Has anyone used spectra/dyneema or similar hi-tech ropes to lash their crossbeams to the hulls? I vaguely remember a post years ago saying strength was great but lack of stretch caused problems. I'd appreciate any input as I'm about to buy 200 metres of rope for my Pahi 42.
Cheers,
katfish
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Wed, 02/12/2009 - 12:36
#1
Pahi 42 Cross beam lashings
Mon, 07/12/2009 - 23:54
#2
Re: Pahi 42 Cross beam lashings
The lashings are supposed to stretch a little. It seems to me that the ability of wharram catamarans to flex is an advanced feature of the designs. It would be easier to design, build and assemble a boat that didn't flex, but if you get the boat put together right so it flexes smoothly (many of them are not right and flex too much or noisily)then you've got a better boat. High tech line for the lashings would not just waste a lot of money but eliminate this advanced feature, and place greater loads on parts of the boat than the design calls for.
Tue, 08/12/2009 - 23:24
#3
Re: Pahi 42 Cross beam lashings
Thanks for that Glenn, you confirm what my thoughts are and what I may have read some years ago. I have now bought the prestretched poly braidline.
Katfish
Sun, 30/01/2011 - 19:27
#4
Re: Pahi 42 Cross beam lashings
The ability of the lashings to have a minute amount of give to them is indeed a defining feature of the Wharram designs. If you look at cats with the beams rigidly attached you will usually see damage over the years. This will range from gelcoat cracking to the bolts shearing to the aluminum tubes cracking. This is because the shock loads of the beam to hull connections are extremely high.
But on the other hand any flexing between the beams and hulls will also affect the rig tension. This will absorb energy and result in lost speed and pointing ability.
I tie my lashings using double braided polyester line. This has, for a modern line, a fair amount of stretch(%1-3 depending upon load). Then I will make my frapping turns with a spectra line that is one size smaller in diameter. I take the tail of this line and attach it to another beam with a 4 to 1 handy billy and pull it forever more tight. This gives me very tight lashings. I can still go onto one bow and wiggle the boat and see/hear some movement, but it is a very small amount. I have been unable to get my lashings tight enough to become completely rigid. The tightest I can get them seems to be just right. Deliberately tieing loose lashings with stretchy line will result in a soft rig without the ability to keep any headstay tension. This is my opinion and I am sure that others will have different thoughts.