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Old 25-03-2009, 19:09   #16
Kai Nui
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Good decision. The most common cause if dismasting is spreader failure. I would consider $850 to be very cheap insurance.
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Old 25-03-2009, 20:38   #17
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Extemp,

Your spreaders are the fancy type that reduce windage to minimum. Racers even claim lift from them. It's a NACA airfoil: NACA airfoil - Wikipedia, the free encyclopedia

The other type that makes sense for cruising is the type that is built from aluminium round stock (forward pipe, aft pipe and zig-zag cross-supports between them). You'll see them on some modern rigs. This type has more windage but also the positive side that they don't chafe the sail. Which is really only important if you have aft-swept spreaders.

The difficulty with "having some spreaders built" is that you need a calculation of compression force that they get. Next, a nautical architect must draw and calculate it so that it will last at these levels of load. You get it: it's not like welding something up. I would bluntly ask for discount but hey I'm Dutch ;-) But I would order original because it'll be the cheapest solution when doing it right.

And like Kai Nui says: it's a common cause of dismasting. What you can do is ask them if it's possible to beef them up a bit because you obviously had a failure, and to have them create working drains (both ends should have one).

This might sound strange but I'll write it anyway: instead of making the spreaders stronger, you might want to check if it's possible to make them shorter instead. This is possible if the angle of the shroud at the masthead is more than 12 degrees. You can easily measure that now the mast is down. If you see 14 degrees or more, you could ask the local rigger that question. The way this works is that if it's shorter, the angle with the shroud becomes smaller and thus the compression forces go down (significantly). If your shrouds are not very old, this would only make sense when you have Norseman/Sta-lok fittings because the shrouds must be shortened too but possibly not enough for a new swage.

When putting the rig up, make sure the vertical position of the spreader-tips are okay. The spreader should have equal angles with the shroud both above and under the spreader. This often means the tip should be a little up. Having this angle right means that the spreader only gets loaded in compression. If the angle is off, you also get up or down forces at the tips. Remember that the shroud is stretched during tensioning so this check must be done after tensioning. The shroud tension is also a factor in spreader failure: if there isn't enough pre-tension, you get shockloading. With 1x19 wire the general rule is that they must be pre-tensioned to 20% of breaking strength. The leeward shroud should never go slack.

cheers,
Nick.
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Old 26-03-2009, 18:39   #18
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Extemp,
And like Kai Nui says: it's a common cause of dismasting. What you can do is ask them if it's possible to beef them up a bit because you obviously had a failure, and to have them create working drains (both ends should have one). cheers,
Nick.
Convinced!
Now I just have to make my best deal.
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Extemp,
This might sound strange but I'll write it anyway: instead of making the spreaders stronger, you might want to check if it's possible to make them shorter instead. This is possible if the angle of the shroud at the masthead is more than 12 degrees. You can easily measure that now the mast is down. If you see 14 degrees or more, you could ask the local rigger that question. The way this works is that if it's shorter, the angle with the shroud becomes smaller and thus the compression forces go down (significantly). If your shrouds are not very old, this would only make sense when you have Norseman/Sta-lok fittings because the shrouds must be shortened too but possibly not enough for a new swage.
cheers,
Nick.
I think my shrouds are in pretty good shape so I'll leave the geometry alone. Along with that I would think that for the same lateral force at the mast head, more compression would occur on the mast and compression post and perhaps a bit less tension on the chain plate that the upper shroud was attached to if the upper spreader was shorter. I agree there would be less lateral force at that spreader height. The total energy would be the same, but the distribution of forces would change.
Could be wrong.
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When putting the rig up, make sure the vertical position of the spreader-tips are okay. The spreader should have equal angles with the shroud both above and under the spreader. This often means the tip should be a little up. Having this angle right means that the spreader only gets loaded in compression. If the angle is off, you also get up or down forces at the tips. Remember that the shroud is stretched during tensioning so this check must be done after tensioning. The shroud tension is also a factor in spreader failure: if there isn't enough pre-tension, you get shockloading. With 1x19 wire the general rule is that they must be pre-tensioned to 20% of breaking strength. The leeward shroud should never go slack.
cheers,
Nick.
I agree to bisect that angle and that due to the friction of the shroud through the spreader (trying to pull it down) it needs to be checked after tensioning. When the shroud is slightly tighter then slack I push it up to the extent that I can within the play of the joint.
Rigged and tuned my mast last spring with the help of Ivan Dedekam's book "Sail & Rig Tuning". Worked out well. Shortened my roller furling as much as I could without cutting my foil. The PO had way too much rake and after I set it up last spring it actually felt like it had less weather helm.

