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Thread: Commander Compression Post Discussions

  1. #46
    Join Date
    Mar 2006
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    San Francisco - or Abroad
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    430
    Perhaps we are missing something in the communication... but...

    You say that there is no failure now... Unless you are planning a drastic remodel why would you need to move the post in the future??? Besides - the addition of this solid pad would NOT prevent you from doing anything you can do now as this modification does not change the manner of attachment of the post/cabintop connection...

    Perhaps you are not confident of the strength/durability of the suggested repair?

    Consider that the original cored construction has done quite well all these years...

    Solid epoxy is much stronger... And it is as excellent material for compressive resistance...

    Let's consider:
    The top of your post has a metal bearing plate which is some 6" in diameter. (The mast base is 8" - but let's consider the smallest area as an example as it is the weak element in this scenario)...
    This plate bears on the inside of the cabintop below the Balsa core (which is already solid FG and will remain. You'll only remove the balsa core and will replace the FG layer at top.)

    The compressive strength of epoxy varies a bit depending on the product, type of product, and manner of application, but it will range between 5,000 and 10,000 lbs/sq-in. Glass makes it stronger, but let's ignore that...

    Let's say that you use bad epoxy and your install is full of holes and poorly applied... so we'll use 5,000 lbs/sq-in.

    The bearing strength under these circumstances for the solid epoxy pad will be as follows:
    The Area of the 6" plate at top of post 28.26 sq-in x 5,000 lbs/Sq-in = 141,300 lbs

    So you see - the pad is actually the support system's new strongest point - far from being the weakest... the mast will crumble, the compression post will become a pancake, and everything -including the keel - would be pushed out the bottom of the boat WAAAY before the bearing pad you build even starts to consider failing....
    Last edited by Rico; 06-24-2010 at 10:59 AM.

  2. #47
    Join Date
    May 2002
    Location
    Manchester, MA
    Posts
    151
    Rico,

    Attached to posts # 5 & 6 are earlier pictures of my compression post. The post cap has worked itself even further into the ceiling. Or if you prefer, the ceiling has dropped even further around the compression post cap. My point is that if I leave that where it is, I effectively will capture the post top by strengthening the area above it. I only asked if someone had been able to raise the ceiling enough that my post would be free to move and or remove. When I open the area above the cap, will the ceiling return to it's orginal form or do I have encourage (read force) the ceiling up to it's original contour.
    Last edited by John; 06-24-2010 at 01:34 PM.
    John G.
    Valhalla
    Commander No 287

  3. #48
    Join Date
    May 2002
    Location
    Manchester, MA
    Posts
    151
    I have a dremel like tool and for it I have 1 in + fiberglass reinforced cut off wheels. Can I use those to cut the deck to open up the void? Or am I better off going to Walmart and get their $29 angle grinder for that job?

  4. #49
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    Mar 2006
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    San Francisco - or Abroad
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    Ahhh... I see.
    I would suggest that you bring the cabin-top to its intended position for a proper repair job. The subsidence is due to the failure of the core and even though you would eliminate further deformation by making the repair where the pieces sit now, the best solution is to do it right. After all, once your commander is all shippy, you will not want to see that issue at the top of the post. It will not look right.

    I imagine that if the cabintop does not pop back-up on its own, you can help prop it up into position fairly easily... Then do the repair as suggested. This is an important area, but it will not be hard to get it sorted out.

    Your dermel-like tool may do the job, but it is a great big job for it... Not the best tool for this application. An Angle grinder with a cutting wheel, or even a skill saw with the proper blade would serve you best. Angle grinders are quite versatile. I'm sure you'll use it a lot if you cannot borrow one for the job, and end-up buying one...

    BE careful with it though... They are powerful and can do lots of damage! (I am working on healing a nasty abrasion from one at the moment!)

  5. #50
    Join Date
    May 2002
    Location
    Manchester, MA
    Posts
    151
    Rico,

    I am about to make the big leap, take a header off the tops, cut a hole in deck. I have a friend that is going to loan me his 6" angle grinder. Mask is at hand. Power to the boat. Can I cut a 5 in. diameter circle in the deck.? Can I mix up a gallon of epoxy to fill the void? Curious minds want to know.
    John G.
    Valhalla
    Commander No 287

  6. #51
    Join Date
    Mar 2006
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    San Francisco - or Abroad
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    430
    It sounds like you are on your way!

