Daggerboard catamarans

[44'cruisingcat]

Guess it's typical of this forum. You have a few people who've actually done something, saying it's possible, and the herds who haven't, saying it's not.

[catsketcher]

Cases are cheap

The cases on my cat are quite light - much lighter than you would think. I made them with about 3 layers of 600gm db and some 19mm cedar on the middle section. But if you get the engineering right the cases don't need to be strong. (A note to anyone thinking of using light laminates - include a laminate of thin sheathing cloth for water resistance). It was a long time ago now but I could easily throw my 2m tall cases around the shed - they probably were 10-12 kg all up.

The cases attach at the bottom of the hull, and at the cupboard tops (my boards go below the deck when down). These two points are very strong - lots of glass (and uni kevlar down bottom to stop hull splitting in catastrophic impacts). If we were in a production setting then you could make the cases pretty easily and cheaply over the boards, like I did. My boards are cedar but you could use the Tennant method to churn them out in a production setting.

One of the real reasons people like keels is because they simplify the diesel and rudder setup. I have outboards on my boat but if I put saildrives in they would be unprotected and below the keel of the boat. I would lose the ability to take the ground, which I really like.

On my (and I think 44C's cat) we use outboards and kick up rudders to allow us to take the ground. If you want diesels you probably have to go shafts to get the prop towards the stern and a bit protected by the hull bottom. Pescott cats have smaller rudders than my cat that don't kick up. Kick ups are a bit of a pain to build compared to fixed rudders. That means some more cash.

I would think some of the extra expense of a daggerboard cat may come from these complications.

Interestingly I have never seen a minikeel cat been able to stay within cooee of Kankama - the small correction factors intrigue me. I have only ever been passed (and grudgingly at that) by much larger daggerboard cats. Going to windward it is almost as if we are in different breezes when we sail with minikeeled cruisers.

As boats are designed in a spiral you will probably find it very difficult to do a proper examination of the impact of keels. Anyone who designs a keeled cat will probably make less performance based choices on weight, mast height, hull width, dinghy weight, sailcloth choice, targa bar windage etc. A daggerboard is an easier to see statement of intent from the design brief - "This cat must sail really well to windward". There were some Chincogan 40s that had boards rather than keels so these would also be interesting to know about.

[hwturner]

Check out the Catana owners yahoo forum. Tons of great discussions from daggerboard cat owners, many having sailed around the world and in all conditions. Very friendly and responsive group.
https://groups.yahoo.com/neo/groups/CatanaCats/info

[admiralslater]

As some of you may have gleaned I have some connection with Pdq yachts ,my father was the designer of the 36 and 32 . I state this for clarity. When my wife and I specs our 36 one of the things that we (I ) wanted where daggerboards. We wanted boards strong enough for full loads and max efficiency when racing . The first thing was figuring out where they should be and what angle fore and aft they should be and what impact that had on the main bulkhead and as the trunk goes through the bulkhead close to the outside of the hull , we had to make the trunk strong enough for those loads . since the 36 has narrow side decks placement of the trunks had to allow them to come through the deck as well . Then with the new intrusion in the interior of the hull standard liner moulds had to be adjusted which was labour intensive .
Since the standard boat has LAR keels the a special plug had to be made to fill in that spot on the hull and that required hand fairing after words .
And now the trunk and board design . With the available space we had to pick a naca foil that fit our space and was efficient and could be made strong enough in the confines of our needs . The initial design was sent for finite element analyst . This told us that to make the board stiff and a reasonable weight carbon was the only answer.
Part of the specification was the board to be adjustable under full load ( it is ) which required the use of slippery plastic runners in the trunk and around the top of the board . After this design has done the plugs for the trunk and board was transferred into the computer of the 5 axis milling machine which then went on a cutting spree for many many hours .
After that the moulds and parts were produced with about 2000 dollars worth of carbon ( in 2003 ) in the boards .
Then installed with line drivers and turning blocks with deck reinforcements and add the line .
When you go below on her you don't notice the changes and it all looks normal on deck as well .
When mAking a production boat there are many things to think about that a diy guy does not have to .
I have made cheap boards for othe boats I owned and they worked ,but I could not sell them to any one .
Short answer 25 grand is not unreasonable

[tp12]

Apples and oranges are being discussed here. Some people are talking about the cost of designing boards for a keel boat, then building them etc... some are talking the cost of just building them. 44c's boat was designed for them already; he's talking about the cost of building them.

