Minimum cruising cat-size & cost

Heres a pic, ---- scroll down to Jhojuin Japan. Item. 3. Types of structure.

http://search.imesh.com/webResults.html?src=ieb&q=Truss beams

 

Too complex for my needs - what is the cheapest/easiest/BEST beam option?
Wood vs Aluminium vs ply diy?

 

I saw one of these boats in Maine last year. It was full of 4 or 5 Germans who had crossed the Atlantic and worked their way up the East Coast of the States:






http://www.2hulls.com/catamaran_for_sale_by_owner/drifter.html

I think I'd be too scared in anything smaller than this.

 

Pen Duick IV sailed most of the world- a large all-aluminum trimaran looking like a spider on 3 sticks. Its crossbars were aluminum tubes that I saw when it sailed to Hawaii.
There have to be large aluminum tubes available for this task.- streetlight posts or ???

 

YES---and we all know what happened to Pen Duick IV.(Manureva)

 

hey oldsailor, we don't. The French guys I spoke to felt sure Manureva got run over by shipping. Also Colas had changed the multiple alloy tubes that made up each beam, to boxed alloy plate versions, much the same as any box beam of today - so the platform was beam/tube connected quite differently to when Tabarly had Pen Duick IV (and also Colas in the early days of owning the boat). That boat had done untold thousands of miles too in that earlier beam configuration, set Atlantic and Pacific records (and later a world circumnavigation record with the altered beams) ... so she was an old and well travelled boat when she was lost/run over.

 

OR--Suffered from fatigue failure in her welded aluminium joints. Age hardening fatigue failures are a known phenomenon in finite stress reversal conditions of aluminium structures. Fluctuating stresses in seagoing conditions defy normal mathematical calculations. The structure of Pen Duick IV / Manureva was a heroic leap ahead into unknown territory, and it was much more probable that she broke up, than was hit by a ship. That last assertion was a French way of saving face.

The same excuse was made for the loss of Arthur Piver.

 

The French multihull designers I spoke with were all adamant that Manureva's beams broke

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

The scary photos I saw of Manureva's welds breaking after record runs were enough to convince me. I do wonder though if Wharram style lashings would be the way to go with aluminum beams. Once you lose the welds (except for phil the fatigue of the tubes becomes easier to calculate. Theoretically......

 

You guys are probably right and I remember seeing photographs of the frightening alloy tube joint cracks too - but Colas knew that before he singlehanded around the world and rectified the damaged beams by going to alloy boxes. Anyway, the French crews I talked too still believe he was run over because conditions were light at the time and Colas had been in radio contact just before he "disappeared." I mean all of this is conjecture - we don't really know.

 

Alloy versus glass

Gary

If we look back through the history books we can see failures of both alloy and composite beams. My take on this is that the alloy beams FT, Trumpeter, Searunner 31 demountable were more problematic than the wood/composite alternatives.

Having said that I am very much looking into welded trusses for a few jobs. They would be nice and so much easier to engineer. Of course alloy is incredibly well proven in masts and the Bucc 33 28 and 24 all went well with alloy. Of course Lock didn't weld the Bucc beams and put them into compression with the use of a waterstay. Clever guy that Lock.

cheers

Phil

 

Never ignore shipping ! It is too bad he didn't have floatation in the boat, the wreckage would have answered that question. Just about every kind of beam has been broken, good engineering, construction and knowing when to throttle down all seem important. I like the fatigue resistance and ease of working with wood (miracle fiber W). The bucc beams are an elegant solution though I hate having beams that depend on a waterstay. Have any Buccs had that happen? It is bad enough to lose a mast but a waterstay going could cost a beam, mast and capsize if Murphy gets involved.

 

Waterstays are clever

The Twiggy has twin waterstays. My old one broke one but the other was fine. The waterstay is a fine idea as it changes the beam from a highly loaded cantilever to a much lower loaded compression strut. For the same beam a waterstay reduces load markedly and makes you safer. Nowadays they are a bit out of fashion but if you don't like wire then make one out of composite.

cheers

Phil

 

The waterstays on the B24 are made of flat SS bar and are probably the strongest item on the boat. The guy who bought my B24 rammed a steel marker buoy and took the impact on the Port waterstay. No damage and it probably saved the boat from more serious damage if it had struck the hull.

 

I like the flatbar concept. A friend with a wing deck piver added waterstays because the horizontal beams flexed too much. Has anyone measured the drag of slicing a waterstay through the waves?