Propeller churns up water

thereitisgone

Hello all, looking for a bit of advice. Bought first boat at start of last season and drove it all season no problem. This spring needed to gelcoat a lot of the hull of the boat that went well but had engine and tilt system of boat and i grinded the edges of the propeller where they had hit something small, but now i notice when i open the engine up it kinda throws water up just behind the boat, no real notice in power difference. I think its probably where i grinded the prop it has like a 1 cent size piece knocked of it. Starting holidays after 1 week so will take it out of water then put new prop on but is there anything else that could cause the engine to throw up the water like this. Its a Yamarin 435 with a 50 hp 2 stroke. Thanks for any help.:)

fergal.b

I would say it's the prop unless you have bent the cavitation plate. Also check that your trim is going down all the way.

thereitisgone

Is the cavatation plate the flat bit above the prop , pretty sure its ok but will check again when i take boat out of water. Removed the zinc Diode also, does this have any influence when put back on, it can only go one way as the prop hits it but does a slight change of angle do anything bad.

fergal.b

Yep that's the plate. With the anode removed do you now have a hole in the plate and the water is been forced out of that by the prop.

thereitisgone

no the anode was on it always just maybe it was not set at exact degree i read somewhere that it shold be off set a little bit but i bolted mine on straight by eye, dont think this is the problem but just trying to cover everything. Am going out tomorrow so will have another look and try take picture. If nothing else you will see what lake lohja in finland looks like from the back of a boat.

fergal.b

They are off set to counteract porp walk were as the prop turns it also moves the boat sideways in the direction the prop turns it's very slight but with it straight you will find the boat will turn on it's own so you set it like a little rudder to keep it straight, I don't think thats your problem.

thereitisgone

Ok thanks very much fergal will change prop in next week or two and let you know how it works out.

ISAW

thereitisgone wrote: »

Ok thanks very much fergal will change prop in next week or two and let you know how it works out.

Im not experienced on engines but I know fluid dynamics and physics
If your engine has sufficient power and your prop is a distinct size then even with the optimal trim you should reach a threshold in terms of RPM for a given prop. after that adding revs will only cause cavitation. In other words your prop can be overpowered. So

1. Don't deliver full throttle - when you get to optimum that is it adding power will only slow you down

2. trim, sea conditions and maybe fluid density e.g. fresh or salt water might affect this.

3. Use a smaller engine or a bigger prop.

I could be totally wrong about the above. What do you think?