Back by the transom, on both sides just above the tie down u- bolts there are 2 approx. 1 1/2" dia. ring with rubber flappers in them. They look like they could be drain valves, but I noticed that at times they are under water at anchor and could let water run into the bilge if they didn't close. Does anybody know what they are there for ? I can see rust streaks on the inside of the boat

Here is a picture

In 2002 they got rid of those as they were drain holes that were not required.

Looks like a drain for the molded swim platform.

After looking more into this, your best bet is to probably just sell the boat to your son for $10k and you can by a brand spankin' new pontoon.

Our old 34 Vyper (2001) had that also. That's what I figured they were for is to drain the water in the swim plat form.

As a matter of fact they got rid of them between the time they built BillR's boat and my boat in late '01.

Its like a baffle drain for the swim platform, Seadoo Jetboats use to have these. Another analogy would be external flaps on exhaust tips. Lets water out but not it, It really does look like and I always worried that it was going to take on water but never failed.

My HIN is 02 and it has them 92D102 is the last numbers on my hin 92nd vyper built