question about tuning a boat

[fshrmn330]

I have a 18.5ft allison xst with a yamaha pro v 150. The boat will only run 50 mph wide open at 6000 rpm. My father in law has a boat twice as heavy with the same motor but will run 60? It has a 23 pitch prop Which i was told was about right and a jack plate but no low water pickup so i cant raise it too much. The boat runs great just seems like it should be alot faster. What are you guys opions?

 

[AThornton]

I would definitely think you would be pushing more than 50. Maybe someone with more tuning knowledge will speak up and help you out

 

[Skeeter]

How far below the pad are you running your prop? Do you have a water PSI gauge? A 150 on a 18' Ally should run ALOT faster than 50.

 

[fshrmn330]

I do have a psi gauge but its not working. Ive been restoring the boat and havent gotten that far yet. My prop sets pretty deep but im scared to raise it too much without a low water pickup.

 

[minner]

I would think you would be near level with the pad if not slightly above. Definately need a water pressure guage.

 

[wrechin2]

Even running deep, it should run a lot better than 50, it would just be scary to drive.

1st question.....Is this GPS speed or speedometer speed? Speedometers are very INACCURATE. I ran a calculation on the given rpm and speed and it show you are slipping 32%. Most boats will have around 10-15% for a average and I have seen some with 6%. I also feel it should need a bigger pitch prop given the boat. It should fly! Also makes a big difference in what 23 pitch prop you have. You can have 10 different 23 pitch props and each one will run differently because of different characteristic of the prop. That is why there are so many choices when it comes to props. Good thing is that Mercury props will fit your engine. I have ran Yamaha props on Mercs but never reversed. Where are you located? I have a few props that one day when I go to the lake we may be able to hook up and test a few HP props on your boat.

 

[fshrmn330]

Im not sure wrenchin what type of prop i have, i just know it has 23 stamped into it. I would definitely like to test a few and to see the difference it makes. My father in law has a spare raker 24 that we were gonna try. I would also like for you to see how far i can safely raise my jackplate. Most of the boats weight is in the rear and its sits really low to the water and ive had a few people tell me i could raise it quit a bit. I live in rock spring ga. We definetly need to get together. Oh yeah and the speed was by gps.

 

[wrechin2]

There are so many differences in props it is unreal. Keep us up to date with what you find.