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Old 23-01-2012, 13:43   #1
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Marinized Engine With Which Transmission ?????

Hello, I am currently building a 36 foot sailboat as a liveaboard and am trying to figure out which engine to use. Im going to go with a diesel engine probably an older one, no particular one yet. This will be an auto engine so I will marinize it. How do I know which transmission I should use? Please help, I know some about auto parts but next to nothing about Marine propulsion.

Thank you,
Jake
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Old 23-01-2012, 20:13   #2
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Re: Marinized engine with which transmission?????

Most marine engines are converted automotive or tractor engines. I doubt you can convert one as cheap as you can buy one. The one advantage to build it yourself is your intimate knowledge of the engine and drive system. Most boats in my part of the country have between 20 and 50 hp. Just my two cents, Mike.
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Old 23-01-2012, 22:10   #3
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Re: Marinized engine with which transmission?????

The engine is such a central part of any boat, and such a pain if it causes problems that adding to the risk by marinising your own may not be worth the hassle.

Most marinised engines are based on generator or tractor motors - ones that run at constant speed for lengthy periods.

If you can find the money I'd strongly suggest going new, with an oversized transmission.

If money is a problem it will almost certainly be cheaper, quicker and easier to find a secondhand proper marine engine/transmission. Try to get the control panel and the engine/gearbox controls as well.

While it is very nice to have a big engine a smaller one is much cheaper to buy and to install. Have you worked out what your minimum size is?
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Old 23-01-2012, 22:43   #4
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Re: Marinized engine with which transmission?????

The plans call for 20-30HP, if I go the route of marinezing my self do you have any suggestions as far as generators or tractors? Also if i just have the engine how do I know which transmission to buy?
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Old 23-01-2012, 22:53   #5
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Re: Marinized engine with which transmission?????

Take the final weight of your boat and use 5 hp for each ton of displacment. In earlier years the formulae was 3 hp but today cruising is motoring for 30/40% of the time. For a 35 ft boat of no racy character 40 hp would be fine. Or around that figure.
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Old 24-01-2012, 04:10   #6
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Re: Marinized engine with which transmission?????

IMO, go Perkins or Yanmar. Transmission, ; the gearbox manufacturer will tell you which model for the HP of your engine. Keep it simple, mechanical rather than hydraulic. Home-made heat exchangers are a can of worms waiting to be opened, - getting just the correct amount of cooling to run not too hot,- not too cold for extended periods is not somewhere I'd like to go. Fitting the transmission is just a matter of an adaptor plate between the engine flange and gearbox, but that assumes you have a reasonably equipped workshop and some mechanical aptitude.
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Old 24-01-2012, 11:04   #7
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Re: Marinized Engine With Which Transmission ?????

In my opinion you are better off going with a used marine engine. You'll spend less money and have the proper ratio of gearbox to engine.
I prefer Perkins and Yanmar but Isuzu and Kubota make acceptable engines too. I like the old Velvet drive transmissions.
I have an OM636 Mercedes convert in my boat with a Velvet Drive transmission.
If properly cared for they last a boat's lifetime.
Good luck.
kind regards,
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Old 24-01-2012, 11:24   #8
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Re: Marinized Engine With Which Transmission ?????

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Originally Posted by SkiprJohn View Post
In my opinion you are better off going with a used marine engine. You'll spend less money and have the proper ratio of gearbox to engine.
I prefer Perkins and Yanmar but Isuzu and Kubota make acceptable engines too. I like the old Velvet drive transmissions.
I have an OM636 Mercedes convert in my boat with a Velvet Drive transmission.
If properly cared for they last a boat's lifetime.
Good luck.
kind regards,
I agree with this approach, and the mfr. choices mentioned. My understanding is that Yanmar parts are relatively inexpensive and widely available. Make sure the engine you choose is fresh water cooled.

If you really want to build, find a good rebuildable engine with parts available. Rebuilding a good marine diesel is far more sensible than trying to marinize an engine IMO.

Check out this site:

http://boatdiesel.com/

Excellent source of info, and classified section could be a source of an engine and/or parts.
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Old 24-01-2012, 11:31   #9
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Re: Marinized Engine With Which Transmission ?????

jakegator
jakegator,

Why doen't you just go here and buy one of these cheap. Trany and controls included
jakegator

Brand New 27 HP Marine Diesel for $5500 in Oz
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Old 24-01-2012, 14:16   #10
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Re: Marinized Engine With Which Transmission ?????

Perkins and velvet drive. Perkins parts are everywhere and dont necessarily have to be marine. velvet drive is bulletproof and reliable. Get the upgraded crank oil seal.
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Old 24-01-2012, 14:35   #11
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Re: Marinized Engine With Which Transmission ?????

