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Old 08-01-2019, 11:22   #1
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Replacing an inboard diesel when the original isn't present

I have a 1984 starwind 27 that was originally powered (from what I can gather) by a yanmar 1GM. A previous owner removed the motor a replaced it with an electric system of some kind. Subsequent to that, another owner removed the electric sytem and batteries.

I added an outboard to it, which works for my uses pretty well but I am interested in putting either a diesel or electric inboard motor back in. I have replaced motors in inboard/outboard style motorboats boats in the past, and a pretty handy with boat and car mechanics.

Where I am running into issues is in finding documentation on how this system was originally set up. The prop and shaft are still in place, but I am unsure what kind of motors will mount to the shaft, whether a particular transmission is needed, what the shaft rpms should be etc. I feel this would be easier if this was a replacement, but is a bit tricky with the original system being gone, including motor mounts.

I don't think such documentation exists specifically for a starwind 27 but does anyone have any tales / details / links about similar boats? The setup seems pretty standard but not having any experience with straight shaft sailboats I'm not sure where to start exactly.
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Old 10-01-2019, 08:54   #2
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Re: Replacing an inboard diesel when the original isn't present

The way to approach this is the same as if it was a new model boat being powered for the first time. That is, take the length, beam, draft and displacement of the vessel and plug it into a hull resistance/ powering program and determine how much horsepower is required to push the hull to various points along the drag curve. With this info you can quickly see where the hull sweet spot is and at what point it becomes difficult if not impossible to exceed. If you are an experienced boat builder you probably already know this from past experience.

As this is an experienced boat, you may already have one limiting consideration, and that is the existing shaft, and possible restriction on prop diameter.

So you need to decide how fast you want to be able to push the boat, and how much power it will take to do that. Then you add a safety margin and consider that to be the optimum hp. Begin to check which engines are available with that level of power and see whether they can fit the available space and offer transmission ratios that can work with the available propeller space.

Measure up the engine room and make a profile drawing (side view) of the engine room and it's relationship to the prop shaft and begin to compare this with drawings of the available engines in your power range. Of course this is a snap with CAD programs which the boat builder might have, but it was done with pencil and paper for years , and can still be done that way.

Then you use the engine dimension drawings and build a set of engine beds to support the engine/transmission in the proper relationship to the existing prop shaft and glass the beds into the hull. Set the engine on the beds, turn the key and away you go. Of course, there are a few more steps, but you get the idea...

Next mail I'll crunch a few numbers so you get the idea.

DougR
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Old 10-01-2019, 09:18   #3
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Re: Replacing an inboard diesel when the original isn't present

You can adapt the shaft with a coupler, so that's not a big deal. The biggest adjustments are often the glassed in supports that the motor mounts on top of. Height may need to be changed. However, maybe you could find a 1 gm or 2 gm used that will fit right in! The 2gm is a lot smoother engine.
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Old 10-01-2019, 15:33   #4
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Re: Replacing an inboard diesel when the original isn't present

So a little looking for Starwind 27 online shows:
LOA - 26.6'
LWL - 22.5'
Beam - 9.6'
Displ. - either 5200 lb. or 5500 lb. depending on keel model-- I'll use 6000lb for full load conditions
Theoretical hull speed - approx. 6.3 or 6.4 Kts.

Additional looking shows several for sale, one with 1GM Yanmar @9h.p., several with Westerbeke 10, one with Perkins M-20. Probably the Westerbeke 10 was the std. engine and the M20 might have been a repower.

A little calculation work shows that 10 hp. should push the boat around 5.7 or 5.8 Kts in the full load condition, so if the W10 was the std. engine, the boat was a bit underpowered. There could have been several reasons for that, such as ready availability of engines, cost, engine room fit, etc. With 15 hp. the vessel should reach hull speed in full load condition, and any power more than that is just money in the bank....

My suggestion is to look for an engine in the 10 to 15 hp. range. Examples are:
Volvo Penta D1-13, Yanmar 2ym-13, Beta 14 or 16 and there are probably others. Any of these engines will probably require a propeller in the 13" to 14" diameter range with a 2:1 reduction gear and three blade prop. So now is the time to measure how big of a prop you can fit under the hull while still retaining about 12-15% of the diameter for tip clearance. Going for more hp. might be tempting, but you need to be certain there is room enough for a prop that can absorb that extra power, and an engine room big enough to hold that more powerful engine.

So collect some dimension drawings for the engines that you might be interested in and start to compare those drawings to the engine room drawings that you already made, and you will soon see what's possible and what isn't.

From here on it just gets to be nuts and bolts, glass and resin.....

Hope this helps.
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Old 11-01-2019, 10:16   #5
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Re: Replacing an inboard diesel when the original isn't present

To add my opinion my boat is a bit smaller than yours, 21 ft OA, 19ft WL displacement MB. Displacement, prob around 2.3 tons. (so not far off yours). So, I SUGGEST, using mine as a reference, we had an 18hp 2-lung SABB in it . That was a bit elderly, I put in a 24 hp Bukh, and am extremely pleased with it. It burns about 1.05 litres/hour (just over a quart if you're a cousin), for 5.2 knots. My experience with similar size yacht auxiliaries is that you would be well advised going for a 15 -20 hp unit. Yes a 10 will work in nice smooth water, clean bottom, lots of things in your favour. Sometimes life can be a real BITCH, that's when some additional horses would be worthwhile.
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Old 11-01-2019, 10:54   #6
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Re: Replacing an inboard diesel when the original isn't present

I too think 10-15 HP at least would be nice. But my heavy Contessa 26 had a 6 (7?) hp Bukh in it and was fine.
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Old 11-01-2019, 15:00   #7
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Re: Replacing an inboard diesel when the original isn't present

What our British friends call the "fitment" of all the new parts may be some fun. Plumbing in an exhaust properly, so it doesn't restrict or backflood, as well as trying to line up an engine and transmission, and perhaps rebuilding the engine bed, which the PO's may have modified, may all require some patience although it is "just fitment" to a real engineer.(G)

Between the cost of an engine, fuel tank, exhaust system, all the plumbing, all of what sounds like something new to you (the "fitment")...if the outboard motor has been suiting your purposes, it might be worth leaving it alone.

If the fitment sounds like something that won't push your limits...then by all means.
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