Picking the Right Prop for My Setup

[cptbraine40]

1) Performance issue you are trying to correct
Good holeshot without killing too much top speed
2) Current prop manufacturer, model, aluminum or stainless as a minimum.
Solas Rubex 14.25x19 4 Blade Aluminum Prop
4) Wide open throttle RPM and speed with an average load (very helpful)
Right around 4700 RPM
Speed around 40 mph (GPS)
) Engine/drive make, model, year, and HP
Mecruiser 3.0lx (135hp) with Alpha One Gen II (1.98 Gear Ratio)
6) Boat make model, year, length and weight
1991 Tidecraft
17 feet in length
2300 lb total (gas, people, gear, beer)

I am really wanting to switch to a stainless steel prop for better holeshot and mid-range performance. I realize that I may loose some top end speed. Any suggestions
1. Prop manufacter
2. Should I go with a 4 blade 19 pitch stainless steel go to a 3 blade 21 pitch stainless steel

 

[Starcraft5834]

the 4 blade 19p will give you the best hole shot and best overall performance.. the ss prop may move you a bit faster,, your hole shot will suffer.. if you have a boat load of people, gear and beer, the ss 21p IMHO is to much prop for a 135hp motor

 

[steelespike]

You should check out the Merc. Spitfire prop.There is a independent test on the forum today.
And I found another on the net the other day.If you normally run a 21" 3 blade with decent speed but poor hole shot
It may be possible to use a 20 or 21" Spitfire.Both the tests the props were changed for same pitch

 

[cptbraine40]

Thank you so much for the information Steelespike and Imperiral, I reallay appreciate it!!!!!!

 

[KYsean]

You should check out the Merc. Spitfire prop.There is a independent test on the forum today.
And I found another on the net the other day.If you normally run a 21" 3 blade with decent speed but poor hole shot
It may be possible to use a 20 or 21" Spitfire.Both the tests the props were changed for same pitch

I'm pretty sure the Spitfire will come in 19 or 21 but not 20P. Sounds like the 19 would would work fine for OP. If he needs to up his RPM's then the next pitch down would make him very happy.

 

[Texasmark]

All things equal, porting for the hole shot is the best solution I can see. BTDT Porting (usually) only affects the hole shot; sometimes it can jump into the picture on tight high speed turns but a little trim/throttle adjustment can overcome that. Once up to speed they are sealed off. Ports allow the engine to unload and gain rpms necessary to get the hp up when the engine is under the most severe load... in the hole. You can have the prop tuned for your best WOT performance and still have a great hole shot.

"Size matters" and that applies to the holes. The size of the hole needs to be such that you can punch the throttle in the hole, the rpms will run up immediately to 2-3k rpm range initially. The boat will start responding and gaining speed and rpm till speed is sufficient to seal off holes; after you have planed out. Then the "new load" of solid water will drop the rpms, but they will return along with your WOT speed as you accelerate. It feels like in the old days when you had a stick shift transmission in your car and had over drive where the engine rpms dropped and the speed increased.

Holes too small....no effect. Holes too large.....too many rpms and not enough thrust.

Varying size plugs are available for you to tune your ported prop to your particular situation. They sell all that on this site.

Not discounting the benefit of the 4th blade but it has it's costs and they are at WOT....you loose efficiency with more blades and that was proven way back when.....like when Merc used to ship new outboards of significant hp, like the 1000, first 100 hp OB with a 2 bladed prop.....but the fewer the blades the more vibration and less heavy load response.

What the 4th blade does gain you is better hole shot and better cruising control, especially at/near planing speeds, boat control in large swells. Butttttt you gotta get the rest of the parameters right for it or any prop to work for you.

HTH,
Mark

 

[MikDee]

Here's some good info on Prop venting:

http://www.marinemechanic.com/site/page76.html