instantly turtling

So we recently came across a 1988 Hobie (from the nationals regatta) that had been stored in a barn since the early 90's. It is in great shape, came with a minty trailer, and was a great deal so we bought it. It is nice and tight, sails great, but when I went to teach the kids how to right it, it instantly turtled as soon as we capsized it. Keeping in mind that this was the first time the boat had seen water in over 25 years, what would cause the hobie to instantly turtle? It was comical, almost like there was a cannon ball at the top of the mast. I am assuming that it has to do with the comp tip, but what would make it so heavy? Any thoughts as to the cause and the remedy would be appreciated. Thank you.

The mast should float somewhat as long as there is no water in it. It has to be completely sealed. If the conditions
are choppy or rough, it will eventually turtle anyways. But, you said it went down immediately.
Two ways to check if your mast has water in it:
1) Weigh it. The mast alone weights about 43 pounds.
2) Grab the mast in the middle and rest it on your shoulder and then tilt it fore and aft a little. If there is water
in it, you will hear it slosh back and forth. I have a mast with the comp tip and a very small amount of
water in it. It seems to be trapped in two areas. Some in the aluminum lower mast and some in the
fiberglass composition tip. I think it is condensation.

Anyways, I have a Baby Bob float on my mast to prevent turtling. I sail on a lake and do not want the end
of the mast possibly dragging on the bottom.

Take a hot day.....and a black mast....and the heat build-up inside the mast....
and dip the tip of the mast into cool water....as in a capsize....and WHOOOSH!
Water will suck into the mast UNLESS the mast tip and hounds are perfectly sealed.
Sounds to me like you need to re-silicone any through-mast holes.

The other reason for an instant turtle might be crew not getting off the 'hull in the air':
and given the geometry of the hulls in a capsize, even the weight of a ten year kid will drive the H16 into a turtle position.

Welcome to the Hobie world.

Keep safe

_________________
2015 H16, with spin,
SOLD 1989 Hobie SX18 Sail # 1947 "In Theory..."
'Only two things are infinite, the universe, and human stupidity. But I'm not sure about the former.'