Concrete Canoe Build

The polished plug for this year’s concrete canoe.

Every year the engineering department at the University of Hawaii Manoa participates in the American Society of Civil Engineers (ASCE) national collegiate competition where each school has to build and paddle a concrete canoe. We know exactly what you’re thinking, “can you even make a concrete canoe that doesn’t sink?” and more importantly, “why would you want to?”

As you can imagine, it takes a lot of effort to design, mold, build and finish a concrete canoe and that’s where a handful of local businesses stepped in to help. Fiberglass Hawaii helped the students procure materials while local canoe manufacturers, Kamanu Composites and Jay Dowsett, allowed students to use their facilities, mine their expertise and sometimes even their personal materials all in an effort to help make the best finished concrete canoe possible.

We sat down with Nick Herrera and Reyn Yoshimura who are part of this year’s UH competition team. You may remember Nick from our Rocket Build blog from last year. Nick has worked for Kamanu Composites for several years now and has some great knowledge on canoe building which is a big plus for this year’s upcoming competition.

Fiberglass Hawaii (FGH): So it looks like you guys have been busy lately. We’ve been seeing a lot of you in the shop. Tell me what are we looking at right here?

Nick and Reyn lining up the foam on the CNC machine

Reyn Yoshimura (RY): This right here is the plug that Nick helped us make. We cut the foam using Kamanu Composites CNC machine. We took it over to Jay Dowsett’s place where he helped us mold it over the weekend.

FGH: That’s so cool that you have these guys with all of this knowledge lending a hand. How long did that take to cut?

Nick Herrera (NH): It took about eight hours to cut it out.

FGH: That is crazy! Most people probably think that it takes like 20 minutes to cut out foam on a high-tech machine. How big was the block of foam you cut the plug out of?

NH: 12’ by 4’ by 9 1/4”. We had to do multiple cuts too. The bottom is two pieces, 8” deep and the top is 6 pieces that are also image28” deep and then we glued them all together.

FGH: How did you guys do that?

NH: We just glued them together with epoxy and then puttied the seams. After that we glassed the entire plug using some 6 oz cloth and 3:1 epoxy we got from your shop.

FGH: Very cool. How did you guys get such a smooth finish?

NH: After we glassed it we puttied the outside, let it cure, sanded it and then just did that a few times until it was smooth. Then we primered the outside. After that, we sanded, wet sanded and then buffed the primer out.

The polished out plug

FGH: Sounds like a lot of work already! What’s the deal with this competition? It sounds counterintuitive for an engineering department to want to build a super heavy and slow canoe.

RY: I guess it’s kind of like the whole feat of being an engineer, trying to do something that’s really challenging. The whole idea is to make a concrete boat float and light.

FGH: It still sounds crazy to me. Plus you have Nick who makes super fast canoes with Kamanu which has got to be tough to think about making a concrete canoe.

Note the bumpy finish and rounded nose from the previous year
Note the smooth finish and sleek design of this year’s canoe

RY: Yeah, but it’s a national competition that’s been around for a long time so it’s pretty cool in that sense.

FGH: What do you have to do to win this competition?

RY: There are four categories. Final product, which includes what the canoe looks like. There’s a display day that everyone displays their canoes at. There’s the racing. There’s a men’s sprint, men’s endurance, women’s sprint, women’s endurance and then there’s a coed sprint race.


FGH: How many people are paddling the canoe?

RY: For the regular races there are two and in the coed race there are four paddlers.

FGH: How much would a four man canoe weigh if it was a traditional fiberglass lay up?

NH: About 200 pounds.

FGH: How much will the concrete canoe weigh?

RY: This one will weigh about 300 pounds.

FGH: That’s really not as heavy as I thought it would be. So wait, how do you pop it out of the mold if it weighs 300 pounds?

NH: We haven’t figured that out yet.

RY: We’re going to get there.

FGH: I am glad I don’t have to try to pop a beast like this out of a mold! How have you done it in the past?

RY: Well in the past we had a male mold so it was easy to do.

The concrete canoe curing inside of the female mold

FGH: Why did you do a female mold this time?

RY: The finish on the outside comes out so much nicer this way. It comes out perfect, ready to go.

FGH: Well luckily you’re engineers so you’ll figure out a way.


RY: Check this out. This is traditional concrete (hands me a concrete cylinder). And this is what we use (hands me another concrete cylinder that is much lighter).

FGH: What the? Why is it so much lighter?

RY: It’s a huge difference! We use glass bubbles as a filler. You guys brought in K37 for us because you stock K25.

FGH: How did those work out?

RY: It worked out great as you can feel. The glass bubbles actually make it stronger too unlike other glass bubbles that are weak.

FGH: So it helps to hold it together, add strength and keep it light?

RY: Yeah, there’s less trapped air.

FGH: Sounds like a lot of materials and work go into each step.

NH: Yeah, you guys helped us out a lot with the glass, resin and fillers. It wouldn’t have been possible without Keizo (Kamanu Composites), Jay, and you guys.

FGH: Very cool. When are you guys going to get this out in the water?

RY: Concrete usually takes 28 days to reach its full strength. After that we’ll do some filling and more sanding and then seal it. Probably late January 2016.

FGH: Well I look forward to watching you guys test paddle this soon. Good luck and we’ll be seeing you soon.

Stay tuned for the follow-up to see how Nick, Reyn and the rest of the UH engineering students do in this year’s concrete canoe competition to be held in June in Tyler, Texas. Fiberglass Hawaii is dedicated to selling the best materials available. If you don’t see something in one of our stores or online then feel free to ask us about it and maybe we have an alternative or we can bring it in for you. We also love being involved with our customers and contributing our time and knowledge so let us know if your school or club has a project that requires a little extra guidance. Be sure to follow us on Facebook and Instagram. Shop 24/7 at the all new