    See what Jerry has done on his commander for reference... Some lovely work there - you should follow his lead. And maybe you'll want to incorporate the mast base in your repair as he did... That is a great idea.
    http://www.pearsonariel.org/discussi...1672#post21672

    Cut a circle big enough to get to good-solid material... Since you already have a failure I would expect that the area will be the 8" circle (mast base), plus at least 2-3 inches around the perimeter which has suffered deformation. Make that whole area solid... Much less than a gallon!

    I would not use pure epoxy. Use a bit of thickener and some glass mat on you repair. Jerry posted a good description of the process a few post above here...

  7. #52
    Join Date
    May 2002
    Location
    Manchester, MA
    Posts
    151
    I have a great mast step made of micarta by a PO. It is approximately 8" in diameter. I am hoping that I am able to cut a 5 in. circle and clean out underneath. If I have to go further, I will, but then will have to be neater in the replacement area. Because of the mast step, I will have to match the curve in deck so I get a good seating.

    So the plan is to cut as carefully as I can, clean it out and then stuff it with filled resin......Sounds like I am doing a turkey, doesn't it. How much time to allow for the epoxy cure is a mystery but with some contemplation, I'm sure it will come to me. The other task is insure that the cabin ceiling returns to it's original contours. Easy beans ...ja'think.
    John G.
    Valhalla
    Commander No 287

  8. #53
    Join Date
    Sep 2008
    Location
    Brooksville, FL
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    714
    John

    I would like to offer a few suggestions that might make your job easier.

    1.) For the small area you are working in a 6" grinder might be to large. I use a 4" grinder to grind in the bevel around the hole after I have cut it and even that seems a bit large at times.

    2.) To cut the hole I often times use a small trim router similar to the one at this link. It allows me to control with a high degree of precision the depth of cut.

    http://www.google.com/products/catal...CAcQ8wIwADgA#p

    3.) If there is any balsa core intact under the cutout remove it carefully. It was bonded pretty well to the bottom skin which is often times very thin and fragile. Don't try to rush it just get it up slow and easy.

    4.) Epoxy resin by itself is very brittle. You need the glass reinforcing to make this area strong. So cut all of your glass fabric pieces before you start putting things back together again.

    5.) To keep a lot of resin from running down through the two holes that the mast step bolts through and dripping on your cabin floor you can wet out the top of the bottom deck skin and on a piece of visqueen (plastic) wet out the bottom piece of glass you will be putting in the hole. Then put the glass in the hole and make sure there are no air bubbles under it. Then let that start to kick and set up before you proceed with the rest of the glass. In addition I would use a couple of pieces of tape on the bottom of the holes to make sure nothing drips on the cabin sole.

    6.) This repair will really take a small amount of epoxy. So mix small batches of epoxy so you don't waste it and it does not set up on you before you can use it all.

    I hope this helps and I wish you the best on your project.
    JERRY CARPENTER - C147
    A man can succeed at almost anything for which he has unlimited enthusiam.

  9. #54
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    May 2002
    Location
    Manchester, MA
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    Jerry,

    I am not fortunate to have a trim router but I have a regular router. Any reason not to use that and a 1/4" bit to cut the hole? I don't think the top skin is thicker that 3/8's and probably closer to 1/4." I have talked to my friend regarding borrowing his grinder, and he has some 4" blades for it. I think I am in good shape tool wise.

    I don't think I understand what you are suggesting to do in the void area. My plan was to fill the entire area with filled epoxy and keep stuffing until I had the void filled and then build the deck area up to match the deck using glass mat. I I have a couple of choices for filler in the void including glass fiber, micre balloons (I don't think it's a good choice) or one of the other solid fillers.
    John G.
    Valhalla
    Commander No 287

  10. #55
    Join Date
    Sep 2008
    Location
    Brooksville, FL
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    714
    John

    A normal sized router should do the trick just fine. I like the little one but would certainly use one of my other routers if I did not have the little one. Also you will find that the top skin of the deck is closer to 1/8" thick than it is to 1/4" thick. The balsa core in the center of the deck is 3/8" thick and then you have the bottom skin of the deck that is close to 1/16" thick.

    As far as the suggested repair I will draw a picture as soon as I can get some time later today and post it for you. But here are a couple of things I can tell you now. First, the tickened epoxy only goes between the top and bottom skins around the perimeter of the 5" hole you will cut through the top skin. And that assumes that the balsa core is degraded in a larger area than the 5" dia. cutout. While I'm on the subject, you need to know the only way to give the thickened epoxy body so that it will not sag out and run out of the area you are putting it into is to use cabosil (also known as fumed silica). You will want to use micro fibers or 1/4" glass strands to give the epoxy strength after it is cured but you will also need to mix in cabosil to thicken it to a peanut butter consistacy so it will stay where you put it.

