Ultimate goal: The right Prop

[Souter 21]

Hi new here and in the UK

I run a 115 Evinrude Fitch 2003 yr. This is on a 21ft GRP fishing boat with cuddy. Its a Souter 21 also known as a Pirate 21. The boat is heavy for its size. I have now managed by raising the engine and re-propping to get 5250 RPM at WOT and about 22knts. This is with a 3 Blade Solas 15" pitch prop. If I trim up as much as poss
When I bought her she had a 18" SS Raker giving me only 4000 RPM at a push.
I am thinking a 4 blade will me up quicker and help overall. Now would I be thinking a 15" SS would be the way to go or could I use an Ali prop not only to save a few bucks but also save my motor if I whack it. Please give me your suggestions.
Solas, Ballistic what do I buy.

Many thanks

 

[jestor68]

Re: Ultimate goal: The right Prop

Your WOT rpm range is 5500-6000 rpm. HP is rated at 5750 rpm. By only turning 5250, you are not even developing full power.

To develop full power and achieve best cruising performance, I suggest going down to the Solas Rubex 4 blade 11" pitch. This should gain about 700 rpm; putting you at about 5950 rpm. Your motor will thank you for not being lugged anymore; and reward you with more spirited performance and a longer life.