Conference unifix::sailing

    Never having done it personally, I would caution against this if you
    have a fin keel or a keel not adequately supported structurally.   
    
    Careening can be done by two methods, using a carrening grid and
    bulkhead as found in areas with large tidal ranges as in Europe or a
    soft and gently sloping beach area where the boat can lay down as the
    tide falls.  This is very common where possible for painting, and
    maintenance that can be done before the tide comes back up.  
    
    The latter requires better weather than the former and a lot of padding
    to keep the topsides from getting scratched.  Old tires work well for
    this.  The process usually requires a kedged anchor fore and aft, off
    shore to keep the boat square to the beach and on ashore to help it lay
    down properly.   
    
    Either way, you need a tidal range greater than the draft of your boat.  
    
    You can get a transducer mounted inside the hull usually in oil inside
    it's own container bonded to the inner hull.  There was discussion in
    here of models somewhere.  
    
    Brian

Re:            <<< Note 2159.0 by PCBUOA::MWEBER "Michael Weber" >>>
                     -< Careening 27' Sailboat with keel >-

At the risk of having my note set hidden by some sneaky moderator :-) ...

A couple of years ago I fitted a Huminbird 400.  Rather than mount the
transducer on the transom or bore a hole in the hull, I secured the
transducer on the inside of the hull with a 2 part apoxy.

I estimate that it was shooting through 3/4 inch of 21 year old fiberglass
and was accurate to 100 feet, so I lost the ability to do 400 feet (in a
body of water where only a few places exceed 100 feet).

Regards,
Keith

    I also have never tried drying out our boat, but I have seen it done at
    a permanent (non-floating) town dock in Maine (Tenants Harbor). The
    boat was tied to the dock with substantial fendering between the boat
    and dock. Halyards were taken to the far side of the dock and used to
    pull the boat against the dock as the tide went out. The trick was to
    ensure that the boat was heeled a bit toward the dock so that it rested
    against the dock once the water was gone. Clearly an operation
    involving some risk and one best done on a calm day. I'd do it if I had
    to. 
    
    Laying a boat on its side on a beach is not something I would ever try.
    As the tide comes back there is a real risk of water filling the
    cockpit, cabin, etc, before the boat begins to float. Drying out on a
    beach could be done safely with large vessels with fairly flat bottoms
    (eg, Columbus did it on one or more of his voyages to the New World as
    I recall). Doing it with a fin-keeled yacht is (IMHO) too risky to
    contemplate.

A couple of years ago I got stuck on muscle bank in Small Harbour, Maine.
As the tide went out, the boat was left on its side.
The returning tide filled me with foreboding, however the boat began
to lift again before the water even reached the toe rail.

This of course depends on hull shape. (I have a Cape Dory 25.)

I did attach an anchor rode to the main halyard to heel the boat
with the deck facing UP the slope, otherwise the 
returning tide might not have been so friendly.

I passed the time by giving the prop a good cleaning :-)

	Mike

RE: .1

I have a fin keel -- so you have a good point there. The Transducer is
presently mounted as you sugest -- in oil inside the hull -- and the
scoundrul leaks incessently. The whole of my interior (storage below
bearths, etc) has a fine film of oil on it from healing, rolling,
pitching yawing, what-have-you, and I want to rid myself of this
approach. Further, I find the gain on the depthsounder is very sensitive
when mounted inside the hull -- either I get lousy shallow water
performance (not nice -- isn't this one of the main reasons we like
these things so...) or else I get false readings when in deep 
water like *B*I*G* fish swim below me (and I'm sure they do sometimes
but not this often. I've hung the transducer overboard (secured 
with tape) and was very satisfied with it's in-water performance.

My boat has a 4' draft and my rough calculations are that the tides
in the Salem Harbor area are about 9' -- should be plenty ...

RE: .2

Epoxy'd right to the inside of the hull??!! There's a novel approach. 
How did it perform for you?

