Conference unifix::sailing

Yes, the balance of a four cylinder engine is much better than the 
balance of a three cylinder engine, and hence the four cylinder engine 
will run more smoothly. The greater smoothness would predispose me to a 
four cylinder engine.

But ....

A four cylinder engine has a few more parts than a three cylinder. Thus 
it is likely to be somewhat more expensive to manufacture, maintain, and 
repair. More parts (all else being equal) mean less reliability. 

The difference in fuel consumption between a three and a four cylinder
engine probably isn't large. The four cylinder engine should have better
air flow and combustion efficiency, but also has more internal friction.
Diesel specifications usually give fuel consumption as lb/hp/hr. Lower
is of course better. 

Overall, I'd prefer a four cylinder engine because of the smoother 
running. Diesels are rough enough at best. 

    re .1	Only a minor nit, but its my belief that sometimes more
    parts can lead to higher reliability when they are less stressed.
    I would guess that might be a factor with something that becomes
    significantly better balanced when the extra parts are added.

    	Reg
    

re -.*

For a cruising boat, parts availability may be more important than reliability.
I learned this the hard way, when a charterer bent the shaft and broke the
flex coupler on my Faryman diesel. This oddball part took three weeks
and lots of phone calls to obtain. (The diesel itself was 100% reliable during
the three years I owned it.) If you go with a common make and model of
marine diesel engine, you won't go too far wrong.

--RS

I  am looking for comments regarding the best HP for my  boat.  I 
have  an  opportunity to purchase either a 20 or  30  HP  rebuilt 
Kubota diesel engine;  the price is the same for each. Note,  the 
Kubota  is  one  of  the engines that  used  to  be  marketed  by 
Universal.  So  my question, is a 20 HP engine enough  or  should 
should  I go for the 30? But first, let me explain why I want  to 
change my present engine.

I have a 1979 Hunter 30 that is powered by a 12 HP Yanmar diesel. 
On  the last day of last season, the cylinder head gasket  leaked 
raw  salt water into the combustion chamber and I had  to  remove 
the  engine. The engine is apart in my garage and  is  repairable 
but  I am going to replace it with a larger engine because 12  HP 
is  not enough for the boat. For example, I average  between  1-3 
knots when powering into rough seas with a strong head wind. Even 
with  relatively calm seas and strong head wind, the best  I  can 
get out of the engine is 5 knots. Without the wind, the boat will 
get  up  to 6 knots. This may not seem like a problem but  I  can 
assure  you, traveling through Wood's Hole against  the  current, 
into the wind can be nerve racking and there have been times when 
I became too friendly with #4 at the Hole.

These are the engines' characteristics:

Engine #1:

The  smaller  engine  is  a Model  20  rated  for  16  continuous 
horsepower @ 2800 RPM with a maximum output of 20 HP. 

From the curves:

          torque ft-lbs        cont. HP           RPM
          ---------------------------------------------
               32                   7             1200
               34                  10.5           1600
               33                  14             2200
               29.5                16             2800

It  has 2 vertical cylinders with a 3 inch bore and 3.25  stroke. 
It  weighs  in at 365# and displacement is 45  cu.  inches.  This 
engine  is  slightly  easier for me to install  than  the  larger 
engine but I don't consider this to be the deciding factor.

Engine #2:

The  larger  engine  is  a  Model  30  rated  for  24  continuous 
horsepower @ 2800 RPM with a maximum out of 30 HP. 

From the curves:

          torque ft-lbs        cont. HP           RPM
          ---------------------------------------------
               51                  12             1200
               52                  17             1600
               50                  21             2200
               44                  24             2800
This  engine  has  3 vertical cylinders with the  same  bore  and 
stroke  as above. It weighs 425# and the displacement is  68  cu. 
inches.


I am not trying to make a "power boat" out of my sail boat but  I 
damned sure want to be able to push through Wood's Hole any  time 
I  feel like it without concerning my wife about our  ability  to 
get  through. Also, when I get stuck in crappy weather  with  the 
wind  on my nose and don't feel like tacking, I want  to  average 
better than 1-3 knots. 

Thanks in advance-

Joe Howarth

    
    You've probably already been through all these, but just for exercise,
    the considerations I can think of are:
    
    	o Size of the new engine -- will it fit in the space available
    	  and still leave enough room for everything else, including
    	  access for periodic maintenance?
    
    	o What's the difference in weight from the old one, and could that
    	  be a problem?  (Doesn't sound like it)
    
    	o Assuming you are using the old prop shaft, stuffing box, and
    	  prop, will any of those have to be changed due to the increased
    	  power?
    
    	o And the one I would be most concerned about:  The engine bed.
    	  I would think you would want to beef up the engine mounts,
    	  perhaps significantly, to handle the extra weight, torque,
    	  thrust, and vibration.
    
