Trying to design my own cat.

I wear my sunglasses at night and when asked I say... because the sun is always shining on me.

J

 

Designing my own catamaran, flat vs. cambered sails, etc.

The crab claw sail doesn't have to be a flat sail if you don't want it to be. Just cut some curvature in the sail edges that bow out towards the spars. The more curvature, the more belly (camber) the sail will have.

To see some unusual thinking about wingsails and home boat building with radius chine hulls, see http://dunnanddunnrealtors.com/Catamaran.html . There is a link at the bottom of the web page that explains putting camber in a junk sail using cut camber - see Arne's page.

 

Worst case twisting force on each beam should be the weight of one half the boat's weight devided by two. As JCD explained, worst case it would be the boat, fully laden, on two opposing ends supported, the other ends suspended in air.

Keep in mind water is fortunately somewhat forgiving in the sense that the hulls will be pushed (sink) into the water, and it is highly unlikely that the rig would experience a dead load on two opposing sides, unless you park it on some rocks of course.

The width of the hulls and the strength of your beams would determine how stiff your rig is. Narrow hulls would experience more twisting point load force when the one hull fore or aft is lifted because a smaller leverage area is provided. Wider hulls would have a bigger lever with which to keep the other hull in line. So the forces on the beams should be more up and down, not rotating or twisting.

 

Lloyds has a rule for connector beams on catamarans

Lloyds' Rule for Special Service Craft Rules - Part 5 Chapter 5 Section 4 covers catamaran connector beams.

For the boat shown at http://dunnanddunnrealtors.com/Catamaran.html ,the rule resulted in 2 beams that weighed about 800 pounds each, composed mostly of unidirectional carbon fiber and vinylester resin, with some +45-45 glass uni to take wracking strains. The beams were about 1/2" in wall thickness, and a little over 1' wide x 3' high, with each beam attached with 10- 1" diameter ss bolts at each end.

 

OldYachtie,
those old-style designs look great. Wouldn't it be nice to see the sailing clubs filled up with boats like that! I hope more and more people get hooked into this retro phase. I want my boat to have an earthy casual feel, with wood tones and 'old paper' sort of colours. It will all be fake though...to save weight and I don't like maintenance.....so I'm not as retro as some.
You raised an important point in the other thread, about the inability to cleanly reef a crab claw. I am still researching this. Sure, the spars can be closed together to spill power, but I wonder how that distorted sail shape will behave in strong winds. Lots to read....

Hi Fanie
I've decided I'm happy with the width of my hulls. Still trying to work out what to do with the beams and rigging. Lloyds rule, as mentioned by OldYachtie, and all other rules, will be considered after I have worked out the ergonomics.

J, if you wear your sunglasses at night, most people won't ask why, because they will think you might be blind and they won't want to offend you

 

For the boxy I'll probably make GRP beams. They won't be as heavy as OldYachtie's though, but that's a BIG yacht and only two beams.. If you can get decent allu pipes or structured profiles they shoud do the trick and is much less work.

 

Richard,

Claws don't reef. The distorted, or concave conical shape will create vertices which will rise and create lift. It will behave fine. It used to be that vessels in distress would go to bare poles. Now, it has been demonstrated that heaving to is the best way to deal with storm conditions.

By heaving to you maintain way in a zig zag 45 degree course crabbing sideways. This crabbing creates a "slick" of disturbance on the surface which promotes "calm" conditions. Worse comes to worse...heave to and keep the claw drawing efficiently for the conditions.

J

 

"Now, it has been demonstrated that heaving to is the best way to deal with storm conditions."

In all candor, "J" I not only don't agree with you, but doubt that you have ever experienced any serious storms at sea in small craft.

In really serious weather, even boats which can heave to, which is not all boats, and perhaps not the majority, would not dare to turn into the waves, and would be unable to hold any canvas up.

The only controversy among experienced multi-hull sailors is whether it is better to lie bows on to a large parachute, or to run with a drogue, in the worst weather. I'm in the 'run with drogue' camp, because I have experienced huge breaking waves and would not have tried to turn towards them for any money. I call myself 'OldYachtie' for a reason, you know.

 

OldYachtie, I'm interested too in what it's like - won't you elaborate the conditions and actions in those kinds of weathers please.

 

Storm management tactics

Hi, Fanie

My experiences are in monohulls. I am working on building a multihull, and have been doing much reading about multi-hull storm management.

In September-October of 1971, I was sailing a monohull fin keel sloop, an Erickson 35, from Hawaii to Seattle. I was caught in huge waves and was surfing with the mainsail up. We couldn't get the mainsail down, which was the beginning of my interest in sails which cannot jam under any point of sail in any weather when you try to take them down. You had to turn to windward in that boat to take the mainsail down, as is true of many marconi rigged boats. The waves were huge, but breaking only at the tops of the waves.

