Polycraft 455CC Prop sizes

[cheno]

Thanks Piscator,

Thats awesome performance for a 40hp piscator.

I went for a run with the 12" yammy prop this arve and still only got around 50kmh @ WOT. The acceleration is still tops and the revs are down a little 6000rpm instead of 6200 @WOT. I talked to Solas about the set up and when he talked me through it it appears that my motor is too low.
He suggested that having it too low would be knocking off around 200rpm and 1.5 knots or so.

Therefore have just jacked it up onto the third hole from the top tonight (It was on the second top hole). Given that, maybe the 60hp will be able to swing a 13 pitch after all ?? We will see.

BTW. How much spray does your CC poly put out at the transom when the motor is trimmed in. Also, does yours have a bow up attitude? With mine its as though I cannot get quite enough negative trim.

Cheers

[piscator]

Hey Cheno

If anything, at rest, the boat sits slightly bow down due to the back hull extensions. Your motor is also about 28kgs heavier which may put the bow up a little, what else do you have down the back that maybe weighty?, battery?,fuel?, livey tank?

Underway you'll find these things respond really well to the trim button - if you've got a heap of spray inside the leg around the two extensions then either your motor is too low or you've got it trimmed in too far.

In flat water where you can hit WOT and stay there I can trim out until there is no spray at all, the hull doesnt porpoise and the steering is nice and light.

On the question of WOT rpm's I thought your 60 was the same as my 40. WOT ought to be between 5000 and 6000 with full HP attained halfway between. I wouldnt have any prop on mine that meant I could sustain 6200 for any length of time.

As you say, good performance for a 40, the money I saved from a 50 or a 60 will still be buying me petrol for a couple of years yet...

Cheers
Brett

[Cloud_9]

your right piscator 6000 Rpm is the max revs recomended so any more and your shortening the life span of your engine, sugest you go up 1 pitch, you'll get more speed at less revs, or at least same speed with less revs.
you cant beat stainless props theres no flex in the blade like with ally and they cut the water cleaner for less drag a Ally prop can loose as much as 1" of pitch under load

Cheers Cloud 9

[cheno]

Tested the new 12"prop after lifiting the motor up one hole. Much quicker- 61kmh in the Brissie river @6100 WOT
Filled my 65l evakool full of water to simulate load.

Then

Went for a spin around peel today to test the new set up

Had wife + dog = another me on board.

Still got to 6000rpm @ WOT 57kmh trimmed out.

Can do full lock at high speed turns without any cavitation at all. Perhaps i could go up another hole to the top one?

However, she does tend to porpoise a bit too much for my liking though. Even at around 4500rpm. Battery is under console and front hatch has extra chain plus two anchors in it. It would seem that this is not enough though. Perhaps a couple of sand bags would work but I'm not too keen to add extra weight that does nothing.

Anyone tried a foil on these things?