Most of today's designs have shorter overhangs, which gives a longer waterline allowing narrower beam and a shallower hull. This gives an impression in the water of a much larger, sleeker vessel without added weight, giving the boat a lighter displacement/length ratio. Lowering the ballast ratio (essentially dead weight), lowers the displacement required, making it easier to achieve an ultra light displacement. Ballast is the greatest single weight in any boat. By reducing ballast more weight can be saved then any other single item. This also relieves the hull of a concentrated strain, thus avoiding heavy framing in way of the ballast.

     Many people believe that ballast is stability, while in fact it is the center of total weight and the hull form together which are the key factors. Ballast is a way of lowering the center of weight while adversely affecting the hull form. It is possible to get very good stability without ballast; just ask any multihull owner. Ballast really becomes effective at high angles of heel whereas hull form (as in a multihull) is effective at low angles of heel. The interplay of ballast and form stability is the compromise every Architect has to make in designing a boat. Heavily ballasted boats tend to sail at high angles of heel because of their poor form stability. This is caused by the slack bilges and deep sections needed to get the required displacement to carry all that ballast. Less ballasted boats do not require as much volume under water, so their New U.L.D.B. hulls are shallower. The shallower hull has more stability at low angles of heel and is more comfortable to sail. The trick in any design is to get good initial stability from the hull form while using enough ballast to give adequate range of stability for safety.

      I once read an article by an Architect of repute that stated that anything over 30% ballast ratio was a waste of time. He went on to point out that as you increase your ballast ratio you devastate the hull shape. You do increase the ability of the boat to carry sail, but at a higher angle of heel. What is more, the distorted, heavier hull form has more resistance. Preliminary work carried out by my company, Bray Yacht Design And Research Ltd., has indicated resistance goes up twice as fast as sail carrying ability. Still, ballast ratios have continued to go up.

      Let us have a look at the effects ballast ratios have on displacement. Using "Jennifer" which was designed for Cruising World's design competition, let us try 50% ballast, and then 25% ballast. The design originally has a conservative ballast ratio of 37%. Jennifer's displacement is 11,500 lbs. of which 4000 lbs. is ballast. To get a 50% ballast ratio the displacement needs to go up to 16,000 lbs., with 8000 lbs. of ballast. Quite a jump in displacement and double the ballast to gain an extra 13%. Its a vicious circle. More ballast means more weight so more ballast is required to get that 50%. We cannot simply add 2000 lbs. to the original 4000 lbs. because that pushes up the displacement too.

     50% of 11,500 lbs. = 5750 lbs. So 2000 lbs. additional to 4000 lbs. of existing ballast = 6000 lbs. of ballast. 7500 lbs. of original boat + 6000 lbs. of ballast = 13,500 lbs., but 6000 lbs. of ballast is not 50% of 13,500 lbs. What is more, a larger motor will be needed as well as larger spars, more sail, etc. All this is more weight. More weight means more ballast and so on. But if we deduct 1500 lbs. from the original 4000 lbs. of ballast that gives us 2500 lbs. of ballast on 10,000 lbs. of displacement, a 25% ballast ratio.

      The lower ballast ratio means almost 1/4 the weight in ballast, a saving of 5,500 lbs., a much greater saving than canvas pipe berths or inadequate structure. But what happens to the stability you may ask? The stability curves show you clearly. The character of the curve is the same, the range of stability is the same, only the amount of power is different. This means the lightly ballasted New U.L.D.B. boat is not able to carry as much sail but then it does not require as much sail as it is a lighter boat. The smaller sailplan is easier to handle and less expensive.

      This indicates to me that many of today's designs are headed 180 degrees in the wrong direction, in the name of tradition. In fact traditional working sail ships used very little, if any, permanent ballast. Ships such as the tea clippers were the first vessels to use permanent ballast as a regular part of their design. Ballast ratios varied between 8 and 14% with temporary trim ballast used in small amounts to trim the vessel or set the vessel down to it's lines when sailing unloaded. Otherwise cargo was the main ballast carried. It is my contention that ballast in yachts was introduced by the builders as a trimming ballast to lower the yacht to it's lines. Remember in those days there were few Naval Architects and no one specialized in yacht design. Most commercial ships were built from a half model carved by the shipwright. If a ship showed a good turn of speed or good load carrying ability then sister ships were built. If a client wanted a yacht he chose from a host of commercial designs. Even when yachting became more of a regular thing it was still the commercial architects who designed the yachts, using the same heavy displacement hull forms they were familiar with. At launching time, once a vessel was fitted with its luxurious appointments then it could be ballasted to its lines. From then on it has become common practice to allow as much as 50% for ballasting after all equipment has been accounted for in the design.

