Posts: 3478
Location: Elk River, Minnesota | Hiya,
Any chance of getting some pictures of the motor mounting and the stern of the boat?
Looking at the weight of the boat (900 pounds), and the gear ratio of the motor at 1.85:1 maxed out at 60hp, I would bet that the motor is over propped by about 2 inches or so.
I'm running a boat that weighs just a bit more than the esox magnum at 961 pounds in a console version and maxed out at 90 hp with a 2.1 ratio. I'm running a 17 pitch prop and am just a touch under max rpm, and a tad slow out of the hole.
With a gear ratio turning a motor 1.85 turns with one turn of the prop, I have a pretty solid feeling that the prop is just too much to turn.
In the normal mounting position for the motor (basically standard on most boats), the motor is mounted one hole up off the transom. This puts the cavitation plate even, or sometimes just below the lowest point on the transom, which allows for good overall handling and performance. What I am betting is happening in this case, is that when the boat gets on plane, the motor is too weak, thus the prop just doesn't bite the water. This can happen with a higher pitch prop when the motor does not reach an RPM level that can handle the prop. When a motor is over pitched, getting out of the water is slow..almost painfully slow. Then, when on plane, the motor is not turning enough rpms, so the prop cannot bite the water and still hold the bow up.. so....the bow stays down, and the prop gets too much exhaust since it is not being thrust far enough away fast enough, drawing it into into the prop, or the prop is too close to the surface and pulls air in. if the latter is the case, it can be offset a bit with a cupped prop, but going to a cupped prop reduces rpms more, and a lower pitch is needed to offset the reduced rpm. In many cases, one can raise the motor if they go to a cupped prop.
If you lower the pitch, the higher rpms will help the motor keep the bow up and not allow air or exhaust to enter...better grab, better out of the hole performance, and overall a much better handling boat too. He'll be able to trim the boat and it will respond.
I'd say see if he can get an 11 x 13 semi-cleaver yamaha prop and go from there for a test run...I think he will be pleasantly surprised, and he can potentially move the motor back up to it's original position.
Steve
Edited by VMS 9/30/2010 7:53 PM
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