prop for a 454

[wmattk]

I got a,454 magnum with a bravo 1 outdrive. right n i W I have a 15 x 17 ss prop on it (3 blade). I get around 30mph @ 4200rpm. how do i speed it up.

 

[Getaway]

Not sure if you can get much faster. I have the same boat with the Alpha drive. My 15x17 pitch aluminum prop would get the boat to 36 mph, but I would fall off plane easily. Not good when boating heavy seas in the Great Lakes.

About 4yrs ago, I switched to the 16x16 aluminum prop and at 4200 r's I run 31.5 MPH. She cruises nice around 3200 at 24-26 mph and stays on plane down to 16/17 MPH.

 

[The Magic Bus]

I have a 15x19 on my 88' 268DA and get 36mph at 4000rpm.
Same motor and out dive. Dialing in the trim tabs and outdrive tilt also helps.

 

[bergs]

Not sure if you can get much faster. I have the same boat with the Alpha drive. My 15x17 pitch aluminum prop would get the boat to 36 mph, but I would fall off plane easily. Not good when boating heavy seas in the Great Lakes.

About 4yrs ago, I switched to the 16x16 aluminum prop and at 4200 r's I run 31.5 MPH. She cruises nice around 3200 at 24-26 mph and stays on plane down to 16/17 MPH.

I don't have my prop in front of me at the moment so I couldn't state the dimensions (it's a 3 blade though), in addition to this post and other information I've read, I feel like I need to make improvements here as my 268 Weekender falls off plane anywhere under ~25 mph (as indicated by the boat's speedo). Takes about 8 seconds to get up on plane but cruises nicely around 3500 RPM @ ~30mph....which seems off when I read a couple responses in this thread.
I am still working to understand props so my knowledge is somewhat limited but I know that I need something more as I don't feel it digs out of a hole well enough and the time to get up on plane is something I'd like to cut in half.

I spent the better part of this past Labor Day weekend on Lake Winnipesaukee (NH) trying to figure out what the boat needed in order to get around my concerns and I was not satisfied by Monday. The one thing I didn't try was using the trim tabs to get out of the hole but did not think it was necessary. Wouldn't my outdrive angle have a greater effect on this over using the tabs?

Somewhat of a threadjack, yes, but I didn't see the value in starting a new thread for basically the same quesion.

 

[Getaway]

I don't have my prop in front of me at the moment so I couldn't state the dimensions (it's a 3 blade though), in addition to this post and other information I've read, I feel like I need to make improvements here as my 268 Weekender falls off plane anywhere under ~25 mph (as indicated by the boat's speedo). Takes about 8 seconds to get up on plane but cruises nicely around 3500 RPM @ ~30mph....which seems off when I read a couple responses in this thread.
I am still working to understand props so my knowledge is somewhat limited but I know that I need something more as I don't feel it digs out of a hole well enough and the time to get up on plane is something I'd like to cut in half.

I spent the better part of this past Labor Day weekend on Lake Winnipesaukee (NH) trying to figure out what the boat needed in order to get around my concerns and I was not satisfied by Monday. The one thing I didn't try was using the trim tabs to get out of the hole but did not think it was necessary. Wouldn't my outdrive angle have a greater effect on this over using the tabs?

Somewhat of a threadjack, yes, but I didn't see the value in starting a new thread for basically the same quesion.

My boat fell off plane at speeds under 25 mph as well until I went to the 16x16 prop. 16x16 means: 16" diameter, 16 pitch.

For ease of understanding, a 16 pitch means with 1 turn of the prop, the boat moves 16" forward. Your prop is a 15x17 which is 15" diameter, 17 pitch (17" of forward motion per 1 turn of the prop). The lower the pitch number is equivalent to changing the gear ratio in the rear differential of your truck or like going from 4-wheel HIGH to 4-wheel LOW. The lower the 2nd number, the higher the engine will have to rev to attain a given speed. This does a couple things, it gets the engine up on the torque curve quickly which will make the boat jump up on plane faster/easier and it also takes away from your top speed by raising the working RPM's of the engine.

The higher the 2nd number, the harder the boat will work to get on plane, but once the engine starts to rev up, the faster the boat will go, it will just take a long time to get the engine reving higher. It is like starting a stick shift car out in 3rd gear.

Now, the 1st number is just prop diameter. The larger the diameter, the more water the prop will push. This will help the boat stay up on plane at lower speeds and it also improves the handling of these bigger boats. This will also scrub some top end off the boat so the engine wont rev as high and the top speed will go down slightly.

FYI, the biggest diameter prop you can fit on an Alpha1 is 16". Not sure on the Bravos.

When taking off, leave your trim tabs alone and lower your drive all the way to the farthest down position. This pushes the boat up on plane quicker. As you come up on plane, start to raise the drive up little by little. This will pick the hull up out of the water, make the boat handle better and increase your speed. At that point, use your trim tabs to correct the attitude of the boat. You can bury the trim tabs down on take off, but that leaves you a lot of extra things to do as the boat planes out. My trim tabs are generally always at the same attitude and I will make small corrections based on waves/boat loading etc. With the 16x16 prop, I don't need the extra down force from the trim tabs to get me up on plane.

Hope this helps.

 

[bergs]

^^^

Thank you.

Based off the numbers on the prop, I currently have a 15x15.

78116A45 15P

Definitely some room for improvement

 

[268 Frakenboat]

Getaway,
Thanks, that is great info. Are you running a aluminum or stainless prop? What brand are you using?

 

[Getaway]

Getaway,
Thanks, that is great info. Are you running a aluminum or stainless prop? What brand are you using?

Mine is an aluminum 16x16 either Quicksilver or Michigan Wheel prop.

I don't remember which brand, but it is definitely one of those.

 

[FHDOG]

I run a 15 1/2x15 4 blade Revolution4 prop on my 250DA. It turned that boat into a faster and much nicer handling vessel.