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PostPosted: Fri Jan 12, 2018 9:40 am 
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Joined: Mon May 22, 2006 2:21 pm
Posts: 13
Location: Italy
The two pieces mast of my HC 14 was bent in a capsize.
Only the lower piece of the mast is bent, the upper part is straight.
The riveteted internal sleeve (the one that connects the two parts of the mast) broke, so I ordered a new one.

Here my request for advice:
1: is there something special I should look for when removing the old broken sleeve and installing the new one? Maybe the correct alignment or a way to rivet it?

2: how should I straighten the bent extrusion? should I heat it beforehand? at what temperature? Should I anneal it or just warm it a bit? I want the mast to keep its tensile properties.
I will work with a blacksmith who has many tools but not that much experience with aluminum.

Thanks in advance
Leone


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PostPosted: Sat Jan 13, 2018 9:22 am 
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Joined: Thu May 03, 2007 2:28 pm
Posts: 79
Location: Chicago
I assume you are talking about a curve and not a dented mast. I straightened the gentle curve out of the aluminum bottom piece of my H16 comp tip mast last year.

I checked with my local auto body shop to do it for me and the owner recommended against heating the aluminum. He recommended a jig and suggested I check with the local awning shop.

I wound up just doing it with sandbags and a hydraulic bottle jack (and a couple of handy farmers). We laid the mast on sandbags with the curve up, put a 3 foot (1m) long board on top at the apex and a jack on top of that with a solid platform over it (like a vehicle). Pumping the jack, it pushed the mast down and the board kept it from denting. We slowly bent the mast in the opposite direction of the curve several times, going several inches to an opposite curve each time. We'd move the mast and jack as the apex point moved. The curve essentially started moving up the mast and disappearing. Be careful to support the aluminum part and not put pressure on the upper composite portion.

I re-set the comp tip in another mast several years ago and the best tool I got for that was a riveter with long (1m) handles. Those stainless rivets with top hats are really hard to pull with hand riveters.

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1989 H16
2009 H16 squaretop


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PostPosted: Mon Jan 15, 2018 9:16 am 
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Joined: Mon May 22, 2006 2:21 pm
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Location: Italy
Thanks!
My answers (and new questions...)

Yes, the mast is just bent. No dents.

What do you mean by:
Quote:
We slowly bent the mast in the opposite direction of the curve several times, going several inches to an opposite curve each time
Quote:
?
I have an image of what you did that is on a straight plane, maybe was there some empty space under the sandbags below the curved part of the mast? and by how much should I, in case, bend the mast backwards? I would like to avoid ending up with a snake-like shape...

My new question: I am worried that the extrusion may collapse under the jack's load. How did you avoid collapse of the elliptical shape? Just applied delicate and incremental pressure?

Thanks
Leone


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PostPosted: Mon Jan 15, 2018 10:07 am 
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Joined: Mon May 09, 2005 10:25 am
Posts: 3510
Location: Jersey Shore
In the US, we do not have two-piece masts like you describe. Here, the masts are either one-piece solid aluminum or they are two pieces where the lower section (below the shrouds) is aluminum and the upper section (above the shrouds) is fiberglass (comptip). Masts in the US do not have an internal aluminum sleeve. But you could probably install your sleeve in the same way that we install a comptip. If the fit is snug and straight, then just rivet it in. If the fit is loose, then you can coat the surface with thickened epoxy, insert it into the mast, make sure it's straight, and then let the epoxy cure. Once the epoxy is hardened, install the rivets.

For the bent section, using heat is not recommended. Hobie uses tempered aluminum for the masts. If you heat it up too much, you could remove the temper which will reduce the mast's strength. You're better off attempting to bend it back cold. As described in the previous post, use a long board to help spread out the load at your jack and support points so you don't accidentally crush the mast.

sm


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PostPosted: Mon Jan 15, 2018 10:16 am 
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Joined: Thu May 03, 2007 2:28 pm
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Location: Chicago
Quote:
maybe was there some empty space under the sandbags below the curved part of the mast?


yes, exactly. Here is a picture that shows how we set it up. You can see that the mast is bowed downward, which is the opposite bend (it was upwardly convex), and the amount of the bend we are applying at the moment this photo was made is a little more in the opposite direction of what we were trying to fix - maybe by a couple inches.

Image

Quote:
by how much should I, in case, bend the mast backwards? I would like to avoid ending up with a snake-like shape...


We did this very slowly. We would pressure it for a minute or so then release and look. We started out with a little bend and as it had no apparent effect we would do a little farther. We were worried about creating an s-curve, too, so we would just flex it, release it and eyeball down the luff track, then repeat. I think having a longish board on top to cause a wider flex point helped. Also we adjusted the distance between the sandbags to change how sharp the curve was. Bit by bit feeling our way along is all I can say. It was hard to tell exactly where the inflection point was as it moved along the mast. There are a surprising number of engineers on here - maybe they can make the process more scientific?

Quote:
My new question: I am worried that the extrusion may collapse under the jack's load. How did you avoid collapse of the elliptical shape? Just applied delicate and incremental pressure?


By collapse do you mean dent or shear? That's what the long 2x4 board on top of the mast is for - to spread the load and keep it from being a point load. It flexes too, but not as much as the mast. And yes, we'd apply pressure then eyeball it over and over. We didn't want to over-correct anywhere and the only way I could think was just to try to do a little at a time. In all it only took us an hour or so.

Note the sandbags at the left side of the mast are well down-mast from the joint with the composite tip. My question for others is - if I think I have a slight bend in my comp tip, how would you straighten that? It's a fiberglass tube right?

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1989 H16
2009 H16 squaretop


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PostPosted: Thu Jan 18, 2018 7:42 am 
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Joined: Mon May 22, 2006 2:21 pm
Posts: 13
Location: Italy
The picture says more than a thousand words. Thanks

My mast is bent, compared to yours, more at the upper tip of the main aluminum extrusion. I guess I will need to take extra care when applying pressure, because in my case the wooden board will sit ON (or very near to) the tip of the extrusion. This is what I meant when I said I was worried about collapsing the extrusion; I feared that the side (or the tip) of the mast may lose its shape under pressure.

I think I will weep the broken internal sleeve while straightening the mast, in order to protect the tip from damage.
Then I guess I'll have a hard time getting the sleeve out of the mast...

In Europe we have (for the H14s and H16s) the option of a two-piece mast, for easy car rooftop (trailerless) transportation. Not for safety as in the US with the comptip.
I also have a h18 and I was convinced that the H18s comptip tapered mast would be better in strong winds than the regular all aluminum I have. But that's another story


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