I am interested in ROVs for several years. As we know, the most popular ROV manufacturers are Seabotix and Videoray. They produce ROVs that they are capable of diving to several depth ratings. For example, depth rating for Videoray Scout and Explorer is 75 m, and Pro4 is 305 m. In addition to this, depth rating for Seabotix LBV150 is 150/200 meters, LBV300 is 300meters.
Here is my question. What is the main criteria for varying depth ratings? Is this Sealing types or main material of body or what?
Especially ROVs of Videoray are looking so similar to eachother. Their thruster system is same in the sense of sealing methods. They are using oil cartidge. Also main body and dome are looking same. What do you think about this ?
I'm not sure exactly what limits the depths of the other ROVs, but I suspect it's similar to what limits us: pressure limitations of large waterproof containers. For OpenROV, the flanges of the main endcaps fail right around 100m, closely followed by general failure of the main tube. There are some simple ways to improve this (which we're experimenting with now), but getting air-filled containers to handle lots of depth requires some fairly heavy-duty construction.
The main limiting factor for working depth has to do with two main things, materials and design.
By changing any of them or even by modifying only one of those factors, working depth can be significatively improved.
The most obvious effect of pressure on vessels is collapse. Over a given stress, that depends on building material, the "hull" will fail. Stress distribution can be minimized by properly designing dimensions and shape.
But ... there is a not so obvious effect that mostly affects the parts joints, and leads to the structure (understood as the joint of parts) failure a lot before. This effect is distortion.
As parts change their shape due to external stress, joints are distorted. If they are fixed (glued, welded ...) the stress excess is accumulated IN the joints, that will eventually fail.
If joints are not fixed (Articulation, closing flanges, hatch covers .....), the shape distortion will distort the openings, leading to the fail of the closing devices.
As distortion happens a lot before collapse, the pressure hull must be designed from the "Distortion limitation" point of view, better than from the collapse condition.
Improving ROV's working depth can be achieved by:
1- Fitting two acrylic rings inside the E_Tube, working as frames, for preventing the midsection from shrinking.(Rings position can be easily calculated for results optimization with rings dimensions minimization)
2- Modifying the position of the flanges seal rings.(When only working against the inner side of the Tube, the more external pressure-the less efective pressure on the seals)
If watertight hatches from real ships-subs are observed, it jumps to the eye, that beside the tangential seals, a normal gasket is always fitted, being the second a lot more important than the first.
For really high working pressures, the flanges section would have to be conical instead of cylindrical. In such a way, that as pressure grows and the container(Tube, Hull, ......) shrinks, the contact angle between the tangential gasket and the closing flange (hatch cover) remains almost constant.At the same time, a second ring seal has to be fitted at the external side of the tube beside any mean for limiting the opening distortion (reinforcement coamings).