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Old 20-12-2006, 08:25   #46
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Frank - get rid of that wooden backing plate... IMHO, it's not sufficient. You can all correct me if I'm wrong, but I've been taught you need a steel backing plate on winches and other high-load components. The washers can bend the wood where they sit, not giving you as great an area of load distribution as if you had steel, which doesn't bend and distributes the load across the entire area of the plate.

PS: Can a sail take the pressures listed in your example without ripping? Very difficult analysis to perform, but very good shot at it! I'd say at those load levels, it doesn't matter what you bedded your hardware with. You're boned. ha ha ha
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Old 20-12-2006, 08:47   #47
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Originally Posted by ssullivan
Frank - get rid of that wooden backing plate... IMHO, it's not sufficient. You can all correct me if I'm wrong, but I've been taught you need a steel backing plate on winches and other high-load components. The washers can bend the wood where they sit, not giving you as great an area of load distribution as if you had steel, which doesn't bend and distributes the load across the entire area of the plate.

PS: Can a sail take the pressures listed in your example without ripping? Very difficult analysis to perform, but very good shot at it! I'd say at those load levels, it doesn't matter what you bedded your hardware with. You're boned. ha ha ha
The gunwale the winch sits on is an inch thick. I did check the washers at the end of this season and there does not seem to be any issue. I am only flying 189ft^2 of sail on those winches.

I did consider the idea of the sail being the weakest link but I go so long winded anyways.

Using load = SA * WS^2 * .00431 with my head sail I would need to be sailing in about 120knots of wind to achieve the loads for sheering the bolts. My headsail is rated at 23knots apparent when fully unfurled.

It really is an excersise is hyperbole isn't it?
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Old 20-12-2006, 09:41   #48
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Your numbers are interesting and start to make clear the forces that are potentially involved.

The effect of multiple bolts and a backing plate of steel increases the holding power beyond the shear strength of just the bolts otherwise you wouldn't need a backing plate. Distribution across a bigger deck area gets to be important as the whole mess could tear a hole in the deck with enough force. It's probably the one result that might happen once you seriously overload the winch - the deck gives out before the bolts break.

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Since I use the Sta-SET X 3/8 line for sheets all the above could boil down to you can glue your winch to the deck. This Of course that would mean the deck has to be able to hold, including all the layers needing good bond and such.
I would think the deck would delaminate well before the winch flies off like a rocket. Depends a lot on the type of deck. The deck core would shear pretty easy. Even with it holding the constant deflection over time will fatigue the deck. That is where through bolts play well with a backing plate. It really increases the holding power of the deck by a large amount. The idea is the deck should be the point of failure assuming the sheet or the clew don't fail first. The sail could blow a hole in itself at the extreme and thus reduce the force quickly.

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Using load = SA * WS^2 * .00431 with my head sail I would need to be sailing in about 120knots of wind to achieve the loads for sheering the bolts.
I think "sailing" in 120 knots would be an imprecise term for it<g>. If you review the rigging numbers you may find your mast is long gone before the winds get to 120 knots. Obviously so much is going on at that point it would be hard to really predict what would happen.
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Old 20-12-2006, 09:54   #49
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Quote:
Originally Posted by Pblais
Your numbers are interesting and start to make clear the forces that are potentially involved.

The effect of multiple bolts and a backing plate of steel increases the holding power beyond the shear strength of just the bolts otherwise you wouldn't need a backing plate. Distribution across a bigger deck area gets to be important as the whole mess could tear a hole in the deck with enough force. It's probably the one result that might happen once you seriously overload the winch - the deck gives out before the bolts break.
Or the winch will deform. The prawls will give. At those loads, which I suspect you would never come close to in real life, there are many weak links.