RE: .3

Yeah, Columbus did this every 4 months or so to recaulk. If you want
an interesting book to read over the winter, I sugest "Admiral of the
Ocean Sea". Did you know that the Santa Maria could have been saved?
Many interesting things and well written...

Michael
"Latitude"

Re:              <<< Note 2159.5 by PCBUOA::MWEBER "Michael Weber" >>>
                                -< Thanks all >-

>RE: .2

>Epoxy'd right to the inside of the hull??!! There's a novel approach. 
>How did it perform for you?

I think it performed well.  As I said, it appeared accurate to just over 
100 feet.  Have since sold the boat.

When installing I was careful to create a pool of epoxy and then placed
the transducer gently into the pool.  You can use that grey weather 
stripping stuff to form the sides of the pool.  The idea was to immerse
the bottom of the transducer (to a depth of perhaps 3/8 inch) and not 
have any bubbles in the epoxy (so stir gently).

Regards,
Keith

    There is also a discussion somewhere in this conf. about putting an ABS
    plastic pipe, cut and fit to the hull with epoxy and then filling the
    pipe with oil and putting the transducer in that.
    
    By all reports it seemed to work, although if I recall the discussion
    was around the best type of oil ... Oilve - 10W30 - Crisco etc.

    Mike
    
       I read an article where they said to use pvc threaded pipe for
    putting the oil into. Expoxy the pipe to the hull. Add oil. Drill a
    small hole in a threaded pvc cap, put the transducer into the oil, run
    the wires through the cap, and silcone the cap threads and hole.

    On our previous boat a BRISTOL 24 I used a piece of 6" PVC shaped on
    one end to fit the contour of the hull at the place I wanted to mount
    it. I cut the piece about 6 to 7 inches long and mounted it to the hull
    using two part epoxy making sure that it was vertical. I fashioned a
    round cap out of lexan and glued a rubber gasket on the edge that would
    be contacting the PVC. I mounted the transducer in the center of this
    cap and and lowered it into the PVC pipe. I filled the pipe with water
    with a little bleach in it to stop any growth. I secured the cap onto
    the PVC  with Machine screws into tapped holes in the PVC. This worked
    very well for the 4 years that we sailed the boat. You could use
    Mineral oil instead of water if you wanted to leave it year round. I
    was able to read depths to 300ft with no problems.I disassembled and 
    cleaned it each fall at haul out.
    
    Bob p 
   

I guess there must be air holes or such in the epoxy. It is a PVC
pipe, threaded on both ends, with one cap epoxied to the holl 
and the pipe epoxied to the cap. Filled with Mineral Oil, the
transducer is threaded through the top cap which is then screwed
into the pipe which has teflon tape on both its outer threads and
inner threads where the transducer is. 

When sitting at anchor it seems to be more accurate when hung
overboard (the transducer) than when in the Mineral Oil. In
the oil I get variations much larger than expected -- the mean
of which is what I get when it's overboard (which agrees with
a sounding line I also dropped overboard which showed 15.5 ft). 
It may be a rash deduction on my part but it would seem from 
this behavior that it's performance, in general, should be 
better in shallow waters (which is when I want it to be the 
most accurate!)

Michael
"Latitude"

    We have two depth sounders -- one with the transducer mounted through
    the hull and one inside a mineral oil-filled box epoxied to the hull.
    The depth readings from the two sounders generally agree fairly well --
    usually to within two to five feet at depths of 60 feet. The through
    the hull mounted transducer used to be mounted inside the hull. I don't
    recall any significant increase in maximum depth after mounting it
    through the hull (it is only supposed to have a 300' capability). 
    
