New Prop for Westerly Konsort with Betamarine 20hp

[freebird1]

As part of re-engining my Konsort, I need a new prop. Different companies have given different suggestions. I only want a fixed two blader.

The main choice I am making at the moment is either 14x9 as suggested by CastleMarine prop calculator or 12 x 11.25 as suggested by the Betamarine contact. The Beta chap suggested this was more efficient.

Max diameter is 14" and that is already pretty close to the hull (1.25" clearance). I currently have a 14" x 13".

Your thoughts?

 

[sailorman]

both of those suggestions would be ok.
the rule of thumb if you add 1 inch to the dia reduce the pitch by 1 inch
swing the max you can

12 x 11.25
13 x 10.25
14 x 9.25

so 14 x 9 is ok

 

[philip_stevens]

So what is wrong with another 14x13 as the 20 Beta is probably the same as what you have removed - most Konsorts have a Bukh DV20.

I changed the two blade prop for a three blade prop of the same size and pitch, on our (previous) Konsort, and the Bukh 20 had no problem with it.

There is a link to a downloadable prop calculator on the WOA website that you could use, to check yourself, but it is in the Members Only section.

 

[sailorman]

it will depend on hand of prop beta v Bukh
gearbox reduction

 

[doug748]

I have a 13" * 10 1/2" on a Contessa 32 - same engine. Seems ok, lets it rev to over 3000.

 

[sailorman]

that would equate to 14 x 9.5 then /forums/images/graemlins/wink.gif

 

[doug748]

That is right.
Must say I know nowt about these things and have always considered prop calculations as a more academic facet of Black Magic.
I like your rule of thumb, which I have not seen before. Thanks.

 

[freebird1]

I think I will go for the largest diameter as it works fine with the current engine.
Yes Sailorman - different gearbox ratios are the reason for the change.