Wharram and webbing beam straps

The current line is double braid polyester, so jacketed. If I try a single wrap of dyneema, it will be straight 12 braid and I will put a chafe wrap on the area under the strake.

The block under the beam is a wood support block. They are added when the boat hulls are complete in whatever thickness is required to get all the beams level.

 

...I well remember the looks of the guys anchored next to us, when, for demonstration, I started jumping up & down on one of the sterns at the right frequency....the flex looked frightening! this was our Tangaroa Mk I with the original brackets, but I had added rubbers under the beams as well, so maybe the flex was a little less than without these. (OTOH I had widened the cat a bit...)
On hard beats upwind (e.g. Red Sea) I always marveled that the boat did not simply come apart. The stress on the connecting structure must have been considerable (I had put a cutter rig with an aluminium mast on her, so upwind was not too bad...for a a Wharram, & she could be driven a bit...)
(The going was WET then, WET!)

 

...the lashings give me the heebie-jeevies! Just imagine what a nasty minded guy with a carpet knife could do!

 

Yes, my Tiki is wet to windward, and I'm very glad a friend made me a decent cockpit surround. The front plastic windscreen makes all the difference for comfort, even if the Wharram purists decry the aesthetics.

As for the vulnerability of the lashings, I've never thought of that. I suppose someone nasty enough could do it, but then they could cut my dyneema stays too. I don't think its likely enough to worry about though.

 

There is a poly-kevlar line that is lower stretch than just poly. Maybe you could try that.

It may be different, but my canoe uses rubber lashings for the outriggers. If I tie it wrong (shoestring on top one pass under gunwhale) it does not work well. If done correctly, I am able to stretch the rubber lines a lot and the stretch actually makes the connection better as the line wants to return to normal (elastic). This is done by wrapping the lines through the hole under the gunwhale first and then I can pull on the lines like mad and shoestring tie over the first super tight crossing of the aka. The line with dyneema won’t be able to be stretched and the line won’t work back to its equilibrium (much).

Maybe the elasticity of the poly rope is part of what makes the connection work. I recall the old video. Those guys were really working that line to stretch, hanging all their weight. And for some reason, three guys were doing it, not even 2, iirc.

I think you are on the right track modifying the lines, but not sure if dyneema will stretch enough, or pre-load.

Maybe this elastic feature was as important. A low stretch line may be less elastic and solely rely upon the original effort.

I don’t know the elastic properties of dyneema vs your ccurrent rope, but jist wanted to touch on the subject as the rubber lashing elasticity is what make my outrigger lashing work so well.

It will be interesting to hear what happens.

 

Fallguy,

Thanks, you've given me a couple of ideas. I have a little kevlar/kevlar dbl braid and will experiment with it. I have a source for more at a very decent price. Only problem with it is that you can't melt the ends and have to seize them.

The other idea was from your description of the old lashing video and you knotting the rubber lashings on your canoe. It may work if I can take a single lashing and either cross it or even knot it to hold the tension in each wrap. I'll have to get help for that. Will need to find a knot that will work to lock it without losing tension.

I still think webbing and a mechanical tensioning device would be better, but unless I can find a buckle that will hold 40KN, there's not much future in that. There's plenty of crazily strong webbing available (20mm 40KN) from highline suppliers, but none of the webbing buckles are rated for more than half that.

If I knew whether the 6 wraps of 8mm double braid were for strength or for controlled elasticity, I would know if I could use the 22KN buckles.

 

I think that is going the wrong way. Say you have a line or web that you can only stretch 1mm under the maximum tension you can apply. Then the beam only needs to move 1mm, say by compressing one of the surfaces on which it rests, for your lashing to unload completely and be free to slip. If you have something that you can stretch 10mm, and tension is proportional to stretch, then 1mm movement still leaves you with 90% of the tension. Lashings should have stretch, you should use that stretch, just have enough line that you don't need to stretch your line close to the breaking point.

For a lashing, I would avoid dyneema or kevlar like the plague. Give me a stretchy rope, and enough wrappings that I need to stretch it only to no more than about a quarter of the breaking strength, giving me a safety factor for wear and sunlight.

 

With the arrangement shown in the picture you can't use webbing, you would need wider blocks on the hull and longer beams to accommodate its width.
The only way to get rid of the lashings without changing the boats structure is with custom steel hardware. That could be a pair of U bolts and a pair of turnbuckles to tension them, or custom lower and upper straps connected via long bolts.
Here's what you could do instead:

1. Buy a bottle of liquid soap. This will serve as lubricant.
2. Find a sturdy piece of hardwood about 3-5ft long, 3-4 inches thick. Think pickaxe handle. Put a notch close to one end and make it comfortable to grab with your hands without getting splinters.
3. Get at least one helper, the heavier the better, arm him with a hammer or similar.