As far as selecting a transmission, manufacturers rate their transmissions differently for recreataional and commercial use. Use the commercial rating. It is the most conservative, and is the horsepower the manufacturer rates the tranny for for long term use. Don't exceed the commercial rating.

The diameter propeller you will use will determine the optimum RPM your shaft should spin. Divide your engine's RPM by the shaft RPM to determine the reduction ratio required. The correct reduction ratio is a big deal, you will loose significant efficiency otherwise.

The larger diameter your prop the lower the shaft RPM and the higher the prop efficiency. If you want motoring efficiency you want to use a large diameter prop. But of course this will increase drag under sail. As always, everything on a sailboat is a compromise.

If you want to get a good understanding on this subject I suggest you buy a copy of Dave Gerr's book The Propeller Handbook.

If you buy an industrial/automotive diesel you have the option to keel cool it, which will eliminate the need for a water pump">raw water pump, heat exchanger, raw water strainer, etc. This is a very reliable way to go, if you learn enough to design and build it properly.

Good Luck,

Paul
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Old 24-01-2012, 18:16   #12
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Re: Marinized Engine With Which Transmission ?????

There are a couple of things to think about when converting a auto engine to any industrial application. The biggest one in my opinion is that most automobile engines have a injection pump that controls fuel flow by throttle position as opposed to rpm (governed) by throttle setting. What I mean by this is you set the throttle on an auto diesel and drive it will speed up and slow down with load (for example going down hill or uphill). It will not hold it's RPM like a tractor or marine engine. Genset engine may use and injection systems designed to hold a single RPM so the generator will output 60hz (in US) and are not adjustable. Finding a governed injector pump for some auto engines is an expensive proposition; possibly costing you more that a used marine engine.

As far as what transmission to use with the engine. Most industrial engines are built with an SAE bolt pattern and all you have to do is find a transmission with the same SAE bell housing. Many autos do not come with a standard bolt pattern and as such an adapter plate will need to be made. As far as gear ratios; that has already been well attended to by Paul.

My personal opinion is get a used marine engine with the correct ratio transmission. If you figure out what hp and gear ration you want start looking now so you are not in to big a rush and can wait for the right combo to show up. I would not rule out such engines as an older Volvo, Sabb (these have the prop pitch change so no tranny is necessary) or even a small Detroit 2-53 or 3-71 (these have an extremely good reputation and have cheap parts too). I will admit I am partial to the older Detroits; I wasn't until I owned one and now I don't think I would own anything else.

Hope that helps.
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Old 24-01-2012, 19:00   #13
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Re: Marinized Engine With Which Transmission ?????

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Originally Posted by Nadejda View Post
I would not rule out such engines as an older Volvo, Sabb (these have the prop pitch change so no tranny is necessary) or even a small Detroit 2-53 or 3-71 (these have an extremely good reputation and have cheap parts too). I will admit I am partial to the older Detroits; I wasn't until I owned one and now I don't think I would own anything else.

Hope that helps.
Interesting that you like the Detroits. Can you tell me the HP ratings for the 2-53 and 3-71? And do you like the 3-53 as well?
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Old 24-01-2012, 19:51   #14
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Re: Marinized Engine With Which Transmission ?????

Well first off I need to eat a little crow. The 2-53 I mentioned is not a common engine and as such you would be looking at either a 3-53 or 2-71.

The hp for the 3-53 is around 100 hp and the 2-71 is 68 hp.

There are several reasons I like the Detroits. First and foremost is their reputation for reliability; many of these engines get 20k + hours on them and are still running fine. This is due to the fact they are heavy built industrial engines, along with each cylinder having a seperate self contained injector (you can lose injectors and the engine will keep running), they utilize accessory drives for the water pump, fuel pump, raw water pump and such (eliminating most the v-belts) and their parts are available world wide. The other reasons would be that I love the sound and I like to rebel against the norm. They are not quite as efficient as many modern engines but in my 40 ton sailboat we only burn 1-1/2 gal/hr at 6 knots with our 6-71; that isn't bad in my opinion.

The trend today in small marine engines is to make them lighter with higher RPM; engine weight and speed is a major factor in longevity. I like many of the older engines because they were heavy and slow.

Hope that helps.
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Old 24-01-2012, 20:09   #15
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Re: Marinized Engine With Which Transmission ?????

Yes, thanks. I did some research and concluded that the 2-71 might be one I could use at 68hp, for a 15 ton boat. One downside is that it is apparently very noisy. Do you happen to know of anyone using that engine in a sailboat?

I could not find much info on these engines on Boat Diesel. Do you know of another site that has some diagrams or pics that show where the service access is? (I need access to the starboard side) Also transmission info.

The 3-53 might work as well, even though I don't need 100 hp.

Your fuel consumption sounds great to me for that big a boat.

Thanks.
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