Centerboards and hatchboards


I have a Jordan drogue set up to be deployed off the stern of my boat exactly like the ACE drogue mentioned by Mary and Edwin Arnold in the March/April issue. I have yet to deploy my drogue but have only made one ocean passage so far. A few questions:

Should I have my centerboard up, down, or 50% down? My boat draws four feet, four inches with the board up and eight feet with it down 100%.

The author mentions that the companionway should be strengthened to withstand the full impact of a full-breaking crest. Will one-inch-thick boards be adequate or is more required? Would marine plywood of 3/4-inch thickness be adequate or should I go to one-inch-thick (or thicker) if I go for plywood? Another alternative (perhaps the easiest one) is to add a layer or two of fiberglass to one or more sides of my existing companionway boards, which are about one-half inch-thick solid wood. Would that be a possible solution? I do not want to design a bank vault; just want to be sure I have a solid companionway.

Forest Golden

Portsmouth, R.I.

Answer: In extreme conditions the centerboard should be set all the way down. A boat’s propensity to capsize is governed, in part, by its mass moment of inertia and its hydrodynamic drag in the rolling direction. A boat with a deeper draft (centerboard down) has more resistance to roll than a boat with a shallower draft (centerboard up). If the centerboard is weighted heavily, its weight lower down gives the boat more stability to resist rolling; this is the mass moment of inertia effect. The exposed area of the centerboard drags a lot of water along with it on each roll, so that is the hydrodynamic drag effect.

Together, these two effects absorb the energy of impact from wind and waves, which could lead to a potential capsize. This assumes, of course, that the centerboard is a snug fit and does not bang around in the lowered position, which could cause structural damage to itself and the keel. For more information on the science of seaworthiness and capsizing, refer to Seaworthiness, The Forgotten Factor by C.A. Machaj (International Marine, 1986).

As for companionway hatchboards withstanding full impact by a breaking wave, no one knows how much power is in a breaking wave. How long is a piece of string? There will always be that one mother of all waves that will destroy anything.

On our 27-foot sailboat, which my wife and I sailed across the Atlantic, our three companionway hatchboards were about 10 inches tall, 20 inches wide, and 1/2-inch thick, made out of teak veneer plywood. Plywood hatchboards would be easier to handle than adding fiberglass to the boards you already have. Make sure the jambs are very strong. There is no sense in having strong hatchboards if the jambs break out on impact.

Keep in mind, too, that not putting the hatchboards in place, and having them fall out of place in an extreme roll, are both more serious considerations than how strong they are. In extreme conditions, make sure the hatchboards are locked in place (lock the sliding hatch over them) so that if the boat rolls they don’t fall out. More boats have been lost due to the hatchboards falling out in a capsize, allowing the boat to downflood, then to them breaking under a wave impact.

Eric Sponberg is a yacht designer based in Newport, R.I.

By Ocean Navigator