Outboard Props

[Mo Money]

What determines if a prop will have good low end power vs high end power.Other than corrosion resistance and strength is there any other reason to buy a stainlees over aluminum?

[muddog]

I think pitch makes the difference,when I had a ski boat we played with different props until we got the hole shot power for lifting the skier quicker,as far as alum. or stainless the price difference is huge,I have heard that stainless has no give like alum. that if the prop doesn't give something else will,but that is dock talk you need info from someone who knows what they're talking about---there's my one cent :shrug:

[Joe Schwab]

When I bought my Duckworth outboard it came with stainless prop. I liked to positive feel of stainless and had tried several aluminum props to be sure. They felt mushy on the hole shot. However after one high speed collision with an underwater object that completely destroyed my lower unit and then a low speed bump that barely cracked the prop but bent the prop shaft I have retired the stainless to aluminum. My insurance company was delighted with my decision. I went from an 18 pitch to a 17 and find my RPM's slightly higher and my cruise plane much better at 3600RPM. Stainless props are tough, but at what expense?

[judyfish99]

I'm with you, Capt. Hook. Rather have a bent prop....

[Draggin' Bait]

If your object was maximum speed you would probably opt for the SS prop. At WOT it will deform less and perform better.

[Catching Nemo]

Got stainless.... not anymore.

http://www.ifish.net/gallery/data/500/medium/4055p1r.jpg
http://www.ifish.net/gallery/data/500/medium/4055p2.jpg

After the damage this prop did to my lower unit, I think I will stay with aluminum from now on. Insurance replaced the prop but it is now a spare and I use aluminum as a primary.

SS has less flex, will give you a better hole shot, and the difference is noticeable, but so are the repair $'s.

[yankemnbankem]

looks like that prop got to much cowbell! :smash:

[Mo Money]

what does 17,18,19 pitch refer to?How does that number go along with top end speed or low end power.If you go from 18 to 19 would that give more top end or low end power?Who knows what all this means.Yoy guys with the seahawks and the yamahas,What are you using ?

[treegolfer]

The higher the number for the pitch means faster speed at equal RPM. Lower pitch equals faster acceleration. A 19" pitch would be faster at a given RPM than an 18". This is all theoretical though, depending on hull, horsepower, etc. You can put too much prop pitch on and lose speed because the motor doesn't have enough power to reach higher RPM.

treegolfer

[Fish-n-Fever]

This might help explain further about prop sizing.

Prop sizing (http://www.fishwis.com/articles/Props_pick_the_right_one.pdf)

Ron

[Poi Dog]

As a rule of thumb, you pick up about 200 rpms for every degree you reduce the pitch of your prop. In other words, if you were running 4000 rpms at a 19 pitch, reducing your pitch to 18 would increase your rpms to 4200, and a 17 would increase your rpms to 4400, etc. It is essentially like down-shifting gears in a car, so you can get more low-end torque, but you forfeit speed on the top end. Of course this is just a rule of thumb, and there are a lot of variables that can affect the gains achieved through re-pitching.

[Joe Schwab]

Essentially the lower the pitch the slower you will travel at a given RPM. Each turn of the prop causes the boat to travel forward a certain distance. Like adding teeth to a gear, the higher the pitch the further you will move per RPM. When you reach too high of a pitch you will start to lose RPM due to the load being too high for the horsepower.

I prefer to use the largest diameter prop I can fit on the unit and pitch it accordingly to acheive plane at medium RPM range. For my boat that is 3600 RPM. It stays nicely on plane and the engine is not lugging.

Every boat is slightly different.