A Photo & Discussion Forum for Wharram Design Enthusiasts
Hi everyone! I am sure many of you have some good ideas about this - how tight should the lashings for the standing rigging be? I have a Pahi 42 with conventional rig (ie bermudan cutter with boom). I am using dynema rope for all the lashings from shrouds and stays to chainplates etc. What I am puzzled by is that dynema doesn't stretch (or so I am told..) but I can't get my rigging to stay taught. I am thinking that possibly the problem IS the dynema - that because it doesn't stretch it is difficult to get it really tight in the first place. Anyone else using dynema, or any suggestions?
Thanks - Andy
Hi Andy. I'm not expert on this but I think that, Wharrams catamarans having a degree of independent pitching, require some flexibility in the rigging too. Dynema isn,t stretchable but, lashing and knots do give somewhat when taught hard. I would in fact live a good slack to all rigging in order to avoid strong compression loads to the mast and supporting beams.
The rig does not need to be bar tight. Dyneema does stetch or settle a bit.( I used it for beam lashings and was disappointed at the stretch, which it does not recover and so went back to using prestretch stuff. At least when it does stretch it recovers again.)
What I did was sail close hauled on one tack, take up the slack on the leeward shrouds and then tack over and do the other side. Seems weird to be undoing the lashings holding your rig up while sailing offshore, but it works and so long as you dont slip overboard while doing so is quite safe! On the T38 there are two side shrouds for the foremast and if you do one at a time the other is always there should something unexpected happen. The main mast aft shrouds take no load on the leeward side.
If you have to go real tight, do a couple of turns on the lashing and then take the tail and attach it to the mainsail halyard and sweat it up that way. All you might be doing though is flexing the beam the mast is resting on!
I used to have the lashings very tight, even used the main (and only one) winch with a halyard to tighten the rigging... the tightening point was till right before I saw the mast bending... but it proved to be wrong as later my experience was. with that method you put unnecessary stress on the masts, since they will bend naturally under the normal use (they are just attached to the top, so nothing is avoiding the mast to bend under the wind forces. I noticed that the lee rigging was always lose, no matter how tight I was making the lashings, it was always lose at the lee side (which is to expect anyway, but the funny thing is that they were lose always) so I observed the mast, and I saw that the mast was much more bent than when I was using a less tighten lashing. Its also true that i did not made a 'scientific' research by taking notes of the wind / sea state/ sail combination . it was just a guess and figuring it out thing. from that point I was loosing the lashings to a 90 or even 80% of what i was doing before and seems to work well.
Note: after the sailing season I took the masts off and observed that the rigging at the top was pretty wear out , and even one of the ropes that carries the block and is fixed to the top, was in so bad condition that i was surprised that it didn't broke.both wooden mast had the ropes 'printing' on the top, which is an evidence of the high pressure and stress that this part of the mast is supporting. each masts foot was also in a bad shape, even though they rest in a nice leather pad.
After 8 to 10.000 nautical miles done with the boat I start to understand how things works better. This is not a sloop where I used to have the rigging like violin strings, its pretty the opposite, of course common sense is necessary. the point that I like is the one that holds the masts in site without noises and without any movements in the mast foot, and the front stay decently straight while under stress. If I hear noises, either there is too much sail on , or the rigging needs to be tighten. when on passage in open ocean, we stop the boat for 15 minutes at mid afternoon to make a general overview of the entire boat, bilges included. that resulted in a good practice and avoided bigger damages. we always found something to be fixed and being stopped makes any job MUCH easier, faster and less risky for us and the material.
to finish I will tell that i like to sail close to the limit , and I always fly the most sail that I can, sometimes too much.
I have a classic with the cutter rig and dynema lashings and I tighten them up as much as I can. The lee shrouds do get loose and the forestay(s) are never tight enough. I'm redoing a couple of crossbeams this summer and notice with one of the crossbeams out, the rig is much looser. Then I realized that the mast load in the center of the crossdeck is trying to force the center of the beams downward and the result is added slack in the rig. When I remount the new beam I will be making the rig loose to allow the beam mounts to be tightened without resistance from the rig. I use running backstays when adjusting the shrouds so the mast doesn't come down...
On my tiki 26 with all synthetic standing rigging, I used regular dyneema for the shrouds and bridle, but used dynex dux for the forestay. I get the rig as tight as I can by leading the halyards to the bows first, and use a frapping line on the halyards to pull the mast forward against the shrouds. Then I get the lashing between the bridle and the forestay as tight as I can. Then I lead the halyards to the sterns, put the frapping line on, pulling aft on the mast. Then I take any slack out of the deadeyes on the shrouds. I just use my strength, such as it is! No winches.
The dynex dux forestay does not stretch, and so keeps a steady tension in the rig better than a plain dyneema forestay.
I've been trying that way too, but the problem is that the mast (in my case a wooden one) will stay bent to the wrong side if you tight it too much. after you finish the sailing day you should check how the mast look like , in my case it was bent... i guess that the tightening point would be to a point where you still feel the lee rigging still a little bit lose.
it also depend on how much wind and how much sail you have on, of course. I had all sails up and 17 knots wind at least. this makes that the mast bend a lot (more than 4 inches in the midpoint) under those conditions.
The reality is that what I was doing was taking up the slack, but not creating any real tension. So that when we tacked over there was still a bit of slack to be taken out on the otherside. For me it gave me the right amount of tension. To get the masts up straight I simply eyeballed it and whichever side needed the greater tensioning, would determine which tack I began with! If the mast top needed to move to port a tad, I would start on starboard tack.
Hi all - thanks for your comments! Just been out for a few days sail over to Tallinn so was offline. I like Dave's suggestion to tighten the lee shrouds "a bit" while sailing - I can certainly see that the possibility for over-compensation is there. I have also been thinking that of course with Wharrams the whole boat, hull & rig, are one living system, and of course the tightness of the hull lashings will affect the rig as well, so before I do more rig ajustments I'm going to try tightening the lashings!
Andy, keep in mind that James Wharram is recommending a degree of pitching freedom. He suggests that the bows move one foot to the other in the horizontal plane. Lesser than that, will substantially increase stresses to the all structure.
Hi Raf - do you mean a twist around a horizontal axis going through the central mast support beam (in my Pahi 42's case, ie the short beam)? So for example if port hull was perfectly horizontal, starboard bow would be able to flex to 1 foot above or below port bow? Difficult to judge, but we currently have flexibility in the hulls & beams. We often face very confused seas when passing high speed ferries which make huge wash (more like surf!) and of course as this is not a consistent sea state or swell, it suddenly puts a lot of strain on the rig and hulls when the boat is bouncing around in that soup! I am wondering if the dynema lashings are too unforgiving - as they don't stretch (supposedly). Dynema acts like wire, and certainly THAT is not recommended for the standing rigging lashings. If anyone can recommend a brand of prestretched polyester that they are using that would be helpful. It's difficult to purchase "old fashioned" ropes here now, so I might have to order some online...