Boat speed

[ripcurl2785]

I have a formula 233 this is a very heavy boat i am running a ford 351 into a mercruiser alpha one with a 3 bladed prop. What can i do to increase my speed the boat tops out at around 23mph at about 4300 rpm is there anything i can do? will a stanless prop help? all input is appreciated.

 

[ZmOz]

Re: Boat speed

Stainless prop will help. Otherwise, you'll need to do something to the engine to increase it's horsepower.

 

[phatmanmike]

Re: Boat speed

edlebrock makes some real tricky intake manifolds for that 351, aluminum, marine compatible, just bolt on and gain 1- 30 hp. check em out. that engine is so easy to trick out, way easier than an outboard. camshaft would way boost your power and they are less than 100 bucks. and dont forget go fast bottom paint and what about lighten your load

 

[Jdeagro]

Re: Boat speed

The boat should run at least in the low 30's based on my experience. I had a 24 Searay sundancer week ender. I weighed about 5000 lb.<br />WOT was about 32mph at 4500 RPMs and cruising was best at 25 MPH.<br /><br />Sounds like there is something not right, either the engine is tired, or the prop is slipping (hub if it is rubber) or the prop is flexing too much under a load. <br /><br />Do a compression check on the engine.

 

[mattttt25]

Re: Boat speed

agree that speed sounds way low. is that checked via gps?

 

[rickyp52]

Re: Boat speed

Or could it be in knots rather than mph?

 

[ripcurl2785]

Re: Boat speed

its in mph via gps i dont know what is wrong. It has an aluminum prop maybe i will switch to stanless and the engine has les than 400hrs on it. The guy who installed the engine said the 351 made about 260hp. i cant figure why its going so slow

 

[rickyp52]

Re: Boat speed

Sounds like something is wrong. I have a 24 ft Sea Ray Sundancer that weighs in at 4500lbs, powered by a 5.7 260 HP and alpha 1 od and depending on how she is trimmed WOT is 4300-4500 rpm and top speed is 32-34mph. I also run an aluminum prop, not SS. You're a whole 10 mph under that for a relatively same size and weight boat. Don't know what to tell ya.

 

[Jdeagro]

Re: Boat speed

Don't bother going to a SS prop yet. I also ran an alluminium prop. Is your current pro new? have you had is checked? Etc.

 

[ripcurl2785]

Re: Boat speed

im trying to figure out what type of prop is right for the boat

 

[Northern Eclipse]

Re: Boat speed

What pitch prop to you have 19 or 21? if is a 19 go down to a 17 if a 21 go down to a 19, you still have a few hundred rpm to achieve from that motor to get a final top rpm range or the boat has gained weight from water trapped beneath the floors. How well or poorly does your boat get up on plane?

 

[Bondo]

Re: Boat speed

Is this a Trailer Boat,<br />Or a Dock Boat ???????????<br />Is the present Prop Dinged Up ??????<br /><br />Bottom Growth,+ Dinged Props will Really Slow you Down........<br /><br />Just going Stainless Isn't going to pickup 10mphs........

 

[BrianTindall]

Re: Boat speed

IF your engine is 260hp, with an Alpha drive at 1.5 to 1 ratio, a 19" pitch prop should net you 25 to 28 mph at 3000 rpm and around 36 to 40 mph top end (or better) at 4400rpm or so. This is from my own experience not tech data. Are you sure it's not a 302 (5.0l)? That would explain the low speed. If it is a 302, you probably have a 15" pitch prop to get that rpm.

 

[ripcurl2785]

Re: Boat speed

i dont know what the gear ratio is in the boat but im trying to get that info from mercruiser what is the standard gear ratio?