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new spreader test ... and ... whoops !


waynemunro

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great day out sailing down here, first day out testing the new spreader that I had put on during the week. My gaff had been getting caught on my shrouds and was not turning much to the side. I had decided to put on a spreader to move them out a bit at the top.

Sail started off excellently. the wind was predicted to be around 10 knots but was significently more than that, I reckon at least 20, but we headed out anyway - me, another two adults and one young'un. The sailing was going wonderfully, the spreader working great, the wind was piping, and the swell coming up (around 3 ft), we heard a small creaking a couple of times, and put it doen to maybe one of the cable clamps slipping a bit and kept on going..

.. anyway to cut a long story short, a couple of hours later there was a bit of a 'crack' and a glance up at the top of the mast revealed that all was not rosy - it seems that the extra torque applied byt he spreader put significent side forces on the bolts through the mast and the top section of the mast split down the middle... oh well not the end of the world, we dropped the main, and motor sailed back with the outboar and the jib. returned without problem but the waves seemed much worse when not under sail (I know people have said that before, but I have never beleived it)

anyway, repair shouldn't be too bad - glue it back together with epoxy, and some form of strapping (maybe a stainless steel band) to stop it happening again... unless anyone has a better idea.

there should be a couple of pictures below , sorry that I never took any of it before I wrecked it.

[attachment over 4 years old deleted by admin]

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I'm not at all surprised the mast split with that set up. You have a nice lever applying force to the two inline bolts, prying the grain apart. Also the upper bolt is contributing to trying to seperate the grain- they are all in one line down the center of the mast.

When you are hard on the wind, all the pressure on the spreader is downward on the weather side- it didn't have a chance of holding.

Yes you should put a band around the mast at the spreaders- something to help the wood stave off that spliting force. That's what traditional gaffers would have. Would be best if it was directly under the spreaders with the spreader bolts going through it fore and aft. Or at least a metal plate on each side running beyond the spreader top and bottom, but then you get two MORE holes in the stick. I'd pick the metal band.

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Sorry to hear of your problem. That is why I am going to use a krans Iron (sp) on my mast. No photo yet, it is still at a machine shop being worked into the schedule. The said he would do it cheep if he could do it at a slow time. It will be made from 2" id. x 1/8" x 3 1/2" stainless steel pipe with 1/4" rod for loops. I will also be running the halyards down the shrouds and not the mast to get them away from the gaff jaws.

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I had a slightly longer mast, so I did not use a spreader your size, but still needed some extra space to separate all the connections in the top of the mast. Having 4 wires connected to the same drilled hole in the metal strap as in the plans, did not look nice at all.

I figured that even a small spreader with a similar layour as yours would run the risk of splitting the mast, so I decided to use only ONE BOLT, regardless of other details. By using one bolt the spreader can rotate slightly as needed, without causing a local rotation moment in the top of the mast. I simply used two separate SS straps from the sam bolt (in my case this was sufficient to solve the spreading of shackles), but I am sure your spreader will work just fine with one single bolt (may be a slightly larger one?) and a washer on each side of the spreader to allow the necessary rotation.

The steel strap around the mast will also work, but that is a way of attacking the symptoms, not the cause.

Good Luck!

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Spreaders are not meant to be cantalievered out like that. They spread the shrouds, which then attach back together further up the mast. Our rig is really not set up to have spreaders. You could go to a taller mast by a foot or 18" and then one could think about setting up a spreader. There are some remarkably high loads that spreaders and the rigging apply to things, so you should expect to break parts if you testing rigging changes which haven't been worked out.

Sorry to be grumpy, but we've been seeing a lot of spreaders which have been engineered oddly. Take a long, close look at how other boats (not other Weekenders, but bigger Marconi rigs) have been set up.

Mike

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I think people are adding spreaders to get the shrouds out away from the gaff jaws. I haven't found that necessary, and my mast is about 9" taller than the plans. I do use a band around the mast to attach the stays to, as well as the blocks for the halyards. Here's a pic of the black-painted bands (they are galvanized fence post bands):

mtop1.jpg

These pictures aren't that clear, but they show the galvanized fence post band with stainless steel rings captured on the bolt in the band, and in the second pic, the shrounds attached to the rings:

stndring.jpg

sidering.jpg

My mast is a round, hollow mast, so I was concerned about putting bolts through it.

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oh well.. I'd be the last to claim that I knew what I was doing... though with the benefit of hindsight I know enough mechanics that I should have been able to see that this was going to be a problem.

I'll re-think and maybe do some calculations for the repair.

on the lighter side I guess I am now right up with the NZ americas cup team.

