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Old 19-02-2013, 20:55   #1
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YM Single 12hp on Cascade 29?

The boat I've been looking at is a 77 Cascade 29 (production boat). Is has been repowered from an Atomic 4 30p to a YM 12hp single cyl. Quit a reduction.

All I'd use it for would be in and out of harbor, and if I get into trouble. I do coastal cruising off Oahu.

All things being equal, if I were comparing two C29s, one with Atomic 4 30hp, the other with the YM12, how much price difference?


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Old 20-02-2013, 04:26   #2
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Re: YM Single 12hp on Cascade 29?

Don't be fooled by the 30HP rating of the A4. At the most common operating speeds of about 1,800 rpm, they only put out about 15-17 hp at best.

Actually, the A4 experts over at Moyer Marine Atomic 4 Engine Rebuilding and Parts seem to rate the horsepower even lower than this. Here's parts of a prop selection article.

A good prop selection for the Atomic 4 is one which will allow the engine to develop a maximum of at least 2500 RPM, while retaining enough efficiency to allow for a cruising power setting of approximately 2000 RPM (at which point the engine produces 16 horse power).

The problem in selecting props for direct drive Atomic 4 engines is that there is a very small range of props which are small enough to allow the engine to turn at such a high RPM and still retain the efficiency necessary to move the boat well at less than maximum RPM. For whatever reason, many boat builders throughout the years tended to install propellers that were too large to allow for the factory recommendation of a cruising RPM in the range of 2000 RPM. In fact, many people report maximum available RPM of 1500 or less, which limits cruising horsepower to 10 horse power or less.

So, the apparently underpowered, single cylinder diesel may be very comparable in actual power output to the A$.


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Old 20-02-2013, 15:29   #3
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Re: YM Single 12hp on Cascade 29?

If the diesel runs and doesn't smoke or overheat you're very much better off with it. Most Atomic 4 gas engines I've known have become anchors.
kind regards,
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Old 20-02-2013, 19:49   #4
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Re: YM Single 12hp on Cascade 29?

This boat has an offer in on it pending sea trial.

I heard from the "scuttlebutt" that it has sat there forever and the owner was having trouble getting it to start.

Now I am looking at a Columbia 26 (1966). That's suppose to be a solid little cruiser for an old fart. Has a 6hp outboard in aft well. I think this version the Col 26 has room for a small inboard.

Tango Charlie
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