I have had a bizzare accident with my Blade and need the collective advice of the group.
On a recent Saturday outing to the Long Beach, CA beach cat launching area named Claremont, There was one cat set up on the beach, mine, and about 50 kite boarders. I was debating whether to risk singlehanding my boat in the brisk winds and as I watched in horror, an out-of-control kite sailor came up the beach and in passing my sailess but rigged Blade, caught the tip of the mast with his kite line, and casized the boat on the beach. There was nothing to slow the mast down except the sand.
At first we didn't notice any damage so just put the boat away.
This last weekend I verified that the mast is bent slightly to starboard just at or below the diamonds and also has a several degree twist to starboard at the tip.
Questions for the group are:
Anbody been successful taking this kind of bend and twist out of a mast? I'll try to get pictures of the condition later.
Did you do it with the diamonds on or off?
I'm contemplating a couple of levers with attached clamps shaped to fit the contour of the mast section. One guy pulls the other holds steady to remove the twist.
For the bend, just apply adequate pressure in opposition to the bend and...
So what do you think?
John

The bend in an aluminium mast is no problem (as long as there isn’t a “crimp” in it) just release the diamonds and support the head and base of the mast on anything off the ground (two timber work horses are good or two chairs but not on any sharp edges, even to the point of putting a pillow under the top and bottom of the mast) then looking along the mast with the bend upwards sit on the maximum point of the bend rock up and down exerting enough pressure to gradually take the bend out. Always check by looking along the length of the mast every couple of “bounces” to check your progress. Don’t be surprised at how much “weight” you have to put on the mast to get it to respond. When the mast is straight then continue to “bend it in the other direction to duplicate the approx’ bend in the opposite direction. After which reverse the mast and in the same way take that bend out of the mast.
The reason that you put a reverse bend into the mast then remove it is because when the original bend occurred one side of the mast section has been slightly “stretched” and if you simply remove it there is still a bias in the wall from one side to the other. By duplicating the original bend the other way, then removing it you have evened up both walls and the bend won’t show up as a different bend characteristic from tack to tack when your sailing as it would if you only removed the original bend.
The twist is another thing entirely. Firstly check when the diamonds are disconnected completely to see if it is only due to the position of the bend and the diamond tension that the mast only appears to have a twist and then check after the bend is removed, the “twist” may disappear with the bend. Other than that I have removed dozens of bends in Aluminium masts but I have never seen one twisted except straight from out of the dies during manufacture.

I assume you have the details of the kite surfer involved, I would wait for the insurance assosrs report from his insurance company. I assume you do have these details and he was insured?

When you bend the mast back and forth like this, dont you weaken the walls (material fatigue) too much for the mast to be dependable afterwards? I know aluminium is pretty brittle when bent back and forth, but perhaps the elongation and stress is too small to significantly affect the material?

Bending the material should actually harden it and make it stronger and stiffer.

A simple experiment is to bend a wire coat hanger and try to straighten it. It's very hard to do because the material at the bend has been work hardened.

I believe fatigue only occurs after it's been done a heap of times, ie. in the thousands of cycles.

Well, this is the case for steel, fairly sure it's the same for aluminium alloys.

Ok, I am no engineer, just describing what I think I have seen. But the harder the alloy become, will it not also become more brittle? It's moot when it comes to masts of course if you have to cycle it a couple of thousand times, but it's interesting to know.

Oh yeah, definitely, if it becomes harder it also becomes more brittle. That's my understanding anyway, I could be wrong.

I don't believe it is anything to worry about though, ie. it won't become so brittle that dropping it or hitting it with a hammer will smash it.

It also depends on how much it has been bent. From the description given, it doesn't sound too bad. If you can see any "stretch marks" in the material near the bend, it may be too far gone.

And stretch marks would indicate that plastic deformation have taken place, or is that too simplistic?

I straightened a mast that had bowed just above the spreaders using a hydraulic trolley jack and piece of heavy duty steam pipe. Strap the ends of the pipe/beam to the bare mast (about 18 inches away) using 3 inch lifting/tie down straps using several turns to spread the load area. Place the jack under the centre of the bend/bow which should also be in the centre of the beam. Using a wooden block on top of the jack to prevent point loading raise the jack slowly until a moderate reverse bend can be seen. Slowly release the pressure and check alignment. Repeat using increased pressure if required.
I have known two people to take the bend out a mast by sitting at the ends of the mast with the bend resting on a sand dune but the trolley jack method makes it easier to judge the reverse bend being applied to straighten the mast.
I reduced a bend of 5"-6" inches measured at mast tip to less than 1/8" on the unsupported(diamonds removed) mast.

Technically, my understanding is that plastic deformation has already occured if the mast is bent as described. Plastic deformation is defined as a material not returning to its original shape once a load is removed. Elastic deformation occurs when the material returns to its original shape once the load is removed, this happens all the time just through everyday use.

Just from limited experience with aluminium in general and some smaller dinghy masts, small bends that don't have stretch marks can be easily removed with little fear of weakening the mast. Stretch marks indicate that dislocations have occured in the materials crystal structure and I believe that is when fatigue may become an issue, and straightened will be almost impossible anyway.

Thanks guys. I'll work on the bend with the diamonds off, then check out to see if the twist is still there. The bend and twist is slight and went unnoticed for two weeks which still doesn't explain how I let the kite sailor get away without getting the proper I.D. Another lesson learned.

Been here.
Taipan superwing.
Sure, you have to release the diammands.
But DO NOT have a point for bend that is too small.
I tried three times to bend strait with the mast between two posts.
THe mast is very stiff..to actually bend. I got tired and did not put the padding in where the post was just below the bend and the mast caved as point of contact was too small. It is now strait but has a dent in it. ; (
So I went and got a second hand A class carbon one.

The mast will straiten. The spar maker told me to put the mast between two supports. Then tie a yoke around the bend point to sprend load and pull the mast down toward the floor using a reduction unit and turn block. Then release and look and then take it down a little more. release and check until the bend moves.

Take your time. Be patient.

Bend aluminium too often and it will get brittle and break.


Anyone know how to get a dent out of a superwing?? : )

You may need a superman... <img src="http://www.catsailor.com/forums/images/graemlins/smirk.gif" alt="" />

You'd be happy to see the kiwis get through to the finals of the LV Cup. Do you reckon they can go all the way? It appeared their heavy weather (if 15 knots is considered heavy) performance in the last race was exceptional.

I removed a dent on a Prindle 18 mast by placing a small hydraulic plunger inside the mast and pump up the oil pressure. I had borrowed this hydraulic plunger from a car body repair shop. Most time was spend on making special shaped elements that would distribute the load evenly over.

It can be done, and it was done.

Wouter

If the twist does not disappear, how can it be removed?

It will go if the mast breaks and is replaced (insurance) actually here that would have been a legitimate insurance claim replacement for the mast if the twist cannot be “professionally” removed.

Sure the twist wasn't there originally?

Excellent Wouter. Thank you.