Foil-Assisted Guide Boat

Foil-Assisted Guide Boat Courtesi ACI/Caleb Johnson

This 31′ foil-assisted aluminum catamaran was designed by Jutson Marine Design and built by ACI Boats of Port Townsend, Washington. Aside from good seakeeping, the boat also can access shallow-water landing spots, allowing passengers to step ashore via a fold-down ramp.

Designer Scott Jutson checked in with us from New Zealand as he was waiting to board one of the last flights back to Vancouver, Canada, to ride out the coronavirus pandemic. He reported that sea trials just finished for a new design built by ACI in Port Townsend, Washington: a 31 foil-assisted aluminum catamaran with an asymmetrical hull shape for the Alaska guide market.

“The hullform represents a new development for us and the builder, and it really works,” Jutson said. “The client’s brief was for remote operations by an Alaskan guide for fishing and hunting. Distances traveled (in a relatively small boat) require excellent seakeeping, speed, and fuel economy. Longest run requires a steady 35-knot cruise. The boat is powered by two Suzuki 350 DPs with 22.5 [57.15cm] props and has a fuel capacity of 300 gal [1,136 l] in two tanks. Performance at full load [7,500 lbs/7.9 t] sees a top speed of 44 knots and an optimal cruise of 35.8 knots at 4,650 rpm with a range of 1.39 nm/gal.”

Jutson, whom we portrayed in 2014, also emphasized the design of a new hullform that features an extended waterline to a plumb stem and a semi-symmetric bow shape for rough water stability. The foils go across the tunnel’s full beam without center struts and are designed to be load and trim tolerant so the performance delta between light and full load is relatively small. Construction is welded aluminum plate using 5086 grade for high-load areas (bottom and frames) for maximum strength and minimal weight.

Foil-Assisted Guide Boat Courtesy ACI

Modified asymmetrical hulls and foil assist help the vessel perform in rough conditions, averaging 1.5 nm per gallon at 30 knots during tests with 2x 350-hp Suzuki DP outboards.

“We are very familiar with this size catamaran,” said builder Cory Armstrong. “In fact, the 30 by 11 [footer] is our most popular model.” ACI’s symmetrical planing cats achieve about 1 nm/gal over 30 knots, Armstrong added. For the new Jutson design with the Hysucat foil configuration (for more on this type, see Gunther Migeotte’s “Hydrofoil-Supported Catamarans,” PBB No. 157, page 68) the target was a 25% improvement in fuel economy and a 50% or more reduction of vertical accelerations. Armstrong said, “We ran several trials from light to fully loaded conditions, and in all cases we achieved better than 1.3 nm/gal up to 35 knots, and at 30 knots of cruising speed the boat was in the range of 1.5 nm/gal. Most notable was the seakeeping, particularly in mixed chop [when] we ran 30 knots in some pretty nasty stuff. I was extremely pleased with the added benefit of foils in conjunction with the modified asymmetrical hull in her ability to handle rough seas while maintaining excellent fuel economy.”

Scott Jutson, 275 West 18th Ave., Vancouver, V5Y 2A8, BC, Canada; tel. 604–760–2549.

Armstrong Consolidated, LLC, 2900 Washington St., Port Townsend, WA 98368 USA, tel. 360–385–1203.