Canting Keel boosts speed, and risk

The Australian December 24, 2005

By: BOB ROSS

The introduction of the canting keel enables the biggest maxi yachts to be lighter, carry more sail and be considerably faster in all winds.

But there are safety issues. Grant Wharington’s 98ft Skandia was disabled when the canting keel mechanism failed during a Bass Strait gale is last year’s Sydney to Hobart race. She eventually rolled over and sank after Tasmanian water police rescued the crew.

And the engineering safety requirements are hugely expensive with the newest 98-footer Alfa Romeo (Neville Crichton) and Wild Oats XI (Bob Oatley) reported to have cost $10 million.

The Performance benefits have been startling. Typical running speeds in fresh winds for the two newest 98ft maxis have lifted from 20-22 knots to 26-32 knots.

Even more significantly, in her first race at Hamilton Island race week in August Alfa Romeo was doing 11.75 knots to windward in only eight knots of true wind. Previously, the maxis used to struggle in light winds to reach their theoretical designed upwind speeds.

They are also dominating the handicap placing, even in short-course racing. Before, in a long race like Sydney-Hobart, they had little chance against the smaller boats unless they could split away from them on a favourable weather pattern that left smaller boats in lighter air and calm.

The CBTF (canting keel twin foil) keel is a thin strut with a bulb of lead ballast secured at the tip. By canting the strut up to 55 degrees to windward, the necessary righting moment for a given hull and sail plan is comfortable achieved with 25-50 per cent less ballast than required for conventional keel.

The net result is a lighter overall displacement for a given hull and sail plan, hence higher power-to-weight ratio.

The forward foil, as well as the aft steering rudder, is needed to stop the yacht slipping sideways when the keel is fully canted to windward.

The two rudders and the lighter displacement also make the CBTF boats easier to turn.

Another benefit is the ability to angle the leading edge of both the forward and aft rudders about three degrees to windward so that the boat can sail dramatically higher to windward with virtually zero leeway (side slip).

Canting keels have been used by single-hander and double-hander ocean racers on the Open 60 and Open 50 classes for about 15 years. But they only came to the fore in fully crewed ocean racing three years ago when Oatley fitted a CBTF to his new Reichel/Pugh 60ft Wild Oats.

CBTF was developed and patented by DynaYacht in San Diego, California, and applied firstly to small yachts. The design team of John Reichel and Jim Pugh, also based in San Diego, signed up to use it on Wild Oats

Wild Oats won the big boat division of Hamilton Island race week so easily that CBTF was picked up quickly by Ron Disney, for his new California-based Reighel/Pugh 86-footer Pyewacket and German Hasso Plattner for an R/P86 that McConaghy Boats built in Sydney.

Wharington’s re-built Wild Thing and AAPT, the former Nicorette 90-footer chartered by Sean Langman for Hobart race, have canting keels with twin foils but not the “collective” steering system linking the two rudders of the CBTF system. They do have the ability to raise the forward foil for downwind running.

Crichton, who is extremely safety conscious, has expressed reservations about canting keels but reluctantly accepted the technology to remain competitive at the front of the fleet.

The stainless steel ram that cants the keel on Alfa Romeo is massive. If it fails, two manual locking rods will pin the keel in place on the centreline.

Alfa Romeo has water-tight bulkheads, with doors, behind the forward rudder and ahead of the aft rudder.

“If we lost either one of the two rudders, we should not sink and if the keel failed, the fore and aft bulkheads should keep the boat afloat,” Crichton said.

We have safety margin of 3:1 engineered into the boat; it should withstand loads three times those encountered in normal sailing. But the canting keel certainly adds another complexity into sailing and if it fails, you have big problems.”

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