Too much cavitation from new prop?

[CaneCutter79]

With the videos below, does this sound like too much caviation? I'm happy with my current motor setup. I just don't want to damage my lower unit, the prop, etc.

The prop is a new 17-pitch 3-blade Turbo1 on an 85hp Evinrude with a 15.2 tri-hull fishing boat. I have great lift and the fuel mileage is great. I've increased my mileage a good bit with the new prop.

On the first video, you will eventually hear the prop cavitation at the end of the clip.


On the second video, this is at WOT with full trim (what I usually run). The motor sounds like a "V8" engine with all the cavitation. Is that OK or is it going to damage anything?

 

[trendsetter240]

Re: Too much cavitation from new prop?

I watched and listened but it sounds fine to me. What RPM do you get a WOT trimmed out? You might be over-reving the motor a bit. Mine sounds similar at 6600RPM.

It's not likely that any cavitation is happening. Ventilation is when the prop blades break the surface and the RPMs increase dramatically with little or no speed increase or even a speed decrease.

 

[CaneCutter79]

Re: Too much cavitation from new prop?

No chance of over-reving here. I only get 5,000rpm WOT at 37-38mph from the 17-pitch. My old prop was a standard 3-blade steel 19-pitch with much less rake and cup. It would slip if you over-trimmed but I got 39mph and 5,100rpm from it. The agressive rake and cup from this prop reduced my RPM by 100 and my speed by 1-2mph but I have a lot of bow lift.

I like the prop. The boat rides a lot better and gets better mileage even with the agressive blade design.

 

[trendsetter240]

Re: Too much cavitation from new prop?

Well, if you like the way the boat rides with that prop and you're not over reving I'd say enjoy it.

Normally cavitation happens when there is something disrupting the water stream ahead of the prop like a transducer or damage to the hull.

Cheers

 

[steelespike]

Re: Too much cavitation from new prop?

Just to be sure we are all clear Slip is the efficiency of a prop driving through the water. Actual forward motion compared to theoretic movement through a solid.
It varies depending on the prop & boat around 15% is acceptable.
Venting , called by some "cavitation" and the prop pretty much loses its grip on the water.Cavitation is usually only seen as slight damage to the prop surface and not felt.
Your motor sounds fine but I believe it needs to run closer to 5,500 on todays fuel.
If you add any load you will be lugging.

 

[CaneCutter79]

Re: Too much cavitation from new prop?

If you add any load you will be lugging.

I wish I could get 5,500rpm.

As for lugging, my buddy weighs about 290 and I?m 190. My boat is only 15.2ft long and it's a heavy tri-hull. Even with (2) 6-gal tanks, three marine batteries, tackle and about 5-6 rods a piece on the bow, I lost all of 1mph on my top end. The boat was leaning to one side sitting still but when you punch the throttle, she jumps out of the hole and rides level with roughly the same bow lift. We were both impressed considering he had a 18ft Ranger with a 200 Venom.

 

[hwsiii]

Re: Too much cavitation from new prop?

cane, your prop slip and cavitation are below 6%, and that is excellent, so in my opinion you are in great shape. To gain the other 500 RPM you want you will need to reduce your prop pitch by 2".



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