Calculate pitch, diameter, cup, and slip for Acme Marine CNC-machined inboard tournament ski, wakeboard, and wakesurf boat propellers.
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Acme Marine manufactures 100% CNC-machined inboard propellers engineered specifically for tournament waterski, wakeboard, and wakesurf towboats (such as Nautique, MasterCraft, Malibu, Centurion, and Supra). Towboats operate with high ballast weight and low speeds, requiring precise diameter, pitch, and blade cup calculations.
V_{\text{surf}} = \frac{\text{RPM} \times P}{\text{Ratio} \times 1056} \times (1 - \text{Slip}_{\text{ballast}})Due to 3,000–5,000+ lbs of added water ballast creating high hull drag at 10–12 mph wakesurf speeds, inboard towboats experience higher slip (18%–28%) than light planing runabouts.
Scenario: A wakeboard boat with a 1.50:1 V-drive running an Acme 2249 (15 x 14.25 with 0.105 cup) at 3,600 RPM pulling a surfer at 11.2 mph.
Theoretical Pitch Speed: (3,600 × 14.25) / (1.50 × 1056) = 51,300 / 1,584 = 32.39 mph.
Wakesurf Speed Delta: 32.39 - 11.20 = 21.19 mph.
Ballasted Towboat Slip: (21.19 / 32.39) × 100 = 65.42% (in semi-displacement surf plow mode).
CNC machining from solid forged NiBrAl (Nickel-Bronze-Aluminum) blanks provides micro-precision blade geometry, symmetrical rake, and balanced tracking that traditional sand-casting cannot replicate.
Blade cup is a curved lip along the trailing edge of the propeller blade. Cup acts like additional pitch, gripping the water more aggressively to reduce slip under heavy wakeboard ballast.
Direct-drive ski boats mount the engine amidships with a 1:1 or 1.23:1 ratio for flat wakes. V-drive wake boats place the engine in the rear with a 1.48:1 to 2:1 reduction ratio to swing large 15-to-17-inch props.
If your boat struggles to reach surfing speed (10.5–11.5 mph) with full ballast tanks, or if the throttle is pegged at 100% without holding cruise control, you need to down-pitch 1 to 2 inches.
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