help, need advice on outboard hieght

[LANCETHOMAS]

Hi, i just bought a 98 glassport bass boat with a bad locked up motor. I changed it to a 115 hp johnson and need help with the hieght of the out board please. take a look at the pictures and tell me if it is to high. I can only get about 40 mph with it trimmed out. It looks about 2-3 inches above vent plate. Thanks i am new to this site but it is been very helpful.

 

[redfury]

Re: help, need advice on outboard hieght

By no means am I an expert, but from my intensive reading here, this is what my cumulative knowledge points me to....

Since the rear of the boat has a "hitch" in it, it's going to allow water off the keel to rise up to the "upper" transom. That area is where I'd adjust my height to. I'd think that you are dragging too much motor in the water and raising it a couple of inches could be beneficial.

Raise it up and take it out. If you have cavitation problems ( air in the prop ), you'll know it when you start taking sharp turns. If that doesn't happen, then you can try raising it another notch and test it again.

It's a lot of fiddling, but you'll appreciate the efficiency and running depth of the boat when you get it dialed in.

 

[LANCETHOMAS]

Re: help, need advice on outboard hieght

Thanks, i was thinking it was to high because i was going by the lower hull of the transom. But i am new to this and didn't really no. On my other boat that i took the motor off of ran at 5600 rpm at wot and was about 49 mph. But it was a old hydrasport trihull bass boat about the same size. This one maxs out at 5000 rpms at wot and about 40 mph. So i lost 600 rmps and speed. I no two boats are not the same but i still should not have lost any rpms. So you think i should go by the step in the back of the transom instead of the bottom of the hull. I can take more pic. if it would make a little more helpfull.

 

[rockyrude]

Re: help, need advice on outboard hieght

You want to go by the lowest point of the keel. At wot that "step" should be out of the water. The generally accepted starting point is to have the cavitation plate 1-1 1/2" above the keel.
btw-- pretty unique design though

 

[redfury]

Re: help, need advice on outboard hieght

Yeah, I'd run off of that step. Jserb had a similar thing with his boat since it had a detached mount for his twin motors on the big scarab. Since they were set back from the original transom, they had to be higher up to compensate for sitting lower when the angle of the boat on plane was taken into account.

Of course, all of this is the reason for the beauty of a jack plate on a boat