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Capt'n,

Do you know the designed size of the forestay? I don't know how they size standing rigging, seat of the pants, rule of thumb or genuine engineering. A combination I'd bet. I'm the senior designer for an engineering department (but not an engineer). In our industry, and probably most, the engineer figures 1 1/2 times 65% of the allowable material strength for a given member. This means that if the stay would see 650 lbs of load, the engineer would look for a cable that can take closer to 1500 lbs WLL. So, properly sized there would be no reason to increase. Marine applications may differ from architectural, but I would think the same safety factors would apply.

Don
 

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Is there an easy way to tell the largest diameter forestay i can use with my furler? I would like to oversize it, and just do not know.
Why do you feel the need to oversize the head stay, do you think that is necessary?

The max diameter is probably limited by the bushings inside the foil / drum.

If you know the make/model of the furler you might find info on the web (Google is your friend)
 

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Schooner Captain
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Discussion Starter · #7 ·
Why do you feel the need to oversize the head stay, do you think that is necessary?

The max diameter is probably limited by the bushings inside the foil / drum.

If you know the make/model of the furler you might find info on the web (Google is your friend)
I need to strengthen all my rigging, I may encounter 120KT winds.
Only the forestay will be stainless, the rest is getting converted to amsteel. The only other item that will stay stainless will be the foreward mast to the first spreader. This will reduce weight aloft, as well as strenghten the rig. I will also be splitting the backstay to two the entire way to the top of the mast.
I want the strongest rig I can have for where I would like to go.
 

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I need to strengthen all my rigging, I may encounter 120KT winds.
Only the forestay will be stainless, the rest is getting converted to amsteel. The only other item that will stay stainless will be the foreward mast to the first spreader. This will reduce weight aloft, as well as strenghten the rig. I will also be splitting the backstay to two the entire way to the top of the mast.
I want the strongest rig I can have for where I would like to go.
The winds you may see are only half of the equation. The rigging does not need to hold up against the wind. The rigging only needs to provide counter torque against the righting moment of the boat. Once the force of the wind exceeds that required to lay the boat flat to the water, there will be no additional forces on the rigging. In other words, if the boat will heel at 80 degrees in a 80 kn wind, then the rigging will never have to stand up to a 120 kn wind.

Another thing to consider is, if the weakest link breaks, what's the result? Personally I would see the rigging breaking as the preferred result if compared to what happens when a bulkhead rips up through the deck. In both cases the mast comes down, but in the latter case you've also got a big hole in the deck which is open to the ocean.

Essentially there are lots of forces and counter forces involved. Making one section (rigging for example) exceptionally strong without looking at where the forces will be countered may end up with an unbalanced system and no effective gain in security. If you're serious about doing such modifications then it would seems reasonable to engage a naval architect who can do the proper calculations and find out how to best spend your money.

GTJ
 

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Discussion Starter · #9 ·
so then what is the leading cause of demasting? Is it not a weakened rig above the deck? do to wear, or corrosion?
The key for me is a roll over. I don't know if much more tension can be put on a rig then a roll over.
That is what we are prepping for, above and below deck. BEfore we get to the horn, the floors will all be latched, all batteries will be secured, I am even changing the companionway steps latching so they cannot come up when up side down. That is a real outcome of being stuck in a nasty storm. And I will do what ever I can do to keep the boat as together as I can, and undamaged as I can.
 

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SailingJackson's point is that you are looking at one part of the standing rigging, which is the forestay. The mast and it's rigging are a system and if you increase the strength of just one part (the forestay) without doing anything for the other parts (mast, tangs, chainplates, hull) you are just moving the point of failure without increasing the overall system strength.

I'd also be concerned about using amsteel for the standing rigging. Dyneema can make great standing rigging, but the pros do it with Dynex Dux and other higher end dyneemas that have been heat treated and prestretched to avoid constructional creep. Standard Amsteel will elongate over time.

If you are going around Cape Horn and think that the boat needs these improvements I would at least get advice from a good rigger. I'm certainly no expert, I just know a little bit of the basics -- enough to be concerned about your approach.
 

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Discussion Starter · #11 ·
I had given thought to moving the back stay from the thru deck rig shared with the rear mast uprights, to the outside of the hull. they are nearly there now, so 4" outboard should not change much. This way I can have an overbuilt "tripod" supporting the forward mast. the bow connection for the forestay is super strong, and tied down half way to the waterline in a big 4" wide strap creation.

 

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While you should have a substantial boat/rig to sail around the Horn, trying to beef one up to survive a roll is futile. As one said above, you're just transferring the point of failure. It may just rip out of the deck. Focus on avoiding a roll and having multiple options to heave-to, chute anchor, drogue, etc. I think Skip Novak suggests a very heavy mainsail and a fourth reef.
 

