another prop question

[refg3880]

i know this has been asked before but i can't seem to find the right answer using the search function:

I'm a newbie boater bought a 88 bayliner with a 85 force outboard. it has the original prop on it: marked 13.5x17p flat blade but is in rough shape, i bought a Michigan 072107 13.25x17p and the boat lost 5 full mph and the motor sounds strained and at wot i get blow out in the turns. i do not have a tach. i put the old prop back on and right back to 32mph

the question is: is the 17 cupped hurting me? does anyone make a flat 17? would a 15 cupped fix it? is 32-33 mph about right for this boat?

thanks bob

 

[steelespike]

Re: another prop question

Welcome,You should read the stickies at the top of the page.
get us as much info as possible.
I'm surprised your getting blow out with a brand new prop with cup.
Is it truly cupped?
Getting you rpm right is important for best performance and motor health.
The motor needs to be able to operate near the top rpm rating at wot.
Unfortunately without the rpm its impossible to evaluate your setup.
The Force isn't noted for its speed. 33 is reasonable depending on the size of the boat.
Is the speed by gps?
You might be able to borrow a shop tach,buy an induction tach or an optical tach.
Or maybe find a Force tach.
Yes a 15 would help your rpm and power but suppose you really need a 16 or a 14 to be right? could be expensive trying to find the right prop.And then without the tach you don't know if your right on.