Hey guys,

there’s been a little device / setup I’ve been meaning to post on for a while, it’s relatively simple, so I’ll try to keep it short. I know the Volvo Ocean 65s have Venturi-filled ballast tanks too, and reading that is what prompted me to figure out how that could be done. It’s pretty simple, and may be well known / obvious to some of you guys, but it wasn’t to me. 😉 Relying on the venturi effect means the system can only pump water around when the boat is moving, but it saves you the bother of having to pump all that water around by hand.

To work, you need a ballast tank which is airtight, and has an inlet at both the top and bottom of the tank.(*1) Furthermore you need at least one venturi-system to generate some negative pressure, that could be a venturi bailer (I’m not sure if that’s the correct term in English but I mean those bailers you have in dinghies), or a venturi tube of some sort, with a connector at the throat (just see the wikipedia article on the venturi effect and you’ll see what I mean).

The system has three states:
- When filling the tank, you connect the top of the tank with the venturi, and the bottom of the tank with an inlet in the water, so the air is sucked out of the tank and the water is thereby drawn in.
- When the system is sealed, everything is closed and nothing happens.
- When draining the tank you connect the bottom of the tank to the venturi and the top of the venturi to the air, to draw the water out of the tank and suck air in.

If you have the components all set up, you only need a single manually-operated 5/3-way valve to switch between the three different states, and some way to open/close your bailers(*2) or retract your venturi tube, to avoid paying an unnecessary drag penalty when the system is not in use, and to reduce the chances of seaweed getting caught up in / clogging up your system.

What do you guys think about this system? Personally I’m not quite happy with the either one of the two venturi-solutions just yet, maybe one of you has another solution! 😊

Cheers,
Marco

Footnotes:
(*1) Alternatively you could have a single inlet at the top, but with a ‘straw’ that goes to the bottom of the tank and a separate fitting for the top and bottom of the tank respectively.
(*2) - As a more detailed note: the bailers, since you are using them as a pump, have to be inside a closed compartment of some kind, with a hose running from the bailer-compartment to the valve. That makes opening closing them easily a bit more tricky.—Ideas? You’d also need one bailer for each direction of travel for a shunter.

Marco,

A sketch would be helpful…
How is your venturi working… in both directions?
Or is it a mobile device that you immerse and orient in the water only when you need it?
I had come up with a system of 2 dinghy bailers (or equivalent, but bigger-stronger) facing each other and one valve to fill up and drain 2 tanks on ends of the ama, but I have never tested it or even run some calculations to figure out how fast one would have to go to fill up how tall a tank…

I will put together a sketch as well…  😉

Laurent