I'm back - with an important centerboard box install question

Discussion in 'Wooden Boat Building and Restoration' started by OrcaSea, Aug 9, 2019.

  1. OrcaSea
    Joined: Oct 2014
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    Location: Arlington, Wa

    OrcaSea Senior Member

    I'm back.

    It's been a while - changes in jobs, death in the family, etc., etc. - life.

    But I have continued work on my basket case, which has turned into more of a bucket case, or maybe a handbag case would be more appropriate.

    Just to get caught up: This...

    [​IMG]

    Has turned into this...

    [​IMG]

    BUT...along the way I found this at the centerboard slot...

    [​IMG]

    The original builder over-tightened the bolts attaching the centerboard box to the keel, which led to a lifetime of leaking, as apparent by the layers of attempts to mitigate the ingress of water I found on the interior.

    Replacement of the keel was out of the question, so, I did this...

    [​IMG]

    I removed the entire centerboard box, removed the bolts, plugged the bolt holes with dowels and epoxy, pushed the keel back into shape and filled the cracks with epoxy and milled fibers, smoothed and cut a new keelson (my nomenclature might be incorrect - the original drawings call this piece the "keel" and the underlying heavy structure the "keelson" - I always thought it was the other way around...?) and epoxied it into place, glassed, sanded, sealed, sanded, sanded, primed, sanded, sanded, painted, sanded, painted, sanded, painted and flipped until finally it looked like this...

    [​IMG]

    ...Which brings us to now.

    I have designed a new centerboard box. This is just a rough design sketch, but gets the idea across...

    [​IMG]

    It will sit between the forward most (visible) and aft-most (visible) ribs here...

    [​IMG]

    Finally(!), this brings me to my question: Since installing a new centerboard box while the boat was inverted was out of the question, and since I didn't want to weaken or disturb the already damaged keel further by boring more holes in it (and frankly, I wasn't so sure of the engineering in the first place) what is the best way to fasten in the new centerboard box?

    I have left the (now) top side of the keel rough with the repair incomplete on purpose until I can answer this question.

    Do I epoxy & fillet the centerboard box in place? Is that enough? (The forward post on the box fastens to the coaming of the cockpit with brackets to help with torquing).

    Or, do I cut a rabbit in the footing/bedlog of the centerboard box, install a flange that extends to the full width of the keel/centerboad box interface (this will give me a flat of 3/4" to work with), continue the repair of the keel to a smooth mating surface, and fasten it in with lag bolts into the 3/4" keel and 1/2" keelson with an appropriate glue/sealant as best I can. Like this...

    [​IMG]

    Or, so I do a hybrid install with a flange, fasteners and epoxy? Making the new mounting flange just a bit - 1/16"? - deeper to allow for epoxy with milled fibers between the keel and the centerboard foot/bedlog so I don't have an epoxy-starved joint?

    If anyone has stuck with me this long, bless you, but I would appreciate any input as i am ready to start in on this soon bu am at a loss of how best to proceed.

    Thanks!
     
  2. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Good looking little boat OrcaSea. You can count yourself as a hero for restoring her as far as you have gone.

    I would think to do a small rabbet to set the box into the keelson. Probably not necessary but good craftsmanship in any case. I would prefer to have some sort of bracing that connects the top of the box to the floor cross member. A simple pair of triangular shaped gussets will probably suffice. The board is a sort of lever that will place a sideways load on the top of the case, so some reinforcement is in order there. Some boats have a seat at the case (box) location that secures the top of the case from torque loading.
     
  3. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Will the boat have floorboards over the frames? Will it have a kicking straps?

    There are several reasonable ways to do this, but given the state you found the original keel in, I think you want to route the loads away from it to the greatest extent possible. One option is to extend the webs or cheek pieces right through the slot and leave them a bit proud on the bottom, say about 1/2 their thickness, then fillet to good new wood and glass thoroughly. You will need a sloppy slot so the glass forms the only bearing surface along the bottom inside of the slot. The slot should only be close fitting at the top and bottom edges, there should be loads of rattle space in the middle of the box to prevent water squirting out the top. And even the top and bottom shouldn't be snug, but about 1/8" of clearance.

    Instead of flanging to the keel member, can you use a floorboard on top of the frames to do the same thing? This becomes a permanent part of the boat, although it doesn't have to be epoxied, it can just be bronze screwed. 3/8 x 3 1/2 white oak is about right for this. You can then make matching drop-in floor grates for either side. These are handy as beach furniture as well. Just make sure you can get to the centerboard pin.

