Boat hull design: how it impacts performance

The search for the ideal family cruiser can be a complicated business at the best of times, especially if you’re looking for a new yacht less than 30ft long.

Gone are the days when Jaguar 27s, Maxi 84s and Mirage 28s were widely used by charter companies and private buyers alike.

These days, sailors hunting for smaller cruisers have little choice but to browse classified ads and brokerage lists.

Many conflicting factors are needed to achieve that most elusive of goals – the best compromise between seagoing performance in a full range of weather conditions and maximum living space when in port.

I say ‘in port’ because maximum accommodation space when at sea is less relevant.

If you are not in the cockpit and sailing, you could be down below cooking (as securely as possible), eating (spilling as little as possible), in the heads (as briefly as possible), navigating (as accurately as possible) or sleeping (as comfortably as possible).

The size of the areas used for these tasks is often seen as insignificant compared to how effectively each task can be performed.

Then there’s the small matter of weight.

New boats with heavier displacements for their size are rarely seen at boat shows these days for one simple reason: they cost more to build.

But that doesn’t mean they are ‘out of date’. Far from it, because the cruising sailor – whether she or he is looking for massive or moderate amounts of accommodation below – will find a heavier displacement boat with a lower centre of gravity more forgiving and less twitchy to sail than a lighter boat with a voluminous interior.

Boat hull design: waterline length grows

One notable change to boat hull design has been gaining ground recently and becoming widespread.

Like many design evolutions, it traces its origins back to the racing world.

There is a saying that ‘racing improves the breed’ and this can be true even in the world of cruising yacht designs.

This trend relates to overall and waterline length. In the past, waterline length was invariably far shorter than overall length.

Elegant bow and stern overhangs were the visible evidence.

The reason was that a yacht’s Royal Ocean Racing Club (RORC) and later International Offshore Rule (IOR) handicaps were partly based on its static waterline length.

As later racing handicap rules put less emphasis on static waterline length, racing boat designs developed increasingly ‘upright’ stems and transoms.

As a result, the waterline length often becomes similar to overall length and thus makes an important contribution to hull speed.

Cruising boats have been quick to follow this fashion, and some modern cruisers (such as the latest Dufour 32 and 34) now have race boat style near-vertical stems and sterns.

But the cruising yacht derives an extra advantage from this development in addition to increasing its speed potential.

By increasing waterline length in relation to overall length, the designer wins extra space below.

This can be put to good use by making the forepeak a bit longer and taking the bunks further forward.

So as well as going faster for its overall length, the new generation ‘long waterline’ cruisers can pack in more accommodation.

I believe that many future cruising designs will move closer to vertical stems.

Accommodation at a premium

It’ll be fascinating to see how yacht design evolves over the next 10 years.

The big builders will be looking for opportunities to upgrade their products – if only to increase their ability to compete with ever-expanding fleets of sound second-hand yachts.

To see how far this trend has progressed over past decades, you only need to compare the shape of, say, a Rival 32 or Contessa 32 with their modern equivalents.

The Rival achieves its headroom because the hull is deep, while the freeboard remains moderate and the coachroof is low and sleek.

The modern equivalent, on the other hand, has a shallower hull with higher freeboard and coachroof to achieve similar headroom.

As a result, the Rival has more boat under the water, while its modern equivalent has more sticking up above it, putting the centre of gravity higher and increasing windage.

As Scotty said to Kirk on Starship Enterprise: “You cann’ae defy the laws of physics, Jim.”

Then compare the maximum beam. A Contessa 32 (9ft 6in/2.9m) has enough to accommodate settee berths and a table in the saloon, with sufficient cabin sole width to move around the boat.

The heads compartment is located between the saloon and forecabin and has sufficient space for ‘the necessaries’.

The modern cruiser, on the other hand, has a greater beam to length ratio, so the cabin sole is wider.

The enlarged heads area needs more space so it moves aft to where the beam is wider.

It’s more spacious… but does it work any better when the boat is bouncing around in a lively seaway, rather than sitting motionless in harbour?

And what about those large aft cabins? They are luxurious in harbour, but perhaps not so user friendly when a tired crewmember is grabbing a bit of shut eye on a cross-Channel beat.

There’s a lot of space to roll around in – compared to being held snug and secure in a narrower quarter berth.

Performance in wind

But the real difference between the moderate beam and lower freeboard of an older style design and the wide beam, wide stern and high freeboard of some contemporary designs becomes most apparent when sailing – especially when the wind is strong.

