Rigging loads for T38

[Jamie Rohan]

Hi all,

I am about to commit to a Dynex Dux rig for my Tiki 38 but I want to be sure about sizing.

Can anyone tell me the design loads for the standard Wharram rig for this boat (that is crab claw soft wing schooner)???

Thanks

[kim whitmyre]

Jamie, what I did on my tiki 26 was look up the breaking and working loads on the 5/32" SS wire specified in the plans. Then I did the same for dyneema: I ended up using 1/4" dyneema for the shrouds, and 3/8" for the forestay and bridles.

The breaking load for the 1/4" Amsteel I used is near 6700 lbs, compared to the 5/32 SS wires' breaking load of 2100 lbs. The 3/8" Amsteel breaking load is near 14000 lbs. Amsteel Blue is stronger. And Dynex Dux (heat-treated SK-75 dyneema) is even stronger. Dux is almost as stiff as wire, and I have heard that while stronger, it is less forgiving: almost like wire. I'm not so sure that a Wharram needs Dux, not that it wouldn't work.

Here is a comment from a rigger on Sailing Anarchy:

"3/16" DSK75 dyneema is around 5800# breaking where as 3/16" vectran around 4750# and 5/32" 7x19 is 2100#. I think the 3/16" Dyneema is a better choice; higher tenacity, higher strength, better UV. And because you would be working at a smaller percentage of breaking strength, compared to vectran, creep becomes a smaller part of the problem especially on something that is easily adjusted.

The key to making this strop is to prestretch the line; because the dyneema fiber is so slippery, it takes a very high load to remove the constructional stretch. Once you do that, you will find that dyneema and vectran "feel" very similar, in terms of stretch."

I prestretched my rigging as best I could, and still tightened it 3 times after the initial installation. What this means is you have to allow for this by making your synthetic rigging shorter than the wire rigging . This allows for the what the rigger says above about the constructional stretch, namely, that the rigging will get longer as the constructional stretch is removed. If you made it the same length as wire, you would not be able to get the constructional stretch out: slack rigging!

Here is a shot of my starboard shrouds and dead-eye lashing. The lashing line is 3/16" Amsteel.

I'll post a large shot on the main page for a better close-up view.

[Jamie Rohan]

Thanks for your info Kim

"what I did on my tiki 26 was look up the breaking and working loads on the 5/32" SS wire specified in the plans. Then I did the same for dyneema: I ended up using 1/4" dyneema for the shrouds, and 3/8" for the forestay and bridles."

I don't have plans for the Tiki38, so I was wondering if anyone who does could give me idea what they suggest for the design loads on the rig, and suggested wire sizing/working/breaking loads.

[kim whitmyre]

Jamie, I'm sure some of the Tiki 38 builders will chime in here soon. Are you working with a rigger, or do you plan to do the splicing work yourself?

[Ron Hall]

The wire size specified for the T38 is 1/4 inch for the shrouds and 5/16 for the forestay. I made all of mine 5/16 stainless 7X19 wire (7X19 so the deadeyes could be spliced in). The 5/16 wire has a breaking strength of around 3000 kilograms (6600 pounds) as I remember it. I don't know the safe working load for the wire, nor how much (if any) allowance was made for deterioration of the wire over it's life. I also don't know the loads on the rigging, but you could get some idea just by using half the weight of the boat being lifted through the rig geometry and dividing by four. (I'm guessing this will come out to be about 2500 pounds for a ten thousand pound boat, but I haven't actually gone through the exercise.)

So I would size the soft rigging to have a safe working load of around 3000 pounds and a breaking strength of around 10,000 pounds, and use whichever is larger. This is certainly overkill, but I don't know what the deterioration of the synthetic fibers are to UV and chafe, and it also allows for the unknown, as there simply isn't as much data on the performance and problems of soft rigging as there is on wire. I know how wire fails and what early signs of wear and failure are; I don't know what this looks like in soft rigging.