    So I would add 3 more floors to bear the floorboards, bevel the chinelog so it drains inboard, drill limber holes in all frames in the center and in the gussets at the chinelog, run the box cheeks out the bottom, and flange the box with the first floorboard.

    I'd also get the boat completely rigged before gluing anything in place because the box will probably be were several pieces of control hardware get mounted, and you will want to integrate those mounting points into the design. Hiking straps and mainsheet tackle and vang tackle and the board pennant need providing for, and you can clamp a little kicker to the cb housing for transport. Halyards and downhaul can be made off to the forward post if you don't like cleats on your mast.

    Managed to dredge up an old sketch - Centerboard suggestionsSeeing as I have used only Daggerboards and Leeboards https://www.boatdesign.net/threads/centerboard-suggestionsseeing-as-i-have-used-only-daggerboards-and-leeboards.50689/#post-692627

    [​IMG]
     
    Last edited: Aug 10, 2019
  4. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Some great suggestions here. I can only agree with the idea of the rabbet in the bottom logs of the centerboard case, extending through the "keel/keelson" structure, just like in the diagram.

    My experience is that exposed plywood edges should be avoided at all costs, even with an epoxy cover. I suggest as well, the gap between the hull plywood and the bottom centreboard log should be up to 1/4" wide, and not only filled with Epoxy but with Fibreglass strands. Do not use just Epoxy and Microballons or other filler. That join is going to get a lot of stress, as well as normal wood movement.

    Yes, you are definitely going to need some sort of brace/seat running from the top of the box to the gunnels.

    Righting.png
     
  5. OrcaSea
    Joined: Oct 2014
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    Location: Arlington, Wa

    OrcaSea Senior Member

    Hey everyone, thanks for your suggestions and information. A lot to think about and process.

    Messabout, thanks for the kind words. This boat was a mess! But, ya know, it's got me back into woodworking and I've picked up a 14" bandsaw, drill press, miter saw and more hand tools than I know how to store. And the fact that it was made about the same time I was adds a lot of symbolism to it's resuscitation ;)

    This is a pic of the original box and forward configuration, and how the forward box post connects to a knee-style bracket at the coaming. You can see the old box was pretty rudimentary and where the bolt holes went down through the bedlog of the box and into the keel. I did not see any evidence of damage or looseness, cracking, etc., from centerboard torquing, but given the changes it is something I will need to address, and I think building an over-all stiffer, stronger box will help distribute those side loads better to that forward post. Also, I think this box was taller than it needed to be, so building it to the minimal height required (well above the waterline, of course) and hanging the centerbord and pivot as low as I can should make it stiffer yet.

    [​IMG]

    I plan on the same configuration, and that should address some of the torque issues, especially forward where the force from the centerboard will be focused. I had to rebuild all the ribs you see in the pic in my previous post, and the center one has that awkward end-grain fastening issue, so i think I have an opportunity there to form some sort of triangular brace that attaches to an upright at the midway of the box web. That will stiffen the web and give me a good fastening location to stiffen against lateral force on the box. I could do something similar with the aft box end and the aft rib, as well.

    This is one of the dozens of Lightning-inspired copy-cat boats that were popular with mid-century home builders (offered in a popular sailing magazine and probably made in '58 - like me!) but is a 3/4 scale (or smaller) version and so is a 'sit-on' rather than 'sit-in' boat, so I want to be careful about trip hazards in the cockpit, so I can't set them out too far, but that ties into an idea philSweet offered that I have also thought often about.

    Phil, I am not settled on kicking straps yet, though, but as I will likely be single-handling this boat most of the time it would probably be an important safety feature, since it is a 'sit-on' boat. I have often thought about the flooring (the original design had removable plywood floors that rested on the ribs) and have considered something very much like what you have suggested - a built-up ledge, inboard and outboard, onto which removable floor grates (I like the nautical look of half-lapped deck opening covers) can fit. And that would give me an opportunity to tie in the triangular braces that Messabout spoke of, possibly in place of, or tying in to, the upright frame pieces at the ends of the box.

    This is a 'slice' of the box that shows the box webs located in rabbets (the webs will be the only high-quality ply) and that will be the only ply I use. The centerboard is 1/4" steel plate. I think the gap of the centerboard cut is around 3/4" to 1" wide, so I may very well have the room to extend a rabbet on the bedlog into the slot. How I would get a router or saw to make the slot wider would be a trick though...

