We were sailing in the sierra mountains this weekend and had very strong winds while some rain swept in. We were having a great time until the clew plates ripped from our jib. On the lake we just rolled up the jib and then sailed with just the main for a while before bringing it home. Now it is time to assess the damage and figure out what it takes to put it back together again.
I've checked Murray's and a new set of plates and rivets is pretty cheap so I'm going to do that. Before I hit buy on the order though, I'm wondering if anyone has any suggestions for how to reinforce the sail before I put the plates on and anything else I should put in the order.
I have another purchase I've put off a while that I'm thinking of ordering while I'm at it. I don't have a righting line (other than a think line that is attached around the forward crossbar) so I'm thinking of the basic "Stretch Righting" setup. I normally sail with myself, and 2 sons (16 and 13) on a small lake.
You can add more dacron to the sail, and then a new clew plate but in my opinion.. if your sails are giving out in a gust... probably time for new sails.
Andrew, I'm not sure it was his sail that let go. Looking closely at the photo, only one hole is torn out, that would be where the blocks were attached. The rivets did not pull through the material. It looks like the rivets let go, leaving the jibs full load on the single hole where the blocks attached.
A brand new sail cannot take that load on a single point, so it rips through.
In a strong wind the clew plate stays straight, but it doesn't want to, it wants to conform to the bend in the sail. The rivets are then required to hold a tension load, trying to separate the two halves of the clew plate. A rivet normally is designed to mostly hold a shear load. Centre peened usually fail from the rear side when exposed to tension, looking at them you can see how little material is on the back side.
I had the same thing happen on an N5.7 mainsail. They used centre peened rivets, & the rear of the rivets were corroded from salt/age. The sail itself had seen fairly light use.
I heard the rivets letting go, as soon as that happened the hook on the main tore through the material.
In my case both plates fell on the tramp & were saved.
If you elect to fix it, think about the science behind a clew plate. Holding the forces without tearing through is not simply a function of using 10 rivets to spread the load, that will not last. The strength comes from the 2 halves of the plate squeezing the material tightly, in essence spreading the load over a distance equal to the top edge of the plate. Use vice grips, two strips of hardwood & screw clamps, or some similar setup to hold the plates tightly together BEFORE you start pounding the rivets.
Try not to hit the rivet 50 times, that tends to harden the rivet, making it brittle. Aviation rivets ideally only get hit 6 times to compress (and slightly expand the shaft) along with peening the end. The tin bashers in the hangar use pneumatic guns that give 6 hits to trigger pull. IF the rivet isn't "right", they don't hit it again, it gets drilled out & replaced. I also know that the rivets have shelf life, I've seen them baking them in an oven before use.
Edited by Edchris177 on Aug 06, 2012 - 08:09 AM.
-- Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap --
Andrew,
The sails are definitely old, but given it is just the boys and I out playing around on the lake, the fact that we don't get max performance from them I don't believe has been an issue for us. New sails are in my future, but I've been hoping to put that off a while longer. Not that I'm against a good excuse
Chris,
I looked at the plates when I got home tonight, it is definitely the rivets that failed. There is a good deal of corrosion on the plates, and all the rivets that are left are missing their backside. The sail itself has 2 tears, one from the jib sheet block and one rivet hole, the rest of the holes are intact.
I'm thinking some sail tape, new clew plate and rivets then hopefully that gets me a couple more trips to the lake this summer/fall and then maybe new sails for Christmas.
You should get a couple more years out of it. Just make sure things are tightly clamped together when you rivet.
Setting rivets is not hard, but there is science behind it. To bad ERICE isn't your neighbour, he has probably drawn more rivet on Boeings than anyone on this forum.
You need an anvil on the front side, not a 100lb blacksmith anvil,(though that will work), but a piece of solid steel against which you set the rivet head. This is critical. It prevents movement or absorption of energy,the rivet shank is forced to absorb the energy of the blow, & expands somewhat, making a very tight fit. The rest of the energy expands the end.
