A structural question ...

Discussion in 'Sailboats' started by ath, Jun 8, 2005.

  1. ath
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    ath Junior Member

    If you have seen my previous thread, you know that I have a lot of wood rot but also termite damage. The main structural components including the mast/beam support and main bulkheads have been damaged and need to be replaced. The mast is coming down today.

    The mast/beam support is made of 2 sheets of ply and shaped. Apparently, this seems to be a common problem on Cal 25's (see photo of another boat). I'm wondering why I should replace the old ply beam with a new one if they don't seem to hold up too well (poor caulking job - also probably hadn't been recaulked since the boat was built in '76)

    Do you think I could put in a custom aluminum piece? If so, where should I be careful about loads, where it is attaching to the deck and beam? The current piece is flush to the underside of the deck and is flush against the beam. But aluminum is stiffer .... etc. Worried about where it comes in contact with the glass.

    If not, any suggestions about what else I can use?
     

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  2. water addict
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    water addict Naval Architect

    It's hard to tell from your pictures what all the surrounding structure looks like. It's important to know how the ends of the beam will attach. As far as using other materials for the cross beam- you can use whatever you want, because the applied load is the same- provided the surrounding structure is designed to handle the reaction forces. This is a big if though from looking at those pictures. I would not assume from those that the original structure was properly designed!
     
  3. ath
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    ath Junior Member

    A different view

    This may help. I was thinking that the plywood support would bend a little more that aluminum and would transfer loads. You're right though, the original design has room for improvement
     

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  4. Karsten
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    Karsten Senior Member

    If I get it right the mast sits on top of the door cutout in the bulkhead. Since you replace the bulkhead anyway why not move the door cutout so that the bulkhead supports the mast?
    If that's not possible you have to strengthen the part of the beam that spans across the door plus maybe 10 inches on either side. I wouldn't be too worried about the rest.
    Since the critical part is only small but highly loaded I would use some epoxy resin and unidirectional carbon fibres. They are very well suited for jobs like this. Also make the beam as deep as possible (reduced head height through the door). First laminate some fibres transverse on the underside of the cabin roof to strengthen it. Then build up your beam using plywood or something like that. To finish the beam laminate some carbon fibres on the underside of the plywood. The vertical distance between the carbon fibre layers is what gives the beam stength and stiffness.
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Your boat has lasted 30 years, so it seems unlikely that the deck beam as originally designed is inferior, in fact I'd say quite the other is clear, from the life of an obliviously neglected area.

    Most of these failures are a result of lack of care. The photos show, plainly, that there's been leakage from the weather side of the cabin roof, through the wiring hole(s) into the roof beam. The signs of neglect have been visible for a long time and now a new owner has the task of fixing years of "maybe it will be all right" mentality. Welcome to the world of used boats.

    This is a common difficulty and the best course is to remove the bad sections and install new ones, with a mind to keep up on the maintenance, so you don't have this problem again. It's likely the bedding under the mast step, the boot, bulkhead sleeve or whatever technique was used to make the wires passing through the cabin roof water tight, failed from lack of attention (bedding doesn't last forever) In any case it should be reasonably easy for you to see there were several avenues of ingress for water to take, rotting out the laminated beam. Had the bedding, pass thru connector, fasteners, etc. been attended regularly, this wouldn't have happened, but it's a rare thing for these issues to be addressed anymore. This is not a design flaw, but a care failure, on the part of former owners.

    I've heard of other, similar failures in this model pocket yacht, but a quick review of some owners and it became apparent that they didn't keep up after the step area and related gear (masthead/speader light wiring)

    You can try to re-engineer a new structure to fix this, but you'll find that the cabin roof crown (curve) isn't just a section of a circle, but a defined curve, with the most curve on the centerline and flattening out as it gets near the cabin sides. Bending a piece as you've suggested, with the bottle jack and all, shows good thought processes and problem solving, but will result in a curve unlike the one it needs to fit. Your best bet is to make a template of the curve as it looks (after the stick is yanked) right now (dent in the roof and all)

    You can then transfer the curve to a flat area for laminating a new beam. You'll find it isn't very fair (smooth curve) and it probably has a few humps and hollows in it as you sight down the line of the curve. You'll want to fix this and it's easily done with a batten and a few nails or weights.

    Personally, if it was me, I'd do this on a table, using clamping blocks made of hardwood screwed down to the shape of the curve. I then position more blocks well off the face of the curve and use wedges to force the material to take the curve. Basically you'll have a couple of dozen blocks screwed to the table with enough room to fit all the laminating stock in-between with a little room left over to slide the wedges in. These two rows of blocks will be in the shape of the curve. Cover the table and the blocks with plastic packaging tape (epoxy doesn't stick to it) so you can release the beam and blocks when all is cured.

