New Yamaha F70 prop question

[burghangler]

I recently purchased a new F70. My old motor was a Johnson 70 two stroke. The prop that is on the old motor is perfect for my boat (16' Crestliner) My question is, going from a two stroke to a four stroke, should I change my prop pitch/size? I was running a 3 blade 13 3/4" with 15" pitch. (Both motors are right around 250lbs)
Thanks

 

[steelespike]

Re: New Yamaha F70 prop question

The Johnson has a 2.42 ratio the Yamaha a 2.33 I'm thinking a 14" pitch should get you about 6000- to 6300 rpm.If this is a new purchase the 14" should be considered a starting point dealer should assist you in selecting a prop best for "your" needs.

 

[82rude]

Re: New Yamaha F70 prop question

your dealer wont let you test props?mine did and believe it or not we actually nailed it the first time.my 60 etec is dead on perfect with a 17p on a ss160 starcraft.

 

[jestor68]

Re: New Yamaha F70 prop question

The Yamaha might run about 195 rpm slower based on the ratio difference alone.

 

[steelespike]

Re: New Yamaha F70 prop question

Perhaps we should get some boat info.
There are 16 footers that weigh about 300 lbs. and others more sophisticated at about 900 lbs.

 

[burghangler]

Re: New Yamaha F70 prop question

Im finding my boat weighs about 800lbs without fuel, people and gear.

 

[burghangler]

Re: New Yamaha F70 prop question

If I was running a 13 3/4"
15p, how much would it effect performance to go to a 13 1/2" 15p?

 

[jestor68]

Re: New Yamaha F70 prop question

Why don't you test with the prop that you have and see what happens?

Edit: never mind. It came to me that you can't do that.

 

[burghangler]

Re: New Yamaha F70 prop question

New motor didn't come with a prop

 

[jestor68]

Re: New Yamaha F70 prop question

New motor didn't come with a prop[/QUOTE

You could put your data into the Mercury prop selector and it'll recommend a size.

 

[burghangler]

Re: New Yamaha F70 prop question

Used mercury prop selector, and Yamaha performance app, ordered a 13.5"x15"p, 1/4" smaller diameter with same pitch as old two stroke motors prop. Gonna try it out, if Its not what im looking for I'll return it for a different one. Didn't want to go through local dealer for the huge price markup, the motor I bought from a dealer in florida was under msrp, local dealer quoted me around $1000 over msrp