Wharram and webbing beam straps

First post on the forum. I have found a wealth of specialized knowledge here and appreciate it. My posts tend to be long, but such is my nature... I hope someone with relevant experience or knowledge will have the patience to work through it.

I have been sailing my Wharram Tiki 38 solo for about 2 years now. The recommended method of lashing the beams has been problematic, basically a major pain.

The biggest problem seems to be getting reasonable and equal tension on the multiple wraps before doing the frapping. I have tried lanolin so the wraps would slide over each other, and even a come-along to tension them. After many attempts, I have not found a method that works well. One or more of the lines is always looser. This works its way out in rough seas and they loosen up. After any multi-day rough passage, I have to retighten them.

Plans call for six wraps of 8mm polyester double braid. It's rated at about MBS 3000lbs, SWL 400lbs per strand. That gives a gross MBS of 18000lbs and a gross SWL of 2400. Given that the strands are never equalized, I suspect the actual figures are significantly lower.

A two inch polyester strap is rated at MBS of 12000lbs, the ratchet mechanism at 5000lbs. A 2 inch dyneema strap has plenty of strength and I am pretty sure I can make a tensioning bracket that will be adequately strong, but locking buckles all seem to be rated significantly under this.

My initial thought was to make a simple two-part bolted bracket of Aluminum angle that could be used to pull the two ends of the webbing together to tension it. This would require a locking buckle on at least one end so the initial adjustment can be done by taking up the slack and locking it off with the buckle. I have not been able to find buckles that are rated for a load similar to the six wraps of line.

Two inch webbing with a ratchet would seem to be easier still but with both possibilities, my concern is the strength of the webbing and buckles. Will the friction of the webbing around the beam significantly decrease the actual load on the buckles?


Has anyone with a big Wharram or other larger multihull succesfully used either webbing or ratchet straps? If so, please share your experience. Otherwise if anyone can comment on the various load parameters and give me some insight, I would appreciate it.

 

I used 1-1/2" ratchet straps for connection from float to beams on a 27' proa some years ago. I really liked the setup, easier than lashing and no creep. My main concern longtime was was ratchet material, stainless steel ratchets weren't readily available.

 

Thanks Skip, good to know.

SS ratchets are easily found now, though how 'stainless' they are is another question I have a few smaller SS ratchets and a couple are showing some rust after just a few uses. Knowing that, regular freshwater rinsing and applications of corrosion spray are probably required.

 

I think the original Wharram system with metal brackets and rubber was simpler. I sailed a Tangaroa 34 for a while. Have you consider it?

 

Thanks Gonzo. I'm really looking for a solution to the problem that doesn't require modifying the boat if possible. Although I haven't looked for many years, I seem to remember the classic beam mounts required bolting a base down?

I have thought about another possible solution. My standing rigging is all dyneema. The stays are tensioned by a multi-wrap thinner cord through a hard eye on the stay and a shackle on the chainplate.

8 or 9mm dyneema would be more than strong enough, even in a single wrap. After loading to remove construction stretch, there would be very little subsequent stretch. Even if they did loosen, re-lashing the few wraps through the hard eyes would be simple.

If I made a covered dyneema strop with hard eyes at both ends, long enough to almost go twice around the beam, I might be able to use the same multi-wrap system to get the necessary tension.

I may experiment with one or two of these as I'm in Grenada for the hurricane season and specialized items are a bit of a pain to get hold of.

 

The design on those boats assume a flexible connection. Dyneema has very little stretch compared to polyester and may create too much stress at the connection. The lashings I've seen are wrapped not too tight. Then they are tightened by lashings at 90 degrees. From your description seems like you are trying to pull from the lashings to tighten them. I don't think it is possible to get even tension like that.

 

No, I'm not trying to get the real tension in the initial wraps, just to get them evenly snug. All the real tension comes from the frapping turns you wrap around the main lashing.

When I apply the frapping turns its easy to feel a few strands are looser than the others. My guess is that this laxity works it way into the entire lashing.

It may just be the nature of the beast, though I haven't heard other Wharram sailors talk about this. Mine work loose pretty much after any windward sailing in even moderate seas. If that happens early on in a 2 or 3 week voyage, theres not much that can be done about it.

You may be right about the need for flexibility but I do know that after a re-lashing, whatever movement there is is barely discernable.

 

With the original brackets and rubber the bows would pitch over 10 inches off from each other.

 

I apologize, I’ve only seen it done in videos and probably unworthy of any remark. I seem to recall seeing a video with the fella preloading the lashings with his entire weight on wetted lines and maybe he was also using a puller. I apologize, spent 15 minutes looking for the video. It was 3 islanders working together iirc.

@oldmulti may have some advice or even know the video to which I refer or perhaps @tane

I think the dyneema has been tried on the inner.

ps _ this is NOT the way I saw it being done on the video; was totally different with an overwrap, I admit being out of my league, but hopefully can start some chatter, lashing starts at 3:50

 

Thanks Fallguy, that's actually quite helpful. It reminded me of the video, which I saw somewhere years ago. If its the same one, it was a traditional craft, and he was demonstrating a locking pattern for the individual loops of line.

That makes me realize that I'm probably on the right track in wanting them tight. Wharram really doesn't say anything about the lashings except that they should be 'tight' and that you should 'pull hard' on the frapping turns.

The only more detailed instructions I've seen come from Boatsmith, who was a Wharram approved builder in Florida. I don't think he's in business any more. In a video on a Tiki 30 build, he said they should be so tight as to allow absolutely minimal movement.

My big question now is an engineering one. Just how strong do the webbing straps and components need to be to handle the loads currently taken by the 8mm line?

Many years ago, pre-social media days, I did see a blog from a builder who chose to use webbing from the start. I've searched and that seems to have dissapeared.

 

Yes, I believe we are referring to same video, glad you saw it. I seem to recall they ran for years under the lashings.

I think the question may go beyond the webbing change. Just to be clear, if the ‘system’ is setup for lashing with rope; then using webbing might require reengineering of the entire connection.

There are a few people on this forum who are capable of calculating the forces on the vessel, I’m not one. To be honest, I don’t quite follow how you get from lashings to webbing.

Maybe volunteer all the specs of the boat and some pictures of the area and drawings of the plan and see if anyone offers to help. I must disqualify.

Boatsmith has retired I believe. He is a great guy.

 

It should be equivalent. Both rope and webbings have a rating which makes it easy. However, webbing will fold and wrinkle when wrapped, so the fibers will have uneven loading.

 

He wants to use a single strap. But to do so would require remodel of the hull connection as he suggests.

OP-I suggest you call John Franta at Colligo Marine and see if he has any suggestions before you modify the boat.

 

The Tiki 30 was designed to use straps as it was a trailer sailor. I would talk to Hanneke Boon contact details on the Wharam website. Apparently Spirit of Gaia went around the World without needing to tighten ge lashings. I would avoid dyneema. There is a you tube film about an old Crowther ply cat that broke up mid ocean. They lashed her back together but the dyneema literally sliced the hulls up ply glas and all. I guess dyneema lashings on a wharram may just slice the beams or the ply.

 

I think that the first step is to determine if the perceived problem is actually a problem. Wharrams are supposed to have loose connections.