    The engine mounts were probably designed to be adequate for the
    original engine, but probably not for more than that, unless the boat
    was originally designed to accept larger power options, and the 12HP
    was not the biggest option.
    
    In fact, one Hunter 30 I was in had considerable vibration throughout
    the boat when the engine was running, to the extent that I would be
    concerned about the strength of the engine mount structures and
    surrounding hull area, at least in that particular boat.
    
    The problem could be exacerbated if the new engine is capable of power
    much beyond that necessary to achieve hull speed, since the extra power
    would then be spent in creating a big bow wave, with resultant strain
    on prop, shaft, bearings, and especially the mounting area.
    
    There was a story in Offshore a while back about a boat that had
    inadequate engine mounts.  The engine flexed the whole hull area around
    it so much that eventually the hull developed cracks and weakened 
    further until water started coming in, with predictable results.
    
    It should be possible to beef up the bed area if you think it needs it. 

    I would not think twice about the going for the larger engine as long
    as it fits and doesn't require moving your prop shaft.  The benefit of
    the extra torque will be very noticable in a sea.  While I primarily
    race, I had speed under power as a major factor in buying our current
    boat.  There is nothing so nice as simply knowing that if you have to
    get somewhere you can count on your engine to average 6 knots or
    better.
    
    The engine mounts are easy to beef up.  A buddy of mine is completely
    redoing a 1979 Carter designed 40 footer including replacing the
    engine.  The old engine was trashed, but too small anyway.  We built up
    the new mounts by using foam  forms and layering glass and carbon
    fiber.  The surrounding area was beefed up by putting in transverse
    stringers.  We overdid it, but since the engine was out and it was easy
    to do we erred on the side of strength.  
    
    By going to a three cylinder from a two, you will probably experience
    less vibration, but in my view many manufacturers do not spend enough
    attention on the mounts so beefing up is a great idea.  If you are
    going to do this project, the incremental time and expense will be well
    worth it!
    
    Dave

re .4:

Your problem is more than simply engine horsepower -- you also have to 
have the right propeller. If the propeller is wrong (eg, diameter and/or 
pitch too small), you simply won't get enough thrust to get the speed 
you want regardless of the engine's horsepower. I wouldn't be surprised
if you do have a less than optimum propeller. There is a book by Dave
Gerr that discusses all this. With a different propeller your present 
engine might be adequate.

One advantage of the bigger engine is that you can run it more slowly
for the same power output. Our 25 hp diesel is significantly quieter
running at 1800 to 2000 rpm (5 to 5.7 knots) than at 2400 rpm (6 to 6.5
knots). The increased noise is so obnoxious that we run the engine over
2000 rpm less than 0.5% of the time. 

Admittedly, the horsepower required increases extremely rapidly near and 
past hull speed, but I would guess that 20 hp would be ample. Based on 
fuel consumption, our boat (32' and 12000 lbs) needs about 8 hp to 
achieve 5.7 knots in calm seas. When it comes time for a new engine, I 
would not get a more powerful one.

More considerations:

I've been told by several diesel engine dealers that it is better to run
a diesel fairly hard (I'm not sure why). This would tend to say that
the 20 hp engine would be preferable to the 30 hp. 

How much does your present engine weigh? How much does the fore-and-aft
trim of your boat change with shifts in weight distribution? The 30 hp 
engine is likely a good bit heavier and may well sit further aft than 
your present engine. This will result in stern down trim. 

Using more horsepower means burning more fuel (the increase is roughly 
linear with the increase in horsepower). Will reduced range under power 
be a problen for you? 

    re:  Engine mounts
    
    It's also worthwhile to closely scrutinize the mounts and vibration
    dampening pads that come with the new engine.  
    
    A friend bought a new engine for his boat and had some misgivings about
    the small size of the "feet" and the stiffness of the rubber pads that held
    the block off from the hull.  Re-assured by the manufacturer, he
    installed the engine only to have a mount crack while on trip to Maine.
    
    It may be a good idea to check the robustness of the mounting hardware
    against that of other engines of comparable size.
    