    The reading from a depth sounder might not agree with a lead line for a
    couple of reasons. The depth sounder makes an assumption about the
    speed of sound in water, which does vary with salinity and temperature
    (whether this is significant in shallow water I don't know). And too,
    the return echo used to give the depth reading may not be from the
    surface of the bottom, especially on a soft bottom. One of our depth
    sounders is a fish finder that gives an indication of bottom density --
    the wider the depth line, the softer the bottom. Sometimes the line is
    quite wide. On an uneven bottom the depth may be from the highest area
    of the bottom or the lowest, whichever gives the strongest echo.
    

RE: .12

Presently mounted in mineral oil, I am satisfied with my depth sounders
performance in deep water. All other reasons mentioned in this thread
asside, it is also shallow water performance that I want to improve.
In my note (.10) what I was getting at was the DIFFERENCE in performance
between performance under the same circumstances. But tell me, how did
your two units perform in shallow water -- the one in mineral oil vs.
the one in water?

Michael

    re .12:
    
    When you have one depth sounder, you know how deep the water is. When
    you have two, you don't. Which one is correct? Or are both wrong?  Our
    two depth sounders give approximately the same answer in shallow water
    (plus or minus a couple of feet) when underway. I've always assumed
    that bottoms are uneven and that therefore some variation in depth
    readings  is to be expected. At anchor the two sounders generally give
    the same answer, but there may still be some variation. To use your
    example, assume that the water is 15.5' deep. My depth sounders display
    depth to the nearest whole foot. So 15.49' would be displayed as 15'
    and 15.50' would be displayed as 16' (assuming rounding to the next
    largest integer). A vertical movement of .01' is rather small. I don't
    worry too much about absolute accuracy. 
    
    Alan
    

    Alan,
    
    Surely it is more complicated than that ?  I would have thought that
    the depth sounder is only accurate to about 10-15% and that such
    factors as frequency, heeling, type of material the sound has to travel
    through, temperature of the water and type of bottom would all factor
    into the equation. I suppose that if you have two equally calibrated
    depth sounders that they should be the same or similar, but different
    types with different mountings would (I suppose) read quite
    differently.  

RE: .13

S'pose what I'm getting at is, "does the fiberglass which seperates the transducer and seawater when the
transducer is mounted inside the hull have any effect on performance?" 

Michael
"Latitude"

    re .14:
    
    Graham, absolutely, the factors you list do indeed affect the reading
    displayed by a depth sounder. However, if two transducers are mounted
    close together and the boat is motionless in shallow water, then I
    would expect that the displayed depths would be at least nearly the
    same. 
    
    By the way, I have noticed that, in my case, sounder A sometimes
    apparently receives an echo from sounder B's pulse since sounder A
    displays a clearly incorrect depth (eg, 824' when the true depth is
    about 60'). I usually only use one depth sounder at a time.
    
    Alan

    re .15:
    
    My experience, and that of others, indicates that the only effect a
    solid fiberglass hull has is to reduce somewhat the maximum depth at
    which the sounder will display a reading. The reduction is difficult to
    quantify. Our nominal 300' maximum depth sounder will sometimes not
    give a depth reading in 60' when the bottom is soft mud (or something).
    Occasionally it will display a (probably) correct depth of well over
    300'. 
    
    

    
    	A solid `glass hull will only take a little of the power away, thus
    Alan's return-strength observation. Balsa or foam core will affect it a
    bit more, but not render it useless  below, say, 50' of depth.
    Salinity, temp, etc. should not account for even 10% difference. You
    don't see a fresh/saltwater switch on fatho's. Many problems end up
    from mechanical failure; switches or connectors corroding. But then, I
    had one that I returned with a design fault; it would `lose its mind'
    now and then.
    	I have no data to support me, but I'd bet a well-epoxied transducer
    would perform as well as the oil-bath setup. If there's balsa, dig thru
    it and glue it down to glass.
    
    	Scott

    My NKE does get effected by all you mention and then some.  Most
    notably is the air bubbles when surfing off a wave.  I have seen the
    recorded depth jump by an order of magnitude during this.  The sailing
    computer recognizes improbable changes and clears the screen to reset
    the emitter.
    

