How do I add a transom extension to my monohull sailboat?

[Seafarer24]

I have a 1974 Cal Cruising 35 with a lot of modifications by previous owners. One of these includes a diesel generator shoe-horned into the aft port corner of the boat under the cockpit seat. While it fits the location perfectly, it is the worst place to concentrate that much weight. I would like to add a transom extension to help minimize the impact of this generator and give myself a better place to mount my propane bottles and fenders.

Not my boat, but a good picture of the stock stern profile:
Botany Bay


I have seen similar to what I want done on this same model, though their extension is a sugar-scoop while mine might not be. I have asked them about this and have not yet received a reply on how they went about building the extension:
Windfall

[gonzo]

Which one is your boat type, the one with the reverse stern or the vertical?

[PAR]

I just recently preformed this on a Catalina 22 style of boat. It's transom was plumb and he wanted a sugar scoop, so . . .

It's not especially hard, but will take considerable laminating skill to make a seamless and serviceable extension. You should consult with a boat carpenter or designer so you can get a laminate schedule that will perform the tasks you ask of it. Judging by the one image above, it looks like they could have faired in the extension a little better so you couldn't see the transition.

What are you looking to get out of the stern addition?

[Seafarer24]

1) Additional buoyancy to offset the weight of the diesel generator installed at the very aft end of the boat

2) A smooth wake from a nice clean exit instead of dragging my transom through the water.

3) Two 10# propane tank lockers

4) Storage for my fenders. I bought very big fenders from a 60' motor yacht and figured that would be a great place to put them. Out of the way, yet accessible, and since they are light-weight they can be stored aft without consequence.

5) A strong mount for a Cape Horn Windvane

I'm not entirely sold on the sugar-scoop design Windfall used. I was thinking about more storage with my design, and perhaps ladder rungs going up at least one side of the transom. The rungs would be flush with the transom and the space ahead of them recessed. The portion below the waterline to perhaps 6" above it would be foam-filled and the lazerette locker created by the extension would be self-draining.