OTW Ballast tank sensors and tank size

[Thorbrandr]

Has anyone tried moving them? The trim on my R Class is generally very good, but too much down plane on the bow results in the ballast tank sloshing forward, and stopping the dive until I force the stern to drop. With the ballast tank empty, she rides perfectly. With it full it will just settle to the bottom. It is ALMOST perfectly sized. I need a tad more volume. Moving the sensor up about 5 mm would probably do the trick.

Added: I don't really have any foam to take out higher in the hull at the point where she hangs in the dive due to being down at the head.

Chris

[goshawk823]

I would call Bob and ask him. it's his design, and he is always will to help on his products. why not go to the source for your answer?

[SubICman]

Is Bob accepting calls atm.?..I know he was recently in an accident.

[DrSchmidt]

Kann you install a dividing wall in the tank, that almost reaches up to the top of the tank and that prevents the water from freely flowing from back to front of the tank, triggering the sensor when you get a downward pitch?

[Subculture]

A horizontal baffle like the R&R system tank pictured would reduce this problem, but would mean slicing open the tank, which will be tricky as they're solvent welded together.




Ultimately with the OTW system you do have to accept some limits as a consequence of having an exposed water surface and venting/compressing air into the dry spaces as the tank fills.

[wlambing]

Aren't OTW tanks baffled as they come? All of mine are, I have 3, all different sizes. Each has 3 baffles in the MBT.

[SubICman]

Same, except I have 2

[Subculture]

They have vertical baffles, which slow the movement of water down but don't eliminate it. If you're filling your ballast tank whilst diving at an incline, then the problem will be exacerbated as the filling pipe is mounted in the forward bulkhead of the tank.

[goshawk823]

Is Bob accepting calls atm.?..I know he was recently in an accident.

yes, he is. feel free to call him; he's recovering from the accident.

[Thorbrandr]

Kann you install a dividing wall in the tank, that almost reaches up to the top of the tank and that prevents the water from freely flowing from back to front of the tank, triggering the sensor when you get a downward pitch?

it has a single baffle in the middle.

Chris

[Thorbrandr]

They have vertical baffles, which slow the movement of water down but don't eliminate it. If you're filling your ballast tank whilst diving at an incline, then the problem will be exacerbated as the filling pipe is mounted in the forward bulkhead of the tank.

I was considering putting it on the rear wall for this reason.

On a static dive or at slow speed, all is fine. The R class normally sits a bit low on the stern. Doing the fast dive with down pitch on the forward planes is when this happens. I either have to do a aircraft type flare maneuver or slow significantly to finish the dive.

Chris

[Subculture]

Unlikely to make much difference. You have to accept that any system that maintains an exposed water surface will have some performance trade-off.

[RCSubGuy]

yes, he is. feel free to call him; he's recovering from the accident.

Just a PSA... people are referencing Bob Dimmack, not the RCSubGuy, who is in good shape (physically of not mentally)

Carry on!

The "other" Bob

[Schmitty1944]

Has anyone tried moving them? The trim on my R Class is generally very good, but too much down plane on the bow results in the ballast tank sloshing forward, and stopping the dive until I force the stern to drop. With the ballast tank empty, she rides perfectly. With it full it will just settle to the bottom. It is ALMOST perfectly sized. I need a tad more volume. Moving the sensor up about 5 mm would probably do the trick.

Added: I don't really have any foam to take out higher in the hull at the point where she hangs in the dive due to being down at the head.

Chris

Do you have the hole drilled between the ballast tank and dry compartment or does your ballast tank just pressurize the air inside itself (not vented)?

This might be a stoopid idea so feel free to flog me for it but how about a momentary by-pass button that allows the pump to continue running even if the probes detect it is full? I would use a channel on the transmitter that has a momentary switch/button so that you have to hold it to activate and it can't be left on. Inside the boat would have a simple on/off relay/switch that disconnects the wire to a probe when activated so the pump still runs until you let go. If you don't have the hole drilled the pump has it's own limiting factor in that it can't pump once the air pressure reaches a certain point but will not hurt anything.

If you do have the hole drilled then this is a good way to flood your boat and not a good idea.

Jason

[Subculture]

AFAIK all the larger OTW (110mm dia) modules are vented via a hole drilled in the forward compartment a short distance above the probes. OTW did have a smaller system which I understand used a gear pump and pumped into a sealed tank, but I'm not sure if that's been discontinued.

The 110mm OTW system is essentially an evolved version of Nick Burge's compressed air modular system. OTW used to supply their kits with Craycraft modules, which were a commercialised version of Nick's system, but the chap that made them moved into other areas, and Bob Dimmack had to find a replacement.

For a few years OTW had no modules, but eventually came out with the system you see today with a slinger style water pump replacing the bespoke compressor of the Craycraft design. This pump has good flow but can only make fairly low pressure, so venting into the dry compartment is necessary to get any reasonable fill of the tank in a recirculating air system.

I would say bypassing the water level probes is guaranteed way to flood your module, I wouldn't do it.

If you want a ballast system that you can fill whilst crash diving at angle and can also trim for differing water densities, then an alternative dive system is probably on the cards.

I hope my posts don''t come across as damning the OTW system. It's a low maintenance system which needs no consumables and it deals pretty well with boats that require medium to large ballast tanks.