The SeaStar HC5358-3 (MPN HC5358-3, UPC 731957916846) is a front-mount outboard hydraulic steering cylinder designed for Yamaha-powered boats where the cylinder needs to mount UNDER the engine’s steering arm. 8.34 cubic inch displacement matched to SeaStar’s standard 1.7 cu in or 2.0 cu in helm pumps for the typical lock-to-lock turn ratio on center consoles, offshore fishing boats, bay boats, bass boats, flats boats, and other outboard-powered hulls. Designed specifically for Yamaha 150-300 HP outboards and compatible with most BRP 200+ HP outboards (verify cowling clearance for your specific engine before purchase). Independent engine tilt for twin and triple engine installations means each engine can tilt independently of the others – critical for proper trim adjustment on multi-engine boats. New 8-hole end gland design for improved serviceability – rebuild the cylinder seals on the boat without removing the cylinder if needed. State-of-the-art proprietary SeaStar sealing system with superior resistance to repeated compression set – the cylinder rod seals stay tight over the thousands of helm cycles per season without losing pressure or developing leaks. Heavy-duty barrel design built for the harsh salt-water environment. Positionable Stainless Steel O-Ring Boss (ORB) fittings for easy hose routing – rotate the fittings to the exact angle that gives the cleanest hose run on your specific engine and transom layout. Compatible with the SeaStar PA1200-2 Power Assist Pump for fingertip steering control. Meets ABYC and NMMA certification standards. Designed and manufactured in North America. 2-year limited recreational warranty from SeaStar Solutions, the global leader in marine hydraulic steering technology.
The SeaStar HC5358-3 is the front-mount hydraulic steering cylinder for Yamaha outboard powered boats – one of the highest-volume replacement and OEM cylinders SeaStar produces for the recreational marine market. For owners replacing a failed cylinder, upgrading from mechanical cable steering, or rigging a new outboard installation on a Yamaha-powered boat, the HC5358-3 is the standard correct cylinder when the install requires the front-mount, under-steering-arm configuration.
Front mount vs back mount – what it means. SeaStar offers two outboard cylinder mounting configurations: front mount (the HC5358-3, where the cylinder mounts on a bracket ahead of the engine with the rod connecting back to the engine’s steering arm) and rear mount / splashwell mount (where the cylinder mounts behind the engine on the splashwell or transom). The right mounting style depends on your specific engine and boat – some Yamaha outboards mount most cleanly with front-mount cylinders, others with rear-mount. The HC5358-3 specifically is the front-mount variant where the cylinder needs to fit UNDER the steering arm on Yamaha outboards – the standard configuration for Yamaha 150-300 HP four-stroke and HPDI 2-stroke outboards on most center consoles, bay boats, bass boats, and offshore fishing boats. Verify your specific engine’s mounting requirements before purchase – using the wrong mounting style cylinder requires re-rigging the steering install.
Yamaha 150-300 HP fitment. The HC5358-3 is engineered specifically for Yamaha outboards in the 150-300 HP range – this is the engine power band where front-mount cylinder geometry, displacement, and the under-steering-arm clearance all match Yamaha’s engine bracket and steering arm dimensions. Also fits most BRP (Evinrude / Johnson legacy) 200+ HP outboards, but verify cowling clearance for your specific engine – some larger 4-stroke outboards have cowlings that interfere with the cylinder at full trim or full steering lock. Check the SeaStar fitment guide or contact SeaStar tech support with your specific engine model and horsepower if uncertain.
8.34 cubic inch displacement. Cylinder displacement is the volume of hydraulic fluid the cylinder moves per full stroke – it determines the lock-to-lock turn ratio when paired with a specific helm pump. 8.34 cu in is the standard displacement that pairs with SeaStar’s standard 1.7 cu in or 2.0 cu in helm pumps for typical recreational-boat lock-to-lock ratios (5-6 turns lock to lock with the 1.7 helm, 4-5 turns lock to lock with the 2.0 helm). For boats where you want fewer turns lock to lock (sportier steering feel, less wheel work in tight maneuvers), the 2.0 helm pairing is correct. For boats where you want more turns lock to lock (better straight-line control, less twitchy at high speed), the 1.7 helm pairing is correct.
Independent engine tilt for twin / triple installations. On multi-engine outboard boats (twin, triple, quad outboards), each engine needs to be able to tilt independently of the others for proper trim adjustment and beach-launch scenarios. The HC5358-3’s hydraulic geometry allows independent engine tilt – the steering tie bar and cylinder rod accommodate the relative tilt motion between engines without binding or hydraulic pressure issues. For single-engine installations, this isn’t relevant. For multi-engine setups (common on center consoles 26+ ft), independent tilt capability is meaningful.
