prop size?

[mercrude]

1981 15' rinker bowrider just took a 1981 mercury 70 hp ob off and put a 1990 Johnson 70 hp ob with power t/t how do I determine the prop size?

 

[walleyehed]

Re: prop size?

Guessing here, but I'd say add 2 inches in pitch because the merc was crank rated and the newer eng. is prop-shaft rated........

 

[walleyehed]

Re: prop size?

I should have said this would be true as long as the gear ratios are simular.........Sorry!<br /> I'd still consider a 2" increase though...