March 25, 2016

Balance and seaworthiness

WHAT MAKES a small sailboat seaworthy? That’s a question often asked by adventure-seekers who are planning to buy a boat to sail around the world. But it isn’t easy to answer because seaworthiness is the happy result of a lot of factors, including the experience of the skipper and crew. Nevertheless, there is one factor that is often overlooked. It’s called balance.
According to Tony Marchaj, a sailor, pilot, naval architect, and research scientist, “Almost by definition, seaworthiness cannot be achieved if the boat is badly balanced.”

So what do we mean by “balance”? That question was answered by a famous British designer, J. Laurent Giles. He said good balance is “freedom from objectionable tendencies to gripe or fall off the wind, regardless of angle of heel, speed or direction of wind.”

He added that a well balanced boat had an easy motion in a seaway, that is, she passed easily over the waves, neither tending to plunge the bow deeply into the next wave ahead, nor throwing her nose high in the air as a wave passed the fore body. She would also unfailingly lift her stern to a following sea.

“One requires of the balanced yacht that she should retain the utmost docility and sureness of movement in manoeuvering at sea, in good or bad weather,” he added. “She must maintain a steady course when left to herself, but must be instantly responsive to her helm so that the heavier seas may be dodged if circumstances permit.”

And another important quality: “ She must be capable of being left to her own devices, sailing, hove-to, or under bare poles.”

That sounds like a very tall order to me. What sort of hull has this wondrous quality of balance? Here’s Tony Marchaj again:

“In a narrower sense, this means that the inherently balanced hull does not substantially alter its longitudinal trim, and does not alter its course during the process of heeling and rolling.” In other words, to be well balanced, a hull should immerse about the same volume of topsides forward and aft when she heels.

Marchaj points out that many of the good old boats still sailing now were either designed for, or affected by, the old International Offshore Rule, which produced shallow, beamy hulls with pinched bows. “Usually, when they heel, the stern is lifted and the bow falls. Consequently, these boats are difficult to control by rudder and are unseaworthy.”

If the bow digs in as the boat heels, a boat will try to round up into the wind, of course, not only because of the wedge effect of the forward sections but also because the center of lateral resistance has moved forward while, at the same time, the center of effort of the sails has moved outward and gains more leverage. This is when the person at the helm suddenly finds the tiller up under his chin. Not that it does much good, anyway,  if the boat heels too far and the rudder comes out of the water.

Luckily, most people don’t often sail in sea conditions that challenge the full seaworthiness of their boats. But if you should be of a mind to cross an ocean or double Cape Horn, balance might be a good thing to keep in mind as you search for the right boat.

Today’s Thought
Everything splendid is rare, and nothing is harder to find than perfection.
— Cicero

Tailpiece“Are you allowed to smoke at school?”
“No.”
“Are you allowed to drink at school?”
“Of course not.”
“How about dates?”
“Oh dates are fine, as long as you don’t eat too many.”
(Drop by every Monday, Wednesday, Friday for a new Mainly about Boats column.)

7 comments:

57 Degrees North said...

I'm not a huge fan of the term "sea kindly"... Having worked offshore in the Gulf of Alaska, I can attest that at some point regardless of hull design, you will encounter a sea state that's going to kick the mother lovin' crap out of you. Wheelhouse windows blown out, standing rigging ripped from the deck... Sometimes all you can do is quarter into it, hang on and pray. A hull design that unfailingly lifts her ends to the seas and quickly rolls back to center after being knocked down is far more desirable than a comfortable ride.

I understand (and mostly agree with) the concept of a "balanced boat" in the context of your post, but sometimes, when the rubber hits the road, things can become pretty elemental.

When the chips are down, it becomes a simple contest of endurance. Who is tougher, the sea or your boat? Given enough time, the sea will always win. A strong well-built boat is often a greater comfort than any mathematical theory. I wish I could remember where I read it, but the late Colin Archer (and who better?) had some interesting ideas on what constituted seaworthiness. A "sea kindly" motion as we understand the term didn't factor very large...



Melissa P said...

hi,
just out of interest, me and my partner have just taken on a boat, what we believe is freelance you mention in one of your earlier posts in 2013, and from the book, but was renamed by the previous owner. We are currently going through it at the moment to clean it up and get it nice and tidy again to use. would you want to have any pictures and be kept updated at all on our progress ? would love if you had any old photos of it as well.
best regards,
melissa

John Vigor said...

Melissa, Freelance was a 30-foot 6-inch Lavranos design built in Durban, South Africa, in about 1982, sloop rigged and transom sterned, with a full keel cut away up forward and an outboard rudder. Very similar to a Camper Nicholson 31. The Freelance design was actually named the Performance 31 by Lavranos, but was commonly known in South Africa as the Morgan 31 after the builder's name. Last I heard, Freelance was in Britain. Is this the boat you're talking about?

John V.

John Vigor said...

Melissa, you've hit the jackpot. It's Freelance. Please e-mail me at

xxggx-5474105800@sale.craigslist.org

Cheers,

John V.

Mike K said...

The comment about old IOR boats needs some challenging surely? OLD IOR boats, ie pre mid 1070's weren't shallow hulls, they were (by modern standards)quite heavy, deep hulls with plenty of rocker, narrow at both bow and stern. They had a reputation for good balance and excellent upwind speed in fresh conditions, but hard to manage downwind in a breeze as they would roll badly and dig a hole in the water. Newer (after mid - late 70's) IOR boats became progressively lighter, shallower, flatter and more beamy at the stern. Improvements in foils meant they maintained good upwind speed (perhaps while sacrificing some balance) while being easier and faster to sail off the wind. This trend has continued ever since, with hulls becoming ever lighter and flatter, even for 'offshore' cruisers.

Melissa P said...

Just tried to use that email address above and unfortuantly it says no longer in use, me and my partner was wondering if you could shed some light on her weight, as when we had her lifted out the boat was 6.3 tonne with no masts, and any tanks we know about empty apart from 1/4 tank of fuel by the plans I have been kindly given by her designer. She should have a sailing weight of 5.7 on the plans it shows a 100litre water tank in the keel, on inspection we have only found a 40 litre tank that looks to have been used for fuel in the past. We are trying to find out what is under this as it looks to have been installed after her build, was this something you possibly did before leaving South Africa, if so could you shed light what may be under this tank as we are a bit stumped at the moment.

John Vigor said...

Melissa, most boats gain weight as they get older. I wouldn't worry about it too much. As far as the aft tank goes, it was just as the plans showed. It was formed by using the sides of the boat with a flat fiberglass top built over it. But by the time we bought Freelance the tank had been used for diesel fuel. It was foul with algae and unusable. We had not time to get it cleaned out properly, so we just left it empty and installed a small day-tank of a couple of gallons on top of, and aft of, that main tank. We didn't use the engine much.
I don't want to put my private e-mail on the Internet, so if you want to contact me directly, either give me your e-mail here, or else send a message to the editor of the magazine Good Old Boat, asking her to pass it on to me. Her address is karen@goodoldboat.com
Cheers,
John V.