Revell Type VII with Windshield-washer Pump and Closed Water Tank Ballast System

[redboat219]

Decided to post this in it's own thread.

Revell's 1/72 Type VII utilizing a windshield washer pump/ closed tank equipped with a pinch valve.

http://www.u-modelismo.com/foromodelismonaval/index.php?topic=1379.0

Crude but effective.

If this was a a wet hull with a proper WTC could we get away with a smaller tank or less powerful pump?

[reddevil]

I´ve already read this thread some time ago, and are thinkihng about using this system for mu second VII C. In fact, the system I´m trying in my first one is very similar to this one. It really works fine.

[He Who Shall Not Be Named]

As the video demonstrates, RCABS -- the devices it employs, and the lack of space in which the bladder can contort -- seldom is able to get a scale model depicting a double-hull type submarine up to the SCALE surface trim waterline.

A waste of space in any boat that needs a reserve buoyancy greater than 15%. So, modern Soviet and just about all other type boats, RCABS is a poor choice of ballast sub-system for a model.

Which makes it useful In just about any American single-hull type submarine from SKIPJACK up to the present. Dangerous, single-hull designs, featuring low freeboard, are more suitable for RCABS type ballast sub-systems.


M

[redboat219]

This is NOT RCABS

[He Who Shall Not Be Named]

This is NOT RCABS

I stand corrected. This is not a 'classic' RCABS, in that it does not employ a flexing bag or inner-tube. However, in operation, it's every inch a ReCirculating Air Ballast System.

No bag in this model. But it suffers the same problem as the bag type RCABS sub-system: Too much gear in spaces that could have been given over to a full ballast tank.

In this model it looks like he's using a pressurized ballast tank. The pump has to overcome an ever increasing air pressure within the ballast tank as water is forced in. Then it stalls when the back-pressure reaches a critical level.

Correct me if I'm wrong, but does not that ballast tank only fill with a fraction of the water it could hold if it were vented?

If so, the sub-system is a waste of space: the pinch-valve, the pump-controller, the unused (dry) portion of the flooded ballast tank, and the pump. They all take up room that could have been dedicated to ballast water space if he opted for the simpler, higher ballast water capacity gas sub-system.

I'm not inclined, Romel, but if you want a ruling on this being, or not being, an RCABS sub-system, why don't you contact the man who popularized it: Art Broader?

I'll defer to his definition.

M

[redboat219]

You're mixing apples with oranges.

How can this be RCABS? In RCABS and it's variant RCABS-R air is cycled back and forth from the dry space ( or air tank) into the ballast tank ( or air bladder) hence the word Recirculating. There's no recirculating air in this system, air remains inside the tank and us only pressurized.

[reddevil]

I think that this system is the very, very cheap version of OTW DESINGS one. In my version the tank is OPEN, and reliefs through the periscope after passing a SUBTECH TEE valve. I do realize that this system doesn't gives you any failsafe but the sub returning to deck awash if you have correctly balanced her. I know it's not the better way to go.

[redboat219]

The same hardware can be adapted to Pump-Aspirated Vented Ballast. The tank has a vent on top and a flood valve in the bottom (the pinch valve can be utilized as the flood valve) Opening the flood valve lets water into the tank. To surface the flood valve is closed and the pump activated. Air reenters the tank through the open vent pipe.

[Subculture]

The OTW system is rather different- it works at much lower pressures than a system with a sealed ballast tank.

Unless a tank vents to the atmosphere, then it can be classed as recirculating. Most systems tend to operate at modest pressures, as they pressurize the internal cavity of the watertight compartment, and high pressures would put a strain on shaft seals. In the case of systems like piston tanks, which tend to employ jack screws, that also makes the system inefficient, as jack screws load up very quickly when under pressure, as 80% of the power put into them is lost in friction. If pressure is limited to two or three psi, then the piston tank(s) work very efficiently.

The OTW system uses a pump that can't work beyond about one atmosphere. It has a pretty good flow rate though. To enable the pump to work efficiently, and also to permit better use of the ballast tank volume, air is vented into the dry space areas, probes in the tank switch the pump off when the tank is full or empty.

Back in the early '90's a system was developed by Eden model submarines (later taken on by Sheerline models) which had a completely sealed tank, and used a centrifugal pump to pump water in. The pump makes about 40-45psi before it stalls, which is enough to fill about 70% of the tank. Clearly this is quite a high pressure, so the tank needs to be built very well, otherwise there will be tears before bedtime. Larger Sheerline boats incorporate a brazed stainless steel tank, perhaps overkill, but it does ensure you won't get problems.

As the tank maintains an exposed water surface, unless it is very short, it needs to be baffled to prevent sloshing. The system is popular here in the UK, and also seems to be quite popular with Spanish modellers (less so with other European countries). It's simplicity, low cost and inbuilt mechanical failsafe are two major benefits, but it does require a tank at least 30% larger than systems which use all of the tank.

Keeping displacement down above the surface waterline is the best remedy to avoiding an overly large tank. Injection moulded plastic model kits are perhaps one of the worst culprits, as they tend to have fairly chunky cross sections above the waterline when compared with say well laid GRP, etched metal or even vac-formed plastic models.

Careful work with sanding tools can improve matters considerably, but going too thin may make things fragile, as styrene has little strength compared with metal or GRP.