Prop “blowout”

[Luv2whelie]

Hey guys! So here’s the deal: I have a ‘97 Crest pontoon with an Optimax 135 on it. I’ve had issues with cavitation and or ventilation and yesterday put a new 17p 14.8” prop on it (what it came with originally). Local boat shop lowered motor a notch end of last season. SO.. I can go out on it now, and it’ll run great, good holeshot, 30mph at 4250rpm. Life is grand. Or maybe not? I may leave my Cove and when I try to rev over 3000rpms it may lose traction and rev up to 5000 rpms regardless of trim! I find I can’t adjust it to not have this happen. Or it may do great all day! Brand new prop and hub yesterday didn’t fix it. Cavitation plate is maybe an inch or two lower than transom.. I’ve fought this problem for 5 years or so. One last thing, every now and then my engine rev limits for no reason. Even at 3000ish rpms.. restart clears it up. Thoughts before I set it on fire?

 

[Scott Danforth]

welcome aboard

where is the anti-vent plate with respect to the water? that is most important on a toon as the transom could be anywhere.

the fact you are still ventilating.....most likely you are still too high.

in reality, 'toons need a powered jack plate AND powered trim to handle weight transfer and different loading.

 

[Sea Rider]

Is prop having aeration issues when on flat calm water cond, how about close turns at speed ? If with any of both situations drop one hole down and test again. Prop will spin at a higher water bed level achieving better thrust to work with.

Test on flat calm water cond, trim must be set at 90 deg and load evenly distributed on deck. Report youir findings.

Happy Boating

 

[Faztbullet]

Which model Crest? 3rd toon? You need a prop with large ears(we call em mouse ears") as performance props don't work well on a toon. Need like below..

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[h=1]Mercury BlackMax 3 Blade Aluminum Pontoon Propeller [/h]

 

[BillP]

I think there are two primary reasons pontoon boats like to cavitate. Hull speed is too slow for the rpm/prop pitch and the other is engine mounted too high. This is seen on large heavy displacement boats with outboards with high pitch props too. Large area round blades with flatter pitch fix that or lowering the engine. I lowered the engine on my 20' toon with 50hp 4 stk to fix most of the problem. It would still lose grip every now and then when heavily loaded with 6 people and picnic stuff. Toons are more sensitive in this regard with weight so running light was never a problem after lowering the engine.

 

[Texasmark]

You don't have a "ported" prop do you? Ported: holes of varying shapes (round or square) and sizes just below the leading edge of each blade.

Ported props were designed for heavy arsed Bass Boats as an aid in getting a good hole shot with a prop tuned for WOT and go-fast operation. Putting such on a toon would act like the Bass Boat while still in the hole and the port would be injecting exhaust gasses across the prop blades making for a light load on the engine and excessive rpms with reduce thrust to propel the toon. ?????????