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Mankster · 28-01-2008

Ahh they are hollow, thats ok. Its the buoyancy of the butterfly nuts I was thinking of, their weight is insignificant relative to the weight of the sub. Don't use any foam above your desired waterline, or your sub will sit very low when surfaced. The two 825ml piston tanks are the very minimum needed to achieve the desired waterline (the protoype Engel Typhoon used 4x 500ml tanks arranged in a twin shotgun type arangement, but proved costly). If you cant increase the capacity of the ballast tanks, you have to reduce the buoyancy of the top hull (reduce volume - buoyancy is proprtional to volume, weight is immaterial).Thining out the upper hull by sanding, cutting out excess below the conning tower etc, helps a lot. I used no foam at all and took great pain to reduce the above water line hull volume, and mine only just scrapes the scale waterline. Russian subs are all double hulled and hence have relatively high surface freeboard compared to US/Brit boats.
If you need more postive boyancy, don't dont add foam, remove lead ballast instead. Foam is only really needed to raise the centre of buoyancy above the centre of gravity to maintain stability (stop the sub from rolling on its side); but this this sub has so much lead in the base that the CofG is pretty low already. Also it has twin props so no torque roll either.

28-01-2008	#96 (permalink)
Mankster Scale Model Member Join Date: Oct 2005 Location: London My Models: RC Postwar Subs and Naval ships Visit Mankster's Gallery Posts: 271	Ahh they are hollow, thats ok. Its the buoyancy of the butterfly nuts I was thinking of, their weight is insignificant relative to the weight of the sub. Don't use any foam above your desired waterline, or your sub will sit very low when surfaced. The two 825ml piston tanks are the very minimum needed to achieve the desired waterline (the protoype Engel Typhoon used 4x 500ml tanks arranged in a twin shotgun type arangement, but proved costly). If you cant increase the capacity of the ballast tanks, you have to reduce the buoyancy of the top hull (reduce volume - buoyancy is proprtional to volume, weight is immaterial).Thining out the upper hull by sanding, cutting out excess below the conning tower etc, helps a lot. I used no foam at all and took great pain to reduce the above water line hull volume, and mine only just scrapes the scale waterline. Russian subs are all double hulled and hence have relatively high surface freeboard compared to US/Brit boats. If you need more postive boyancy, don't dont add foam, remove lead ballast instead. Foam is only really needed to raise the centre of buoyancy above the centre of gravity to maintain stability (stop the sub from rolling on its side); but this this sub has so much lead in the base that the CofG is pretty low already. Also it has twin props so no torque roll either. Last edited by Mankster; 29-01-2008 at 12:06.