Hidden downside in beefing up new shrouds?

[Dody]

Originally Posted by OrangeCrush

Yes this is a big issue that I had not really considered; thanks for doing the math. (that's why I love this forum)

The mast is deck stepped and the deck is supported with wooden compression posts, so at some point I would indeed start caving in the deck.

... and, if you think further ahead, where is your wooden compression-post (posts as you say) standing on and attached to?
I am not familiar with Pearson-boats, sorry, but I would be very surprised if it should not be standing and be attached to your keel. 276 KG of additional force from the top might or might not have an impact, depending on how strong your boat was built in the first place, how young/old and worn she is today, and/or if some previous owner has made an attempt to modify her to increase the strength of the hull.

In your case it would "only" be 276 KG of force extra on the keel and 138 KG between chainplates and Mastfittings (sorry for staying with Kilograms, I don't feel confident with kN and not with lbs either). Please, don't get me wrong, I would not dare to compare your boat with a Beneteau, but, just to give you an idea: A few weeks ago a mate of mine was wondering if he should replace the 8 mm wire to the next up which would be 10 mm, on his 8 year old Beneteau. The forces involved in his case would have been 5 Tons (!!!) more in compression on his keel (keelstepped mast) and 2.5 Tons on each side extra on the chainplates and the masthead-fittings, all this on a toothpick-rigg, chainplates and their backings calculated to the absolute minimum, on a hull that is built as lightweight as possible and a keel-section that can't even take drying out on a slip. And all these extra forces without even considering what would be happening when the "normal" forces caused by waves, wind and the interaction with the keel come into play.

To get what I mentioned in the beginning about the state of your boat clear: on the other hand, a mate of mine who is a boatbuilder, bought an old Beneteau Oceanmaster 35 as a present for his daughter. She is living in Ushuaia/Patagonia. He stripped the boat completely, added bulkheads, stringers, frames every 35 cm, re-built the whole keel-section and re-inforced her, installed a different and stronger rig, re-inforced the deck, installed proper handholds and did something about the very vulnerable window-sections, proper chainplates were installed and and and. He's got her back together again and is on his way to deliver her to his daughter. But, this boat now has a very different setup and can't be compared with what one usually finds on the market. You didn't say, so of course I don't know if something similar has been done to your boat.

Anyway, I think you'll be more than happy if you just replace with what you had and I do think it's a good decision

Cheers Dody

[kjdavie01]

This is false - someone was leading you on! The amount of force required to support the mast is the same regardless of the size of the wire, and varies only by the tension you provide as you tune the rig. It's a certain number of pounds/Kg. Wire size - bigger or smaller - is immaterial.

Originally Posted by Robin3

Aside from considerations of weight, bigger diameter wire will need more tension applied toit achieve the same mast support result I believe, thus putting more strain on the hull. I'm not an engineer but that was what I was told many years ago when I too considered upping the dia on a re-rig. Atthat time it was suggested I used same diameter but dieformed wire which was much stronger with no increase in weight or diameter. Is dieform wire even available now?

[Dody]

Originally Posted by kjdavie01

This is false - someone was leading you on! The amount of force required to support the mast is the same regardless of the size of the wire, and varies only by the tension you provide as you tune the rig. It's a certain number of pounds/Kg. Wire size - bigger or smaller - is immaterial.

Sorry, believe me, it's not! Stainless steel looks nice but it can't take vibrations, and it can't take sudden impact-loads. And, like everything else, it stretches under tension.

If you want to use stainless rigging-wire you can't just have it hanging loose around your mast, even when it's keel-stepped. Every single wave, every single gust will put sudden impact loads onto the wire as the mast and the boat moves and you will break it within a very short amount of time.

To make this material work in your favour, you have to tension it to a certain amount. It still won't last forever, but investigations came to the conclusion that, if you tension it to about 15 - 20 % of it's breaking-strength, the sudden impact loads caused by the impact of the sea, the wind and the counter-balance of the keel get reduced to a level that causes less damage to the wire and makes it last for a longer amount of time.