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Below is my own opinion:
I would not go with the amsteel. What about when you are all hunkered down below in a storm and something begins to chafe on the rigging? Wire rigging is much better to withstand chafe. I would make sure your chain plates and bolts are all good. Add an inner forestay and running backstays- that way if you loose the top of your mast, you can jury rig the lower. This is an interesting article about a man who sailed 3 times around the world non-stop and how he prepared his boat. In any case, no matter what you do or how strong your mast and rigging, it might still come down.


Also:
Project Endeavour: Jon Sanders' Triple Circumnavigation of the World

The refit:
http://john.curtin.edu.au/endeavour/refit.html

'The hull [was] strengthened with a matrix of additional internal stiffening, linking hull, deck and major stress areas. Watertight bulkheads were fitted fore and aft, other bulkheads being strengthened considerably. A new fin keel was cast of 5.08 tonnes with a VCG above root of 0.66m (previously 4.25 tonnes, 0.84m VCG) suitably designed to generate less bending moment at the root (3.35 tonne.m as opposed to 3.56 tonne.m). The rudder stock was rebuilt and the skeg deepened by 300mm to improve rudder strength (bottom pintle added) and increase directional stability. A heavier section mast (250mm x 175mm) some 2m shorter than the original rig was chosen from the Rolly Tasker Spars range. The mast is deck stepped, unusual for an ocean voyaging yacht: this is a characteristic of almost all Perth based yachts as they must 'shoot' the Fremantle bridges to reach the Indian Ocean. Consequently the local spar manufacturers are expert at deck stepped tabernacle systems.

'The standing rigging (stainless) was increased to 7/16 in diameter uniformly for ease of repair and cannibalising. At Jon's request, every stay was backed up in some manner, resulting in twin forestays, double inner forestays, twin cap shrouds, twin intermediates, in-line and aft lowers, three backstays and a pair of runners for good measure. No calculations or load predictions could justify this configuration but events during the voyage have shown that experience and intuition can still lead science and engineering. The two obvious problems with such a rig are the nightmare of tuning and the increased compression loading under the deck. The former was left in the capable hands of Jon whilst the compression was taken by a further two support posts underdeck.
 

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Amsteel, while a wonderful material, is not sutable for standing rigging. No reputable dealer should recommend it as such. Dynex Duc is a dyneema line that has then been heat treated and annealed and is sutable for standing rigging. While they are made from the same chemical elements, they are not the same. As for chaff... It isn't really a problem, even with ceramic blades this stuff is hard to cut, and where wire is sized for strength, Dux is sized for creep, resulting in a line that is 2-3 times the strength of the wire it replaces.

Frankly I think your plan to re-engineer the standing rigging is a bad one. Some navel architect spent a good bit of time getting a degree in this stuff and what you have is the best solution he could come up with. Unless you have the same basis from which to work you are just as likely (or more so) to come up with something worse not better. If you are serious about this, then you need to employ a NA to run the calculations to figure out what the best option to strengthen the rig is.
 

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If you really want your rig to stay up in a capsize situation, then I'd scrap the alloy masts and go to wood.
When I encountered a relatively mild cyclone off Fiji, my 65 year old boat (gaff rigged) was capsized 3 times, mainly because I didn't have enough sea room off the western reef, so we were actually trying to beat in 100+ knots of wind. Suffice to say, my main mast, a tree about 60' feet high and the mizzen (a laminated wood mast) did not come down. The main had just been rerigged with new 5/8th inch rubber coated galvanized wire (I don't remember the size of the mizzen rig, or it's age). Don't get me wrong, there was plenty of damage, including the main boom, broken in 2 places, all the lifelines and stanchions were torn off the boat, just to name some. But both masts did stay up.
Perhaps rather than trying to get your present boat up to the task, you might be better served finding one that was designed and built for the voyages you are envisioning. Also, you might want to scrap the roller furling gear on a boat you intend to sail in 120 knots of wind. That is a tremendous amount of windage aloft and it surely will increase your chances of capsizing, considerably.
 

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..........
Perhaps rather than trying to get your present boat up to the task, you might be better served finding one that was designed and built for the voyages you are envisioning.
..........
Maybe get in touch with Brent. He's around here somewhere and his boats.. well, they say they can stand up to anything and, from photos posted on this forum, I'd believe it. :)

EDIT: FWIW, many old-time yachtsmen used to rig a spare stay (or twin head-stays, or both) that remained tied to the front of the mast during extended cruises. It might be something worth considering - especially if you're using rope.
 
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