May 4, 2013

Canoe Building – Floatation

Bow Floatation Ready For S-Glass
This past week Kevin and I built the floatation chambers (for canoe #2, White Lightning). Floatation chambers increase the buoyancy of the canoe to ensure it will float even when completely water logged. The displacement of water alone will keep the canoe afloat with people and gear in it. However if you start taking on water or completely water log the canoe, you will not have enough buoyancy to stay afloat. This lack of buoyancy could get very dangerous on windy and rainy days. So to solve this problem we add more buoyancy to the canoe by creating air chambers at the bow and stern.


Inspired by Wenonah (a major Kevlar canoe manufacturer), we decided to build our flotations as a square step that fits into the bow/stern. This is contrary to how James Moran describes how to build the floatation in his book Building Your Kevlar Canoe: A Foolproof Method and Three Foolproof Designs. He describes building a tear-drop shaped piece of foam that fits in the top of the bow/stern and extends to the bottom of the canoe at roughly a 45* angle. When doing this method for the DragonFly (first canoe), it was incredible challenging to accurately shape the tear-drop and you lost more foot room for the person at the front of the canoe.


To build our “step” that forms a water-tight floatation compartment, all we need to do is cut a piece of foam that is our riser and one foam piece that is our run (horizontally). The process of cutting the foam was trial and error. We used a band saw to cut and then slowly cut the pieces to shape by take a little bit off at a time. We stuck the foam in the respective bow/stern end and used a wide (3/4″) felt tip marker to trace the shape of the canoe onto the foam. This allowed us to get closer to the correct shape with each cut.

Once we were at the size necessary, we made a back-cut at roughly 45* around the edge of the foam. The angle of this cut will face toward the inside of the chamber being created so you will not see it. The purpose is to allow for a tighter fit of the foam against the fiberglass/Kevlar from the outside of the chamber. Note that when the pieces of foam are in place they fit fairly tight. We basically wedge them into place.

From there a little bit of sanding to taste and you are ready to S-glass the floatation. OR you could take it a next step and build cup holders into them as Kevin decided to do. I will speak more to the cup holder in future posts.

Tracing the shape of the canoe onto the Riser foam.

Tracing Canoe Shape Onto Bow Floatation Foam

The shape of the canoe traced onto the Riser foam.

Stern Rise Foam With Shape Traced On It

Cutting the Riser foam on a band saw.

Cutting Rise And Run Foam On Band Saw

Test fitting the Riser foam and marking it again to trim it even closer to the shape of the canoe.

Stern Floatation Rise Foam In Process Of Being Cut To Shape

Tracing the shape of the canoe onto the Run foam. I am running the marker along the gunnel.

Tracing The Shape For The Run Onto The Foam

Almost completed bow floatation step.

Bow Floatation Almost Complete

The final bow floatation step completed and ready for S-Glass.

Bow Floatation Ready For S-Glass


Beyond the book Building Your Kevlar Canoe: A Foolproof Method and Three Foolproof Designs, another great Kevlar canoe building resource is


April 18, 2013

Canoe Building – Key Rib Measurements

Below are a few of the key installation measurements for widths and distances of the canoe ribs. These ribs help ensure the bottom of the canoe does not “oil can”; meaning it does not flex towards the inside of the canoe upon the weight of the exterior force exerted by the water.

Width of ribs
Rib Width

Measurement from inside tip of bow to the first rib
Bow to First Rib

Measurement from inside tip of the stern to the last rib
Stern to Last Rib

Rib height from the gunwhale (forward of canoe)
Foreward Rib-to-Gunnel Height

Rib height from the gunwhale (aft of canoe)
Aft Rib-to-Gunnel Height

Distance between gunwhales
Rib Distance Apart


June 15, 2011

Canoe Mold Build Day 8

Filling spaces with mud

Filling spaces with mud

Day 8 we focused on finishing up shaping and sanding the mold. As I have mentioned before this step of the process is about care and patience. Take your time to get the mold just right as the canoe is going to come off as a complete duplicate of the mold. There is not going to be much flexing or twisting that will allow you to “correct” any oddities in the shape.


Due to the fact that Moran gives us the guidance of having up to a half inch of gap between the foam, we realized that mud was going to need a decent amount of time to dry at that kind of thickness. So in an effort to speed up the drying time and reducing cracking I started the mudding with a simple crack filling layer. All I did was filled the large cracks that I knew would take at least few days to dry. And I was correct, the larger cracks took almost 3 days to finish drying.

Another technique I used to avoid cracking in the mud was to add water to the premixed mud. Out of the packaging the mud is about the conistensty of cake icing. To get a smoother application and less cracking I added water to achieve a consistency of pudding. While this does increase dry time the decrease in cracking is well worth it since you will spend less time applying additional coats plus you will not need as many coats. There was no precise measurement of water I added, it was essential based on visual consistency.

