Monday, August 27, 2012

Glued-Lapstrake (Clinker) - Another Approach

Trailer and car-top boats are my specialty for a number of reasons - the primary one being that I don't have the resources to live near a deep water anchorage and so carvel-built boats kept on a mooring are beyond my means. 

Tom Dudgeon moored in very shallow water.
(illustration taken from Coot Club by Arthur Ransome)

But in many ways this state-of-affairs has turned out to be to my advantage. Large and deep boats are unable to visit the hundreds of thousands of superb shallow water destinations which abound along the coasts of most countries, and a cruise in a large boat can mean being imprisoned in a cabin or on a deck which is in constant motion while the crew view the exciting coastline from a long distance out. Every bar-crossing is a stressful event and very few nights on a cruise provide real rest because of the responsibilities of anchor watch.

On the other hand the dinghy cruiser can work up tiny creeks, cross bars where a mishap simply means stepping into ankle-deep water and pushing the boat across the obstacle into the calm on the other side of the bar. Some of the most enjoyable cruising I've done (all in dinghies - sail and power) has included sessions of travel along the coastline with the boat just outside the shore break. This is most exciting and enjoyable stuff, providing close-up views of beach, rocky headlands, mangrove creeks, breaking reefs, entrances to bays which are invisible to the crew of boats further offshore etc. Sailing, poling or rowing across flats covered by two feet of water is challenging and deeply satisfying. The options available to the beach-cruiser are manifold....

Alec Morgan's camp ashore on an island in Moreton Bay during a solo beach-cruising expedition. The trip was of about five days duration, and involved a whole range of coastal activities including exits and entries across surf bars.
I still suffer from a desire to spend nights aboard bigger boats, snug inside a cabin surrounded by sounds of the sea, listening to rain drumming on the deck. However, my wife, who has actually cruised and lived aboard larger boats for approaching nine years full-time, has told me the dream is frequently better than the reality. For her, cruising in a centreboard dinghy for the first time was a true and enjoyable revelation.

Anyway, I've found myself spending a life involving small trailer boats, and I still get excited every time I head out (and in when I'm tired/cold/hot/scared/hungry/sun burnt/hypothermic....)

Graham Faulkner's Periwinkle in the beach slop
Son David and me approaching the shore after a very wet and cold sail  - heavily reefed and going like a rocket.
An extremely important element in successful beach-cruising is light gear, and light-weight boats. It is no fun not being able to haul a boat up past the high-water mark, and even worse being unable to get a boat back down the beach to the water. Also, late middle-age has taught me that manoeuvring a trailer around the yard by hand has become more difficult than it was.....

Launching the Francois Vivier Aber I built for Dr. Paul Truscott. She is quite a large boat for her length, but the entire package can be wheeled around on land on her trailer by a single person with relative ease. As you can see, launching and retrieval are a breeze, without even having to immerse the trailer wheel bearings.
Very light-weight hulls can be built using cold-molding techniques, foam-cored construction and glued-strip planking, but all of these methods are fairly complex and/or expensive. My choice of methods for light-weight, inexpensive, quick, and simple construction include stitch-and-glue plywood and glued-lapstrake (clinker) plywood.

Periwinkle under construction using glued-lapstrake techniques.  Most of the weight in the internal structure gets left on the mold strongback.
Will Shrapnel's boat being built using the stitch-and-glue method. This is my Fleet design  - a very light boat.
Recently I was commissioned to build an Annapolis Wherry Tandem from a Chesapeake Light Craft design. I was interested in building this boat having previously read about the patented "Lap-Stitch" method devised by Chris Kulczycki. "Lap Stitch" is a trade mark, but I can't make this program insert the symbol!

Cover shots from Chris Kulczycki's book The Canoe Shop in which I first read about the "Lap-Stitch" construction method. That is John Harris, owner of Chesapeake Light Craft, in the paddling photo.
"Lap-Stitch" combines the advantages of both glued-lapstrake and stitch-and-glue construction methods, meaning that a shapely glued-lapstrake hull can be constructed without having to use a strongback and station mold set-up, saving time and making the somewhat intimidating glued-lapstrake construction method accessible to inexperienced builders. What makes this possible is that the overlapping planks have a rebate machined into one edge instead of needing a varying bevel planed along the edge(s) - something which worries many beginners. The key, though, is not that the beveling operation is avoided, but that the inner edge of the rebate "hooks" onto the edge of the preceding plank allowing properly developed planks to be stitched together in a manner very similar to that used in normal stitch-and-glue.

A drawing I did to illustrate the difference between Glued-lapstrake and "Lap-Stitch"
Any true stitch-and-glue design relies on extremely accurate panel development and panel cutting in order to have the hull adopt the correct three-dimensional shape, and the same remains true for "Lap-Stitch". Once the hull has been stitched together, it is positioned upside-down and relatively low-viscosity epoxy is run into the open lap rebate and allowed to set. Not only does the technique require the accurate panel development and a defined rebate, but it also needs an adhesive which is truly gap-filling in a structural sense - and the adhesive must be runny enough to work into the gaps under gravity - but not so thin that it runs all the way through to drain out on the inside! As far as I can see, only epoxy is practical for this, and it must not have much of the glue thickening additive included in the mix.

