Tweaking a Hollis H160

[PfcAJ]

Sounds like you need an extra hand! I would agree that a slightly neg/nose up scooter is preferable. Neither are great. I'm not too familiar with the design of the Hollis, does it's buoyancy change with depth? Gavins and similar get a little heavier when deep due to o-ring compression. Is that a thing with your scooter?

 

[boulderjohn]

Sounds like you need an extra hand!

Or legs. I kept it in tow position above my thighs while using really mini frog kicks. I was warned that clipping the nose to an upper D-ring in that kind of flow could result in some severe face whacks. I think that in such circumstances again I would just hand off the scooter (what are buddies for?) and go completely manual.

I would agree that a slightly neg/nose up scooter is preferable. Neither are great. I'm not too familiar with the design of the Hollis, does it's buoyancy change with depth? Gavins and similar get a little heavier when deep due to o-ring compression. Is that a thing with your scooter?

Not that I noticed. The O-rings (2) are completely inside the body. I never went below about 100 feet.

 

[tstormdiver]

does it's buoyancy change with depth? Gavins and similar get a little heavier when deep due to o-ring compression. Is that a thing with your scooter?

Like John, I never had mine past 100', I never noticed any change in buoyancy.

 

[rjack321]

People have added sealed PVC tubes to excessively negative scooters in the past (like the Tekna/Mako). They 2 x 3" diameter sch 40 tubes capped on the ends might do it. They are butt ugly though.

Overall sounds like the tube on this scooter is too short for the mass of the motor. You could switch to li-ion batteries (a custom pack) and use fewer of them. That would give you roughly the same burntime but less mass so you might be able to balance it out. I say might because the motor is still too heavy for the length.

 

[boulderjohn]

People have added sealed PVC tubes to excessively negative scooters in the past (like the Tekna/Mako). They 2 x 3" diameter sch 40 tubes capped on the ends might do it. They are butt ugly though.

Overall sounds like the tube on this scooter is too short for the mass of the motor. You could switch to li-ion batteries (a custom pack) and use fewer of them. That would give you roughly the same burntime but less mass so you might be able to balance it out. I say might because the motor is still too heavy for the length.

That idea came to me whilst lying awake in bed one night recently. I just bought one of those flat rubber straps with the hooks on each end that are used a lot like bungees. Stretched tight, it just fits around the cylinder. My plan is to place it near the propeller and put some small bungee loops under it, so that a little sticks out of each side. I can then place a tube through each one. It will end up kind of like a weight belt in reverse. I won't have an easy way to test it for a while. I like the idea because I can simply not use it in salt water, where I assume it will not sink like that.

 

[rjack321]

Cratos makes a neoprene sleeve which fits over a Tekna shroud to solve your exact problem. While it does compress at depth, if you are mostly using the scooter at places like JB (ie not terribly deep) then its an ideal solution.

 

[Cratos]

yes you could use a neopren cover, or as stated get a longer body tube, adding boyance tubes will help but then your destorting the water flow over the body to the motor.

 

[formula1mb@aol.com]

Here's a site about homebuilt ROV's with buoyancy tips. Talks about using pink wall foam from Home Depot and that he tested it to 200 ft. Maybe get some of that and attach strips to the body?

Homebuilt Rovs

 

[Cratos]

You can weight the nose for balance (level it out)then do the neo cover for surface buoyancy I add about 2 lbs on the mako's to level them out. not sure how much on the H160's I have not had one in the shop. I can get the covers made and sell them for about 60.00+ shipping

 

[Jon Nellis]

Test the threaded rods that hold the batteries with a magnet to see if they are actually aluminum. If not, change them to aluminum.

If they are aluminum, change them to fiberglass, which is about 25-30% lighter. (assuming they are not metric - McMaster-Carr)

Good luck,
Jon