Dinghy Design and the 1970s Revolution

This is my take on how planing dinghy design has progressed over the years. I've also created a relationships chart showing what I consider to be the major design influence routes between the development classes.

The earliest record of a sailing boat planing seems to be in Dixon Kemp's "Yacht Racing Calendar and Review" for 1891. This contains a race report which states that a Racing Sailing Canoe on the Thames called "Snake" had "the extraordinary power of rushing over the water at ten or twelve miles an hour, probably more, without any wave-making apparently; only a wide smooth wake is seen astern. Yet at five or six miles an hour she makes waves like any other boat.". "Snake" was designed by Theo Smith of Oxford. It seems clear from the description that the writer wasn't familiar with the concept of planing - this may have been before even powered craft were capable of planing. The term hydroplane seems to have been coined in 1895. How much these racing canoes influenced dinghy design is an interesting question, but as Linton Hope racing canoes are recorded as planing in the early part of the 20thC, and Hope was the predominant designer in the early days of the National (later International) 14 foot class its hard to believe that the concept was unknown.

In the older books at least the first "deliberately designed" planing dinghy was Uffa Fox’ revolutionary 14 "Avenger" (1927). However, in addition to the British canoes, there’s also good evidence that light and flat American, New Zealand and Australian boats could and did plane before "Avenger", but no evidence as far as I know that this was a deliberate design aim. It doesn’t see to have been something they considered. On the other hand Uffa had deliberately set out to make a boat that would plane like a motor boat or seaplane hull, and perhaps even more importantly wrote the books that talked about it. When you look at early "boats that could plane" like the Kiwi Patikis or maybe Thames A Raters (if the Raters did plane very much in practice - this is uncertain in their unique environment) I think I see their planing capability as being a side effect of a shape chosen for other reasons rather than a design aim. One of the things that leads me to believe this is knowing a little about Norfolk Broads lake boats from the 30s. Many of these had big powerful sterns and what look like planing type shapes, but are far too heavy to plane. These 1930s built hire boats for instance have maximum beam quite well aft, flat hull sections throughout and a very Bruce Farr-like transom, and their design goes back to the Linton Hope tradition with the Raters and so on.

I also have a somewhat heretical suspicion that the reason Uffa won quite so many races in "Avenger" was not the hull shape - the flatter floored Linton Hope boats look as if they ought to be capable of planing - but that, in order for his planing theories to work, he was the first to deliberately sail his boats substantially flat, playing the mainsheet, rather than tending to let them heel like a keelboat in the older style. A revolutionary new sailing technique is worth far more in performance than any advance in hull design! There's some support for this in Uffa’s "Sail and Power" (1936) in which he says "It seems that the Americans do not understand dinghy sailing, for they let their dinghies heel over, which slows them, and it is chiefly due to this we have beaten them on every occasion."

But I digress. In the thirties Britain was at the leading edge in dinghy design. Peter Scott and the trapeze, Ian Proctor’s 14s, Jack Holt’s Merlins and many others spring to mind. However by the early 60’s development in the U.K. had started to stagnate. To my way of thinking most British dinghy classes originate in this period (even though some were designed a lot later). I call this the "1st Generation" of planing dinghy design, characterised by plenty of rocker, fairly narrow flat transoms and a tendency towards V sections.

One of the causes of this stagnation was that the 60’s dinghy boom was built about one design classes, which competed more on detailed specification and choice of materials between FRP (glass fibre/polyester resin) or the generally superior plywood. Another factor was an unfortunate tendency in the 14 class to immediately outlaw any development that appeared to have a significant effect on boat speed.

Meanwhile in Australia and New Zealand things were very different. The Antipodeans took Uffa Fox’ maxim "Weight is only of use to the designer of a Steamroller", and applied it almost univerally - or that’s how it sometimes seems to an outsider. For example the late Ben Lexcen’s (then Bob Miller) prototype for the Contender was about 80lbs lighter than the minimum weight imposed on the class by the I.Y.R.U. when the boat was given International status. These developments seem to have originated in the 1950s in New Zealand, and in the late 50s and 1960s New Zealand and Australia were a hot bed of radical innovation that was quite unappreciated in the Northern Hemisphere. It all seems to have started with John Spencer. Virtually unknown in the U.K., this ex Civil Architect started designing boats that exploited the new marine plywoods and waterproof glues to the full. In 1951 he designed the first Cherub, and followed this up with other boats that were all primarily intended for the ordinary bloke to be able to build and sail. A key factor in his boats was always light displacement (= less materials for the same size boat = more boat for the money). Amongst the youngsters who would hang round John Spencer’s Yard, do odd jobs and talk about boats were Ron Holland and Mark Bethwaite. A young Bruce Farr turned up there on at least one occasion too.

At the same time similar concepts were influencing Australian sailing. In the Eighteen Foot Skiff class Bob Miller (later to change his name to Ben Lexcen) introduced a new boat that had half the crew, a third of the weight, and half the sail area of the previous boats, and went a third as fast again! The designs he introduced led to an explosion of new ideas down under. John Spencer’s designs reached Australia when the Bethwaites migrated to Australia in the late 50s, and the whole dinghy scene was very dynamic and progressive. For instance foam sandwich boats were already being home built in New Zealand by the late 60s.

