Propping for max HP?
#13
21 and 42 footers
Platinum Member
#14
Registered
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I dont see how overpropping nets fuel efficiency. Reducing prop slip, I can see , but overpropping by pitch? Just because an engine rev's less, doesnt mean its using less fuel. If it takes 50% throttle opening, to turn a 30P prop at 60mph, or 40% to turn a 26P prop at 60mph, I'd think that the 26p would net better fuel economy. Generally speaking, most boats require a certain HP number to go XX mph.
We have single speed transmissions basically. One of the benefits of having an engine propped where it can go to 6000rpm, vs 5000rpm, is better performance from idle to wot. Hence why a diesel engine that makes big torque at 1500-2500rpm, but is dead at 3000, doesnt work well in most high performance boats. The torque number is there, but the powerband isnt. Throw a multspeed tranny in there, and its a different ball game..
Today I was fooling around with my new challenger. Cruising at 70mph, the engine was making 24hp and 73ftlbs of torque. Keyword, cruising. Now, what kind of power you think it takes to get a 38 Cigarette to cruise at 70mph? About 600hp per engine, or 1200hp total. Think about that next time you wanna tune your boat for a "lean cruise" .
My vote, is if the engine has the components to withstand your peak power number, prop it for that. Most likely you'll have a boat that planes better, accelerates better, and is easier on the drivetrain. .
We have single speed transmissions basically. One of the benefits of having an engine propped where it can go to 6000rpm, vs 5000rpm, is better performance from idle to wot. Hence why a diesel engine that makes big torque at 1500-2500rpm, but is dead at 3000, doesnt work well in most high performance boats. The torque number is there, but the powerband isnt. Throw a multspeed tranny in there, and its a different ball game..
Today I was fooling around with my new challenger. Cruising at 70mph, the engine was making 24hp and 73ftlbs of torque. Keyword, cruising. Now, what kind of power you think it takes to get a 38 Cigarette to cruise at 70mph? About 600hp per engine, or 1200hp total. Think about that next time you wanna tune your boat for a "lean cruise" .
My vote, is if the engine has the components to withstand your peak power number, prop it for that. Most likely you'll have a boat that planes better, accelerates better, and is easier on the drivetrain. .