	The description of a tranducer working from the
	inside of a hull with no need to cut a hole is attractive.
	Consequently, last year I purchased a Standard Communications 
	Horizon DS45 with a plastic thu-hull transducer.

	I installed the transducer inside a 4' pvc pipe that was 
	epoxyed to the hull and filled with mineral spirit - similar
	to note 2199.9

	The sounder always displayed the 'no signal' indication.
	Over the side, it gave the depth perfectly, but over the side
	in a bucket of sea water I always got 'no signal'.
	I called Standard Communications and asked if the
	in-hull puck transducer might give a better result - the
	technical person told me he was doubtful.

	Fortunately West marine took it back with no complaint.

	I may try the experiment again next year with a different model.

	Mike
	

RE: 20

This pretty much parallels my results with my DS10 (see begining of thread). 
I didn't, however,
try the bucket experiment -- neat idea. I trust it was a plastic bucket. How
far was the transducer from the bucket bottom?

I have been following this with great interest. I bought an echosounder at the
beginning of the season, and intend to mount it inside the hull to avoid cutting
through the bottom of the hull, which would be complicated on my boat by the
hull shape - the transducer would end up at about 40� to the vertical unless I
also fitted wedge blocks, etc.

I bought an inhull fitting kit - 6" or so of PVC pipe, a tube of epoxy filler,
and a sachet of castor oil. It also included a tight-fitting lid. The sounder
manufacturer recommended testing various locations in the boat to get best
performance (air in the water, possible electrical interference, etc). For
testing, they said, "Stick the transducer to the hull with chewing gum. Nothing
else - not children's modelling clay, plasticene, or anything else - use chewing
gum". The reason was to avoid air bubbles in the material which could affect
performance significantly. I cannot get my sounder to work at all like this,
although it is fine if I hang the transducer over the side. Again, I do have a
significant thickness of gum across most of the face of the transducer to get it
vertical on a steep hull side, and I am planning to actually use the fitting kit
and just glue the whole lot in at a likely seeming place without being able to
test first. I still do not know how directional the transducers are - do they
actually need to be vertical, or are they actually effective across a fairly
wide angle - presumably so, or depths would change significantly with angle of
heel?

Maybe it's my own fault for buying a cheap sounder in the first place :-)

- Brian

    Brian,
    
    Did you chew the gum first?
    
    (Sorry, I couldn't resist) ;^)
    
    Is your hull cored or solid fibreglass? Most of what I have read say
    it will not work successfully with a cored hull that is not solid
    grp.
    
    Before I mounted my transducer in a 6" pvc cleanout with mineral oil,
    (which works great, by the way), I tried sticking it to the hull with
    glazing compound. I got absolutely nothing. I would presume, however,
    that the chewing gum advocates know of some of what they speak.
    
    Can you build a dam out of something (like glazing compound), and pour
    in a puddle of mineral/castor oil just deep enough to submerge the face
    of the transducer?
    
    Bill
    

Directionality:

Sailboat transducers are not very directional, because of the need to
accommodate heel. However, if you mount it at 40 degrees off vertical, it
will probably not work very well on one tack, because it will be more than
50 degrees off vertical on that heel. The manufacturer can probably supply
you with a diagram showing the transducer's field of view.

Through hull mount vs inside mount:

My transducer is mounted through the hull. That way its performance is the
same as the manufacturer designed it to be. It is theoretically possible to
mount a transducer inside the hull, but it will work only if there are no
significant reflections from the attachment system, and if the attenuation
is not too high. Generally, there will be an echo every time you go from one
material type to another. If the materials have similar densities and
propagation speeds, and the interface doesn't have bubbles, etc, the reflections
will be negligible. It's also possible for the sound to couple into the
air inside the boat, and then echo off the boat hull and couple back into
the transducer housing. In order for the depthsounder to work properly, the
possibly weak echo from the muddy bottom must be significantly stronger than
all the stray echos coming back from the attachment system and the boat
interior.

