Daggerboards Catana 44

[sloboats]

I have a broken board and need info building new daggerboards, I was going to use the good board for a mold, but not sure on the core. My first thought was to have the bottom 2' solid glass and the rest 8lb closed cell foam. I do not want the board riding up in the trunk and it has to be sacrificial as not to hurt the trunk. Appreciate any ideas or help.

[AD28]

You don't give the age of your boat, and there are distinct differences and designers of Catana catamarans

You may want to contact Donnie Brennan of Diversified Marine in Mobile, Alabama (251) 473-7080, who has molds for Catana 411 (3d generation Catana, designed by Christophe Barreau) daggerboards

[sloboats]

Sorry, the Catana 44 was a Crowther design built in 1995

[AD28]

Actually it's a transitional boat. Crowther died in 1993. Barreau is main designer from 1994 on.

If your board has that much solid glass down low, it is definitely different than the Crowther designs, which have only a few inches of solid, and then have hollow breakaway area above, and have fill at the top. There are large bolts at the bottom of the earlier boards to allow them to drain.

Call Donnie - the 411 boards should be the same core/design as yours. The molds he has are taken from a 1995 C411.

[UNCIVILIZED]

Originally Posted by sloboats

I have a broken board and need info building new daggerboards, I was going to use the good board for a mold, but not sure on the core. My first thought was to have the bottom 2' solid glass and the rest 8lb closed cell foam. I do not want the board riding up in the trunk and it has to be sacrificial as not to hurt the trunk. Appreciate any ideas or help.

The general modality of thoughts on boards is this: You want the trunks to be stronger than the boards, as the boards are far easier to fix after a collision than are the trunks. Plus which, broken board wont allow water into the boat, whereas broken trunks will.

You may want the first several inches, to a foot or so (max) to be solid, so that the tips wont be damaged if/when the boat is resting on them on the hard to dry out.

From there, you'll want stiff, strong, foam cores. And for the bottom few feet to maybe be a bit weaker than the rest of the boards, so that the tips are sacrificial for groundings, & severe impacts with a floating object. Albeit, that (strength) differential, has as much, or more to do with the board's layup schedule, as with the cores.
For in my studies on the matter, generally, the core is the same strength/density throughout the entire length of the board.

Also, the vast majority of the semi-custom, to custom designs out there, have purpose designed systems which cause the board to retract vertically when it strikes a heavy object at speed.
It'd be worth talking to your boat's designer(s) about this. As well as some custom designers, to look into the possibility of retrofitting such a system.

Because the primary reason for the automatic kickup system, is to cut down, or fully eliminate any damage to the trunk when you strike something. In addition to cutting down on the damage which is caused to both the board & the trunk.

And also, most semi-custom, to fully custom multihull designs of any size, have replaceable crash boxes/blocks (inserts) which fit into the trunk, along with the board itself. Right behind it, & also wrap around the board's aft end, to aft third.
With them being made out of high density foam, designed to absorb such impacts.

Then in bigger boats, they also have integral composite structures, built into the foam crash blocks. Which are designed to crumple when the board strikes something with sufficient energy. Just like a crush zone in an automobile.
First the foam takes some of the energy of the strike, & if it doesn't absorb it all (along with the board kicking up), then this composite & foam crush structure takes the rest of the energy from the impact.

So then, again, they're one more component which mitigates damage to the board itself. And all but eliminate any damage, to the trunk & boat. When working in conjunction with the board's kickup system.

