I read that an owner removed ballast (to cure a leak) I want to do so to get weight of boat below threshhold of portable unpowered on the canal network. I then use tanks for water ballast is then also emergency bouyancy and swap keel for alu if pressed. I will remove pullpit and rails to reduce weight further (thy will need a good home) Also cos roof is Totaly rotten thinkin to remove it (and windows) and recreate with proper companionway and nice portholes, it'd be nice to get further details tips n hints from owner. Dya think I can do while in water ( I keep emergency putty at hand just in case)
I'm not clear about what you mean by the phrase "threshhold of portable unpowered". Is there some regulation on the canals that reduces the licence fee for craft below a certain weight? Is that the principle aim behind the desire to reduce weight?
While getting rid of the ballast will lighten the boat by some 440lbs that still leaves you with some 1200lbs, which is still pretty hefty to count as "portable". The steel work is hollow tube and weighs almost nothing in relation to the main GRP structure. I don't see it as a worthwhile weight saving option at all. That's not to say that some sailors would not welcome a cheap pulpit and cockpit guard rails if you really wanted to dispose of them.
I'm also struggling to understand the thought behind removing the roof. Do you mean simply to replace it with a new roof configured slightly differently. I assume so as you refer to portholes. That too risks wrecking sailing qualities.
Do you plan to sail her again. I suppose so when you talk of the possible need for an alu keel and the reference to water ballast. Water is not as dense as concrete and iron, so to put an equivalent weight back it would occupy far more volume. However, with the compromises implicit in all you talk of I wonder if you're worried about the sailing qualities of the boat.
Other boats that use the same hull as the SeaHawk don't have a lifting keel plate at all. They just rely on the shape of the hull. So I'd be inclined to ignore a replacement keel. Mind you, the designs have less less weight and sail area and all who've tried both them and a SeaHawk report they are pretty useless sailing boats.
The design of a sailing boat is a tricky equation that has to have the right amount of sail to move the boat while having both enough weight to keep enough of the hull in the water so that, together with a suitable keel, it will go where you point it. If it is not to be blown across the surface of the water like a child's balloon and there's not much weight you'll need a much deeper keel and that will require a significant redesign of the internals of the boat.
In short, I fear that you have two mutually exclusive objectives. Having a boat that is light and I recall you were talking of making pedal powered while also making it a worthwhile sailing craft. I strongly suspect that you'd end up with a pile of plastic that does neither job well.
However, if you do proceed with the plan to remove the ballast I'm not sure if we have anyone who is active on the forum that has attempted removal of the concrete and scrap iron that you'll find in the keel. I understand those who have used a Kango Drill and I strongly suspect that all were ashore at the time. I guess such a drill can be pretty fearsome if you press too hard in the wrong direction and at the wrong moment, but I would have thought if you're careful there should be no reason for not attempting it while still in the water.