To keep the crew happy and the boat ‘on track’, you need to be more alert when assessing sail area, trimming sheets and steering the boat.

Why should this be?

We’ve all occasionally seen a boat with a wide beam and stern suddenly round up in a stiff breeze.

While the skipper struggles to apply more helm, the rudder aerates then loses its grip.

A wide, shallow-hulled boat with a broad stern is more prone to such gyrations because the immersed shape of the hull changes dramatically as the boat heels.

The older-style boat with balanced ends and a deeper, heavier displacement hull retains a similarly balanced immersed shape even at considerable angles of heel.

The ultimate example of this was the ‘metacentric’ hull championed by the great Robert Clark – whose famous designs included Sir Francis Chichester’s Gipsy Moth III (winner of the first solo Transatlantic Race) and Sir Chay Blyth’s British Steel (the first yacht to girdle the globe sailed single-handed and in the wrong direction).

To see how ‘balanced’ hull lines look when the boat is heeled, select a suitable yacht laid up ashore, stand facing her bow (and then stern) and lean your head to one side.

You’ll soon see the differences if you repeat this exercise on a modern broad sterned boat.

And what happens to the wide-bodied, broad-sterned hull when it heels? Why does this encourage loss of directional stability?

It’s down to immersed shape. As soon as the hull heels, the enormous buoyancy in the wide aft sections (which increases when heeled) lifts the stern as the immersed shape changes.

So it begins to lift the rudder out of the water (unless the yacht has twin rudders).

Adapting sailing techniques

Given that the majority of sailing families and charter companies still prefer the space and comfort offered by high freeboard, wide beam and broad sterns, how does one avoid the broaching scenario?

It boils down to appreciating the attributes of such hull shapes and sailing them accordingly.

The most obvious way to stop the change in the immersed hull shape as the boat heels too far is to stop this happening in the first place by sailing the boat flatter.

Just because the skipper sailing a nearby ‘balanced ends’ design is lounging on the leeward side of the cockpit with the tiller loosely held between finger and thumb as the boat’s deck dips elegantly towards the sea in the gusts with the wake stretched out behind, don’t think you should (or could) be doing the same.

Just tuck in a reef or roll in a bit of headsail – or both.

Most modern hulls sail straight at around 15° of heel. But let the boat lean much further and you risk getting into broach territory.

Besides which, if you sail her flatter, she will sail quicker. As an added bonus, you won’t alarm the children or spill the gin!

As wide boats encounter strong winds (especially when sailing upwind), correct mast rake and flattened sails also help directional stability.

If you have too much aft mast rake, this will increase weather helm, which aggravates the situation.

The same applies to full sails.

A Cunningham or flattener takes ‘the belly’ out of a mainsail and moves its draught forward.

Also check that the jib sheet cars are not too far forward, reducing ‘twist’ at the head of the foresail, thereby increasing its power.

Continues below…

Above all, don’t over-sheet the mainsail. If a powerful gust still succeeds in catching the skipper off guard, the first port of call is the mainsheet.

If you have a traveller, drop this down to the end of its track. If not, you may need to ‘dump’ the mainsheet – having first warned the crew and made sure there are no heads in the way.

Boats with short mainsheet tracks located on the roof in front of the main hatch are also tricky because the fall of the sheet is beyond the helm’s reach.

In this case, the crew needs to know what to do and when. Anticipation is essential for nipping a broach in the bud.

Motor-sailing is another area where owners of wide-sterned yachts need to be careful.

If you are confronted by a long beat in strong winds, your yacht will point higher and sail faster (with sail reduced) with the engine running at low revs. But if you let a broad sterned boat heel too much, the prop gets too close to the surface as the stern is levered out of the water.

As a result, the engine can ‘race’ – which is not good for it.

Excessive heel when motor-sailing is also not a good idea because the engine’s oil can cease to circulate properly.

The best of both worlds

What type of hull shape does give the best compromise between ‘balanced performance’ and maximum accommodation – and between light and heavier displacement?

As in many walks of life, the old adage of ‘moderation in all things’ gives the best clue.

Very low freeboard can mean a wetter ride, while high freeboard can add to windage and lift the centre of gravity.

An excessively narrow stern can induce rolling when sailing down-wind in a blow, while a fat stern can encourage broaching up-wind in heavy gusts.

Narrow overall beam reduces initial stability and space below, while excessive beam means you need to sail the boat flatter.

As ever, a sensible compromise can be the answer.

Which brings us on to more mundane developments in hull detail and deck design.

