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Thread: STRONGBACK DISCUSSION etc.

  1. #1
    Join Date
    Sep 2001
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    Northern MN
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    STRONGBACK DISCUSSION etc.

    113 needs a new beam and since Ebb has broke the mold I think we're going to laminate a new beam similar to his. Fortunately for me, I have a friend that is well versed in the ways of wood. He's laminated everything from fishing nets to display cases to full blown foot bridges. He also finds my anxiety regarding this piece humorous. To him it's just another arc, but as we all know it's the backbone of our beloved little craft. So we've done some research and mixed his experience with a little nautical input. Here is where it has to end up. One of the previous owners did a repair(hack) job on the area NEAR the mast step but not really. As far as I can tell all they did was cut out the cabin liner in that area cut through the inner skin and then glue it back in completely cockeyed and unfair. Off by a strong 3/16" Not to mention that the inner skin is still mobile under the step. So we'll put in our strongback and main bulkhead first and then go topside and finish the job.
    p.s. I know-I know the plywood head liner doesn't look original. But it's stuck really well to the fiberglass so we'll deal with it. Actually it may facilitate in adding handholds forward.
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  2. #2
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    Gettin Jiggy with it

    This is what we're going to use to make our strongback. Well, most of it at least. Made from scap wood that has acumulated over the years. I traced the radius onto the jig base from a pattern made from 113's cabin top. The pattern was exact-so it included all the waves and woobees. Then I faired line to give a smooth arc the was the best fit at the twelve contact points of the jig knowing that some of the strongback will need to be ground away and some spots may need to be filled when jacked into place. Then I built up the two by four blocks along that line. The blocks on the ends of the arc are just stop blocks to keep the plys from running wild. They are in the same plane or angle as the sides of the coach roof but they are 3/8" wider so we can shape the ends of the strongback to a smooth edge. The greatest unsupported span of our strongback will be 24" so I'm opting for a slimmer, trimmer beam than Ebb. I'm planning for 2 3/4" wide by 3 1/2" tall. The four pieces of wood spanning the blocks are 2 3/4" off of the jig surface and are there to keep the plys from slipping off eack other when pressure is applied with the clamps. They are pre-drilled and mounted with screws so they will be removed to allow the glued plys to be introduced to the jig, then replaced and 'snugged' as needed when the cranking starts. It all sounds straight forward doesn't it? Wish us luck or send beer!
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  3. #3
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    338 sends LUCK!

  4. #4
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    strengthening the strongback

    I was thinking of doing the repair recommended in the manual where you add steel plates to either side of the beam under the mast. Where I didn't see any bowing there before, or very little, it seems to be more pronounced now.
    But I have lots of questions.

    I guess I don't really understand why adding the plates would strengthen the strongback--they wouldn't really be resting on anything so they wouldn't actually bear any weight.

    I met someone who did this on an Albin Vega but he recommended strongly that you not jack up the beam first, because of all the unknown stresses you might inadvertently add. He just added the plate to the beam as it was. Any opinions?

    I pulled off some of the formica around the beam to see what was under there and I'd like to keep going with taking it off but it continues behind the lockers. Any suggestions for how to cut it flush with the top surface of the lockers? Also, I've been warned against doing this, the part I took off came off very easily but I guess if some of it is better adhered you could actually damage the bulkhead. Opinions?

    also, I found three bolts already going through the beam--is that normal?

    Robin
    Mischief #44
    [SIZE=3]Robin[/SIZE]

  5. #5
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    you might press the SEARCH button up top here
    and type in 'compression beam'
    and wade thru some of the stuff.

