problem with prop??

[mikeyf]

I'd like to say hi to everyone, but also apologise for raising a question as my first real post. (I knew I should have joined a few months ago rather than reading the posts as a guest).

Anyway, I'm trying out a high five prop 21 pitch as I damaged my orignal prop on my second outing this year.

My boat is a Searay 175 sp with a 3.0l alpha one whhixh was fitted with a 21 al prop.
With the high five fitted the engine easily spins it up to speed and the boat gets on the plane much quicker and handles much better. However, it reaches 4500. Rpm and about 40mph with still a bit to go on the throttle, but when I move it the last bit nothing else happens (no increased speed or rpm).

Can anyone help with an explanation? The wot quoted for the boat is 4600-4800, so i know theres not much in it but I'm wondering if I have the right prop or should I have a 19p.

I should also state that the rev limited is not kicking in, stopping further rpms etc.


Anyone???

Thanks

Mikey

[OCRDA]

Does it increase if you trip it out a bit more ??

[mikeyf]

Sorry don't understand trip it out more. If that was a typo and don't mean to offend. Nothing happens if I trim it out more.

[OCRDA]

Sorry should have been TRIM !! sounds like prop might be too big then !!

[odyssey aka Blue streak]

Sounds like yo have run out of power. IE the prop is to big. If you stay with the same outer diameter prop but drop the pitch down to 19 you will gain some where between 200 and 300 rpm.

quite a rare prop a high 5. we use them at work on the tenders. They are using the Yanmar 4 by engines and bravo 1 leg. Barrus say we are one of the only people to use them.???? dunno how much truth is in that ???

If you have access to a range of props try some thing along the lines of the mercury Rev 4 prop. Its a 4 blade and try a 21" as you have less surface area you should find the revs come up a bit with that prop to.

[mikeyf]

Thanks guys, your help is much appreciated.

I was dreading that response as I don't have access to many props and was hoping this prop was the one.

Cheers

Mikey

[Bokito]

HighFive isnt representive, its 13-1/4 diam which will destroy efficieny on a heavy inboard

21p is ok, 3 blade or 4 blade 175type boat and 3.0eng.

[larby]

I'd agree that a 5 blade isn't ideal on a boat/engine that size, a 4 blade should have more than enough grip and you'd see more top speed and better efficiency with it. (what Bokito said basically)

That said, if you don't have access to another prop easily, you could send your hi-five to a prop company such as propeller solutions and they could alter the pitch to 19 for you for much less cost than you'd imagine. I'd expect it to be under £100.

Cheers, James