Daggerboards vs keeled hulls

Well put Ray, While our keel will beat off a lee shore we did the math and found a dagger will improve windward mileage by at least 10%. We are keeping a shallow keel for grounding and puting in an offset board. Since we try not to motor any improvement is significant.

 

Another consideration in choosing daggers or LAR keels is what kind of sailor are you? Do you enjoy tweaking lines and such or do you like to "set it and forget it". I'm a tweaker so I like to have daggerboards to play with. Others may not like the hassle.

On the subject of running aground, a daggerboard can be usefull as a "feeler" in muddy bottoms. When poking around the mangroves I keep my boards all the way down. If I touch it is a simple matter to pull them up and back out. My 46' cat draws 7' with the boards down, less than 24" with them up so this allows some leeway. If I hit some flotsam or a reef and mangle a board it is fairly simple to build a new one. This can be done with the boat in the water and with materials available in most areas.

Mike

 

Tweaker is not the best term in this day and age. Too many chemical addled "cooks" use the term and unfortunately at times dump the waste into the waterways......We sort out our boats performance and upgrade systems when we can for efficiency. Better sailing performance means going farther with less money.....Hopefully past where the "gassed" crowd hangs out!

 

I would have to say that in my experience, fussing with daggerboards really isn't much of an issue. You perhaps, could, mess with them as much as you wanted but I seldom do more than 'set and forget' while sailing for the day. Even then, I only use one anyway.

 

I strongly suggest that you heed Richard Woods's comment. He clearly states the advantages and disadvantages of each kind of appendage, giving you the information you can use to make your own decision. He is a respected catamaran designer with many years of experience. One thing to consider is this: if you have to ask that question it appears that you are new to multihulls, perhaps new to sailing. If so and if you are chiefly interested in cruising, you might consider simplicity an important advantage over somewhat higher performance. To a new sailor, simplicity translates directly into safety and reduced stress and fatigue. Ultimately the decision should be based on your own motivation in sailing, not others' ideas about what you should or should not do.

 

Somewhat related thread: http://www.boatdesign.net/forums/multihulls/wave-splitter-catamarans-5741.html

 

Ditto. You get the impression from what some people say, that you're constantly trimming daggerboard like you'd trim sails in a race.

In reality you don't. Even round a race course you'd only move them a couple of times.

 

LAR keels possibly have advantages judging by shuttleworths efforts.
See....

ps the white items sticking up are hatch covers not centre board tops in the shot in the water.

 

That's true, but Shuttleworth also designs for daggerboards, even in his larger boats. One article of his I found especially interesting was this:

http://www.john-shuttleworth.com/Articles/NESTalk.html

This was a talk e gave on multihull seaworthiness. He lists 3rd and 4th generation cats as having "Sophisticated retractable daggerboards and rudders."

In this article:

http://www.john-shuttleworth.com/Articles/S70.html

He discusses the result of tank testing to decide on the choice for a 70 foot cruising cat. Tank testing determined the most effective option to be a single daggerboard, but, he says:

"The results showed that a single daggerboard was the best option. However as a compromise we decided to use two shallow keels to protect the rudders and propellers, and then to have one daggerboard in one hull to give extra lift upwind when needed. The shallow keels are also an efficient way of increasing the buoyancy of the hulls, thereby increasing the payload capacity."

For a cat of modest size, I think kick-up rudders, a single daggerboard, and an outboard make for the safest and most efficient configuration.

Almost all of Shuttleworths designs under 45 feet or so seem to have daggerboards, though I'm sure he'd put keels on a boat if a client insisted.

 

So you think Shuttleworth would compromise his good name and safety record at the clients request?

By the way the picture came from his "whats new" section.

 

I don't think anyone is saying LAR keels have no advantages here. They have advantages and disadvantages. As do daggerboards.

 

Why do you think LAR keels would compromise his good name and safety record?

One of his designs, the Lynx micromultihull, which is a production boat, was made with LAR keels. I just think his preferences are pretty obvious, judging by what he's written on the subject.

 

Yes but after his first season racing the first Lynx owner changed it to daggerboards because it was too slow (but then was not much faster with boards fitted).

I raced against it with my F1 rig 24ft Strider and beat it in both configurations in every race

Incidentally, the boat in the previous pictures is the Rodann 26 from Canada, but built in China. It is a Shuttleworth Cheetah design from the late 1980's

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

And to stir the pot a little bit, here is a direct quote from my designer, specifically regarding his cruising cat, from the study plans:

This cat is designed with dagger boards. If I were foolish enough to put keels on it, I would expect keels to generate 1000lbs (453 kg) of lift at 10 knots. They will also cause 85lbs (38kg) of drag at that speed.

Boards of the same area will generate 2400lbs (1089kg) of lift, more than double the lift of keels and with just 70lbs (32kg) of drag.

Oddly enough, a catamaran with a large house needs great foils even more than one with no house. If it can point high, the projected area of the house is minimized. A cat with a large house and low aspect ratio fin keels is the worst combination. That huge house is jammed to windward showing most projected area from a big leeway angle.

Keels on catamarans create a unique hazard running aground. If a monohull runs aground, the crew can heel the boat and kedge off. A catamaran with keels cannot do that. If you mush into a mud bank with fin keels, you wait until the tide comes back to lift you off. If you crush into a reef, you must haul out at the next stop. With boards, and the accompanying crash blocks, crushing a reef with the foils merely means repairing the boards, underway. Of course, if a cat with boards mushes into a mud bank, they simply pull up the boards and make a U turn to back out.

This is a quote about a cruising design from one of the most respected designers in the USA - Kurt Hughes.

I can't say there is anything incorrect about his quote, in my personal opinion and from my personal experience at sea.

I might also add that probably the most well known designer in the USA, Chris White, also has boards on all of his cruising cats.

Based on the value and popularity of either of these designers' boats, I'd assume they probably have it right, as does Morelli and Melvin.

 

That quote says more about you and your designer than the subject at hand.
Since when has pointing ability had anything to do with whats in the water.
Vmg and height of the "track" sailed are a function of the leeway prevention system. Pointing ability is a function of sail plan and the guy on the waggle stick (helmsman).


So lets see you heel a catamaran that is aground that doesn't have keels.