How Are These Number On 15' Tri Hull With 70hp Johnson

[gsrsol84mm]

1967 Dixie Tri Hull, 15' with 1998 Johnson 70hp. Just installed the tach yesterday and ran the boat today with myself, my wife and my 2 year old son. Could only get 4900-5000 rpm's WOT at 33.8 mph. The prop looks like a stainless 13x19. The Bimini was up.

We pulled my 12 year old son and his friend in a tube today and the boat seemed to get out of the hole without any problems. Myself, my wife, my 2 year old, my 12 year old all in the boat pulling another 100 pound 12 year old. Doing 4000 rpm's for about 28 mph.

How are these numbers ? is the boat performing as expected ? Is 4000 rpm's a good cruising speed for this motor ?

Would appreciate any feedback, thanks.

 

[steelespike]

Re: How Are These Number On 15' Tri Hull With 70hp Johnson

If your sure the new tach is accurate you need more rpm. Was your speed by a gps?
You need numbers closer to 6,000 but before doing a prop; check your motor height.
The antivent(cavitation) plate just above the prop shouild be a little above the bottom of the boat. you can check with a straight edge from side of keel to the plate.Be sure the motor is in excellent tune and the throttle plates in the carb open all the way.Prop is in excellent condition and bottom is clean and smooth.
Let us know your rpm after checking these things.