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Top Section Rivet Stress and Placement

Where do you place your top section collar rivet

  • Toward either side randomly

    Votes: 0 0.0%

  • Total voters
    36
  • Poll closed .

gouvernail

Super Opinionated and Always Correct
There is an accompanying where have you been putting the rivet poll.

I used to put the rivet aft. Eventually all top sections seemed to bend aft. I would end for end the top section and get another equal life before the second bend would ruin the mast. I never trusted straightened masts so I bought lots of masts.

Ken James, a Laser sailor and engineer made a case for placing the rivet on the side. Hank Kleespies, phd engineer who at that time designed tail sections for jet fighters could not refute Ken's "put it on the side" suggestion so we swithced to side rivet sailing.

I have not bought a new top section in four years. Each time I rig I check for bend. If I believe I can see any bending, I place the rivet on the side which would allow the mast to bend back to straight. if I can see no bend, I alternate the rivet from starboard to port each time I rig the boat.

Certainly one man's experience is just that...anecdotal. But, So far I have probably saved not only the funds for extra top sections but I have not torn a sail or say frustrated watching my friends sail off while I got a tow home.

What has been working for you? failing??
 

Murphs

New Member
very interesting

i was told by everyone at my club when i got my first laser to put the rivet towards the gooseneck and have been doing so ever since

your post certainly puts a new perspective on it.

do you put the rivet perpendicular to the goosneck or just anywhere on the side?
 

gouvernail

Super Opinionated and Always Correct
Murchs wrote>>> "do you put the rivet perpendicular to the goosneck or just anywhere on the side?"

I take the time to ATTEMPT to put the rivet exactly in the middle of the side. 90 degrees from the back or front.

When the mast develops a slight bend, it is usually aft. I turn the mast 180 degrees or with the rivet on the oppositre side from when the bend happened, or such that the top section makes lots of leech tension and go sailing until the mast is straight again.

The primary difference between putting the rivet aft and putting it on the side is:
Once the mast bends aft with the riveet aft, you need a new mast. You cannot sail with the rivet on the front very long without busting the mast at the rivet.

I don't know about the actual physiics behind all this but:
1. Since going to the side rivet system, I have experienced small bends. The top sections have universally bent back to straight again without going past and breaking. That surprised me.
2. I have not had a mast bend much. All the aft bends described above and straightened have been so mild I had to roll the mast around to discover the bends.
3. I have been told that slightly stretching aluminum does something which hardens and stiffens it. The mast is NOT stronger. it is only stiffer. after stress.
4. I have been told that the concept of aluminum masts getting old and flexible is incorrect. if the mast is cracked it will be less stiff but if it is not cracked or dented it only becomes stiffer with use. Cycles and bending back and forth on a laser are really very few. They make airplane wings from aluminum and airplane wings bounce and flex for years and years and years without getting soft.
5. Usually, the appearance of a small bend is caused by the plugs and collar becoming pushed to one side of thier available space to wiggle. You can remove the collar, wrap tape around the mast to fill the space between the collar and mast and re rivet the collar to help at the collar. You can add extra rivets to the bottom plug to stabilize the plug. I use four rivets on the plug.
 
very interesting perspective indeed....I'm wondering though, because the whole point of putting the rivet towards the gooseneck is to put it in compression. If the rivet site is half in compression and and half being stretched, i would think that's almost as bad as being completely stretched. Anyone have a reason not to? I understand the argument from a bend-perspective, but the rived thing came from strength/weak spots in the first place.
 
I stand corrected. After talking to my dad (an engineer), he said that the rivet on the side wouldn't be in compression or stretch. Another thought he had, though, was that it doesn't matter which way you face it, as long as you're consistent. Metal fatigue happens because of metal bending back and fourth, not necessarily just from bending in one direction. Therefore, as long as you keep it just one way and don't throw it in willy-nilly, it shouldn't make much of a difference.
 

Steven

New Member
What about those that have older (1988) Lasers that have the top section that has 2 rivets on the collar?

I've always aimed the lower rivet towards the gooseneck.

My top section is not or ever has been bent and is in excellent shape, should I after about 10 years of sailing on this boat, end over end the top section and install the collar with a single rivet as with the newer boats?

I also understand that the older top section are stronger (rumours), the only top sections I've seen break are on newer boats 1995 to present.
 
computeroman2 said:
Another thought he had, though, was that it doesn't matter which way you face it, as long as you're consistent. Metal fatigue happens because of metal bending back and fourth, not necessarily just from bending in one direction. Therefore, as long as you keep it just one way and don't throw it in willy-nilly, it shouldn't make much of a difference.
My husband has broken two upper laser spars. We talked about it with other Laser sailors and it turns out that the last upper spar my husband was alternating where he was putting the rivet each time he sailed to prevent mast bend. He would align the rivet to the gooseneck (back) and the next time out he would align the rivet to the front. The upper spar was about a year or two old. Well, a tropical storm formed offshore and brought about 25-35 mph winds to our protected waters and he had to go sailing. The upper spar snapped and we think that it was his alternating the rivet. Now we are lucky we have a local sail maker that can fix the sail sleeve properly. He is back to aligning the rivet to the gooseneck only.
 

161919

AT SSC
What I do to keep the mast lasting longer is, depending on the use, after some time (1.5 -2 yrs) I invert the mast, placing it upside down. I just move all the parts to the other end of the mast. I usually place my rivet backwards, as I already broke several tops (they used to come with two or three rivets, by the way, not just one)
 

vtgent49

Member
Hi,

I agree with the Gouv's idea, having the rivet on the side is almost equal to neutral effect on strength in a straight back pull such as vanging/2 blocking.

Reversing a slight bend by switching to the other side may successfully work harden the spot, without substantially weakening that area. Work hardening only occurs when the metal takes a permanent bend (plastic deformation) not just pumping the vang or whatever.

I'm kinda lightweight, so I don't really have this problem. Maybe a wimp also, lol. However, I do use '96 or older spars, even on my new boat, and even though softer may make for a better sail shape.

A tight fit between collar/top and between collar/bottom will help reduce the point load that causes the problem, and I've always taped these up to be tight.

I have reversed tops (end for end'ed) and can't quite bring myself to drill a hole for a rivet in the original spot. I put the rivet below the top/bottom joint, countersunk into the bottom of the collar. Quite illegal I'm sure, but this eliminates any concern about stressing the rivet hole. Any engineer should be able to learn from their's or others mistakes.

I've never seen one of these mystery carbon tops, but if they have the rivet in the same place then I'll be seriously disapointed. Vanguard has made many subtle changes for the better in USA boats. Why not move the offending rivet? Why this one eludes them and the other builders is a mystery to me. Changing the Builder's Construction manual doesn't require a vote by us.

Al Russell 182797
 

49208

Tentmaker
vtgent49 said:
I've never seen one of these mystery carbon tops, but if they have the rivet in the same place then I'll be seriously disapointed. Vanguard has made many subtle changes for the better in USA boats. Why not move the offending rivet? Why this one eludes them and the other builders is a mystery to me. Changing the Builder's Construction manual doesn't require a vote by us.

Al Russell 182797
Last I heard (and the test tops I saw) did not use rivets at all. The collar was glued on, as it should be.

Not sure if these were the same sections that were tested down under, but the reports there also said the fittings were glued on. http://laserforum.org/showthread.php?t=504&page=3
 
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