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Old 02-05-2023, 10:21   #1
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Replacement Inboard Diesel

I removed the 1975 Volvo Penta MD2B /HY (HY stands for remote hydraulic drive) from my 30' sailboat. Before I did that I mounted a 6hp long shaft outboard to the transom. The outboard works well for my needs-motoring out to the bay and sailing.
But I do want to eventually install a smaller inboard diesel not like the 500lb 23 hp that was originally in there which was really overkill. The original hydraulic drive and propeller remain in the boat and are in good shape. I really like my C&C 30 1/2 Ton sailboat and plan on keeping for years.

My question: what inboard diesel would be a fit for the hydraulic drive? Does Beta Marine, for instance, still produce a small diesel for a hydraulic drive type transmission.
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Old 02-05-2023, 10:35   #2
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Re: Replacement Inboard Diesel

Do approach this with caution.

The designer did not leave extra space in any direction, so a different engine may not fit. He placed the stringers for the engine mounts, the mounts, the distance from the tranny to the prop shaft, the cooling water seacock, electrical connections, exhaust, and the throttle and shift cables in convenient places for that motor. Everything on the new engine, if not a direct replacement, will not fit or will be in the wrong place.

One forum member who did replace with a different engine actually built a cardboard model of the new engine so he could straighten all that out. Others may have not realized what they were getting into.

Good to hear that you really like your boat. Best wishes for a long happy relationship.
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Old 02-05-2023, 11:14   #3
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Re: Replacement Inboard Diesel

Our original Volvo was replaced by at Beta and we've had a good experience. My adivce is to call Beta and see what they say.
Good luck with your repower.
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Old 02-05-2023, 17:48   #4
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Re: Replacement Inboard Diesel

Depending on usage and expectations, electric might be a viable option. If not, other posters have noted that there may be considerable adjustments to make. Don't underestimate the cost of the engine mounts themselves as well.
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Old 02-05-2023, 21:23   #5
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Re: Replacement Inboard Diesel

Note that with the hydraulic drive the alignment of engine to shaft is not critical since there is not direct mechanical connection. Engine drives the hydraulic pump, pump has hoses to hydraulic motor which is connected to the shaft... and he isn't proposing to change the hydraulics as I understood his post.

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Old 04-05-2023, 11:14   #6
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Re: Replacement Inboard Diesel

That's correct; I am not changing the hydraulic drive and propeller.

I don't know of any other sailboats like mine, 30' C&C 1/2 Ton (only 12 produced for a special order from a sailing club) other than the Westsail 32 that had a diesel engine with hydraulic drive.

Let me know if you know of other sailboats with diesel + hydraulic drive, thanks.
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Old 04-05-2023, 13:12   #7
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Re: Replacement Inboard Diesel

Quote:
Originally Posted by stanirish View Post
Let me know if you know of other sailboats with diesel + hydraulic drive, thanks.
I think maybe the old Scampi 30? Another (very successful) half-tonner, as it happens.
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Old 05-05-2023, 08:00   #8
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Re: Replacement Inboard Diesel

Fortunately your problem is really simple, all base engines you might consider have industrial applications and mounting a hydraulic pump on them is routine. Your pump has an SAE shaft and mounting, all you need to do is match them with the supplied bellhousing and flywheel. A company like for example https://www.hayescouplings.com/ can usually supply all needed material. In the unlikely event that a suitable combination of adapters is hard to find, you just make your own from a piece of 1" Al plate.
To better understand SAE measurements read this: https://www.sbmar.com/articles/under...-measurements/

As for a suitable engine, the MD2B is rated 25hp at 2500rpm, most of the small contemporary engines are rated at 3600rpm, so you either live with the power they can make at 2500, or you change the prop to match the new rating.
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