Tripper Canoe Mold - First coat of mud

Tripper Canoe Mold - First coat of mud

Tripper Canoe Mold - First coat of mud

Tripper Canoe Mold - First coat of mud

Filling spaces with mud

Filling spaces with mud


June 8, 2011

Canoe Mold Build Day 7

Foam shaped from side

Foam shaped from side

Day 7 was all about the shaping of the foam. Tony quickly stepped into the role of master shaper while Kevin worked on rough shaping and I did foam strengthening. By the end of day 7 we had completed the shaping and sanded the surface of the foam smooth.


Tony shaping foam

Tony shaping foam

Kevin shaping foam

Kevin shaping foam

In the day 6 post I mentioned that a rasp was an essential tool for shaping the canoe according to our testing. In day 7 as we went about shaping the canoe we realized the rasp was AMAZING for achieving a uniform and desired shape. While the dual action sander was great for smoothing the rough surface the rasp left behind, it was poor tool choice for shaping the foam. The sander with an aggressive 60 or 80 grit had a tendency to dig into the surface too much on account of the 5″ disc of the abrasive areas. The rasp was about 2″ wide making it just a bit wider than the foam strips. This 2″ of width was combined with a diagonal stroke across the mold a very uniform and consistent cut across the foam was delivered. Kudos to Tony for discovering this technique. The only major challenge we had with the rasp, and the sander, was the foam vibrating or bowing in when running the tools over it.


Foam reinforcement

Foam reinforcement

To overcome the challenge of the foam strips flexing when rasping and sanding I embarked on a mission to strengthen the foam strips from within the mold. To strengthen the foam I added strips inside the mold in between the strongbacks that went laterally across the foam strips. I used scrap pieces of foam from the initial foaming of the strongback. I broke pieces ranging from 3″ to 6″ depending on the curve of the area and then I laid a nice 1/4″ bead of hot glue across the piece. Once the glue was in place I would position the piece and hold it there until the glue setup. It was a slow process that was hard on the back due to being in a laying position on the ground. While the process was slow (I actually did this over the next 4 days before the official day 8 meet of Kevin, Tony, and I)  it did yield great results. The strength across the mold was MUCH stronger and allowed for much faster shaping. Moran mentioned that 5/8″ plywood for the strongback offered more glueing surface for the foam that resulted in greater strength, although we used 1/” plywood. After going through this strengthening process I would recommend using 5/8″ plywood for additional foam strength. If I build a second mold I will be using the 5/8″ thick plywood.


Once the right lines and curves of the canoe are achieved with the rasp it was time to use a dual action sander with 80 grit sand paper to get the smooth surface that we need for mudding the canoe. The sanding process did not take that long since it was just a smoothing and not a shaping operation. It was helpful as the canoe achieved a smoother surface as we did find areas that needed more shaping to achieve the desired curve or line. As with each step of this process just take your time and be patient. While for most parts of the build the next step offers you the ability to correct issues with the previous step, it is best to avoid having to fix these issues later. Care now will save time later.

Bow & Stern Trimming

Foam shaped from top

Foam shaped from top

Trimming of the bow and stern seemed daunting as mistakes here lead to time consuming foam repairs, but it was fairly simple. Just take your time and be gentle. We used a flat hand saw with a flexible blade. We ran the blade down each side of the bow/stern while flexing the blade to match the contour of the surface leading up to the bow/stern. After we ran a cut down both sides on the bow/stern we had a very nice edge. While the foam did have some gaps in it due to placement of the foam it was no big deal as we were able to glue chunks of foam in to help fill those spaces. Remember Moran did mention that you can have up to 1/2″ gaps in the foam as the drywall can fill it. However, I would not recommend exceeding a 1/4″ gap between the foam. The mud in the 1/2″ gaps takes too long to dry and is quite brittle. It is a better use of your time to glue in some small chunks of foam.

In ensuring that the bow/stern were true we did use the measurements from the bow/stern sketches to help validate that are work truing the mold player through into having a true bow/stern. As we were shaping and sanding the bow/stern they seemed to look crooked or off, but by the measurements and plumb they were correct.

Key Learnings

  • Rasps are great for shaping. Be sure to use a diagonal pattern as you run the rasp across the canoe.
  • Adding additional support inside the canoe to run across the 1 5/8″ strips of foam will greatly increase the effectiveness of using the rasp and shaping consistently
  • A dual action sander with 80 grit paper is the way to smooth out the rough surface left behind from the rasp.
  • The shaping process takes much longer that you would think.
  • Using measurement from the bow and stern sketches is helpful for accurate shaping.
  • Avoid gaps larger than 1/4″ in the foam. Moran says 1/2″ but it takes too long to dry and ends up being too brittle.
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