I'm working on a seaplane and find myself doubting about the specific nautical term for a keel placed between the bilge keel and the main keel. This might be a bit academic in nature since I have a working way of naming it, but I'd rather take the chance to find if it's correct or just a fossilized mistake.
My working term is "sister keelson", which is commonplace in seaplane design, but something tells me it's not really right, as in naval engineering a keelson is the inner structural element that holds ribs against a keel.
The second nearest term would be "docking keel", because of its location, but that implies it can be used to beach the craft, which it may not be necessarily designed for.
I can't add images right now, but a google image search for "sister keelson seaplane" will give you pictures of what this is, while a search for "sister keelson" will point you to the inner elements that would be used in a wooden hull boat.