minimum 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

 

[R.Johnson]

Re: minimum clearance between skeg fin and prop

When dealing with this size engine, a one inch increase could well make quite a change. I doubt if the clearence is causing the problem. What was the RPM's on the 12"?

 

[nordy]

Re: minimum clearance between skeg fin and prop

The RPM's was above near 6100, the ignition limiter being activated.
Without speed limiter the rpm would be even higher.

Peter

 

[tashasdaddy]

Re: minimum clearance between skeg fin and prop

i thought may be a smaller diameter, but brp only show, 10 1/4 props.