heading
as a reference. Thus as the vessel moves about, the image remains steady except
of course for other objects in motion. 

Do continual heading changes make using the electronic bearing line (or 
whatever Furuno calls it) difficult? 
 
At the very least I would think that it would make determining if you're on a 
collision course with a target somewhat difficult and problematic.

>>>> It surely can. If for example you are trying to determine the CPA, closest
point of approach, it can become a two person operation. One operates the
Radar (EBL & VRM) while the other takes heading marks and records sucessive
relative bearing and ranges. After two or more points a captured, you can
quicking determine if there is a potential for collison and the CPA.

Does anyone have any idea how the detection probability varies with 
target distance, sea state, weather, target reflectivity, etc? I'm sure 
that the radar makers would like us to think that the radar will see all 
targets, but I'm quite sure this is not so.

>>>> This is an inverse square problem at best. That is, detection depends on
the receiver's senitivity threshold and the amount of energy in the reflected
beam. Since the beam traverses the target distance twice and is spreading out
all the time (inverse square) and there was considerable energy loss during the
reflection, it is easy to see how quickly the detection probability falls off
with distance. And then there are all the other factors which, as you have
already mentioned, further reduce the effectivness. 

I'd like to have a radar to
make overnight or longer singlehanded passages safer. The Furuno has a
guard zone, and any target within that guard zone sounds an alarm.
Targets inside the guard zone don't cause an alarm. The guard zone
appears to be rather narrow. So, what is is probability of detecting a
target while it is within the guard zone? The farther out the guard zone
is, the less likely a target is to be detected. The closer the guard
zone, the less time to react to a dangerous situation. What is the
tradeoff? How much assurance does the guard zone really provide?

>>>> The guard zone feature is most often adjustable. With two VRMs (variable
range marker) one is set as an near boundary and the other is set as the far
(outer) boundary. Anything detected between these extreme will sound the alarm.
Not sure how the 1730 works, but most can be set for narrow or wide zones.
My experience with the guard zone is that it is can drive you crazy with false
alarms. It can tell the difference between real targets and noise and since
you want the Radar tuned for maximum detection, noise is the order of the day.
I would never depend on a guard zone for anything other than reduce the chance
of something sneaking up on me while I wasn't looking (busy plotting).

After
all, a Furuno 1730 is likely to be about $3000 installed (plus another
$1000 for electrical system improvements). While I don't much like to,
I've so far been successful at navigating in fog without radar and with
loran and dead reckoning. Is radar really worth $4000? (I'm not
convinced that the less expensive radars would meet my needs.) 

>>>> I'm a little puzzled by this reasoning. For myself the inexpensive Radars
offer a tremendous step up in saftey during restricted visability. Alan you've
said you've been successful without it and those same techniques will be helping
you even after (if) you install Radar. The smaller Radar would also address
your power comsumption problem. You can get by with much less than 4 amps.
 
After
all, I could go cruising for six months on $4000. This question of
detection probability is especially important given what has been said
regarding reduction in range in fog, rain, etc. If one has radar, the
tendency may be to depend upon it too much, or to believe that it
provides more safety than it really does. After all, big ships with
radar run into each other with some regularity. 

True...true. Luck on your choices.
Jerry

    I have been thinking about adding RADAR for awhile and finally decided
    to plunk down a deposit on a Furuno 1720 at the show.
    
    Alan raises some fine points, I won't try to address them all but for
    what its worth my thinking went something like this. I wanted RADAR for
    increased safety and convienance at night and in the fog. Since we keep
    our boat in Maine we see almost as much of the later as the former, the
    later being far less predictable. I see the RADAR as a supplement to my
    normal navigation tasks, it will be used to confirm my EP and as
    another level of confidence that the ATN is really "just a half-mile
    ahead. Even with RADAR I wouldn't assume that there isn't another
    vessel around just because its not on the screen, if there is one on
    the screen it means be extra alert. 
    
    I have a thirty foot sailboat, in rough conditions lots of things get
    blurry so I'd suspect ANY RADAR would show what's out there jumping
    around a bit. The ability to compute collision courses and maneuver to
    avoid is not one of my concerns, if it's big enough to be seen it's big
    enough to avoid by a wide margin!
    
    I picked the Furuno primarily because it has multi-level(4 levels)
    quantization. I believe that the ability to detect several different
    levels of return signal strength will help me to better tune the set
    and perhaps not miss a weak return because I've decreased the sensitivity
    to get rid of sea clutter or rain showers. The other thing that sold me
    on the Furuno was a stand-by mode that not only stops the antenna from
    sweeping but also blanks the screen - in this mode current draw is much
    less than 1 amp. 
    
