Thoughts on Waterballast.
Velocity Girl has been renamed ‘Richard House Hospice’ for their 10th Anniversary year and in particular for our 2 handed entry into the Round Britain and Ireland Yacht Race starting on the 6th June, 2010.
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Many offshore race boats use waterballast; in this article I will try to describe the benefits for racers and cruisers alike.
What does waterballast do?
A yacht’s hull is designed to be sailed between upright (for downwind) up to a maximum of around 23 degrees of heel (upwind). More than this amount of heel and the hull shape becomes inefficient and the foils (rudder and keel) become more horizontal in the water and start to lose grip. A heeled hull shape wants to turn the yacht more into the wind forcing the helm to apply more and more rudder if not controlled; any more than 5 degrees of rudder is really slow and will eventually cause the rudder to stall, which is when the boat rounds up uncontrollably.
As the boat heels more than 23 degrees everything starts to deteriorate, the boat slows down, becomes a handful to steer and makes excessive leeway as the keel and rudder lean over and stop doing their job properly. Adding crew on the rail or waterballast will significantly reduce heel by increasing leverage against the force of the wind and providing more righting moment (the resistance to heeling generally provided by the keel). Without these options you would now have to start de-powering the sail plan.
Weight on the rail (either crew or waterballast) is vitally important to speed, pointing and ease of steering. You can imagine the advantages of water ballast on a longer race like the Fastnet when as skipper you may be trying vainly to keep a mutinous crew on the rail for several days and nights in all weathers.
In gusts crew on the rail or waterballast is helpful as the extra righting moment dampens the effect of gusts and the boat will often sail through without rounding up or needing to ease sails.
‘Velocity Girl’ weighs around 3500kgs, so the extra weight of
crew or waterballast is a significant proportion of her weight. Being able to
pump the water out in around 7 minutes when not needed gives an advantage over
fully crewed boats in light airs; and in really horrible weather keeps weight on
the rail a lot easier than some!
When to use Waterballast.
When the sail plan is fully powered up for speed and pointing the waterballast should be filled as the angle of heel approaches 20 degrees and before any de powering of the sail plan. Extra righting moment is most helpful upwind; it pays on a reach as the yacht will still heel excessively in strong winds. On a run waterballast is not required as the extra weight causes the stern to drag and the yacht can become sluggish to quick changes in course and direction. Safety in a light boat downwind is increased by keeping her speed up, keeping her agile and light on her feet and moving on top of and not burying into waves.
What boats might use waterballast?
Some boats are designed and built with no expectation that crew will ever sit on the rail or that the owner will be interested in maximising performance; these boats generally have a low ratio of sail area to displacement and often suffer in light winds. These would be typical holiday charter boats.
Other boats have a more generous sail plan and are designed to be sailed by larger crews, but are often owned and sailed by a couple or small family. These boats may benefit the most from water ballast to make up for the lack (or unwillingness) of crew to hike, or will need reefing earlier and may still be a handful to steer in strong winds or gusty conditions.
Finally some boats are designed to be sailed short-handed with either a larger keel and or water ballast providing the stiffness for a larger, faster sail plan. Of course at the top end of the scale some boats have everything, large crews, waterballast, canting keels, huge rigs etc for maximum power.
A Description of the system on ‘Velocity Girl’.
‘Velocity Girl’ was designed and built with a 325 litre (equal to 325 kilos) sea water tank on port and on starboard. These tanks are connected by a 4 inch pipe, with a guillotine type valve half way between the two tanks to allow water transfer. The tanks are filled by a 45 ltr per min ballast pump (this draws 15 Amps per hours in use); with the associated pipe connectors, bends in the system and the height (1.2 mtrs) that the pump has to lift the water, the Port Tank can be filled in 12 mins and the Starboard Tank in 15 mins (meaning a real world fill rate of around 28 ltrs per min).
The tanks take around 7 mins to empty, gravity obviously helps enormously. Only one tank is used at a time. The tanks have three air vents in the deck, to vent the air as the water fills and there is a large ‘Gusher Titan’ hand pump as a back up to empty and fill if the electric ballast pump fails.
The 4 inch connecting pipe means that when the guillotine valve is pulled from the cockpit the sea water drains by gravity to the leeward side in preparation for a tack. It takes around 12 seconds for the water to swap sides and a 100% transfer is achieved. So a little bit of planning is required to anticipate a tack.
Of course forgetting to transfer the water before tacking or leaving the handle up after the tack allows the water to go quickly back whence it came...... When used properly this system provides the equivalent of 4 – 5 crew on the rail; who never complain, don’t need feeding and when the wind goes light can be ditched. One factor about food and drink over a Fastnet type race is that you may provision for around 5 litres pppd which may mean with a 24 hours contingency no less than an extra 150 kilos of water to be dragged around the race track.
Sea water is generally used for ballast as it can be filled, emptied and adjusted to the exact amount of righting moment desired. Some cruising boat split their fresh water into two tanks allowing transfer between port and starboard that provides some but not all the benefits of a sea water system.
Fitting water ballast.
Designing waterballast into the initial build can mean reducing
the amount the tanks intrude into living space and maximising position. It is
important to keep weight, including crew centred, so having the tanks around
amidships prevents pitching which is really slow.
Many yachts have retro-fitted waterballast for short handed cruising or racing and a quick search on Google will find these projects well described. It is important for anyone considering this to consider the amount of space required, the structural strength of the hull and where to run all the pumps, pipes and air vents. Several people who have done this in fairly modest boats claiming better performance and comfort.
A summary of benefits include:
• Less reefing or changing of headsails.
• Higher pointing.
• Easier steering.
• Less weather helm
• Extra weight only when needed.
• Smoother through gusts.
• Reduced leeway.
• Increased waterline length and speed.
Waterballast can take up valuable living room inside the yacht.
It can also reduce your Angle of Vanishing Stability AVS, the minimum AVS for
offshore racing is 130 degrees. ‘Velocity Girl’ has an AVS of 150 Degrees which
is good and this is only reduced to around 145 Degrees with full waterballast,
meaning she is a very safe and stable yacht.
If you have waterballast your safety certificates for AVS and STiX (Stability Index) are calculated in worst case scenarios for waterballast. So if AVS or STiX is marginal waterballast can reduce AVS below minimum requirements, which may be riskier if caught out with full waterballast in a capsize.
Everyone will be aware of the horror stories of round the world race boats losing keels and turning upside down and staying there! This is mostly caused by the excessive width and flat tops of the cabins which makes them very stable upside down, mind you when it is all working as it should they are incredibly fast; on the recent Fastnet ‘Velocity Girl’ had only just rounded the Scillies to meet most of the Open 60’s already on their way home.
IRC boats and most cruisers are much narrower and this combined with higher coach roofs makes these boats much more likely to right within seconds.
IRC is the most common handicap system for racing in the UK. IRC will measure (rate) the enhanced performance of waterballast which will add time to your clock for any given race. So waterballast shouldn’t give a speed or time advantage over other boats; however the reduced need to change sails or reef and the much more stable path upwind can count for much more.
On a short-handed cruising or race boat I suggest the arguments for water ballast are compelling if included in the design and build as it could really transform the characteristics’ of a yacht that otherwise would be a handful for short-handed or even fully crewed sailing.
I hope you have found this article interesting. The Round Britain Yacht satellite race tracker can be followed live on the Royal Western Yacht Club website www.rwyc.org .
If you have enjoyed or learnt something from this article please consider visiting our Just Giving webpage and making a small donation to the ‘Richard House’ Hospice.
Wishing you safe and fun sailing.
Richard and Sharon
You can download a copy of this article in Word.