Switching RH Prop For LH prop

[Triple Helix]

I have the opportunity to purchase a much needed new prop for $100. The pitch, diameter and bore are all the same but it's a lefthand prop and my boat is set up for a right hand prop. Can I just switch my forward and reverse cables and essentially run in reverse or would there be other mechanical concerns I'm not aware of? My motor is a 27 HP Isuzu Pisces on a sailboat. I'm not sure of the type of transmission.

[Triple Helix]

My other option would be to stay RH with a 20" diameter prop with the same pitch up from the original 16". The costs for both options are about the same as I've found good a used one.

[colemj]

It will all depend on your transmission - it makes little difference to the engine. You will need the same gear ratio and assurances that the thrust bearings, lubrication, etc are OK for prolonged reverse operation.

If you have a saildrive, most of them are OK running either way.

As for increasing the diameter 4" and keeping the pitch - unless you have the clearance and were significantly underpropped with the old prop, you will probably have trouble with that one.

Mark

[S/V Antares]

You likely have a mechanical gearbox (ZF, TMC, Newage, PRM) and you cannot change RH to LH. This is because in reverse the main and layshaft are connected by a spur gear that is very small and cannot handle the continious duty. If run this way for long it will fail.

What gear box do you have?

There are prop calculators online. Just plung in the HP , Waterline, Max RPM etc and get the proper info before wasting your money.

Most small diesels rotate Counter clockwise or left hand (Looking at the flywheel end). The gearbox input is LH but the gear reduction changes this to RH.

[model 10]

The Paragon trans in our boat was burned up back in the day running from VA to the Bahamas in reverse because of bad info, so I would be careful. There are good deals on props all over. Even if you could run it backwards, you would be wearing in new wear patterns on the gears and probably shorten it's life.