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Originally Posted by Pblais
I would think the deck would delaminate well before the winch flies off like a rocket. Depends a lot on the type of deck. The deck core would shear pretty easy. Even with it holding the constant deflection over time will fatigue the deck. That is where through bolts play well with a backing plate. It really increases the holding power of the deck by a large amount. The idea is the deck should be the point of failure assuming the sheet or the clew don't fail first. The sail could blow a hole in itself at the extreme and thus reduce the force quickly.
Agreed

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Originally Posted by Pblais
I think "sailing" in 120 knots would be an imprecise term for it<g>. If you review the rigging numbers you may find your mast is long gone before the winds get to 120 knots. Obviously so much is going on at that point it would be hard to really predict what would happen.
I can think of precise terms for it, but I don't think that sort of language is allowed here.
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Old 20-12-2006, 10:58   #50
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Fun exercise. I liked this little exploration of "potential force on the rigging." Thanks, Frank and Paul. It was thread drift, but good thread drift.
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Old 20-12-2006, 11:41   #51
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I liked this little exploration of "potential force on the rigging."
It's useful to understand why a jib sheet is as big as it is beyond a nice feel to the hand. The forces at work are quite large and the danger to life and limb is very real even at wind speeds we see commonly in fair weather.

Sail Area X wind speed squared X .00431 makes some interesting numbers
for a 500 sq ft sail

5 knots = 54
10 knots = 215
15 knots = 485
20 knots = 862
25 knots = 1347
30 knots = 1940
35 knots = 2640
40 knots = 3448

These are at least wind speeds you might really encounter.
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Old 20-12-2006, 13:38   #52
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Are those figures lbs Paul?? That's not as high as I was expecting.
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Old 20-12-2006, 15:55   #53
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Yes, it's pounds. It's a static load computation "rule of thumb" formula. It's hard to tell how much it accounts for the drag of the boat, sail shape and trim all would effect the value too so it's just a sort of fun number to throw around. It probably is less accurate at the high and low ends of the scale too.

What numbers did you expect? For planning purposes I'm not sure what you would use for a working load safety factor probably 2 to 3 at least. When you throw that in you'll find a number closer to the strength you would actually buy for lines and design as loads. You sure wouldn't run right on the edge of breaking for very long and expect any lifespan for the gear. Fatigue due to tension / compression wears things down. It can melt rope.

These are static loads and the real killer are the dynamic loads. The 10 to 50 knot gust hurts bad - snap, crackle, pop. Those computations are real work to compute. The static loads really are not much of a problem but the dynamic loads are the ones a boat can have a hard time with. Suddenly gravity is pulling in conjunction with wind and/or wave and the dynamic loads increase quite quick and quite high. The mass of water and the boat are a lot more than the mass of the air and you see what the wind numbers look like. Water moving at even a slow velocity packs a huge load as anyone struck by a wave knows first hand.

So while we are talking static loads we really need to think of numbers higher for what we may build. Dynamic loads and safety factors will drive the requirements a whole lot higher. More like the numbers you perhaps expected.
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Old 20-12-2006, 15:58   #54
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More good figures, Paul. Very interesting. I suppose that set of data is precisely why we put in reefs and furl the genoa as the wind sets in. I'm pretty sure I won't ever see 2000lbs of pressure on my line at any time, unless I made a horrible mistake.

I'm a nervous nellie (very cautious) when it comes to overpowering a boat that is also my home. Yikes!!
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Old 20-12-2006, 19:50   #55
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Originally Posted by FrankZ
3M lists 5200 as having a tensile strength of 700PSI.
The Harken 16ST has a base diameter of 4.75 inches. With a perfect bond and without the water channel in the base we would get 12389 pounds of tensile strength. There is no data for sheer that I could find. They do mention a whopping 1350% elongation before breaking which I thought was interesting.
The number don't quite work that way unless the pull on the winch is straight up, which of course it is not. It is however very close to horizontal, and is trying to tip the winch over and/or shear it off. The tensile force is actually concentrated on the side where the winch is being lifted. The glue bond will stretch and tear. If you glue down a large mainsheet winch it WILL rip off.

You do (indirectly) point out a fallicy of the agrument that says "I'll use an adhesive to help my screws hold" Adhesives like 5200 are so flexible (wintess the huge elongation at failure!) they would exert very little additional force until the screws completly failed.

If you use wood screws and adhesive on a large mainsheet winch it will rip off. Witness Alan's report earlier in this thread.

It is true on a given boat it might be difficult, or even, impossible to through bolt a large mainsheet winch with a metal backing plate for FRP or plywood installations. If your only choice is to use wood screws, that means the boat is poorly designed. It does not mean it is acceptable practice.