    Then in the area where you have the 5" cutout you will wet out possibly as many as 8 layers of 1708 biax cloth one at a time to build the core area up to the 3/8" thickness that that original balsa core took up. Then when you are built up to the the point where the glass is filling the core area and even with the bottom of the top skin you will lay down the 8" circle of glass first to get a complete bond with the entire beveled area and the glass you put in the core area. After that you will follow with the 7" circle of glass and then the 6" circle of glass and if the center is still slightly below the surrounding deck area one more layer of glass 5" in dia.

    When all of this sets up use the grinder to knock down any high spots and mix up some more epoxy to use as a fairing compound and this time you will need to use cabosil and microballoons. Probably about twice as much microballons as cabosil. The cabosil once again gives the epoxy body and keeps it where you put it and the microballoons will make sanding it later much easier.

    Does this help or would you still like the picture? I'm happy to do it but I have some work I need to get done before I can.
    JERRY CARPENTER - C147
    A man can succeed at almost anything for which he has unlimited enthusiam.

  11. #56
    Join Date
    May 2002
    Location
    Manchester, MA
    Posts
    151
    Jerry,

    If I understand what you are saying, once I have cleaned out the bad core, I fill the void until I have a 5 in. hole from deck to ceiling. then I proceed to lay in glass matting until I get to the deck level. At that point I start using increasing sizes of mat to rebuild the deck as it was. I can then grind to match the deck, fill if needed and stand back and admire my work. Oh, yes, then I can remove the Gator tape (great stuff by the way) and re-drill the holes to mount my mast step.

    I plan on placing a soda straw over my mast light wires and hopefully leave them so they can be removed or fished if needed. This does mean that the glass will have to be layed gently with a slit on one edge to accomodate the wires. Also, if the ceiling does not rebound around the compression post cap, my plan is to cut 2 semi circles of 1/4 plywood and gently jack up the ceiling until it matches the surrounding area an the compression post has a litlle wiggle to it.
    John G.
    Valhalla
    Commander No 287

  12. #57
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    Sep 2008
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    Brooksville, FL
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    714
    John

    I believe you are following but just to make sure I will post a picture later possibly as late as this evening.
    JERRY CARPENTER - C147
    A man can succeed at almost anything for which he has unlimited enthusiam.

  13. #58
    Join Date
    Sep 2008
    Location
    Brooksville, FL
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    714

    Picture

    John not sure if this picture will do more to explain or confuse but anyway here you go.

    Name:  RECORE.jpg
Views: 377
Size:  18.5 KB

    If this confuses I will try again.
    JERRY CARPENTER - C147
    A man can succeed at almost anything for which he has unlimited enthusiam.

  14. #59
    Join Date
    May 2008
    Location
    Excelsior, Minnesota
    Posts
    323
    John,
    Jerry's above repair is very proper and the best and most permanent fix. Here is a quick and dirty repair that should get you at least another 40 years out of the mast step.
    Use a 5" or 6" hole saw to remove the top skin, scrape out the bad core and dig it out from the edges until the balsa you are pulling out looks clean and dry. Using the same hole saw cut out a plug from 3/8" plywood. Draw a 8" circle around your hole and taper the edges out to that. Pack thickened epoxy into the void between the skins and lather up the bottom of the hole, stick in your plywood plug, butter everything up with the thickened epoxy and apply your repair plys of glass mat wetted out with epoxy. Pre cut your repair plys, mask off a large area and have every thing laid out and ready to go 'cause your going to be a sticky mess. If you put on 4 or 5 sets of rubber gloves you can keep peeling them off when they get too messy and you want to pick up a tool or something. The repair could be done with polyester resin instead of epoxy if cost is a factor, its not as good, but thats what the rest of the boat is made of.
    .02 cents
    Mike

  15. #60
    Join Date
    May 2002
    Location
    Manchester, MA
    Posts
    151
    Repairs have gotten more complicated. You can see pictures in the Mast Step discussion. I now have an open area of about 8" x 8" underneath the mast step. The compression post/wedge has already broken through the cabin ceiling. I am faced with raising the roof (really) and then rebuilding the entire structure. Also I did slip and there is a 1" puncture in the cabin ceiling. Fortunately, I am using a 1/4" bit in the router. Rather than continue duplicate discussions, I will continue the discussion in the Mast Step, as most seem to read both. Suggestions are welcome.
    John G.
    Valhalla
    Commander No 287

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