The evolution of a water ballast system

Some years ago, I was discussing the performance of my heavy-displacement cruising boat, a Nicholson 32 Mk X, with a good pal of mine. Now Jalingo II had many enviable qualities and sailed well in a blow, but was somewhat reluctant to sail anywhere at all in light airs. Powered as it was by an ancient single-cylinder Saab diesel engine that would set the cutlery dancing gleefully in the galley drawer, this limitation was a little irritating.

Somewhat predictably, the discussion soon converged on the ideal cruising boat for my partner, Mary, and me, which among other things would sail well in light airs but carry its canvas well in a blow. The aforementioned pal, being a yacht designer with expensive habits to support, readily warmed to the developing concept. “Ever thought about water ballast?” he asked. And so the seed was sown.

After much deliberation, we sold Jalingo II and commissioned the designer, Andrew Simpson, to design an 11.5-meter (38-foot) performance voyaging boat that we decided to name Alacazam. Long keels and heavy displacement were out. A new world of righting moments, length/displacement ratios, sail area/displacement ratios and prismatic coefficients emerged; one small step for the designer, a blind leap of faith for us! Alacazam was to be lightish, beamy, fin-keeled — and moderately water-ballasted.

Unlike water-ballasted ocean racers, which are dependent on water ballast for their design righting moment, Alacazam’s system would only provide the additional stiffness associated with having half a dozen crew sitting on the windward rail. The benefit being that water, unlike warm bodies, would not complain in foul weather, need feeding or require a place to sleep. With the ballast tanks empty, it would still have adequate stability under sail, but would need reefing earlier.

Gravity transfer

The seawater ballast is transferred by gravity between two pairs of tanks built into the wood-epoxy hull at the extremity of the waterline beam. This is well below the point of maximum beam but provides the following benefits: As the boat heels, the righting moment increases due to the extended horizontal distance between the center of buoyancy of the hull and the center of gravity of the water ballast.

If caught with the water ballast on the wrong tack, the converse of the above applies such that the heel to leeward is not dramatically affected. Consequently, the leeward tanks can be flooded without the need for pumps, prior to tacking, to get the ballast on the windward side, and subsequently emptied by gravity.

However, the cruising man in me was reluctant to forego the increased freshwater capacity that the ballast tanks could provide. This would mean, however, that to remain within the design displacement, some discipline would be required when we came to take onboard our cruising kit and caboodle. “Everything is a trade-off,” we were reminded. We reasoned that it would be a simple matter to later convert to a seawater system, but not so simple to revert back to fresh water after saltwater contamination.

So Alacazam came to have a freshwater ballast arrangement, using a 40-millimeter-diameter reinforced plastic hose and fittings throughout. Either port or starboard ballast tanks are filled via the deck filler, and the isolating ball valve closed.

The drinking-water tanks (the domestic tanks) are off-the-shelf 135-liter (35-gallon) Vetus polypropylene units, the aft ballast tank has a capacity of 250 liters (65 gallons), the forward ballast tank 210 liters (55 gallons). The ballast tanks are built into the hull sides as part of the structure and, like the remainder of the hull, are sheathed with woven rovings and epoxy resin.

The Vetus tanks are isolated from each other through Y-valves on the inlet side and the supply side, which is intended to prevent any cross contamination. Water from these tanks is delivered through manual pumps to the galley sink, and the washhand basin in the heads. Once empty, they are replenished from the ballast tanks.

Simplicity being one of the key criteria in Alacazam’s design brief, water-ballast transfer was to be by gravity. Although this requires the manual operation of two valves before tacking, it represents no great hardship, as the system is only to be used on long offshore tacks. In a short-tacking situation the water is equalized between the four tanks and closed off. On opening the valves, the water flows from the windward tanks into the leeward tanks, thereby reducing the righting moment and allowing the boat to heel further to leeward and the transfer rate to increase. Provided the heel angle ultimately reaches about 20°, the transfer is completely achieved. If not, sheeting in and bearing away does the trick. Tacking first and remembering about the ballast afterward requires a return to the original tack. This can be embarrassing and is best avoided!

The benefits of ballast

This system was used in Alacazam’s first season, during which it was clear that the water ballast was well worth having, the evident benefits being several. On the wind, Alacazam heels about 6° less for the same sail area and wind strength than it does with the tanks empty, and it sails quicker as a consequence. The concentration of weight in the center section of the boat noticeably improves the fore-and-aft stability and, coupled with less heel, reduces pitch and roll appreciably.

Although this system worked well in practice, improving both performance and comfort, the water transfer was a slow process, and we had no way of knowing when all the water had drained across. Furthermore, the replenishment of the Vetus tanks from the ballast tanks represented something of a problem, as the inlets are at the top of the tanks, and the outlets from the ballast tanks are at the bottom. Water is funny stuff, and gravity is particularly uncooperative in inducing it to go uphill. Consequently, Alacazam had to be heeled to an alarming degree to achieve this transfer, which, of course, the water ballast did its best to resist.

So we now have abandoned the gravity approach and installed a pressurized system deploying two 12-volt Rule centrifugal pumps. One pump is used for the transfer to starboard and the other for transfer to port. Transfer is known to be complete when the pump’s hum changes pitch and the digital current meter registers a drop in current consumption.

