Peter Poland reveals how bilge keel yachts and twin-keel designs won his respect – those that could sail well and stand on their own two feet…
Back in the late 1970s, I found myself on the horns of a dilemma. For the last decade or so I’d dismissed bilge keels and twin keels as ugly and performance sapping appendages. To my eyes, they invariably had the look of casually designed afterthoughts that had sprouted beneath nice hulls just to enable the boat to stand on its own two feet.
The boats that my company built, on the other hand, were aimed at serious sailors and I rashly assumed that anything other than a state-of-the-art fin keel or hydrodynamically efficient lifting keel would never be likely to satisfy this market.
Then my own personal boating needs underwent a change, so I had to take a flyer. Breaking my own rules and ignoring my preconceptions, I went out and spent my own hard-earned loot on a second-hand twin keeled Westerly Centaur.
Why? Because my factory and home were on the East Coast but a lot of high-profile sailing activity took place down south. So I needed a habitable floating base that could be parked on a cheap mud mooring and be able to follow the regatta circuits on which the boats I built (Sonatas, Impalas, Deltas, Medinas etc) competed.
This boat had to provide a general all-purpose home from home. And a bit of undemanding weekend pottering would be an added bonus. With my limited budget, there was only one obvious solution at the time – a Centaur.
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I soon discovered that the Centaur’s windward performance – while adequate – was hardly stimulating, especially when compared to the close winded precision of a Sonata or Impala to which I’d become accustomed.
As a result, the Centaur’s Volvo Penta motor got a lot of use when the wind went light or ahead, whereas on a reach or a run she performed satisfactorily and got us from A to B with a minimum of fuss and at a respectable speed. And she also offered comfort down below – despite the Centaur being only 26ft long I could stand up.
All of which got me thinking that maybe there could be more to these twin keel things than immediately met the eye. And as the sales of our fin and lifting keel speedsters began to slow over the ensuing years, I could not help noticing that the sales of our bilge or twin keeled competitors seemed to be on an ever-rising upwards trend in the 1970s and 80s.
If we were to continue as a viable boatbuilding business, maybe we’d have to cast aside our prejudices and take a long look at these two-legged options.
So I took courage in both hands and asked our designer whether he might be willing to consider agreeing to design us some twin keels. I hastily added that of course – being the genius that he undoubtedly was – he was bound to come up with something far better than anything that had ever graced a cruising yacht’s bilge before.
Then I stood back and awaited the inevitable broadside of shock, horror and indignation. “Well,” said David Thomas (who had never designed a slow yacht in his life), “I might. I just might.
“But first I’ll need to think about it. In case you’d not noticed, twin keels have far more variables than a fin keel. The positioning of the roots relative to the centre line, the splay, the angle of attack are all variable and important. I’ll have to think twice as hard and for twice as long.”
I took this as a ‘yes’ so left it at that. And patiently awaited developments.
History of bilge keel yachts
Of course, bilge and twin keels were not a new phenomenon. They had been around for many years. When researching an earlier article on the Westerly story, I’d been fascinated by the development work done on his twin keel and twin rudder yachts by Lord Riverdale. As had my sales manager, Andy Cunningham, who wrote an excellent treatise on twin keels.
Lord Riverdale’s first twin keel sailboat was the smaller self-designed 25ft Bluebird of Thorne, built in 1924. Later Riverdale built the bigger Bluebird of Thorne (50ft) in the early 60s that he designed in collaboration with Arthur Robb. He claimed that tank-tested models indicated a 15% improvement on his earlier twin keel designs.
Bluebird of Thorne’s owner, Lord Riverdale, had designed and built a string of cruising yachts (all with twin keels) over a period of around 40 years prior to the culminating glory of his and Robb’s 50ft steel twin keeler.
Riverdale also liked to draw the distinction between what he called ‘bilge keelers’ (meaning boats with a ballasted or unballasted centre keel and two stabilising bilge keels) and ‘twin keelers’ (boats with twin ballasted keels).
To go further back to bilge keel basics, it was probably Maurice Griffiths who did most to put bilge keel benefits into practice and bring creek crawling and ‘upright drying out’ to numerous leisure sailors.
Classics such as the 1957 Eventide 24 and 26, Waterwitch and 1968 Golden Hind 31 (to name but three of his many popular designs) all came with bilge keel options – featuring a substantial central ballast keel and two supporting bilge plates. The resulting shallow draught would never provide dynamic windward performance; but that was not Maurice Griffiths’s aim.
He set out to supply honest, seagoing small yachts that would be equally at home in the rough and tumble of a hostile North Sea as they were weaving between the withies and nosing their way into peaceful and shallow backwaters.