I expect the trend towards setting fixed windows into cruising yachts’ topsides to develop further.

As designers find neat ways to engineer this and builders source stronger adhesives and ‘glazing’, hull windows will get bigger and more numerous.

It’s nice to be able to sit in the saloon and still see out.

There are also a few changes to yacht design being brought about by global warming phenomena and our desire to save energy.

Some builders now incorporate substantial structures to support a bimini over the cockpit.

As these develop more, they can also carry solar panels, a wind generator, a radar dome and the transmitters and aerials for electronic gizmos.

These structures can fulfil many useful functions. If summers become hotter and sunnier, a bimini could become as useful in the Channel as it is in the Med.

The cockpit itself will also get more use as a social and dining area, so the current trend towards well designed fixed cockpit tables could develop further.

An Oceanis 48 model we chartered even had a light socket beside the cockpit table so an outside lamp could be plugged in for al fresco dining at anchor after dark.

Sail wardrobe

This leads us to deck layouts and sail handling systems.

To start at the bow, most sailors now take roller headsail systems for granted.

But more builders are following the example of firms such as Hanse by offering self-tacking jibs as standard.

True, there is an extra cost element; especially if the owner also buys a full-sized Code 0 headsail for reaching or beating in light winds.

But the ability to sail closer to the wind – thanks to the close sheeting angle – and to tack without touching a sheet makes a pleasant change.

A fractional rig with a larger mainsail and smaller headsail also has many advantages.

And when someone comes up with an economical ‘in boom’ mainsail reefing system operable from the cockpit, you have a low-effort-high-efficiency sail plan.

‘In mast’ mainsail reefing puts extra weight where you don’t want it (up in the air), necessitates an inefficiently shaped mainsail (without horizontal battens) and is a nightmare if it decides to jam when the sail has been partially rolled.

And what about the rig itself?

Most production cruisers have aluminium masts held aloft by stainless steel standing rigging.

The racing fraternity, however, is beginning to choose carbon fibre masts.

As a result, huge amounts of weight are saved aloft.

The more weight you put up in the air, the more ballast you need to plant under the boat to counteract it.

Carbon spars currently cost considerably more than extruded aluminium tubes. But things can change.

I see a day when the cruising yacht can increase its stability and reduce its tendency to pitch by cutting down on weight aloft.

Such rigs may start as pricey extras – but some owners might happily pay the premium. And what might disappear?

Perhaps it’s time for yachtsmen to go ‘cold turkey’ on teak and help save a few rain forests?

It’s already happening in yacht interiors where builders offer veneers in light oak, cherry and other lighter woods as an alternative to teak.

Some of these finishes look very elegant. Teak decks also consume many venerable trees.

Do we really need to slap hundreds of kilos of teak and Sikaflex onto decks when there are effective lookalike equivalents such as Flexiteek, Tek-Dek, Esthec and Permateek?

Boat hull design and its impact on speed

When it comes to hull shape, a boat of moderate displacement will be steadier and better mannered – even after squeezing in stern cabins with double beds!

After One Tonners stormed the sailing scene and opened the door for GRP fast cruiser spin-offs, other Ton Cup rating bands soon followed suit.

These high-profile international Ton Cup regattas gave designers and builders massive PR exposure.

Ton Cuppers of various sizes became hot development projects and those who headed the field were quick to cash in, offering de-tuned versions to the fast-growing cruiser-racer market.

Following the One Tonner, the next size down was the Three Quarter Tonner.

Typically around 33-34ft (10-10.4m) long, this Ton Cupper makes a very popular size of fast cruiser that is quick and powerful enough to cover distance at speed, yet compact enough to be handled by a small crew.

Little wonder that as Three Quarter Ton designs evolved between the 1970s and early 1990s, they became the inspiration for many top selling production fast cruisers.

Unlike the One Tonners before them, Three Quarter Tonners came on stream after the old RORC rule had given way to the new IOR and the later Channel Handicap System (CHS) regime introduced in 1983.

So long keels with attached rudders, deep-bilged ‘wine glass’ hull sections, relatively narrow beam and heavy displacement hulls no longer held sway.

The world of performance sailing had moved on to fin and skeg or spade rudder configurations, flatter bilged hulls, broader beam and pinched ends (later replaced by wider sterns).

The Three Quarter Ton field proved to be a fertile ground for a new generation of designers who challenged the established greats such as Olin Stephens, CA Nicholson, Alan Buchanan and Kim Holman.

