Design - NAU Concrete Canoe 2026

Source · Final Design Report · April 2026

Hull Alternatives

Three candidate hulls were evaluated against four weighted criteria. All dimensions in inches. L = length, w = width (beam), h = depth.

Hull A

Selected · Final

Dimensions: 18 × 30 × 18

Cross-Section: Arch

Rocker: No

Best constructability (arch, no rocker)
Solid primary stability
Straightforward mold fabrication
Lower maneuverability (no rocker)

Score · 1.18 ✓

Hull B

Notched · Rocker

Dimensions: 18 × 30 × 18

Cross-Section: Notched

Rocker: Yes

Good primary stability
Better maneuverability from rocker
Notched section hurts constructability
Reduced straight-line speed

Score · 1.00

Hull C

Arch · Rocker

Dimensions: 16 × 30 × 16

Cross-Section: Arch

Rocker: Yes

Highest stability (low profile)
Best maneuverability
Shorter hull reduces capacity
Rocker complicates the mold

Score · 1.17

Hull Decision Matrix

Stability and straight-line speed carried the highest weights, given the 3 Sprint vs. 2 Slalom race breakdown at the ISWS Symposium. Scores shown are weighted (raw × weight).

Criteria	Weight	Hull A (Arch, No Rocker)	Hull B (Notched, Rocker)	Hull C (Arch, Rocker)
Stability	40%	0.50	0.50	0.67
Straight Line Speed	25%	0.17	0.20	0.17
Maneuverability	20%	0.17	0.22	0.25
Constructability	15%	0.34	0.08	0.08
Total Weighted Score	100%	1.18 ✓	1.00	1.17

Source · Final Design Report · Table 3-1

Mix Design Decision Matrix

Four trial mixes were batched and tested per ASTM C39, C143, C496. Density was weighted highest (30%) because the canoe must float under load.

Criteria	Weight	Mix 1	Mix 2	Mix 3	Mix 4 (Selected)
Density	30%	78.4 pcf	83.6 pcf	58.6 pcf	67.2 pcf
Compressive Strength	20%	3,350 psi	3,180 psi	520 psi	2,260 psi
Tensile Strength	10%	500 psi	440 psi	72 psi	360 psi
Workability (Slump)	20%	10 in	2 in	6 in	2 in
Cost	10%	$800	$800	$1,200	$1,000
Durability (1–3)	10%	3	3	2	3
Weighted Score	100%	69.9	67.8	53.4	84.3 ✓

Source · Final Design Report · Table 2-12

Final Hull Design — Hull A

Technical Specifications

Length Overall: 18 ft
Beam (Width): 30 in
Depth (Height): 18 in
Cross-Section: Arch
Rocker: None
Hull Thickness: 0.5 in
Cross-Section Area: 26.31 in²
Moment of Inertia: 834.07 in⁴
Concrete Density: 68 pcf
Compressive Strength: 1,900 psi
Max Bending Moment: 224.22 lb-ft
Factor of Safety: 2.06

Arch cross-section paired with zero rocker delivers the highest constructability score while maintaining a 2.06 capacity-to-demand factor of safety with carbon-fiber mesh reinforcement.

Hull A Infographic (UGRADS Poster)

Fig 4-6 · Orthogonal FEA · Max 73 psi

Construction & Fabrication

From mold to pour to finish. A female foam mold was chosen so the entire canoe could be placed in a single day. Flex-seal lined the interior for a smooth cure. Concrete was batched per ASTM C685.

Cutting cross sections — Mold · Step 1

Foam insulation board cut into 4'×2' sections, cross-sections drawn with labels (A1-A4, B1-B4…), then hot-knife cut.

Cross section alignment — Mold · Step 2

Cross sections glued together in order, wooden frame fitted to compress the length and prevent separation during cure.

Final canoe mold — Mold · Final

Interior sanded, black flex-seal coat applied to prevent concrete from bonding to foam. Vaseline layer added for demold.

Concrete batching — Batching · ASTM C685

Materials weighed per cubic foot: cementitious first (fly ash, slag, Portland), then aggregates, water, admixtures, fibers last.

Unloading canoe — Transport

Cured canoe transported from NAU Field Station to the competition site. Painted with RIT-dye space theme — stain only, no surface paint (ASCE rule).

On water — Race · NAU PLUTO

Paddle-tested on water — floats, tracks, races. Mission accomplished.

Cost of Construction

Materials budget for the Mix 4 final design, mold construction, and finishing.

Line Item	Category	Estimated Cost
Concrete mix (Mix 4 — per Table 2-12)	Materials	$1,000
Foam insulation board, glue, flex-seal	Mold	$350
Carbon fiber reinforcement mesh	Reinforcement	$275
RIT dye, sealant, finishing supplies	Finishing	$180
Stand lumber + paint	Display	$120
ASTM testing consumables (cylinders, etc.)	Testing	$150
Transportation fuel & trailer	Logistics	$220
Total Estimated Construction Cost		$2,295

Estimates · Final numbers in the Final Report