Regards,
Extemp.
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Old 26-03-2009, 22:28   #19
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Extemp: that is the best book I've seen on this subject ever. It's also the thinnest so easy to get to the info and do the job. Could have had more info on ketch rigs though...

About the spreader: I didn't mean compression forces on the mast because those will be the same, I meant on the spreaders. If you make the upper spreader shorter, you reduce the "turn" that the wire makes at the spreader-tip. The shorter you make it, the straighter the wire gets, the less compression force on the spreader. If the wire is straight, compression force is zero. At the same time you reduce the angle of the wire with the mast-head. I think riggers agree that 12 degrees here is more than enough. So anything over 12 degrees means extra load on upper spreaders that could be prevented. Brian Toss has a post on this on his website.

ciao!
Nick.
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Old 27-03-2009, 19:02   #20
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Extemp: that is the best book I've seen on this subject ever. It's also the thinnest so easy to get to the info and do the job. Could have had more info on ketch rigs though...
ciao!
Nick.
Very easy book to follow.
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About the spreader: I didn't mean compression forces on the mast because those will be the same, I meant on the spreaders. If you make the upper spreader shorter, you reduce the "turn" that the wire makes at the spreader-tip. The shorter you make it, the straighter the wire gets, the less compression force on the spreader. If the wire is straight, compression force is zero. At the same time you reduce the angle of the wire with the mast-head. I think riggers agree that 12 degrees here is more than enough. So anything over 12 degrees means extra load on upper spreaders that could be prevented. Brian Toss has a post on this on his website.
ciao!
Nick.
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I agree there would be less lateral force at that spreader height. Regards,
Extemp.
Lateral forces being the same a compression to a horizontal element. We agree.
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The total energy would be the same, but the distribution of forces would change.
Could be wrong.
Extemp.
What I was trying to say (and may not be anymore successful this time) is that other forces change once the compression decreases on the spreader (due to the shroud being straighter). And I think that some of those changes would include less tension on the shroud chain plate and more compression on the mast and compression post. This would not be the case for the shroud in its static state as you would tension that to the same spec's. But I'm thinking that due to the geometry change with the shroud tensioned to the same spec, the compression on the mast would be more, even in its static state with no additional horizontal force on the mast head. This relationship would become even more obvious as lateral force was applied to the mast head. The thought being, with the same pull (tension) on the chain plate (static state), less of that energy would be canceled out by less opposing horizontal forces at the spreader (due to the spreader being shorter and the shroud being more straight line). I'm not saying that the tension on the chain plate would decrease as more lateral force is applied to the mast head. I'm say that it would be less than it would be if the spreader was its original length (longer) with the same force laterally applied to the mast head. I can prove NONE of this as I am not an Engineer. Maybe one can straighten me out.

As I write this I'm thinking that what sometime whirls around in my head should be kept to myself, but I've type it now so I may as well click send.

Regards,
Extemp.
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Old 29-03-2009, 09:13   #21
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Yes, I start thinking like I did during my studying years again ;-)

The mast only bends in the fwd/aft plane. The sideways force from the spreader is cancelled out by the spreader on the other side. This means that the total force as seen on all chainplates equals compression force + mast bend (=wound spring, energy storage). So I think that length of the spreaders only make a change in the distribution of the forces when they are swept aft (they bend the mast if so).

I tried to draw the vectors in my mind, not on paper, so I could still miss a point... ;-)

ciao!
Nick.
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Old 29-03-2009, 10:18   #22
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I would think welding it would be fine. Many masts are welded out of two extrusions. Any tapered mast is welded somewhere. Aluminum boats are welded "everywhere" . Going on gut feel, Where your break is is probably not a bad place for the weld. The spreader is in compression so the strength at the weld is less of an issue than if it was flexing. Hard to believe water would stay in a spreader though. IF you think that really happened, dill a hole in the bottom to avoid future issues.
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Old 29-03-2009, 11:34   #23
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Yes, I start thinking like I did during my studying years again ;-)

The mast only bends in the fwd/aft plane. The sideways force from the spreader is cancelled out by the spreader on the other side. This means that the total force as seen on all chainplates equals compression force + mast bend (=wound spring, energy storage). So I think that length of the spreaders only make a change in the distribution of the forces when they are swept aft (they bend the mast if so).

I tried to draw the vectors in my mind, not on paper, so I could still miss a point... ;-)

ciao!
Nick.
I am not an Engineer, but work with many.
I'll get one of them to work this out with diagrams and equations.
I don't imagine the vertical forces (or relationship) change much due to spreader length, but now I'm curious if my hunch or instinct is correct.
It may not come quickly (They've got real work for them to do), but I'll post when it does.

