Hi bellman, (from Doug BELL😉) This is another 'How long is a piece of string question'! Only way to find out is to build it, and do a payload test. Put weight in it until it floats to the waterline and upright and stable. I use chunks of lead and lead balls (fishing weights). Weigh the lead. Easiest way is to weigh the empty hull first, then again with 'payload'. Difference is your payload weight for the hull, including all equipment, decks, superstructure etc. Before you glue any other parts to the hull weigh them and subtract from the payload test weight as you go. When compete you should then know how much weight you have left available for equipment. Weigh the equipment; motors, shafts, electronics, batteries etc. Anything 'left over' is the ballast you need. Try to fit it inside as low as possible, the lead balls are good for final trimming. When all is correct simply pour a little resin over them to hold them in place. Only time I fitted ballast outside, a long steel bar keel, was on my U26 sub. But then U Boats had such an emergency 'drop keel' so it looked 'Right'! Happy building, Doug 😎
"Retirement is when you stop living at work - and start working at living!" i.e. boat modelling!" 舰队的海军上将 😉 Doug
With my sailing pilot cutter Cariad, when the hull was largely complete I put her in the bath an put weights in until the waterline was reached. I then weighed the weights. I then tried to make the bulb keel slightly lighter to allow for trimming.
I would make provision for the bulb keel at an early stage of construction. I didn't do this and it was a right pain!
Hi Bellman My Club sail several similar boats as well as an Ibex. They are all fitted with detachable keels which are fitted prior to sailing but can be removed for transportation and display. Our sailing waters are large and exposed and without the keels the models would not be able to be sailed. On the water the keels can not be seen.
I tried a long keel on my Cariad and it was not a success as the keel tended to keep the model in a straight line. I now use a detachable bulb keel.
The amount of lead will depend on your model and its overall weight. The bulb keels are a fibreglass moulding that we fill with lead to bring the model to waterline after inserting fore and aft threaded rod into the bulb. You will need to have holes in the keel to let the rods thro and long enough to be above the waterline. I fit a plastic tube and wood support inside. A washer and nut hold the keel in place. Before filling with Resin weigh the resin in the tin and remove that amount of lead from the bulb. Once set I use silicon to make a good seal between the bulb and hull and which remains attached to the bulb. Attached are pics of my Cariad.