It might also be worthwhile to consult a rigger, preferably someone who has experience wil the soft rigging; even if they don't have experience with the fibers, they can do the load calculations. It might also be useful to consult the manufacturers of the fibers and the line in sizing the line to the load. The tech reps I've dealt with have mostly been helpful and generally unbiased.

I'm curious about using soft rigging for the forestay. Are you using a roller furler or a jib with hanks? I would worry about the wear of the hanks on the line, and wonder what you know about that. I intend to replace the wire on Mouzzer with soft rigging and add a roller furler in a few years, so am interested in the discussion.

Ron

[kim whitmyre]

Ron, re the hanks:

These are not hard to splice up yourself, but they can also be purchased in different sizes at Colligo Marine.

If you look under my photos, there is a shot looking up the forestay that shows these soft hanks on my tiki 26.

[Jamie Rohan]

Hey thanks Ron and Kim for your info. I will have a chat with a rigger in Australia if I can get hold of them on skype. I'm in Brunei (SE Asia), and it will be very much a DIY job. Hence the advantages of the soft rigging and splicing. I am hesitant to trust any SS wire that I could get locally (probably a "copy" wire from china!). Also hesitant to trust any swaging done here by non-boaty types. It was local (chinese) SS chain that broke, and recently brought down my aft mast. The 1x19 rig that was on it when i bought it was too short, so i used some SS chain to make up the difference. Anyhow, i will keep you posted on how i go.

[Jamie Rohan]

Hey Ron, i'm guessing you have the T38 with the schooner rig and soft wing sail??, like mine.

Since i'm planning a re-rigging, i'm staring at the fwd rig and wondering why there would be double aft shrouds? I understand that its a "nice to have" in case one breaks, but the rest of the rig is single shrouded. There doesn't appear to be any purpose. Can anyone offer a reason? Otherwise i'm thinking about leaving off the lowers, and saving a few kilos of weight, and $$$.

[Jamie Rohan]

Oh and another question for those patient souls that have built their T38's, or have access to plans!. Can someone describe for me how the mast shroud "cleats" are constructed. These little bitty hooks at the top of the mast which the shrouds loops hook around. Do they have a thru bolt or something other than epoxy holding them on?

[Ron Hall]

Jamie,

Mouzzer has the soft wingsail gaff rig as hown on the T38 plans. I'm not sure why Wharram doubled the aft shrouds on the foremast, but I did think about it as I was building the boat. The loading on the forenast shrouds is the greatest, as it takes the load of the jib and foremain together on the wind, and the foremain and spinnaker off the wind. The foremast moves around quite a bit in the mast casing because the shrouds can never really be tightened down because it's hard to get the deadeyes really tight and the boat wracks a little bit as she sails, changing the masthead hull distance. If the wind is over fifteen, our leeward shrouds are hanging fairly loose, but it doesn't seem to be a problem.

I think Wharram doubled the shrouds to spread the load, since its's greatest on this mast, and perhaps as an in place spare. It's hard to get the tension on the shrouds exactly the same, but it probably works out as you sail. The other reason they might have doubled the shrouds is fixity. By having the tension on the mast taken up in two places several feet apart, you basically force that piece of mast to remain straight; that is, any bend in the mast due to rig loading (and the masts do tend off in the middle) must start below the lowest cleat, and the fact that the top of the mast is fixed above that point stiffens the mast for some distance below the lower attachment point and consequently forces any bend down lower. Consequently, the mast is less likely to be forced out of column due to sideways forces from the rig operating in the middle of the mast.

Thanks for the picture, understand about the soft hanks. hadn't considered that before. Good solution, but I would still monitor for chafe.

