79 S&S porposing?

[CleanCarShop]

Begins around 38-40 mph...tried moving everyone forward...no fix. there is a small imperfection around the rudder, I have heard that small dents or holes in the gel-coat can cause porposing....other wise i never knew this to be an issue with this hull, any help?

[MakeMineaS&S]

Maybe a dinged or bent prop.

Seriously, it's back there turning what, like 3800-4000RPM at 38-40MPH?

That's a HUGE impact on the water, and more than a tiny gelcoat crack or whatever. I'd check the prop first. After that...

What is the boat doing up to that speed?

At a steady rate at say 30, 32, 34, 36, how is the ride? Porpoising? Uneven? Check it at different speeds and different engine speeds.

Let us know.

[thatsmrmastercraft]

Porpoising isn't unusual in these boats. My '77 will if the load isn't just right, or if there is enough chop to get it started. The old answer is to add some weight in the bow.

[ski_king]

Can also be caused by a waterlogged hull.

[burner]

Our 94 ps 190 does the same at 40+ mph, I put a new oj prop on this year, which is more specific to wakeboarding. I chalked it upto the new prop, but i have noticed it behaves better when i'm in the boat alone, so I'm sure weight distribution is a factor.

[oldairboater]

If it isn't a new thing then it can only be caused by design, weight distribution, propulsion push angle, or water foil effect from deflection. Some boats porpoise from just design.

[thatsmrmastercraft]

The fact that newer boats had a hook added makes one suspect the there was some design issue involved.

[oldairboater]

Interesting how things revolve. I remember several boats made in the 70's with distinctive hooks. They were fast and sometimes unstable when slow or making violent maneuvers.The fact that newer boats had a hook added makes one suspect the there was some design issue involved.

[CleanCarShop]

Thanks for the answers so far...here is what i have done, and or learned today. the boat rides perfectly up to say high 30 mphs to low 40's. at 40 it begins and gets worse at a steady throttle. slow down and it goes away. I was told a bad or aftermarket prop can cause this. I was told that the hull may be weak/delaminated and flexing. I was told the hull may be water logged and the extra weight in the rear maybe the cause. ( seems like five 180 lbs guys in the front seat would make up for that, it did'nt).

today i discovered....
The starboard stringer between the motor and transom is wet, solid but wet. the fiberglass cloth is popped away for about 2 1/5 feet I can push on the cloth and it moves, i drilled holes through the fiberglass mat and stuck my finger and a screw driver into the stringer, wet but still quite solid.

of all the motor mount lag bolts that screw into the stringers two are stripped, on on each side.

when i began working on this boat it was not on the trailer properly, i do not know how far foward it should be, i DO KNOW, that it is transom heavy, no tounge weight? and i THINK it is on the trailer right....

Am i water logged? delaminted? are these the same thing?

[CleanCarShop]

cut the fiberglass away from the stringer, removed about 38 inches of starboard stringer between aft motor mount and the transom. stringer is solid from aft cut to transom, wet but solid from foward cut to motor mount. I plan on replacing the removed section with a piece of doug fir...west system. On the outside of the repaired stringer i will add a 3/4 inch piece of plywood incorporating the aft motor mount bolts this will span the foward joint of the repair and the aft joint of the repair, all will be coated with west system and layed in the boat, covered then in fiberglass cloth and west system. only doing the starboard side...port seems solid little to no moisture. i have only removed the fuel tank, and cut away 4 inches of the floor parallel to the stringer. never done anything like this before. hope it works

[Cloaked]

It's in the hull. Been there with a brand new one in 1979. In later years when Ski Supreme went out on their own, the guy that worked at MC (and left to go to Ski Supreme) later explained to me the issue. It was in the mold. Take it for what it's worth. He was there.

I tried most of what has been mentioned here. Sold it later on with the disclosure that it had the issue. Guy didn't care. It didn't do it until 37 + MPH. He didn't use that speed and above, so he took it.

[CleanCarShop]

Took two cedar shake shingles...8 1/2" wide, 12" long, from zero to 1/4" thick mixed up some west system epoxy and stuck them to the bottom of the boat 12" off center, just ahead of the transom about 3/4 of an inch. attached aluminium tabs with a slight downward bend to the trailering edge of the shingles. first test run we saw 38 mph and no issues. was starting to porpoise at 33 mph prior to this(unsure of accuracy of speedo). next test will be with the little tabs removed. We went with this idea because of the work we did to this boat. Our goal is to make it look like an older chris or century ski boat. We did not want to add traditional trim tabs to the transom. Still unsure of WHY this boat was/is porpoising in the first place.

Stock prop, not significantly water logged, not delaminated as far as we can tell.

[dmminfla]

Took two cedar shake shingles...8 1/2" wide, 12" long, from zero to 1/4" thick mixed up some west system epoxy and stuck them to the bottom of the boat 12" off center, just ahead of the transom about 3/4 of an inch. attached aluminium tabs with a slight downward bend to the trailering edge of the shingles. first test run we saw 38 mph and no issues. was starting to porpoise at 33 mph prior to this(unsure of accuracy of speedo). next test will be with the little tabs removed. We went with this idea because of the work we did to this boat. Our goal is to make it look like an older chris or century ski boat. We did not want to add traditional trim tabs to the transom. Still unsure of WHY this boat was/is porpoising in the first place.

Stock prop, not significantly water logged, not delaminated as far as we can tell.

Would you happen have a picture of this boat?

[CleanCarShop]

pictures of the boat on my profile page/ album I will be posting more soon we just went through it and re-worked a few details, added custom made front and rear vent covers, new gold decals and new three braided line as rub rail.....if you want pics of the trim tabs i can post some by the end of thed week

[jipster43]

I'd love to see this boat in the water!

JP :)

[CleanCarShop]

More pics of this boat over the coming weekend...need a chase boat to take pics from