    It seems to me the only advantage for a small boat cruiser like me in
    moving up is better target discrimination and range at a cost of larger
    investment and increased power consumption.
    
    Launch date is 5/15 - I'll let you know if it lives up to my
    expectations soon thereafter!

    I bought radar (Furuno 1830) because it gives me additional navigational
    information to support my decisions, particularly in times of reduced
    visibility. I don't rely totally on it nor do I 'cut things closer
    because I have it. I guess the question is "Over the life of its use
    will it give me $4000 worth of information?". For me, the intuitive and
    perhaps not precisely defnedable answer is yes.
    
    Guard Zones
    
    The guard zone of an 1830 can be set as either all or a sector of an
    annular ring (donut) or as a circle. I have found I am able to achieve
    enough gain to discern all targets and, with the use of tuning and sea
    clutter adjustments eliminate false alarms from noise.
    
    Blurry targets in rough seas
    
    My anteena is 35-40 ft above the waterline..certainly there is some
    oscillation of the target presentations and as the boat cycles to
    leeward, target drop out of windward targets because the antenna is not
    parallel to the sea...It doesn't matter what radar you have, unless you
    gimballed your antenna, you learn to adjust and observe 2-3 passes of
    the antenna and mentally interpolate...the 1830 has a plot mode which
    leaves a faint trail of 'moving targets'...This helps remove the
    oscillation from your target trend calculations.....Since prudent
    seamanship says give a WIDE berth to potential obstacles we're not
    talking about measuring CPA's in Feet..Offshore, CPA's of less than a
    mile call for radio contact and course adjustment increase distance
    off. Coastal navigation in fog is a little trickier but I'd rather have
    approximate knowledge (oscillating) than none at all.
    
    Standby on the 1720
    
    On the 1830 the antenna still rotates in standby....I'd be surprised if
    the 1720 did not.
    
    Integrated Compass with Radar
    
    Integrating a fluxgate compass with radar was one suggestion for
    eliminating target oscillating due to rough sea...supposedly because
    you could set the display to read a specific direction up...I'd watch out
     with this one .....I don't know of any radar that features selecting
    any specific direction as up. Some allow NORTH UP, but not many, if any
    of the lowend ones do. Usually the first feature level of compass
    integration allows absolute rather than relative bearings.
    
    
    Tom
    
    
    
    this one... 

re .27:

>>    Guard Zones
    
>>    The guard zone of an 1830 can be set as either all or a sector of an
>>    annular ring (donut) or as a circle. I have found I am able to achieve
>>    enough gain to discern all targets and, with the use of tuning and sea
>>    clutter adjustments eliminate false alarms from noise.
    
How thick (distance) is the guard zone? Does the thickness vary with the 
maximum range selected or is it selectable or is it fixed? If the guard 
zone is fairly narrow, a high speed boat might cross it undetected, 
especially in rough conditions.

How do you know you see ALL targets? I can accept that you probably see
most targets, and have some (variable) probability of seeing any
particular target. This is really the critical question for me since I
would/could only justify a radar if it provided a very high certainty of
seeing any and all targets in the guard zone. The problem with
singlehanding is 'who keeps watch while I'm sleeping?' 

    Guard zone re:.-1
    Thickness of the guard zone secotr ring is 'infinitely selectable' and
    remains the same when you change ranges.
    
    The guard zone is set in the following way(its alot easier to do than
    to explain):
    
   1.  Using the track ball you place the cursor at the outer and most
    counterclockwise point of the sector you desire to inscribe and then
    you press the guard key.
    
   2. You then move the cursor inward and clockwise, an enlarging ring
    section appears on the screen. You 'drag' the cursor to the most inward
    and clockwise point (diagonal corner of a radial rectangle) you want.
    Pressing the guard key define the second point and thus the ring
    sector. If you rotate completely clockwise you define a complete ring
    of thickness defined by the range of the ending point.
    
    
    If in step two you move the cursor counterclockwise you get a circle
    (no partial secotrs and no "thickness")
    
    
    (re:.-1)  How do I know I see all the targets.
    
