Flat sections are the price of performance
The first time I became aware that a big boat could slam like a dinghy, Dick Durham writes, was at the helm of a freshly-launched Beneteau Oceanis 423 in the summer of 2004. I had taken a bare boat charter from Skye to visit the Small Isles and the Outer Hebrides, off the West Coast of Scotland. After we left Canna the north-westerly wind fell light and so we started to motor and that’s when she started slamming, thumping the negligible seas with disturbing vibrations that echoed through the boat. It seemed unnatural and set up an anxiety in me that I might cause damage to a brand-new cruiser.
I later learned I wasn’t the only one worried about potential damage from slamming. In 2001, Groupe Finot Naval Architects and the School of Engineering Sciences, Ship Science of the University of Southampton carried out joint research into the ‘effects of slamming on offshore yachts.’
They fitted sensors on two Open 60 yachts which made delivery trips across the Atlantic and also on an Open 50 which made a solo crossing of the same ocean.
After extensive and complex analysis, the conclusions included: ‘Considerable bending and torsional vibrations are initiated by slamming.’
The point is that these flying wedges are racing boats and many argue that their design and construction should not be the dominating dimensions for a safe, comfortable, ocean, cruising yacht.
And yet for two decades or more this potentially dangerous hybrid has been the aspiration of production yacht manufacturers chasing speed and increased internal volumes.
Following the 1979 Fastnet Race disaster which left 15 yachtsmen dead, 75 yachts capsized and five sunk, improvements to design safety were made, but did they go far enough?
In 2004, marking the 25th anniversary of that disaster, naval architect Rob Doyle, of the Ron Holland design office in Cork, told the Irish Times that in spite of a broad sweep of improvements being made in terms of harness and hatch design, better hull shapes and stronger deck gear, the possibility of another disaster remained, largely because of a return to the dangerous obsession in some quarters of putting performance ahead of stability.
In March this year, Rob told Kraken News: ‘The trouble is these days it’s the boat show that’s the bottom line…no-one critiques boats anymore, you never hear of a bad boat. It’s because the manufacturers are going to sponsor something or pay for an advert…the industry’s too fluffy. People are being told they can sail a 56 -footer solo across the Atlantic, yet there are some boats out there now which should have never even been launched.’
He said there was too much faith put into digital calculus: ‘The computer says “Yes” which produces a copy and paste industry where one boat is simply scaled up to produce another. Now they are wider, fatter hulls with greater freeboard because they’re all looking for that voluminous interior and because of wide, shallow cockpits, all the crew are “on top” and not inside the security of the cockpit. It’s no longer build me a boat that protects me, instead interior fashion is dictating naval architecture.’
His design company will put a year’s research into a superyacht before even any line drawings are produced, but on smaller boats: ‘Nobody wants to spend that amount of time, they want you to dust off the plans of some floating caravan and who cares as long as the royalties keep coming in?’
Even the Recreational Craft Directive (RCD) a regulatory board with good intentions, has been ‘exploited,’ with boats creeping over the threshold of Category A by ticking various regulatory boxes, Rob added. It has seen today’s market swamped with yachts that are being sold as cruisers but with hull and cockpit designs developed from racing yachts, which has now left the unsuspecting boat buyer with nowhere else to go.
Several new boat testers I have worked with over the years have told me stories about bulkhead doors and locker drawers jamming after the craft, under test, had gone through some slamming upwind.
Many of the household names in seaworthy, offshore boats, have or are switching from traditional integral keel/skeg-protected rudder, long-deadrise and curved stem, to bolt-on keels, spade rudders, flat, wetted surface ‘planing’ sections and plumb bows.
In the light of this you have to ask is there a potential for GRP strength to deteriorate due to the glass matrix breaking down or losing strength if micro cracking of the fibres is caused by flexing from the continuous slamming that some hull forms suffer from when going upwind?
I asked naval architect, David Cannell, a Fellow of the Yacht Designers and Surveyors Association (YDSA), the following question:
‘It would seem that micro-cracking will be inevitable if a lightly laid up hull section flexes when slamming. I know some production yachts twist and vibrate when pushed hard to weather and I wonder whether structural damage occurs to some extent or other with slamming so violent that the whole yacht shakes and shudders?’
He replied: ‘In reply to the points made by you, yes, I agree, the modern hull form is far more prone to slamming, particularly when motoring upwind. GRP failure occurs when the fibres start losing their hold in the resin. Perhaps it is fortunate that most yachts are lightly used, otherwise the number of reported failures would be very much greater.’
I shared a berth with Atlantic sailor, author, and formerly cruising editor of the U.S. Sail magazine, Charlie Doane, during his visit to the Thames Estuary some years back and part of the debate we had appeared in his well-received cruising guide, The Modern Cruising Sailboat.
In the 2010-published book Charlie discusses the pros and cons of basic section shapes in traditional and modern hull build.
In so doing Charlie puts his finger on the pulse of the modern designer:
‘One great advantage of a low-deadrise hull is that a flatter bottom helps a boat get on top of the water and plane if the boat is light enough and conditions are favourable. This and the fact that they are generally easier and cheaper to build is why low-deadrise hulls are the most common type today.’