Order of operations:
Dump the rope into a bowl filled with liquid soap, work it in with your hands. Anchor one end to the appropriate height for frapping as vertical as possible (tie the loop to another rope that goes to a fixed point, simplest is to pass it under the hull and tie it to the beam). Pass it over the beam, give the free end a few turns over the wood piece and pull hard using the wood as a handle. Now get the helper to put the hammer handle end on the rope on the corner of the beam and lean on it with all his weight (he is now a human clamping device). Repeat the pulling and clamping process over every corner the rope goes around until you have your 6 wraps. Begin frapping by threading through the loop as usual and under the opposite leg of the wrap. Then take the big piece of wood, put the notch over the wraps where the loop is, wrap several turns of the free end over the wood handle and use the whole contraption as a lever to squeeze the two legs of the wrap together. Get the helper to pin the rope against the hull, take another turn of frapping and repeat. Hammer the wrapping legs while applying tension with the lever.
Obviously the longer the lever the easier it will be to properly tighten the wraps. Use enough frapping turns to make sure all wrapping turns are bar tight. If they are not, undo everything and repeat from the beginning.
Last step is to wash out the soap from the line using plenty of fresh water.

It's absolutely irrelevant if you use low strech polyester, dyneema or a combination to lash the beams, if the wrapping isn't bar tight it won't work.

 

I hate the strap idea. Sure, I’m not a Wharram guy, but here is my reservation:

Suppose you find a suitable ratchet strap. All the forces present on the boat using a dynamic system are not there using a system with zero give. So, something else might give. It isn’t my job to know or determine the next failure point in the system, but one exists. Would the ratchet strap break before the support structure? Do you know the uts of the lashing blocks? See? As a builder, I don’t like to make the nut so strong the bolt shears easily, or pick any system.. you don’t want to design without respecting the other components.

A good example in boats is when you tie a rope to the boat. The cleat really needs to be stronger than the rope. When a ship is tied to a dock; you don’t want the point of failure to be the cleats, etc. Saw a few videos of cruise ships snapping ropes. That is the desired failure mode.

Anyhow, didn’t want to say it, but not a fan of the ratchet here.

 

careful with kevlar! Does not like bends! (I could pull out the kevlarcore of a genoa halyard in 6" pieces,...meters of it!)

 

Thank you everyone for the input.

I had hoped to find someone who had converted to a system that would be easier and more efficient. Being solo, the wrapping method is not easy to do, and since they work loose frequently, my technique is clearly not working.

I did read of someone doing a T38 with webbing and brackets many years ago but that seems to be lost.

Rumars is probably right about doing the wraps the way he describes, no matter what line I use. I'll try that first, though may review the Polynesian 'cross-over' video to see if that method will work for locking the individual wraps. Rumars, is the soap to allow the ropes to slip over each other?

It will have to wait until I have the boat in the yard for new bottom paint. I think it would be difficult to do that degree of tensioning from a dinghy.

If they still loosen after that, I'll have someone make me U bolts and make the damned thing solid!

 

Yes, the soap is to lubricate the ropes and allow them to slip while frapping. If you're trying this alone, lubricate only the part of the rope that goes into the wraps, and use a big clamp to keep tension while threading the loops.
Tightening with the lever works even from a dinghy, but of course it's more comfortable on land. If the rope slips on the lever it can be helpful to drill a hole trough it and thread the rope trough it before wrapping it around the lever, but of course this lenghtens the procedure.
Another thing I have seen done is to use an additional separate rope for frapping, you tighten one loop on the normal frapping, lock it, then tighten the other frapping, and so on.
Thing is, the lashing has to be tight as a guitar string, that's the only way they will last.

If you're willing to do some work on the boat, the easiest way is to epoxy two hardwood blocks on the inside of the hull, corresponding to the lashing blocks on the outside. Then you drill a big hole trough the deck and this blocks and insert steel bars with straps top and bottom, secured with nuts. This results in the least amount of metal fabrication.

 

Sounds like you have a fair amount of experience with Wharrams. I appreciate the info. I will keep the idea of the U bolts straight through the deck as a possible back up.

 

Just some crazy outside-the-box thinking but what did the Polynesians do years ago limited with such primitive technology?

 

Bluebell, I don't think anyone truly knows. There are modern examples of lashed boats still in use and traditions of construction, but by the time the Europeans got to Polynesia, the age of Polynesian exploration was mostly over. Cook saw large voyaging catamarans but no one recorded much detail. There is little record of them after that. The climate on tropical islands is pretty unfriendly for preservation of wood and natural fibers, so there's a very limited archeological record. No written Polynesian language at the time either.

I think when the resurgence of interest in the 60s and 70s, and big voyaging canoes were being constructed, a lot of it was based on limited drawings and assumptions from old traditions.