    In a nut shell, draw out a nicely faired (smoothed out) curve as closely following the original as possible on a table (a sheet of ply and some saw horses works well) screw down some blocks (a little taller then the laminate is wide) along the curve. estimate the thickness of the total lamination and add a 1/2 inch or so, then screw down the outer row of blocks, across from the ones set down earlier. Cut some wedges on the table saw, with an 8:1 ratio at least and trim the pointy ends so it's a 1/4" thick. Use the same stock you used for the blocks on the wedges (both blocks and wedges need be strong) I'd cover the laminating area with tape before you screw down the blocks. Cover the blocks and wedges with tape too. Now you're ready for the dry run.

    Mill your laminating stock (thin is good) and bend them into the form. You'll have to talk to them a bit, use a soft hammer and tell them how much happier they'll be in a boat as a very important beam. Slide in you wedges and tap them home or near so. This step will save you much pain, trust me. Once you've got the details worked out in the dry run, butter the laminate stock with unthickened epoxy, set them down and then mix up some thickened epoxy using West System 403 Microfibers (it's the best for laminations) plus a little colloidal silica (for additional strength if desired) and butter each piece with this mixture. The mixture should be about as thick as good ketchup (the kind that doesn't come out of the bottle easily) maybe a little thicker. This will be a messy thing, but it's not hard and if you did a few dry runs, should go like clockwork. Work evenly and quickly, 'cause the stuff's curing as you work. Slide each piece into the mold, stacking the gooie mess until all are in place. Don't worry about the ends (they should be over length anyway) slide in the wedges until each is in and hand tight. Working from the center out, tap them in, until the laminate is resting on it's blocking. You may have to go "round the world" so to speak to get them to wedge the stock into place. Tap down the edges to make them evenish (the stock should be wider and longer then needed) and insure there is goo coming out every seam. Clean up the seams with a putty knife and chase down drips, run and sags while the epoxy is workable, other wise you'll be cussing with a belt sander.

    Wait a few days and pop it from the form, which may require the wedges be smacked with a soft hammer again (you'll get a lot of enjoyment from this task, every once and a while) then it needs to be milled to the proper dimensions. I usually kiss the sides in the table saw to even things up, then drag out the plane, sanders or shapers. If you use several layers of thin stock for you lamination then spring back will not be bad, but the thicker the stock then the more you can expect spring back (the curve will try to relax it's shape a bit) which can be compensated for when drawing the curve or placing the clamping blocks. A good starting point for this spring back is a 10% tighter curve radius.
     
  6. ath
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    ath Junior Member

    The best ways to increase strength ...

    I greatly appreciate you taking the time to contribute so much thought to my problem. You are absolutely right; the damage is primarily from negelect. Caulking should be checked religiously and replaced annually sometimes. The design is a good one to have lasted so many years. I think I even said that in a previous thread.

    The design at the time the boat was built was very successful. Cal Jensen Marine was very successful. But since then there have been many numerous advances in construction and design. If the boat were to be built again today, I'm sure many new techniques would be applied (it probabbly wouldn't look anything like the original).

    The first boat I restored was in Sydney harbor when I was fifteen. It was an all wood 26' sloop called a Swagman. My father and I replaced the deck and a lot of the hull planking, painted, varnished etc. It took all Summer. In high school I managed a fleet of Solings and other various boats that were part of a sailing school where I taught. I was responsible for maintaining the fleet which included repairing all the damage caused by novices - a broken mast, glass repair etc. I also helped restore a Columbia 52' that had been stolen and gutted for drug trafficking which we later used for charter.

    While at the sailing school I first came across Cal 25's. I've always liked them. My interest in this boat is outfitting it for long cruises or at least coastal cruising and island hopping. I hope to extend my cruises as I gain more confidence in the boat. My secret wish is to sail it back home to Sydney (it may not be this boat).

    And this is where I'm at. Since I am completely restoring the boat, I would like to take the opportunity to apply new techniques to reinforce and strengthen the boat wherever possible. The drawings I've attached are not my own. They are from other owners who had experienced the same problem and from Cal Jensen Marine that provided a template (the piece is actually curved like that). I have the ability to create a new piece and I will definately use the excellent instruction provided here in the forum if it comes to that. But I'd like to do something better.

    I know this seems like a lot to do about a little old boat and maybe it's not that interesting of a subject. Trust me, I'd do many irrational things to get a chance to ride a Finot Open 60 - or even look at one up close for that matter. What can I say. I've been sailing, racing and working on other people's boats since I was four and I finally have my own boat ... Any of the valued experience from this forum would be greatly appreciated.
     
