Ventilate while cornering.

[jedimaster]

Ok, so I have run a 19pitch aluminum for a few days now, and I am seeing ventalation at high speed maneuvering. If I trim down its ok but I never had this problem with the 17 pitch. I much prefer the top speed of the 19 over the 17.
I want to get an SS prop, Hole shot is fine, slip is ok, and rpm's are sitting at 4600 RPM's at WOT, with a rec of 4200-4800 for my motor(Mercruiser Alpha One).

The Aluminum is uncupped.
Here are my thoughts If someone could offer some suggestion on what one to try that would be great.

18 Pitch cupped 4 blade SS
19 Pitch 3 Blade Cupped SS
21 Pitch 3 Blade Uncupped SS

If you think I should use something other than whats listed I am all ears.

 

[jedimaster]

Re: Ventilate while cornering.

I should also say this is for a 17 foot bowrider, with a 140 mercruiser. I am looking for a top speed cruising performance versus low end. When I am tubing I will swap out to the 17AL.

 

[Tail_Gunner]

Re: Ventilate while cornering.

What is your rpm when your running the 19 alum??? Or 17 for that matter..

 

[jedimaster]

Re: Ventilate while cornering.

4900rpm wot 17pitch Aluminum
4600rpm wot 19 pitch Aluminum

The thing I am trying to do is go to an SS and gain some bite in the corners, I am ok with the speed and hole shot from the 19 Aluminum, I would mind getting more top speed as the hole shot is still pretty good with the 19.

 

[MikDee]

Re: Ventilate while cornering.

Usually a larger diameter of the same 19" pitch will ventilate less.

 

[Tail_Gunner]

Re: Ventilate while cornering.

4900rpm wot 17pitch Aluminum
4600rpm wot 19 pitch Aluminum

The thing I am trying to do is go to an SS and gain some bite in the corners, I am ok with the speed and hole shot from the 19 Aluminum, I would mind getting more top speed as the hole shot is still pretty good with the 19.

Those figure's seem a bit under the mark, can you find out your gear ratio, aka even a older 3.0 should turn a 17' glass boat to 4900 with a 19 pitch alum and glasstron does make a good hull...............Umm this is not a tri-hull is it?? and is your tach correct????

aka i have a similar 17' starcraft that turn's a 21@4800 rpm and a 19@5100 rpm with the 21 doing top speed and the 19 is a tube puller, gear ratio 1.98 i very sure.. Following a old tried and true would put you into a 15p ss with some cupping and getting you about 48-4900 rpm wich sound's a bit shy.....unless you have a 1.66 gear ratio or something similar

 

[jedimaster]

Re: Ventilate while cornering.

I was under the impresion that the alpha was a 1.94 gear ratio.
Its an '88 - not a tri hull.

I would assume the tac is working an is correct how can you tell? I tried counting but the flywheen moves too fast.

Gear ratio according to this anyway,...http://www.saltwaterfishid.com/sterdrive-gear-ratios.htm