Wooden Boat Construction

Wooden Boat Construction – Backbone assembly


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“Where do you start?” That’s a question I hear a lot when folks are asking me about building a boat. It’s a good question; it’s an obvious question, and it has a deceptively simple answer.

“I start with the backbone” I tell them.

“You mean the keel?”

That’s the response I almost always get. And I explain that yes, the keel is an important part of the backbone, but that it is just one component in a large assembly of pieces that provide the foundation for the rest of the boat. But I am always hesitant to go much further, because it gets confusing pretty fast and I often suspect that the whole answer is more answer than they wanted. Even on a small boat there are quite a lot of pieces. Each providing a different structural purpose and tied together by a web of screw, lags, and bolts to support each other and the frames and planking that are to follow. To make matters worse, each of these parts might carry any one of a number of strange names that vary from region to region and builder to builder. Names like Apron, Hog, Gripe, deadwood, and shoe just to get started. With a little patience, and by taking things one piece at a time, the lay person can make sense of the jargon, and how it comes together to become the backbone for a small traditional boat.

You may be familiar with the parts and names already, but I intend to plow tediously through all of them for the benefit of those to whom they aren’t familiar. All this stuff is a bit dry, I warn you, but It is good stuff to know and worth plowing through. I will do my best to keep it simple and moving along.

A great boat to illustrate this structure is the Connecticut River Drag boat. This is an 18’ boat from the Whitehall family, but it is bigger and heavier than the sleek rowing Whitehalls most are familiar with. She has more beam, and timbers of heavier size or “scantlings”. This boat was a hardworking fishing boat, used to “drag” nets from the stern in the shad fishery at the mouth of the CT river in the mid 1800’s. It is a handsome boat with a great history. What makes her a particularly good example is that she has a complex hull, with almost all of the same parts that you might see on boats of a much larger size.

Although I said earlier that I start with the backbone, that’s not exactly true. Before I can make any sawdust or shavings, before I can make the first cuts for the new boat, I need to have carefully lofted the vessel. A good lofting is essential to being able to layout and shape the individual pieces of the backbone.

In essence a completed lofting is like a full scale blueprint of the boat. It shows the craft from several perspectives. Most importantly for this purpose are the profile and half-breadth or “bird’s eye view”. Using the lofting, I can carefully lay out each piece of the boat, I can source timber of the appropriate size, and then cut and shape it with confidence that it will fit together to the adjoining pieces.

This is boatbuilding not sculpting, there is neither need nor reason to form the backbone from a single piece. Doing that would make for a weaker boat and prohibit easy repair. It is both easier and stronger to work the components as smaller pieces on the bench and then fasten them together into a whole.

With the lofting for the drag boat complete, I am ready to start working with wood, actually building the boat. Since I have the information to make each piece by itself, the pieces can be made in any sequence. To keep it easy, I’ll start at the bow and work my way back.

The Stem

The STEM is the foremost piece of the backbone. Its primary purpose is to provide a solid place for the ends of the planks to land upon and fasten to as well as take any impact to the bow. The stem, like most backbone parts, should be made from a strong, rot-resistant hardwood to ensure it will take years of abuse and hold fasteners well. The planks will land onto a groove carved into the stem known as the rabbit. Most of the backbone will follow the path of the rabbit from stem to stern; so the rabbit line in the lofting is the line most referenced in laying out the pieces.

While some stems are made from two pieces to facilitate the creation of the rabbit (an inner stem, beveled along the front to match the planking, and an outer stem which caps the plank ends and protects them from damage), more commonly on traditional boats the rabbit is carved into a single piece with a lot of slow careful chisel work. When planks come into a boat an extremely steep angle, more landing is sometimes needed. In this case an “apron” is added. This is a wider piece than the stem that is fasted to the back side to build up the back rabbit. The stem for the dragboat requires no such additions. It can be worked out from a piece of stock 7/4” X5” X2.5’.

