Velvet drive gear ratio 1980 34 Mainship?

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Dwk

Dwk

Senior Member
Joined
Jan 21, 2014
Messages
410
Location
USA
Vessel Name
Patty Ann
Vessel Make
Mainship 34 MK1 1980
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
 
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.
 
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.
 
David Kimmel said:
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
Click to expand...
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.
 
Don't know if this really helps but: We have twins and a 40'er, they're 1981s. Theyre a flat 2:1.
 
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
 
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
 
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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