115 HP 6 Cyl- 1980 Boat Speed

G

Grandview

Cadet
Joined
Jun 2, 2009
Messages
8
I have a 6 cylinder 1980 Mercury on a 1988 Vanguard Phantom that has a 13 X 19 prop. The boat is 16.5 feet long and is fiberglass(open bow) and is basically a ski boat. I'm trying to determine if the engine is producing the appropriate speed for this boat and motor combination. The WOT is about 5500 and the motor runs fine.

The top speed is about 38mph with one person in the boat.

Is this reasonable or should I be looking at any improvements to the motor?

Thanks.
 
75TowerOfPower

75TowerOfPower

Petty Officer 1st Class
Joined
Apr 17, 2009
Messages
331
Re: 115 HP 6 Cyl- 1980 Boat Speed

I have a 15.5' Trihull that is fiberglass with a 79' Merc 115 and I can squeeze out 38 mph too. I know how you feel about wanting to get more out of it. But i can't help on getting more out of it. I did recently add a StingRay hydrofoil and that helped the hole shot and the stablity.
 
C

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,137
Re: 115 HP 6 Cyl- 1980 Boat Speed

It takes a lot of power to produce high speed on the water. I would test the compression of the motors and if it is 125PSI or greater and even on all cylinders, you are likely getting all the performance that rig can generate. PTT will add some speed, if you do not already have it. A jackplate could add some performance as well. If you can get 500 more RPM out of it, you can switch to a 21 Pitch prop.
 
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