Why hulls are not symmetrical

THE OWNER of a 28-foot Cape Dory sloop was once upset because his rudder post did not come up through his cockpit on the exact centerline. It was, in fact, offset by about an inch or so to one side. Was this normal? he wanted to know.

But what he was really asking was: Is it okay for this not to be symmetrical? The human brain loves symmetry to the extent that it will forgive all kinds of mistakes. If something’s wrong it doesn’t matter — as long as it’s equally wrong on both sides. It’s more important that mistakes should match.

Unfortunately, things don’t always turn out the way the brain would prefer them to, as demonstrated by the Cape Dory’s rudder post. In fact, there are many, many boats that emerge from the manufacturing process rather differently from what the yacht architect so painstakingly designed. In the heyday of one-off wooden yachts, a naval architect was well pleased when a 35-footer came within 6 inches of its designed overall length.

Even today, in this era of improved precision, it’s not always possible to match a finished boat to those beautifully faired lines on the designer’s drawing board. For example, one experienced contributor to the Cape Dory bulletin board confirmed that when he worked for Sam Morse, building the famous Bristol Channel Cutters, it was quite obvious that the hull mold was asymmetrical.

Now, Sam Morse boats are renowned for the quality of their build and finish, and BCCs have always been top-of-the-line cruisers. Even so, “One had only to stand behind the boat and look forward along the garboards (where the lower part of the hull joins the keel) to see the difference between the port and starboard side of the boat,” he wrote.
“I noticed this difference quite readily when installing the ballast. The lead castings for the ballast reflected the hull’s asymmetry.”

Sam Morse is not alone. BoatU.S. Magazine quoted the owner of a 2007 C&C 115 who discovered his deck was off-center by 1 1/2 inches. The builder responded: “One of the norms of the industry is that no builder guarantees symmetry. Even in strict one-design classes there are variations ...”

A hull that is not symmetrical will probably list to one side, of course. That fact, combined with an offset rudder and a mast that is not quite on centerline, might make a boat a race-winner on starboard tack and an absolute dog on port. On the other hand, the mistakes might tend to cancel each other out so that you end up with a reasonably normal boat on both tacks.

It is difficult to predict in advance what the overall effect of an asymmetrical hull might be. We are dealing here with changed centers of buoyancy and gravity, and possibly with the center of lateral resistance, too.

But, to get back to the Cape Dory man’s question, does a little asymmetry really matter? Not in most cases, I venture to suggest. I learned this from personal experience. One morning I was happily cleaning my teeth when I noticed to my horror that the middle of my top teeth did not line up with the tip of my nose. In other words, my center of sniffing was displaced to starboard of my center of chewing by about one-half tooth.

It was rather a shock to me to discover after decades of looking at myself in the shaving mirror that I had an asymmetrical face. I immediately took action to disguise my disfigurement. I learned to smile infrequently; and on the rare occasion when a smile was essential I learned to open the outer ends of my lips in light-hearted happiness and keep the middle parts firmly clamped shut.

Then, after considerable research, I learned that many people, if not most, are asymmetrical in one way or another. The length of legs can differ. One eye can be slightly higher than another. Women’s individual breasts frequently differ in size and pointiness. And I finally noticed that one of our most famous national TV newscasters has a nose running northeast and a jaw sloping southwest — and it does not impinge one whit upon his pomposity.

So I don’t worry about my nasal/dental asymmetry any more. Well, not most of the time, anyhow. I have found, though, that on meeting an interesting person of the opposite sex, my nose now bends itself slightly half a tooth to port to line up with my top teeth. It does this quite automatically without any urging from me and I take this as a happy sign of how Nature compensates for all our inadequacies. Which means that you shouldn’t really worry too much if your rudder post is offset, your center of buoyancy is skewed, or one ear sticks out more than the other.

Today’s Thought

There is no excellent beauty that hath not some strangeness in the proportion.

— Francis Bacon

Tailpiece

Commander: “What blankety-blank put these goddam flowers on the navigation desk fer chrissake?”

Lieutenant: “The Admiral did, Sir.”

Commander: “Purdy, ain’t they?”   

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