The Forefoot

At some point the stem must transition from a vertical or near vertical run to the horizontal run of the keel. The piece that makes this change is called the FOREFOOT, or GRIPE. It tends to be one of the more strangely-shaped pieces on a boat, with a fussy overlapping joint on each end. With a boat like the Drag boat, this piece creates a nearly 90-degree transition and requires the use of either a grown crook, a lamination, or a series of smaller pieces bolted together in order to avoid severe grain run out and the resulting weakness.

I love to use grown crooks here when I can. If you can find one, they are usually the quickest, most elegant solution. On my most recent hull to this design, I could not find a crook of adequate size when I needed it, so I laminated the piece instead.

Laminates are great in many ways. They are strong, stable, and resistant to splitting. Also, with a little extra length in your stock, you can integrate the stem and gripe into a single piece and do away with one joint in the boat.

That’s what I did on this project, and while in some ways stronger, it also makes things more difficult. Aside from the headaches of prepping laminates, and the mess of gluing them together, treating the stem and gripe as a continuous unit makes shaping the piece far harder since the gripe is the area where the rabbit goes from uniform width to a progressively widening fish shape on this boat. But with patience the work can be laid out and cut even on this larger more awkwardly shaped piece.

The Keel

Moving along the boat, the gripe is in turn secured to the KEEL. There are two general types of keels in small boats: plank keels and tracking keels. The Drag boat gets the former.

Types of Keels

Common to centerboarders, a plank keel is more or less what it sounds like. It is a heavy plank (in this case a 6/4” oak board), shaped something like a fish: wide in the middle and tapering at both ends (in this case 11” at the middle and 1and 3/4” at the ends).The upper edges of the keel plank are beveled to follow the rabbit and meet the run of the garboard plank in a caulked seem. The additional width in the middle allows material to be cut away for the centerboard trunk without weakening the piece overall. It also lets the boat sit easy when beached.

A tracking keel can be as simple as a plank on edge, or a more elaborate carved timber. It tends to be deeper than it is wide, and extend well below the planking to give the boat a “grip” on the water, to keep it from sliding off to windward (if a sailboat) or traveling in a straight line (if a rowboat).

On a heavy timber keel, a rabbit is frequently carved into the piece, just as was done on the stem. But more commonly in small boats with either plank or tracking keels, is for the top edges of the keel to be beveled to follow the run of the garboard plank in a caulked seam. In this case there is no back rabbit at all supporting the garboard, leaving only the floors (will get to these shortly) or the frames to fasten the plank to. When a back rabbit is desired (as in a boat that will be frequently tailored where a simple caulked seam might dry out and open up), a common solution is yet another piece known as a hog, or keel batten.

The Hog

The hog is a board secured to the top of the keel and acts very much like the apron does for the stem. Wider than the Keel and thick enough to allow fasteners to hold the plank in place, its bottom edges are beveled to provide a continuous landing for the inside of the garboard. The Drag boat uses a hog on the back third of the boat. To support the region where the rabbit rises back up and leaves the waterline.

The Floors

Sitting evenly either on top of the hog, or directly on the keel are the FLOORS. The floors are essentially cross-sectional fillers, almost like permanent molds. On the Drag Boat they are 1” thick and 4-6” tall, spaced about 12” apart. Despite their small size and simple shape, they provide a critical role of tying the keel to the planking and frames and supporting the often abused bottom-most planks. They also provide the additional service of acting a floor joists for supporting the boats floor boards or “sole”.

The Deadwood

As the rabbit continues to travel aft it must sweep up at some point. Sometimes a plank keel is sprung or bent to carry this transition, or the timber of a tracking keel might be set at an angle to allow it to be carved to follow. But equally common is the arrangement employed in the Drag boat. Here, the keel remains at the boat’s bottom, matching the width of the rabbit but no longer carrying the planking. Instead, as the rabbit moves aft, it rises up off the Keel onto the “Deadwood”.

