What size props? Volvo AQ130 / 270 setup

[elv_1986]

I am trying to find out what size props I should be running on my boat. She is a 28ft planing cruiser.

Currently, my old Volvo AQ130's are trying to push 15x19's which I think is a little over pitched!! From calculations I think I should be running 14x15's?

Does anyone run this setup on a similar size boat, what prop size do you have?

Thanks!

 

[Spi D]

Your engines are meant to reach 5100 rpm at WOT.

Provided they produce the nomimal power (=are in good nick) you should change props until the 5100 can be reached. Weight is one of the biggest factors affecting the power needed to move your boat, so make sure you remove any dead weight before trying further.

Once down to your normal load let her run flat out and see what rpm you get. Rule of thumb says that one inch less in pitch makes 200 more rpm and vice versa, so by knowing what you have, calculating what you need is quite simple.

When you have 5100 rpm at WOT the overall ratio/load on engines are right and you'll see best possible overall mpg.

The only true way to check if rule of thumb is valid in your case, is by testing.