Daggerboards vs keeled hulls

Uh... pointing ability has *everything* to do with what's in the water. Isn't that part of what this entire thread is about?

So you are saying a boat with no lateral resistance in the water is going to point well because of sails and a super hero on the helm?

Also, you may want to take another try at reading the post. It doesn't say anywhere that you heel a catamaran aground.

Are you seriously questioning the expertise of Kurt Hughes?!? lol

 

There can be no debate:

1) A multihull with daggerboards will always sail better than one with LAR keels
2) A multihull with daggerboards will always cost more than one with LAR keels

When I had my Eclipse catamaran in the UK I dried out twice a day, every day, without damage, as do hundreds of other boats (monohulls and multihulls) in the UK and France where the tidal range is large (20ft in Plymouth, up to 40ft in France). Yet after leaving the UK I only dried out twice in five years and 15000 miles, once in Maine (USA) and once on the Pacific coast of Costa Rica.

I did once run aground hard by sailing at 8 knots into an uncharted coral reef off Nicaragua. However the hull was undamaged. Just as well as we were 400 miles from the nearest safe port. The board WAS damaged though, about 500mm x 150mm chunk was taken from the trailing edge. But it was 4 months later before we had a chance to fix it. So it certainly wasn't a cruise stopping moment, even if it was a heart/boat stopping one

The sail forces from the rig are counterbalanced by the forces from the underwater foils. It seems sensible to me to keep them in proportion.

In other words, don't have a big racy rig with rotating mast and high tech sails and then fit LAR keels. Equally if you are fitting daggerboards there will be little performance gain if you use crosscut dacron sails

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Maybe Bruce was trying to make a point about the difference between "pointing" and "going."

A boat with no boards could conceivably "point" high, but make so much leeway that its VMG was abysmal.

But I can't figure out what he means about heeling a cat that's aground. That's pretty hard to do.

 

I have to disagree about Richard's crosscut sail comment. If your boat makes significant leeway with a LAR keel a daggerboard will help no matter what the rig. Keeping the sizes in proportion is of course necessary. More sail= more board.

 

Sorry I forgot to mention you among my prominent designers, Richard!

 

Equal and opposite forces

Although I am happy for Michale to have his opinion on boards it does seem to fly in the face of fact. Boards have been used in heaps of cruising boats and owners have put them in their next boats too. So the boards must be fulfilling a function well or the people would not put them in their subsequent boats. I have run into things with boards up and down and still like my boards very much.

Much of my cruising time has the boards fully up. Square running, broad reaching. The boat is faster and safer this way. The boat tracks much straighter than a similar keeled boat and is easier to sail. Bashing back against the trades we sail but the minikeel cats tend to motor sail. This suits the way our boat is set up. Is our boat better or worse - no it just suits us fine.

As to why we need daggers or keels. The function of the underwater appendages is to provide lift (in the sideways plane it is equal and opposite to the the main rig force). They do this only be slipping through the water sideways - leeway. A daggerboard (high aspect ratio) will produce greater lift than a same area keel at much less angle of attack (leeway). A keel has to get dragged sideways faster to produce the same amount of lift. This means you get more leeway and less speed (the hulls are designed to go straight and have more drag when crabbing more).

You can make dagger cases silent too - just mould them off the board. Mine have never made a sound. As for worries about the hull - I have unis led around the back of the case forward and have cut the bottom of the board off and then glued it back on. This gives a fuse for the board if it strikes hard. I have never had to glue on my spare tips I saved from building the boards 11 years ago.

And I also have stub keels for slipping - 2.4m long and 100mm deep - good for piece of mind on a dodgy slipway.

cheers

Phil

 

Edging toward misleading there, Catsketcher.

Sorry, Catsketcher, it's fine to expound and defend your position on boards versus keels, but not to go past fact into fancy. I've personally chartered and sailed a 42 foot cat designed by Vince Bartolone, with symmetrical deep parabolic section hulls and mini-keels, no boards, and a big fully battened deeply roached main and lapper in the whitecapped Maui-Molokai-Lanai channel going to windward at 45 degrees apparent, the boat surging over the waves at sixteen knots and above, regularly touching nineteen. On a reach--a wild and wooly 22 knots. Designed right, a cat without deep appendages can still go to windward. A good one does not "tend" to motorsail to windward. The tendency depends on the quality of design, lading of the boat, quality of construction and whether the designer's plans were followed, design and condition of rig, cleanliness of bottom, and a myriad of other factors. You make it sound too general. Let's stick to arguing fairly. Why not make your points without edging into too loose generalization? After all, you're trying to help someone, aren't you, not win a war? Put the facts out and let the guy make his own decision.

 

Sixteen to nineteen knots to weather, wow,thats got to be one of the fastest boats on the planet.

 

No GPS

We didn't have GPS thirty years ago, so who knows, but the principle stands. That boat didn't need no #@$& motoring to weather.

 

Well, speed through the water does not equal VMG. The boat might have been screaming along, but how do you know it was making a lot of ground to windward while doing so?

I'm sure that like any other design feature, LAR keels can be done better or worse, but I think it has to be accepted that the average multi with keels is not as weatherly as the average multi with daggerboards. The boards have better lift to drag ratios. That's certainly not to say that LAR keels can't be perfectly adequate, but I don't think there are any racing multihulls these days with keels.

