qouestion about mounting big outboard

[mmjokerr]

I have a 1999 18ft fisher marsh hawk with a 120 force. I bought the boat used. I have a question about the way the outboard is mounted on the boat. It is bolted to the transom but it does not sit on the transom. Whomever mounted the motor used a set of hole that actually has the motor about 1-2 inches about the transom top wall. When running full speed I barley have to use the trim button to make the boat plane out and once I do get it planed if I try to bring it any higher it starts to porpoise bad which I know a boat will do but this seems to happen with a minimum movement of the trim. Other thing I noticed is that I get a rooster tail off the corners of the back of the boat to where the water will actually come back into the boat. So I guess my question is would it help to lower the motor is it possible its to mounted to high? If not does anyone have any ideas to fix above issues

[Barnacle Bill]

A motor is mounted at the correct height when the anti cavitation plate is even with the bottom of the boat. Or as close as possible.

[Scrapper]

IBFSHN is right...that is the best place to start...if you do no have a jackplate I would have the plate even with the bottom of the boat. A jackplate would put the motor away from the transom and you wouldn't get as much water in the back of the boat. I would pull it down where the plate will be even. You also take the chance on it being too high and loosing water psi. That should take care of the porpoising. Are you loosing bite in tight turns?? That is also a sign of engine being too high.

[mmjokerr]

Yes if I am wide open throttle and planed full up and make a sharp turn I slide like a car would. I have to trim all the way down and get the front protion of the boat connected withthe water to make a turn sharp turn at 45 MPH

[mmjokerr]

I do have a picture of the back of the boat posted in the eletronics forums asking about mounting my 997 transducer. Not sure if you can look at that and tell me if its to high or not

[Scrapper]

Well, you do need to trim down to make a turn anyways...when you are up on plane at WOT there should be 1/3 or less of the boat in the water...of course that depends on the motor to weight ratio. The spray should start from behind the drivers seat anyways. I have to trim down on my Ranger to turn sharp when running fast...you have to get the keel down in the water or there is nothing to "catch" and cut the water as you turn.

You need to put the boat on level ground....ie..concrete...get a level...level the put the level on the bottom of the boat...the lowest point...bottom pad...whatever you want to call it. Then do the same with the motors anticavitation plate...trim it to where it is level. When they are both level...you'll level the boat hull with the trailer jack. When that is done measure from the bottom most point of the boat to the floor....then measure form the center of the propshaft to the floor. Record what the difference is. That is your Prop to Pad setting. In example...most Ranger 300 series boats run best at around 3 1/2" below pad....meaning the prop shaft is 3 1/2" below the pad. Now this is a fiberglass stepped pad hull. The point here is, we need a base number. Something to go off of. Without a jackplate it will be alot of work...but the end result will be a better running and safer boat. Do you have a three or four blade prop?? Stainless or aluminum?? What is the pitch of it?? This could also be a prop problem. If you have lost your cup in your prop...the curvature of each blade...which does happen over time, you will lose bite...or "blow out"...this is when the motor revs very high and you slow down...like spinning out. I would guess that your P2P setting should be in the 3 1/2" to 5" range...if its less than that it needs to go down..much higher than that and you take a chance on loosing water pump psi and overheating. If you are close to 3 1/2" we need to probably go down...if you are 4 or 5...I would say the problem is elsewhere...ie the prop. let us know what you find out.