Water ballast

Is water ballast a potentially useful tool that will bring comfort and possibly improved performance to a sailboat? Opinions are divided, so what do you think?

This article starts with a confession. Shindig can carry water ballast though we've hardly ever used it. This is largely because we spent about a decade cruising the Mediterranean where the winds are often light (or non-existent) unless blowing like a troup of banshees. But next year I intend to put it to the test and see if it shapes up as a truly useful cruising tool. In the meantime let's regard it as an experiment.

You see, as a once designer of multihulls, I’ve always liked sailing fairly upright. It’s civilised and comfortable. Those that like their lee rail well buried are, of course, welcome to their thrills but the thought of my breakfast cuppa thus imperiled is, for me, offensive.
And, of course, boats work better when they heel less. The racing brethren have known this for years which is why you will see most of the crew with their legs dangling over the toe-rail, their combined weight helping to keep the boat on its feet. But this isn’t without its downside. For those that have never tried it, I can tell you that it’s not a lot of fun.

Some years ago we were in the Bay of Biscay heading for northern Spain, close reaching at seven knots or so. We first spotted her lights astern shortly after midnight, and they gradually brightened with every hour that passed. She was catching us fast. The dawn revealed a tall rig and corn tan Kevlar sails. No surprises there -- a racing yacht.

We had just about finished breakfast when she drew abreast. Now we could see her crew, bright in their foul weather gear, hiked out on the rail like a row of macaws. I raised my coffee, eliciting a dispirited wave in response. They had probably been there all night. For, such is life in the offshore racing game, where the price of glory is exacted in bodily discomfort.

Yet there’s no denying that the ability to transfer weight from one side of a sailboat to the other can do useful things to stability. On lighter displacement boats where inessential weight is always an anathema, a pound on the rail is worth several dozen on the keel, particularly at small angles of heel. To have your boat sailing more erect makes both the hull and the sails more efficient. This translates as less hull drag, less weight on the helm, and significant gains in sail drive for any given spread of canvas. So, although the role of being human ballast is a cruel betrayal of what most of us would hope of a sailing life, it does serve a useful purpose. You can console yourself in the knowledge that the boat is sailing faster and, while you’re sat there, it gives you time to reflect on how there must be a better way.

And there is. Perhaps mercifully, since those mind-numbed unfortunates across the water had already suffered enough, they didn’t know that we too had hefted some ballast to windward. More specifically, some 380kg (850lb) of water -- equivalent to about four husky deck apes on the rail -- had been pumped into an off-centre tank and hadn’t uttered a word of complaint since we had left La Rochelle.

Of course there’s nothing new about transferable water ballast. The more extreme race boats -- particularly those like the Open 50s and 60s intended for epic ocean events -- have been using it for years, though popularity among this breed has since swung (the word being more than usually apt here) towards swinging keels. Many illustrious designers -- Sparkman & Stephens, Bruce Farr, Steve Dashew amongst others == have incorporated the concept into their faster cruising designs. Yet, despite the promise it offers, water ballast remains a subject on which many cruising sailors are openly skeptical, sometimes downright hostile. And, although a few smaller trailer-sailors fill sea water tanks situated on the centreline to act as temporary ballast -- the tanks being drained when the boats come ashore -- so far as I’m aware, not a single production yacht has gone the transferable route.

Making the case
My own view is that it’s each to his own taste. Water ballast may not be for everybody but it certainly makes sense to me. Coming from a background in multihulls, I’m an unashamed enthusiast of sailing as fast as is practicable and see no reason to surrender too many of those advantages simply because I now sail a keelboat. I use water ballast, not as the primary source of stability, but to add stiffness to a boat which, with a ballast ratio of 38%, is already intrinsically stiff.

I must also distance myself from those magnificently outrageous sea sleds that scream around the world in pursuit of glory in such events as the Around Alone Race and the Vendée Globe. Their ballasting systems may be OK in that twitchy world where speed is everything, but they’re much less suitable for cruising.
Let me explain. The illustration below shows two quite different boats at different angles of heel. The top boat carries its water ballast high, as far outboard as possible in a manner common with racing craft. By contrast, the lower boat – my own boat Shindig, incidentally – carries it low.

At this point we should ignore the hulls’ inherent stability and look at the righting moment contributed by the water ballast alone.

•    Let’s start with both boats floating upright. The righting moment contributed by the water ballast is determined by the position of the downward gravitational force from the water ballast (G) and the upward force from the hull’s centre of buoyancy (B). The top boat has the clear advantage.

•    Now let’s heel the boats to 30°. In both cases the water ballast moves upwards: but also inwards for the top boat and outwards for the lower one. The righting moments are now pretty similar with both boats enjoying useful additional stability from the water ballast.

•    Finally a 90° knockdown. The top boat is now in serious trouble because the righting moment has become a capsizing moment – not exactly a healthy situation. By contrast the lower boat still retains lots of positive righting moment and emerges the clear winner.

Conclusion: Water ballast can be beneficial but not if it raises a vessel’s Centre of Gravity

When I came to rough out Shindig’s design I agonised over whether to use sea water or fresh -- the latter as an emergency supply, should the main tanks become contaminated. I almost immediately opted for sea water, reasoning that to have almost instantaneous control over a vessel’s displacement is also useful. For example, no one wants to lug around lots of extra weight in light airs but, as supporters of heavy displacement quite rightly claim, it most certainly has a pacifying influence when it cuts up rough. Expressed simply, heavy boats have a more comfortable motion because the upward accelerations are damped by inertia.

The ability to vary the displacement gives you a degree of control over this. Although I’ve yet to put it to the test, I can imagine circumstances -- say, running downwind in heavy conditions -- when it would help calm the situation and slow the speed if both tanks were filled.

Pump action and gravity
The various tasks of filling and emptying the tanks, and transferring water to side to side are accomplished by a single centrifugal deck-wash pump acting as the heart of the system. The water is admitted and ejected though the same seacock and can be generally shifted around in any direction by operating the four shut-off valves and two Y-valves. It looks more complicated than it is. I’m sure you can work out the various permutations by yourself, but I can assure you that all functions of taking on, discharging and transferring the water ballast can be achieved by operating those valves. Feel free to work out how for yourself!

And once you have the water on board the business of hefting it about is done by simply throwing over the Y-valves. It then takes just over two minutes to pump the transfer from one tank to the other. Or you can simply let gravity do the work. A few minutes before a proposed change of tack, the appropriate valves are opened to allow the water to drain downhill to leeward. In stronger winds it’s sometimes necessary to ease the sheets to compensate for the loss in stability. In balmier conditions an increase in heeling works in favor of the transfer process.

Now, it has to be acknowledged that you wouldn’t want to be doing this, say, short-tacking up a narrow channel but, if on the same tack for more than an hour or so, the increases in comfort can be startling.


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