Just as a guiding principle when I'm trying to work something out...I always try to talk to someone who has done it before me. That person I'll give more weight than someone who is speculating or who just has theoretical knowledge. It appears to me that this forum doesn't work the same way. Here we see opinions and speculation given the same weight as the experiences of those who've done it. It's ludicrous.

[Cavalier MK2]

Originally Posted by catsketcher

Cases are cheap

The cases on my cat are quite light - much lighter than you would think. I made them with about 3 layers of 600gm db and some 19mm cedar on the middle section. But if you get the engineering right the cases don't need to be strong. (A note to anyone thinking of using light laminates - include a laminate of thin sheathing cloth for water resistance). It was a long time ago now but I could easily throw my 2m tall cases around the shed - they probably were 10-12 kg all up.

The cases attach at the bottom of the hull, and at the cupboard tops (my boards go below the deck when down). These two points are very strong - lots of glass (and uni kevlar down bottom to stop hull splitting in catastrophic impacts). If we were in a production setting then you could make the cases pretty easily and cheaply over the boards, like I did. My boards are cedar but you could use the Tennant method to churn them out in a production setting.

One of the real reasons people like keels is because they simplify the diesel and rudder setup. I have outboards on my boat but if I put saildrives in they would be unprotected and below the keel of the boat. I would lose the ability to take the ground, which I really like.

On my (and I think 44C's cat) we use outboards and kick up rudders to allow us to take the ground. If you want diesels you probably have to go shafts to get the prop towards the stern and a bit protected by the hull bottom. Pescott cats have smaller rudders than my cat that don't kick up. Kick ups are a bit of a pain to build compared to fixed rudders. That means some more cash.

I would think some of the extra expense of a daggerboard cat may come from these complications.

Interestingly I have never seen a minikeel cat been able to stay within cooee of Kankama - the small correction factors intrigue me. I have only ever been passed (and grudgingly at that) by much larger daggerboard cats. Going to windward it is almost as if we are in different breezes when we sail with minikeeled cruisers.

As boats are designed in a spiral you will probably find it very difficult to do a proper examination of the impact of keels. Anyone who designs a keeled cat will probably make less performance based choices on weight, mast height, hull width, dinghy weight, sailcloth choice, targa bar windage etc. A daggerboard is an easier to see statement of intent from the design brief - "This cat must sail really well to windward". There were some Chincogan 40s that had boards rather than keels so these would also be interesting to know about.

We put a Newick style case into the Nicol designing it into the new interior during the rebuild where the interior was gutted. It is more robust than yours but I could lift it. It is well supported at the load points.

A wood interior and case can look great with parts finished natural. Building molds for a one off beyond a lam table and universal corner mold would certainly get expensive, smoother costs more but there is monkey fur.

The benefit of some flex in a board is to reduce shock loads in rougher conditions. This is how a airplane wing works.

My personal choice involved keeping some keel for grounding and shallow water running and yes the kick up rudder is the current project. This is the approach I'd suggest for a keel cat conversion to retain some of the benefits if the sailor had a boat he likes already but wanted more windward performance. I think your comments on the design spiral and mindset are on. If the cruiser is going to turn on the engine for upwind or light airs a daggerboard is probably not going to be worth the effort or expense.

[SVNeko]

It depends. If you go for fashion and keep the board top below the deck at all times, a la Gunboat or the new big Seawind, you better make the trunk strong. Several Gunboats had the board pivot and punch into the living area. Most were then retrofitted with longer boards and a slot that goes through the deck.

[Cavalier MK2]

Originally Posted by SVNeko

It depends. If you go for fashion and keep the board top below the deck at all times, a la Gunboat or the new big Seawind, you better make the trunk strong. Several Gunboats had the board pivot and punch into the living area. Most were then retrofitted with longer boards and a slot that goes through the deck.

This might have been operator error. I'm not familiar with Gunboat trunks but most are reinforced at regular intervals. If you have the board upper end between areas of reinforcement breaking through a thin sidewall is certainly possible.

The deck does offer reinforcement but in some cases there are options where the "deck" is. On my tri the main reinforcement deck is at the underwing level, 1/2 way down the trunk and tied in very well to the sheer, main bulkhead,beam, sub bulkhead, and interior structure. Every foot or so there are reinforcement intervals up to the cabin top which is also well braced and tied in.

I'd suggest to daggerboard owners that they familiarize themselves with the features of their trunks and mark the control lines so the board is positioned correctly at the different levels of immersion.