Deadwood generally refers to a piece of filler timber that’s main purpose is to help build a wooden “fin” in the stern of the boat. It is often made from the same material as the rest of the backbone, but deadwood can become quite substantial in some boats, and at the end comes the stern post (in a moment!) whose grain is running perpendicular to that of the deadwood and keel.

The differences in swelling where all these pieces come together can make for joints that are hard to keep closed. This is especially true on small boats that go in and out of the water a lot. On the Drag boat I use cedar for the deadwood to ease this problem. Since the piece is just filler, it don’t need to be strong like the oak, and cedar is much more stable. A bonus is that the deadwood is often a piece requiring a great deal of shaping in all direction, curved on three sides flat along the bottom. Carving this out of a hunk of oak would be a serious chore!

Aft End – Stern Post, Transom, Stern Knee

Just three primary parts left, and they all tie together here at the busy aft end of the boat. The STERN POST comes first. This is the vertical timber that defines the back edge of the boat. On a double ender, it is similar if not identical to the stem. But on a transomed boat like the Drag boat, the stern post provides the support for the transom. Because of the problems mentioned earlier with differential movement, I like to make the stern post out of as stable a wood as possible. But here, I do need the strength of a hardwood. My solution is to use either cherry or locust. It’s a small difference but back here every bit helps.

A boat’s TRANSOM provides the landing for the aft end of the planks. It must be thick enough to get a good long fastener into without splitting. And it helps to use a stable wood that will resist cupping and the resultant stress on plank ends. On top of that, it is one of the few places on a boat that varnish makes sense. Easy to sand and maintain, with high visibility to show off a wood’s beauty. I like quarter-sawn cherry for transoms, since it is stable, rot-resistant and beautiful. It is secured to the stern post with a few large screws.

On most small boats this would complete the back bone. But some boats (like the Drag boat) see heavy use from the boat’s stern. In this case the loaded nets were worked over the transom. To accommodate the additional stress, a STERN KNEE is fit to help tie the stern post to the hog/deadwood assembly. Here again you could use either a lamination or a grown crook. The knee is not all that large, and you can almost always find a crook if you want it.

Tying it All Together

A few words on tying it all together now that the parts are all named out. I am a big believer in a few well-placed, large fasteners rather than a lot of small ones.

  • Gripe/keel connection: Low-profile carbide bolts are great. 3-5/16” bronze is perfect on a boat this size.
  • Hog to keel: Screws are good for holding down the hog to the keel.
  • Floors to keel: Long bolts for the floors to the keel, usually two each set at a slight “V” orientation. Longer bolts still tie the hog-deadwood-keel sandwich together.
  • Stern post to deadwood: A few blind-pocketed bolts help to tie the stern post to the deadwood.
  • Stern post to keel: A variety of joints and techniques are used to hold the stern post to the keel, with the mortise and tenon the most common.
  • Transom to stern post: Screws and lags are used for the transom to the post.
  • Stern knee to stern post and hog: Screws and lags work again here.

Stopwaters

Glue? You can try. All of these pieces are going to work and move. The joints of the backbone are a great place for rubbery adhesives like 3M’s 5200. Rigid glues like epoxy are probably a waste of time at best, and a leak promoter at worst. All of the joints will probably give at some point which is why we installed STOPWATERS in every joint that passes through the rabbit.

Stopwaters (or stop waters) are just what they sound like. They are pine or cedar dowels that are hammer-fit into holes drilled across any joint that passes through the rabbit after assembly. This way, as water begins to migrate from outside the boat to inside, it first meets the stopwater, which swells to block off the plane of the joint and keeps the water from traveling any further.

The backbone completed and assembled it a great thing. You can see the profile of the boat that will be built onto the foundation. It is a nice point to stop for a little break, and admire the profile of the beautiful boat that is taking shape in the shop. Keep the break short – because this is just the start. There are molds to make and place, planking to wrap and fit, frames to bend….it just goes on and on. But do – take a moment and appreciate the beautiful starting point you’ve created, the backbone of your wooden boat.

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