Had the discs for the WTC machined today with a groove for the O ring. Question could this be secured in the groove with silicone? Cheers Tom
Why would you want to do that? Just let it sit in the groove without adhesive, when you button up the seal compresses. if you bond it in, it makes it difficult to change, and you will need to replace at some point. If you're using axial compression of the seals, you may want to consider using silicone o-rings instead of nitrile. Unlike nitrile, the usual choice for o-rings, silicone is pretty much inert to o-zone, this means you can leave them exposed to the air and they don't degrade. The disadvantage with silicone is it's more fragile than nitrile, and you have to be careful what lubricant you use on them. You shouldn't require any lubricant with axial compression of the seal, and silsicone o-rings tend to be softer, so they 'squish' up better.
Polymax.co.uk supply silicone o-rings. They have a £10 minimum order, so get all the seals in one hit.
Regarding the slanted surfaced waterline versus the level submerged position. The early Holland boats took this to an extreme, with a pronounced bow up attitude when surfaced, and level or perhaps a little bow down when submerged. In the case of the Holland boat, this was achieved by offsetting the position of the main ballast tank, positioning it forward so that with it empty the vessels C.G is aft of the centre of buoyancy. With the tank flooded the C.G moves forward, and the boat levels off.
Unfortunately different water densities, will have an impact on your submerged trim. So how do you deal with that?
Well if you're using a single main ballast tank like the OTW system, you can add a means of weight shifting, or fit auxillary trim tanks.
In the case of the afore mentioned Holland class boats the boat had a smaller ballast tank used for trim. The main tank was completely flooded, and then the smaller tank, which was positioned directly over the submerged C.G, was used to adjust the final few pounds of buoyancy.
Thus the boat could be adjusted for differing water conditions without upsetting the longtudinal trim. Water density only varies by about 1-2%, so this tank can be very small compared with the main tank. All the submarines I've looked at use main and trim tank systems, in models this is rarely followed, as it means building two separate systems independent of one another, so the trim and main tanks are usually merged into one system. In the case of the Piston tank/Engel system, the trim can be very accurately set, but you still require two tanks to permit accurate positioning of the boats longitudinal C.G.
In the case of a boat like your S-class, a trim tank would need to be about 120-150 ml assuming you're using a 12cm diameter cylinder 100cm long. Another alternative is to make a sliding tray for one or more of your battery packs, and couple this to a servo, so you have a proportional method of weight shifting.
Another method sometimes used is to have a small set of trim tanks mounted fore and aft, these are coupled together via a reversible pump (peristaltic or geared), with a fixed quantity of ballast pumped fore or aft to modify the boats angle. This is closely follows fullsize practice, on small submersible craft, mercury is often used, larger boats pump water. For a model, I think shifting the battery is better, because it's easier to implement, and it's totally proportional and therefore easy and repeatable to control.
