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Old 09-18-2017, 02:37 PM   #1
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Velvet drive gear ratio 1980 34 Mainship?

The ID plate on Velvet Drive is worn and gear ratio isn't clear. Perkins T 6.354 provides power with 4 blade prop. I'm certain it's 71/72 series Velvet Drive but not certain of gear ratio . David
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Old 09-18-2017, 03:13 PM   #2
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David, the reduction gear should be on the rear of the transmission. It may have the ratio stamped on a plate or the casing itself. The 34 Mainship was designed to run above displacement to about 11 knots. I figure from that the the reduction is about 1 1/2.
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Old 09-18-2017, 06:55 PM   #3
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Our '78 34 has a 2.10 to 1 model 10-18 clutch which my understanding is it's a RH rotation clutch only unless you swap the pump porting plate . Our Perkins is a counter-rotating model. Apparently Mainship used whatever they could get their hands on when they installed the engines. Some were built with left hand turning engines & they used a 1.88:1 clutch which could be reversed the output at the clutch to get the wheel turning to the right.
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Old 09-18-2017, 07:04 PM   #4
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Quote:
Originally Posted by David Kimmel View Post
The ID plate on Velvet Drive is worn and gear ratio isn't clear. Perkins T 6.354 provides power with 4 blade prop. I'm certain it's 71/72 series Velvet Drive but not certain of gear ratio . David
Get a photo tach. With Boat in gear measure the RPM at the crankshaft pulley and then the propeller shaft. Devide the two measurements together to get your ratio.
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Old 09-18-2017, 07:31 PM   #5
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Don't know if this really helps but: We have twins and a 40'er, they're 1981s. Theyre a flat 2:1.
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Old 09-19-2017, 12:15 AM   #6
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Both the 71/72 series come with the following gear ratio's dependent on your prop build specs as 1.00, 1.52, 1.91*, 2.10, 2.57, 2.91:1.00

So with out the actual plate ID i would get your self a laser RPM checker run your engine in gear @ say 1000 rpm and check the out flange for it's RPM , how ever if your transmission is slipping this figure may not be 100% , but checked over a minute the average can be determined fairly accurately,

The laser checkers are cheap around $30-50

Cheers Steve
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Old 09-19-2017, 12:23 AM   #7
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Forgot to say, the 71 and 72 series are different in length, withe 72 series @451.8 mm and the 71 series @ 429.01 mm , so a quick measurement will also tell you that,

Measurement is from flange where bolted to housing to end of the out put coupling of the transmission,

Cheers Steve
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Old 09-19-2017, 07:04 AM   #8
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I'd be willing to bet you have a 1.9:1 ratio.
The 1978 models mostly came with 2.1:1, but after that they went to 1.9:1.
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