CarolinaBurt
Active Member
Hi Guys, a friend has a real problem with porpoising in his 1979 SST. This is a complete hull repair/restore with a fresh rebuilt 1988 XR4 2.4L Mercury. The boat suffers porpoising so bad that he cannot get it to speed. Even with negative trim, the boat cannot be driven past the porpoising problem.
Things I know -
1) The hull and pad are perfectly straight - Nothing convex that would normally make porpoising worse and nothing concave (hooked).
2) I mounted a 4" jack plate and have the propshaft 2.5" below the pad (both set at level like we're supposed to do)
3) I mounted a water pressure gauge so he could raise the outboard - the higher propshaft should have reduced porpoising, give easier steering, and reduce gearcase drag. The 2.5" is as high as the stock "small" XR4 case will go up.
4) 2 batteries - 1 each in the lockers just behind the driver/passenger seats (where the factory put them).
5) 80 lbs trolling motor on the bow
6) 10 gallon tank in the transom well 1/2 full (50 lbs approx)
What am I missing? Help/input needed. I've been driving my own Allison and others for 20 years, this one has me confused.....
Thanks, Gordon
Things I know -
1) The hull and pad are perfectly straight - Nothing convex that would normally make porpoising worse and nothing concave (hooked).
2) I mounted a 4" jack plate and have the propshaft 2.5" below the pad (both set at level like we're supposed to do)
3) I mounted a water pressure gauge so he could raise the outboard - the higher propshaft should have reduced porpoising, give easier steering, and reduce gearcase drag. The 2.5" is as high as the stock "small" XR4 case will go up.
4) 2 batteries - 1 each in the lockers just behind the driver/passenger seats (where the factory put them).
5) 80 lbs trolling motor on the bow
6) 10 gallon tank in the transom well 1/2 full (50 lbs approx)
What am I missing? Help/input needed. I've been driving my own Allison and others for 20 years, this one has me confused.....
Thanks, Gordon