  6. #6
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    Robin,
    Think of the two plates as splints if you like, but the plates and bolts are really operating as a lever. You know how you can lift a heavy object rather easily by using a long board with something 'jammed' underneath it close to the object your lifting. Well, you can also stop heavy things from moving using the same priciple. In this case the heavy object is the load of the mast step and we want to stop it. The plates work in conjunction with the bolts to form levers and fulcrum.
    I don't have the manual memorized yet so I can't recall if it asks you to relax the standing rigging slightly before jacking. But if the mast has been stepped and unstepped several times and if the standing rigging has been adjusted or tensioned in accordance with the changing (lower) mast step you may have to relax it before jacking. I, personally, would jack the beam before starting to work on it. It's not realistic to think you can take all of the sag out of the beam by jacking it up. However, restoring the cabin top to its original shape or very close to it would be very desirable for an afternoon's work. Without a doubt, jacking up the beam against fully tensioned standing rigging or lifting the cabin top beyond its original position would not be good.
    The three bolts allready there? No idea. As sencondary and tertiary owners we sometimes run across some strange @*&#!
    Careful on removing that laminate! That's exactly how our redo got started. If your heart's set on it try removing all the trim that's necessary first then lay a piece flat metal stock (like a framing square) on the cabinet top or face to protect it and provide a straight edge. Then score the laminate repeatedly with a utility knife. Instead of going for broke in one pass with the knife try eight or nine consistent passes. Heat the laminate with a heat gun or one furious hair dryer and slide a 6" putty knife behind the laminate to work it loose. Then try to 'snap' it off along the score. Work in straight lines. I, more than others, understand the need to snoop but keep in mind you'll need to put something back. Know when to say when! Most of all really study what you find. For what it's worth, Tony G

  7. #7
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    Sep 2001
    Location
    Santa Cruz, California
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    Strengthening the mast support, strongbacks etc.

    Thanks to Bill for your continuing efforts and to Dave (marymandara) for your efforts to discover and or produce masthead replacements and rudder shoes etc. Rather than respond on that thread in the "General - Off Topic" forum, I am asking for this new one on the topic of "Strengthening the mast support, strongbacks etc." in this "Technical forum"

    My big technical problem right now is serious structural damage to the mast support area and strong back caused by a recent accident, and also a damaged mast head fitting. I have looked at the Association Manual and various threads on this site in regard to reinforcing or augmenting the strongback, and finding the necessary parts. The information seems to be spread all over, but the available information is incomplete.

    I have found and reviewed photos of the main salon side of stainless steel plates added to the strongbacks in Sirroco and Orinoco Flow, but would be interested in shots of those installations from the forward cabin and also photos and text descriptions of approaches taken by others to deal with mast compression and mast support issues.

    I had no personal issues in this area whatsoever, until two days ago, but in a harbor tabernacle-related accident on July 28th, my mast was driven downward and aft into the deck thus cracking the laminate or solid section under the mast clear through to the cabin liner. A previous owner unstepped the mast and modified the deck section with epoxy in time past in a manner which will not be clear to me until destructive testing has been initiated. I imagine that I may have my hands full shortly.

    I have not been able to determine the extent of damage to the masthead fitting. It took the brunt of th eimpact, but transferred much of the force down the mast into the deck.

    Just knowing that new mast head fittings may be available soon is very helpful to me.

    I fear that the repairs may be both expensive and costly time-wise.

    It would be nice to have all of this information in one thread on this forum. So if you all see fit, I could use some photos and words of advice in this area.
    Scott

  8. #8
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    Scott,
    Perhaps a shorter winded person than me for this........but if you do wade back and weed thru the compression beam and/or bulkhead posts there is a wealth of info.

    You have to remove the mast to access damage to the mast base area. And you do have to forensic what the DFO did there. It would indeed take enormous forces to do structural damage IMCO because the compression bulkhead and framing distributes the loads.

    You separate out what the new accident caused, what the DFO caused (ie what his repairs were,) and what time has caused to the area by shrinkage of interior structure and the constant pushing of the mast down by the rigging. And decay that might be present in the composite (balsa core) and the beam. Then you figure what it will take to fix it - and what level of repair. If you a DIY then why not run it by the 'workers' on this forum?

    I found, anyway, that the cabin top returned to its natural curve with the mast and the mast step removed, or nearly so, you can assume the cabin top was a fair curve befor the mast was set there. Then probe and assess the actual damage. Take photos!!!


    [It is kind of like talking in your hat when you can't see what you are talking about. Descriptions sometimes take too long in words to form a mental image in the reader. Assuming the damage is extensive and the rise of the cabin aft f the mast was what the mast was forced into.... the drill is the same: ie remove the rigging and the mast. An actual crack in the molding of the cabin HAS to be posted here. The curves and radiuses make it immensely strong. Please post pics of the damage. I'm imagining something like a mortar shell If the pieces can be coaxed back to their former position then repair is really a piece of cake. A logical series of steps. Even a hole there would be easy to fix..]
    Last edited by ebb; 07-30-2004 at 05:27 PM.