East Coast pottering is a specialised and delightful pastime that can only be enjoyed to the full in a shallow draught yacht that is capable of drying out – whether by mistake or on purpose.
Then along came Robert Tucker and his popular twin keel plywood pocket cruisers such as the Silhouette that took off in 1954. Around the same time, a French designer began to play with twin keels.
François Sergent designed the attractive 22ft Sargue with a beam of 7ft 5in; generous for that era and with reasonable accommodation. Several of this mahogany strip planked twin keeler (drawing 2ft 4in) were built, and they not only sat happily on the Breton mud – they sailed well.
The designer said: “In passage races in the St Malo-Granville area one won two firsts and a fourth in three starts against deep keel boats and centreboarders.” It’s a pity none of them made it over to our UK shores. With pleasing performance and Gallic grace, the Sargue class looked a cut above what was available over here at that time.
Mass-produced and affordable bilge keel GRP yachts only really began to fill up our foreshores after Denys Rayner set up Westerly Marine in the early 1960s. Enthused by the tractable sailing he had enjoyed in his earlier bilge keeled designs such as the jaunty little Westcoaster, he decided that the time was right to invest in a new GRP cruiser.
And so the Westerly 22 was born in 1963. The twin keels drew just 2ft 3in and gave a ballast ratio of 33.3% while a long central ‘keel’ supported the rudder and gave a secure ‘three-point landing’.
The Westerly 22 sailed adequately, sat happily on a drying mooring, and the 22 Young Tiger was seaworthy enough to make a transatlantic crossing in 1966. The longer coachroof of the later Westerly Nomad (1967) improved accommodation.
Following on from the 22’s success and Westerly’s bursting order book, Rayner pushed ahead with 25ft and 30ft models that used the same keel recipe. The burgeoning market for family cruisers was growing fast after the post war dinghy boom.
In a remarkably short time, Westerly sold almost 1,000 of these Rayner-designed yachts and the bilge keel revolution was well and truly on its way.
But even their greatest fans will admit that the sailing performance of these early models was unspectacular. Their modest draught meant that lateral resistance was minimal, so leeway when sailing to windward was considerable compared to that of a yacht with the extra bite given by deeper keels.
And the drag incurred by all that surface area on three shallow appendages cut speed through the water – especially in lighter airs. But the early Westerlys sold like hot cakes because they brought economical sailing, low cost drying moorings and carefree coastal cruising to thousands of sailors taking to the water ‘en famille’ for the first time.
As Westerly pushed remorselessly ahead, other players soon entered the twin keel market. Thames Marine set up on Canvey Island in Essex and, over many years, produced hundreds of Snapdragon cruisers. Like the early Westerlys, these boats were not – by any stretch of the imagination – racers.
While a few models offered a centreboard keel configuration, the majority were twin keelers. Accommodation was always spacious and later models had a pleasing look, thanks to their nicely proportioned coachroofs.
At the smaller end of the market, makes such as Leisures, Silhouettes, Hurleys, Tridents, Macwesters, Cobras and Alacrities – to name a few – offered twin keels as standard or as an option.
But nobody was yet putting that much thought into the designs of the keels themselves. Some builders even produced twin keels that were an integral part of the hull moulding, then filled the GRP keel cavity with iron punchings.
As a result, the keel had to be vertical (to release from the hull mould) – which is far from ideal from a performance perspective. Add a fibreglass moulding filled with iron, and it is a disaster waiting to happen if the boat dries out on rough or rocky ground.
Once the GRP keel base is worn down or punctured, saltwater can get in and rust the iron, whereupon the rest of the fibreglass keel ‘casing’ can get blown away from the rusting iron ballast inside.
The next real leap forward in twin keel design came courtesy of the originators of mass-produced GRP twin keel cruisers – our old friends Westerly again. As Denys Rayner’s health was fading, he enlisted the young David Sanders to take over the running of the company. Unlike Rayner, Sanders was no yacht designer. “Go to Laurent Giles,” advised Rayner.
He was aware of the bilge keel development work and tank testing that had been done by Jack Giles so reckoned design firm Laurent Giles was the most likely to take twin keel design to its next stage. It was wise advice.
When I asked Barry van Geffen (later the MD of the Laurent Giles design office) how the new generation twin keels as first used on the Centaur came into being, he said that Laurent Giles’s research and tank testing had been very revealing.
“What was learned had a significant impact on keel design, as it was discovered that through various angles of attack, heel and yaw, there was a marked change in efficiency (lift versus drag) with keels that were aligned exactly fore and aft on the hull.
The LG [Laurent Giles] team considered all the implications, along with Westerly’s insistence that for production reasons both port and starboard keel castings should come out of the same mould – and settled on a design with a 2° toe-in and veed keel base.”