    - gene

    I agree with .7(check prop).  A three blade prop will improve your
    performance in high wind and waves.  I have a Catalina 36 which came
    with a two blade prop and has a Universal 25XP diesel (23 HP).  I had
    problems with wind over 15kts.  I also discovered the prop was under
    pitched as I could exceed the max RPMs in smooth water by 400 RPM.
    
    Usually when you go to a three blade from a two blade you need to
    reduce the pitch by 2" or so.  In my case I used the same pitch and my
    performance was greatly improved and it now tops out at the recommended
    top RPM of 3200.  At 2800 RPM I can achieve almost 7 kts in smooth
    water and 5-6 kts in most wind conditions.  The three blade is much
    smoother than the two, more power in waves, and much better in reverse.
    
    As far as the number of cylinders, the more the smoother it will run. 
    Also the larger engine will allow more pitch, thus reducing the RPMs
    necessary for a given speed so your economy would not be greatly
    affected.
    
    A previous reply talked about engine weight.  On a 30' boat this could
    be a significant factor in boat balance.  You may be able to move gear
    in lockers to counter this.
    
    Chuck
    

    When buying my boat new in 1983, I faced a similar problem since I was
    special ordering an engine that the manufacturer did not normally
    install in my model of boat.  I opted for the larger engine (45hp vs
    35hp for a 36' boat) and I have never regretted it.  When we brought
    the boat down south we could power right thru the mud bars that
    everyone else was getting hung up on.  As far as the extra weight and
    fuel goes:  the difference in engines was 150lbs - insignificant
    for an 18,000lb displacement boat.  And for fuel usage, we have never
    used more than 50 gals. of diesel in one New England sailing season
    and we are out every weekend.  I also agree with previous replies:
    you must have the correct transmission/propeller ratios.  And with
    a bigger engine you will have a bigger propeller which may cause the
    propeller to "windmill" while under sail.  (My propeller will turn the
    the transmission AND engine when left in gear).   So you may want to
    replace your propeller with a folding prop or plan on fitting a brake to
    prevent the shaft from turning while under sail so your transmission
    bearings, propeller shaft and cutlass bearing do not wear out prematurely. 

    The comments about matching the transmission and prop reminded me of
    Fat Tuesday.  The builder had a "deal" on Isuzu tractor engines.
    He installed a 75hp engine and hooked it up to a hydraulic transmission
    rated at 40hp.  We didn't know this at first and kept blowing the
    o-rings resulting in hydraulic oil ALL OVER the interior.  Very nice!
    
    Turned out we had to keep revs under 2000.  Very frustrating to have a
    monster engine that had to be babied.  
    
    As for the prop, a three blade prop will slow you down under sail
    significantly.  Like a half knot more than your fixed blade two blade
    prop.  We have a Max prop feathering prop and love it.  Not cheap, but
    what in sailing is?
    
    Dave 

My  thanks  to Alen, Dave, Chuck, Gene, Gomes  &  Goodwin  (first 
names?)  who  took the time to respond with  their  thoughts  and 
suggestions regarding the 20 verse 30 HP engines for a Hunter 30. 
I  should  have  mentioned that the Hunter  30  displaces  10,000 
pounds  plus  maybe 500 extra pounds that I've added to  it.  The 
Yanmar  YHM12 weighs about 225-250 pounds. I don't know how  much 
the  fore-aft  trim  will be impacted by  a  heavier  engine  but 
probably not much.

The  most  important  comment was related to the  engine  bed  or 
risers. What I have now will support a 20 HP but probably  should 
be  beefed up for a 30 HP. That translates into work,  more  work 
than  I  really look forward to. So, I'm leaning towards  the  20 
rather than the 30 but the jury is still out. 

I want to make a couple of comments on some of the questions  and 
suggestions  that came back. First, I think the comments  on  the 
propeller  are  right on the mark. I expect that I will  have  to 
change  it. Alen, if your reading this, do you know where  I  can 
get  a  copy  (borrow  or purchase)  of  Dave  Gerr's  book  that 
discusses  this  topic?  The 20 HP's torque  is  relatively  flat 
between  1400 and 2200 RPM. At 1800, the related HP is 12 and  at 
2200,  the  HP  is  14. My goal would be to  match  the  prop  to 
somewhere in the 1800 RPM range for maximum torque. The boat  has 
a  1"  bronze shaft and it should be OK for the 20  or  for  that 
matter, 30 HP. 

Dave and Gomes suggested a Max prop (I assume a folding prop is a 
Max  prop) but I don't I want to break the bank this  year  after 
going for an engine with plans for a new reefing system, traveler 
and maybe used sails. Probably, I'll take the hit in speed with a 
3 blade if I can't get what I want with a 2 blade. 