In the absence of a pneumatic rivet gun, you can use another small block of steel, or a chisel type tool with a concave, or flat head. (I have used a coarse pin punch) Set that against the back side & strike 6 good blows.
Research may show a duo, one holding the anvil against the rear, & calling "draw", "rivet".
What they are doing during "draw", is striking the material beside the rivet, to force it tightly together, then the call "rivet", is the actual peening of the rivet.
-- Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap --
Centre peened, notice how little material was expanded on the backside, that is where they usually fail.
Make sure you get the right size rivets, both diameter & length. If you run into problems, go to your local aircraft repair operation, ask for an AME who does sheet metal.
-- Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap --
I don't understand the talk about peened rivets. The only kind of rivets I've seen used on a beachcat were pop rivets. I had the clew plate fall off a Hobie 18 factory sail just as I was going to launch for a regatta at Ocean Springs one year, all the factory rivets had disintegrated but the plate itself was fine. Borrowed a pop-rivet gun and had it re-fastened in a few minutes, used it that way for a couple of years before I sold the boat.
There are supposed to be rivets and new clew plates in the kit I ordered, but I don't know what kind of rivets. I didn't order express shipping so it will probably be a week before I get it.
I have experience with pop-rivets as I've used them a lot on cars (another hobby is I race cars with my brothers), but I have no experience with peened rivets, but if that is what shows up I'll find some spares to try first.
Pop rivets are very common on Cats, usually because many of the attachments are "blind". That is, there is no access to one side of the connection. You simply cannot get a bucking bar inside the mast, or most parts of the hull.
Pop rivets are hollow, they work by pulling a pin through the hollow rivet. The pin has a small knob at the end that expands the shank of the rivet as it is pulled through.
Normal rivets are solid shank, & are supported by an anvil(bucking bar) on one side, then peend by hammer or pneumatic tool on the other. The first blow or two serve to swell the shaft, making for a tight, waterproof connection that strongly resists the two pieces ability to rotate. The final blows form a head, so it cannot pull out.
They are stronger & more fatigue resistant than pop rivets, hence their wide use in boatbuilding, bridges & aircraft.
If you look at the clews on Nacra sails, you will see they are all solid shank rivets, which have greater resistance to shear than pop rivets. In this case they have a small divot in the end. A small round end bar is inserted in the divot & struck, (most likely a pneumatic gun was used that contained the small nub, thereby rendering the process simple & quick, literally one pull of the trigger)resulting in the center peened end you see in the photo. You can see there is not much material on the backside, two decades of corrosion, & the little ring tends to fail first, allowing the plates to separate.
Normal rivets have the entire end flattened, it is a stronger end, but doesn't look as good, especially if some monkey just wails on it with a hammer. The other reason center peened was probably used is the end result is an almost flush fit, perhaps more desirable than the end that would normally protrude, leading to chafing of material & maybe flesh.
I don't have a better photo, but this shows the small ring left on the backside of the rivet. If your sails were done this way, give a close look to the head & clew plates. I have one ib that shows most of them ready to fail.
-- Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap --
You can peen the blind side of a pop rivet to make it cleaner. The tough part is getting the nail head out. After that you start it mushrooming with a spike shaped cold chisel then pound it flat (with a piece of solid metal for backing like a vise). Ive also seen stainless bolts with loctite used.
Pop rivets will work fine in a sail plate as long as they are the right size and are stronger than aluminum- stainless steel as an example. The backing plate acts as a washer. They just present a potential for damage to the sail when rolled up for storage.
Edited by klozhald on Aug 07, 2012 - 11:37 AM.
-- Sheet In!
Bob
_/)_____/)_/)____/)____/)_____/)/)__________/)__
Prindle 18-2 #244 "Wakizashi"
Prindle 16 #3690 "Pegasus" Sold (sigh)
AZ Multihull Fleet 42 member
(Way) Past Commodore of Prindle Fleet 14
Arizona, USA --
Cool, learn something new every day. With my skills at swinging a hammer (ouch) I think I'll stick to pop-rivets, even though those solid ones are no doubt stronger when installed right.