The bucket experiment reported in an earlier reply shows how sensitive the
depth sounders are to obstructions in the signal path. The same experiment with
different shapes and types of buckets (plastic, wood, metal, fiberglass) would
probably yield substantially different results.

Most depth sounders have a delay gate that causes the unit to ignore echos
immediately after the "ping" is launched. The manufacturers like to keep the
gate as short as possible, because it sets the minimum depth that the sounder
can sense. On some units, the delay is adjustable. If all spurious reflections
come back within the delay period, the depth sounder will probably work
OK through the hull.

Wedge blocks:

If you're not planning to race the boat, this is a straightforward and
predictable solution to your problem. It will cost you some small fraction
of a knot.

--RS

RE: .22

A sonar type signal, such as what your transducer emits, simply falls apart if air
is introduced between the source and the reflection. If you have a cored boat hull
-- many fiberglass boats are -- then the only way to know for sure is to psudo-mount
the device and observe it's performance. 

Take your PVC pipe and shape it so that when set against the hull floor (Presently, mine
is near the bow under the forward V-bearth)  you get a close fit. Then apply your sealer
and mount it in place. Before the sealer dries (Silicone, epoxy, or whatever) fill the 
PVC with oil (I use mineral-oil) and drop in your transducer. If it performs to your
satisfaction then let the sealent dry. If not, put a roll of paper-towels 'downhill' of
the PVC, pull the PVC up, clean up, and try again -- remember, the sealent isn't dry yet.

The directionality of transducers varies but (excluding those fancy 'forward-looking'
fish finders) is generally between 10 and 16 degrees. Remember though, that the greater the
angle introduced - the greater the error introduced. (My Trig is rusty, anyone got any
figures for the error introduced on, say, a 15 degree tilt with a 20 foot depth?)

I started this thread with the intentions of moving my transducer to a thru-hull from
its present internal mount. Lately, however, I've been exploring ideas of mounting
the transducer on a type of gimble and putting the whole assembly in oil. This would ensure
that the transducer is ALWAYS pointing straight down irregardless of heel. 

Michael 

    Re: various recent
    
    I have never been a great gum chewer, and the task of getting through a
    full packet of 6 or 8 pieces was almost more than I could manage :-)
    
    I don't see why gimballing is relevant here. If the transducer is
    largely non-directional (as mentioned in the last couple of replies
    somewhere) then the sounder will respond when the echo gets back. If
    the pulse happened to have reached the sea bed off the axis of the
    transducer, and the echo came back the same path (the shortest path
    between transducer and seabed) the only thing you have lost is possibly
    sensitivity. The "on-axis" echo will take longer to get back and will
    be ignored, just like any echo that does not come back from the nearest
    point.
    
    I am not too worried about sensitivity. I am more concerned to know how
    far the bottom is from my keel shortly before I hit it :-). More
    practically, it would be easier to measure depth for scope when
    anchoring than the leadline (= rusty bolt line in my case). However,
    one of the previous respondent's comments re the "chewing gum" trick
    not working in his case (even if he used a chewing gum substitute) but
    having success with an oilbath reassures me, and I will give that a try
    as soon as I can.
    
    - Brian

RE: .26

>> I don't see why gimballing is relevant here. If the transducer is
>> largely non-directional (as mentioned in the last couple of replies
>> somewhere) then the sounder will respond when the echo gets back.

There is an asumption being made here that the echo WILL get back.
Most transducers have a working range of 10 - 16 degrees off center.
When heeled over within this working range I would suspect that 
the amount of error will be small at best. But what happens when
the boat heels over to something outside of the working range, say 20
degrees. (In really heavy weather, it's nice when the boat is heeling 
any less than 20 degrees!) It's at this time a gimbal could be a nice 
addition.

