I have a 25 foot cat, I was told to try running a LH prop on it for more performance. Is this just BS?

Ayuh,... What Drive,..??

Bravo One

would not see how a single screw would matter left or right.

Ihave hurd of boats being happyer pulling one way then the outher with a single screw.

Try everything you can, then make your own conclusion, every boat and set up is differant. Just put the drive in reverse and change prop.

The inertia of the motor by itself may torque the boat one way (you see a car lean one way when you rev the engine when stopped),while the prop can counter balance some this. Even some well known twin engine vee bottoms had one counter rotating engine.

Here is how I see the RH and LH prop on a single engine boat. Typically on a single engine boat it is an RH and the boat will naturally want to lean to the left or the port side from the torque. This works great if you have a hot wife or girlfriend that doesn't weigh too much since the extra torque will naturally want to torque the boat to the port side or the same side your wife sits. Since she weighs less than you the boat will fly nice and level. The LH option on a single would be for those guys that have larger wives or BBW's riding shotgun that need some extra torque to the starboard side to compensate for the junk in the trunk.

ok, is standard rotation set up so prop torque cancels out engine torque? or do they add to each other?

rh rot makes boat lean left? engine torque wants to pull left side up. so i guess they are set up to cancel each other's torque. and the second part; if she weighs enough you need to change balance of the boat, removing the excess weight will trim boat better...