What exactly is the purpose of the H-beam other than structural support. I am having a difficult time finding such an item and I am thinking I could just use another length of pvc pipe and a pool noodle. Would that work okay?
The H-beam is not actually there for structural support; it's intended to allow the "football" floats, used with standard SeaPerch ROVs, to be mounted onto the vehicle. The hole athrough the middle of the football float is too small to pass a 1/2" PVC pipe, so the H-beam is used instead.
If you wish to use 1/2" PVC pipe and pool-noodle type floats, they will work, but please note that they are good only for very shallow water. When the noodle floats are submerged more than about five feet, the water pressure makes them compress too much in size, thus reducing their water displacement, and therefore reducing their buoyancy. In other words, the ROV will go down and not be able to come back up. Some noodle floats may also absorb a little water, also reducing their buoyancy. It's best to use fairly small noodle floats (not as long as the standard football floats). If the floats have too much buoyancy (at the surface, for the noodle floats), too much ballast is needed. When the ROV is more massive, as with lots of ballast, it will not be able to move as well as a less massive vehicle. To keep the ROV nimble and easy to maneuver, try to minimize the total ballast weight, matched to the buoyancy of the floats, such that the ROV is nearly neutrally buoyant, with slight positive buoyancy to enable it to return to the surface if the vertical thruster fails.
Another approach for floats, if you don't want to use the H-beams, is to use the 1/2" PVC pipe, as with the noodle floats, but build your own simple floats using 1" PVC pipe with end caps. Standard 200 PSI pipe (not the heavier schedule 40 type 1" pipe) works well. Attaching 14 inches of 1" PVC (200 PSI) pipe with cemented-on 1" PVC end caps to each of the 1/2" PVC pipes on the top of the ROV (using 4 8" tie wraps (get the heavy-duty type), provides adequate buoyancy, with a little ballast (less than needed with the almost too-buoyant football floats). The cost for the 1" PVC pipe approach is less than the standard football float and H-beam approach. When mounting the PVC pipe floats, be sure to slide the 4 tie wraps to the center of the 1/2" PVC pipe while you tighten them, with the PVC pipe float tilted at about a 45 degree angle to the top of the vehicle frame. Then, when you slide the tie wraps back out along the float, with two wraps all the way to the ends, and bring the float back to level with the vehicle frame, the float will "bind" against the PVC elbows, due to their diameters being larger than that of the 1/2 PVC pipe where the wraps were tightened. Once the wraps are in place, you can handle the ROV by the pipe floats without them moving around. A neat advantage of this method is that you can adjust the front-to-back vehicle "trim" (levelness in the water) by just sliding the pipe floats fore and aft. That's much easier than adjusting the ballast to achieve a level attitude.
The 1" PVC pipe float approach is being used by more than 300 students in the Pacific Northwest and a similar number in Alaska this year, at considerable cost savings compared to the football floats, and the parts are available at just about any hardware store.
- Hope this helps,
Rich
This sounds great Rich! Thank you for letting me know about the 1" pvc pipe alternative. I think this will work out just great for us. Your description was thorough enough that I think we will have no problem implementing it.
Thanks again!
Julie in Flagstaff, Arizona
If you want to use the 1" PVC pipe floats, detailed written procedures showing how to build and install them are available. These procedures, and others, are planned for publication in the updated SeaPerch Construction Manual as "options" (appendices containing construction options and enhancements are being added in the new manual). The new manual should be available at the SeaPerch web site soon.
Rich,
I would be interested in the procedures on building and installing the PVC floats that you have described. You could email them to at toby.ratcliffe@navy.mil. Thanks so much.
Toby Ratcliffe
STEM Outreach Coordinator at the Naval Surface Warfare Center, Carderock, MD
