Hull Shape for Down-Wind Sailing

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JimC

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Most modern cruisers have their maximum beam well aft of amidships and have broad transoms. This is claimed to give good performance off the wind. However with so much reserve buoyancy in the stern, steep following or quartering seas kick the stern up sharply pitching the boat nose-down and contributing to wild steering and fear of broaching.

I should have thought that a hull with more balanced ends would be steadier downwind, something like the Contessa or Sadler 32s which have small transoms lifted well clear of the water, or ultimately a double-ender. A large proportion of boats renowned for their seaworthiness seem to have been double-enders ( Deal luggers, whaleboats, RNLI lifeboats of former days etc.), yet the modern yacht is at the opposite extreme.

Anybody got any thoughts on this ?

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Well, that's what we all used to think, before the marketing men got into the act and told us we were all wrong. My own limited experience of these modern dinghy type shapes tells me that it is absolutely vital to get weight aft when running in a sea; this is not something that I like much.

<hr width=100% size=1>Que scais-je?
 
2¢ worth

If the boat and the crew are strong enough to keep up the drive downwind, there's no doubt that the flat bottom/broad transom hull shape is the way to go for downwind speed. It certainly promotes planing which is when, on any affordably sized boat, you begin to see double figure speeds. That shape works well off wind - witness the current breed of 'open' long distance racers where their weather routers try to pick courses that keep them reaching or running rather than beating. There is a trade-off with upwind performance, at least there is until someone works out how to get a keel boat planing upwind.

For a trad shaped hull, downwind sailing in a blow can be a very rock'n'roll experience, and a lot slower. On the S&S 41 footer (1970 design date) I used to race aboard - which was a very reassuring boat to take upwind (one Solent race we had 45kts apparent minimum, gusts to 65 kts, and no probs except salt-impaired vision) - steep downwind angles in a seaway used to induce incremental rolling, and unless the trimmers worked very hard to keep depowering and repowering the kite, a broach would inevitably occur, usually after the third successive roll. In steep seas and big winds we would always sail broad reach-gybe-broad reach rather than anything approaching a dead run. Meanwhile, more modern designs would sail closer to the rhumb line and plane past.

My view on what a modern well mannered cruiser needs is a bit less beam than todays AWBs, but still carried well aft, a deeper forefoot with more of a curve, less of a knuckle where the stem transitions into the bottom, and more avoirdupois in the keel to keep the boat on its feet when going upwind, so that it's not levering its rudder out of the water and broaching.

Which is what, I suspect, Hunter has achieved with its Stephen Jones designed Mystery.

<hr width=100% size=1><A target="_blank" HREF=http://www.writeforweb.com/twister1>Let's Twist Again</A>
 
Re: 2¢ worth

The famous S&S downwind rock'n'roll! Remember it well in a Swan 47 which otherwise sailed like a dream.

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I'm uneasy about a double-ended (canoe) stern which might be prone to pooping. Some aft buoyance is desirable, but not enough to encourage broaching.

Ken's right the choice is between a fast, light semi-planing hull which will tend to surf rather than broach, versus a traditional all-round steady tracking heavyweight. The latter is still more suitable for short handed cruising in a small to average length yacht, IMHO. But the rolling in open ocean swells - that takes some getting used to.



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Re: €0.02 worth ( = $ +23%)

All depends on the circumstances. A downhill boat may suddenly have to turn round in eg a MOB situation. Or when the going gets too heavy to continue downwind. The Fastnet enquiry showed that the best all round type of boat was something like a Contessa with balanced ends and quite a heavy ballast ratio. ie if capsized it will come back up quickly.

Adlard Coles criticized the double ender concept when the stern was relatively narrow - like on his Tumlaren. There was not enough reserve buoyancy to lift to the waves and he kept getting pooped. A Colin Archer on the other hand has a pretty blunt point at the end which allows aft buoyancy plus a means of splitting the wave. I believe a very seaworthy design would be something like the Hans Christian family of boats. IMHO.

John

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G'day JimC,

The Holland 30 has a small and high transom and can be a pig to control downwind, makes the narrow ends theory look a bit sick.

<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.
 
Th most obvious is never easy (Konkordski)

Actually its a combination of Bruce Farr flat iron ends coupled with dynamic front end winglets .... but why ????

Cruising is cruising and cruising is cruising in comfort. Cruising is taking it as it comes in comfort .... and I don't know of any average production AWB that has cruising in mind.

It's all circles. It's all marketting guru led circles where the marketeers don't know a doughnut from a bit .... AND, we're all getting suckered down the Saatchi & Saatchi path .... Have you seen their latest perfume TV advert where they know more about how to untail a self tailing winch ..... ????



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Re:Steadiness or speed

The fastest racer I've seen off the wind is a thing called "Slam Full Tilt" it looks like a great big Merlin Rocket and was the fastest thing round the Solent cans. It didn't win much though as the rules and ratings kicked it senseless.

