Torturing A Mast Back Into Straightness

Discussion in 'Boat Design' started by viking north, Dec 14, 2015.

  1. viking north
    Joined: Dec 2010
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    Location: Newfoundland & Nova Scotia

    viking north VINLAND

    I thought this a very appropriate next thread to "Panel Stress" :) . After purchasing what I call my "Fill In' boat (A 30ft. Paceship) I discovered the main mast was damaged. It had about a 1 in. bend in the fore & aft direction about 10ft up the 33ft. mast.. At the time of purchase the mast was stored and strapped on the trailer under the boat and the seller had cleverally taped the rigging hiding the bend. Other than kicking my own trusting *** it did provide me an opportunity to do something i have never attempted before and thought i'd pass it on. I was fortunate in that it was a gradual bend, no kinks, almost perfectly oriented fore and aft and spread out over an area of about 20ft. I recently learned that the mast had been bent and in use as such for years. During an attempt to lower it a mishap occurred and the mast was dropped. I will post the procedure I used over a couple of postings to better describe how i went about it. Two of the photos attached show the holding jigs spaced about 20ft. apart ,I.E. over the length of the gradual bend and equal heights above the floor. Next I placed the jack at the approx. center of the bend. Basically there was some slight damage here showing the impact point. I placed a dense foam pad between the jack and the mast and began the torture. I firmed up the jack to mast contact and using a propane torch I heated the mast along the sides and top about 3ft. either side of center with just enough heat that you can still "quick touch" without burning your hand. The idea here is not to heat it enough to alter the metals temper but allow it to take the gradual stresses without snapping. Patience plays a big role here. It took me two days to heat/jack torture this bent section into a 4 in. bow opposite the 1 in. bend. I then left it as such for 24hrs. and checked for straightness using a string as I will show in my next posting. My initial 24hr. torture session took about a 1/4 to 3/8 in. out of the bend damage. My second and third torture sessions took worked up to 36 and 48 hrs. which successfully reduced the damaged bend to 1/8 inch overbend hoping to compensate for any metal memory. ??? :D
     

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  2. viking north
    Joined: Dec 2010
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    Location: Newfoundland & Nova Scotia

    viking north VINLAND

    Mast Straightening Torture

    After all the head turning, teeth gritting and eye squinting JACKING, one has to check the results, providing of course it doesn't all go to hell with a bang. :D I am still truly amazed with the forgiveness and strength built into these mast sections, far beyond what i ever expected. Anyway checking the results as shown by the photos attached is just a simple matter of setting up a string, spacing it equally off the mast on either end . In this case 1.5 in. blocks and checking with the same along the line. Note, this test was at the end of the 36hr. torture session. From 1in. down to 1/8 in., getting very close.:eek: If anyone out there can add to this nerve racking procedure i would really appreciate it as wearing a jock strap while stepping over the stressed tube to get to my tool room for 4 days was no fun. :D

    P.S. Mr. Moderator I possibly should have posted this under Boatbuilding if so I stand corrected :)
     

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  3. SukiSolo
    Joined: Dec 2012
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    Location: Hampshire UK

    SukiSolo Senior Member

    I've used a much cruder way of straightening dinghy extruded mast - find suitable fence with uprights, find centre of bend, wedge in position and gently spring until the first sign of yield!. Works great, but only on even bends, 90+% of the time the track is dead straight afterwards.
     
  4. viking north
    Joined: Dec 2010
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    Location: Newfoundland & Nova Scotia

    viking north VINLAND

    For smaller extrusions I can see where fence posts and forked trees might come in handy. Even at that I would imagine one would have to be careful not to overbend as a result of overpowering the smaller sections. Something i neglected to mention was the extrusion size of approx. 3.5 X 5 whose resistance to bending or breakage just blew me away. The pump handle on the 7000lb. jack was under as much stress as if i were jacking up my 350 series Dodge Camper. I think the key is to very gradually torture it back into shape. Give the metal time to stretch and compress. One of the big concerns I read about is the metal can become what is termed "Work Hardened" (brittle) . In my case the bend was so gradual and over such a long arch I am not too concerned. In addition, after seeing the stress I put it thru, i'd say it's about 100% over engineered anyway :)
     
  5. cor
    Joined: May 2008
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    Location: Alaska

    cor Senior Member

    There is no need to take 36 hours to bend it. The same results could be had in 3 seconds. How many hours did it take for the bend to happen when it was damaged?
     

  6. viking north
    Joined: Dec 2010
    Posts: 1,865
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    Location: Newfoundland & Nova Scotia

    viking north VINLAND

    My thinking was not to shock it a second time. The initial impact of damage would have almost instantaneously compressed the metal on the impact face (fwd)and stretched it on the opposite face.(aft) In this case the aft or sail slider grooved face is where the much heavier metal is. Being such logic dictates there was more stretching than compressing happening per given length of the section. Thus straightening would entail the opposite. Regard less I wasn't taking any chances. I had another 40ft. piece of tube of the same dimensions and could have fabricated another mast no problem but wanted to save it for my Motorsailer Project. This Paceship project is just my "fill in" boat until the motorsailer is completed.
    On another note, I see you are located in Alaska, my Uncle operated bulldozer building the original Alaska highway. I just completed an historical study(hobby) using Google Aerial Views as my maps of some 23 of the Aleutian Islands. It took me some 3 months as I viewed firstly the complete coastline of each prior to their interiors . My interest mostly being the Japanese Occupation Bases and the Allied action against them. I was surprised to discover that the Royal Canadian Air Force played a role as I am ex RCAF and was unaware of such. Amazingly the runways, building foundations and bomb craters are still very visible.Development on the Islands since the war is also quite interesting right out to the last island in the chain. I came across a number of hunting /fishing camps and what looks like farms on different islands. Interesting also nothing grows on those that were used for nuclear bomb testing. A very remote and beckoning part of the world.
     
    Last edited: Dec 15, 2015
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