      As a yacht designer, I think pleasure craft should be attacked at a new angle. Cruising and racing yachts carry a vary narrow and predictable range of payload weight. Whereas a 50 foot commercial ship could change draft 3 or 4 feet between empty and loaded, yachts change less than 6 inches. In yachts it is therefore very easy to predict the sailing waterline and characteristics. It is also just as easy to calculate the weight of the completed vessel and work out a hull shape which will give the desired stability. Because commercial ships vary their draft over such a range and because they are beasts of burden their hull shape usually approximates a rectangle with some consideration (but not a lot) being given to resistance. With this hull form not only can the most amount of weight be carried but the best stability characteristics can be maintained throughout the range of draft. It certainly would not do any Architect credit to have a vessel of his design capsize at the dock while being loaded, although it does happen.

     So what I am saying is that pleasure craft do not need to resemble commercial craft in hull form as their two functions are entirely different. In my research to evaluate this ballast/stability question I have reassessed my thoughts on form stability and how to get a wider range of stability from the hull. This has lead me to a hull shape which is not revolutionary to the eye, but is in the purest of technical sense. In essence I have looked at the hull forms of trimarans and racing scows to create a hull form which will give me stability equivalent to existing vessels without all the dead weight. Not that this hull form can not be used with ballast, but just that heavy displacement distorts it to the point where it becomes less effective. The lighter the displacement the more effectively it works. I have used this hull form to varying degrees in all my designs including the 'Jennifer' and have found it to always yield the same effect. In sailing the one design 'Bray 7.5' we have found that the boat rolls less in a chop, has good stability, very good interior space, and excellent speed. The Bray 7.5 weighs 2300 lbs. complete as a racer/cruiser including spar, galley, head, four good size berths and an outboard. A 7 h.p. outboard pushes the B7.5 to 7 knots and we have easily reached 9 knots under sail in a 15 knot wind. The boat prefers to sail upright and is easily handled.

     In light displacement boats crew weight becomes an increasingly important factor. The three racing crew on the B7.5 contribute one half of the total righting moment. Because of its light displacement the boat feels tender initially and can be easily heeled if the crew are not prepared to hike. In a larger boat crew weight becomes a much lesser factor. In displacements over 10,000 pounds four crew have little effect on stability. An ultra light racer/cruiser would have to over 45 feet to be above that displacement. An U.L.D.B. as a cruiser would still retain the advantages of a racer/cruiser but not to as high a degree. Some extra displacement would have to be allotted to carrying of stores and cruising gear. With the invention of reliable reverse osmosis water makers it is possible to have unlimited water supply without the weight of large capacity tanks. The use of some water ballast could also be incorporated. Such a vessel could carry the usual cruising gear in good comfort but would still retain the speed that would make the most successful Admiral's Cuppers envious.

     With cruising speeds in the neighbourhood of 10 knots on a 45 footer passage times would be cut in half. As smaller auxiliary, spars, and winches are required the boat would be less expensive too. The smaller sailplan would make the boat easier to handle by a minimum crew. Our hypothetical 45 footer would have somewhere in the neighbourhood of 600 square feet of sail. Not bad for a 10,000 lbs boat.

      One advantage that has been noted in the O.S.T.A.R. when a U.L.D.B. hit a fish boat at night, was that the lack of weight allowed the boat to stop quickly and so much less damage was done. In fact the U.L.D.B. was able to make repairs and sail on unassisted.

     I.O.R. boats and racing centerboarders with all inside ballast have been known to pitch less. It seems that everyone is aware of the need to keep weight out of the ends of the boat but the same applies to weight down deep. Once a boat starts pitching all that ballast is swinging through the water and would gladly continue to do so. Those boats with inside ballast pitch less and go to windward better as they do not shake the wind out of their sails. Heavily ballasted boats carry their ballast much higher up in the keel and in some cases right up into the bilge. (See figure 1.) The lightly ballasted boat carries it's ballast lower allowing it to work more effectively and do the work of a much greater weight. Also the top of the keel can then be used for a water tank thereby also contributing to stability (as I did in 'Sarah'). One of the biggest safety features of a low ballast ratio is that no matter whether your boat is foam cored fiberglass, aluminium with foam sprayed in, or laminated wood, the large hull surface area with light weight will make the boat positive buoyant. Even if the boat is cut in two, each part will remain afloat. This is the one good feature of multihulls that carries over into this type of yacht. You can remain in or on your boat until you are able to make repairs, pump out the boat and continue on. In survival conditions your chances are far better out of the water and not exposed to the elements. Also you will be able to live out any rescue time in relative comfort in the boat. The large size of the vessel afloat will also be easier to spot then a small life raft at sea.

     When I originally began work on this project in 1974, it quickly became apparent that it would be possible to do a monohull with all the advantages of a multihull while retaining the ability to right itself at high angles of heel. A single hulled boat suitable for extensive cruising, capable of great average daily runs, of low cost as exotic materials are not required to achieve the light weight, capable of being home built, unsinkable, and with a superior motion. In fact it may even be possible to do an all out racer able to keep pace with the fastest of ocean multihulls. Now that would be an achievement!

Reference Material.