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Bump's World - February 2018
February 28, 2018


ULDB stands for, ultra light displacement boat. The yacht designers use a formula of displacement in tons divided by the waterline line length x .01 cubed. This gives them a number to compare weight versus length on different boats.

Yachts over 300 are considered heavy displacement, 200 to 300 medium , 200 to 150 light, 100 to 150 very light, under 100 ultra light.

In the 1970's the IOR measurement rule became the predominate handicap system. IOR (International Offshore Rule) favored heavy boats, that were tippy and had short waterlines. Yacht designers all around the world worked this rule to make their boats win the major regattas. Your goal was to have a fast boat per its' rating. Most of these boats did not sail very well due to the design of the hull. The ends were pinched to keep the waterline as short as possible making them out of control in a breeze down wind. Because they were heavy, the windier it was the more boats tried to go faster but could not so they sank in their own wake, causing huge resistance and again loss of control.

A designer in Santa Cruz California, (Bill Lee), also known as the Wizard, decided designing boats to this IOR reduced the fun in sailing. Fighting big boats with huge loads that are trying to sink was not fun.

Bill designed a boat call "Merlin" and ignored all the IOR design constraints. This boat was also built for the Transpac race, which goes from San Francisco to Hawaii. Due to the Pacific trade winds, it is a downwind ride.

Merlin broke the record and everyone raved about going downwind at 15 plus in total control. There are several other races in California which again are downwind rides. The feeling was, these extremely light boats with a lot of sail area are good downwind but can not go up wind.

Bill Lee then designed and built a Santa Cruz 27, 33, 40, 50 and eventually a 70. These boats were raced around the buoys and did amazing well. The owners raved about how much fun they were having.

Other ultra light believers jumped in with designs of their own. Ron Moore with the Moore 24. George Olson with a complete line of ultralights,25, 30, and 40. Terry Alsberg with his Express line of 27, 34 and 37.

At the same time this was happening a group in Southern California decided that IOR was detrimental to designing and building boats that were fast and fun to sail. They created a system call PHRF. PHRF opened the flood gates for these ultra light boats to compete without being killed by IOR.

The days of Ultra lights being just downwind flyers was also fading as the new ULDB were designed to go fast up wind also. A lot of us began drinking the ultra light tea and going to the ULDB church. Church was held every Sunday where ever there was a sailboat race.

These ULDBs were not only just light, they had long waterlines and very full hull lines. The maximum beam section, usually in the middle of the boat was carried all the way aft giving the boat a lot more interior volume. The bigger stern also created more form stability so the boats were way more stable down wind. Because the boat is so much lighter than the medium displacement boats the drag was way less, so instead of digging a hole to sink into the boats get up and go, which is also called planing . They also accelerate quickly on the downside of a wave, again greatly increasing the speed.

In the 1980s IOR died and was replaced by IMS, another measurement rule. IMS was a little better for extreme boats like ULDBs but still not great. IMS was replaced by IRC which was replaced by ORR etc. All these measurement rules continue to favor heavy slow boats.

I love sailing on ULDBs. They are fun to sail. The revolution in yacht design from Santa Cruz was a huge asset to sailing. It is always good to sail fast.

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Bump Wilcox