first, thanks for being here, guys like me do somethign totally different in life, and we apprecieate being able to pick your brains when needed.

I have a 31' profile V Hull with 24 pitch 4 blade props. At WOT I run 4400 RPM at ~60 mph, running stock, 330 hp 454's.

I am going to increase horsepower to about 430 per motor, and want to run mid-70's.

What am I going to do with the props to get there?

Thanks a million for your help.

It depends how fast you want to turn the motors. I assume 5000 will be fine. If so, the props you have now will be fine test platforms.

One thing though, 200 hp gain will probably not get you 15 mph with your hull.

What is the weight of your boat?
What is the year of the hull?
What drive and gear ratio do you have?

I want to run thru some calculations and need a little data to do this.

Julie

Hey Julie,

Thanks a million for your help. Boat weighs about 8000 loaded, 7000 with 1/4 tank and one person, light on gear. It is a 1993 hull, and I run a 1.5 gear ratio.

I estimate a 10% slip, but am not sure about that, I am guessing there.

Again, thanks.

Just a guess... you may pick up 5-8 mph. mid 70s will be tough. IMO

ummm, not good. I was running 59/60 at 4400 RPM before, I figured I was picking up 200 HP, 800 RPM, and losing about 600# from the engine compartment, I read somewhere it takes 15 to 20 hp to make one MPH, so 200 should equal 10 mph, and the added 800 rpm should get me a little more, and the weight was a bonus.

what am I missing? are shorties the answer to get to those speeds? Profile says this is thier fastest hulls, so what do I need to do to get the added speed besides gobs and gobs of hp, which would test my drives....

Hello Dean51267,

First lets start with your old set-up. Running at 4400 RPM with a 24P 4B (Bravo I props?) which are actually a 23P, with 1.5 gears at a speed of 59-60 MPH (GPS?) you have 6% slip, which is unlikely. We typically see that low of a slip number with 6B props. So we need to verify this data , please.

Were you running 4b Bravo I props?
Is your speed of 60 MPH a gps speed?
Which 454's do you have?

Julie

With the engine up grades you'll more than likely be raising the rev limiter slightly. With the engine you mentioned in the first post, you wont want to spin it more than the low 5's. I'm guessing your changing a bit since you mentioned the weight decrease. If indeed you gain 200 hp, the 800 rpm is possible but not guaranteed. With the current slip you gave us (I figure at 7.29%) you will hit 70.5 mph at 5200. I agree that slip sounds low. If you remove weight from the boat things will improve too.

Of course this is theoretical but usually quite accurate. As you attempt to get higher and higher speeds, it always seems to take more than you anticipated.

Again, using the current props as a test base seems to be a great and obvious choice. Don't buy props till the engine work is done and a baseline is accomplished. Let us know if you would like to test some propellers.

Take care.

the props are 23P Revolution Hydromotives, not Bravos, does this make a difference

Julie,

West KY just said tell you hello....

dean