The cleats on Mouzzer are made per plans of white oak, and attached to the mast with two number 14 sel;f-tapping screws that are at least three inches long. (They may be longer (I don't remember) but I do remember I had to special order them.) The cleats were also epoxied in place, with large filets all around. The force is mostly directed against the mast and down on the the thumb part of the cleat, so the force is taken by the screws (in shear) and the filets (in compression). If you only used the screws, they might eventually start to crush the softwood of the mast and possibly fail at some point in the future, so I think you need both the screws and the epoxy. The upper part of the cleat retains the shroud loop if it goes slack, but never takes any real force. The cleats themselves are perhaps four or so inches long, about 1 1/2 inches wide, and somewhat over an inch in depth, with a cutout on the mast side for the shroud about an inch tall and maybe a 1/2 inch out from the mast (about the size of the shroud).

The aft mast in practice generally hangs from one shroud, and I worry more about losing that shroud when the rig is stressed, mostly from fatigue at the eyesplice making the loop. I know at least one other T38 has lost that shroud there, but saved the mast because they kept a forward halyard led to the two beam as a precaution. The forward shrouds on the mainmast are the most vulnerable to this, as the mainmast moves around quite a bit in the waves, jerking the slice back and forth. I think that some of the builders with soft rigs have gone to making a separate loop to go around th mast, and then connecting that to a loop on the shroud, allowing the splice the freedom to move back and forth, but I don't have any hard data on how it was done or if it worked. The aft shrouds are supported at least in part by the mainsheet and are I think less of a problem. I have one halyard on the forward side of the mainmast, and on long passages I would keep it fastened down to the two beam as a precaution. Some of the other builders who have put soft rigs on the boat should chime in here, as I would like to hear more.

Ron

[Jamie Rohan]

Hey that's some excellent info, thanks for that Ron. I see your points regarding the fwd mast double rear shrouds. I'll have a bit of a think about this one. Maybe i should just stick to the plan, and spend the $$! However, it is the forestay that i'm most concerned about. Because i have a furler, it looks like i'll keep this one stainless.

On that subject. is there any means of rigging that would keep the mast "upright" if any ONE shroud was to break (except of coarse the fwd mast shrouds which we've discussed)? As you know, if the f'stay breaks, or any aft mast shroud breaks, you loose a stick! I don't want to go to the complexity of doubling every stay. We can't have a triatic stay, coz it would interfere with the gaffs. So you think that taking fwd halyards down to a fwd beam (or bows, in the case of fwd mast) would do the trick? I've got double fwd halyards on both masts. I guess this could be a reasonable backup to the most likely stays to fail (fwd ones)

Thanks for your details on the mast shroud cleats. Mine seem to be coping fine, with no sign of stress, so i'll leave them alone. Presently the shroud loops have a tube of PVC to protect the mast, I guess I should have these with the Dynex shrouds when i fit them.

Thanks again for your advice.



Ron Hall said:

Jamie,

Mouzzer has the soft wingsail gaff rig as hown on the T38 plans. I'm not sure why Wharram doubled the aft shrouds on the foremast, but I did think about it as I was building the boat. The loading on the forenast shrouds is the greatest, as it takes the load of the jib and foremain together on the wind, and the foremain and spinnaker off the wind. The foremast moves around quite a bit in the mast casing because the shrouds can never really be tightened down because it's hard to get the deadeyes really tight and the boat wracks a little bit as she sails, changing the masthead hull distance. If the wind is over fifteen, our leeward shrouds are hanging fairly loose, but it doesn't seem to be a problem.

I think Wharram doubled the shrouds to spread the load, since its's greatest on this mast, and perhaps as an in place spare. It's hard to get the tension on the shrouds exactly the same, but it probably works out as you sail. The other reason they might have doubled the shrouds is fixity. By having the tension on the mast taken up in two places several feet apart, you basically force that piece of mast to remain straight; that is, any bend in the mast due to rig loading (and the masts do tend off in the middle) must start below the lowest cleat, and the fact that the top of the mast is fixed above that point stiffens the mast for some distance below the lower attachment point and consequently forces any bend down lower. Consequently, the mast is less likely to be forced out of column due to sideways forces from the rig operating in the middle of the mast.

Thanks for the picture, understand about the soft hanks. hadn't considered that before. Good solution, but I would still monitor for chafe.

