Engine/Transmission/Prop HELP

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View attachment V7172pg3.pdf I have seen some of the posts on this forum and some of you guys know a lot about marine power,transmissions and props.Perhaps you would be able to assist me.I am at present building a Wharram Tiki 38 which i want to power with a automotive Nissan sd22 (same as used by chrysler marine in the 80s)60 HP at 3800Rpm.I am hoping to use a BW Velvet drive 72 with a longshaft coupled to a 18"x10 or 18"12 props.I already have the engine and 2 Props.
I am really struggling with the marine/transmission lingo.My engine looking from the back i.e stern rotates anticlockwise, my props looking from the back i.e stern need to rotate anticlockwise so the transmission woud need to rotate anticlock from the stern in forward.as far as I can tell around 2-1 reduction should work.
The BW 72 alo has a way higher power range would this work.
I am looking at a used BW 72 which i am waiting for the specs on as these were available in different rotations.
Your assistance wold be greatly appreciated.
Regards Chris
Durban SA

 

Standard rotation for both the Velvet Drive 71C and 72C transmissions are counter-clockwise as viewed from the output coupling. Even if you wanted to use a clockwise engine/ Prop. The same transmission can be used by merely changing the oil pump configuration which is a 10 - 15 minute job assuming the trans is not hooked up to the motor. Not sure about 2.0 ratio? You may have to go to a higher ratio with your boat size ( weight ) and power. In any case rotation is not an issue since it can easily be changed.
Velvet Drive transmissions can turn in either Direction, but ONLY in the same Direction as the Motor, in forward gear. The oil pump direction must be set to the desired Forward direction [ten minute job previously stated]. It is NOT recommended that transmission be run in reverse gear to obtain forward motion.

 

Hi Jango.Thanks for the reply. is the transmission a solid unit, it would be well within its power rating so in theory last well.
Regards Chris

 

Both the 71C & 72C are more than adequate for your application. The 71C for up to 380 - 400 HP and the 72C to around 550 HP. The 72C will not be as smooth shifting into forward gear, since pressures are higher and shift will be abrubt. However either transmission should last "forever" assuming they are currently in good condition.

 

Thanks for your quick response. I think i am going to go with the velvet drive,I will have to make an adaptor to fit it to the Nissan motor.
Regards Chris