Mold description: Half of a 4-inch PVC pipe (inside span 3.75 inches) forms the leading edge. Two plywood pieces (3.5 ft × 16 in) are hinged to the edges, forming a triangular trailing section when closed.
Cross-section area calculation:
Volume: Length = 3.5 ft = 42 in → Volume = 35.316 in² × 42 in = 1483.26 in³ (0.8583 ft³).
Foam mixing (2-part, 2 lb/ft³ density):
Assumption: Typical yield is 2 ft³ of cured foam per gallon of mixed liquid.
With 3 wing/legs each 50% submerged in seawater (density 64 lb/ft³):
Thus, the total model weight should be approximately 82.4 lbs to float with half of each leg submerged.
| Dimension | Model | Full Scale (×6) |
|---|---|---|
| Length (span) | 3.5 ft | 21 ft |
| Chord | 17.765 in | 106.59 in (8.88 ft) |
| Thickness (max) | 1.875 in | 11.25 in (0.9375 ft) |
Full-scale volume per leg: 0.8583 ft³ × 216 = 185.40 ft³
Half-submerged volume per leg: 92.70 ft³
For 3 legs: 3 × 92.70 = 278.10 ft³
Weight of displaced seawater: 278.10 ft³ × 64 lb/ft³ = 17,798 lbs.
Assumptions: Legs oriented vertically (span vertical, chord horizontal), flow along chord (low Cd direction). Submerged height = half of span = 10.5 ft. Frontal area per leg = submerged height × max thickness = 10.5 ft × 0.9375 ft = 9.844 ft². Drag coefficient (Cd) = 0.2 (based on frontal area for streamlined shape). Seawater density ρ = 1.99 slugs/ft³.
| Speed (mph) | Speed (ft/s) | Drag per Leg (lbs) | Total Drag (3 legs, lbs) |
|---|---|---|---|
| 1 | 1.4667 | 4.21 | 12.6 |
| 2 | 2.9333 | 16.8 | 50.5 |
| 3 | 4.4000 | 37.9 | 113.6 |
Assumptions: Overall efficiency (motor + propeller) = 50%. Power = Drag force × velocity.
| Speed (mph) | Shaft Power (W) | Electrical Power (W) |
|---|---|---|
| 1 | 25.1 | 50.2 |
| 2 | 200.9 | 401.8 |
| 3 | 677.9 | 1355.8 |
Note: All calculations are based on the given mold dimensions and stated assumptions. Actual results may vary with specific foam expansion ratios, seawater density, drag coefficients, and system efficiencies.