Stainless Steel Mooring Spring Shock Absorber (for 6–10 mm Lines)

The stainless mooring spring shock absorber is a classic solution for ensuring smooth, controlled movement of your boat when moored to a dock or buoy. While rubber snubbers absorb shock by stretching an elastomer, a mooring spring does it by the deflection of a metal spring – a method that offers high capacity and long service life. Using a stainless steel spring ensures the device can remain installed permanently outdoors with no worry of corrosion or loss of elasticity.

Construction: The mooring spring consists of a coil spring made from thick stainless steel wire (316 grade), with an eye or hook on each end for connections. When the mooring line pulls taut, the spring stretches; when the line slackens, the spring contracts back. This cyclical action cushions the motion. Our spring models come in different wire diameters and lengths to match various loads: the smaller springs (6 mm, 7 mm wire) are shorter and easier to stretch – meant for lighter boats, whereas the larger ones (9 mm, 10 mm) are longer and stiffer – to handle the needs of heavier vessels.

Choosing the right size:

• 6 mm model (6 mm wire Ø, ~31 cm length) – recommended for boats up to about 8 m (approx 25 ft) or around 3 tons displacement. Usually paired with ~10 mm dock lines (or thinner). This size provides significant cushioning for small yachts, runabouts, RIBs, etc.
• 7 mm model (7 mm wire Ø, ~36 cm length) – for boats up to around 10 m (33 ft) or ~4–5 tons. Typically used with 12 mm lines. A mid-range spring offering a balance of elasticity and stiffness for medium vessels.
• 9 mm model (9 mm wire Ø, ~46 cm length) – for boats up to around 12 m (40 ft) or 8–9 tons. Fits ~14–16 mm lines. This spring is more robust and can take serious strain – suitable for large sailing or motor yachts, especially when mooring in exposed areas with surge.
• 10 mm model (10 mm wire Ø, ~52 cm length) – for boats around 14–15+ m (45–50 ft) or 10+ tons. Used with ~16 mm lines. Our heaviest-duty model, designed for tough conditions and big vessels. This spring has more travel and higher stiffness to control the motion of very large yachts. (Note: sometimes referred to as 11 mm wire in catalogs – essentially the largest size.)

Installation: To integrate the mooring spring into your line, typically shackles or pre-made rope eyes with thimbles are used. The spring has eyes/hooks at its ends – connect one end to a deck cleat or bow eye on the boat, and the other to the mooring line leading to shore. If your line ends in an eye splice (with thimble), just shackle that eye to the spring. If not, you can tie the rope directly through the spring’s eye with an appropriate knot (e.g., a bowline around the eye). Do similarly on the dock side: you can either place the spring between two separate lines (one tied to shore, one to the boat) or attach it into a single line using carabiners/shackles at each end.

Benefits in use: The mooring spring greatly reduces dynamic loads. When a passing boat’s wake or a wind gust hits, instead of your rope snapping taut like a guitar string, the spring takes some of that shock. This protects not only the lines from breaking, but also the attachment points (cleats, bollards) from being yanked out or bent. The boat also “rides” more gently – less abrupt jerking means less wear on your mooring setup and a more comfortable time on board (no sudden jolt when a wave hits the dock). This is especially valuable at night – the springs reduce the jerking and creaking of lines, helping the crew sleep peacefully.

Made of stainless steel, these springs are durable against the elements – unlike galvanized steel springs, here there’s no coating to wear off and rust, so they can last for years. Maintenance is minimal – we recommend occasionally rinsing the springs with fresh water to remove salt buildup and checking shackles/connectors for tightness. Essentially, once installed, the stainless snubbers can remain on your lines, ready every time you dock.