This is the only photo I have which shows the rebate machined along the edge of a plank.  Here I am cutting through one of the tabs holding the plank into the plywood sheet after the shapes have been cut with a CNC router. You can see the routed rebate under where my left hand is gripping the plywood.

Annapolis Wherry Tandem during the initial stitching-up process
Plenty of stitches required. I elected to use plastic cable-ties instead of the  copper wire  recommended by the manufacturer of the kit. I find the cable-ties are less likely to damage the soft plywood, and are easier to tighten and to remove. You can just make out the "jigsaw puzzle" joints used to join the planks longitudinally. I will have more to say about these in a coming post, but in the meantime I'll be using scarph joints on my boats.
Here you can see the stitches on the inside of the hull.
In this photo you can see where I have run the epoxy into the gaps of the plank laps. I am fastidious about  gluing-surface preparation, and I took exceptional care to get the epoxy into the gaps to the maximum extent. Although I used a hypodermic syringe without a needle to run in the epoxy, the process was messy and slow. At this stage the epoxy had cured and I had removed the ties holding the laps. The remaining ties are the ones holding frames and bulkheads in position.
This is a section through one of the plank laps at the transom, showing the rebate, the initial low-viscosity epoxy which I worked into the seams with great care, and then above that the more thickened epoxy which I used to completely fill the seam.  To be done properly, the job requires great care and attention to detail.
I don't have any suitable photos, but this drawing shows a section through a conventional  glued-lapstrake hull showing the beveled laps with parallel-sided glue lines.
200gsm (6oz) woven glass set in epoxy over the flat bottom panel and the first two planks on each side of the Annapolis Wherry Tandem. The wide white lines are epoxy fillets used to fill out the internal plan laps so that the glass cloth will lay fair.
External glass cloth over the bottom panel and the first plank (garboard strake) on each side. The internal and external glass shown is as per instructions.
Recent photo showing external paint nearing completion

A long and lean boat - awaiting final internal sanding and painting

Well, that is a brief run-down on "Lap-Stitch". I think it has a place for some people - especially beginners. However, like all boat-building methods, it does require serious attention to detail, and should not be taken lightly. For myself, I'll stick to the normal method using a station mold and strongback, as I like the tighter glue-lines and neater work. My opinion is that I could have built the strongback, mold and the boat using conventional methods faster than by going through the messy gluing process and filling of hole associated with the "Lap-Stitch" system. But that is just my own opinion, and I can see a real place for "lap-Stitch" as long as the plank patterns are accurately deigned and cut, and that the person doing the work is happy with relatively heavy epoxy use in comparison with conventional glued-lapstrake. I'd say the building process is more simple for a tyro than the conventional method, but not any faster.


  1. Hi Ross,
    I've been following your blog for a wee while and read your article in Watercraft, very interesting.

    I agree with you on the amount of enjoyment to be had from a small boat. I'm just back from a Dinghy Cruising Association Camping and Sailing Week in Chichester Harbour UK. Great fun.

    I also agree about clinker ply, I've built two stitch and tape canoes and two Clinker Ply dinghies, and had wondered whether there was a hybrid method similar to the one you describe, but seeing your comments I'll take Clinker Ply anytime.
    Best Regards

  2. Graham,

    I like the idea of being able to combine the jig-less construction of S&G with the structural and aesthetic advantages of clinker - but I think the joint compromises are too great. Like you, I'll stick with the proper methods.

    Best wishes,


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  4. Hello Ross.
    Just came across your interesting article on glued clinker.
    I was first introduced to glued (resorcinal)clinker while serving my time at W A Souter Cowes,some 55 years ago.
    The craft was a National Twelve. Mahogany planking with conventional browing off and rebated hood ends, but no fastenings and no bent timbers. Seven planks per side and only one pair per day. (before the days of Epoxy of course)
    Coinsidently I am at present developing a glued clinker ply Solent Scow, similar to your "lap stitch" but without stitches. I'm using fine guage screws tabbed between with epoxy and tape. and fully taped when screws are removed.
    Turn over and fill lands after. Intention is to market full size patterns, photos and instructions.
    Best regards,

  5. Ross

    Greetings from Perth, Western Australia.

    Most interesting Annapolis Wherry design and photo sequence. Rowin g performance ++!

    The internal photo appears to have the glass definition crossed. I expect you were using the industry standard 2 ox, 600 gsm chopped strand mat. This may clarify for other readers.

    A related fact, for weights.

    If you allow for a typical 2.5:1 resin/glass ratio, 300 gsm glass becomes 1050 gsm total laminate. Thus you can think 1 kg/m^2 of laminate per 1 oz (300 gsm) of glass. Nice easy number!

    Peter Edmonds

    1. I am sure Ross isn't using chopped strand mat. It doesn't work with epoxy, you have to use woven cloth.
      That is a great rule of thumb 1oz cloth=1kg per sqm laminate.