I have a 2015 Bennington QCW Tri Toon Sport tower with a Yamaha F200 on the back. It has a Yamaha reliance series 3 blade 15 pitch prop. For pretty much as long as I've owned it, I can never push this motor up through the RPM range without it starting to cavitate at about 2500-3000 RPM even with the trim all the way down. If I back off of it and baby it, I can get it to grab all the way up to about 35 mph. The worst it acts though, is when I have a load of people on there and I want to nail it to go somewhere. Mostly just spins out and I have to play with it to get anything going mph-wise while other boats just streak away from me. I know my boat is pretty heavy boat to push, but I'm looking for prop or other suggestions that would let this boat hook up and bite even at the sacrifice of top end mph.
Cavitation issues
- Thread starter stbentoak
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JAMS
Well-Known Member
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I run a 4 blade SS 14.25X14 on my 150 and love the performance. I have the 21LL SPS package.
Vikingstaff
Moderator
That just doesn’t sound right. You should be able to trim out cavitation and then find out how well your prop is performing at WOT (although 15p doesn’t sound necessarily off for your set up). I am wondering if your motor is just mounted too far up out of the water and if that’s what is causing such an extreme cavitation issue for you…?
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Well ironically when I bought the boat, I originally was going to buy a Yamaha SHO/VMAX engine for it and my dealer said it would be too short of a shaft so he recommended the F200 which he said would be appropriate. I'm not an expert on determining whether the engine is setting deep enough or not but the prop is definitely below the center tune. Whether it's far enough below or not could be a question. Two thirds of its life is spent going 10 miles an hour so it's not a huge issue, but I certainly would like to have it be more responsive.
Jack M
Moderator
Check with Ken at propgods.com.
He can help you .
He can help you .
jcr159
Well-Known Member
I think the too high mounting is an issue probably. a couple pics will help. that said, most motors come in a regular and long shaft model... based on this comment, your dealer may not have used the right lower unit...
The cavitation plate on the motor should be a couple of inches below the center tube bottom. Pontoons also tend to have people in the front which can lift the motor too high. Onss tilting the motor slightly up will push the stern down as you try to accelerate. What is the top WOT RPM you can teach and at what boat speed. From these numbers you can gind prop slip.
Potomacbassin’
Well-Known Member
A Q-line boat is heavier than the other downline models, and add the sport arch and you're likely well beyond the capacity for a 14.5 inch diameter Reliance to "grab" water and overcome all of that weight and drag.
You need a new prop - one that either had more diameter or blade area. You can achieve getting more blade area several ways including going to a 4-blade prop. If you stick with a 3-blade you'll probably want to get into a 15" diameter model. It's possible you're ventilating but I would start with the prop first as that's pretty apparent (at least to me) that's at least part of your issue. You should also verify that you have a 25" shaft instead of the 20", as well as optimal mounting height. All of these factors can add up to you blowing out at such low RPM. Dirty toons will also add drag and lead to early blow out.
You need a new prop - one that either had more diameter or blade area. You can achieve getting more blade area several ways including going to a 4-blade prop. If you stick with a 3-blade you'll probably want to get into a 15" diameter model. It's possible you're ventilating but I would start with the prop first as that's pretty apparent (at least to me) that's at least part of your issue. You should also verify that you have a 25" shaft instead of the 20", as well as optimal mounting height. All of these factors can add up to you blowing out at such low RPM. Dirty toons will also add drag and lead to early blow out.