Prop blade tip clearance required ?

[Boo2]

Hi,

I've heard that you can get a knocking noise and damage to the prop if there is not enough clearance between blade and hull but can anyone tell me how much propellor blade tip clearance is required ? Prop is a 17x12 3 blade folder by Radice.

Thanks,

Boo2

 

[DownWest]

15% of the diameter and not less than 8%. Courtesy of Ian Nicolson.
DW

I loosley remembered it as 10%, but checked.

 

[PCUK]

Yes,10% is a rough minimum. Too small can also scour a groove in the hull.

 

[charles_reed]

15% of the diameter and not less than 8%. Courtesy of Ian Nicolson.
DW

I loosley remembered it as 10%, but checked.

Agreed.

 

[Pye_End]

Is it a saucer shaped hull, or a traditional wineglass. You can get away with less with the latter, but probably not with the former.

 

[Boo2]

Thanks to all for the replies,

Boo2

 

[Colin K]

Is it a saucer shaped hull, or a traditional wineglass. You can get away with less with the latter, but probably not with the former.

Thats interesting i have only got 1/2" clearance on a 14 3/4" prop and I get no noise, wearing of the hull at all. I do keep an eye on it mind.

Cheers Colin.

 

[rjp]

I've also seen the 10% figure quoted but have considerably less, maybe 5% and have never had any problem, but I would be happier with more.

 

[PuffTheMagicDragon]

I have a 'wine glass' hull and the clearance is around 3/4" on a 14" 3-bladed prop. The shaft is offset and the prop lies at the side of a skeg. The only 'problem' that I am aware of is that one of the cockpit drains is right in line with the blades and they tend to suck air down the drains when at high revs, thus ventilating the prop and losing grip. Solved it by keeping the valve for that drain closed when motoring.