Cavitation at 4,000 rpm

[KSMCCL]

Just purchased 2013 24' Avalon Windjammer tritoon with lifting strakes on inside and outside of all three 25" pontoons. Having cavitation issues at 4,000 or higher rpm.

Powered with 2014 Honda 150 hp 4-stroke. Dealer setup outboard with 15x17 aluminum prop. Engine mounted as low as possible. Do you think I need different prop size? Any thought or ideas?

Thanks,
Kelly

[HandymanHerb]

Let us see some pictures of the rearend, you can even include some pic's of the boat , and how do you have it loaded when it happens ?

Welcome, glad to have you with us and I sure some of the smart guys will get on soon to help

[KSMCCL]

Water was choppy, had 8 adults of average size 4 in front, 2 in middle seats, and 2 on rear loungers.

[HandymanHerb]

Pictures work better at 640x480

[justrfb]

Hello Kelly.
I am by no means and expert and I am sure more people will chime in here but it is my limited experience and knowledge that the main "cavitation plate" on the outboard motor has to be level with the bottom most portion of the transom it is mounted on. Your engine looks a few to several inches too high. Your marina will have to figure a way out to get it lower. Looks like a jack plate is in order... Good luck and safe boating.

Sincerely,
Rich

[rancherlee]

4 blade prop helps ventalation issues quite a bit. I've notice a lot of pontoon manufactures have gotten away from running strakes all the way back to motor on center pontoons also. I didn't have an issue with ventalation issue before I added strakes to my center pontoon but sure have them now! I've had to drop my motor all the way down on the transom and run a good stainless 3 blade or 4 blade aluminum to keep it from venting and it's still very trim sensitive. I can NOT run 3 blade aluminums anymore, I just blow them out past 4500rpm. My theory is that the negative angle of the strakes trap air and feed it directly to the prop, some of the better handling toons on the market have the strakes stop about 2' before the transom and/or have a notched transom on the back that acts like a setback plate.

[Bamaman]

If your boat is loaded moderately (2 people, 1/2 tank of fuel), is your boat then ventilating at any speed? What are your maximum rpm's? If you trim the motor down slightly, is it still ventilating?

Your Honda runs a 2.14:1 gear ratio which is a little lower than some other manufacturers. The 17 pitch prop sounds like the correct prop for your boat. If you're over-reving, you might need to drop back to a 15 pitch.

What does your dealer say about the ventilation problem? It should be up to him to get the boat's performance right. I agree that you may have a engine height problem.

You know, we ask so much from our aluminum barges, including carrying both light and heavy loads efficiently. They're all just one big compromise.

[RcgTexas]

8 adults of average size 4 in front

Weight distribution might be a problem. Before spending to much money try loading her a little heavy aft and see if it makes a difference.

[Cycleman07]

From the looks of it the motor is set a little high. The cavitation plate should be set even with the bottom of the middle log.

[KSMCCL]

Wish I had an easy way to lower the OB a little. Dealer just gave me a 14 1/2 x 15 stainless to try. Going to see how that performs on Sunday. My wife wanted the darn rear lounges so not perfectly setup to put extra people in back comfortably. Hopefully this new prop will help.

Thanks for all the feedback. Has anyone tried removing the last 2 ft of strakes on the center log and had better results?

Thanks,
Kelly

[rancherlee]

That's a lat ditch effort, definatly try to correct with propping first. I like the speed and turning of the strakes but hate the very touchy ventalation. Best prop I have tried on mine so far is the 4 blade mercury spitfire, it just flat out grabs water but is a good 3mph slower than my stainless 3 blade. I use it for water sports. I'd like to try a 4 blade stainless but I plan on upgrading to a 115 for next year so I really don't want to dump 400$ on another prop. I might cut some of my strake off the back BUT I have the tools/welder In the garage to play around with aluminum and an old pontoon.

[Bamby]

Is it "New"? From here it looks like someone put a short shaft motor on a transom that needed a long shaft. A long shaft would have provided about an addition 5" in which you could have utilized a couple and still been in real good shape. With what you have now a anti-ventilation plate may be your only option to minimize the problem.

[rhorne]

When testing the s/s props, get the right pitch and then if you need to, you can have a good prop shop add some cupping to the tip. This will help with cavitation. I have a Tahoe which is very similar to your toon. Lifting strakes on all 3 toons. I don't have any cavitation problems and I am running in the 2nd hole.

[KSMCCL]

Dealer sent me 14 1/4 x 15 stainless prop to try. Took the family to the lake today and cavitation problem appears to be solved with the new prob.

Full throttle resulted in 5,500 max RPM and 36 mph maximum speed.

Boat loaded with:
25 gallons of gas
700 lbs passenger weight
Plus BBQ and cooler

Does this sound about right, or should I try another prop to get RPM up to 6,000 WOT?

FYI, I have kids that will want to go tubbing behind the boat if that makes any difference?

Thanks,
Kelly

[Bryden24shp]

Glad to hear the new prop fixed it. Yes, I think you are probably spot on. Unload the family, ditch the grill and run it unloaded. I bet you'll be over your 6000 R's and probably running in the low to mid 40's. Feel the wind in your hair at WOT and you'll be driving a Baja next summer!