Hardtop : Not a Dog’s Breakfast

Question: How do you incorporate sheet loading on the hardtop?

Answer: When approaching the design of the hardtop, we not only had to consider the main sheet loads it would have to carry, but we also had to incorporate ventilation, a place to mount solar panels, as well as provide an accurate base for an integrated full enclosure that coordinates the hardtop to the deck. This approach is necessary with all design and development but surprisingly, it is not always observed in the marine field where it is evident that there is little integration of any aesthetic forms, and at times, functional lines.

There is a disproportionately high sheet loading on a catamaran due to its high righting moment and its large roach sail plan. The Antares has an approximate main sheet load of 7,000 pounds. That means that the wind and loading are trying to rip the hardtop off the boat. We have to look at what’s supporting the track and what’s holding the hardtop on.

The construction of the hardtop incorporates a carbon fiber reinforced beam structure to support the track, and in conjunction with the stainless support structure for the hardtop, is subject to finite element engineering analysis. That same loading analysis is carried through to the spars. The hardware used to secure the outhaul is the top end of the Harken catalog. Because the loading on the outhaul car is large, the use of “big boat” hardware is necessary. I’m somewhat puzzled by the afterthought we see all too often in the market. It is irresponsible to build a hardtop with traveller without structural analysis. No monohull owner would accept an ill conceived, home-built design, but all too common the catamaran market is littered with non-integrated design which results in a dogs breakfast.


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