prop help

[Redneckboat21]

Ok i bought an 1989 Invador and it has a 19 pitch i guess and i think i also have a 21 or 32 i am not sure how to tell what the pitch is but i want a better top end speed and also help getting up and go faster where the boat can flatin out on the water faster and both props are 3 blades. i have no idea about props and pitches

 

[matthewpa]

Re: prop help

We first need to start out with some more details such as: Boat weight, length, engine size, what is your current performance (need RPM's at wide open and speed, with GPS is better as speedos are usually off). Is it an i/o or outboard?

 

[Redneckboat21]

Re: prop help

We first need to start out with some more details such as: Boat weight, length, engine size, what is your current performance (need RPM's at wide open and speed, with GPS is better as speedos are usually off). Is it an i/o or outboard?

the boat weight i am not sure of at the moment and it is 16.1 feet long and it is a valvo i think a 120 hp and the rps is about 4 to 5 sometimes 6 and i am not sure what the topend is i have not went wide open i am scared i will blow the motor if the rps go off the geage and it is an I/O

 

[matthewpa]

Re: prop help

A 19 or 21 pitch sounds about right on that boat. What are you expecting for wide open speed? You also are talking about a huge rpm range. This motor should max out around 4700-5000rpm. You most likely going to be in the 30's for top speed. Remember though. You will not be able to run at WOT all the time on these motors, they just are not designed to do that. You also will not have a magic prop that will give you the best holeshot and top end speed. You have to compromise on what you want.

 

[Redneckboat21]

Re: prop help

ok but how can that be when i got a jetski and i can go about 45 50 on it and it is only a 70 hp motor and what is WOT

 

[matthewpa]

Re: prop help

Your not on a jet ski, your in a boat and weight is a huge factory. WOT is Wide Open Throttle.

 

[Redneckboat21]

Re: prop help

ok if the ski has only 70 hp and the boat is about 120 how can the ski go faster than the boat when it has more hp

 

[matthewpa]

Re: prop help

A jet ski has very little weight when compared to a boat, it also has much less surface area actually touching the water. The more surface on the water, the more drag. An easy comparison, a Mini Cooper is a very small car with little weight and little horsepower. A larger BMW in the 3-series is much heavier has much more horsepower, but yet the Mini Cooper still performs in 0-60 acceleration better.

 

[Redneckboat21]

Re: prop help

oh ok but i was like in the high 30's to the low 40's with out full throttle

 

[Redneckboat21]

Re: prop help

would i need to get a Hydrofoil Stabilizer or what would that help the boat to do

 

[matthewpa]

Re: prop help

Boat speedos are usually off some and your RPMs seem to be all over the place. When you were at those speeds, what was your RPM readings?

 

[rad1026]

Re: prop help

you are a very patient man Matthew

 

[Redneckboat21]

Re: prop help

i will let you know sunday because i plan to take it out saturday

 

[Redneckboat21]

Re: prop help

you are a very patient man Matthew

why you say that to him

 

[Redneckboat21]

Re: prop help

Hey Ya'll I took my boat out today and i had a 14x21 pitch prop on and the rpms were about 5000 or little more and speed was 37 and that was WOT. The prop was also making a weaird racket noise and my grilfriend drove it and i looked at the prop and it was shanking bad to me and it did not do that when i had a 19 on there i was woundering if the 21 was too much for it or is that too small. could i use a 4 blade on my prop or does it have too be 3?