I have a 44 ft Marine Trader with *a single 120Hp ford lehman. So far I am quite happy with the engine but I would like to have a auxillary engine to get home should there be any problems with the main. I am looking at the Yanmar 36hp outboard diesel engine and wonder if will it be enough sail my boat back to port?? I like the idea of using the outboard as minimal work will need to be done. Any suggestion?
Outboard Aux Engine for Marine Trader 44
- Thread starter edwin
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my only experience using alternate power to move my boat was terrible. We towed my lugger about two miles and I would not soon do it again. The tow vessel had twin 454's. I don't know about the outboard idea because the prop is so small. If you feel uncomfortable with the single I would start looking around for a twin.
RickB
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Isn't a BoatUS towing policy a lot more effective and considerably less expensive?
Codger2
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*It certainly is and I have one, but for those who cruise in desolute areas with their single engine trawlers, I'll bet this subject has crossed their minds more than once. What I can't understand, however, is that if you are going to bolt an OB on your swim platform or stern, why not an appropriate sized gas OB?
RickB
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*Ah so ... yeah, it would take them a while to get there.edwin wrote:
Hi rick I am staying in south east asia and we do not have the luxury of getting a US boat tow around here.*
sunchaser
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Ed
A few thoughts:
<ul>[*]A diesel outboard may be*less reliable than your 120 inboard. I'd suggest a gasser.[*]Keeping the prop in the water with a moderate swell requires an extra long shaft, I've seen this problem/solution on trolling*outboard motors used for fishing[*]The outboard should be very well sealed since it will be partially submerged from time to time on the back of a heavy trawler. Newer ones are well designed for this type of service.[*]A good supply of onboard spare parts for your 120 may be a better solution. These spare parts I* call the "hang ons" such as starter, water pump, alternator, HX pieces, hoses, fuel pump, belts and filters. So long as the engine is now running OK and the exhaust/elbow system is in order any breakdowns should be to the "hang ons."[*]With warm water, good lungs, fins and a mask you can clear*prop fouling. Add line cutters if you don't have them.[/list]
I know of many serious*blue water cruisers who have singles and a wing engine. The wing engine hours are minimal and only get used to keep them limbered up.
A few thoughts:
<ul>[*]A diesel outboard may be*less reliable than your 120 inboard. I'd suggest a gasser.[*]Keeping the prop in the water with a moderate swell requires an extra long shaft, I've seen this problem/solution on trolling*outboard motors used for fishing[*]The outboard should be very well sealed since it will be partially submerged from time to time on the back of a heavy trawler. Newer ones are well designed for this type of service.[*]A good supply of onboard spare parts for your 120 may be a better solution. These spare parts I* call the "hang ons" such as starter, water pump, alternator, HX pieces, hoses, fuel pump, belts and filters. So long as the engine is now running OK and the exhaust/elbow system is in order any breakdowns should be to the "hang ons."[*]With warm water, good lungs, fins and a mask you can clear*prop fouling. Add line cutters if you don't have them.[/list]
I know of many serious*blue water cruisers who have singles and a wing engine. The wing engine hours are minimal and only get used to keep them limbered up.
Regarding the power needed for an auxiliary engine, we have a single engine 47ft Selene (65,000lbs) with a back-up Saildrive (SD50) driven by a 56HP Yanmar.
It has only been used in moderate sea conditons and fortunately has never been needed as a "get home".
Typically, it drives the boat at about 4-5 kts running at about 3,000rpm (max 3,600).
The \yanmar engine always starts first pull but is noisy compared to our Cummins main.
Because the SD50 is off-center steering is less sensitive and problematic at slow speed.
Nevertheless, it is quite comforting to know that theer is a "spare" if you ever need one!!
It has only been used in moderate sea conditons and fortunately has never been needed as a "get home".
Typically, it drives the boat at about 4-5 kts running at about 3,000rpm (max 3,600).
The \yanmar engine always starts first pull but is noisy compared to our Cummins main.
Because the SD50 is off-center steering is less sensitive and problematic at slow speed.
Nevertheless, it is quite comforting to know that theer is a "spare" if you ever need one!!
Capn Craig
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There aren't too many new ideas in the world.* These pictures are of a boat I considered making an offer on before buying my Californian.* The boat was located in a rather desolate area of Mexico, Gulf of California.* The OB was a 10HP Yamaha if I recall correctly.* The shift/ throttle controls were located behind the lower station.* I never got to the stage of phisically looking at the boat and do not know how well it worked.* This was a gas 2 stroke.* One risk of a diesel OB I see is that if the problem with the main is fuel related, the OB isn't going to help much.* I tried a similar approach mounting a 10HP Honda on the Swim Step of my old single engine gas inboard cruiser.* Steering with the rudder in front of the OB was next to impossible.
