Outboard Propeller ?

[TKilgore]

Does anyone have experience with or know the difference between a three blade and a four blade O/B prop?(other than the obvious)



Is there an advantage to the four over the three. If going to a four, would a pitch change be necessary? With props of the same pitch, would RPMs be lost with four?



Thanks



Tom

 

[JLEONARD]

Most of my knowledge and experience is with inboard boats, but the basics are the same.

The most efficient prop would be a one blade, but we know that isn't practical. That being said it goes that a 3 blade would be more efficient than a 4. The more blades, the more they mix up the water and make the water turbulent for the next blade.

But they can do some blade geometry changes to help make up for that. . such as changing rake angles, blade surfazce areas, etc.

And depending upon the speed of your boat and where the prop is (like in a bass boat) a 4 blade prop may offer some advantages over 3.

You will need less pitch if you go with more blades to keep wot rpm the same.

Also changing from aluminum to stainless may necessitate a pitch change. Aluminum is weak so the blade tips must be thick. They also flex under load (chnging pitch)

Stainless is stronger so the blades can be thinner, and it also does not flex as much (keeping pitch the same).

Your best bet is to find a prop shop and talk to them about what you need specificlly for your boat and the type of boating you do.

Hope this helps.

Jay

 

[LSMITH]

A four of the same pitch will get you out of the hole faster but your RPM at WOT will likely be excessive. You will gain with a same pitch 4. Stainless props if you run in soft bottom areas is a really nice change, you get out of the hole quick and faster top end speeds to boot.



Jay gave you the best advise up above. Find a prop shop and talk to them. There is a certain amount of voodoo and PFM in the propping of a boat for the best possible performance. They may even be able to tweak your current prop and get you what you need. A really good prop shop is fairly rare, when you are asking around there will be one or two names that pop up time after time. Those are the ones to talk to.



PFM=Pure F (uhhhh Freakin ) Majic.

 

[TKilgore]

Thanks for the info

I would have thought the 3 blade of equal pitch would have higher RPMs because the 4 would grab more water (what do I know) and the 4 would act like a "power" prop.



Anyway, thanks for the input



Tom