    [​IMG]

    Honestly, I haven't even gotten to the points of running a straight edge longitudinally along the ribs to see if the floor grates will sit flat or whether I will need to build spacers or shims between the rib tops and the floor grates, but that is something i will do soon while fleshing this out.

    I feel pretty good about controlling the torque of the centerboard, but another concern is that the mainsheet tackle comes down from mid-boom to a block mounted towards the aft top of the centerboard box, so vertical stress there is a concern, so perhaps i can modify the aft box end assembly to include lateral bracing to the aft rib, as well.
     
  6. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    "How I would get a router or saw to make the slot wider would be a trick though..."
    Have you got a Jigsaw ??
    36438774-professional-electric-jigsaw-orange-isolate-on-white-.jpg
     
  7. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Meh - get a tool :)

     
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  8. OrcaSea
    Joined: Oct 2014
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    Location: Arlington, Wa

    OrcaSea Senior Member

    Ha! Good choice. I love that channel... I'm a ferry ride and a couple very pleasant driving hours from Leo's site, and I have often considered volunteering a couple days of camera work to give him a break...
     
  9. OrcaSea
    Joined: Oct 2014
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    Location: Arlington, Wa

    OrcaSea Senior Member

    There's a little bit of an issue in that - for the simplicity of the drawing - I did NOT put the curve of the keelson in the drawing, knowing I would have to lay that curve out, mark the bedlog up to match and cut it on the bandsaw. I don't have steaming gear and trying to make a 3/4" mounting flange conform to the curve of the boat would be problematic.

    Honestly, I am wondering if continuing the repair of the upper surface of the keelson to a good, clean mating surface, marking where the plugged holes are (to avoid the repairs) and just installing the bedlogs per drawing, counterboring the bottom for the mounting bolts and then fairing them in wouldn't be the easiest but still effective approach. I would still tie in to the ribs with stiffeners at the fore and aft box closures and vertical stiffeners at the center rib, of course, as i think the original design was weak in that respect. I have also considered a centerboard box web doubler at the pivot point for the centerboard and tying that in to the forward closure of the box, as well, to help transfer the torque to the coaming knee brackets at the top of the box. I want to put in a rubber seal at the base of the box, and accurately cutting and fitting recessed joinery complicates that, and I am also concerned about doing too much joinery at the base increasing the chances of paths for water ingress, which is what doomed this little boat from the start. In all my tech, hobby and construction endeavors I have learned there's a lot to be said for the effectiveness of simplicity.

    It is, after all, a fair-weather little daysailer, and I won't be racing the thing or trying to cross the Sound in it. Probably praying for enough puffs of wind to get me back to the boat launch on a local lake, is more likely ;)

    [​IMG]
     
  10. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    Cheer up, it's not that hard.

    What you do, is make a template of the rectangle size that you want the new slot to be. Make it out of rigid mdf, or similar, as thick as you like.

    Next, using scrap bits of timber, using levels and hot glue, and position the template in the correct alignment, and spaced correctly with the keel line.

    Obviously, the template will not sit flush with the hull, so you run multiple small vertical sections of timber, vertically down to intersect the hull, glued to the inside of the mdf "slot" and mark where they intersect on the hull. You then can draw the line to cut with the jigsaw.

    I have tried to illustrate the process.
     

    Attached Files:

  11. OrcaSea
    Joined: Oct 2014
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    Location: Arlington, Wa

    OrcaSea Senior Member

    Man...steel don't grow on trees, evidently...$99 US for the plate to make the new, properly sized centerboard. and that's for cold rolled. $280 for stainless. Oh, well, it must be done.

    This is my design for the new centerboard box. It's probably slightly overkill for the boat it's on, but better safe than sorry. I think I have decided on installing the box per drawing - repairing and resurfacing the top side of the keelson, marking the bolt locations and installing bronze bolts through new locations through the bedlogs and new keel I installed on the bottom, and counter-boring the keel slightly for the heads. If the boat were still flipped the thought of building a rig to create a new slot and doing some sort of insert would be more feasible, but I don't have room under the dolly to build up any kind of router guide with it right-side up. The thought of doing that accurately with a stand-off tool, a heavy router at arms length on my backand an extra long end mill was giving me nightmares ;)

    Here we go. Now, time for spending lots of money, milling timber and letting the chips fall where they may.

    [​IMG]
     

  12. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Umm, I didn't realize you aren't able to turn the boat upside-down.

    You can build that jig on the inside too, you know. As for a "router guide", I don't know where you got that.

    I was just suggesting ways to mark a jigsaw line. It doesn't have to be really precise.
     
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