keel vs board bottom

Discussion in 'Construction' started by bkoehler, Dec 24, 2019.

  1. bkoehler

    bkoehler Active Member

    Aug 10, 2008
    Hi All,

    I am helping someone with a new construction: wooden hull. It is wide enough and has a fair mount of "flat bottom" area so I was considering assigning her with a "board bottom" over most of the hull and only extend keels off the stern where the keel raises up from the very bottom.

    Anyone have thoughts, pro or con, about the different methods?

    Thanks in advance.
    acomputerdog likes this.
  2. bsgkid117

    bsgkid117 Well-Known Member

    Feb 8, 2013
    I always prefer a double keel to outline the water channel, after glassing you can always cut away any excess wood. I'm not sure what you mean by board bottom. I do a double keel that keys into the ribs to lock the hull together. Once it's all together I cut the ribs out of the double keel area and put in a thin piece of 1/16 plywood to serve as the bottom.
  3. GregMcFadden

    GregMcFadden Facilitator RCWC Staff

    Dec 6, 2006
  4. Anvil_x

    Anvil_x Well-Known Member

    Nov 4, 2017
    Park Falls, WI
    So....... I'm doing both....

    I do the same as above illustrated by Greg, but in making the ribs, I put a 1/8 indent in the bottom of my ribs, then use a 1/8 Sugar Maple Board to fill that. So I get a flat bottom from the board, and also have a full set of keels.

    I've only done it on post-refit US Standard Types, since they've super-wide hulls. I'd suggest it for a California/Tennesee/West Virginia post-refit.

    Anything else, consider just making an indent that is as wide as your water channel keels so that you make a flat center. I did that with Idaho when I first tried it out. lemme see if I have a pic......


    The Maple board sat a little prouder than I wanted (1/16"), but it was my first attempt. I sanded everything as close to tolerance as I could before I glassed her.

    So, since Idaho is a Two-Pump Chump, the maple board widens from 3" under the channel (my channel is 2.5 " wide, so the board covers to the outboard sides of the channel keels) to 6" under the pump wells where the pumps sit side-by-side.

    So, you can see where my channel keel ends, and the pump keels continue the work. The board allowed me to test the ballast pretty nicely since I have a continuous hull. Any unneeded ballast pockets can be filled in later with board insulating foam from home depot (like 2 bucks for a hobby-sized sheet). I glass the inside of my hulls, so the toughness of the underlying material isn't super-critical.

    Wow holy crap loading these pics was like standing in line for the DMV... Sorry I tried loading the pic like five times, and nothing worked. failed every time. Not a problem on my end, my internet's not throttled right now.

    Anywho, to add a bit of integrity to the hull, I drilled the board, ribs and keels then epoxied nails into the holes, trimming the excess nail length off with a dremel. So while the pump keels and the channel keels overlap significantly, the transition is a point of weakness. in that spot, the board acts like a third keel. Hence why I picked Sugar Maple.

    Sorry the other photos didn't load. I'll try to edit this tomorrow and pop up the pics.

    Overall though, it's not a hard technique to implement, and if done right, can add a lot of strength to the hull.
  5. Kotori87

    Kotori87 Well-Known Member

    Nov 8, 2006
    During my time in Western, I saw several different major methods of wooden hull construction. I'll start with the methods in-use when I started, and go up from there.
    1) "Classic" keel-and-ribs construction. This is a bottom-up method that generally includes a strong central keel, with ribs in the middle and a subdeck on top. The keel provides the bulk of the strength, the ribs provide shape, and a one- or two-piece subdeck is added on top.
    Pros: Strong hull, if built properly. Cons: poor damage control. Also, there's a keel taking up a bunch of height on the centerline, where you want to put other stuff like CO2 bottles, pumps, etc. This method doesn't see much use anymore.
    2) "classic" baseboard construction. Starts with a big flat board on the bottom, often tapered, with a couple of keel pieces at the bow and stern. Ribs are added on top of that, with a subdeck built up between the ribs using small blocks of wood.
    Pros: Uses smaller sheets of wood than a similar hull with classic keel-and-ribs construction. The built-up subdeck helps with complex deck shapes, for example the funky curves on some Japanese battleships and cruisers, and the sharply curving atlantic bows of some other ships. Better centerline space than "classic" keel-and-ribs, and better damage control. Cons: The subdeck lacks strength, and small mistakes in your ribs are very noticeable in the finished product. This method also doesn't see much use anymore.
    3) "top-down" keel-and-ribs construction. This method starts with a nice thick subdeck. Add a keel underneath to hold the ribs, slot the ribs in place, and voila: a new construction method.
    Pros: much stronger hull. These things can take some serious strain without damage. It's strong enough that you can cut out sections of keel and parts of ribs to build a water channel, mount CO2 bottle or cannons, etc. Cons: you have to cut out sections of keel and parts of ribs to build your water channel, mount your CO2 bottle, etc. You can either grind them out with a dremel (easy but ugly) or cut them out by hand with a small saw blade (time-consuming and tough, but better-looking). Does not work well for decks that swoop up and down or have other funky curves. This method is currently the most common wooden hull type in the WWCC's fleets because of how many ships we built like this.
    4) "twin keel" keel-and-ribs construction. Similar to the top-down keel-and-ribs, except most of the keel is split in two. It requires some clever joinery to go from a single keel to twin keels, but once you figure that out, you're home free.
    Pros: two keels makes for a very easy water channel. Clears space in the middle for CO2 bottle and other equipment without having to cut or grind stuff. Makes twin-skeg boats like the Iowa much easier. Cons: only works for flat-bottomed boats. Cruisers and destroyers are SOL. Also, the transitions from one keel to two keels are a potential weak spot that requires reinforcement. This method was just coming to prominence when I enlisted. It saw use in a Montana, my VUs, and the Gascoigne.
    There are plenty of other ways to built a wooden boat. You could easily mix a baseboard style with twin keels, or use a very thin non-structural baseboard so you have less bottom to cover. You could use twin keels and a subdeck, with a second subdeck-like horizontal profile forming the bottom edge of your penetrable. And lots more that I either forgot or haven't heard of yet.

    The one thing I'd suggest if you're planning some sort of baseboard is to mark it up before you start cutting. Put a bunch of parallel lines parallel to and perpendicular to the keel, spaced one inch apart. They will be helpful in accurately placing your hardware. You can always sand off pencil lines later if you don't like them, but you can't add them once the wood is cut and installed.
    buttsakauf likes this.