I had to steer for about 36 hours, as my wife just wasn't strong enough to fight the tiller. We didn't dare turn into those huge, partially-breaking waves, because the likelihood of being turned over was very obvious if had tried to do so.

In contrast, in my next boat, a moderately long keeled boat with a junk rig designed by Blondie Hasler, (Batwing,) I never had any trouble reefing or furling sails, in any amount of wind, on any point of sail. It sailed better to windward than its detractors imagined, but was hardly sparkling to windward, as it tacked through 100 to 110 degrees. This sail was flat, with no camber. Since then, the cambered junk sail has been invented, and junk rigged boats will now tack with any other standard cruising boat.

I remember one huge storm in 1978, between Fiji and New Zealand, in which I was awakened and told by my wife that she had just been standing on the side of the doghouse. We often sat sideways, legs up on the seat, athwartship at the dinette, and that meant that the boat had heeled so sharply that it must have approached being knocked down. We turned and ran under bare poles, until the storm blew out. We weren't going fast enough for running without a drogue to be dangerous-we were doing about 4 knots.

In such a cirumstance, a multihull would be in danger of surfing down waves so fast that it could bury its bows and pitchpole. If you are sailing really fast while running bare poles, therefore, drogues would be appropriate. I like the look of the Galerider or the new Fiorentino Shark drogue. If money is in short supply, either could be imitated by the home seamstress. This is the tactic recommended by Gregor Tarjan for catamarans.

Eric Hiscock, the grandfather of today's cruising community, had a low opinion of heaving to as a storm tactic. In his opinion, modern boats (modern in over 50 years ago!) didn't have long enough keels to heave to reliably. The only current advocates of heaving to are the Pardey's, who have a boat that Eric Hiscock, now passed away of old age, would have regarded as old fashioned. Hiscock recommended running, with long bights of line as drogues, if necessary, as the preferred tactic for dealing with dangerous storms.

My new boat will have an aerodynamic version of the junk rig, with the battens forming a wing shaped sleeve that will conceal the masts, and hinges in rigid battens to provide camber. Similar rigs have been used already, such as the Swing-Wing, and the Gallant rig. My rig will, in effect, be a cross between the two.

See: http://www.svaphrodite.bostekanesthesia.com/ and
http://www.themultihull.com/wharram2/bf9.htm

 

Good call. I'm sure you saw the joking picture of the mono hull fan guy who preyed beside the bed 'Oh Lord I went sailing in a multihull today... and I liked it !'

I think we do not gain enough knowledge about difficult conditions, any one can take a bathtub on the ocean under favourable conditions, it's when the weather changes when it becomes different. Was in it only once with my power boat that I wasn't sure I was going to make it, hence the cat I'm working on.

Maybe you should start a tread storm survival tactics, lots to gain by it ?!

Sorry for hijacking your thread Richard.

 

OldYachtie, perhaps there are times when heaving to is more appropriate, to avoid being blown off-course to a more dangerous location. I have had no experience in anything other than small dinghies, and the most I have sailed in is 35 knots (in a bay), so I wouldn't dare to assume that either you or J is incorrect.
I imagine it would be good to have either option available....running with drogue or heaving to. I guess it's up to the skipper to have a good feel for the boat and the conditions.
Great posts! I'm glad you started this topic J.

I'm not sure at this stage whether I will go with a 'semi crab claw' like the sunfish, or a full-on claw like Glenn Tieman's boat. I have been speaking to the Proa_file Group at yahoo and they have been very helpful.

Anyone got any more stories or advice about handling a dangerous storm??

 

Fanie, you just got in before me. Hijacking? No way!! I like this topic.

 

I cannot speak from a sailing point of view, but it can be really dangerous skidding down a wave as OldYachtie pointed out a cat may do. If you get it wrong the keel bites into the water and wants to veer to one side. Even the powerboat does this. I intend to make me one of those sea anchors with the multiple funnels on them... sorry the name evades me now... What I like about it is you can let out as many funnels as you like to change the amount of drag you set as required by the situation. The single sea anchor is set, you have to live with the amount of drag it has.

Worst water I was on was popping knobs everywhere and no aparent sequence... didn't know where the next was going to come from, bad. Got my grey beard there

 

Jordan Series Drogue

'I intend to make me one of those sea anchors with the multiple funnels on them... sorry the name evades me now... What I like about it is you can let out as many funnels as you like to change the amount of drag you set as required by the situation.'

Hi, Fannie-I couldn't talk my wife into making one of those. There are lots of man hours in those things. They published the plans for making one in the magazine "Multihulls." ( http://www.multihullsmag.com/ )

See: http://www.sailrite.com/drogue-bag-captain-navy-135

I never heard of putting out different amounts of cones depending on the amount of drag you want, though. I don't think that was a part of the designer's thinking. You put the part with the funnels at the end of a whole lot of nylon line, so adding to it would take even more, and they have in mind some 600' or so of line to begin with. See http://www.jordanseriesdrogue.com/