DUMB QUESTION OF THE DAY,

ok so i have never owned a "real boat" before. i have only had jon boats and kayaks, but in a trade recently i got a 15 foot sportscraft made in 1971 with a mercury 650 on it. now my question is when i look at the stern of the boat under the outboard there is two holes one on top and one on the bottom about 4 inches apart. i understand one is the ballast (i dont know which one). now the boat didnt come with a plug so i had to buy one. it only fits in the top hole. ok understandable, so the bottom must be the ballast, Right? now where i got confused is when it rained the other day and the boat filled with water it started to poor out of the bottom hole when i lifted the front of the trailer off the ground... i dont know im confused. i feel that if i put it in the water that it will fill with water and sink. please help. im a beginner.
 

The top hole is probably for a livewell or a deck drain and it does not get plugged.  The bottom hole should be the boats drain hole.  Try the plug both on the inside and on the outside of the boat where the hole goes through the transom.  Some boats are designed to be plugged from the inside and some from the outside.

i cant get to them from the inside. also the "standard" plug doesnt fit into the bottom hole its a little bit to small but if you put your fingers in it you can feel that it is threaded as though something screws into it. the bottom hole is less than an inch from the bottom of the boat. i added some pics of my boat and the problem i have

 

 

The bottom one uses a screw-in plug.  You should be able to find one at a local boat shop.

I'm not sure of the size plug. It's a screw in and made of brass

ok perfect, just bought one. now moving onto the top plug. do i leave that plug in? is there even a ballast in my boat?

ok perfect, just bought one. now moving onto the top plug. do i leave that plug in? is there even a ballast in my boat?

The only boats that have ballast are top of the line modern wakeboard type boats and giant sea going vessels..  I am sure your old tri-hull ski boat does not have a ballast tank.  Does the boat have a built in cooler or a live well.  Is there not a hose running to the top  hole?  If so see where it leads to.  Most old ski boats like that have a drain in the elevated front deck floor for water to drain out.  We had a very similar Glastron but the front floor drained out on the side of the hull and not the back. 

no livewell and no hoses so im going to plug both holes and see if she floats... thanks guys for the help!

remember to bring extra plugs for both if you are plugging it from the outside.  Always good to have spare plugs and could make a big difference between a "funny thing happened" to a completely horrid day that ended in disaster.

good idea! thanks bud