Wharram and webbing beam straps

[gonzo]

Wharram was OK with loose connections. He claimed that part of what made his designs sea kindly was that the ends could pitch about 10 inches off from one another.

 

[tane]

Wharram was OK with loose connections. He claimed that part of what made his designs sea kindly was that the ends could pitch about 10 inches off from one another.

my Tangaoa MK1 (rubber blocks as per plan), when jumping up & down on a stern at the right frequency twisted about that-looked alarming & raised some eyebrows on the boat anchored nearby...
loose lashings, that might slip seem an alltogether different matter to me...

 

[fallguy]

My outside observer opinion is that you ought to videotape your work and post a link here of the after 500 miles as well; perhaps someone seasoned will offer you ideas.

 

[BGW]

Thanks Tane, you made the most important point: if they were staying tight and the boat moved about a bit, that's one thing. But they are starting out tight and loosening up, which is quite a different matter and why I consider this a problem.

I am no videographer but can try to film the process as best I can singlehandedly.

 

[tane]

the fact that they are stretching despite being Dyneema seems to indicate, that a critical loading has been exceeded.
The original system - rubber from under tramcar sleepers (no fabric inside) was first improved by me by placing this soft rubber under the beams too (to make the boat stiffer), & the final improvement was replacing all oft this soft rubber by layers of reinforced converyor-belt rubber (discarded on Christmas Island/Oz). Boat was still flexing a lot, of course, even though thze conveyor belt stuff compressed very little. I had increased the beam when building the boat, btw. & put a Newick-style cutter on it (aluminium mast at 50% WL). Sailed pretty good for a Wharram...those were the days...

 

[BGW]

The lashings are not dyneema. Its all to plans with 8mm polyester double braid.

 

[tane]

how about trying dyneema? There are tapes too, btw.

 

[BGW]

Ha! If you read the beginning posts, I started out looking for ideas on webbing and buckles. I found some dyneema webbing that would be suitable for the narrow space where the line loops around at the bottom. (See the fotos to understand that). The issue was finding buckles. The only suitable buckles are for tensioning high/slack lines and are expensive. Since I need 14 of them, it wasn't a realistic option.

There is also the question of strength. Are the 6 loops of 9mm polyester double braid line at ~2200kg per loop required for strength or for the controlled stretch?

 

[gonzo]

Can you use u-bolts?

 

[BGW]

That is an option I have considered. I would probably have long stainless bolts made up or maybe use all-thread, and mount them through plates over rubber pads top and bottom. I think that would be easier than having u bolts made up. But before I do that I will probably try a dyneema loop at the bottom with hard eyes wide enough to take the 6 wraps without binding. At least that way, I can tighten them while sailing. I'm looking at a few eye choices now.

 

[gonzo]

Dyneema will creep with time. This is the data from the manufacturer: Assuming the lines are tensioned to 20% of the rated breaking strength, the line would creep ~0.1% per month and have to be retired in about 8 years.

 

[tane]

I wrongly thought, that below a certain load Dyneema would not creep...I stand corrected!

 

[HelmutSheina]

I had 4mm Dyneema on Wharram rudder lashings but they work better not so tight.

 

[tane]

entirely different application...

 

[HelmutSheina]

Yes agreed, would not have it on beam lashings.