It sounds as if, perhaps, your boat may not have these. But talk to the manufacturer about such. And also, you'll need to find out from them, the following about the board;
- The core's specifications.
- The layup schedule for the board. Including the orientation of each layer of fabric.
- The specifications or each layer & piece of fabric used in the original construction of the board. As fabric strengths, even for the same type & weight of fabric, can vary HUGELY from one fabric maker to the next.
As in it's physical properties can be 2x or more, greater, from one brand to the next.
Also, the type of sizing on the fabrics, which is what helps the resin bond to them, again, can vary quite a bit.
~> In terms of their performance (as they form an integral part of the physical strength & stiffness properties of the fabric itself).
~> And also they govern what types of resins bond well to them, & which ones do not.
- The specifications of the resins used in the board's construction. As their physical properties vary from one to the next also.
- Whether or not you'll need to vacuum bag the skins onto the cores, when laying up the board.
- If the resins used, need to be post-cured, once the initial cure is completed. And if so, what the "recipe" for this is. Meaning, at what temperature, & for how long do things need to be baked.
- Also, you'll need to know to what NACA foil sections the finally finished board needs to be faired & templated to.
- As well as what type(s) of finish(es) can be, or need to be applied to the board.
For example, can you/should you use graphite, mixed with epoxy, to flow coat the board with when it's finished. As such coatings make the board slipperier with regards to moving it up & down inside of it's trunk.

Although the choice to use such final coatings, also depends upon how much, if any, of the board which you leave in the water when you're not sailing.
Because if you leave much, if any of them down, then you'll be wanting to use some type of antifouling in lieu of putting a graphite coated finish onto them.

And not to make you loco, or to purposefully adding even more work & complexity to the job. However, now might be a good time to talk to the boat's manufacturers about the possibility of adding crash blocks/cassettes to your board trunks.
Or changing their aspect ratio, & or foil section, etc.

I hope that that helps. Although I know that so much in the way of details regarding daggerboard construction, probably complicates things quite a bit. In addition, of course, to being a LOT of information to read & digest.

Feel free to run any questions by me which you might have. About the above, or about the topic in general. And too, Kurt Hughes http://www.fastcomposites.ca/site/ has a Lot of information about boards & trunks, on his website, as well as in much of the other things which he has written. Ditto on John Shuttleworth http://www.shuttleworthdesign.com/index.html
That, & with some digging, I can come up with some companies who build such items. Ditto on firms which carry the materials that you'll need.
http://www.fastcomposites.ca/site/ is one, for example.

Good Luck!


PS: A good website to study most of these topics on is www.compositesworld.com
And might I recommend doing a smaller, less pricey project or two first. Using both the materials & techniques which you'll be using to build your replacement board.
Also, FWIW, Kurt Hughes, who with all of his boat building experience (which is substantial), & his considerable design expertise, had the rudder for his personal, 40' trimaran, built by a company that specializes in such items. Back when I first met him, in the mid '90s.

[barnakiel]

A friend lost one and he was forced to buy a new one. They are not easy to build (he had the empty water ballasted ones).

b.

[UNCIVILIZED]

PPS: My apoliges, I goofed & inserted the incorrect address for Kurt Hughes. The proper one is Kurt Hughes Multihull Design - Catamarans and Trimarans for Cruising and Charter

[Privilege]

Uncivilized,

Thanks so much for all of the info. I too am in need of a pair of dagger boards for my 44' cat. Unfortunately, 'Privilege Marine' were bought out and they no longer have the board molds and have offered no input into the making of new ones so I am starting completely from scratch and will make my own.

I had intended to copy a guy making molds on YouTube but thanks to your input, it appears that his boards would be too strong for my trunks. His were made up with laminating wood and covered in glass. You make a good point about the need for them to be sacrificial.

I'll have a read of the links you posted and hopefully get some ideas as to how to go about making them.

[cruisersfarm]

Exactly what uncivilized said.

Do that.

[44'cruisingcat]

Originally Posted by Privilege

Uncivilized,

Thanks so much for all of the info. I too am in need of a pair of dagger boards for my 44' cat. Unfortunately, 'Privilege Marine' were bought out and they no longer have the board molds and have offered no input into the making of new ones so I am starting completely from scratch and will make my own.

I had intended to copy a guy making molds on YouTube but thanks to your input, it appears that his boards would be too strong for my trunks. His were made up with laminating wood and covered in glass. You make a good point about the need for them to be sacrificial.

You could build them like this, but say, only to3/4 length, then add foam at the bottom 1/4 with light glass over it, as the sacrificial part.