Regards,
Extemp.
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Old 29-03-2009, 11:42   #24
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I would think welding it would be fine. Many masts are welded out of two extrusions. Any tapered mast is welded somewhere. Aluminum boats are welded "everywhere" . Going on gut feel, Where your break is is probably not a bad place for the weld. The spreader is in compression so the strength at the weld is less of an issue than if it was flexing. Hard to believe water would stay in a spreader though. IF you think that really happened, dill a hole in the bottom to avoid future issues.
There is WAY TOO MANY people making sense here!
I'm so confused .
One thing is clear. If I replace it, my poor judgment (with regard to this) will not be part of my own demise.

Regards,
Extemp.
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Old 29-03-2009, 11:44   #25
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$850 for a pair of spreaders?! Are you sure they aren't an exotic berylium-titanium alloy, rather than plain aluminum?

Brokerage fees are often best avoided by using the post office, instead of UPS or other carriers. That's a perq the postal systems give themselves to gain a price advantage.

But I'd also suspect the split is from excess tension and a faulty weld opening up--not freezing. In any case, when you get 're-spread', you might want to fill the spreader with high-density insulation foam, that will prevent the problem recurring. (Although I've never heard of a spreader trapping water that way.)

You might consider contacting some surplus dealers (i.e. Sailorman in FLL) and asking if anyone has similar spreaders available for you. That price is just way out of rational.
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Old 29-03-2009, 12:19   #26
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$850 for a pair of spreaders?! Are you sure they aren't an exotic berylium-titanium alloy, rather than plain aluminum?
You might consider contacting some surplus dealers (i.e. Sailorman in FLL) and asking if anyone has similar spreaders available for you. That price is just way out of rational.
I thought the price was high, but when I never got any responses saying so, I just figured it was one of those boating things. I'll explore what I can.

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Brokerage fees are often best avoided by using the post office, instead of UPS or other carriers. That's a perq the postal systems give themselves to gain a price advantage.
Point taken. Not sure if they are willing to ship this way.
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But I'd also suspect the split is from excess tension and a faulty weld opening up--not freezing. In any case, when you get 're-spread', you might want to fill the spreader with high-density insulation foam, that will prevent the problem recurring. (Although I've never heard of a spreader trapping water that way.)
Like you say "In any case". That said, I'm sure there was not excess tension and so could only be that something was faulty.
The foam sounds interesting, so long as it doesn't cause the profile to bulge due to the foam expanding and that pressure.


I know it would be easy to listen for what I want to hear and go with that, but I really do want to do the right thing, for safety and my pocket book.

Thanks Everyone,
Extemp.
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Old 29-03-2009, 14:55   #27
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"Not sure if they are willing to ship this way."
I've met a number of merchants that have odd shipping habits. Usually someone just doesn't know how much they are costing the customer--or themselves--by using a sole shipping vendor all the time with no provision for flexing. But when you speak to a manager and say "You know, you could save me $50 at no extra cost to yourself by giving this to the mailman" they often can accomodate you.
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Old 29-03-2009, 19:28   #28
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I think you are planning to stick with the same spreader length, and I would agree. Shorter spreaders would result in a smaller angle to the mast, therefore greater shroud loads.
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Old 29-03-2009, 20:06   #29
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I've just gone to the boat and taken off the spreaders.
I've attached some pictures with notes on them.

Now having a close look at them, I may contour the profile into wood and roll the damaged one trapped within the wood mold. I would then have it welded with a full penetration weld and then test and inspect it. After that I'm thinking that hellosailor's idea of filling it with foam is a good one and will do that. While foaming it I would keep the spreader trapped within the wooden mold so that the foam cannot bulge the spreader.
I see the success of this laying in quality control, inspection and testing.
If I can live with my self after all this, I'll install it and go sailing.

Anywhere along the way if something is suspect, I could abandon the process, go get a mortgage on my house and buy new ones.


Regards,
Extemp.
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Old 31-03-2009, 16:03   #30
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Welding: I would not worry about the new weld, that will be plenty strong. But I worry about the opposite side where the aluminium was bent out, and will be bent in again when welding the seam. This work hardens the aluminium and can cause failure easily. Just try it with a scrap piece of aluminium: it will quickly break in two pieces.

On construction: you are right, that is the way they taper extruded spreaders, masts, booms etc. I am now convinced this damage was caused by failure under compression, not from ice. With ice, you would see a change of shape everywhere before the weld fails.

On foam: don't worry about expanding foam breaking your welds ;-) If that would happen you should be a happy man and throw them away and buy new ones. The foam is nowhere near strong enough to do that.

cheers,
Nick.
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