Anything with a hint of IOR about it gives you much more roll than rock. The boom end to pole end rolling had to be seen to be believed on many such yachts.

If you want a good balance of upwind groove and downwind control I commend much of the work of Mr Farr. Modern but controlable boats seem to skip out of his office.

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OldSalt

Can only concur - my Jeanneau Rush is a Ron Holland. Downwind at any great speed and I'm fighting like hell for control. It can get very tiring after a short while. Getting as much twist out of the main only limits the action - but you get used to rolling from one beam end t'other

Regards

Donald

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Re: 2¢ worth

when i first saw the mystery, i said to myself that he'd copied my hull shape (Tradewind 35) ... that is if i've got the right boat.

they do go downwind, though, rather well but much better just not dead downwind.

the fundamental objection to AWBs and one that would make me never buy one is the impossibility of getting a decent sleep in the stern compartments. the constant slap of little waves breaking on the underside of the sugar scoop is indescribable ...

Humperdink's trinitella went dead downwind (comfortably) in a F9 from lands end to solent recently and the hull shape is similar to that i describe ..

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Re: 2¢ worth

Not indescribeable ... thought you described it quite well as "Like being in the middle of a party of drunken Liverpudlian women" .. When I raised a quizical eyebrow you elucidated succinctly "Slappers!"

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I think it depends on the underwater design as much as anything. My modern cruiser sits quite low in the water being 8.5 tonnes dry for 37 feet, and therefore rather heavier than most. The hull will never plane but the boat will get up to 9 knots with a wind of about 25 knots on the quarter. It goes to windward at 6.5 plus knots with 15 knots plus, wind apparent. The hull section seems to me rather more rounded and less tea tray than many modern cruisers. I would call the keel medium length and the ballast is lead on a stub that also acts as a well for the bilge. the rudder is well aft and is hung on a substantial skeg. designer Jodel and Vrolik (if I have spelt that correctly).

I crossed the channel with a following force 8, and did not run dead down wind because of the danger of an involuntary gybe, but the boat was comfortable and the steering effort was by no means excessive.

I think that one of the problems with most modern cruisers is that their construction is too light and that as a result they sit on the water rather than floating in it. This makes their sterns much more likely to be thrown around in a following sea.

<hr width=100% size=1>Chris Stannard
 
I helmed a UFO 31 - IOR-ish? - throughout the overnight offshore race of this year's Scottish Series (my Moo' was in dock having been altered by a port tacker). We had 20-30 knots over the deck on one leg of about 20 miles downwind with a sea which had had about 50 miles to build. She had sailed into it very impressively but was disappointingly slow once we'd rounded the turning mark, being hard to push into double figures at all (the owner had reckoned 8.5 was her limit) and that was with limitless surfing opportunities. Later in the week, she showed a strong tendency to pick up death rolls with the kite up in quite moderate waves. Upwind in quite heavy conditions, she was good and with an easy motion: downwind she had to be reined in to be safe and was consequently quite slow and her hull was really unsuited to surfing.
Watch the Sigmas, which are "the best of what was intended under IOR", sailing downwind in a blow. Exciting/entertaining, depending on your standpoint.

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I'd endorse the above for a Rival 38, a classic IOR rule-cheater. For all her other graces, downwind is not her favourite point of sail in any kind of sea. In calm stuff in The Solent etc you can get her up to about hull speed with spinnaker and she's easy on the helm. But in any kind of sea much more than 6 knots gives you snappy rolling and accompanying helmming opportunities. Interestingly though, we have never been pooped even in some quite big following seas her bum always seems to lift just in time.

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Sounds very similar to Aeolus - just longer. Have had 10 knots dead down wind, main and genoa only. Steady on the helm - no suprises, she'll just never, ever plane.

Jeff.

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As far as I can remember, the Sadler 32 was a pig downwind. It roll steered horribly and was always keen to broach. We put the behavior down to the pinched in stern, which, I beleive, was necessary to get the boat to rate 1/2 ton.

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I know. I was there!

>>> Humperdink's trinitella went dead downwind (comfortably) in a F9 from lands end to solent recently and the hull shape is similar to that i describe ..

"Sergeant Pepper" is actually a Seacracker 33 - maybe the Trintella is another name for the same design? It was an amazing experience how easy to handle the yacht was. In the same conditions I think a Sigma 33 would have been about 50% faster but it would have taken nerves of steel and concentration beyond my ability to hold her so close to dead downwind for hours on end. Nine months later I'm still awestruck by how easily the Seacracker handled those conditions.

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Re:Steadiness or speed

Very last year - the new Full Pelt is a keeled version of a 49er, and should be much faster. 36 foot, 2 tonne displacement. Target is to plane upwind in 15 knots true breeze.

The original Full Pelt (mono) did win races. She managed lots of top 10 finishes at Cowes last year in calm conditions that would never suit her. She's now got more sail and gone to live in Switzerland I believe.

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