engine swap need new prop

[muddstopper]

I own a 95 tracker pro 17 aluminum boat. Of course it is used and had several different owners, but the boat is in pretty good shape. Anyways, when I bought the boat it had a 40hp 4cly and after a little motor raiseing I was able to hit 30mph, gps checked, but it seemed the boat was a little under powered. I bought a 89 model 60hp 2stroke mercury. Boat is rated for 60hp. Not much difference in the engine weight. Motor came with a 11x13 ss prop. Speed jumped to 37mph but would start porpoising getting worse the farther you went. Motor already had a whaletail on it. I am happy with the speed, but the engine was turning 5800rps at wot. Not a big problem, just back the throttle down and the boat ran super smooth at 35mph. Figureing I was heading toward a prop swap, I decided to raise the engine to see if it would help with the porpoising. Removed whale tail and Ventilation plate is now pretty level with bottom of hull. Boat hit 40.2 mph, but rpms went up to 6000rpms. Still had slight porpoising at 39mph, but just a little bump bump bump, not the bone shattering bucking bronco ride it had before removing whale tail and raising motor. Any ways, I think I am about as far as I can go just moving things around. Now I need to work on reducing the rpms and am thinking a prop swap should take care of the problem. I am not really looking for a speed increase, but figure a bigger prop might speed things up a mph or two. Mostly just trying to figure out how big a prop to buy. I dont mind buying a new prop, I just dont want to buy two or maybe three trying to get the right one.

 

[Scott Danforth]

put a cooler in the bow to help porpoising

you could change props to a higher pitch, however if you have a group of people in the boat, you will want the extra power your prop has

 

[muddstopper]

I usually fish alone, sometimes with a friend. Boat aint big enough for 3 or 4 folks. I also dont carry a cooler except maybe a lunch mate. I did add a small battery to the front storage bin to run a fishing light. Battery is small, might weigh 20lbs. Took it out today, ran part throttle at 5500-5600 rpm, 35mph with motor trimmed all the way down. I could trim up a little, but rpms would start climbing, 36-37mph at 5800rpms, no porpoising, unless I hit wot, go to 6000rpms and then it would porpoise. I think I will put the whaletail back on, but I got to get the rpms down. Talked to the mechanic at boat shop and he suggested a 10 3/4x15 prop. Since I dont know the guy, I dont know if he knows what hes talking about or not.

 

[Scott Danforth]

you may want to verify your tach. WOT RPM range of 5500-5800

throw the whale tale away.

you can control the RPM with your right hand.

 

[muddstopper]

Yea, the tach has been sort of a mystery. Wouldnt read anywhere near right at first. Changed the settings on the back of tach and seems pretty close now. I can say the motor is screaming when it says 6000rpms. If it is off, it cant be off by much. I probably should get one of those tiny tachs to hook up. I also think I might need to richen up the carb just a tad, darn sure dont run to run too lean at those kind of rpms. I do control rpms with my right hand for the most part, but I have been mostly making test runs and trying different things trying to fine tune the whole setup.. I dont do tournament fishing or anything like that, but I do want a boat that performs and rides good and I am perfectly happy with the 35mph speed of the boat. I topped off the gas tank last night so I will be fully loaded for the next test pass. Going to turn the idle mixture screws out about a 1/4 turn and see what that does. This motor has had a bunch of fooling with by a supposed mechanic that didnt know what he was doing. I aint a boat mechanic, so its taking me a while to figure out how to adjust things and undo someone elses work.