Preview: Topside Seams Show? Consider Splining

LOAFER is one of the lovely Herreshoff 12-1/2 footers (so named for their waterline length) and was built in 1936. Although her freshly-painted topsides looked flawless each year on launching day, it wasn’t long before her caulked-and-puttied seams began to show.  To cure this unacceptable distraction, Eric Dow carefully routed out each seam to half the plank thickness and glued in a cedar spline. He’s done this before and it’s worked. For ten years the splined seams of an identical boat have remained invisible—even though that boat’s topsides were dark blue instead of white. However—and this surely has to be considered—neither of these boats are allowed to dry out much while they’re ashore. They’re housed inside damp sheds where there’s no sun and wind to excessively shrink the planking.

This spring when I visited Eric’s shop and saw LOAFER’s starboard side so nicely splined, sanded, and ready for paint and the port side about to receive the same treatment, I grabbed the opportunity to share his procedure with OCH members feeling that it might be a solution for some of their boat’s topsides.


This is LOAFER with her splined starboard topside already for painting.


Eric’s first move after stripping the planking of paint is to nail on a batten to guide the router. He positions it so the routr bit will bisect the seam. 

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17 Responses So Far to “Topside Seams Show? Consider Splining

  • Avatar

    John Hooge says:

    Maynard—did you know Alan Anderson who also worked at Electric Boat in Bath? I lived with him and Ms Anderson the summer of 71 when Mr. A worked at Underseas Engineering at Perry Submarines. I also worked for him as a “junior oceanographic engineer”. He was a fabulous engineer and man.

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    John "Jack" Detweiler says:

    Lots of great information on prepping a wood boat. I have a 2001 Alerion Express 28 that I had painted over the winter in Herreshoffe Alerion Green. Most of the time was spent in filling the gel coat grazing that was prominent in this vintage boat built by TPI. Any suggestions on how I can paint the white grazed gel coat above deck?

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    Hugh Dyer says:

    As one of LOAFER’s former owners – assuming she is hull #1297 – I am really pleased to see the wonderful care that she continues to receive. Thank you so much for so carefully preserving this timeless treasure.

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    mike douglas says:

    Thanks for your crews endless sleuthing and documenting. Been meaning to spline the topside seams on our 1936 IOD for some time. OK I’m inspired. A couple of questions, what is the most appropriate splining material for a fir planked hull, fir or cedar? Second She’ll come out of the water this November and spend the winter in an unheated shop with a concrete floor until April. Best time to spline fall or spring? Thanks for the prod.
    mike douglas

    • Sandy Lam

      Sandy Lam says:

      Hey Mike,

      We asked Eric Dow for his expertise to answer your question and this was his response:

      “For splining a fir planked hull, I would probably use fir since they are the same wood and density, however it really doesn’t matter. If you have cedar available that would work as well.
      It might be good to let the boat dry for a while, then spline in the spring. “

  • martin Thomas

    martin Thomas says:

    Has this been tried below the water line and does the cedar spline harden up with the epoxy, so as not to be as malleable to the expansion of the planks? Would another glue maybe tile bond work.
    your comment appreciated
    Thank you for the interesting article

    • Avatar

      Maynard Bray says:

      Cedar is so forgiving that probably any waterproof glue would work for splining, but epoxy surely is the strongest and best at filling gaps and voids. Alec Brainerd of Artisan Boatworks glues all seams of his new cedar-planked hulls, but with certain criteria. You can read about his approach in an article by Matt Murphy in WoodenBoat #231

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    Bill Barton says:

    Outstanding process and so artistically done. Amazing restoration.

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    Les Weeks says:

    This brought back memories! About 15 years ago I splined the topsides of my gaff rigged yawl ‘White Cloud’ in pretty much the same way, I cut a mitre on the end of each spline so there was no possibility of a gap and used monel (iron-free) staples, anticipating a few legs breaking off. The gaps in the seams below the waterline were very wide and so I splined just one side (feathering?) to make the gap more caulkable. Her present custodian says that she doesn’t leak a drop.

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    Nigel Purvis says:

    Maynard, thanks so much for documenting this process. Great to see the process unfold. Eric is a master craftsman.

    More photos of LOAFER are available on instagram at @mainemooring

  • Charlie Nichols

    Charlie Nichols says:

    I have a Winer Malone Bahama Dinghy that is VERY dry and you could throw a cat through the seams. This boat will always live on a trailer (and be dry sailed / rowed). The boat is kept in a climate that is VERY dry in summers (Central Coast – inland – CA)After replacing some planking and outside stem worm damage, I’m thinking it would be best to refasten (the existing fasteners are very good, but need to be taken up a bit) and to spline the entire hull. Any thoughts on whether this is a good approach. I don’t foresee sheathing the hull with sheathing or any type of fiberglass treatment. Thoughts? THANKS!

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        Bill Theurkauf says:

        Going between the Pacific and inland CA will be very hard on a traditionally built boat. My guess is that splining while very dry will lead to very high pressure on the fastenings and ribs when she swells, possibly breaking the ribs. Instead of sheathing, you might able to minimize movement/stabilize the hull by installing splines and then thoroughly coating inside and out with penetrating epoxy, followed by several coats of enamel. Similar to the glued carvel planking Artisan Boatworks uses. I’m very interested in Maynards thoughts,

        • Charlie Nichols

          Charlie Nichols says:

          Agree with your thoughts about some swelling and enough space to allow it. Got a note from MB about the possibility of light cotton caulk on about every third seam and splining the other two. That seems like a reasonable compromise. The hull planking does swell a bit with change in the seasons (yeah we do have seasons in spite of what folks say!!!) – I’ll probably give that approach a try. Coating inside with epoxy is a bit too much effort and I’m not sure that it get’s the boat where it needs to be. It could be that would be a next step if the spline a little / caulk a little approach doesn’t do the trick. I’ll share some pics as this project gets going – it has a couple ahead of it for the moment – finish up of a Nutshell 9-6 and then a Brooks Somes Sound 12 1/2 (and a bunch of “distractions” like my growing fleet of O’Day Daysailers that we race here)…but I’ll get there!!!! THANKS! .

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    Philip Myer says:

    Thanks Maynard- I notice Eric was pushing them in not banging with a hammer.

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    Mikkel Pagh says:

    Great tip. Thanks a lot for sharing. The short video bits combined with the text and the photos work exceptionally well for explaining the process.