skipjack27
Petty Officer 3rd Class
- Joined
- Oct 6, 2009
- Messages
- 79
I have a 27 ft flybridge cabin cruiser weighing about 3 tons unloaded. Engine Volvo AQAD41A with duoprop 290 leg with an A2 props.
Had the engine rebuilt recently and the mechanic remarked that the turbocharger was barely cutting in WOT. He thought the boat was underpropped and suggested moving up two sizes. Subsequent cruising has confirmed that despite the "new" engine, we are not even getting up on the plane.
My question is this: it is not at all clear whether we should move up one or two sizes in prop pitch. If we don't move up far enough, obviously we will not get as much extra speed as we should. But if we move up too far: what are the consequences? In other words, if we move up two pitch sizes and that is more than enough to match the engine output, what is the downside? I presume we would overload the engine, leading to overheating, at WOT. So, is it simply a matter of not going to WOT, and keeping the revs just high enough to deliver the rated performance of the boat?
Can anyone explain the pluses and minuses and problems of installing a prop that is too highly pitched for a given diesel engine?
Jeff
Had the engine rebuilt recently and the mechanic remarked that the turbocharger was barely cutting in WOT. He thought the boat was underpropped and suggested moving up two sizes. Subsequent cruising has confirmed that despite the "new" engine, we are not even getting up on the plane.
My question is this: it is not at all clear whether we should move up one or two sizes in prop pitch. If we don't move up far enough, obviously we will not get as much extra speed as we should. But if we move up too far: what are the consequences? In other words, if we move up two pitch sizes and that is more than enough to match the engine output, what is the downside? I presume we would overload the engine, leading to overheating, at WOT. So, is it simply a matter of not going to WOT, and keeping the revs just high enough to deliver the rated performance of the boat?
Can anyone explain the pluses and minuses and problems of installing a prop that is too highly pitched for a given diesel engine?
Jeff