What to check on a Bitts.
A bollard or bitt does one job: it holds a mooring line under tension by friction, through the line being wound figure-eight fashion around two posts, rather than by clamping or gripping the line mechanically the way a winch drum or a mooring hook does. Bitts differ from a single bollard in having two posts close enough together that the figure-eight pattern actually generates friction, and cross bitts add a horizontal bar between or across the posts so a second line can be made fast independently without the two lines…
What sets bitts apart from other mooring fittings
A bollard or bitt does one job: it holds a mooring line under tension by friction, through the line being wound figure-eight fashion around two posts, rather than by clamping or gripping the line mechanically the way a winch drum or a mooring hook does. Bitts differ from a single bollard in having two posts close enough together that the figure-eight pattern actually generates friction, and cross bitts add a horizontal bar between or across the posts so a second line can be made fast independently without the two lines interfering as they are worked.
Main components
Posts
Two vertical steel posts, cast or fabricated, through-bolted or welded to a base plate that spreads the mooring load into deck structure below.
Base plate and deck doubler
The load path from the posts into the hull; deck plating under a bitt is normally doubled or thickened locally because mooring loads concentrate here far above general deck loading.
Cross bar (cross bitts only)
A bar linking the two posts partway up, giving a second, separated point to belay a line so it does not have to share the same wraps as the first.
Sizing and selection
- Safe working load required, set by the ship's mooring line breaking strength and the number of lines expected on that fitting.
- Post diameter and spacing, which need to suit the mooring line size actually carried — too narrow a spacing and the figure-eight cannot develop enough friction.
- Deck reinforcement required beneath the fitting, since bitts are structural attachments, not surface-mounted hardware.
- Layout relative to fairleads, so the lead angle from fairlead to bitt stays within a safe range and does not chafe against the post edge.
Regulations and class
Class societies require mooring fittings including bitts to be sized against the ship's Equipment Number, which sets minimum safe working loads for anchors, chain and mooring equipment, with the bitt's SWL and the supporting deck structure checked at the design stage. There is no SOLAS chapter specific to bitts, but class rules for hull equipment cover their strength, and periodic survey checks for cracking, wastage, and deformation at welds and base plates, since a mooring fitting failure under load is a direct crew injury risk documented in numerous incident reports.
Typical faults
| Fault | Consequence |
|---|---|
| Cracking at the base plate weld from repeated snap loading | Fitting can fail suddenly under a normal mooring load rather than a genuine overload |
| Corrosion wastage at the deck connection, hidden by paint buildup | Actual strength drops well below the rated SWL without visible warning |
| Sharp edges worn into the posts from years of line contact | Accelerates chafe and cutting of mooring lines, shortening line life and risking parting under load |
| Fitting undersized for the mooring lines actually carried after a later upgrade | Lines are worked at a load the bitt was never rated for, especially during heavy weather or emergency towing use |
What to look for in a supplier
- SWL certified against the ship's actual Equipment Number and mooring line breaking strength, not a generic size chart.
- Casting or fabrication quality with NDT records at the base plate weld, the highest-stress point on the fitting.
- Post spacing and diameter matched to the line size in service, checked against the fairlead layout it will work with.
- Corrosion protection suited to a fitting that cannot be taken out of service for recoating without disrupting mooring operations.
Inspect the base plate weld, not just the posts — bitts almost always fail at the deck connection under repeated snap loading, long before the posts themselves show visible wear.