Description of the THW Boat Seat Suspension – TH Series – Seating Height 350 mm – 4S Scandinavian Seat Suspension Systems
The THW marine seat suspension is the full-featured model of the TH series from Scandinavian manufacturer 4S – Scandinavian Seat Suspension Systems, engineered for planing powerboats up to approximately 30 feet operating in rough or choppy sea conditions. The suffix W (for Swivel & Slide) designates the complete version, integrating both a fore/aft longitudinal sliding system (Slide) and a 360° lockable swivel in 8 positions — providing maximum freedom of positioning and orientation for the helmsman or crew aboard any pleasure craft or professional nautical vessel.
The defining feature of the TH series — and its key advantage over the CC series — is its quick weight adjustment handwheel. Rather than requiring a C-spanner to set the damper pre-load dockside, the THW allows the pilot to adjust the suspension stiffness simply by turning the handwheel, even underway if conditions change. This makes the THW particularly well suited to vessels used by multiple crew members of different weights, or to situations where rapid suspension tuning is required without interrupting navigation.
Like all 4S products, the THW is a seriously engineered tool — not a bouncing toy. Its damper absorbs the violent vertical shock forces generated by wave slamming on the hull of fast planing craft, preventing these impacts from transmitting through the seat to the pilot’s lumbar spine and cervical vertebrae. The result is measurably reduced fatigue, sharper concentration at the helm, and genuine physical protection during extended offshore or coastal passages aboard any motorboat or high-speed tender. As 4S emphasises, a quality seat suspension is an insurance policy — and a lasting investment in the boat’s market value.
The longitudinal sliding system offers a travel of 120 mm (5″) fore and aft, and the Swivel and Slide control handles reach 250 mm (10″) from the centre-line. Both handles can be positioned on either the port or starboard side of the unit at the time of installation — a practical feature for vessels with asymmetric console layouts. The swivel locks securely into any of 8 positions across 360°, holding firm under load and vibration without risk of unintended rotation during navigation.
Built exclusively from premium marine-grade materials — stainless steel 316/316L for structural components, 5052H32 and 6061T6 aluminium at 6 to 8 mm thickness for plates and arms, bronze c63000 for articulation parts, and PolyOxyMethylene (POM) for sliding elements — the THW is engineered to withstand the harsh demands of the marine environment over the long term: salt water, UV exposure, constant vibration and the mechanical stresses of offshore operation aboard any sea-going vessel.
The TH series is compatible with RB- (RIB-type Baseplate) and BR- (Big Round) deck plates, covering a wide range of console and cockpit mounting configurations. The standard finish is satin black powder coat and anodising — silver grey and satin white finishes are available at minimum order quantities. Alternative configurations within the TH series include the THS (Slide only) and THF (Fixed), both at slightly reduced stack heights.
All 4S products comply with the most demanding requirements of ABYC H-31 standard, type AO — the most rigorous American nautical safety certification for seat suspensions, valid for any type of boat, any seating position and any navigation speed.
Specifications
- Reference: THW
- Series: TH (Swivel + Slide)
- Manufacturer: 4S – Scandinavian Seat Suspension Systems
- Seating height: 350 mm / 14″
- Swivel: 360° in 8 lockable positions
- Slide: fore/aft 120 mm / 5″
- Damper pre-load: adjustable 60 to 130 kg / 125 to 285 lb
- Pre-load adjustment: quick handwheel — no tools required
- Handle reach: 250 mm / 10″ from centre-line
- Handle positioning: left or right side, decided at installation
- Compatible deck plates: RB-, BR-
- Materials: Stainless steel 316/316L, Aluminium 5052H32 + 6061T6 (6-8 mm), Bronze c63000, PolyOxyMethylene (POM)
- Standard finish: Satin black (powder coat + anodising)
- Optional finishes: Silver grey, Satin white (subject to MOQ)
- Certification: ABYC H-31 type AO (any boat / any position / any speed)
- Alternative models in the TH series: THS (Slide only), THF (Fixed)
Installation / Maintenance
Installation:
- Select the appropriate deck plate for your console or cockpit from the available options: RB (RIB-type Baseplate) or BR (Big Round).
- The seat mounting surface must be absolutely flat — any unevenness will compromise the sliding mechanism and may create a safety risk on board.
- Once the seat has been fitted onto the suspension unit, always ensure the slide stop-screw is fully tightened. Failure to do so risks mechanical damage and potential injury underway.
- The Swivel and Slide handles can be repositioned to the opposite side in two simple steps: pull out the handle (A), then rotate 180° (B). No tools are required.
- Set the damper pre-load using the handwheel to match the pilot’s body weight within the 60 to 130 kg / 125 to 285 lb operating range. Correct pre-load is essential for effective wave shock absorption.
- Where standard screws cannot achieve a secure grip in the deck or console material, use the optional threaded deck inserts (M6: 12 mm / M8: 28 mm) available as accessories.
