Prop Pitch

[Guest]

Hi,
Any info on what to set my prop to?
Its a maxprop twinprop used on a Dehler 34 with a Yanmar 2gm20 engine?

Signs of cavitation on the blades of mine which suggests what?
Too much or too little pitch??

Regards

 

[Sammy]

If it is cavitation then it is too much pitch. But it could be electrolosis caused by stray current or dissimilar metals. Have you got any anodes fitted and are they working?

 

[Roberto]

I posted an article about how to adjust propeller pitch in sailboats, you may find it in the Article section of the site

http://boatdiesel.com/


Hope it helps

Roberto

 

[stuartw]

Cavitation occurs because the blade pressures are too high. This can occur at anytime if the full power- high revs- is applied at low hull speeds, and is irrespective of pitch.

However, I agree with Sammy, in as much I suspect the severe pitting you may have is probably due to electrolytic corrosion.
You must check the electrical connection between the prop shaft and the engine/gearbox. There should be an electrical strap across the flexible coupling. If this is broken or indeed not there at all, then you will get corrosion on the prop itself.

I had exactly the same problem on my motor crusier, and it was the man at Poole Propellers, who suggested that the pitting on my starboard prop was this problem. He was spot on- no strap at all, when I checked.

 

[Guest]

Thanks for the comments guys... I have lost my anode.. must have rattled off the shaft.. but the boatyard guy wasn't convinced that all the damage was electrolysis as some of the damage was slap in the centre of the prop blade and he was suspicious.

I think I lifted her out for inspection just in time..
Extra anodes over side this year!
Next problem is to set the prop up again... after repair..last time boat was going backwards.. fortunately boatyards mistake.. they had to lift boat out and reset the prop at their cost.

Regards

 

[ditchcrawler]

If you know pitch & diameter of original prop try website www.progress.fr & press for english version.This gives info on installation & pitch adjustment of 2 & 3 bladed Max-Props

 

[johna]

Very interesting article to be read in some depth. Can you tell the effect of pitch on prop kick (paddle wheel effect) in reverse. Will a change of pitch increase or reduce the effect

Johna

 

[Roberto]

Thank you Johna.

I am not an expert, I would be tempted to think that an increase in pitch would increase a bit paddlewheel effect in reverse.

However, the beneficial effects of an "optimum" pitch (whatever that may mean) in forward would surely compensate for a loss of performance -if any!- in reverse. The main factor of propwalk in reverse being the trailing edge of each blade becoming the leading edge, I am not sure a difference in pitch would be too significant