Michael
"Latitude"

    I remeber looking at some ultra sound transducers a couple of years
    ago.  I beleive that the trnasducers recommended for sail boats had a 
    solid angle of around 30 degrees.  Thus the sea bottom below the boat
    would still be pinged at a 3o degree heel.  Power boat transducers were
    something on the order of 5 degrees.
    
    For a given amount of energy, the smaller angle will go deeper in the 
    water.  Like wise a low frequency (50khz) will travel further than a
    higer frequency (150khz).  However the resolution will be less.
    
    Coupled with other replies found here, I come to the following
    conclusions.
    
    1.  While verticle is not necessary for a sailboat, it is desirable for 
        two differnt resons. First, what happens when you change tacks? 
    	Second, I would be suspicious of getting a "power boat" transducer. 
    	Heck, literally 90% of all boats are power, and fishfinders use
    	narrow angles too.  The resulting small market for a 30 degree
    	dispersion favors the sail boat being had.
    
    2.	Like you I am more interested in hitting something, than in
    	locating just how deep the water is.  Thus great depth is not
    	important to me.  Also I am likely to be more or less plumb when I
    	come into harbor, so perhaps a power boat transducer is not so bad
    	after all.  I must contradict this, shallow is important with the
    	following.  I have a friend who had spent a couple of years on
    	ocean cruising.  There were two areas where said money was no
    	object in exchange for performance, the head, and a deep (800+)
    	feet depthsounder.  I guess it helps find continental shelf etc.
    	and hence navigation.
    
    3.	You can tolerate a certain amount of slop in your installation once
    	you understand the implications.  Personally, I would align as
    	close to verticle as possible, and I would clean up the outgoing 
    	signal as much as possible.  I do not like to have to make mental
    	adjustments when things get busy.
    
    4.	I am probably price sensitive, more than most.  A cheap unit that 
    	reaches a 100 feet or so, will suit me just fine.
    
    Doug Claflin
    Friday is it for me.
    I can be reached at 508 635 0460 or through my wife BIGQ::MCGOWAN.
    

    Figures on effective usable angles off-axis are interesting - I had a
    figure of perhaps "usable to ~30� heel" in mind, but remembering that
    radiated power and effectiveness of reception are going to both be down
    somewhat this far off-axis, reducing deep-water performance. However,
    with a 16-footer, finding the continental shelf is the last of my
    problems :-)
    
    More practically, I can drill a hole through the hull and bolt the
    transducer in. This would give me an angle of perhaps 30� off-vertical
    (this is _not_ a flat-bottomed boat!), and would therefore be pretty
    poor on one tack. I could fit wedge blocks, which is more work, more to
    leak, and has some (but probably negligible) effect on performance. Or
    I can use the "transducer in a pipe full of oil" internal mount, which
    is easy, does not affect hull integrity, but turns a large area of the
    hull into a sounding board with who knows what radiation pattern (and
    means that I will not know what scope to give when abchoring off the
    continental shelf!). I think I will go for the latter, because it is
    easier to recover from if it all goes wrong!
    
    - Brian

    My Fishfinder (Eagle ultra ID) having just died, I bought an X55 
    of the same make, and as I now am the proud owner of three transducers,
    I thought I would try the shoot through the hull method. So I duly 
    araldited my HS-WS high speed transom transducer approx 3ft in front
     of the keel of my 25ft cabin cruiser, and as close to the centre line 
    as possible. 
    I have only been able to test it in 150 Ft of water, but I was unable 
    to spot the difference, performance wise,  with my old method of lowering 
    the transducer into the water mounted on a aluminium pole.
    This is a much neater method & I trust I'll be able to test it at
    1000ft dephts, before the fishing season closes, mid October.
    
    
    I have still to work out how to mount the speed paddle & temperature
    sensor as my transome normally rides 3 inches above the water.  
    I'm considering making a small right angle mounting bracket that I can
    fit to my wooden rudder blade... However other suggestions greatly
    appreciated...
    