I think it's fair to say that the vast majority of multis with keels are big cats produced for the charter trade, and these are not known as windward speed demons. A decent monohull can often beat these boats on a windward course.

Just as a data point, in last year's Florida 120, in heavy air and big chop, my chunky little 16 foot beachcruising cat, with her low-tech sprit rig and good foils, including a big deep daggerboard, was substantially faster to windward than a couple of Windrider 17's, which have the same sail area in a fully-battened main and jib, with rotating mast-- but with molded-in LAR keels. And the little tris weigh less than my little cat.

I've become a huge believer in good foils. Last year I built the prototype of a cartoppable 14 foot cat, hoping to use barndoor rudders and no boards (because my 16 footer goes to windward acceptably well with her daggerboard up) as a hassle-free, learn to sail, ultra-cheapo cat. It was an attempt to snare the attention of the small-boat builders who buy Jim Michalak designs, and get them to thinking about multihulls.

Well, it was a disastrously poor sailer. It was very bad to windward, and wouldn't tack very well (Slider tacks reliably in all conditions and sail configurations, so I'm spoiled.)

I fought the good fight, trying several different configurations of fixed rudders, to no good effect. Finally I threw up my hands and gave her a pair of decent NACA 0012 kick-up blades, and she started to sail better. Last week, I equipped her with a big deep NACA 0010 board (hung under the center deck) and she was transformed from a complete dog into a pretty sweet little sailboat.

 

Rick - I am glad you got to sail a good cat. Vince Bartelone was the draftsman for CSK so I assume it was a similar style boat. Certainly the CSK boats - Aikane, Patty Cat and Sea Smoke were all great racers and used their thin hulls to make them sail well without boards. Although as I recall even the great Rudy used boards on some of his later cats including Aikane X5.

On the east coast of Oz most cruising cats have fatter 10.1 hulls and with all the appendages of cruising seem not to be able to do the speeds your cat did. Therefore they slip sideways some more as they develop less lift - that's why I said "tend" as if you go out and tick off those cats that sail and those that don't the ones that are motoring do tend to be the minikeel boats.

cheers

Phil

 

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I can't find my book but weren't the early Rudy Choy designs known for their asymetrical hulls?

 

Symmetry of sailing

I am just reading a book called the "Symmetry of sailing". It's a darn good read and seems to give a good quantitative analysis of sailing boat forces without getting straight into calculus. It was written in 1987 and I wish I bought it years ago.

The idea of symmetry is a powerful one. As soon as your boat (cat, mono) is sailing at a constant speed all of the force are equal and opposite. The same goes for leeway. The component of the combined rig and hull and cabin drag that acts at 90 degrees to the boats motion makes for the leeway force. This has to be resisted by the underwater part of the boat.

Now most cruisers exacerbate the whole situation. Some cruising cats have high windage drag - high cabin, lots of aerials, solar panel mounts, high bridgedeck cabin, slab sides that increase the amount of force sideways. Combine that with baggy sails and a kayak or two and you have a heap of leeway force.

Usually if the force is increased a designer would go "Oh - we are increasing this force so I will make the structure better able to deal with it." Say you have more mast compression - make the beam stronger. But here it is different.

In this case designers (instructed by their clients) go the other way. As the leeway force increases they often put less efficient foils on the boats that are less capable of producing a large reactive side force at a reasonable angle of attack. I would think that the boats most capable of dealing with inefficient minikeels are racers with flat well trimmed sails, low cabin windage and light weight that achieve high speed and can therefore need less reactive force and go faster to get the inefficient foil to work at least somewhat well. So some cruising cats get both sharp ends of the stick - high drag above water and to get the same reactive force from their low aspect keels at a low speed they get high drag from their keels.

I am aware of many minkeel cats that do sail well to windward. My own cat has sisterships that have sailed around the Pacific with keels. It seems as though many cats may get the worst of both worlds with an high drag rig combined with a low lift keel. That is certainly asking for less performance to windward.

It may be that if you want to sail well to windward with keels you have to be even more careful than the daggerboard sailors to reduce your windage above the water, trim your sails well, keep your boat light and fast. All the things CSK were doing in the 50s.

Then again you can be like my mum who had a very happy 5 or so trips up the reef on her minikeel 35 foot cat. She said her boat went to windward very well - with twin diesels. She liked it but when I sailed with her (I did a couple of thousand coastal miles on the boat) I tried to sail more. They (she was with my step dad) actually couldn't be bothered tweaking so much. They were happy to have two efficient and very reliable motors to assist whenever required. My boat was designed for me - I like sailing to windward so I got boards. We all had good trips on both boats.

 

Unless it was blowing a gale, sailing at 16 - 19 knots and 45 degrees AWA means you quite likely were not making any progress to windward at all....

 

Yes Doug the CSK boats were usually assymetrical. I don't know the details but Vince Bartelone is down in the 1970 book as being a draftsman and a junior partner. I am guessing that when Rudy stopped designing he went out on his own so the boat would be after that.

In fact I think even Rudy did some symmetrical hulls (with daggers) later on. I need to get my mags sorted but I think there is a multis mag with Aikane X 5 on the cover and I seem to recall it had symmetrical hulls and daggers.

Maybe as cats got wider the assymetric ideal worked less well. With their thin beam the CSK cats would lean over and push the lee hull deeper down increasing the lift from the lee hull and reducing the lee force from the windward hull. A wider cat would do this less so maybe the symmetric hull was less drag.

cheers

Phil