Re: Repropping my cabin cruiser.
Theoretically, the most load put on the outdrive will be at takeoff to planing, that is when you are loading the prop up as well as the engine. You have very little forward speed and yet a lottt of load when you first start throttling up to plane and then getting to the point of transition to planing, the hump. The engine and outdrive are loaded as you are trying to get to plane and over the hump and it requires large amounts of prop thrust and that thrust is at very low water speeds which means they will either break loose (as they do when you are trying to takeoff with one engine) or they will be able to overcome it. You will notice as you are running the boat above planing speed they don't break loose when you gun the engine, and that is because there is not as much load being put on the props, as you have excellent water flow to the props because of your forward movement, the same as a race car can gun the engine more after he gets forward movement going. Most of the time that any props break loose and you are not trimmed up any on the outdrive you are loading everything there is to the maximum with the setup that you are running. The best way to get to plane and create the least stress on everything you can is to fluidly throttle up like you were talking about earlier.
You have to remember that with the new props you have a lot more surface area, which means more traction, think of it like a car that changes from street tires to racing slicks, the extra traction loads everything up much more than before. The load on the rear end and the motor happens at the time of greatest stress, at takeoff.
You have to adjust the trim tabs for the steering, but that does not affect the speed or RPM of the boat.
Changing to the new prop geometry now creates more stern lift, so that means the bow won't raise as much as it once did, which is normally a good thing when you are running in a head sea because it lets the forefoot (which usually has a lott of deadrise cut the waves, instead of when the bow is raised it lets the seas come back further on the hull and slap it and push it up making for a rougher ride, but that may not be the case with your boat.
My idea for helping the prop plane the boat with one engine was to have a prop shop drill ventilation holes in the props so they would be able to reach higher RPM without breaking loose and having to start over. It is a common practice with many of the hitech props on the market today. It may not work, but I think it will. Theoretically it will also put less load on the outdrive and motor anytime you are taking off.
H
