With the design steps over, I moved on to figuring out what wood to build this craft with, but, first, I fired off an email to Gregg Carlson suggesting a few improvements for his excellent program, Hulls. I suggested that he should have the program calculate the Block and Mid-ship Coefficients, which would help simplify the process for inputting the data into KAPER. He promptly wrote me back, and mentioned that he was thinking about setting up a project on Source Forge, and that he had been thinking about adding a feature to Hulls that would round the forms for strip building. I’m crossing my fingers, and if you have any experience with setting up a project on Source Forge, please, contact him. This is, in my opinion, the finest free boat design program on the market, and it would benefit everyone who likes to muck (hmmm. Is that where Nessmuk got his name?) around in boats to have a place like Source Forge lend its talent in developing this program.
Wood Weight for Cedar Strip Kayaks
After reading the email I received from Gregg Carlson, I was motivated to check out lumber supplies in town, and much to my dismay, I found that I’d have to special order clear cedar or I could use pine. In my mind, special ordering is a risk. How could I guarantee that the grain would be like I wanted and the color correct?
So, home I went and into the workshop. In the past week, I had purchased some plumbing T joints, 3/4″ plumbing tubing, and had planned on buying some wooden dowels to make a sail, so I figured I’d get started. When I got to the garage, I noticed a scrap 64″ 2×4 in the corner, so I decided to cut the spars for my sail from it, and when I got the first cut finished, I figured, what the heck, why don’t I rip a couple of 1/4″ inch strips out of the 2×4 and see what they would look like.
So, I set the guide on my circular saw at a quarter of an inch. (When I moved to Grand Marais last year, I gave up my access to a table saw. Such is life.) I ripped two strips and ended up with two 64″ strips and a blank 3/4 inch by 3/4 inch for my sail. Then I did another one. A load of saw dust later and I had my spars and my strips.
Much to my surprise, I found that the pine strips actually looked pretty good. I imagine that they will yellow under epoxy and varnish, but it shouldn’t be too bad of a change.
Still worried about the weight, I pulled out an Eastern White Cedar strip and a Western Red Cedar strip from my last kayak. I cut them to 64″, and weighed everything on a postal scale. Then did a few conversions figuring the weight of 55 – 18′ x 3/4″ x 3/16″ strips, which should be enough to complete this kayak. In my calculations (see chart below), a kayak made with Western Red Cedar will be eight pounds lighter than one built with White Pine, but…
- Wood Type —64″ oz—-18′ oz—55 strips – lbs.—BHc—lbs.—size
- N.Wh Cedar –2.8——–7.14—–25————–.65—-38—–1/4 +
- W. Pine ——-3.0——–10.02—-34————–.97—-35—–3/16
- Red Cedar—-2.2——–7.48——26————–.75—-34—–1/4-
…Pine is a stronger wood than cedar, so I wanted to figure out at equal strength, how much would each wood weigh. (How much wood would a wood chuck chuck if a wood chuck could chuck wood?) So, I picked an ideal Module of Static Rupture PSI of 10,000 and divided the woods actual PSI by 10,000, which gave me something I’m calling the Bryan Coefficient (BHc (for lack of a better name.)) This worked as a percentage of 10,000 that each wood ruptured at. Then all I had to do was divide the pounds for 55 strips by the BHc, and I would have a comparable number of the weight needed to be equal strength. It turned out that for equal strength, white cedar is three pound heavier and red is only one pound lighter than pine per kayak. Now, that is something to think about. If I’m right, then weight wise, pine is actually a good choice for kayak building. To get some kind of verification about the weight of pine used in kayak construction, I posted a question on the Kayak Forum, and received plenty of replies. Justin L. placed his 17.5′ kayak that was 21″ wide at 33.5 pounds with 1/4″ strips before fiber glassing. This was with the coaming finished! Tripp Stanley estimated final finished weight of his kayak would run 50 pounds for a Night Heron with 1/4″ strips 18′ long 20″ wide. Gennie’s 15’7″ 21″ wide kayak built from construction grade pine in 3/16″ strips came in at 30.8 pounds finished! My calculations were pretty close to the mark.