Twin keel changes
So what does this tell us about Laurent Giles’s suggested changes in twin keel design? Firstly, Westerly’s insistence on symmetrical keel foils for ease of manufacture and economic considerations was fortuitous for other reasons.
Early twin keel designs were often asymmetrical – as originally advocated by the Lord Riverdale of Bluebird fame before he realised these were less effective than symmetrical keels. The theory was that the foil shape on the inside face of the leeward keel and flat shape on the outside face would generate lift (like an aeroplane’s wing) and therefore lift the boat up to windward.
Unfortunately, however, the reverse could apply to the windward keel. In addition, the water flow between the keels could produce a braking effect, thereby slowing the boat down. The effect is not unlike putting the brakes on by adopting a ‘snow plough’ stance when skiing down a mountain.
So Laurent Giles’s move to a modest 2° toe-in for maximum efficiency combined with symmetrical foils was the right way to go. The result was a marked improvement in windward performance over older bilge or twin keel yachts. And if they had gone for slightly more draught than 3ft, it would have been even better.
Westerly Griffon 22
But perhaps they continued to learn, because Centaur’s later and smaller sister – the 23ft Pageant – drew only 2in less (at 2ft 10in) despite being 3ft shorter overall. The Pageant sails well and even used to win club races in her early days. And when Ed Dubois came to design the Centaur’s successor – the 26ft Griffon – he went for 3in more draught than the Centaur and drew finer foils with less drag. So twin keel performance continued to improve.
But the early Griffon’s finer keels (with finer roots) also brought boatbuilders’ attention to the often-overlooked risks attached to bilge keels. Westerly fitted their symmetric twin keels by bolting them to small GRP ‘roots’ that formed part of the hull – rather like a GRP version of old fashioned ‘deadwood’. So the finer the keel, the finer this ‘deadwood’ stub also became.
As a result, it needed greater internal reinforcement to resist sideways movement. And the greatest ‘force’ imparted to twin keel roots – where they attach to the hull – is not necessarily encountered when the boat dries out on soft mud. It happens when the boat tries to break free from the firm grip of the mud as the tide returns and attempts to lift the hull clear of this grip. The deeper and more glutinous the mud, the harder it grips and the longer the boat’s natural buoyancy takes to lift it clear. And this is what caused damage to the early Griffon’s keel roots.
Westerly repaired the damage and reinforced subsequent models. But the lesson was there for every builder of twin keel boats to learn. It also explains why a buyer and his surveyor should inspect keel roots when assessing any possible second-hand purchase.
Hunter Horizon 26
So – to return to the request I put to David Thomas in the early 1980s for a world beating twin keel design. What did he come up with? Predictably perhaps, he took his time. We all reckoned he’d vanished into a mystical twin keel retreat. But the design that finally emerged was well worth the wait.
Thomas reckoned that the optimum angle of heel for comfortable cruising (as opposed to flat out racing) is around 15°. So he designed the keels to attach to the bilge with a 15° splay and to be slightly ‘toed in’. This way the leeward keel would be vertical when the boat was heeled 15° – thereby working at its maximum draught and presenting the biggest possible lateral area to reduce leeway.
Then he placed the keel roots as close to the centreline as was feasible while still making sure that the boat would be stable when dried out. The reasoning behind this was that the closer the keel roots are to the centreline, the less likely the windward keel is to break surface and ‘thump’ when the boat is heeled in a seaway.
The final ingredient to the new generation Thomas twin keel designs produced the most animated discussions with the builder. Any sensible designer wants as much draught as possible – to lower the centre of gravity, increase overall stability and maximise lateral resistance to reduce leeway.
The builder, however, wants to keep the draught low to increase the boat’s appeal from a marketing perspective. So a compromise always had to be negotiated, although Thomas usually won. As a result his twin keelers invariably drew more than the equivalent sized competitors’ boats.
And how did such twin keels actually perform? Extremely well. Having done initial trials on a Delta 25 hull, the Thomas keels were declared to be a success by boat testers and buyers alike. The time was ripe to introduce the first Thomas-designed spacious family cruiser that could sail well and stand on its own two feet.
The long-suffering Delta hull was dragged into the tooling shop again and given a brand new deck moulding for full standing headroom, an aft heads compartment and a spacious stern cabin. The new model was named the Horizon 26 and duly won the Best Production Yacht Award at the 1984 Southampton Boat Show.
We then walked into an unexpected marketing problem. Boat owners were so used to Thomas performance and handling that they could not believe that a twin keeler would be anywhere near as good. Some potential Hunter buyers even said that they “wouldn’t be seen dead in a bilge keel yacht”.