Scantlings for boats are sized based on many years of experience, and are well documented in books like Skene's Elements of Yacht Design and other texts. You had better REALLY understand exactly what you are doing before you take shortcuts from the standard way of doing things!

Bill
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Old 20-12-2006, 20:29   #56
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He he, I just shifted my winches to my new outside aftcockpit area. I had to pull up the base that I had adhered down with urathane. I got a screw driver shaft in the drain groove and put the claw of a hammer under it righ against the edge of the base. I pulled with all my might and then I felt it slowly moving and crackling as it moved. Only to find the movement and noise was my fibreglass hammer handle breaking.
I finaly manage to pryze it off and it actually took some of the hard wood pad underneath the base was bonded to.
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Old 20-12-2006, 20:59   #57
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I finaly manage to pryze it off and it actually took some of the hard wood pad underneath the base was bonded to.
The force you exerted with the hammer is nothing compared to what a serious load would have done. I would say if you can remove it with a hammer or small pry bar it never was strong enough to begin with. As you saw the hardwood sheared before the adhesive. If it really was strong enough it would still be there and you would be asking how you could remove it. A through bolted winch won't come off unless you use a very long pry bar and rip a hole in the deck. That is the strength you want.
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Old 20-12-2006, 23:34   #58
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Yes but this was bolted as well. The adhesive was seconds and I guess as discussed above, not really neccesary. When I first bolted these down two years ago, my thinking was, they aren't coming off. The entire aft cabin is going to have to come of before that winch does :-)
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Old 21-12-2006, 06:38   #59
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Originally Posted by GreatKetch
The number don't quite work that way unless the pull on the winch is straight up, which of course it is not. It is however very close to horizontal, and is trying to tip the winch over and/or shear it off. The tensile force is actually concentrated on the side where the winch is being lifted. The glue bond will stretch and tear. If you glue down a large mainsheet winch it WILL rip off.

You do (indirectly) point out a fallicy of the agrument that says "I'll use an adhesive to help my screws hold" Adhesives like 5200 are so flexible (wintess the huge elongation at failure!) they would exert very little additional force until the screws completly failed.

If you use wood screws and adhesive on a large mainsheet winch it will rip off. Witness Alan's report earlier in this thread.

It is true on a given boat it might be difficult, or even, impossible to through bolt a large mainsheet winch with a metal backing plate for FRP or plywood installations. If your only choice is to use wood screws, that means the boat is poorly designed. It does not mean it is acceptable practice.

Scantlings for boats are sized based on many years of experience, and are well documented in books like Skene's Elements of Yacht Design and other texts. You had better REALLY understand exactly what you are doing before you take shortcuts from the standard way of doing things!

Bill
The information I could not find was how ductible 5200 is, or for that matter 316SS. You could have loads of tensile strength but if the material is highly ductible it won't hold the winch, or anything else, down. As the tensile strength of the 316SS and 5200 in my example are close enough and well over the load capacity of the weaker links it would seem that one or the other could be used. That is not the case because 5200 is likely to be far more ductible and if one only used that it would allow the winch to move about quite a bit. It would likely stay on the boat under load, but it wouldn't sit well as it would start to angle towards the load.

I am not suggesting that one take shortcuts, especially with high load applications. Such applications never fail when it is an easy failure, only when the loads are very high and the effects are catasrophic.

I merely started looking at the numbers in a simplistic way as Paul said an adhseive would have no real effect. I don't think the statement is entirely correct, but I think it practical purposes it holds weight.

The simple sets of numbers also do not address shock loads, actual sheet angles, substrate conditions and strength and other loads placed on the winch such as someone leaning on it while grinding. It is also merely one example with numbers that suited my jib sheet installation.

I will say I also suspect that 316SS is more UV and corrosion resistant that 5200, but I don't have emperical evidence of that.
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Old 21-12-2006, 06:41   #60
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Yes but this was bolted as well. The adhesive was seconds and I guess as discussed above, not really neccesary. When I first bolted these down two years ago, my thinking was, they aren't coming off. The entire aft cabin is going to have to come of before that winch does :-)
I suppose you can be thankful that you didn't put the winch down with 5200 onto a steel deck.

Oh and how much fun would it be if you got the 5200 onto the bolt threads and then adhered the nuts on or adhered the bolt into the hole. Oh joy.
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