Ripping the Strips
With my weight calculations finished and in my mind verified, it was off to the store to pick up wood, but for those of you who haven’t built a boat before some explaining is due. In the last episode, I wrote about building a set of forms on a strong back, which when set up resemble the shape of the kayak. The next step is to attach the wood strips to the form. These wooden strips are typically 3/16 to 1/4 of an inch thick and 3/4 inches wide and as long as the kayak. These are either stapled to the plywood forms, or rigged to the forms in some method to hold them to the form without staples. (People use tape, bungee, 100s of clamps, and many other methods to achieve this.) Glue is applied between each strip, and when the glue dries and the whole kayak is stripped out, the staples are removed. The boat is then sanded smooth, and a layer of fiberglass goes over the wood to hold everything together and form a waterproof surface.
But first, the strips have to be cut. Usually, a table saw is used, but if you read closely above, my current shop doesn’t have a table saw. Seeing this as a future problem, I had already purchased a guide for my circular saw. Using this guide as a moving fence, I set the saw for 3/16-inch strips and walked the saw down the edge of the board.
Hey, this is easy, I thought. It turned out that the walking off of strips with a guide and a circular saw was much easier than I thought. So easy, in fact, I think for all my future strip boat projects, I’ll do the same.
Tips for Ripping the Strips
If you decide to rip your strips the easy way with a guide and a circular saw instead of the super accurate way with a table saw, here are a few tips.
- Invest in a really nice surface planer.
- No really, buy a surface planer.
- Okay, I admit. I don’t own a surface planer and my strips turned out nicely. It must be the steady hand.
- This is very *important*. Watch out for kickback from the saw. Kickback is a serious problem when using a circular saw for ripping. Make sure you stand to the side of the saw and not behind it, because behind the saw is a danger zone. I’ve done home construction on and off since I was 13 years old (Thanks, Dad.), and I still had the saw kickback during ripping twice. I was stopping the saw and pulled it out of the cut before it stopped. Be very careful.
- Build yourself a ripping table. I built mine from an 8′ 2×8 and my two saw horses. It gave me a 16′ ripping table 8″ wide to set my cedar and pine ontop of. This holds the board level and makes for more accurate cuts. My sawhorses, of course, now have small groves in the top of them from were the saw extended beyond the board I was ripping.
- Build yourself a jig. It gets extremely difficult to cut the boards as they get into the 2″ wide range. I built a jig to help out by ripping my worst board first. I ripped the strips out of this bad board by first cutting the side that was the best into strips. When I got to about 2″ left, I saved this board to use as a jig. I screwed this jig board onto the ripping table so that when my other boards would get down in size, I would always have 2″ of surface from the jig board.
- Screw a stopper board at the end of the table opposite of where you start to rip the cedar or pine. Only use one screw when you mount this board, so that the board can pivot in whatever direction it needs as you push the board you’re working on against it. This board is a substitute for a clamp, and it also acts as a continuation of the board you’re ripping, so you can run the saw down past the end of the board and get a clean correctly sized cut.
- Use quality ear and eye protection. You wouldn’t want to put an eye out.
The Bead and Cove
The next step in cedar sti … opps … pine strip (Okay, I’ll admit it. I’ve managed to find some cedar after shifting through the entire lumber supply at a town 15 minutes down the road. I ended up with four cedar boards, and one of those four a very nice reddish color.) building is to bead and cove the edges of each strip cut in the previous step. These bead and coves allow that strips to lock into each other and prevent gaps from forming in the hull. You can see how it works in the illustrations below. The cove also acts as a nice glue holder.
To do this, I built a router table out of scrap plywood, and then made a jig with a grove cut into it the exact same size as a cedar strip. Using this jig to hold the strip in place as I ran the strips past the router was a simple and fast process.
With this step over, the next step was to cut the forms out of plywood and set up the strong back and strip the boat. Only 63/64th of the project left to go.