Our Review of Outboard Engines on our 1160 Seawind Lite - Yamaha 25hP High Thrust

For blue water cruisers, auxiliary propulsion defines vessel maintenance, sailing performance, and long-distance logistics. Aboard the 38-foot cruising catamaran Sea Moon, Scott and Sandy of Sailing Sea Moon chose a distinct departure from traditional marine diesels: twin Yamaha 25HP High Thrust four-stroke outboards mounted in dedicated transom wells. After logging thousands of nautical miles across Australian coastal waters, the Indian Ocean, Southeast Asia, and the Mediterranean, Scott conducted a technical review evaluating whether outboards can reliably power an ocean cruising catamaran.

The Seawind 1160 Lite optimizes multihull performance through weight discipline. While conventional catamarans carry heavy inboard diesels, sail drives, and raw-water through-hulls aft, the Lite variant replaces that machinery with outboards and carbon fiber crossbeams. This engineering assessment analyzes the hydrodynamic benefits, fuel curves, electrical tradeoffs, and reliability encountered by the crew during years of continuous passagemaking.

The Naval Architecture of Lightweight Outboard Catamaran Propulsion

When Scott of Sailing Sea Moon commissioned the Seawind 1160 Lite catamaran SV Sea Moon Catamaran in Australia, opting for twin Yamaha 25HP High Thrust outboards over conventional inboard diesels marked a deliberate engineering departure tested thoroughly across Sydney, Pittwater, and coastal New South Wales. The naval architectural rationale focuses on weight reduction. In cruising multihulls, concentrated weight in the hull ends induces hobby-horsing and increases pitching resistance. By eliminating twin 30-horsepower diesels, sail drive legs, cast-iron engine blocks, and heat exchangers, the Seawind 1160 Lite sheds over 400 kilograms (880 pounds) aft.

Seawind molded dedicated fiberglass wells directly into the bridgedeck inboard of the twin spade rudders. Transom brackets secure each outboard, while helm tilt switches activate electro-hydraulic lift actuators. When raised, the cowlings tuck beneath flush deck hatches while the lower gearcases, propellers, and saltwater intakes clear the waterline entirely. This retraction eliminates underwater parasite drag, prevents marine biofouling at anchor, and preserves clean laminar flow across the hulls.

Hydrodynamics, Dual-Thrust Propellers, and Rough Sea Telemetry

During extensive bluewater sea trials conducted by Scott of Sailing Sea Moon aboard the Seawind 1160 Lite catamaran SV Sea Moon Catamaran—originating from the sailing grounds of Sydney, Pittwater, and coastal New South Wales, Australia—the twin Yamaha 25HP High Thrust outboards proved that gear reduction is paramount for multihull propulsion. Standard outboards utilize high-speed gear ratios unsuited for displacement hulls. The Yamaha T25 incorporates a 2.08:1 reduction gearcase paired with an oversized, low-pitch Dual-Thrust propeller, generating substantial bollard pull to arrest forward momentum and push into steep head seas.

The primary challenge arises in short-period chop or confused ocean swells. Despite extra-long shaft legs, pitching can cause propellers to cavitate near the surface as sterns lift. To counter aeration, Scott adopts an active motor-sailing strategy. By hoisting the mainsail and steering 20 degrees off the true wind angle, the sail generates aerodynamic lift, dampens pitching, keeps the leeward propeller submerged, and prevents cavitation in turbulent sea states.

Fuel Consumption Curves, Safe Storage, and Passage Range

Analyzing fuel consumption telemetry recorded by Scott of Sailing Sea Moon aboard the Seawind 1160 Lite catamaran SV Sea Moon Catamaran across Australia—from Sydney Harbour to the sheltered reaches of Pittwater in New South Wales—reveals distinct operational profiles between motoring and motor-sailing with twin Yamaha 25HP High Thrust engines. Under calm conditions, running a single outboard at 3,000 to 3,500 RPM yields 5.0 knots with a fuel burn of 5.0 liters per hour (1.0 liter per nautical mile). When motor-sailing with the mainsail drawing, fuel consumption drops to 2.5 liters per hour at the same speed.

