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2.0 I believe !

April 8 2010 at 2:48 PM
Paul  (no login)

Response to Transmission on your Hat 427's

Funny you should ask, was discussing this with a good yacht broker friend of mine a couple days ago. The motors came out of a 37 Hatteras and I believe they're 2.0:1, will verify. He was laughing at the fact that the prop might cost more than the transmission.

The thinking is, with a gear reduction and the same shaft as my 38 Express, I could easily handle about any pitch the motor would take and not be stressing the equipment. So it looks like a 21" pitch would be needed to get up into the 40s with a 2.0:1 transmission.

Running a hotted up motor at 4500 rpm, shaft speed would be 2250 x 25 = 56,250 inches per minute.
Since 60 mph is 63,360 inches per minute, the ratio shows the 25" prop would be calculated at 53.26 mph, with a probable slippage of nearly 20% for that boat don't you think, resulting in 42 miles per hour. If slippage was 15% then speed would be more like 45.28 mph. Going to a 26" pitch would get you another couple miles per hour up to 47.09 using the same 15% slippage factor on that deep V not-real-fast hull design. Certainly would be a custom prop order for sure, but it would never tax the transmission that's for sure. It doesn't cost much money to dream. happy.gif If it turns out to be a 2.5 or 3.0 then all bets are off, and I'm in the transmission business.



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