how do i get top speed from props?

[irbracer]

hi everyone, i know this website is for RIBS but thought i would see if i could get some info from you guys anyway.

I race IRB's with my local surf club on the gold coast, we race 377 gen 2 single hull thunder cats and are wanting to get more speed from our props i am just wondering what is the best way to do this?

Cheers!

[Roflhat]

What engine have you got on it? How many splines is the prop and what pitch and diameter?

Going up in pitch will give you a higher speed but with less acceleration, generally in the surf you want a lower pitch prop.
If you are using an aluminium prop you can gain performance all-round by changing to a stainless steel prop.

[simsy]

fit a little rev counter, and choose a prop that revs the engine to the very top of the stated normal rev range...

[lukewhiting]

If your in the surf a 4 blade will give smoother power delivery, faster acceleration, less cavitation & better handling but in open water won't be quite as fast as a 3 blade prop.

If its a 50hp tohatsu usually a 14pitch works well. But in the surf a 4 blade will give the best all round performance. Try raising the engine, that'll give you much more speed in these boats!

[irbracer]

cheers for the feed back!
we run stock 25hp tohatsu within the slsa guidelines and rules, and four blade props ranging between 9.0 and 9.9, of which we are wanting to get worked to get the best out of, is there and small aspects such as how much cupping or little of there should be?
cheers!

[Cookee]

Originally Posted by irbracer

cheers for the feed back!
we run stock 25hp tohatsu within the slsa guidelines and rules, and four blade props ranging between 9.0 and 9.9, of which we are wanting to get worked to get the best out of, is there and small aspects such as how much cupping or little of there should be?
cheers!

It's very small subtle differances in props that make a big difference and I would take it to a prop guy and get him to sort it out - it's very easy to mess a prop up if you don't know what you're doing!

[Roflhat]

Originally Posted by irbracer

cheers for the feed back!
we run stock 25hp tohatsu within the slsa guidelines and rules, and four blade props ranging between 9.0 and 9.9, of which we are wanting to get worked to get the best out of, is there and small aspects such as how much cupping or little of there should be?
cheers!

9 to 9.9 pitch? that's going to seriously limit your top speed. My mate's got a Ceasar Surfcat with a Tohatsu 30 running and the 13p prop wasn't enough. He's now running a 10x15 Ron Hill chopper, but it could easily spin more.
If you haven't already get a tach (tinytach are good) and an accurate GPS to measure your speed, these will help massively when tuning props.

[irbracer]

Yeah I understand there is a lot more improvement for top speed but it comes with the sacrifice of acceleration which still plays an important part in these races as they are only over 120 meters with a a doughnut around the first bouy and a patient pick up on the second, we are mainly losing speed on the run back to the beach.

[Maximus]

Originally Posted by irbracer

Yeah I understand there is a lot more improvement for top speed but it comes with the sacrifice of acceleration which still plays an important part in these races as they are only over 120 meters with a a doughnut around the first bouy and a patient pick up on the second, we are mainly losing speed on the run back to the beach.

Don'nt Throw an Extra Burger on the Barbi??
I mean...When the Prop's sorted...anyway to make the Rig itself lighter/ faster?

[shedsmith]

Talk to performance propellers on the Brisbane river, you need a tachometer before you you know anything.

[matt h]

Think its sorted now. It was 3 years ago!

[shedsmith]

Ha I'll look at the date next time, been a long day