After a bit of head scratching a solution was found. Every demonstration boat for this and subsequent Thomas cruising Hunters had the twin keel option. Any client asking for a trial sail in a fin keel version would be politely told “I’m afraid we only have one demo boat for each model and it’s a twin keeler. So why not try that and if you aren’t impressed, we can always build you a fin keeler.”
It worked a treat. Initial scepticism invariably turned to disbelief followed by delight. Sometimes a client was taken on a trial sail without being told what sort of keel lurked beneath the waterline. When invited to have a guess after returning to the marina, it was amazing how often the client thought it had a fin rather than twin keels.
Bilge keel yacht design evolution
As the years passed by, Thomas’s twin keel designs continued to evolve and performance got even better. In one memorable demolition derby Round the Island Race, a Thomas-designed twin keel Horizon 32 took the heavy winds head on and won its class and its entire division.
The twin keel Horizon 21 and Horizon 30 also excelled in the CHS divisions. Recently a twin keel Horizon 232 helped her octogenarian owner Murdoch McGregor win the Yachtsman of the Year Award for sailing solo around Britain.
Meanwhile other designers began to tweak their twin keels. Ranges such as Moody, Sadler and Westerly also moved up a gear in performance. Thomas refined his twin keel designs by adding long hydrodynamically shaped bulbs to their bases. These had the effect of throwing the centre of gravity even lower and lengthening the ‘footprint’ on which the boats stood when they dried out.
The extra weight located in bulbs lower down also meant keel foils could become finer and narrower, reducing drag. Other boatbuilders have taken note, with ranges such as the American-designed but British-built Legends displaying prominent bulbs on their twin keels.
So, as marinas get ever more expensive, will more builders offer twin keels on their smaller models? Interestingly, the answer is ‘yes’. But it’s not coming from the UK. It’s coming from France.
French bilge keel yachts
In the past there were economical marina moorings aplenty available in France, so twin keels did not feature high on the French agenda. But now things are changing. The cost of a marina berth in France is still reasonable compared to the UK: but only if you can find one.
The French Nautical Federation reckons there is now a shortage of around 50,000 marina berths. As a result, twin keels (or bi-quilles as they’re called over there) began to appear in greater numbers.
Now, with the exception of the traditional and long running Biloup Range, French twin keels are expanding the design envelope. Archambault, the builders of the Surprise range, decided that their hugely successful One Design (7.65m) cruiser-racer would have an increased market if they also offered a two-legged version.
Designer Michel Joubert went for deep (1m) twin keels with narrow chord foils and race boat bulbs on their bases. The roots are well inboard and the performance is said to be exceptional.
RM-Fora Marine specialises in multi chine plywood-epoxy hulled cruisers, invariably with twin keels. The latest models, from the pen of leading French designer Marc Lombard, are anything but conventional.
Draught is generous (for example the twin keel RM890 draws 1.5m) with keels that are as fine as you’ll find on a top-level racer. And the bulbs on their bases are just as sophisticated.
These RMs are exciting and versatile boats, although I wonder whether their futuristic looks and multi chine wooden hull construction will find favour with many British buyers. I hope so, because the combination of a plywood-epoxy hull with a GRP deck offers excellent insulation and a substantial strength to weight ratio.
The Django 7.70 designed by Pierre Roland and built by Marée Haute in France has also proved to be a speedy twin keel 25-footer capable of crossing many oceans. Christophe Mora and Carina Juhhova are currently in South Africa after sailing L’Envol across the Pacific and Indian oceans. Their progress reports on intothewind.fr are fascinating.
So far Django 7.70 L’Envol has crossed the Atlantic, cruised down the East coast of South America to Patagonia, across the Pacific and sailed the Australian coastline before moving on to South Africa.
The Django range comprises the 6.70 (lifting keel only), the 7.70 (fin or twin keel), 9.80 (fin or twin keel) and 12.70 (fin or lifting keel). The twin keel Django 7.70 that I tested was a total delight.
The future of bilge keel yachts?
So what lies ahead? With only a handful of French yards offering new twin keel boats, there is a dearth of choice in the new boat market. Of course, sailors can always buy second-hand while they await new arrivals. But be sure to get those keel roots surveyed and check rudder and keel bases for grounding damage.
I can’t help thinking that as designers come up with ever improved twin keel designs, something will soon have to give. As British marina costs move beyond the means of many boat owners and French marinas reach maximum capacity, maybe there’s a new twin keel dawn just over the horizon?
Exciting new twin keel designs might even persuade production boat builders to market new boats under 30ft again? Some may even sprout foils and try to fly!
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This feature appeared in the April 2023 edition of Practical Boat Owner. For more articles like this, including DIY, money-saving advice, great boat projects, expert tips and ways to improve your boat’s performance, take out a magazine subscription to Britain’s best-selling boating magazine.
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