ive seen the bottom of a keel with a length of lead attaches to instead of a keel weight hanging down. keep it light up top and weight as far down in the keel area as possible. A few years ago at warwick was a HMS Bounty done a pirate ship with NO KEEL attached, the gentleman had built it from plans and ensured the keel was lead filled with lead as low n the hull as possible from the outset, yes the boat was motorised, but it worked.