pm203

I have heard two schools of thought regarding more blades, more stress on the the drives.One opinion is that with more blades such as 5 or 6, there is more stress on drives. The other opinion is that with more blades, there is less vibration and less stress on the drives. I am currently running 6 bladed Herings and like them alot.I know that with a six bladed prop, the actual size of the blades are smaller.And, with six blades, there is always more blade in the water. Also, another factor is supposably, with a Hering, the prop is so well built and balanced, that it is much better for stress on a drive, than say a stock Merc prop....... Does anyone really know and why?

Harper220

great subject, I'll be interested to learn more about this also, since I switched from 4 to 5 blade props last year. everything you mentioned I have heard also, so this should be interesting.

Pat McPherson

From what I have heard/read, more blades are easier on the drive if you are putting the power through the drive that it was designed for.
If you bolting 750HP to a Bravo XR then a 4 blade is easier on the drive then a 5 or 6 would be because it will slip more.
Great topic! I too will pay close attention to what the prop gurus have to say.
I have been considering going to a 5 blade, but I only have a stock Bravo hooked to a 450HP/502 and I am hard on my equipment.

throttleup

There are many variables that effect the load on the drive, of course props are one of them. More blades can reduce the stress on a drive, especially in surfacing applications through a reduction in vibration. In situations where the water is choppy enough for the boat to bounce out of the water but the drive still remain in the water the more blade keep a more consistent load on the drive. Of course a full launch in the air and not pulling back on the throttles with a 6 blade prop will load up the drive more than a 4 blade.

Most of it comes back to style of throttling and boating. Weight of the boat the boat has a lot to do with the load on the drive as well. An 8000lb boat with 2 drives loads up the drives more than a 4000lb boat with 1 drive, especially in rough water.

The standard prop shaft will hold up to 5 and 6 blade props but only with conservative power and smooth water. Even the larger XR prop shaft will break with conservative power.

I think water conditions have a greater overall effect on drive loading than the number of blades on a prop.

Matt

bbladesprops

This question comes up often. I have covered it on some of the previous threads too.

Adding blades can effect the drive life in both ways.

The easiest way to look at it is that more blades offer a more constant load. This can wear parts faster if the drive isn't designed to handle the torque and hp being put through it. However, when the props are surfacing (most of today applications) the shorter duration from load to unload can actually add life to the drives pieces parts.

You really need to specify the situation/application and then say, "which prop will make my drive last longer?" We can use slip to add life to certain drive set ups with exaggerated power.

Basically, any number of blades on the drive designed to hold the hp you have, should hold up just fine. That doesn't include launching the boat or drag racing from dead stops. Driving technique matters!

Pat McPherson

OK then, I'd like to ask about my application.
1997 24' Superboat, 3500lbs dry, 450HP/502, standard bravo drive (2004 model). The prop shaft is 5" below the bottom if that matters.
I'm currently running a 28p 4 blade prop and I am considering buying a 5 blade next.
I don't drag race but I do catch air when the going gets rough. I am pretty good at throttling back when I catch big air.
Would going to a 5 blade stress my drive more than the 4 blade does?
Thanks

throttleup

Considering the weight and power of the boat you should be fine with a 5 blade and a standard prop shaft. This is assuming the drive is in good condition.

WOT rpm also plays into the drive loading as well. Turning a small pitch propeller at a higher rpm will load the drive less than a large pitch at a lower rpm.

The 5 blade prop will load the drive more in certain conditions; such as accelerating, getting on plane and when launching the boat and not throttling properly. You will notice less vibration as well with the 5 blade prop.

Matt

bbladesprops

I'm trying to remember the drive you have. But even a standard Bravo 1 will handle the power you are delivering with the Maximus. You are also relatively deep which dissipates some of the re-entry loading in normal operation. The drive life is up to you and your habits now.

We should continue to discuss the specifics of the 5 blade on your hull though.

(B1 is here.)