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skipperdude
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*How big was the rudder?
SD
Capn Craig
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*How big was the rudder?
SD
*Rudder was 12"tall x 8"f-b.* Boat weight was in then 10,000# range.* I think the biggest problem was that the rudder was about 4' in front of the outboard due to the large size of the swim step.* But bottom line the rudder didn't do much without being in the prop wash.* I never had to use the setup.* Good thing.* If I had to use it, I could have steered by sitting on the transom and using the boat hook zip tied to the tiller of the OB.* I envisioned it working far better than it really did.
skipperdude
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Capn Craig
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I've pondered the idea after trying it and failing, over several delicious Miller Lite's and have come to realize it is not possible from a physics basis,* A boat steers by rudder by pushing the stern in the oposite direction as the intended turn.*** To turn to port the rudder swings to port, creating stern thrust to starboard.* If the prop is considereed the axis of rotation for the turn, then pushing to starboard behind the axis, pushes the bow to port, and Voila! we turn to port.* When the rudder is in front of the axis, the opposite happens.* swinging the rudder to port pushes to starboard and the boat pivots about the axis and turns to starboard.* Damn that''s backwards.**** I didn't know this when I tried it.*** It is really amazing how smart the delicious Miller Lite's make a guy.
All kidding aside, over a long distance, I might have been able to steer backwards, but the boat became very directionally unstable, as the things you compensate for, wind, current, etc became more of a problem.
All kidding aside, over a long distance, I might have been able to steer backwards, but the boat became very directionally unstable, as the things you compensate for, wind, current, etc became more of a problem.
dvd
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It is perfectly logical that a couple of beers will make one smarter. As everyone knows, alcohol is toxic to cortical neurons (brain cells). Since the most vulnerable cells are the weakest ones, they are the ones that go first, leaving only the strongest, smarter cells remaining.
Trust me, I'm a doctor.
dvd
Trust me, I'm a doctor.
dvd
Keith
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Wesmar has a really cool aux. get-home system that I have not seen before. There was an article on it in the latest PMY. For singles, it uses a belt drive to power your shaft/prop via a hydraulic pump powered by your genset. http://www.wesmar.com/APU.htm
Downsides are that if your prop is tangled this won't help vs. a separate engine/prop. However, I think it's a much better idea than an outboard. I've looked at that idea many times, but there are too many problems with using an outboard as an APU to be reliable.
Downsides are that if your prop is tangled this won't help vs. a separate engine/prop. However, I think it's a much better idea than an outboard. I've looked at that idea many times, but there are too many problems with using an outboard as an APU to be reliable.
Thanks for that picture craig. So if I decide to go ahead I know now I won't be the first to fail..*
*anyway what I am planning to do if I go ahead with the*diesel outboard is I will install a seperate steering system and throttle control on my flybridge. I will have 2 steering wheels! HAHA! My main concern is will the 36hp be enough to get it sailing to 4 knot at least? I've made comparison with the nordhavn get home system. The horse power seem comparable except for the prop size. Are the feathering props much bigger than outboard motor props?
Capn Craig -
Boats don't turn around their propellers, they turn around their center of lateral resistence (CLR).
The turning force is a product of the moment created by the distance between the CLR and the rudder (D), and the velocity of the water moving past the rudder (V).
Moment = D times V.
In reverse, the prop walk is opposite, although weaker than what you are used to. The rudder is also much less efficient since the force is only boat speed thru the water, and not the accelerated flow seen in forward.
In addition you are pushing the blunt end of the boat thru the water rather than the sharp end.
I'm not sure I understand your description of how your boat responds to the rudder in reverse.
Miller Light? Wow, they still make that stuff?
Mike
Palm Coast FL
Boats don't turn around their propellers, they turn around their center of lateral resistence (CLR).
The turning force is a product of the moment created by the distance between the CLR and the rudder (D), and the velocity of the water moving past the rudder (V).
Moment = D times V.
In reverse, the prop walk is opposite, although weaker than what you are used to. The rudder is also much less efficient since the force is only boat speed thru the water, and not the accelerated flow seen in forward.
In addition you are pushing the blunt end of the boat thru the water rather than the sharp end.
I'm not sure I understand your description of how your boat responds to the rudder in reverse.
Miller Light? Wow, they still make that stuff?
Mike
Palm Coast FL
Edelweiss
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Indeed they do Mike.* The drink of choice of my sailboating friends.* (Not entirely true, one of them drinks Rainier, better yet.)*
Funny thing though, I buy both a half rack of Miller Light and Rainier when I know they are coming over and do they drink it?* No. . . They drink my Corona!!* When I go over to their boats, guess what they offer me?* Funny how that works.
-- Edited by Edelweiss on Monday 5th of December 2011 11:46:28 PM
FF
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The question is THRUST , or weather the aux propulsion can get HP into the water.
