God, please don't use the lead, old batteries, and used oil someone else suggested. Our lakes are already polluted enough and all of that stuff is highly toxic. I am betting it would be illegal to sink a boat in your state.
with the foam out of it, and a few large rocks, and no current in the area you sink it ..... I'd say it would stay down. You would, of course, have to tow it and all the other materials to the lake - launch it and your "other" boat - tow it to a specific spot - transfer all the "weight" and "condo material" onto it - then compromise the hull in such a way that it would sink straight down. You could cut some spots out in the flooring and place PVC (in buckets of concrete) or whatever in there ... and in any of the other "open" holes already in the cap.
What you might consider doing -- is ask the Fish & Wildlife Dept ... if it's ok to do it, and if so - would they help ? If it's allowed, they may want you to tell them where it's dropped (or they'd GPS it, if they helped). If they won't allow it, you'd probably be better off selling it for whatever you could get out of it (even if boat is worthless, trailer may fetch some $$).
Just some food for thought ............ luck2ya ........ cp
God, please don't use the lead, old batteries, and used oil someone else suggested. Our lakes are already polluted enough and all of that stuff is highly toxic. I am betting it would be illegal to sink a boat in your state.
If you decide to undertake this job I'd just check to clear any legalities. You never know who might be looking and it could cost you WAY more if procecuted and you have to extract it from the bottom of the lake.
Health nuts are going to feel stupid someday, lying in hospitals dying of nothing.