These youngsters – including Dick Carter, Doug Peterson, Ron Holland and Bruce Farr – must have rubbed their hands with glee.

In 1975, for example, the winning Half Tonner, Three Quarter Tonner, One Tonner and Two Tonner were all designed by Doug Peterson.

Everything changed once rudders became blades under the transom and keels became separate ‘bolt on’ foils with lift-inducing National Advisory Committee for Aeronautics (NACA) sections.

It’s reckoned that the closest to the wind a competent long keel cruiser of 20th century vintage could sail was around 45°.

Yet later, fin keel cruiser-racers could get to around 40°.

Closer sheeting angles and better cut sails contributed to this improvement, but much of the sharpened performance was down to underwater foils that induced lift and reduced leeway.

Boat hull design: a new generation

One of the first ‘new wave’ designers to come up with a GRP production yacht of Three Quarter Ton size was Dick Carter.

He had already excelled in the late One Ton era with the Tina design and was approached by Olympic Yachts to come up with an ‘IOR-friendly’ 33-footer.

The Carter 33 (not to be confused with the more extreme Carter ¾ Ton) hit the scene in 1974 and was an instant success as Olympic Yachts set up dealerships far and wide.

The Carter 33 is a handsome yacht with a sleek, long coachroof. Her cockpit is on the small side but is extremely secure and ideal for long distance cruising.

With an LWL of 25ft 8in/7.8m, a reasonable beam of 11ft/3.35m and higher freeboard than a pre-IOR yacht of similar size, the Carter 33 offers excellent accommodation space for a yacht of that era.

It’s easy to see why it’s still sought after by discerning sailors looking for plenty of performance at a budget price.

But the new generation overseas designers did not have it all their own way.

One successful British designer who’d excelled in the RORC days and made a seamless transition to the new IOR/CHS eras was Kim Holman.

His UFO 34 Three Quarter Ton-inspired design became a popular performance cruiser and retains this reputation to this day.

With a waterlength of 28ft 1in/8.56m and a beam of 11ft/3.35m, the UFO 34 offers good-sized accommodation.

Her ballast of 5,510lb/2,500kg out of an all-up weight of 10,214lb/4,633kg – allied to a 5ft 6in/1.68m draught – makes her a stiff and powerful yacht.

Many UFOs were finished by different builders from mouldings supplied by Colvic Craft, so interior finish and detail varies.

A Landamores-finished example is often the best.

Having made his name in the 1970s, it’s not surprising that another early Three Quarter Ton cruiser-racer to hit the sweet spot was the Contention 33, designed by Doug Peterson.

Following his victory in the 1975 Three Quarter Ton Cup with Solent Saracen, British builders Southern Ocean Shipyard approached Peterson for a GRP production development.

The Contention 33 (launched in 1976) is a fine-looking yacht and sold well.

At 32ft 8in/9.95m overall, she has a waterline length of 28ft 6in/8.68m and beam of 10ft 4in/3.14m which made the Contessa 32’s 9ft 6in/2.89m beam seem skinny.

The Contention 33’s weight of 9,300lb/4,218kg (ballast 4,233lb/1,920kg) is close to the Contessa 32’s 9,480lb/4,300kg (ballast 4492lb/2038kg).

Yet, in common with many racer-derived designs, the Contention has a generous amount of freeboard, wider beam and it’s easy to see how this generation of yacht offers good internal space.

Like the Contessa, she has a narrow stern which makes her great for slicing upwind, but likely to induce scary moments if pushed hard downwind under spinnaker.

The next generation of wider-sterned yachts (that could also accommodate stern cabins) had not quite arrived.

Creating a classic

Ron Holland was another rising star of the IOR era.

He’d already designed Ton Cup winners of various sizes when he was approached to design a Three Quarter Ton based GRP cruiser racer.

But what was more interesting about Holland’s commission was that it came from the longest standing and most revered name in British yacht building: Camper & Nicholsons.

Holland designed a great yacht – the Nicholson 33.

Her dimensions and ‘look’ were similar to Peterson’s Contention 33, while interior finish – especially on the cruising versions – was pure Nicholson; classy, elegant yet functional.

And the prototype of the tweaked racing version, called Golden Delicious, carried off the overall winner’s trophy in the 1975 Fastnet Race.

If you fancy a 33-footer with a fine pedigree but at not too fancy a price, a Nicholson 33 is well worth a look.

The Nicholson 345 that followed in 1979 also has much to offer.