  7. PAR
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    PAR Yacht Designer/Builder

    You're very lucky to have found a template to match the roof crown, which will save a lot of difficult work, that must be done accurately.

    If the boat was built today, it would employ quite different building methods, most of which wouldn't translate well to the older construction techniques. These boats were built heavy, had plywood bulkheads, stringers and reinforcements, heavy tabbing, no real structural grid tied to the liner and hull. Some of the things you can take advantage of are the use of epoxy, CPES, better fabrics and materials.

    Build your beam, fix the bulkhead, remove all the deck hardware (it's leaking judging by the photos) as they need their bedding renewed. Check the fasteners (just replace the damn things) for cracks, etc. Check the hull to deck joint (I've heard stories) under the rub. I find it unlikely you'll engineer a better system under the mast step then what's there. This is a common method of transferring the compression loads from the rig to the hull, when there is a passageway directly under the step. A keel stepped stick would be nice, but you'd half your passage to the forepeak and clutter up the interior with braces (unnecessarily) and the sole with a structural floor (again unnecessarily) A new bulkhead (or repaired if possible) and beam will renew the life of the yacht to her former glory and you can save the re-engineering for other areas that may truly require it.

    The Cal 25 is a hardy boat and the ride to Sydney will be rough on you and the boat, but if sailed wisely could be done, remembering it's not an offshore craft. Reef early to keep the beating to a minimum. Plan the route carefully so you don't get caught with weeks of dead air or beats into storms the whole way. Touch base with your insurance guy.

    I'd not restore the boat as much as I'd make her sound again. New rig, sails, some replacement hardware, structural repairs - improvements will keep you busy and your bank account dry for a while. There are better options for an offshore yacht, that may deserve the attention a person like you can provide and the next owner of this Cal 25 will be quite grateful of your efforts, receiving a good boat in better shape then it should be (maybe even needs to be for a protected waters/near shore craft use she was designed for)
     
  8. ath
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    ath Junior Member

    Structural Repairs

    I agree completely. I keep thinking that if I beef up the boat and make modifications that I can just island hop down the South Pacific and cruise through Sydney heads. Of course it can be done. These crazy people sailed around the world with their three children on a Cal 25 and a sixteen year old boy almost made it in the predicesor to the Cal 25. We'll see. I remember some scary weather down there when we would race offshore. It's a big difference from Southern Ca. Sometimes the swells were so big, a rolling 30 ft, that they would come though the harbour, bounce off one shore and roll onto the inland shore, breaking 10' at Neilsen Park where we surfed them. Surfing inside the harbour! There's a lot of discussion in this forum about Moth's. My friend had an old plywood one and we would sail it out into the Heads, disapearing in the troughs of these mammoth swells. We were nuts. Maybe I've been away to long. I've lost my nerve or I'm just getting older.

    You're right. What I'll probably do is restore it/make her sound, sail it for a season or two, sell it to the right owner and buy or build a 50ft. I single-handed that '52 footer I mentioned and I felt it to very manageable.

    Take a look at this. This is one of the drawings I believe was supplied by Cal Jensen in '76. I think they already knew there was a bit of a problem. I tried dropping the mast myself yesterday with an elaborate rig to start to dig this piece out but I couldn't figure out a way to lift the mast six inches off the step. Taking it to a yard to lift it off with a crane.

    .
    Speaking of new materials. Forgetting cost for the meantime, what other products can I use besides marine ply? I got some answers in this thread. I'm interested in different types of material to replace the bulkheads.
     
  9. SailDesign
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    SailDesign Old Phart! Stay upwind..

    A couple of boats my Dad drew (Menemsha 24, Katama 25) had a similar set-up, and similar problems. The fix was to through-bolt a couple of aluminum or bronze plates (alu being lighter...) either side of the beam, as close to full depth of the beam as possible, extending to the cochroof side. With a little imagination and good cutting, these can be made into a decorative item, as well as functional.
    Steve
     
  10. PAR
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    PAR Yacht Designer/Builder

    I like the idea of this style of reinforcement. I thought the bulkhead was directly under the beam from the photo, but if you have it forward (as it now seems) then the bent aluminum cradle or what Steve has suggested by way of plates could be a quick answer. I'd take the supports (down the sides of the passageway opening) to a floor (not the sole, but what's under it) and tab them in.

    There are a number of materials that can be used for a bulkhead, but you'll have difficulty beating the cost and ease a good grade of plywood provides.
     

  11. ath
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    ath Junior Member

    It is under the bulkhead. I guess the pictures are confusing. Taking them to the floor is a good idea.
     
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