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Old 03-09-2008, 16:13   #16
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Hmmm... weight aloft is multiplied by the distance from your Vert CG. 20# at 40 ft up is an added 800 lb of torque or moment.
Regarding Aluminum chainplates, Aluminum does have similar Ultimate strength ratings as SS. However, aluminum can be very prone to cracking and corrosion when in contact with SS/Bronze etc. I doesnt have the elongation as SS does and so it's cycle fatigue is much worse also. It's Modulus of Elasticity is only a little over a third of SS, so it will bend permanently a lot easier also. I would use alum on an alum boat, but personally would want it as thick as will fit between the turnbuckle jaws and use oversize turnbuckles to give it more bearing area on the pin through the chainplate.

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Old 03-09-2008, 16:18   #17
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Racing a boat in the Olymics for 10 days does not have anything to do with if a design will work over the years. I remember a couple of Americas Cup boats that went to the bottom in seconds. Notable designers too! I agree though, we do need to think out of the box and I am a proponent of "light is right" to an appropriate extent anyway!

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Old 03-09-2008, 17:08   #18

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Easterly, what works in a purpose-built disposable racing boat is not necessarily the same thing as what works in a cost-concious consonsumer market yacht, with a life expectancy of 40-60 years.

Aluminum chainplates may be perfectly good in an Olympic racer that gets a full-time boatwright and inspections on a regular basis. But out in the mundane Real World? Those chainplate are going to be attached to stainless fittings, possibly bronze fittings, and suffer galvanic problems that go unattended form one season to the next.

Never assume that a designer or worker who is trained and qualified in one small field, will be familiar with the problems in any other field. Look at the long lists of boats that have failed--often catastraphically--in races, and you'll see how many highly respected and well paid designers have failed to produce adequate designs.

Keel losses, hull damage (oil canning), rig failures, deck and hatch failures...there's a very long list of professionally designed equipment failures, including EPIRBs that fail to transmit distress signals.

Of course, the design may have been perfectly accurate, and the USER may have simply taken the boat outside of the designed environment. That's where overkill really comes in, you ask "What's bozo gonna do to my product?" and try to make sure he can't do any damage.

Rudder failures? Rudderstoclk failures? You just can't build a rudderstock that won't fail if someone drops the boat on it and bounces it off the bottom. You'd need a massive beam to carry the entire weight of the boat, in a shock load against a solid bottom. And at least in some cases, we know that's what happens to start the failures. Of course, a designer could argue that simply means the conventional rudder design is not suitable for use at sea, and needs to be re-assessed.
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Old 03-09-2008, 20:33   #19
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Originally Posted by easterly View Post
My point is there are ways of making things stronger and lighter and they don't have to cost more, they might not be the standard acceptable way to do things.
Gentle tug here - There is already a thread going about 'What meterial to make chainplates out of."

This thread is more about - For a given material is it better or worse to make it "heavier duty"?

It's a fine line, I know, so carry on.

On Topic - We had our inner stay chain plate fail. It was the second time that same design failed. The first time the rig came down - 8 years ago. The second time one failed the chain plates had been on the boat 7 years - last year.

I had new chain plates made of the same material one size bigger. The reasons were sorta like this:

1 - The chain plate is a flat plate on the deck with a u-bolt through the deck. A backing plate under the deck and a carry through bar from there to the hull
2 - The chain plate failed at the u-bolt to deck plate weld
3 - The chain plate failed in tensile overload, not wearout or shear
4 - The chain plate weld could have been pitted - although not really noticably - weakening the joint

By going to a larger u-bolt I get more tensile strength in the joint to start. As the joint deteriorates (pits) I have more "margin" before the joint is weakend ot the point of failure.

I could bore you with my back on the envelope rig stress estmates but I won't - LOL.

So in my case going to a beefier part was the right answer - do I also need stronger shrouds? No. The shrouds have never failed, the calculated strength vis-a-vis loads is good. The only concern is corrosion in the lower swage which is why they are on the list for replacement this year - 8 years after the rig came down.
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Old 03-09-2008, 20:46   #20
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Years back we cast our own chainplates and hot sockets in silicone bronze. These worked well. Then we shifted up don't know why to 1810 bronze. I guess the breaking strength looked good. Problem was the 1810 was subject to stress crack corrosion. Numbers looked great but the properties when subject to high stress and salt water resulted in loud noises and horrible failures. Cruising Im sticking with design plus and watch the metal. No question metal does weird things under stress and exposed to salt water. standing watch on the night shift in a blow I want the stuff that has been tested. If you want to push some boundaries I thank you for testing.
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Old 05-09-2008, 15:34   #21

