Mast Bend

[CaptainK]

Don't feel too bad, Alan.

I'm in the same boat as you are in!!

May know lots. But not enough in other things?

[GordMay]

I know what I know, and I know (some of) what I don't. The second was much more difficult knowledge to acquire (& accept).
Gord

[ozskip]

Well allan with a rig configuration that does not include a triatic stay if you have the missfortune to have a mast brake or come down because they're independent or each other you loose that just one.I did it by sweeping the spreaders back putting the 2 upper shrouds 35in behind the mast centre.Add a 3rd spreader running foward put a stay from the top of the mast through the end of this spreader and attach to the mast 1/2 way be tween the foot and the spreader like a diamond stay,to stop the backward bend in the mast.Then have rear lowers just behind where the uppers hits the deck and the forward lowers 24in forward of the mast.This config has worked for me for years in past and as i sail bass strait it is well tested.Greg

Wheels, no problem. I will borrow a fish scale and try to get an idea on the spring tension. No guarantees on accuracy here, but it should get you in the ball park. I am not sure about the math to accomodate the larger wire, but if you have time to play with it you might have a really good tool.
The key to a successful writer is the one who has realized that it takes far less time and effort to write down the things he knows that list the things he doesn't
The issue of isolating the masts by eliminating the triadic was recently discussed in an artical I read, but I can not remember where right now. After reading it, I am still not sold. I will take every bit of extra rigging the boat can handle. Just my opinion.

[Alan Wheeler]

I am of the same opinion. The mizzen should never fail. It just simply isn't big enough to see the loads (I think..but am happy to be corrected). So if anything, the extra stay coupled to the main must be of some huge benifit to overall mast strength surely.

The idea of working the math for the tension guage is like this. If I can get a number for several gauge sizes, I might be able to see a % scale. like 1/8 might be 1lb, 1/4 might be 1lb, 3/8migh be 4lb and so on, so it looks like the tension is exponential. See what I mean. So I might be able to predict what a 1/2" wire is based on what was before it.

I figured that was your logic. I will email you as much info as I can put together on the scale I have.

[delmarrey]

As discussed in another thread the tention is 10-15% of max load for size of wire.

I think you are correct about shroud tension, but forestay tension is higher. I believe the forestay tension is supposed to be 20-25%

[Alan Wheeler]

I have had a thought. If my rig wire is over sized, then trying to approach the correct tension of 10-15/20-25% is still going to result in over tensioning the mast is it not?

Any idea of what size wire my boat should have? I am sure it is 1/2" for aft and upper/lower shrouds. It has a brand new foresay and I have a feeling that was droped down to 10mm(3/8"), which is a more realistic size. The inners are more like 5/16"

While I was hunting around the internet for such info, I came across this spread sheet. I hope someone can find this useful.
http://ipsailor.com/Rigging.xls

[BC Mike]

The forestay is further from the mast than the shrouds. If you put too much tension on it you are trying to bend the boat. The shrouds being much closer to the mast can take the tension better. I would suggest they are the same tension, except when you are beating into slop and increase the forestay a bit. If you do not have adjustable backstays I would suggest keeping them the same.
The logis of wyres that are a bit thick is sound so you need to determine what is a sensible tension by other means than wyre size.
Michael

[delmarrey]

Alan,

The down load is only good for IP's. Every boat is different. It all depends on the mast size and hull construction.

The engineer that designed your vessel should have had that all calculated out on wire sizes. If you can get the origonal plans, that would give you the proper wire sizes and then you can adjust from there.

As for the forstay/aftstays they can be variable but still taut. For instance. If your going before the wind, you would loosen the mainsheet which in turn would loosen forstay, that would give you a full-er jib/genoa sail. Then when you tack into the wind you would pull down on your main sheet which would tighten up the forstay and loosen the topbrace and on back to the main/missen backstays. It's all a big balancing act.................._/)


Which way is the bend in the mast?? P/S or fore to aft???

[CaptainK]

Hey Alan.

You ever think of calling Colin Brookes (Mr. Ferroboats) about your mast problem? Or do you know "who" designed. Or even built your mast? And ask them questions about your problem?

To answer the question about what size wire is correct for your boat the formula is RMx2.78/.5xbeam Where RM= Righting Motion, which for a boat with 40' lwl should be about 80000 footpounds. Divide this by the number of shrouds, and then multiply that number by a safety factor of 3. This will gie you the required strength of the wire required for your rig. If you use the proper foot pound tension for that size wire, you shold be safe.
Sorry, I do not recall the formula for calculating forestay loads.
Demarrey, I agree that there are variables. In fact, too many to calculate, but the above is an accepted average, and should be safe.

[Alan Wheeler]

Thanks guy's, this is all very interesting stuff.
Del... the mast has a bend foreward (towards the bow not mainsail) for the first 2/3rds which is good. I mean by good int hat it is not overly bent, has a nice curve and seems to fi the sail nicely. The next 1/4 is straight and then the last quarter takes a bend to the aft (into the mainsail). The result is that the top of the mast is pulling the top of the sail forward, and screwing up the shape of the sail up there and I can't get it to fly howI expect it should do. Now part of that issue, is that I am still in a very big learning curve as to how to fly it and what the shape should be and yada yada yada. I maybe getting ahead of myself and complicating issues by melding to many things together. I tend to be like that, because I am an over achiever, I also tend to bit of a perfectionist and I sometimes expect to much. Slowly learning to chill as I mellow in age
Anyways,one thing I have learn't, is that instead of trying to solve ALL the problems in one instance (which only results in frustration) I have learn't to break things down into parts and solve one at a time (hey, may sound logical for some, but for ones like me, solving the problems of the universe don't happen fast enough. I may have the brains to be a scientist, but I don't have the patience
Anyway's, (once again) I figured that if I solve the issue of the mast as problem one, problem two of learning about sail shape and angle etc etc, should become much easier, as then I have nothing else to blame but myself.

[delmarrey]

Now that I know where the bend is, I believe I can see it in the pic above.

It sounds like a fractional rig except that it's a masthead rig.

If it's keel stepped (?), it must have a natural lean foreward and that would tell me that the topbrace and back stays are too tight in relation to the forestay.

If it's deck stepped (?), then it must have a natural bend in it already. I can't see any rig that would cause it to bend excpt the top and back stays.

It looks unusuall to see the main backstays all the way to the top. If you look at some of the old tall ships you'll see backstays mid way up the main masts.