A Photo & Discussion Forum for Wharram Design Enthusiasts
We went out with my Tiki 21 yesterday in winds from 15 to 20, some 25 gusts. Some chop. We finished with a reef in both main and jib shortly after my daughter took the video.
I had the past week retentionned the shrouds and the forestay.
But after half an hour or so, everything came loose again, and didn't get back the tension on mooring.
Mast was moving in every direction, and leeward shroud was flying.
I do not understand why. I used 6mm (0,236inch) pre-streshed dyneema, and made 60 cm (23 inches) splices.
I would be glad to have some ideas to solve the problem. I am not sure that inox rig will do. Is it possible that the compression on the mast make it shorter? Is the mast too flexible?
Any advice will be welcome, I think I did something wrong, but don't know where.
Eric, While it might be the mast itself, I can think of few more likely possibilities:
There are a variety of Dyneema lines available, some less prone to stretch and creep than others. What specific line did you use? There is even some variation in stretch/creep in the various heat-set, pre-stretched dyneema available. The heat set, low stretch/creep lines are all very expensive, far more so than the 'regular' dyneema.
For sizing, according to Coligo, who seem to have done the most research, the line must be sized for the equivalent stretch to the recommended wire, not for strength. They have all the sizing information on their website. 6mm seems like it would be good for the Tiki 21 but you might check.
But I think this is the most likely based on your description: Did you 'set' the splices by pre-loading them before installing them? The typical dyneema splice should be loaded before use to set the splice. I don't know what the recommended set load is for 6mm but for 9mm it is around 1000kg. Not so easy to attain this force without some effort. There are a few videos on uchoob showing this process.
I wouldn't give up! From the reading I have done, with the right line size and type and pre-loading, the stuff works extremely well and has a number of advantages over wire.
Let us know how this progresses.
Thank you Axel,
Here is what I used.
I ordered this rope:
Samson AmSteel Blue, 3/16", Black, Foot
I was not able to set the splice by preloading but I made quite a long splice, 60 cm.
So, that is not the most creep/stretch resistant line but at 1% stretch with 30% load should be fine. I suspect it is the pre-loading of the splices Eric. One way that it can be done is with an inexpensive hand winch like
Of course, made in China but you can probably get something like this, or a trailer drum winch. I have seen the bigger line splices pre-set with a car but that seems imprecise at best and a bit risky with 6mm line. I don't remember what the average increase in length is but I'm sure you can find it on the Colligo site.
Bonjour depuis la France
j'ai réalisé mes haubans enVectran qui n'ont pas de fluage, mais un allongement de 1 à 2 % si mes souvenirs sont bons, Le diamètre que j'ai utilsé est de 6 mm. dans un coup de vent mon haubanage est devenus mou, la raison était que le capelage en bois de tête de mat avait été fendu par le hauban. Je n'avais pas fait un fourrage suffisant. A vérifier aussi les ligatures des coques,
Here's a rough interpretive translation in case it helps someone:
Hello from France
I made my rigging with Vectran which has no stretch (sic), but around 1 or 2 % lengthening if my memory serves me well.
I used 6mm diameter. In a squall my rigging softened up, the reason was that at the wood masthead area the rigging creased/split the wood. I hadn't provided enough protection. Also you need to check the lashings on your hulls.
ref splicing dyneema:
I used 72 x diameter. 72 x is the factor I have most commonly found in recent advice, these things are changing all the time of course.
I was@Jimmy Green's with some kit of mine a couple of weeks ago, they said it was ample, but they do lock stitch their splices.
As seen from the video this amount of loose rigging cant be due stretching of the ropes. Thing is, even when you do not use dyneema and when you lash many rounds and then few clove hitch knots over lashings, it should not give so much looseness due strain...
What I could think of now is that you didnt tighten enough the forestay lashing before you went out to the sea... at least I tighten it until boat started to moan... (ofcourse do not brake the boat while doing that, but there should be significant amount of tension produced).
Another reason I could think of is that the loose rig can be occurring because of crossbeam lashings – they arent good enough and let the hulls move, so when the forestay gets the load from the wind, hulls get "toed in" a bit, causing the looseness of the rig eventually...