Preview: How to Build a Caledonia Yawl, Part 35 – Assembling the Birdsmouth Mast

27 Responses So Far to “How to Build a Caledonia Yawl, Part 35 – Assembling the Birdsmouth Mast”

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  Ang Roberts says:

  Geoff,
  I’m currently working on a 15′ birds mouth design mast. After watching your videos multiple times I’m still confused as to how to set up the cradles. You explained that you make the half round opening a little oversized to get no interference. What I don’t understand is on a particular cradle at say station #3 for example and the plan calls for a total diameter of say 3″. Is the depth of that cradle from the flat plane on top 1/2 the diameter (1 1/2″) at that station on the mast? I’ve built a prototype 3 feet long and didn’t have to contend with the different thickness of the stays as it was just for practice and learning. I want to get these cradles right in proper scale and placement as possible. Can you help me understand this process?
  Ang

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    Ang Roberts says:

    Geoff,
    In addition to my question above, I will explain how I made my cradles and hopefully you can tell me what I did wrong.
    I made 5 cradles using 6″x 6″ squares and a 3 1/4″ hole saw. Largest part of my mast is 3″.
    These 5 cradles represent different stations from the base to the top and I calculated the center of the hole saw position on a rising scale from bottom to top. That didn’t come out right, and I was wondering if you used the same centerline for each cradle and a different hole saw size to accommodate the taper in the mast?
    Last but not least I want to thank you for these videos! I’ve never built anything like this before and now that I’ve watched your videos, and built a 3 foot prototype, I feel as though I can do the real thing. Thank you! Ang

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      Geoff Kerr says:

      I’ll try to clarify. It may take another cup of coffee. Using a 6″ square for a cradle, mark a vertical centerline. The top flat represents the horizontal centerline of the spar at a given station. The depth of the cut is 1/2 the diameter of the spar at that station. I use a compass to draw the cut, and use a larger diameter (like the 3 1/2″ you proposed), but set the compass so the arc is tangent to the accurate station diameter/depth of cut. This requires using an extra block with a centerline, butted up against the top of the work piece to set the compass point accurately. Once marked I cut the cradles on the bandsaw. I can imagine doing it with a holesaw given lots of creative clamping.

      In simplest terms, the depths of the arcs you cut should diminish as the diameter of the spar gets smaller.

      On the scale of small boat spars I don’t think it matters too much whether you use the same diameter or vary it at each station.

      I hope this helps. If you are pulling your hair out get in touch with me directly and I;ll try to talk you down.

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        Ang Roberts says:

        Geoff,
        Yes, it did take another cup of coffee and yes, I get it! On the drawings I’ve made of my mast and the corresponding dimensions at each station, I was dropping the centerline down at each station, instead of using a common centerline for each station. The hole saw approach was not a good idea as I wasn’t exactly perpendicular to my work, subsequently the cut was not square and was tapered throughout the thickness of each cradle. I’m hoping my skills with a jig saw are good enough, otherwise I’ll have to invest in a band saw to get these cradles right. My brother is on the west coast and has built a 14′ Wine Glass Wherry Pygmy Boat kit, and he has built three stitch and glue Kayaks as well. We are currently converting the Wherry to a sailboat, and he has challenged me to take on the mast, rudder, and centerboard with no boat building experience, so I thank you for taking my novice questions and guiding me forward! Ang

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  John Evans says:

  How well does the epoxy handle heat? I have a mast to build for a 30’ sailboat and I’ve read that epoxy will fail in hotter climates such as the tropics. Great video showing how it’s done. You managed all the multitude of pieces with ease.

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    Geoff Kerr says:

    Cured epoxy is heat sensitive, but my experience is that you and your boat are unlikely to experience the temps that cause it to fail. I have a lingering memory of 160 degrees F as an example of the temp necessary to cause structural failure, but I have no actual reference for that. Perhaps you might consult with tech support with your epoxy brand. I suspect the belief in tropical epoxy failures has more to do with long term UV exposure to unprotected(paint/varnish) epoxied surfaces.

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  William Bernard says:

  Geoff, I want to thank you for all your videos on building the caledonia yawl. I wanted to share some insights I learned trying to build birdsmouth masts.

  The first is that assembling the birdsmouth is alot harder than Geoff makes it look. So practice assembling the mast with clamps without any expoy till you get the hang of it. Once you start expoxing the staves you have about 30 minutes before the expoxy starts to kick.

  The second is that I was having difficulty assembling all eight staves into a good circle . I almost have it and one stave would kick into the center and I would end up with seven sides instead of eight. I solved this problem with a five foot segment of PVC pipe either 1” or 1.25″ diameter (depending on the size of the mast) I would assemble the staves around the pvc pipe which keeps the staves in good position and keeps one from popping into the middle. Leave at least a foot of pipe hanging out the end of the mast. Once you have two clamps on, loosen the clamps and pull the pipe out. Then put a clamp on the middle and work your way out

  Thanks again for your great videos

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  Stewart Lee says:

  Hi, Geoff. Could you tell us roughly how many gallons of epoxy you used for the entire construction? It would be a great help when it comes to budgeting for a CY build.