Now, to what you said: true, the mast doesn't care to a certain level. The trouble is, the bigger the diameter of the wire, the more tension you've got to put on to get rid of the slack. Someone much more clever than me found out one day that the easiest and most logical thing is to try if there is a connection between max breaking-strength and the tension you've got to put on. However, the result seems to be that 15 - 20 % tension compared to the max breaking-load regardless of the diameter seems to do the trick. Just look at the different max breaking-loads of different diameter wires and you'll find out that there is definitely a big big difference between each single step. The trouble is that tightening a wire does not only take out the stretch of the particular wire, but also increases the forces on all components involved. Tensioning the shrouds for example will put more load with each turn of the bottlescrew on the top of the mast, forcing it down onto the keel (or the compression-post and with this on the keel). At the same time, increasing the tension with turning the bottlescrew will give more "pull" on the mast-fitting and the chainplate forcing them "closer" together. Depending on where the chainplate is attached, in the worst case, you can change the complete shape of your boat. I don't want to worry you with that, but I would like to make you aware of what is happening if you don't know.

Ever thought about why insurance companies get belly-aches if you break your mast when the stainless rigging-wire hasn't been replaced for more than 10 years?

Cheers Dody

[Dody]

PS: (editing my post doesn't work any more ...) it's not only that you can change the shape of your boat with tensioning the bottlescrews, you can pull chainplates out if you like, you can break attachments on your rig, you can push your mast through the bottom of your boat and, if things go pearshape, you can even break the whole structure. This is, if you keep on tensioning and go too far.

Nobody wants to do such things, and presumably we all stop before this happens ...

Cheers Dody

[gregorybross]

Brian Toss author of The Riggers Apprentice advises against increasing the size of standing rigging. I sat through one of his lectures at the Strictly Sail Boat Show in Alameda. He is extremely knowledgable.

[sandy stone]

You might be interested to know, I once owned a Pearson 26 (I had the one-design model) and broke an upper shroud in sporty conditions with the spinnaker up. The turnbuckle screw had been cracked, and failed, but the rig stayed up. Good boats.

[OrangeCrush]

Wow I didn't check this for a few hours and it turned into quite the thread. Very informative, and thanks again. Definitely agree on sticking with the 3/16 wire now.

Sandy stone, did you break the turnbuckle up near the masthead? I heard that the older Pearsons had turnbuckles aloft, but it's hard to visualize it or imagine why they did that.

And as for the aluminum rudder shaft, I know its weakness quite well. I lost my rudder suddenly off of Boston last summer and ended up steering with the outboard all the way home to Brooklyn. I was aware of the issue but I had inspected it recently and thought it had years of life left. It broke on a calm day over a small wake, and considering the weather we had already been through on that trip it was very lucky indeed.

If you want to see my boat you can do so here. Not trying to self promote but she is for sale, but since my buyer fell through I thought I'd pour some more money in and sail her to Maine again this summer. Thanks again all.

[Capt Gary]

I have a P 39-2 and replaced all of my standing rigging with the next size up (I'm not near my records, so I can't tell you what the original size vs new size rigging is , sorry. However, I have absolutely no worries with my rig (I also checked chainplates, etc). One difference is that my mast is keel stepped. Performance is great and there is an extra comfort in oversizing a little. I think many people overthink this a lot. I am not racing, so if I added a little weight aloft, it really doesn't matter to me. It certainly hasn't appreciably affected stability.

[sandy stone]

The only turnbuckles on that boat were at deck level. I later owned a Pearson 32 that had discontinuous upper shrouds, and it had turnbuckles up at the spreaders.

[Curmudgeon]

I'd consider one of the new ultrastrong fibers e.g. Dyna Dux or Vectran for your standing rigging. Light, never rusts. There's some stretching if it is not properly pre-stretched and annealed, but wire stretches too.

[Toaster]

The 10% - 15% comes about from the correct design of the standing rigging. The yacht designer - refer to Brion Toss's "Complete Rigger's Apprentice" for details - understands that the maximum load on the mast can be calculated and/or measured (this is called the maximum righting moment). Once this calculation is done, the designer selects the appropriate wire diameter to support this load, taking into account a "safety factor", say 2.5 to accommodate shock loads, and appropriately sharing the load between shrouds, etc. The convention is to choose a wire, that when tensioned to the sort of 10 - 15% of breaking strain, will support that load. Any bigger, it is considered a waste of money, any smaller, the safety factor is reduced.

I highly recommend Toss's book. He explains why eg uppers should be tensioned to to 15-20% of breaking load, intermediates to 12-15% and 10-12% on the lowers.

It follows that if you upsize the wire, in order to achieve the same design goal (managing the righting moment), then you will need to tension to the same absolute value (ie force in N, lbs, kg, whatever) which will be a smaller % of the breaking strain than for the smaller wire.

One reason to consider upsizing, is if you are concerned that the safety factor is not large enough - for instance if you plan on some extreme sailing where shock loads may be more of an issue, or if you are concerned about corrosion in the tropics, etc.

Toaster