Contents and photographs
© 2009 Mark Kennett

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About displacement boats

Contents

The evolution of traditional boats and
modern yachts

steelseiner_Sada

Modern North Atlantic steel seiner. Note very high bows, essential to a heavy boat that must drive to weather under power

When I talk about traditional boats I am generally referring to working boats. These boats, whether powered by oars, sails or engines, evolved under the influence of three principal factors: the nature of their employment, e.g. fishing; the nature of the sea; and economics.

Historically these vessels evolved by trial and error, an empirical process dictated by the demands of their service. A boat’s designer and builder (usually the same person) had no formal training in scientific naval architecture; indeed scientific naval architecture did not really exist in ship design until the Victorian era and was not applied to boat design much before the twentieth century. Instead the shipwright designers of old developed an acute sense of form and function by constant contact with local boat types and by going to sea. They were grounded in traditional marine construction and engineering by an extensive apprenticeship and by working on the successful designs that had developed in their local area through trial and error. As they lived near the sailors who actually used their boats, they got constant feedback on how a boat performed. They adopted new ideas, but cautiously, because to get it wrong could spell disaster either economically or, worse, with a tragedy at sea.

The evolution of a new type went something like this: a local shipwright designer came up with a new or improved boat design to suit a certain activity like trawling, often working with a local skipper. If the design was built and seen to work, others copied it and a new local ‘type’ was born. Shipwrights in another part of the country or in another country would come up with a different style of boat to do the same job. This gave rise to the variation that is evident in traditional boat design.

Shipwrightdesigners were not ignorant peasants. Many were extremely skilful engineers, craftsmen and sailors with a deep understanding of form and structural cause and effect, a sense that is sometimes lacking in today’s computer-aided designers.

fishing smack

English east coast cutter-rigged fishing smack. Note the long keel and plumb stem with distinct, 
rounded forefoot

Why traditional boats look like they do

Until recent times the form of traditional craft was dictated solely by the requirements of their function in the sea. Examining the form and function of sailing and motor fishing vessels will help to explain why they look like they do.

From time immemorial the foundation of any boat has been its keel. This was invariably a full-length structural member, essential in a heavy-duty environment where vessels had to be able to take the ground at low tide and were hauled out on marine railways. Sailing fishing vessel skippers valued the steadiness and straight steering in a seaway that long keels imparted and did not feel the need to ‘cut away’ the underwater profile of their vessels in order to increase agility when tacking. This is not to say that sailing fishing vessels were not smartly handled; but this was achieved by skilful sail handling and big rudders.

cutter-rigged smack stern

This 100 year old English East coast cutter-rigged fishing smack has a transom stern, rare in this type which normally has a counter stern. Note long keel

The builders and owners of traditional commercial craft were well aware that speed on the water is directly proportional to waterline length so they nearly always adopted a plumb or only very slightly raking stem and often used a plumb transom as well. This maximised waterline length. The elegant clipper bow of the American fishing schooners is usually only a slight variation on this stem profile and English and French trawling ketches all use the plumb stem. This imposed a marked forefoot which helped the boats hold on to windward by increasing leading edge lateral plane.

cutter smack - bow

The same smack from the bow. Note plumb stem, distinct forefoot. She has a long bowsprit and carries her anchor slung in the traditional manner

Fishing vessels in their larger sizes are heavy boats and have to carry a lot of gear and cargo. In order for a fishing boat to have sufficient reserve buoyancy to raise the heavy hull to meet a head sea the bows had to be relatively high. But high freeboard amidships was not desirable because it increased top hamper and windage, and made it harder to boat the fish. So the sheer of the vessel swept downwards from the high bow towards amidship and then lifted gently towards the stern imparting reserve buoyancy aft. The fore and aft reserve buoyancy is sufficient for the vessel performing in a beam sea. This is the reason behind the curving sheerline of traditional, heavy displacement boats.

Seiner in Spain

Classic wooden motor seiner seen at Vivero, Spanish Atlantic coast

With the coming of motor-driven fishing boats the hull form had to change. All the desirable features of long keels were retained but bows had to be made even higher because the heavy boats could be driven direct to windward under power. As a result the sheer became more marked, and changes were made to the underwater run aft to accommodate the propellor and its thrust. A wheelhouse was added for the comfort of the crew and the masts became derricks, although a steadying sail was sometimes retained to dampen the rolling. The stem was given a slight rake to accommodate increased flare in the topsides which helped to increase reserve buoyancy forward, and this, combined with a canoe stern or radiused transom, created a usually very handsome boat.

Motor fishing boats retained this classic form until the advent of the shelter-deck trawler and fish quotas, which occasionally resulted in extremely ugly ‘rule cheaters’ of gross form, designed solely to gain extra quota on a given waterline length. Nevertheless the modern fishing vessel is now represented by some superb designs, which unite form and function in a most demanding operating environment.

beam trawler

Modern steel North Sea beam trawler, working near the Kentish Knock, England

How yachts developed

A yacht is a boat that is designed for pleasure and not for work. It can be powered either by sails or an engine.

The sport of yachting started in the 18th century among wealthy aristocrats. They had large vessels built and they raced against each other on an informal basis for large wagers. The yachts were actually sailed by professional crews drawn from the fishing fleet and had a sailing master who was usually a top fishing or pilot skipper.

With the increased wealth brought about by the Industrial Revolution in the 19th century the middle class began to join the aristocrats and yachting became a social phenomenon. Yacht clubs rapidly evolved, racing was formalised and one of the major influences on sailing yacht design appeared: the rating rules.

These were formulated to allow different designs of vessel to take part in the same race on an equal footing. Naturally yacht designers immediately started to ‘design to the rule’ in order to produce winning boats. Winning boats were then copied by other racers and their features adopted by cruising yachtsmen keen to have  ‘the latest thing’. Unfortunately, design elements that win races under a certain handicapping rule are not necessarily the same as those that produce seaworthy, practical boats.

The ‘plank on edge’ cutter, of the 19th century with its ultra narrow beam, and the long, low overhangs featured on early 20th century racing yachts are undesirable, unseaworthy features brought about by trying to cheat the rating rule. This trend, to design to the ‘rule’ and not to the sea, is still with us, for example the overbeamy asymmetric hull of the IOR racer in the late 20th century.

IOR type hull.
Note very pinched ends and fat midsection

IOR boat

Sailing yachtsmen and women have always been more willing to make radical departures from traditional, tried and tested design features than their more conservative commercial brethren. Indeed conservative, proven design is now considered hopelessly dated and obsolete by most yachtsmen and women even though they have no experience of it. The yachting industry, keen to sell new products, has encouraged this type of thinking.

Motor yachts

Motor yachts are not designed under the influence of rating rules. Instead they are influenced by two main considerations: speed and large, luxurious accommodations.

As displacement and depth are both detrimental to high planing speeds, motor yachts are built light and shoal. In order to achieve large accommodations very high deck structures are used, creating the characteristic deck-on-deck appearance and massively increasing windage and top hamper. This feature, together with their tiny high-speed rudders, makes this kind of boat unmanageable in strong winds if one of the two engines fails. Many boats of this type are not suitable for offshore use and even the largest have a limited range
(400 nm for a 65 foot vessel) due to their high fuel consumption.

The average modern production yacht, power or sail, is not designed for continuous service, long distance cruising or living on board.

If you are looking for a practical long-range motor boat, with traditional influences, check out my designs – you might find what you are looking for!

Independence from bow

One of my designs - the Independence 48, a modern boat with a traditional form

Click on this link to read the article discussing displacement boats vs planing boats.