The plus of this is that if/when the sacrificial part breaks off, the remaining board is still watertight and usable, and another sacrificial part can be built on at your leisure.

[UNCIVILIZED]

As to board strength, & their design. Keep in mind that the loads on them are tremendous. Especially on the leeward one when you're going to weather. Because if/when you lift a hull, or begin to, not only is pretty much the whole weight of the boat supported by the board & rudder, but that load is compounded by the shock loads incurred every time that you pass through a wave. So that the load on the board can be several times that of the boat, IIRC.

Added to which, you have to remember that the highest loads on it will be where it meets the edge of the board trunk. So that there's a HUGE point loading on both the skin of the board there, & the edge of the trunk also. As well as the trunk's support structure.

Picture hanging a load off of a ruler which extends over the edge of a table, & then add some shock loads to things. Where are the highest loads, & where's it going to break?
That's pretty much the same engineeing scenario as is encountered with a daggerboard. Only that with a DB, it's a cored structure, so the loads are on the skins, & aren't distributed throughout the thickness of the board.

So it's really something which one should consult with the boat's designer, & or, a well qualified Naval Architect (NA) about.


PS: Thanks for the positive feedback guys!

[AD28]

Perhaps I should mention that Mr Brennan is the US Olympic Team boatwright. He's extremely good at his craft. Builds light, strong, fast. Call quickly, he's a very busy man, and sailing season is here.

The molds I mentioned were built such that he can lengthen or modify them to some degree, which is why I suggest that although your boat is somewhat larger that you contact Brennan.

[Stumble]

If Brennan can and will do it he really is the best in the business. But can him now because he will be leaving for the Olympics soon and will be gone until at least the medal race.

Someone also just posted on another forum thatthey have the asymmetric foils from a 40' tri that may work. But they may also be far stronger than needed. carbon lifting asymmetrical foils - Boat Design Forums

[UNCIVILIZED]

Originally Posted by Stumble

If Brennan can and will do it he really is the best in the business. But can him now because he will be leaving for the Olympics soon and will be gone until at least the medal race.

Someone also just posted on another forum thatthey have the asymmetric foils from a 40' tri that may work. But they may also be far stronger than needed. carbon lifting asymmetrical foils - Boat Design Forums

I know that in some of the various treatises he's written on DB's, Kurt Hughes talks a fair bit about using carbon fiber for them. And it'f for the reasons I mention on how, how much, & where they're maximally loaded.
Obviously the spec's vary from design to design, in his boats, but...
Also, I know that in many/most of the high performance catamarans use carbon in their foils for the seme reason.

PS: I'll have to look into Brennan. Can't say as I know much of him. But Carl (Eichenlaub) was a personal friend. And is still missed. It SURELY was tempting to by Cadenza, but for her keel. Between it's crazy draft, & that hyper-snagging T-bulb.

[44'cruisingcat]

Originally Posted by UNCIVILIZED

As to board strength, & their design. Keep in mind that the loads on them are tremendous. Especially on the leeward one when you're going to weather. Because if/when you lift a hull, or begin to, not only is pretty much the whole weight of the boat supported by the board & rudder, but that load is compounded by the shock loads incurred every time that you pass through a wave. So that the load on the board can be several times that of the boat, IIRC.

I think you're overstating this a bit. Certainly daggerboards have to handle substantial loads, but not the entire weight of the boat, certainly not several times that!

There's no way mine was built to handle 6 tonnes, let alone multiples of it.

But, 27,000 miles later, still intact....

Mine was built using a timber frame, with a central spar of timber with unidirectional glass around it, a plywood skin, with biaxial, then double bias glass over that.

And this is a BIG board, the boat only has one. Big loads, sure, but within reason...

now THATS a daggerboard - Cruisers & Sailing Photo Gallery

I'd also recommend, if you do decide to build one, to start out making it smaller in section than the old board. (Unless you are able to get hold of moulds) Once you start fairing and painting, especially antifoul, they get fatter than you expect. Nothing worse than a board that's too tight for it's case....