Kayak Ribs
Rib gathering in urban environments
Species suitable for green ribs
Making Ribs from Milled Lumber
While building a kayak is mostly a straightforward process, making ribs does require some finesse and practice. A first time ribbing job can often end up with over half of the ribs breaking. However, if you follow a number of rules, your success rate will improve. This section deals specifically with making ribs from purchased lumber. See the green ribs page for info on how to make ribs from wood that you collect yourself.
Selecting Rib Stock
Ideally your rib stock will be green lumber with a straight grain. Green lumber is lumber straight from the saw mill that has never been dried. Green lumber bends more easily than lumber that has been dried. Even if you soak dried lumber in water for several days, it doesn't become quite as limber as lumber that has never been dried. You typically have to get green lumber straight from a mill. Lumber yards generally don't stock green lumber.If you can't get green lumber you will have to settle for dried lumber. In either case, whether your lumber is green or dried, pick something that is straight grained and free of knots.
The grain orientation you pick for your rib stock depends on the dimensions of the stock and the target dimensions of your ribs. The aim is to have ribs with vertical grain. Flat grain, that is, grain that runs parallel to the flat side of the rib invariably runs out of the face of the rib and causes the rib to be subject to breakage when you try to bend them.
A. Cross section of a rib with vertical grain. This is the preferred way to cut ribs since it results in minimal breakage. B. Cross section of a rib with flat grain. While slightly stronger than vertical grain, unless your planks don't have grain runout, this configuration will result in much greater breakage. C. Side view of a rib with grain runout at point D. When you try to bend a rib with grain runout, it witll tend to break at the point D, where the grain runs out.
The best strategy for what size of lumber to get for your ribs depends in part on what sort of stock you can get and on what size ribs you want to end up with. If your target is ribs with a cross section of 3/4" X 1/4" it is best to get a 3/4 inch thick board with flat grain that you then slice quarter inch sections off.
This illustration shows end views of two planks, A, with flat grain and B, with vertical grain. Underneath A and B are shown end views of the ribs you would get by slicing quarter inch sections from A and B. A shows how to get 1/4" x 3/4" cross section ribs with vertical grain by taking 1/4" thick slices out of a 3/4 inch thick plank with flat grain. B. Using the same approach with a 3/4 inch thick plank with vertical grain results in ribs with flat grain which are much more likely to fail when bent.
If you can get 1-inch thick planks with vertical grain, you can slice these into3/4 inch or wider ribs of 1/4 inch thickness with vertical grain.
This is an end view of a one inch thick plank with vertical grain which can be cut into 3/4" or 1" wide pieces (cuts 3 and 4) that you can then cut into 1/4 inch thick ribs (cuts 1 and 2) with vertical grain.
What kinds of wood is good for ribs?
Some species of wood are better than others for making ribs, but often budget and availability have the final say in what you actually end up using. Unless you live in a large city or near boat building centers, your only source of lumber may be a discount chain lumber yard. Get what you can and don't be afraid to experiment. I will list a number of species that I am familiar with and will offer my comments on their suitability for rib making.
There are a number of factors that you need to consider when choosing your rib lumber. Strength is a factor of course but just about any lumber that you can get will be strong enough if cut into 3/4" X 1/4" cross section ribs. Denser wood species like oak tend to be stronger than lighter wood species like cedar. Weight of your ribs isn't a major factor since their total volume in a boat is not very great. Rot resistance is a minor issue in kayaks since they get to dry out between session in the water.
White oak bends well, is strong and rot resistant. I have had good results with it.
Red oak bends well is more readily available than white oak and is strong as well. However, it lacks white oak's rot resistance. I have found suitable boards at discount lumber yards.
Ash bends almost as well as oak and is strong as well and reasonably rot resistant. Can be found at specialty hardwood lumber yards.
Poplar or Aspen bends very nicely and uniformly. It isn't as springy as oak and not as strong or rot resistant but happens to be available in discount lumber yards.
Alaskan yellow cedar bends nicely, similar to poplar. It is fairly light and has negligible grain. Unlike poplar, cedar is rot resistant. However, this wood may be hard to find except near its source.
White cedar While a common tree in the northern US and Canada, it doesn't show up much in lumber yards. I believe it tends to be sold mostly as fence posts and tends to have lots of knots in it. However, it used to be used by birchbark canoe builders for canoe ribs. Lightweight and rot resistant. Worth experimenting with if you can find some.
Assorted softwoods I haven't done any experimentation with evergreen species such as pine and spruce. However, I have seen people have some success with douglas fir. Give them a try if you're feeling adventurous.