- If the seat’s mounting surface is not perfectly flat, use optional aluminium or PVC spacers to level the seating surface before installation.
Maintenance:
- Periodically inspect all stainless steel, aluminium and bronze components for signs of corrosion, wear or mechanical damage. Rinse with fresh water after offshore passages or prolonged exposure to salt spray.
- Lightly lubricate the sliding rail and swivel pivot with a marine-grade silicone or PTFE lubricant to maintain smooth, precise operation of both the Slide and Swivel mechanisms.
- Check the handwheel pre-load setting at the start of each season and whenever the unit changes user. Re-adjust as necessary — the handwheel allows this to be done instantly without tools.
- Inspect the slide stop-screw at the start of each season and after any heavy-weather passage. Ensure it remains fully engaged.
- Replace POM sliding elements if abnormal play or noise develops in the slide mechanism under normal operating conditions.
Our review
✔️ Pros:
- Quick handwheel pre-load adjustment — no tools required, instant setting even underway; a significant practical advantage over C-spanner-adjusted models when multiple crew members of different weights use the same helm station across a season.
- Full Swivel + Slide combination — complete ergonomic freedom for the helmsman, covering rotation, fore/aft positioning and vertical shock absorption in a single compact unit.
- 360° swivel with 8 secure lock positions — precise, stable orientation control that holds firmly under load and vibration without risk of unintended movement at speed.
- Exclusively marine-grade materials throughout: 316/316L stainless steel, thick-section aluminium alloy and bronze c63000 — built for genuine long-term offshore durability.
- ABYC H-31 type AO certification — the highest US boating safety standard for seat suspensions; a meaningful guarantee for both private owners and professional marine operators.
- Handles repositionable to either side at installation — genuine flexibility for port or starboard console configurations without requiring separate product variants.
- Compatible with RB- and BR- deck plates — broad installation compatibility across diverse vessel types and console formats.
❌ Cons:
- Fixed seating height of 350 mm with no built-in height adjustment range — unlike the CC series which offers a 40 mm adjustment window; verify that 350 mm suits your console layout and seat geometry before ordering.
- Compatible with RB- and BR- deck plates only — the SR- (Small Round) option available on the CC series is not offered for the TH series; check your existing deck plate format before purchase.
- Maximum supported body weight is 130 kg / 285 lb — users above this threshold should refer to the 4S BG series, engineered for 110 to 170 kg / 240 to 380 lb.
- Alternative finish options (silver grey, satin white) are subject to minimum order quantities — individual retail orders are supplied in satin black only.
Conclusion
The THW is the ideal choice for helmsmen and marine professionals who want the complete ergonomic package — full swivel, fore/aft slide and effective wave shock absorption — with the added convenience of tool-free, instant pre-load adjustment via handwheel. At 350 mm seating height, it sits between the lower CC series and the taller BJ and NoKa series, making it a versatile fit for a wide range of open console sportboats, centre-console craft and fast day cruisers. Its 316/316L stainless steel and marine-grade aluminium construction and ABYC H-31 type AO certification confirm that this is a genuine offshore tool, not a cosmetic accessory. Before ordering, confirm that the 350 mm seating height is compatible with your console and seat dimensions, that your crew weight falls within 60 to 130 kg, and that your deck plate format is either RB or BR. For those whose installation profile matches these specifications, the THW represents a compelling long-term investment in on-board safety, comfort and vessel value.
Good to Know
- The suffix W means the unit includes both Swivel and Slide. If you only need fore/aft adjustment without rotation, choose the THS (Slide only, slightly lower height). For a fixed pedestal without slide or swivel, choose the THF.
- The handwheel pre-load adjustment is the key feature of the TH series — it allows instant, tool-free suspension tuning for any crew weight between 60 and 130 kg, even underway. This is a significant advantage over C-spanner-adjusted models in multi-user or charter contexts.
- The seating height of 350 mm (14″) is a fixed nominal dimension — add the thickness of your seat cushion to calculate total seated height above deck level.
- Always install the slide stop-screw fully after attaching the seat to the suspension unit. This is a critical safety requirement — an unsecured slide can cause sudden seat displacement and serious injury at speed.
- Swivel and Slide handles can be moved to the opposite side in two simple steps (pull out handle A, rotate 180° at B) — no tools required, and repositioning can be carried out at any time after installation.
- Standard finish is satin black (powder coat + anodised parts). Silver grey and satin white finishes are available subject to MOQ — contact your dealer for lead times and minimum quantities.
- For installations where standard screws cannot grip the deck or console material, threaded deck inserts (M6: 12 mm / M8: 28 mm) are available as accessories from 4S.
- For crew weights above 130 kg / 285 lb, refer to the 4S BG series, specifically engineered for 110 to 170 kg — available in Slide and Fixed configurations only (no Swivel option).
- All 4S products meet ABYC H-31 type AO — the highest US boating safety standard for seat suspensions, valid for any boat, any position and any speed.
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