The cleats on Mouzzer are made per plans of white oak, and attached to the mast with two number 14 sel;f-tapping screws that are at least three inches long. (They may be longer (I don't remember) but I do remember I had to special order them.) The cleats were also epoxied in place, with large filets all around. The force is mostly directed against the mast and down on the the thumb part of the cleat, so the force is taken by the screws (in shear) and the filets (in compression). If you only used the screws, they might eventually start to crush the softwood of the mast and possibly fail at some point in the future, so I think you need both the screws and the epoxy. The upper part of the cleat retains the shroud loop if it goes slack, but never takes any real force. The cleats themselves are perhaps four or so inches long, about 1 1/2 inches wide, and somewhat over an inch in depth, with a cutout on the mast side for the shroud about an inch tall and maybe a 1/2 inch out from the mast (about the size of the shroud).

The aft mast in practice generally hangs from one shroud, and I worry more about losing that shroud when the rig is stressed, mostly from fatigue at the eyesplice making the loop. I know at least one other T38 has lost that shroud there, but saved the mast because they kept a forward halyard led to the two beam as a precaution. The forward shrouds on the mainmast are the most vulnerable to this, as the mainmast moves around quite a bit in the waves, jerking the slice back and forth. I think that some of the builders with soft rigs have gone to making a separate loop to go around th mast, and then connecting that to a loop on the shroud, allowing the splice the freedom to move back and forth, but I don't have any hard data on how it was done or if it worked. The aft shrouds are supported at least in part by the mainsheet and are I think less of a problem. I have one halyard on the forward side of the mainmast, and on long passages I would keep it fastened down to the two beam as a precaution. Some of the other builders who have put soft rigs on the boat should chime in here, as I would like to hear more.

Ron

[Ann and Neville Clement]

On Peace we have used to be a bit distracted whenever we were sailing in strong winds that caused the lee side foremast shrouds to be relaxed enough to wobble about. Then we got some strong bungee and use that to bend the twin shrouds a little together. Ours are quite tight, but with the bungee, it keeps them tight even in strong winds.

[Ron Hall]

Jamie,

If you are going to use stainless for the forestay, suggest you follow Ann and Neville's advice on rigging the forestay. Ann can break in and tell their story, but basically, after it broke underway, they replaced it with a straight forestay with loops for a shackle on both ends, doing away with the eyesplice at the top. The forestay is then shackled to a padded steel line with a loop at both ends that goes completely around the mast. The shackle connects the two ends of the mast line with the forestay. Experience from several boats indicates that there is enough jerking around side to side that the forestay eyesplice can fatigue at the splice and break, leaving the mast unsupported in the front.

When we have the forestay loose, I take the forward halyards down to the ends of the one beam and tension them temporarily using a truckers hitch to hold them in place and move the masthead foreward while we tighten up the forestay. You could leave them in place if you wanted; I certainly think they are capable of holding the masthead temporarily if the forestay should break. On Mouzzer these halyards are normally led to the ends of the two beam (per plans) and go through a rope clutch on their way to the big winch. One is normally up (either for the jib or the chute) all of the time, so they're not available to protect the mast.

I would also suggest the builders make the jib halyard internal, rather than using an external forward halyard for the jib. I am sorry we did not do that. Because the external halyard is led to the starboard end of the two beam, tightening it pulls the masthead to that side. Consequently, when we are on port tack and the wind comes up and we tighten the halyard, then tack, the jib is again loose (because the wind has pushed the masthead to starboard, and tightening the halyard again then puts a frightening amount of force on the mast (at least it seems so) on starboard tack, which is made worse when we tack back on to port and the masthead again shifts to leeward. The remedy is to lead the jib halyard down the mast and then aft to the winch, but this interferes with the leading edge of the foresail and requires extra fittings at the base of the mast. Making the halyard internal is the right choice.

Also would take Ann and Neville's advice about the bungee chord on the two aft shrouds, and getting the shrouds as tight as you can. Very disconcerting to see the shrouds flapping in the breeze.

Ron