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Increasing the diameter of rudder shafts and fittings definitly makes them stronger. To believe otherwise is naive. Lighter doesn't do so well in a collision with a container, nor in carrying sufficient stores and ground tackle , etc..
5 /16th is definitly stronger than 1/4 inch, if the mast is adequately strong.
Mooring bits should also be overkill. All mooring gear should be stronger than the heaviest line you will put on them, chocks included ,even if that is the towline from a tug trying to haul you off a beach. Mine have 90 tons shear strength
A friend told me of a US coastguard guy on the east coast who was killed when a cleat gave way under load and passed right thru him.
I remember an Islander 44 breaking two brand new 1 inch nylon springlines in one day in Rarotonga , break , not chafe thru.
Bow rollers should also be overkill. I remember sailing into PV after hanging my anchor up under sandstone at Isla Isabella.I wasn't the only one. Many boats were repairing broken and bent flimsey stock bow rollers and bowsprits( usually with something equally flimsey).
They should be able to take a load equal to the breaking strength of the strongest rode you will ever use , from all directions, without breaking , or without the rode jumping out. They lost a lot of boats in Cabo in 82 due to this design flaw.
I remember walking down Pier 39 in Frisco and being unable to find a bow roller on any larger boat that wasn't bent. Most were under 3/8th ss plate. I use half inch.
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Old 05-09-2008, 16:01   #22
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Originally Posted by easterly View Post
He was not in the Olympics, he was the US teams boatwright for the last 3 or 4 olympics. I think he may know a thing or 3 about design. I am sure he does not design parts that will fail or that are overweight. My point is there are ways of making things stronger and lighter and they don't have to cost more, they might not be the standard acceptable way to do things. Synthetic rigging, composite chainplates, hybrid drive systems, unconventional sail materials. I bet that when mylar sails first came out there were naysayers. This forum needs to think outside the box once in a while and the people need to be more accepting of others ideas. Tolerance is the key.
Olympic boats are all class racing. Meaning they are identical...essentially. The manufacturer decides the scantlings....or class rules decide the scantlings. The Laser is a perfect example of the first example.

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Old 06-09-2008, 10:02   #23
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back to chainplates.... compare the tangs on the mast with the chainplate size. Many mast tangs are throughbolted SS, one tang on each side of the cable eye. These tangs are not nearly the size of a chainplate. Where is the weakest link? Remarkably, I have heard of more chainplates breaking than mast tangs (maybe I just havent heard about the tangs though) The tangs usually self align, but if the chainplates dont have the proper angle to the shroud alignment, maybe that stresses the chainplate....
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Old 06-09-2008, 11:50   #24
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Originally Posted by Louis Riel View Post
Going from 1/4 inch to 5/16th inch rigging wire for my 31 foter is a total of 17 lbs added for the whole rig, a small priice to pay. I did see a steel Roberts 38 that had gone for 1/4 inch hull plate and greatly regretted it. 3/16th plate has the same toughness as 7 inch cold molded fir, so that was a bit ridiculus.
Put the overkill on small items that frequently break or fail ,like rudders , and leave alone those that rarely break.
Hit a 1/4" steel plate with a 10# hammer and see what happens. Then hit a piece of 7" thick fir with a 10# hammer. Not the same! No comparison!

But back to rigging, and to add to what Paul said in post #8 & 11, Any time you increase the size or strength of one thing you'll have to compensate by beefing up something else. It becomes an endless chore.

If you increase the size of the shrouds then you have to increase the chain plates. And if you increase the size of the chain plates, you have to increase the size of the hull mountings. And before you know it you have a boat that is so heavy you'll need to increase it's length to hold all the weight so it'll sail, or add a bigger motor in the case of powering.

No chain is stronger then it's weakest link!!!! So, something has to break! So, what shall it be????

How about if you rip the chain plate out of the hull?? No, not a good idea. How about if you buckle the mast and it comes tumbling down. (With over side shrouds the tension required is more on lager wires)

On larger boats (over 30') they have multiple shrouds to even out the pull on everything, making it more flexible and that's the secret. Boats have to be flexible to a certain extent, just like an airplane. The boat has to be able to withstand shock loads with in an economically without breaking. e.g. The difference between a piece of plastic and a car tire.

So, if a boat crests a wave of 30' and drops down what do you want to sacrifice? I think one shroud would make you drop sails and make repairs.

The key is to buy a boat that has been engineered RIGHT with shock loads calculated in by an experienced Marine Engineer. And the rest is up to your own experience as a seaman! Know you boats capabilities and do not exceed, period. And if you do, be prepared (life saving gear) just like the racers.

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