Chairman of Kraken Yachts, Dick Beaumont, said: ‘It is for this exact reason I had my own yacht designed and built. The last thing I want to face is going on the plane in a tropical storm…not to mention the danger of broaching and knock-down that such a hull presents.
Who would choose to be out there in a performance dayboat?!’
Charlie then describes the downside: ‘Another characteristic of a flat-bottomed boat with low deadrise is that its hull slams against the water with great force when sailing to windward in choppy water. In rough conditions this creates an uncomfortable, abrupt, jarring motion. It also makes an awful racket that is unnerving. Pounding to windward in severe weather aboard boats like this I have often wondered how it is their hulls are not smashed into pieces. A hull with more deadrise and more wedge-shaped sections slams much less in heavy windward going and is more comfortable.’
Another major disadvantage of such hulls is that it is virtually impossible to heave-to in them. Heaving-to, when the headsail (s) are backed with the helm held to leeward, in order to ‘stop’ the boat at sea, is a useful cruising practice allowing crews to attend to urgent matters, to allow a boat to jog offshore awaiting daylight before entering a strange port, or simply to take a rest from the rigours of heavy weather sailing (see below, Heaving-To).
Jib backed, main eased, rudder tries to turn the boat into the wind.
So much for the flatter sectioned hull, but what of the plumb bow, now almost the first choice of modern yacht design?
The late naval architect and yacht designer, Maurice Griffiths held a firm view.
The former editor of Yachting Monthly, whose biography, The Magician of the Swatchways, I penned, wrote in his seminal work, Post-War Yachting, first published as long ago as 1945:
‘The old-time yacht with straight, plumb stem used to plunge deeply, for there was so little lift in her bow to check the plunge. “Pile-driving” or “dropping into the same hole twice” was a favourite expression to describe this depressing trait.’ Now plumb bows are back in vogue again.
Conclusion:
As far as hull design and build construction is concerned there are five characteristics that must be avoided for safe and comfortable passage making:
- A plumb bow which although faster has low lift. A raked stem is always preferable (see Fig.1).
- A round or flat profile in the dead rise area of the hull forward of the keel, will always cause slamming. A shallow V- section profile will reduce or eliminate slamming (see Fig.2).
- A wide ‘Delta’ -shaped transom will induce the yacht to plane down the front of a wave. This is a stress factor to be avoided at all costs for short hand crews (see Fig.3).
- A narrow short cord length, high-aspect keel, induces an exaggerated ‘bouncy’ pitching motion. This is a see-saw action created in a seaway because the ballast weight is poorly distributed along the hull. A long keel cord will distribute the ballast weight much more evenly and it will also promote good directional stability too, so the crew or the autopilot doesn’t need to make continual steering corrections to keep on course (see Fig.4).
- A light hull and deck structured does not have the impact or puncture strength suitable for world cruising. Instead of the commonly found 5mm or 6 mm hull lay-up, offshore sailors should be looking for a hull lay up of 12-16 mm for 50ft yachts and over.
“Until 25-30 years ago, yachts adhered to the safe and seaworthy design principals that have been learned since sailors first set sail. The sea hasn’t changed.” Dick Beaumont
Ocean sailor refuses to go offshore in a production boat.
A top ocean sailor has vowed never to sail offshore again in a production boat again after facing a severe gale in a Jeanneau 47.
Mawgan Grace, 45, a former RAF pilot, spoke out as boats were preparing for the 58th Rolex China Sea Race which sets off from Hong Kong this month (April).
Mawgan, who trains pilots for Cathay Pacific airlines, sailed in the 2018 edition of the race told Kraken News: ‘We were under storm jib and the slamming was horrendous….all the cupboards burst open. I shook so much I lost a filling. We kept looking at the life-raft and I thought if I survive, I will never go offshore in a production boat again.’
Mawgan, who grew up in Cornwall, England, but who now lives in Hong Kong, owns a 2001 built Amel Super Maramu 53, Adela, which he swears by as she has an integral keel and skeg-protected rudder. He rues the design changes the modern Amels have undergone.
‘They have modernised the design of the boats and frankly it is not to the true blue water sailor’s taste. Now they are like floating blocks of flats. The ketch rig has gone and instead been replaced with a standard sloop rig and the skeg-protected rudders are now twin spades, Henri Amel would spin in his grave I’m sure’ said Mawgan, who, when he isn’t sailing or flying, has raised more than £5,000 for conservation projects in Africa, by running a marathon in Kenya and climbing Mount Kilimanjaro in Tanzania.
Up to 498 Amels of Mawgan’s type were made before they were phased out and replaced by their current Delta shape designs
‘I was told during a visit to the Amel yard that a good boat is a boat that sells, but I think manufacturers are compromising too much in an effort to sell more and more boats…. perhaps marketing is based on the fact that so few people actually go offshore,’ he added.
The loss, without trace, of the brand new Beneteau Oceanis 60, Europa, just three years before Mawgan’s race experience, underlined his mistrust of production boats. ‘She was owned by the experienced offshore sailor and yacht broker Robin Wyatt who I knew of,’ said Mawgan, ‘she was on passage to Subic Bay from Hong Kong with Robin and four crew, hit a typhoon and was never seen again. ‘The thing is when a boat like that broaches the lateral load on a bolt-on keel can cause it to fail,’ he added.
