Hi Jim and Eliot:
Here at Mission Robotics we’ve switched to epoxy-coated floats on all of our BlueROVs. The original intent was to allow deeper diving, as the Last-a-Foam 3318 is only rated to 250m in its uncoated form. We do a lot of testing in Lake Tahoe, which is 500m deep, and wanted to be able to routinely operate in any portion of the lake.
After we started playing with epoxy-coated foam, a number of other advantages became apparent. First, by skipping the plastic fairing and attaching the floats directly to the structure of the vehicle, we could make bigger floats and obtain greater flotation, even more so than the machined foam that Blue Robotics currently sells. This is important when operating in fresh water, which has less buoyancy than salt water. Second, as there is no fairing, there is no air gap between the foam and the fairing, which needs to be “burped” upon diving, and drained upon surfacing. Third, we could shape the forward flotation blocks to mount the upper lights inside the side plates of the ROV, eliminating a “tether trap” that exists when operating a 6-thruster BlueROV2 with 4 forward lights.
The downside, as your post suggested, is that the epoxy coating is not very strong, and hitting anything with a float while exploring will cause cracks in the epoxy, which needs to be repaired. We made a fiberglass-covered (vacuum bagged) set of floats for a BlueROV2 heavy, and although the results were good, it’s not clear that the result was worth the effort involved. This fall we’re going to be experimenting with syntactic foam floats for doing deep diving with ROVs derived from the BlueROV2. You can get syntactic foam in the range of 22-24 lbs/ft3 (compared to the Last-a-Foam 3318 18 lbs/ft3) that is good to at least 1000m. If the foam gets dented it won’t cause structural issues with the remainder of the block, so our current plan is to paint it as opposed to glassing it. Syntactic foam is about 2-3 times the cost of Last-a-Foam, but should require less labor to make completed floats.
If you’d like to see what our epoxied floats look like, you can get a good view of them in this YouTube video where we dove to the bottom of Lake Tahoe (500m):
There’s no particular rocket science involved in the floats, I think we used Total Boat marine epoxy, and we staked stainless-steel threaded inserts into the bottom of the floats.