One of the jobs completed before the TBF race was replacing all of the beam lashings on Little Cat. I had replaced the rear beam lashings after the beam block repair, but had left the others until later. I learnt with the aft beam job that the lashing lines are differently loaded - the inboard lines are way more stressed than the outboard lines. So I used 1/8 dyneema line inboard and regular low-stretch line on the outboard lashings.
The plans specify 5 full turns of 3/16 low-stretch. I tried 3/16 dyneema but it was too bulky, and the 1/8 fitted well. The breaking strength of the 3/16 Robline low-stretch that I use all over the boat is 1,230 lbs, whereas the breaking strength of the 1/8 amsteel dyneema is 2,300 lbs. Another advantage of the dyneema is that it is very abrasion resistant, see picture below of one of the old low-stretch nylon lashings that I replaced - I don't want this happening when I'm out in the ocean.
One of the concerns I had with using dyneema is that it is hard to tie a conventional knot - it is very slippery material. However, once I got things tight it turned out to not be a problem - half-hitches tightened up nicely.
So, the lashing routine is to do the initial windings as tightly as possible using hand tension, and then tie off using several half-hitches.
The boat won't fall apart now, but the next step is to frap the windings to make them really tight. Start by tying a length of line to one side of the windings using a bowline. Then wind the line a couple of times around the lashings and lead the free end away.....
...attach the free end to a purchase - in my case I use the 3:1 from my mainsail cunningham, and anchor it to the adjacent beam or to some other hard attachment point. Then pull hard on the purchase to tighten the frap around the lashings.
Use vice grips to lock the line so that you can ease off the purchase and take an extra winding of the frap and then repeat.
When I'm done, I finish with several half-hitches pulled real tight, and then wind some extra line on so that I have something to work with if I have to attend to the lashing underway (unlikely except for a catastrophic failure). When frapped like this, the lashings are so tight that the boat is stiff and "rings like a bell" (kind of resonates) when I jump up and down on the bow stem (in the water). The dyneema lashings are so tight that I am happy keeping the low-stretch on the outboard lashings so that something will give if I hit something. The use of frappings means that the Wharram hull/beam structure can be stiffened to the extent that it not is not the soft/flexible platform of yore legend.
The plans specify 5 full turns of 3/16 low-stretch. I tried 3/16 dyneema but it was too bulky, and the 1/8 fitted well. The breaking strength of the 3/16 Robline low-stretch that I use all over the boat is 1,230 lbs, whereas the breaking strength of the 1/8 amsteel dyneema is 2,300 lbs. Another advantage of the dyneema is that it is very abrasion resistant, see picture below of one of the old low-stretch nylon lashings that I replaced - I don't want this happening when I'm out in the ocean.
One of the concerns I had with using dyneema is that it is hard to tie a conventional knot - it is very slippery material. However, once I got things tight it turned out to not be a problem - half-hitches tightened up nicely.
So, the lashing routine is to do the initial windings as tightly as possible using hand tension, and then tie off using several half-hitches.
The boat won't fall apart now, but the next step is to frap the windings to make them really tight. Start by tying a length of line to one side of the windings using a bowline. Then wind the line a couple of times around the lashings and lead the free end away.....
...attach the free end to a purchase - in my case I use the 3:1 from my mainsail cunningham, and anchor it to the adjacent beam or to some other hard attachment point. Then pull hard on the purchase to tighten the frap around the lashings.
 |
| 3:1 purchase pulling on inboard mainbeam frapping line |
Use vice grips to lock the line so that you can ease off the purchase and take an extra winding of the frap and then repeat.
When I'm done, I finish with several half-hitches pulled real tight, and then wind some extra line on so that I have something to work with if I have to attend to the lashing underway (unlikely except for a catastrophic failure). When frapped like this, the lashings are so tight that the boat is stiff and "rings like a bell" (kind of resonates) when I jump up and down on the bow stem (in the water). The dyneema lashings are so tight that I am happy keeping the low-stretch on the outboard lashings so that something will give if I hit something. The use of frappings means that the Wharram hull/beam structure can be stiffened to the extent that it not is not the soft/flexible platform of yore legend.
Thanks for sharing it. It is very clear!
ReplyDeleteRegards
Cheers Andres
ReplyDeleteThat's pretty cool "rings like a bell", but I could swear i've read in Wharrams literature that that some motion was expected, or even designed in to the system. I think of the ropes being something like a shock absorber.
ReplyDeleteI aways wonder when I see a Tiki with a solid bimini mounted to the hulls, if there would be some damage at the mounting points down the road.
Thanks for the post, interesting thoughts swirl.
Hi mgtdOcean,
ReplyDeleteI think that you are right. It is tight with the frapping, but its relative (not like bolts or a monocoque structure). I think it will still "give" taking the ground or under loads.
Hello- I have just found your blog and have enjoyed reading it, many thanks.
ReplyDeleteMy own beam lashings on my 31' I tightened in two steps:
Firstly I used a chain winch attached to the end of the line and applied each turn under tension (only partially possible as you are turning).
Secondly I made a rubber pad to use between the head of my Estwing claw hammer and the beam. I wrapped the frapping line (trapping itself) around the hide shaft of the hammer then applied the hammer for leverage with the pad under the head.
At the same time, in both applications I used a large speed cramp vertically on the beam to trap the bindings at each turn.
I discovered the latter technique on my way, and the later bindings were better than the first ones.
So I would say that I'd rather use a strong speed cramp with hard rubber jaws on the line than mole grips, for example.
From what I have read, the pro builders aim for the tightest possible lashings especially with dyneema.
My platforms are all lashed together with dyneema- virtually no mechanical fixings. But I used a high quality low stretch conventional cordage for the beam lashings. I use the hammer with the pad for all tensioning:
I used it to do the rudder lashings also (dyneema). These took ridiculously ages to do(preboring for epoxy then reboring epoxy plugs etc)and I think I would make/use conventional pintles in another life (I haven't got enough lives left to build another boat).....
I have a Tohatsu 20 hp xxlong, don't think they make them any more.