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Ed, just to keep all things straight, I beleave that the fitting at the mast top is called a "Mast Band", while the fitting at the foreward end of the bowsprit is called the "Kranz Iron". Someone please correct me if I am wrong. I too have contructed both items from SS pipe and 3/8 SS round stock. I don't weld but did do the cutting and bending. I have seen Kranz, Krans, and Cranz as the spelling.

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I stand corrected, what I am making is a "Mast Band" I will make a similar one for the bowsprit called a "kranz Iron". I just did a search for the proper spelling of "Kranz Iron" and the only spelling I can find is with a "z". Although the spell check has it with an "s".

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that's a pretty unique device you've got there Wayne. :)

I just let the gaff lay on the shrouds gently and sheet in if it looks like it's developing any load. The thing I don't like about running the halyards to the toerail with the shrouds is that the halyard tension alters on each tack with the movement in the rig. That adds a variable which kind of makes it hard to figure out what is making your boat go well or not.

It's spelt cranse iron. if you did a google on it you'd find quite a few references. I always get the gammon iron and cranse iron mixed up terminolgy wise myself. The gammon iron is the fitting on the stem that the bowsprit passes through.

talking spreaders ...one local boat, Jonquil( a buzzards bay 25) was sailed hard one weekend and the skipper ( new owner)did not realise the implication of letting the gaff lie hard against the spreaders in a breeze. (these spreaders were the rigidly fixed type). He wrung the whole mast, twisting it so badly that it had to be removed and reglued. They then fitted swinging spreaders to allow some give. When I was aboard Lark... the falmouth quay punt, at christmas I noticed that he had this swinging type too. Good idea I think.( If you have spreaders that is)

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yeah, its all your fault Buck :) In reality I do of course have you to thank for giving me the confidence to head out in the higher winds - which is lucky as it seems to be all we are getting around here at the moment (day before was up over 60 knots I think). I'd also like it noted that I was looking for the nice 10 knot day :)

John B: I think I must have something wrong with my geometry somewhere, as when I pulled up my sail before the gaff would actually be tight between the stays on both sides, without any wind, the stays were preventing it turning significently with the wind.

Capt Jake: Good Luck with yours - I think I have figured out how I am going to modify mine, just a quick fix for now, see if ti works then tidy it up - worst case I'll have to make a new taller mast and go back to the old way. I think my spreader is a bit wider than it needs to be, I'm going to drill new holes and mount the stays in a bit, then run lines from the old holes to a mounting near the top of the mast (or maybe a cap), and drill out the top spreader hole to allow the spreader to rotate a little. I think this should reduce the loads considerably, and since it broke in conditions approaching what I think the maximum would be that I'd be out in and still took a couple of hours to go.. if I take a reasonable factor off the loads, I should hopefully be ok.

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Wayne, I feel like repeating myself.

Your spreader is OK even as it is, but should of course only be as wide as actually needed. However, the crux is to allow the spreader to rotate slightly off the 90 degrees to the mast longitudinal axis (which is the correct angle with no wind load in the sails). If the spreader is fixed to the mast by a single bolt and one washer on each side, with limited tightening of the bolt, the rotation will self-adjust and give only axial load to the mast and no bending/splitting force which is what should be avoided.

By the way, I guess you were not tempted to sail during your 60 knots day?

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Hi Knut,

I don't think I can be imaginaing what you talk about, if i allow the spreader to rotate, then won't it just rotate until the shroud lines up with the connecting bolt.

and no, didn't go near the water on the 60 knot day, though if I had not been busy I would have taken out the land yacht and it would have been wonderful.

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Hi Wayne,

if you imagine that the shrouds are perfectly stiff along with the boat hull and the chainplates and the spreader, only the mast is flexible, then the mast will bend because of the mainsail being laced to it from the gooseneck to the throat, with a resultant force somewhere below the midpoint of the luff. This will have the effect that the mast will flex into a low arch and the top of the mast will rotate around the SINGLE bolt through the spreader. In this system, nothing else will move and if the rotation of the mast around the bolt is not restricted, there will be no splitting force.

If you imagine that the spreader has TWO bolts, one above the other at close distance, the mast will still flex and it will TRY to rotate around the two bolts. However, the bolts are not moving at all (in this stiff system)and it is like releasing the bottom end of the mast and rotating it sideways. The midpoint between the two spreader bolts will be the center of rotation and even a small rotation can of course easily split the mast.

I know that in reality it is a bit more complicated because none of the elements are perfectly stiff and the mast is even a cantilever out of the mast box. The important thing is that with a single bolt the spreader itself will only rotate marginally, as much as the shrouds on the other side will allow, without setting up splitting forces. The system is self-stabilizing as long as nothing is breaking.

See sketch, if it appears as planned.

[attachment over 4 years old deleted by admin]

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