Prop question

[b_lish1966]

I have a 1976 starcraft runabout open bow tri hull with 1980 70hp johnson, going to put a new prop on it this year and would like some input from the pros on here as to what I should put on it. Don't know what pitch prop was on it, was painted and quite old so couldn't find any markings. Just want a prop for over all good performance. The boat is 15 feet long, I'd say with a full load I'm looking at 1500 pounds.

 

[b_lish1966]

Re: Prop question

Currently the WOT is about 5500rpm at 28mph.

 

[steelespike]

Re: Prop question

Very difficult to make reccomendation without the present prop size.
It appears you are in the motors rpm range but the speed seems a little low.
Look carefully on the barrel of the prop or under the prop nut for numbers or a prop shop can determine the size.You could get your prop refurbished for a lot less than a new prop.It would be good to borrow a tach to dertermine if your tach is accurate.Pitot speedometers are inaccurate a gps reading would be better.You can optimize your setup, vertical height of the motor.Anti ventilation plate just above the prop should start about even with the bottom of the boat.Then you can raise it one hole at a time to just before venting becomes a problem.Verticle height and trim could give you 2 or 3 mph depending on where you are at now.

 

[b_lish1966]

Re: Prop question

I just bought a solas 13.75 x 15 prop from iboats. Now onto a question about tiny tachs, would like to purchase one but not positive which one, the xlr model indicates it's the most common choice for outboard motors. I have a 1980 70hp johnson, is the xlr model the right one for me.

 

[steelespike]

Re: Prop question

I don't have any experience directly with a the TinyTach.I do know it is a simple install and as I undestand it it uses the plug wires.Someone here no doubt has a tiny yach and can help.They must have a Faqs section or contact us over at Tiny Tach.