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Nelson/Marek GP33

2010 May 3
Here's another boat in the same size range, this time with an LOA of 33 feet, 9 inches to conform to the GP33 box rule. Remember, box rules are designed to provide a "box" of maximum and minimum dimensions that your boat has to fit in to ensure close one-design type racing. But because the designs that fit in the box can vary greatly I call this type of rule a "development rule." Designs will develop within the confines of the rule on the way to finding the ultimate performance answer. This boat, Century Fast, was beautifully designed by Bruce and Greg at Nelson/Marek for a repeat Japanese client, Mr. Hisami Ebina, who wanted a high-performance race boat for sailing on Sagami Bay in moderate winds on windward-leeward courses. The project was managed by Tatsuya Wakinaga, a veteran of America's Cup efforts.

The GP33 rule developed by the ORC encourages light boats with big rigs. The "box" allows for a maximum displacement of 4,470 pounds and a minimum displacement of 4,409 pounds. This design is at the lower limit of displacement with a D/L of 66.25, far lighter for its length than the Dehler and the Elan. Beam max is at the rule's upper limit of 9 feet, 10 inches for an L/B of 3.33, a bit narrower than the other two boats. The transom/beam max ratio is 81.5 percent, so it's not as proportionately broad aft as the Elan and a little beamier aft than the Dehler. Nelson/Marek were kind enough to send me some sections along with a lot of photos. The hull is almost dead flat across the stern and this flat shape extends forward. The turn to the bilge is firm with flared and flattish topsides. You can see in this shape an effort to get form stability at low angles of heel without picking up a lot of drag at higher angles of heel with full topsides. At higher angles of heel the draft of 7 feet, 3 inches, combined with rule max allowable ballast of 2,310 pounds, provides the stability. The fin is a CNC machined steel fin with an upper hollow section to lower the VCG. This results in a ballast-to-displacement ratio of 52.5 percent, and that's great but it does require very careful engineering and design to ensure that the hull is built light. In this case, working with the Lloyd Stevenson yard outside of Auckland, New Zealand, the designers used load cells under the builder's cradle to allow constant monitoring of the boat's build weight.

The fine bow shows no hollows. I find this an exquisite hull form. Seeing this boat hanging in slings at the yard there is nothing about it that would tell you it is anything other than blistering fast. Like the Elan, the N/M GP33 has a flat transom with no camber. This is a common feature of box rule boats where you have an LOA limit and you are trying to milk every bit of sailing length out of the hull. If you added camber to this transom you would effectively reduce the sailing length of the heeled boat. For fun I checked the freeboard at the bow as a percentage of LOA and it is 10.6 percent for this design. The Elan is 13.92 percent and the Dehler is 12.78 percent. If we use the same measurements on our old friend the Cal 40 I get a freeboard ratio of 11.9 percent. What would I do without my well-used copy of Richard Henderson's great book Choice Yacht Designs?

The rules gives strict limits to the rig and not much is left to the designer here other than to engineer the best shape for the spar in accordance with the rule's limits of spar dimensions and VCG, and place it fore and aft on the hull. The SA/D of the GP33 is 34.44. Spreaders are swept 16 degrees. And the headsail sheeting angle is 9.5 degrees. These are very high-powered boats.

The deck features a very long cockpit and a small cabintrunk to provide rule-compliant headroom over the rule-compliant accommodations while minimizing weight and windage. To further reduce weight there is only one winch on the cabintop and the companionway has been shifted slightly to port to make room for more lines to lead to the single winch. The helmsman sits well forward in the cockpit and some crewmembers will sit aft of him. Primary winches are just aft of the cabintrunk. There is no mainsheet winch.

Structural design vacuum-bagged, carbon/epoxy and foam for this GP33 was done by High Modulus New Zealand with keel fin engineering by Machine Designz. Sails are by North Sails Japan and all hardware is Harken.

Century Fast will race under IRC this season while it waits for more GP33s to arrive.
LOA 32'6"; LWL 32'; Beam 9'10"; Draft 7'3"; Displacement 4,470 lbs.; Ballast 2,310 lbs.; Sail area 579 sq. ft.; SA/D 34.44; D/L 66.25; L/B 3.33; Auxiliary Yanmar 2GYM 15-hp; Fuel 9 gals.; Water 15 gals.

Nelson/Marek Yacht Design, 2820 Canon St., San Diego, CA 92106, (619) 224-6347, nmyd@cts.com.

OBE: $475,000
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