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post #1 of 7 Old 08-22-2009 Thread Starter
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Gear Box

I've discovered a note in my Yanmar manual that the orginal owner changed the gear box from a 2.83 to a 2.14. This is on a 3HM35F, 34 hp, 1 inch shaft, PSC34. Can anyone tell me why one would make this kind of change in the gear box and what implications it will have. The vessel came with a MaxProp which is currently on its way back to PYI for a rebuild. If I don't have the orginal gear box I'm not sure how to interpret my RPM's and performance against manufacture specks and fellow PSC of the same class.

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post #2 of 7 Old 08-30-2009
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Carl,
We have the same setup with the 2.14 gear box according to my notes. I'll see if I can verify by checking the stamp plate on the gear box and let you know for sure.

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post #3 of 7 Old 08-30-2009
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If the engine will rev up to its advertised limit and hold it I can't see that any damage will have been done at all. The prop on your boat, I'm sure you know, now turns faster than it did originally. If the engine will not maintain it's limit. or smokes while doing it, or overheats while doing it then a problem has been created and you're going to have to deal with it one way or another.

At 3000 RPM the prop used to turn at 1060 RPM, and now it turns at 1400. Maybe the boat will go faster, but not by much, I'm betting. Once you approach hull speed you have, well, approached hull speed. You're done "going faster".

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post #4 of 7 Old 08-30-2009
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Carl,

If I had to guess, I would venture that when the previous owner switched to a MAx-Prop, he/she concluded after experimentation that the engine/transmission/prop combination would perform better with less reduction in the gearing (i.e., a faster spinning prop).

I wouldn't be surprised if someone at Max-Prop consulted with the previous owner on this. Maybe they still have some notes on file?


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post #5 of 7 Old 08-30-2009
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Carl,

I checked our transmission today and verified it is a 2.14 gear. The stamped plate is difficult to see as it is on the port side of the transmission just below the fill/level dip stick. Yoiu almost need a mirror to read it as it is only inches from the hull. We have the same Yanmar 3HM35F engine and I'll bet your reduction gear is the original.

For the 3 bladed 17" Max Prop, setting at 14 degrees seems to be the sweet spot. We previously were at 18 and the engine would not turn more than 2600 RPM. Now at full throttle in flat water we can turn close to the rated RPM at 3400. We normally run it around 2400-2600 RPM which gives us around 5.8-6 knots cruising speed.

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post #6 of 7 Old 09-02-2009 Thread Starter
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Gear box

John,

Thank you for your time envolved with checking the stamp plate. I wondering if the gear box has always been 2.14 because the comment was dated 1989 and my PSC is a 1989 model bought that year. Coupled with the fact that the Yanmar engine manual lists both gear boxes ( 2.83 and 2.14) as options for my engine. At any rate the MaxProp people are telling my to go with 18 degrees for my situation. My prop is 16 inches, and I must be gaining at least 200-300 rpm's going down in diameter from 17" to 16". FYI, I didn't think my prop looked too bad but it still cost me $1200 to have it re-condition. Almost didn't do it. It will be another 2 weeks before I'll get to trial the prop and know anything for sure.

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post #7 of 7 Old 09-02-2009
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Carl,

I seem to remember something about the option for the different gearbox or maybe Yanmar changed to the 2.14 ratio sometime during production. I'll bet yours is original. Going with 18 degrees for the 16" prop is probably a good move as they recommended.
We were thinking of sending ours back to Max Prop next time we haul for tune up. $1200 might be a deal breaker however!!!
Best of luck and hope you get back in the water soon.

John S.
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