Too little clearance between skeg fin and prop ?

[nordy]

Hello,

I have a 2000 Johnson 30hp.
I changed the serial prop for a 10 1/8 x 13 Vortex having tried the same Vortex prop with 12 pitch before.

The performance with 12 '' was very good but max engine speed was too high, so I tried the 13 ''.

Fixing the prop I noticed very little clearance between its leading edges and the skeg fin, 1 or two millimeters less the prop would have hit against the fin.

Performance was very disappointing, completely different from the convincing 12 '', which had wider clearance (7-8 mm).
A slight deterioration in bite due to the greater pitch would have been normal, but not this.

It seems to me clearance might be responsible for the 13's bad performance.

Does little clearance between skeg fin and propeller really strongly disturb the propulsion ?
What's the minimum clearance so performance is not deteriorated ?
Does anybody know ?

Greeting from Germany

Peter

 

[steelespike]

Re: Too little clearance between skeg fin and prop ?

What was the max rpm?
The 13 inch would reduce rpm by about 200.Doesn't seem it would kill performance but I think little motors are more sensitive to pitch changes.
It sure seems the tab might cause some sort of problems.You could remove enough of the tab to get to the old demension.There may be tabs available to give more clearance.