Engine mounts:

This  deserves   some discussion. The first year that I  had  the 
boat (1979), the engine shook everything so badly that I  thought 
something would break (Goodwin noted that he had the same problem 
with a Hunter). The vibration problem is common with MOST  single 
cylinder diesel marine engines that have  light weight  flywheels 
and engine mounts that are not engineered to the application.  My 
second year with the boat saw the original mounts totally reduced 
to junk so I decided to design my own mounting system.

I  got an engineering product catalog from Barry Controls (  they 
used to be in Watertown, MA) for their vibration isolators. Next, 
I  selected an isolator that was designed for the weight load  of 
the engine, low self resonant frequencies with the best vibration 
attenuation  curves  for  accelerations   applied  in  all  three 
planes.  Three  plane  qualities are important  in  a  boat.  For 
example,  the thrust from the prop is exerted against the  mounts 
and  the vibration is not only in the vertical plane; the  YHM12, 
the piston is horizontally operated.

Next,  I fabricated 2 structures, each about 20 X 5 X  1.25  made 
out of aluminum to install on the risers. The vibration isolators 
were  attached on top of the aluminum structures and  the  engine 
sat  on the isolators. I aligned the engine to the  shaft  pretty 
much with the thickness of the aluminum but I added shims between 
the mount and the aluminum for the final alignment pass. Note, no 
variable fulcrums common to adjustable mounts.

Results:   The  engine  RAN  WITH  NO  OBJECTIONABLE   VIBRATIONS 
TRANSMITTED TO THE HULL followed by 10 years of pleasant motoring 
with  a  single cylinder diesel engine. Of course,  motoring  was 
only when necessary and subject to expected limitations in HP.

Too  many manufacturers select an adjustable mount for  vibration 
isolators  and they have no idea what the characteristics of  the 
devices are. Most adjustable vibration isolators that I have seen 
are good for operation in  the vertical plane only. I will try to 
provide more information on this if anyone needs it.

Joe

    
    Redesigning things like that very often seems to be well worth the
    trouble.  That's great that you were able to reduce the vibrations so
    much.
    
    Did the boat you put the new mounts in have a separate thrust bearing
    (not sure if that's what it's called) to take the fore and aft thrust
    of the propeller shaft, or did the engine itself have to do that?
    
    If the engine took the thrust, then were the mounts designed
    specifically to be able to take such thrust?
    
    Also, did you experience any problems with side-side movement of the
    engine in the mounts causing problems with the prop shaft or stuffing
    box?
    
    Just curious.  I don't have much experience with boat engines, props,
    shafts, etc., but am interested.  The only "learning" experience I've
    had in this area is when my old lightning lost its outboard mount
    (designed and built by me), complete with running outboard, right there
    in the slip area.  My design skills have improved since those days. :-)
    
    Dick

RE: .12,

>>> Dave and Gomes suggested a Max prop (I assume a folding prop is a 
>>> Max  prop) but I don't I want to break the bank this  year  after 
>>> going for an engine with plans for a new reefing system, traveler 
>>> and maybe used sails. Probably, I'll take the hit in speed with a 
>>> 3 blade if I can't get what I want with a 2 blade. 

Just last night I noticed an ad in (Not So) Small (Anymore) Boat Journal 
for a fixed blade prop of unique design.  Its design apparently includes
convex surfaces on *both* faces of each blade; they claim 20% more 
efficiency in forward (or maybe it was thrust, which isn't quite the same,
I know) and something like 60% more in reverse. 

The company is Cruising Designs, I think, from somewhere here in Mass.  
It's got to be more expensive than a regular fixed blade, but probably 
still much less than a Max Prop.  Again, I recall it's 2-blade only, in 
14", 15" and 17" diameters; nothing mentioned about pitch options.  Seems 
squarely targeted at sail auxiliary use.

If you want more info, pls send me mail and I'll dig up the ad for you.

J.

    For what it's worth, a Maxprop is a folding prop, but a feathering
    prop.  The difference is that the folding collapses into a very low
    profile "duckbill" shape.  The feathering prop feathers so that the
    profile is small for and aft, but large from the side.  To work
    properly the shaft has to be positioned such that the feathering prop
    is in the vertical position.  Premarking the shaft makes this easy, but
    we have a window thru our hull to confirm position.
    
    Folding props are actually less resistance but get hammered in the
    ratings for racing.  Not as good in reverse, though.  Folding props
    are, I believe, less expensive than Maxprops.
    