Camper & Nicholsons asked Holland for a ‘bigger sister’ and the 345 put even more emphasis on combining Nicholson quality and finish with genuine performance.

The 345 is 34ft 6in/10.51m long with a waterline of 29ft 6in/8.99m.

Her beam of 11ft/3.35m and displacement of 11,500lb/5,216kg ensures ample internal volume and a more stylised coachroof design gives plenty of light below.

As a bonus, well sailed examples still do well on today’s handicap systems.

Her Three Quarter Ton genes shine through; she’s a quick yet civilised yacht. Cees van Tongeren from the van de Stadt design office designed the Dehler db1 and db2 racer-cruisers which won trophies galore, but these high-tech and stripped out flyers didn’t appeal to cruising families.

However, the Dehler Optima 101 and Dehler 34 – which share the same db1 hull – fit the fast cruiser bill superbly.

They sold in huge quantities throughout Europe.

What’s interesting about the sleek Dehler 34 is that its ‘donor hull’ had enough beam aft to make room for a stern cabin; unlike many other Three Quarter Ton derived hulls.

Owners could enjoy genuine performance combined with the newly popular ‘aft cabin and heads’ layout.

And most agree that the Dehler 34 has elegant looks.

It’s the epitome of the handsome racer-derived fast cruiser. It has stability (3,748lb/1,700kg ballast and an all-up weight of 8,818lb/4,000kg) and boasts decent width side decks and a well-proportioned foredeck.

If ever a boat proves that racing improves the breed, the Dehler 34 does.

Evolving design

Three 34/35ft Three Quarter Ton-inspired Beneteau cruisers, designed by the same team for the same builder over a span of nine years, dominated the market; the Berret-Racoupeau-designed First 35 (1980), First 345 (1985) and First 35.5 (1989).

These three Firsts evolved from Oesophage Boogie, a top Three Quarter Tonner designed by Berret.

The LWL grew slightly in proportion to overall length, maximum beam actually reduced a smidge, sterns got fuller, bows became more upright and the ballast ratio came down slightly.

The 35 and 34.5 keels are a typical IOR shape, while the 35.5 grew winglets at the base of its shallower draught options and its deepest fin had the latest ‘mickey mouse ear’ profile.

But the real differences came in styling and interior layouts.

The First 35 (1980) has a relatively narrow stern so although it squeezes in a couple of wide quarter berths either side, these hardly constitute genuine doubles.

The galley and navigation stations are aft in the saloon, which features settee berths and a pilot berth to port.

There’s a traditional, spacious heads/washroom compartment forward of the saloon and a relatively small forepeak for sail stowage and occasional berths.

It’s a practical seagoing layout.

The 1985 First 345 is slightly wider at the stern, allowing space for an aft double cabin and aft heads; or twin aft cabins with the heads moving to ahead of the main bulkhead.

As a result, the forecabin becomes pokier than the much more spacious alternative on the aft heads version.

I’d go for the single aft cabin version; especially if sailing with a smallish crew.

From an aesthetic point of view, the 345 is a great success.

It showed how competitive race boats could morph into desirable fast cruisers.

Proving its popularity, as was the case with the earlier 35, over 450 First 345s were built.

Then came the 1989 First 35s5, and it showed how fashions had changed.

Not only does the hull profile look very different, with higher topsides, more upright stem, steeply sloping transom and futuristic ‘wrap-over’ windows, the accommodation is given bold styling by Philippe Starck.

Dark mahogany and polished metal features make this yacht’s interior very different. People love it or loathe it.

Extra volume aft makes the stern cabin(s) more spacious. The sail boat rig also evolved.

At long last the small mainsail/large genoa format was replaced by a fractional rig with a bigger main and smaller headsail.

The easily handled fractional rig had finally made a comeback.

This followed other later generation Three Quarter Ton inspired cruiser-racers such as the Dehler 34.

Designers had realised that the fractional rig worked fine within the IOR, CHS and IRC formats and this development filtered through into the production cruiser-racers.

---

Enjoyed reading Boat hull design: how it impacts performance?

A subscription to Practical Boat Owner magazine costs around 40% less than the cover price.

Print and digital editions are available through Magazines Direct – where you can also find the latest deals.

PBO is packed with information to help you get the most from boat ownership – whether sail or power.

• • • • Take your DIY skills to the next level with trusted advice on boat maintenance and repairs
      • Impartial in-depth gear reviews
      • Practical cruising tips for making the most of your time afloat

Follow us on Facebook, Instagram and Twitter