prop size/speed

S

Steve O

Cadet
Joined
Jun 25, 2006
Messages
12
I have a 95 crestliner sportfish 1950 with a 4.3 GL volvo sx drive 190hp. When i first got the boat it had a 15x17 prop. WOT was 3900 rpm. It got on plane terrible with 3 people in the boat. Max speed was 38 mph. I switched to a 15x15 turning point aluminum prop it comes out of the water great now but speed is the same, wot is 4500 rpm where it should be. People I talk to say this boat should do 45mph. Do i need to switch to a 14 1/4 x17 maybe or is this all the faster the boat should be. Any help is appreciated.There is normally 3-5 people in the boat.
 
R

rndn

Commander
Joined
May 20, 2007
Messages
2,323
Re: prop size/speed

You don't state whether your speed is gps or the speedo. If it's the speedo you really can't use the number because they are usually off. You should always prop your boat to reach the suggested rpm's at wide open throttle(WOT). You will probably not get more speed by going to the 17 inch prop you will just take your rpm's too low. You may get more speed by going to a stern lifting prop as certain props can help raise the stern such as a 4 blade SS Stiletto. An SS prop may also on it's own give you a couple more MPH's.
 
S

Steve O

Cadet
Joined
Jun 25, 2006
Messages
12
Re: prop size/speed

It was the speedo and depthfinder they were both the same.
 
45Auto

45Auto

Commander
Joined
May 31, 2002
Messages
2,842
Re: prop size/speed

It's very possible that 38 is the most speed you'll get out of that hull (due to drag and weight) with 190 HP. I have a 16' Mark Twain with 120 HP that does 33 with a 16", 19", 21", or 23" pitch prop (speedo MPH, no GPS). 4400 RPM with the 16. Only difference speed-wise is that it takes longer and longer to come up on plane as the prop pitch increases. Obviously the max RPMs go down. I think it was just below 3000 with the 23".

I've found that most boats are 10-15 MPH slower than the owners like to believe, and burn about 50% more fuel than they claim. My other boat has a GPS that I can download and print out the route plots, speed, heading, distance, etc. When we go out with friends and several boats, I quit showing them how fast and how far we were going because they seem to get real defensive about it!

If you really need more speed, try to borrow a prop to try it before you spend the money and don't gain anything.​
 
S

Steve O

Cadet
Joined
Jun 25, 2006
Messages
12
Re: prop size/speed

Really dont need more speed just trying to find out if i am not running boat at its potential. I usually cruise around 3500 rpms anyhow
 
S

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: prop size/speed

At a 190 hp on a 19 ft boat unless really heavy it would seem the pitch would be in the 20s and speed over 40.Gps is the best way to get your real speed.You may need to look elsewhere for your problem.Compression,tune up
throttle opening all the way?Fouled or damaged bottom?
 
S

Steve O

Cadet
Joined
Jun 25, 2006
Messages
12
Re: prop size/speed

motor and boat good shape, maybe a 14 1/2 x 17 a good try but it will probobly be hard to get on plane juct like the 15x17 was, prop wizard said to use a 14 1/2 x 17if towing or heavy load. Not sure what brand of prop 15x17 was as it mysterously dissapeared from my truck. My kid loves to scrap,metal etc , probobly gone.
 
Tail_Gunner

Tail_Gunner

Admiral
Joined
Jan 13, 2006
Messages
6,237
Re: prop size/speed

Steve O said:
motor and boat good shape, maybe a 14 1/2 x 17 a good try but it will probobly be hard to get on plane juct like the 15x17 was, prop wizard said to use a 14 1/2 x 17if towing or heavy load. Not sure what brand of prop 15x17 was as it mysterously dissapeared from my truck. My kid loves to scrap,metal etc , probobly gone.
Click to expand...


Well the SX drive has a 14''s barrel size.....i once put a prop with 13.5 inch barrel on one and she cavitated badly. Apparently the mismatch between the drive and prop created enough turblence to make the prop a lousy performer....Perhaps 1" more is creating issues too
 
You must log in or register to reply here.
Top