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Motor Height and Water pump intake at WOT ??

Hi All,

3 More Pics - to Show Cavitation burns on the forward facing sides of the blades. As I believe I have stated almost all cruising speed is done at slow speeds < 1.5K RPM for nice enjoyable slow rides (I do vary the speeds some ). But this damage IMO is due to the limited WOT runs I have done and leading me to believe that I'm getting some decent cavitation at WOT that may be causing slippage/rpm surges and perhaps interfering with the water flow to my water input just in front of the Prop.

I Still owe you pics of Ventilation plate location at WOT - as soon as my Gilligan get back from out of state trip ...

I also still cannot reset my password ....
 

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Sorry…It was photos shown from other sites I believe.
 
Hi all, OK It's fixed !!! Quick summary, and I'm leaving out a LOT of Details. IT was the prop .....

Changed from ‎QA2030X Black Diamond 3-Blade Aluminum Propeller - 14" diameter x 11" pitch, Right Hand Rotation, 40 CT - 125 HP Mercury, Black Finish - changed to: Mercury Spitfire 4-Blade Aluminum Pontoon Propeller Prop 13.8 x 11P 488M8026560

More info . IMO, Motor is still too high (not changed) and it's causing dragging and speed loss. This I will follow up in the Spring when I have more time.

Cavitation and Ventilation are often interchanged ... so I'll say it once here. Ventilation is when air from the surface gets sucked into the prop - causing rpm increase and loss of speed. This can be caused by Motor mounted too high, or tight turns, or Motor tilt too high - among other issues. Cavitation is when the prop is pulling water in and pushing water out - but the front of the prop causes such a low pressure that the water changes / explodes state from liquid to gas which causes bubbles - then as the bubbles move across the blade to the edge the pressure increases and the gas bubbles violently collapse. This cause damage to prop surface, vibration to the prop and motor, noise and since the prop is pushing gas instead of air somewhat, Loss of grip, slippage, rpm increases and more .... Cavitation bubbles and prop slippage apparently affected the Water intake for the pumps as well, causing loss of water pump suction. THIS is a complicated issue issue to have and there is a LOT of information and mis information on the web. Changes to motor tilt, motor direction, Blade size/cup/pitch and more can cause this to occur or stop.

I was having Cavitation issues and NOT Ventilation issues. In My case the prop change fixed the issue and added 4 MPH WOT.

Why did I have the issue ?? In summary, That's the way IT was set up by the dealer when I purchased, they installed, the new replacement engine for my pontoon years ago. This problem mainly occurred only at WOT. I thought the way the boat rode/noise level with the new engine -was normal - at WOT so I ignored. I normally used, 98% of the time, the pontoon for slow rides and therefore did not have the problem often. After changing to the better matching prop, it is MUCH smoother overall, Quieter, better pick up from standstill, and so much better. WOT Temp did not exceed 130F.

Thanks All !!! If I have more relevant/changes issues I'll post in the Spring. Now I need to pull for Maint and Winter storage ...
 
Does this mean you won't be purchasing a Bennington?:cool:
 
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