    Dave

    First sentence of the previous reply MEANT to say "is NOT a folding
    prop..."
    
    Dave

    
    	Actually, It's not so much a `hammering' for a folder; you get
    	3 sec for a 2-blade, 6 for a 3-blade. Leaving the stock 2-blade
    	on my boat would have put me at the top of B fleet, rather than
    	the bottom of A, but I couldn't bear slowing the thing down. 
    	I paid around $400, I think, for a 13" Martec folder. They had
    	to `custom-grind' the thing for a metric shaft... which is maybe
    	what I got in the deal! Anyway, the diameter difference is sub-
    	stantial, and I can bring myself to a pretty good stop. Haven't 
    	had any panic, jam-into-full-tilt-reverse yet, but comparing to 
    	my former 2500-lbs vs. 5 hp, it feels like 4 wheel discs.
    	Martec is in California, 213-435-4494, happy to give out numbers
    	and lighten your wallet. Closed Fridays... are they sailing???
    	Oh yeah, fax -3899.
    	Scott.

I got behind in my responses to this note so I'll try to catch up 
to responses .13-.17. 

First,  the  engine mounts regarding Dick  Goodwin's  note   .13. 
Dick,  when I redesigned the mounting system, I was motivated  by 
necessity more than anything else. Aside from the problems of not 
being able to keep the engine mounts properly adjusted, the shaft 
continuously  would "rap" against the periphery of the  thru-hole 
in  the  hull  at various RPM's. No matter how much  I  tried,  I 
couldn't get rid of that problem. Also, the cutlass (sp.) bearing 
wore out after the first season and I had to replace it. When the 
mounts  failed shortly into the second season, I could not  bring 
myself to simply replace them and continue with the problems I've 
described.

I  considered installing a thrust bearing between the engine  and 
the  prop  but  I didn't have enough room. Note,  with  a  thrust 
bearing,  2 universal joints are needed in order to  satisfy  the 
mechanical  requirement for zero velocity on the shaft. A  thrust 
bearing system is by far the best way to go but because I'm not a 
perfectionist, I let the engine mounts absorb the thrust issue. 

It's  been  some time since I did the installation  so  I  cannot 
remember all of the details pertaining to the mounts. In fact,  I 
just called Barry Controls [(617) 787-1555] for engineering  data 
on  their vibration isolators in case I need to replace them  for 
the  new engine. Barry Controls are now located in Brighton,  MA. 
What  I do remember about the installation is that  the  isolator 
could take the same load in all three planes.  I think I selected 
an  isolator capable of about 100-125 pounds. Because the  engine 
was  supported by 4 mounts (isolators), the system could  support 
about  400+ pounds of prop thrust plus the weight of the  engine. 
Remember,  the engine had only 12 HP  and 400 pounds should  have 
been  enough  to take care of the prop thrust. I can  vouch  that 
they show no signs of wear after about 10 years of use.

The engine's movement was restricted to the limits of the  mounts 
and  I  never had any further problems with  side-side  movement, 
stuffing box or cutlass bearings. ALL boat manufacturers could do 
the  same but they elect the least costly  installation  approach 
provided with the adjustable mount.


Props--.14-.17

My  thanks  to John Spencer, Dave Johnston and Scott  Wagner  for 
bringing  me up to date with props. Up until now, I never  really 
considered  the subject so I didn't know the  difference  between 
folding and Maxi's nor about what is offered by Cruising  Design. 
I  did however, quickly find out the difference  between  folding 
and  Maxi's--  $$$$$$$. A Maxi for my boat (14x12 2 blade)  lists 
for over $1100. I want to go faster but --.

I  am interested in following up on both Cruising  Design's  prop 
and also a folding prop. Does anyone beside Scott have experience 
with folders? How bad are the problems with reverse?

Thanks,
Joe

    A third variety of prop you may want to consider is a Brunton-Weil
    Autoprop. Phone +44 787 73611. They are based in Sudbury, Suffolk in
    the UK. They have been around since 1868 and in props since 1908.
    
    They claim :
    	- Automatic feathering
    	- Automatic pitch reduction in adverse coditions
    	- Superior astern performance
    	- Simple installation. Fits existing tailshafts
    	- Automatic pitch increase when motor sailing
    	- All round ahead performance better than fixed pitch propeller
    	- No controls to worry about
    	- Better stopping & Starting.
    
    
    etc etc.
    
    I have a brochure which I could copy and mail you if you want.
    
    Pete