  9. #9
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    STRONGBACK SUPPORT

    Here is a view of the strongback reinforcement plate on the forecabin side. Unpolished ss . . .
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  10. #10
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    Prettier on the maincabin side
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  11. #11
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    Scott,
    I'm very sorry to read of your mishap. It sounds frustrating and painful. Ebb's right, some pics would help flesh-out story on the repair. Once you have the mast off it should be pretty straight forward. As far as FRP goes, if previous work was done in the step area you'll probably need to enlarge the 'reconstruction' to include that work. At least that way you'll know exactly what was done and it be done to your standards. The beam can be handled a number of different ways and all acceptable. Someone once pointed out here that the original design worked fine on these boats for many years. You could simply replace the old with an exact copy. Or, a sandwichedly enhanced version that many Ariels have in them these days. One could even be as unconventional as Ebb and laminate a new stronger beam. He is radical.
    Unfortunately this all takes time. But as you know, there is something emensly gratifying about nursing or mending a boat and making her right again.
    Hope any of this helps. Tony G

  12. #12
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    Aug 2003
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    FOSSIL OREGON
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    what i did

    When i had the mast unstepped, there was about 1/4'' gap between cabin top and beam, so filled with epoxy, and then added this 2'' alum. angle iron, through bolted. Bolted new hinge down through the beam and angle. Will now have two nuts for a nut head gouger, but couldn't figure out any other way to make it stout. The hinge has to rip out the whole piece of 2'' angle now, which ought to make as big a mess as you have someday! Here's a shot of the angle, and the hinge.
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    wet willieave maria

  13. #13
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    Aug 2003
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    FOSSIL OREGON
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    197

    hinge

    used 3/8 bolts. had to make relief holes for heads in top plate. used origional holes of bronze screws, and origional wood step.
    Attached Images  
    wet willieave maria

  14. #14
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    Sep 2001
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    Thanks everyone for the helpful suggestions and the great photos and thanks Ebb, I did search the site for all of the words that I could conceive might lead me to photos of this area. I will now search through the compression beam and bulkhead posts. This accident is not something that I can discuss at this point since it involves other people and a clam that I may have to file.

    I can say a couple of things. I think that when my boat was tabernacled, the previous owner found some delamination beneath the old mast step. He told me that he had added epoxy to the area, and based on other work done on the main deck, I assume that he probably drilled a few holes and pumped epoxy into the voids. That would make more or less a solid section beneath the mast, and strengthen the support of the mast, but of course epoxy does not compress like balsa wood, so a severe shock load (such as one placed squarely in the very center of the mast head fitting, such as running your mast into a concrete bridge member while it is partially lowered in a forward direction) for example would tend to transfer considerable force both downward and aftward, and this might (for example) send offset lateral transverse fiberglass cracks across the deck surface, force the mast step mounting blots through the cabin liner, causing the liner to buckle, and possibly crack the strong back, depress the top of the door frame and separate the door posts and other support members below deck from their intended secure bonds etc. (for example).

    So I am very well aware that removal of the mast and destructive testing of the various elements of the support system will be required beffore repairs can be initiated. The extent of the damage will dictate whether a complete new support system will be installed, or whether the stainless steel brace approach will suffice. I am interested in handing to my surveyor some examples of the fine work that members of this forum have done to deal with cumulative trauma to the strong back so that we might consider them for the accident repair task ahead. The photos that you have posted will greatly assist me in this effort. The more photos, the merrier. And yes, I will be posting some photos by and by.
    Scott

  15. #15
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    Apr 2003
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    Bellingham, Wa.
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    I can't comment too directly on an Ariel mast beam/strongback, as the last time I was in actual physical proximity to one I was about 5 or 6 years old...and my Commander was a Commander...

    All the same, from the photos I have seen it looks awfully similar to the Triton mast beam/compression posts/diagonal braces...which, FWIW, come out completely with relative ease and are pretty simple parts to replicate. I'd be moved to just dig out the old ones and replace.

    Dave

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