Ohio Class, Ballistic Missile Nuclear Powered Submarine, USS Kentucky SSBN737
UPDATE: Current work involves trimming, so data on this page is subject to change within long.
A few things...
There are a few things to keep in mind when getting ready to trim your sub.
First, the positive and negative center of buoyancy need to be aligned on top of one another in order for the sub to align it self without any list,
but the bigger the distance between these two points, the better. If they are right at the same point, there's almost no stability, nor the ability for the sub to upright it self. As a result, I chose to lower the watertight compartments 10mm ( 0.4" ) down "under" the center line of the hull, and towards the keel of the sub.
Second, the positive and negative center of buoyancy need to be in line with the center of the ballast tank. If not, the sub will not dive without developing a list end over end, which would make the sub hard to control when sailing while submarged.
Third, in order for the dive and surface function to be of any value, the surfaced waterline must be above the floatation material. Only exception is if some foam is to compensate for something, only when dived down. (e.g.. if the sail has got positive buoyancy etc.)
If some of the foam is above the surfaced waterline, then the dive function is limited, as the dive function first has to overcome more and more positive buoyancy during the initial dive. You could say, that the weight of the sub is not constant, if some of the foam pops out of the water when surfaced, and that will mess up the equation.
Is the trimming a once-and-for-all thing? No. Trimming is effected by the water temperature (density) and salt level. Just like real life, a ship has a bigger draught in fresh water areas, than in waters with high concentration of salt. Some adjust the trim of their sub before any trip, just to make it absolutely right. If you want that ability, use small lead weights glued on Velcro strips, or similar.
My actual submarine:
Since early construction, I tried to even the negative and positive buoyancy, and at the very least keep an eye on it, during planning and construction. This table shows the results, and buoyancy for each component:
(*1) The bouyancy of the MBT is not the result of the displacement minus the weight because the weight of the MBT is considered part of the weight of the hull / ballast.
It might be necessary to place some floatation foam inside the
hull compensating for the sail. This can be tested by observing the hull when
fully diving the sub. If the bow aligns it self higher than the aft end,
then you will have to add some positive buoyancy aft of the center, and above the surfaced waterline. This way this added buoyancy will not get
into play while surfaced (and not needed), but it will get into the
equation when needed during a dive (when the sail is
All of the WTC's, MBT, the air system, wires, tubes, shafts and rods etc. needs to be secured inside the hull, and the submarine needs to be perfectly trimmed. Here I'll just show you how I did the mechanical mounting and secure fix of these components, and the floatation foam etc.
First test: The initial test and trimming in the wet dock went somewhat ok. No leaks detected.
Issues: When the surfaced trim and righting is ok, then diving is not possible. When diving is possible, then the surfaced trim is all wrong.
It seams that the top / missile deck is too heavy, so tests continue by trying to move foam up, so that the bottom half will hang from the top, not carry it. As it is now, the bottom floats on it's own right where it should.. correct depth and all, but when the top comes on, it all goes bad.
In test two I'll try and move all positive buoyancy up into the top half, so the top will not mess up the self righting. Second, I need to determine how little foam is allowed for diving to be possible. (Eg. What waterline will that give me..)
Second test: Two metal bars was put in the very bottom as fixed weight, correcting the issue regarding self righting. More flotation foam was placed to archive right surfaced water level. Then, by reducing the surfaced water level in the MBT's, I found the exact "point" where surfacing was possible, as well as diving, and where I had an acceptable surfaced water line.
Conclusion: The sub can now righting it self very well, it can dive and surface, and the water line is fine. Now's it's back to the dry dock to fit all the components at their final location. :-)
Third test: The idea with two independent MBT's proved a) difficult to control and b) absolutely not needed. The two MBS's were therefore scrapped, and a new, central MBT was made. Because the dual MBT-idea required a bit of electronics, then the majority of this was scrapped as well. In general: It was a complete rebuild of the inside stuff, but it resulted in a system much more stabile, and simple.
Read more about test three here.
First four pictures are from test 1, the rest are from the process of mounting modules.
Click images to enlarge.