Rode Loads

[Brion Toss]

Hi all,
My friend Josh Kout forwarded this link: http://alain.fraysse.free.fr/sail/ro...ces/forces.htm, which concerns the behavior of different anchor rode configurations. Wonderful charts, down where he discusses static and dynamic loading. Dense-ish math, but you can read on either side of the equations and get the gist. The only down side for me is that he recommends a very weak rope/chain splice.
A very nice companion piece would be: http://www.yalecordage.com/pdf/anchoring_tech.pdf, in which Yale Rope describes how different rope constructions deal with energy. Short form: single-braid is where it's at.
Fair leads,
Brion Toss

[benz]

Does the construction of Yale's Brait differ from Regatta braid? It seems they're both 8-strand braided--not sure how many different ways there are to braid 8-strand. And if they're similar, can you splice them the same way?
Also, I thought the anchoring discussion neglected to take enough account for current/wind at opposition. My pilot cutter is far more affected by current than wind, having a huge wetted surface, so that even a moderate tidal current will hold her sideways to a moderate breeze, and a six-knot current held her broadside to a gale-force squall one time. I'd like to know how much force my boat exerts on a rode when the current is roaring past at near hull-speed.

[Ian McColgin]

Cool sites. Thank you.

[Brion Toss]

Originally Posted by benz

Does the construction of Yale's Brait differ from Regatta braid? It seems they're both 8-strand braided--not sure how many different ways there are to braid 8-strand. And if they're similar, can you splice them the same way?
Also, I thought the anchoring discussion neglected to take enough account for current/wind at opposition. My pilot cutter is far more affected by current than wind, having a huge wetted surface, so that even a moderate tidal current will hold her sideways to a moderate breeze, and a six-knot current held her broadside to a gale-force squall one time. I'd like to know how much force my boat exerts on a rode when the current is roaring past at near hull-speed.

Hi there,
Oh, there are so many ways to do braided rope. For starters, Regatta (and Mega Braid, the nylon equivalent) are 12-strand. But even if they were both 8-strand, there are lots of combinations of twist and helix angle, and these differences can translate, not just to different rope behavior under load, but different chafe-resistance, "picking"-resistance, and how they are spliced. Follow the instructions for the specific rope.
As for the effect of current and wind, I am far from being qualified to discuss aero/hydro-dynamics, but it would seem that the upper limit from either, or both, would be similar. The best data I have is from vessels sailing on their moorings. They accelerated as they yawed, and this would generate hull resistance in the water, as they began to tack, as well as wind resistance. And these were accelerated loads, which would have pushed things even higher.
One of Josh's points was that his boat is quite massive, and the vessel's inertia should be a big factor in the selection of rode type and size.
Fair leads,
Brion Toss

[benz]

Ha ha: most of my cordage is Regatta braid, and I still managed to forget that it's 12-strand. I do like how it splices--someday I'd like to have braided anchor line. Just have to wear out my 3-strand first. A couple more hurricanes like Irene might just do it....

[marujo.sortudo]

Being someone in the process of investigating replacing the 3-strand on my primary rode simply because it's too short, I've started taking a good look at brait. The extra elasticity and the compact stowage both appealed to me. I started modeling lots of different scenarios in Alain's 3-strand spreadsheet (dyn_mix.xls from his page referenced at the top of this thread) to see how different lengths of chain would effect ideal scope at different depths, etc. as I was also considering slightly increasing the length of my chain. I was curious to see how the published info for brait would effect the theoretical model, so I emailed Alain to get his thoughts. He was kind enough to work up some spreadsheets with brait's properties in the dynamic model and we both ran some scenarios through it. It would seem that brait would reduce dynamic overtension somewhere in the range of 15-30% (mostly close to 20% depending on conditions,) and cause a slight reduction in angulation for the same scope (I showed about 0.2-0.3 degrees.) Of course, that's no substitute for real world experience, but seems reasonably compelling for my rode choice, even though it looks like it'll cost me 32% more. Anyway, Alain says he doesn't have any plans to post the brait spreadsheets on his site, so if anyone wants a copy of them to run your own scenarios, please PM me.

Colin Sarsfield
S/V Mimi Rose
Blue Hill, Maine