Originally Posted by Valiant Knight
I had a Solas Rubex 3*13.25*17 aluminium propeller on my 5.2 m Valiant PT520 RIB. When I bought the boat, used, in 2011, it was already equipped with that propeller.
Since one of the blades got damaged, I bought a Solas Amita 3*13.875*19 aluminium propeller.
With the Rubex 17 propeller, the engine, at WOT, exceeded 5500 rpm and went into plane easily, even if heavily loaded.
Now, with the Amita 19 propeller, the engine runs slower: at WOT, under light load, stays between 4500 and 5000 rpm (maximum recommended for the engine is 5500), but will not go into plane with 5 people on board.
Should I go back to a pitch of 17?
Don't you have any boat service who can lend you some prop to test ?
If not I would suggest go back to 17" and 4 blades.
You have mentioned that you damaged prev. prop. Are you sure that everything is OK with gear case ?
Please find mentioned below guide (this one is for Evinrude but rules are common):
Usually one pitch more is 200-300 RPM less so I do expect 5400 as minimum when you jump into 19".
I do have 19" (3 Blades) and 20" (4 blades)
I do have 100-200 RPM less on WOT (normal load)
but better consumption in average range.
I do suggest to check again 17" and RPM.
If you have much lower RPM than before go and check gear case.
They suggest to test RPM use load which you usually have.
If you go always alone, test it with single person.
If you go with family test it with family.
Hope it helps