Thanks for your interest and I'm happy to answer your points, after all, your Shark try-out was the inspiration!!
First up, the nozzle is fixed with an old 3 blade prop that started life at 1.5 but trimmed down to run inside the nozzle which is cut from the same scrap pipe as the rest of this creation. It's steered by a brass D shaped rudder behind the prop but within the nozzle. You can see the clevis and pushrod in the first picture, the tiller is made up from a ball from a ball link soldered onto a 2mm bolt and the clevis is a standard one modded by removing the pin and drilling out the holes to 3mm . I've added another here-
The delrin plugs are retained in the nose and stern free flooded sections by a 2mm screw through the keel, see above picture. A good tight fit of the O-rings hold the plugs into the centre hull. So far!
The 'casing' and the 'ballast tanks' are made from scrap abs cable conduit, rectangular and round respectively and filled with builders foam after drilling all the holes and welding/glueing onto the hull pieces. The only new bought in material was a length of 8 x 10mm styrene tube for the ballast keel, filled[mostly] with lead shot then plugged. The tower/sail is a piece of pipe cut lengthways and two flat arms formed with the aid of a hot air gun and this too is filled with foam to give some top buoyancy, similarly the bow section was shaped by cutting wedges out and hand forming under a hot air gun then weld the seams up.
Yes a lot of fun to make up from what was to hand the only prblem I had was that the first bow section that I tried was pvc pipe which is awful to weld or glue so that soon found where the trash bin was! It's fun to drive too, so far only in a couple of garden ponds, a friend's is a bit bigger than mine and I've yet to give it a proper 'go' up in Norwich- been a bit busy lately with domestic maintenance stuff.
I've got several bits of 3" downpipe scrap so I might have another go in a bigger size which should be a bit easier, though probably will make it a static diver,