cavitation

[john_fox]

??? I have a anew stessco 4.2 RV Catcher with a 30 Hp Yamaha (tiller). I appear to be having cavitation problems in that I have noticed grooving on the inside of the prop blades but I have not noticed any problem in performance. I have changed the prop from a 12 to a 13 and there is still a problem. Has anyone else had this problem .

[adrian]

is the cavation in a turn or straight line ? try and see if you trim the motor down if it still happens or if you can low the motor down . cavation is caused by the prop coming out of the water and trying to push air instead. as for the grooves cant say i've heard of that one
hope it helps

anzac

[NQCairns]

Hi Renard, do you mean that there is some prop burn evident? Where is the inside of the prop blades? How long does it take for the paint to fail on those areas. We will try to help here but a call to an aftermarket propeller company might set you straight faster. If you find out what is going on let us know. nq

[Kerry]

Lets no get Cavitation mixed up with Ventilation as Cavitation has nothing to do with motor height, air etc. The terms describe 2 distinct and different problems.

Cavitation can however be complicated when ventilation also occurs, which decreases pressure on the back of the blades even more increasing the effects of cavitation.

In diagnosing, one really probably needs to closely inspect the actual prop as "grooving on the inside of the prop blades" would mean a lot more with the prop in hand. What is the "inside" of a prop blade as cavitation occurs on the back of the blades generally due to changes in pressure.

Cheers, Kerry.

[john_fox]

Thanks for the replies everyone. What I meant by the inside of the prop blade is that side of the bades that is closest to the transom. Further information is that the the groves are etched into the blade in a single line following the curve of the blade and this process begins apparently straight away as the first time I noticed it was straight after my first run and the same with the replacement prop. I suppose you could refer to it as a burn but to me it is more like etching and it increases in depth with each use.

[bungie]

sounds like you are rubbing on something, sure you are not making contact with the gear box housing ??

[NQCairns]

Hi again, yeah like Kerry and Bungie says, it is damn interesting though considering both standard props cause the same problem, i have never heard of this as typical, on those motors. Does the marking follow a radial line as if you held a marker to the spinning prop and was able mark a circle? if so then I would look for something more physical like a hose fitting when flushing or whatever? All this is a fair way over my head but very intersting!! Hope someone can help more, look forward to a pic if you can post it, dont forget to post the answer when you find it. Just had a thought - how do you tow on the trailer with the engine, could the prop spin in the air and rub like on an ocky strap etc? Good luck.nq

[merv]

mate i had same trouble try asking dealer if they will let you try a couple of props . try a 9 7/8 x11 1/4 f.for a start . i ended up trying solas 3 & 4 BLADES ENDED UP GOING BACK TO STANDARD PROP. I HAVE CHANGED MOTORS TO A YAMMY 40 STILL HAD SAME PROBLEM SPENT TIME DOING TRIALS WITH GOOD FOLK FROM SOLAS PROPELLAS TRIED 6 DIFFERANT PROPS FROM 3 TO 4 BLADES.THERE IS SO MANY FACTORS WITH TILLER STEER LIKE CORRECT LOADING ECT. HAVE YOU TRIED FITTING A HYDROFOIL?HOPE THIS MIGHT BE OF SOME HELP . MERV

[Cloud_9]

Try going to www.mercurymarine.com
on this site flip through you will find propelers and development there is about 5_10 pages on how propelers work and what happens when things aren't right it will explain cause and simptims of your troubles.
hope this is helpful to you.