8-hole end gland design. The HC5358-3 features SeaStar’s redesigned 8-hole end gland – the end gland is the cylinder cap that holds the rod seals and connects the cylinder body to the rod. The 8-hole design lets you remove and reinstall the end gland without removing the entire cylinder from the boat – critical for in-boat seal rebuilds when the rod seal leaks (the most common cylinder service item after years of saltwater use). Older 4-hole and 6-hole end gland designs required removing the cylinder from the boat for seal work. The 8-hole improvement saves hours of labor per service event.
State-of-the-art sealing system. SeaStar’s proprietary cylinder sealing system uses materials and geometries selected specifically for marine hydraulic service – superior resistance to repeated compression set (the deformation seals develop after thousands of cycles), better tolerance for temperature swings (cold engine room to hot summer transom), and better resistance to saltwater corrosion. Practical result: the cylinder maintains tight sealing over years of seasonal use without developing leaks or losing hydraulic pressure – the failure mode that ends most cheaper cylinders within 2-3 seasons in saltwater service.
Heavy-duty barrel design. The cylinder barrel is built heavy for the marine environment – hard-chromed steel rod, anodized aluminum barrel, and stainless or bronze internal hardware. The barrel resists denting and external corrosion that can cause sealing problems on cheaper cylinders. Updated graphics on the current production complement modern boat and motor packages aesthetically (cosmetic, but matters for boats where the cylinder is visible at the transom).
Positionable stainless ORB fittings. The hydraulic line connection fittings are stainless steel O-Ring Boss (ORB) fittings that you can rotate to any angle before final tightening – lets you orient the fittings for the cleanest hose run on your specific engine and transom layout. Critical for engines where standard fixed-angle fittings would put the hoses in awkward routes (rubbing on engine components, kinking around tight corners, exceeding minimum bend radius). Position the fittings during install for optimal hose routing, then tighten the O-ring seal locks the position.
Compatible with SeaStar Power Assist Pump (PA1200-2). For owners who want power-assisted steering feel (the automotive-style fingertip steering effort that takes the muscle work out of helm turning), the HC5358-3 is compatible with SeaStar’s PA1200-2 Power Assist Pump. The pump installs between the helm and the cylinder in the hydraulic line and boosts the helm input proportionally to deliver power-assisted steering feel at the wheel. Particularly valuable on larger boats (28+ ft) and at higher horsepower where the steering effort without power assist becomes meaningful. Power assist is an optional upgrade, not required – the cylinder works fine without it.
ABYC and NMMA certified. The HC5358-3 meets ABYC (American Boat and Yacht Council) and NMMA (National Marine Manufacturers Association) certification standards – the marine industry standards for steering system safety, reliability, and performance. Important for new boat construction where NMMA certification is required for many boatbuilder programs, for marine insurance compliance, and for owners who want documented standards-compliant components.
Designed and manufactured in North America. Unlike many marine components that are imported from overseas, the SeaStar HC5358-3 is designed and manufactured in North America. Quality control, materials sourcing, and engineering responsiveness are all under direct SeaStar oversight rather than outsourced to overseas factories. For owners who value North American manufacturing for quality, parts availability, and warranty support, this is a meaningful differentiator.
Installation overview. Plan for 4-8 hours for an experienced marine DIY installer if this is a cylinder replacement on an existing hydraulic steering system, 8-16 hours if rigging a complete new hydraulic steering system. Key tasks for cylinder replacement: remove the old cylinder (disconnect hydraulic lines, unbolt from engine bracket and steering arm), mount the new HC5358-3 in the same position using the supplied or transferred mounting hardware (precise 1/4 inch alignment matters – misalignment causes tie bar binding within hours), connect the hydraulic lines via the ORB fittings positioned for clean hose routing, top off the helm pump with SeaStar hydraulic fluid, and bleed the hydraulic steering system thoroughly per the SeaStar bleed procedure (start with the cylinder fully extended, then cycle the helm 20+ turns each direction to purge air). Critical: do NOT skip the bleed procedure – air in the hydraulic system causes spongy steering feel that won’t go away until the system is properly bled.
Service and rebuild. The HC5358-3 is designed for serviceability – rebuild kits are available with new seals, O-rings, and hardware for re-conditioning the cylinder when the rod seals eventually wear (typically 5-8+ years of saltwater use). Rebuild cost is a fraction of new cylinder replacement and the cylinder body can serve multiple rebuild cycles. For the common rod seal leak (the most frequent service item), the 8-hole end gland design lets you do the rebuild in-boat without cylinder removal.
