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Eric770

I need a 1:1 transmission for an inboard motor for an Atkins design

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Hi, I'm building a 19' motorsailer with an inboard engine.  It is the Atkin design "Surprise".  http://www.atkinboatplans.com/Sail/Surprise.html  The hull is made, as well as the decking, and it is time to mount the motor. I have a very nice Kohler, v-twin, 30 HP water cooled, fuel injected, non marine gas engine. I also bought a nice transmission, a PRM80. The problem is, I need a 1:1 ratio transmission, not the 2:1 of the PRM. I want to cruise the motor at 2400 RPM (3500 max rpm), and the 10" prop I have needs 2400 RPM to reach the design top speed of 20 MPH. I thought I could change the prop pitch to account for the reduction in RPM, but found it would require an extreme pitch and would have too much water slip. The only solution I see is to 1-find a transmission with a 1:1 ratio (which I have as yet not come across) or 2 - increase the RPM between the motor and transmission in some way. I have explored various belt designs, but at high max RPM 2 x 3500 = 7000, and the 20 to 30 hp, and the constrained space, I need either multiple V-belts, or synchronous belts, which become quite pricey and complicated to mount and couple to the motor and trany. 

Does anyone know of a 1:1 trany that will provide neutral and reverse? or have a suggested solution?

Eric

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