In late 50s/early 60s I identify a "2nd Generation", a little flatter, a little more rounded, somewhat fuller aft, starting perhaps with Westell’s 505 and including Contenders, 470s, Lasers (which look awfully Contender influenced to these eyes) and the like. Back in Britain things were not so innovative as in the antipodes. Most new classes which reached International status were foreign designs - 470, 420, and Laser for example, and it is difficult to think of a English design later than 1962 that has gained significant international acceptance. The 14s, once the great innovators, were smothered under a large number of detailed rules, and most new designs showed little improvement from mid 50’s designs like the Enterprise or Wayfarer. Even Peter Milne’s successful Fireball of 1962 started life as an attempt to emulate American scows, as did Ian Proctor's Topper.

So we reach the early 1970s. In 1974 the Cherub class - the only restricted class to have significant presence in both the Northern and Southern hemispheres - prepared to host its first World Championship in the UK. The class was strong in the UK, with good racing, and 50-60 boats anticipated from around Britain. 5 Australian and 5 New Zealand boats were expected, and all were waiting to see if they could keep up with the latest English designs in UK conditions.
All 10 foreign boats finished in the top 12, and the highest British boat was 5th. The Antipodean boats outclassed the British on every point of sailing in all weather conditions. Something had obviously happened down under!

It transpired that designers like Miller, Bruce Farr, Frank & Mark Bethwaite and Russell Bowler (now a partner in Farr Yacht Design) had come up with a real breakthrough in dinghy design. The new boats had very much flatter sections, wider sterns with almost parallel chines, low rocker, and much more powerful rigs. Seen in Torbay were a whole host of ideas that British classes have since adopted, or legislated against, including double spreaders, gooseneck level bend control, fully battened mainsails, dagger boards, loose footed mainsails, jib battens and rudder gantries.

The first lesson learnt from 1974 was about rigs. The flatter fully battened mainsails, with draught further aft than the English sails of the time were immediately adopted by the U.K. Cherubs, and few soft sails have been cut since. Sail design is very volatile, and influences are difficult to detect, but the Cherub rigs are known to have influenced the decisions by the International 14 and Norfolk Punt classes to adopt fully battened mainsails. Gooseneck level lower shrouds were another feature first seen in Cherubs at about that time which is now in widespread use.

To my mind though, hull design was where the real revolution had taken place. Both first and second generation boats tended to have the centre of buoyancy not too far aft of halfway along the boat. The new Antipodean boats , however, were the first of a 3rd generation. They had very low rocker, fine bows with straight waterlines, and flat sections with wider transoms and almost parallel chines aft leading to a much more wedge shaped plan view and the centre of buoyancy appreciably further aft in spite of rules which tended to force it towards the mid point.

Something of a sideline was a almost uniquely British style of boat that emerged in the 1980s. Somewhat similar to my 3rd generation these boats had rather more rocker, and that located much further aft, along the planing run. While the style appeared to work adequately within one particular development class’ rule set a that time, it doesn't seem to have been influential internationally, and one designs based on that style have more or less died out. I also identify a uniquely British line in the National 12, Merlins and their RS offshoots. These are are very effective low wetted area style of boat, without the blistering offwind speed of the Antipodeans, but very good indeed in lighter winds and confined waters.

Since then many, notably Bethwaite I think, would consider that the "humpless" free planing boats constitute a new design generation. I’m ambivalent about that: I think I’ll see what hindsight has to say when I’m a bit older. The early planing boats seem to have planed as a side effect of a shape chosen for other reasons rather than a design aim, and if my theories about what brings a boat into the low hump/easy transition to planing shape are true (they are probably completely false!) then this may be as much a feature of the wedge type third generation shape when really properly worked out rather than something new.

For what little its worth my theory is that "humpless" hull bahaviour is to do with the combination of dynamic lift and the effect of a fine bow entry on the bow wave system. I noticed with my PlusPlus singlehander that it almost never generated any significant size of bow wave, which was quite unlike anything I’ve sailed before. I was never able to tow test the boat to be sure, but she certainly slipped into planing with no dramatic transition, so she could have been approaching the "free flowing" or "hump free" characteristics. If so, and I did measure up a 49er bow as a significant design input to the PlusPlus, my theory is to exhibit this behaviour a boat must have a sufficiently narrow and fine bow that it exhibits this minimal bow wave - as does a catamaran - and yet have enough dynamic lift available to it to be lifting off its static waterlines long before it reaches "hull speed", which the thinner catamaran hull does not appear to do. I can imagine Julian or Frank B reading this and chuckling at my ignorance though so don’t take this as gospel!

There’s a lot about this in Frank Bethwaite’s "High Performance Sailing" and, in what is in my opinion a better and more balanced picture, his 2008 book "Higher Performance Sailing", the latter especially an invaluable reference for anyone interested in this subject. Things have progressed since those 70s days of course, and steady development has led to boats like the 29er and 49er. Development in the UK was slower, but by 1989 the UK designed International 14s were looking astonishingly like the 1970 Farr Cherub underwater.

Jim Champ © 2005-2013

Major Sources:


Uffa's books,
Fast Light Boats (Graham Anderson)
Higher Performance Sailing (Bethwaite)
[unpublished] (Chris Thomas)


Nel Bethwaite
Peter Tait (Firebug HQ/John Spencer archivist)
Many people on web forums, esp Dinghy Anarchy on SA and the CVDRA Forum.

Jim Champ, 2009

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