A minimum of 1 hp per ton should move the boat , if you can pump that into the water.
Loads easier to do with a hyd unit chained or belted to the shaft and powered by the noisemaker.
A minimum of 1 hp per ton should move the boat , if you can pump that into the water.
Loads easier to do with a hyd unit chained or belted to the shaft and powered by the noisemaker.
RickB
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What?????
Moment is force times distance, velocity is small part of the formula to determine that force.
Rudder force calculations involve several components.
Rudder Force= Cr= 132 x A v(squared) x K1 x K2 x K3 x Kt x N
Where:
v = Speed of the vessel.
A = Area of the rudder.
K1 = Coefficient depending on aspect ratio
K2 = Coefficient depending on the type of the rudder.
K3 = Coefficient depending on the location of the rudder.
As far as the pivot point is concerned, it is usually about a 1/4 to 1/3 of the hull length aft of the bow, it moves forward as speed increases. If the boat is stopped, it is near the longitudinal center of gravity. Going astern, the pivot point is at or near the rudder.
CLR is more of a sailboat term since it is greatly altered by keel design. Power boats use PP or pivot point.
sunchaser
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Ahhh, the pivot point discussion. Rick is absolutely right that the pivot point is nearer the bow for a vessel moving*slowly through the water and*big rudders. But this is one of those discussions that depends on if you are talking about a canoe or an IPS drive twin Grand Banks. Further to complicate it are twin outdrives vs twin straight shafts, bow and stern thrusters*and all manners of hull and rudder shapes. Or a vessel on plane at 40 mph vs a 7 knot Krogen. For sure, the single vs twin debate comes into this during maneuvering while*moving slowly through the water.*If you are a kayaker, surfer or a slalom water skier you will/must understand pivot point even better.
With a little outboard on the swim platform of a 40' plus trawler, pray for good weather and no currents as you move it around. As Fred, Keith and others have said, some type of inboard auxiliary is more common - for a reason. Me, if no*good backup*I'd rely upon mechanical savvy and spare parts to get me out of a jam.
Once again I note the misconception that the*majority of diesel engine failures are fuel related. Don't run out of fuel (a big part of the Boat US statistics), buy fresh, have a good filter system and this issue becomes insignificant.
With a little outboard on the swim platform of a 40' plus trawler, pray for good weather and no currents as you move it around. As Fred, Keith and others have said, some type of inboard auxiliary is more common - for a reason. Me, if no*good backup*I'd rely upon mechanical savvy and spare parts to get me out of a jam.
Once again I note the misconception that the*majority of diesel engine failures are fuel related. Don't run out of fuel (a big part of the Boat US statistics), buy fresh, have a good filter system and this issue becomes insignificant.
jleonard
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*I agree with this. My personal back up plan to the above would be to call for a tow. The secondary backup plan would be to rig the dink with my 15 hp outboard and try to move the boat if I had to(but that would have to be in calm conditions only).
*
Jay says "The secondary backup plan would be to rig the dink with my 15 hp outboard and try to move the boat if I had to(but that would have to be in calm conditions only)."
This will work only if you have enough hp in the dinghy.
I lost power in my sailboat (5 tons) and was able to manouvre it easily with 15 hp in the dinghy. The dinghy hp exceeded the boat hp. When I moved up to a 10 ton sailboat, same dinghy, I was able to move the sailboat with the dinghy strapped on the stern quarter, but only in the direction the current and wind would permit, and the operation required two people, as steering was difficult. Here the boat hp was 55, versus 15 in the dinghy.
I tried once on the 22 ton trawler and gave it up. 15 hp was not enough to do more than exasperate the operator.
I now carry 40 hp on the dinghy, but haven't been motivated to try it as an aux. After all, I have twin 200s.
Now if I was running 250 hp in the dinghy, I wouldn't doubt its ability.
This will work only if you have enough hp in the dinghy.
I lost power in my sailboat (5 tons) and was able to manouvre it easily with 15 hp in the dinghy. The dinghy hp exceeded the boat hp. When I moved up to a 10 ton sailboat, same dinghy, I was able to move the sailboat with the dinghy strapped on the stern quarter, but only in the direction the current and wind would permit, and the operation required two people, as steering was difficult. Here the boat hp was 55, versus 15 in the dinghy.
I tried once on the 22 ton trawler and gave it up. 15 hp was not enough to do more than exasperate the operator.
I now carry 40 hp on the dinghy, but haven't been motivated to try it as an aux. After all, I have twin 200s.
Now if I was running 250 hp in the dinghy, I wouldn't doubt its ability.
skipperdude
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*You had to know this was coming. But sure beer makes you smart.
It made Bud wiser.
Ta da.
SD
jleonard
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SD you stole my line...but I am still laughing
