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Sat, May 28 2022, 00:52Login ] [ Contact Forum Admin ] [ Main index ] [ Post a new message ] [ Search | Check update time | Archives: 123456[7]8910 ]


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Date Posted: - Friday - 09/15/06 - 6:49pm
Author: Capt'n Mike - Gypsy Mariner TM36K
Subject: Transmission Ratio
In reply to: marcus 's message, "prop size m31 w/ perkins 4-107" on - Friday - 09/15/06 - 5:20pm

You can run either a 2 or 3 blade prop, but I'd need to know what your transmission reduction ratio is to run a calculation. For instance, if you are running a 1:1 transmission AND given the M31's displacement (11,500 lbs) and LWL (25'8") and the SHP for the 4-107 (figure 40), you should be able to run a 2 blade 11 or 12 inch prop with a pitch of 5 or so. The 4-107 is more than enough power for the displacement of the M31. You need to check the pitch of your prop AND make sure it is not covered with marine growth. A few barnicles on the prop will have a noticeable effect on power output. However, if you are running a reduction ration of 2:1 then you could swing as much as a 17x10 2 blade, if you have the clearance for it.

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Replies:

[> [> $-107 prop size -- Doug Wilson ,Cactus Tree, - Friday - 09/15/06 - 11:22pm

Cactus Tree has a two blade sailor 12". It must be the original, had Japanese charactures on it and metric numbers.I believe I have a Borg Warner gear, 1 to 1 reduction. I get 5 KNTS at 1300.
Wilmington prop tuned it up and it was in great condition.
Doug.


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[> [> prop -- Randall, Murre, M31, - Monday - 09/18/06 - 12:39pm

Murre runs a three blade 12 inch, 6 pitch prop. Capn Mike's reference to transmission ratio is crucial to your decision. I put a three blade 13 x 8 prop on Murre for a while (seems to be common among other M31s), but couldn't get appropriate RPMs.

Figured out later that the prop was too big for my 1:1 tranny, and a 12 x 6 is a perfect fit (i.e. plenty of reserve power).

I've stuck w/the three blade (the boat came w/a two blade stuck away in a locker) because we do plenty of headwind motoring and plenty of high wind sailing, so the extra drag, for us, is worth the trouble.

RR


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