Gasoline containment aboard a fiberglass vessel demands strict isolation. Seawind positioned the primary 270-liter roto-molded tank forward of the mast base at the vessel’s center of buoyancy. An adjacent ventilated locker holds five 20-liter jerry cans (100 liters reserve). Rigid fiberglass conduits route fuel lines safely through the bridgedeck to aft engine lockers, isolating fumes from living quarters. For ocean passages, six additional 20-liter cans on deck rails raise total fuel capacity to 490 liters, providing a motoring range of nearly 500 nautical miles.

Auxiliary Electrical Systems, Alternator Tradeoffs, and Marina Handling

Executing close-quarters maneuvers and managing auxiliary electrical loads aboard the Seawind 1160 Lite catamaran SV Sea Moon Catamaran has presented Scott of Sailing Sea Moon with distinctive engineering challenges from Sydney, Pittwater, and New South Wales, Australia, to international cruising grounds. Powered by twin Yamaha 25HP High Thrust outboards spaced across a 21-foot beam, differential throttle control allows the skipper to pivot the boat on its axis without helm input. However, because outboards sit inboard of the rudders without wash deflected across the foils, firm throttle bursts are required to initiate rotation in heavy crosswinds.

Electrical management represents another divergence from diesel auxiliaries. Each Yamaha T25 internal charging coil produces only 15 to 16 amps at cruising revolutions. To satisfy domestic electrical loads, Scott relies on an extensive rooftop solar array paired with a lithium iron phosphate (LiFePO4) battery bank. When cloud cover or heavy navigation loads deplete reserves, the crew deploys a portable Yamaha 2kVA generator stored forward, bridging charging deficits while preserving the vessel’s lightweight advantages.

Routine Maintenance Protocols, Haul-Out Logistics, and International Spares

Executing routine maintenance and long-term mechanical upkeep aboard the Seawind 1160 Lite catamaran SV Sea Moon Catamaran has presented Scott of Sailing Sea Moon with practical lessons since departing Sydney, Pittwater, and coastal New South Wales, Australia, with twin Yamaha 25HP High Thrust outboards. Daily inspections diverge from diesel routines; with raw-water cooling, the primary pre-departure check consists of visually verifying a strong cooling telltale stream upon startup. Because four-stroke powerheads do not consume oil under normal operation, dipstick checks are conducted periodically within the compact nacelles.

Scheduled 100-hour servicing centers on lower gearcase lubricant renewal and water pump impeller replacement. In regions with large tides, such as parts of northern Australia, catamarans can dry out on firm sandbanks between tides to access gearboxes. In micro-tidal waters like the Mediterranean, full lower-unit maintenance requires an annual haul-out or complete engine removal, which takes roughly two hours of mechanical labor per side.

Cruising internationally highlighted the global ubiquity of the Yamaha commercial network. Throughout Southeast Asia and remote archipelagos, small shops consistently stocked genuine Yamaha spark plugs, impellers, and fuel filters due to widespread adoption by local fishing fleets. The vessel carries dedicated spark plug sockets, replacement propellers, fuel primer assemblies, and a spare tilt motor, ensuring mechanical self-sufficiency on remote passages.

Comparative Engineering Telemetry & Long-Term Cruising Economics

Comparing empirical telemetry collected by Scott of Sailing Sea Moon aboard the Seawind 1160 Lite catamaran SV Sea Moon Catamaran across Australia—from Sydney Harbour to the offshore waters of Pittwater in New South Wales—illustrates the operational contrasts between twin Yamaha 25HP High Thrust outboards and traditional twin inboard diesel sail drives. The following engineering matrix summarizes weight distribution, hydrodynamics, electrical generation, and long-range cruising telemetry.

The financial reality of long-term ownership favors the outboard configuration. Replacing both Yamaha T25 outboards with brand-new engines costs significantly less than purchasing and installing a single marine diesel engine and sail drive. With expected powerhead lifespans between 1,500 and 2,000 engine hours, cruisers who primarily sail achieve 5 to 7 years of service before repowering. By eliminating sail drive diaphragms, heat exchangers, and shaft alignments, the outboard catamaran represents an accessible, high-performance pathway to global ocean cruising.

Frequently Asked Questions

Addressing common technical inquiries, Scott of Sailing Sea Moon details how twin Yamaha 25HP High Thrust outboards perform aboard the Seawind 1160 Lite catamaran SV Sea Moon Catamaran, reflecting on sea trials and ocean passages originating from Sydney, Pittwater, and New South Wales, Australia.