Prompted by a firm belief in Murphy’s law, a pump bypass was installed, which enabled transfer by gravity, should the need arise. Whilst the plumbing looks simple on paper, the addition of a third dimension did little to aid the installation of the system, which required a surprising number of plastic junctions and bends to get it all in the available space below the cabin sole.

Less than four minutes

With this system, we can now transfer water between the tanks via the operation of a single Marelon Y-valve and the touch of a rocker switch. The pumps draw about 10 amps, and the transfer takes about 3 1/2 minutes. This is longer than the pumps’ 50-gallon/minute capacity would suggest and is due to the additional internal friction arising from the intestinal nature of the plumbing. The replenishment of the Vetus tanks from the ballast tanks is similarly achieved without the drama of the gravity system.

Mary has developed a distrust of shoreside water supplies and now prefers to drink bottled mineral water. Consequently, we always set out with a good supply of bottles onboard, as well as a reserve 30 liters of water in plastic containers, should we ever need to take to the life raft. (It will be interesting to see if she drinks it then.) Furthermore, most of Alacazam’s visitors tend to avoid drinking anything that hasn’t got alcohol in it, and this, coupled with our usual frugality on passage, means that the contents of just one of the Vetus tanks lasts us a couple of weeks or so. Good-quality drinking water was freely available on our passage south from England through France, Spain and Portugal. So far, the likelihood of using the reserve water in the ballast tanks seems remote.

Clearly, lugging half a ton of water unnecessarily around the ocean does not stack up too well against the original design brief for a performance cruising yacht, particularly when coupled with a blatant disregard for the discipline referred to earlier. It was beginning to look as though we should revert to a seawater ballast system as first intended.

But in January 2002, we had an ocean crossing to make — Canary Islands to the West Indies — so we decided to defer judgement until completion of this passage.

On arrival in Guadeloupe, after an 18-day crossing from Tenerife, we had not drawn on the 460 liters in the ballast tanks, and we still had some 60 liters remaining in the domestic tanks. Taking into account the 25 liters of bottled mineral water that we drank on passage, our average usage was 6.5 liters per person per day. At this rate of consumption, we had another five days’ supply left in the domestic tanks. The 30 liters of fresh water in two plastic jerry cans would give us another four days or so. In total then, we had sufficient water onboard (without that in the ballast tanks) for the two of us for about 27 days, and I’m sure we could stretch this to 30 or so without too much difficulty. We made no attempt to collect rainwater in the frequent heavy squalls that occurred in the latter part of the crossing, but we did use it for impromptu showers.

The trade-wind passage being entirely downwind, water ballast served no purpose and did nothing but slow us down. To neutralize the effect of the water ballast, it was equalized in the port and starboard tanks; consequently, both pairs of tanks were half full. Although the tanks are baffled to prevent surge along their 2.2-meter fore-and-aft length, the free surface area when half full gave rise to a lot of sloshing about, which may well have contributed to the incessant rolling; plus, it was noisy … very noisy. If we could have emptied those tanks, sleeping below would have been easier, and we just might have gotten the 200-mile day I hankered after.

Converting to seawater

The number of passages we plan to make in excess of 18 days are very few indeed, so it would seem that the case for converting to a seawater ballast system is overwhelming. This should be quite straightforward and will require relatively few additional components.

The redundant plumbing is adapted to pump seawater from the galley sink discharge pipe into either pair of ballast tanks. The connection is made immediately above the seacock. This point is always below the waterline, so the pump is primed at all times. A non-return valve will be installed to prevent water draining back out via this seacock before the inline valve is closed. Once the tanks are filled, the inline valve is closed, eliminating the possibility of soggy cornflakes and the like getting into the centrifugal pumps.

The gravity-transfer bypass will be abandoned and the redundant plumbing adapted to provide for discharge over the side during the tank-emptying cycle. Before passing through the hull side just above the port-side waterline, the pipe is looped up to the underside of the deck to prevent seawater from flooding back into the system when the outlet is submerged on the starboard tack. A non-return valve was installed in this line for additional security.

If the ballast-transfer pumps fail and we are left with the water in the leeward tanks, then as a last resort I will disconnect the pipework and allow the water to drain at a controlled rate into the bilge, where the bilge pump will deal with it. Prior to taking this course of action, we will need to be quite sure that the inlet side of the system is properly closed off, or supply could exceed all expectations.

This system will retain the benefit of more stability and power on a reach and when beating to windward, without the weight penalty when off the wind. But what about those passages that could exceed 20 days, or those extended periods at anchor where a freshwater shower after a dip over the side makes life so much more enjoyable?

With the galley sink outlet seacock closed, any (or all) of the ballast tanks can be filled with fresh water via a hose in the galley sink. With some additional plumbing, we can get a further supply of fresh water (or seawater when on passage) at the galley sink, and a freshwater shower in the cockpit.

While this freshwater supply will not be suitable for drinking or cooking, owing to the seawater contamination of the ballast tanks, it will be perfectly adequate for washing up dishes and showering sweaty bodies. Any rainwater collected will simply be poured down the sinks to top off the supply as required, leaving the two Vetus tanks reserved for pure fresh water.

So, by this circuitous development, we have arrived at a system that provides the best of both worlds, all without needing another hole through the hull and not a watermaker in sight.

Dick McClary and his partner Mary live in Plymouth, England, but they spend most of the year cruising aboard Alacazam in the West Indies.

By Ocean Navigator