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    Geoff Kerr says:

    As a guess I suppose to be safe you could plan on three gallons of resin and the appropriate amount of hardener. Should be plenty. As the advertising folks say;”Results vary by user”.

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      Stewart Lee says:

      Wow, I expected closer to ten or fifteen! Thanks!

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  Jamie Snodgrass says:

  Hey Geoff, great to watch your video, especially after mangling my way through a self guided effort 3 yrs ago on a 19′ x 3+5/8″ mast for a heavy 19′ dory, my only interaction being the original Wooden Boat article & a sketchy uTube video!

  Oddly enough I came up with a similar approach by guess & good luck (& you know how time consuming that is!)…I was very lucky to get a good result after squeezing glue onto individual staves with 50ml syringes needing endless refills, running out of glue 1/2 way thru, trying to keep the whole deal in place with dodgy jigs made from split 4″ plastic sewer pipe & spanish windlasses with 1or 2 hose clamps & manual scrwdriver.
  You would have laughed your head off or cried or both had you watched!
  I can definitely vouch for 1 sided tapering & tablesaw birdsmouthing which I fortunately guessed upon, but your efficiencies like clamping the staves & glueing in one go with a brush & beautiful simplicities like those simple stable 1/2 round stands & plenty of hose clamps + electric nut driver are going to make my next one a breeze.
  Fortunately I got my first effort straight & true & after clean up it was beautiful, but I’d be crazy not to follow your example next time around, thanks so much. Regards Jamie, Sydney Australia

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  Patrick Walker says:

  Hi Geoff, which thickener(s) did you use in the epoxy for the mast? It doesn’t look like 404. It almost looks like wood flour. It there anything else in the thickener cocktail? – pjw

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    Steve Stone says:

    Hi Patrick, you’ll find lots of epoxy tips and details and a video answer to your question in Part 5 of the series… as Geoff uses the same thickener throughout… in this case it’s 405, the structural adhesive thickener… How to Build a Caledonia Yawl, Part 5 – Epoxy Tips

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      Patrick Walker says:

      Hi Steve, Thx for the quick reply. When I mix 405 with epoxy, it looks lighter than what I saw on film. I guess that is why I was baffled.

      Lastly, this was by far the best and most comprehensive description of a birdsmouth mast since the wooden boat article many years ago (I forget the issue number). Makes me tempted to try my hand at it myself, but your films on Shaw and Tenney were equally good, so I am also tempted to ask them to do it. – pjw

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  Lee Fox says:

  Enjoyed seeing how a birdsmouth spar is glued up and clamped. Thank you Geoff and OCH crew for another great video!

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  James Vibert says:

  Have you found a good way to clean your hose clamps yet?

  • 

    Geoff Kerr says:

    Option 1) Don’t bother
    Option 2) Propane torch and a wire brush with lots of fresh air

  • 

    Grant Carlson says:

    A wrap of packing tape around the spar underneath each hose clamp MIGHT keep them clean.

    • 

      Thomas King says:

      My thoughts exactly. It would help to hold the gooey mess in place as well.

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  James Vibert says:

  I was surprised to see no plugs installed at the time of assembly. We usually install them as we go. It helps to keep everything in proper shape. Cut slightly undersize and bathed in epoxy paste allows the staves to seat properly around them.

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    Geoff Kerr says:

    My plugs should show up in a later installment. I put them in after the fact ’cause that’s the way I do them after wasting too much time trying to fit them too carefully before glue-up. As you note, the key seems to be to make sure they are undersized so the staves fit each other correctly, and to make sure they are completely bedded in thickened epoxy.

    • 

      Grant Carlson says:

      Another approach to plugs is to keep glue away from two opposite seams when initially gluing up the hollow spar, so it can be separated into two halves after the glue has cured. The internal plugs can then be easily dry fit before the final assembly with glue.

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  Geoff Kerr says:

  I don’t install plugs in these particular masts. I’m familiar with the concept, have built masts where that feature was included in the design. Left to my own devices I have determined that it is an unnecessary complication in a mast of this scale. When in doubt do what the designer suggests…or else what you believe. There doesn’t seem to be a pile of broken masts lying around my shop…

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  Livio Muench says:

  How about using plastic cable ties? Cheap and Available.

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    Geoff Kerr says:

    Cable ties are tempting, but not adjustable…so if you need to move one or such you’ll have to cut and start over…I also doubt the amount of pressure you might be able to generate. Try a practice assembly and see.
    I have seen it done with inner tube “rubber bands”, and duct tape, but the hose clamps are tried and true and workable when singlehanding.

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  Grant Carlson says:

  This mast doesn’t get a solid plug from the heel to well above the partners, with steep slopes cut into its top to avoid creating a stress riser?

  • 

    Geoff Kerr says:

    See above for my thoughts.