    In some ways your right I can't be sure I see all the targets..However I
    do ALOT of clear day practice then  I can confirm visually those target
    between me and the visual horizon. I note the target type, big little,
    fiberglass, wood, sail, power, etc. I have done this in 35 knots of
    wind and rough seas..and all visually available targets were presented
    on the radar. They might drop in and out due to mast/antenna roll but
    they were all there.

Perhaps somebody out there has more experience with this and can shed more 
light on the range issue.
                                             ______________
Books I've read claim an RF horizon of 1.22\/antenna height. These books 
specifically state that this is  valid for Radar frequencies.

Therefore It would seem to me that this is the limiting factor in Radar 
range ( I know this would treat the radar beam as a coherent beam, but I 
doubt at these distances returns from the vertical limits of the beam 
spread would get back to the antenna.)

If this assumption is true then the following table gives maximum range 
(total horizon) assuming an antenna height of 40' from WL and various 
heights of targets. Note that a 21+ mile range is not acheived until the 
height of the target is 130+ ft (that's the height of the top deck of the 
largest cruise ship in the world, 974 ft LOA, "Sovereign of the Seas").
Does all this make sense??

     Antenna     target    target     total
     horizon     height    horizon    horizon
        (nm)       (ft)      (nm)      (nm)

     7.716          5       2.73      10.44
                   10       3.86      11.57
                   15       4.73      12.44
                   20       5.46      13.17
                   30       6.68      14.40
                   40       7.72      15.43
                   50       8.63      16.34
                  100      12.20      19.92
                  130      13.91      21.63
                  200      17.25      24.97


Rgeards,

Tom

    Hmm. Not familiar with the radar frequencies, but.... there is usually
    some kind of "ground-wave", which has the effect of extending range.
    I'd be interested in an authoratative answer, though.
    
    And perhaps someone could enlighted us if there is any atmospheric
    bounce, also.
    
    Ray

    I have seen the Corsica Ferrys from 34 nm.But only during the night.
    During daylight it was less then 20 nm.I have a Goldstar 5kW with
    radom antenna.
    
    Peter

    I just completed my first season in 20 years of sailing with a new
    Apelco 9910 radar installed on a 6' stand on the transome.  Used in
    both fog and night sailing I found that I rarely used settings above
    1 mile simply because there was plenty of reaction time at the speeds we
    were traveling.
    
    The most important thing we did is figuring out how to mount the unit so
    it was visible to the helmsman and out of the weather.  We accomplished
    this by buying some L-shaped table leg brackets from West Marine.  They
    are chrome plated brass which use a thumb-nail screw to fasten the bracket
    to a base plate about the size of a postage stamp.

    We fastened 2 L-shaped brackets to the radar display unit.  Then we
    installed a pair of matching base plates on the bulkhead above the chart
    table and a pair of brackets in the lower left corner of the companionway.
    To use the unit, we simply unscrewed it from the bulkhead and screwed it
    into the companionway (using the finger operated screws).  With the hatch
    cover pulled closed, no rain got on the unit and it was always visible by
    the helmsman.

    I would like some comparison of the reliability of a Raytheon Radar
    VS. FURUNO. Raytheon has come out with an R10X radar which has more
    bells and whistles than the old R10. Primarily it has 8 levels of
    quatification, two VRMs and EBLs, and a waypoint locating circle
    when hooked into a LORAN and a fluxgate compass.
    
    Beyond the software enhance ments, I was told it has new components in
    the dome or antenna. Since this is the first year of this product I
    would be interested in others perspectives of Raytheon's quality,
    resulting in a reliable product etc.
    
    The FURUNO which I am also considering is the 1720 which I understand
    has a good track record. The FURUNO has a better display, more pixcels,
    but less software capability.
    
    The price is equal, therefore the question is quality first, and extra
    functionality second.  

There is an interesting letter in the July/August 1992 issue of Ocean 
Navigator. The author, a Circuit Court judge, points out that numerous 
court cases have held (paraphrasing a lengthy letter):

1. If you have radar, you must use it in poor visibility.

2. If you are not using it when a collision occurs, you may be liable. 
   If you are using it and a collision occurs, you may still be liable,
   especially if you cannot show you understand how to use the radar 
   properly, including plotting and relative motion. If necessary, you
   must stop and make time for plotting if the radar shows another
   vessel nearby. 

I would infer that it is not sufficient that someone aboard know how to 
use the radar properly, but that the crewperson actually operating the 
radar must know how to use it. 

Having radar is certainly safer than not having it, but it may add to 
your legal risks, especially if you sail short (or single) handed or 
with inexperienced crew. Oh well.

Alan