17' j craft porpoising.

[T.rev]

Tried this in technical dis.
1968 17' j craft is porpoising when towing skier
120 Johnson with 23 pitch prop.
motor set at the lowest holes for motor mounting.(motor is high on boat)
does around 40 mph (on speedo)
trim at lowest point
rpm at just below 5000
how can i correct this porpoising problem?

[shaggydog]

I just bought a 1968 16' jcraft and was wondering how rare of a boat it was if anyone can help id appreciate it... new user

[mr fun]

just a quick rule of thumb, move some weight foreward, are your tanks in the rear? battery? chances are those things can't be moved easly, but anything else back there like coolers etc. I would bet could help, too much weight aft will definatly affect a hull in this way. fun out

[DoktorC]

Where are finding these old J's??? I'd love to see some pictures.

like fun says move weight to the front or maybe a drag plate or smart tabs..

[Dave Strong]

J Crafts are pretty much an outboard flat bottom, remember years ago they were sold by Canadian Tire. Was a guy used to show up couple times a year with one that had a 2.4 200 on it had a 25 High Five on it, as long as the water was totally flat it ran good. Any wakes or wind and it was a hand full to drive.

Dave

[T.rev]

Hey......
thanks very a lot for the info guys, great stuff keep it coming
tank is in front, filled it with gas, left a person or two on the dock, just a spotter in the boat ,problem not completely gone but what difference.
might try a little less pitch prop to pull skiers up easier....
wow more history would be appreciated as well.

[south599]

a whaletail or foil is something simple to bolt and and reduce porpoising. can also help with holeshot sometimes.