    				Nick

So I'll ask.  Is there something wrong with simply mounting the transducer on 
the stern ?  I too thrashed around with thru the hull mounting and never got 
as good a result as I do from the unit placed right in the water.  Is stern
mounting not acceptable on a sailboat?

Tom

RE: .30

I have tried a stern mount on my Catalina 27 and was not satisfied at all.
On Latitude, the rudder comes right out to the end of the transom -- more
than enough to create turbulance which drive the depthsounder nuts. 

RE: .29
This turbulance also caused havoc with the knotmeter. Temperature worked 
OK though! :-)

I was trying out a loaner unit (Apelco 306 -- nice) but returned it because
of the problems mentioned above and the fact that 1) settings wern't saved
when power was off and 2) there was no way to have the units light come
on when the running lights are turned on (c'mon Apelco) so you had to
jump through all these hoops to do it (possibly with a flashlight) --
and remember the settings aren't saved so you can't leave the light on
all the time. If it hadn't been for 1 & 2 I'd have mounted the 
transducer, etc forward of the keel and kept the unit.

Michael
"Latitude"

    Assuming that the transducer is mounted vertically (when the boat is
    not heeled), I'm not sure that heeling will cause significant errors,
    especially given the all the other uncertainties and error sources.
    
    The manual for our elderly Signet depthsounder indicates that the full
    beam width is 28 degrees (ie, 14 degrees to each side of vertical).
    Maximum power is within a beam width of 18 degrees.
    
    The result of heeling is to cause the depthsounder to look to one side
    rather than straight down. The actual depth will be something like 
    
         (displayed depth) * cos(heel angle-half depthsounder beam width)
    
    For our depthsounder and a 30 degree heel angle, approximately,
    
         actual depth = displayed depth * cos(30-14)
                      = 0.96 * displayed depth
    
    If we're in water shallow enough to worry about grounding, we're not
    going to be sailing at large heel angles anyway.
    

    
    	Not only that, but if 28� is the `Full Power' beam, there are
    points of -3dB, -6dB, etc. which give you an even wider beam. So unless
    you are heeling at 50� or greater over rocks (don't laugh; this
    describes our Wednesday Twilight tactics) you really don't need to
    sweat it. If you _really_ want to navigate by sonar, you'd better
    perform a thorough calibration and contatct the manufacturer for beam
    patterns. Also laminate little cards for current and temp offsets, if
    you're talking depths greater than 250'.
    
    	Or pray that the GPS is really as wonderful as they say!
    
    	Scott

My old (Datamarine?) flash style depth sounder packed it in last summer in
Maine.  The strobe stopped spinning.  The transducer is probably still OK.

I just bought an Apleco 260 fish finder. 

What is the likely hood of the transducer working with the new head.  Are
these things tightly matched or anything like that?  I will call Apleco,
but I can anticipate their answer "We do not advise mix products ..."
The ski industry does this with bindings inspite of some really excellent
heel toe combinations.  A pox on ambulance chasers.

In lieu of using the old transducer, how are the in the hull rigs holding
up.  Holiday II is a traditional hull with a deep wine glass.  The fairing
block would be substantial.  I prefer to mount inside, next the old
transducer (a thru hull).

Doug Claflin
dtn 1-6355

Assuming you had a perfectly tight beam, the look ahead at 15 degree tilt in
20' of water would be 5'.

	lookahead = depth * sine tilt.

This of course requires a flat bottom.

In addition, the solid angle of the transducer reduces this substantially.
For example a 20 degree solid aangle effective makes the look ahead tilt
only 5 degrees.  

	lookahead = depth * since (tilt - (solid angle /2))

		  =  20 * (15 -10)

		  = 1,7 feet. (bascially zero when underway at a rock)

Very late response.  With side scaning sonar available, who cares.

Doug 
dtn 381-6355