You have just come alongside in a marina and topped up the tanks from the dock. The next day the guest towels come out of the machine stiff, dull and slightly grey, and the whites you washed a week ago at anchor on watermaker water were perfect. Nothing changed except the water — and water is the largest single ingredient in every wash you do.
Water hardness
Hardness is dissolved calcium and magnesium. Hard water reacts with anionic surfactants to form insoluble lime soap, which deposits in fibres and on heating elements.
| Water | Typical source | Effect on the wash |
|---|---|---|
| Very soft (0-3 dH) | Watermaker / reverse osmosis, rainwater | Detergent works at low dose; excess dose = residue and over-foaming; can foam-lock a machine |
| Moderate (4-8 dH) | Many EU marinas | Standard dosing |
| Hard (over 12 dH) | Some Med and Caribbean dock supplies | Lime soap, greying, stiff towels, scale on the element; needs builder or a water softener |
Practical actions:
- Test dock water with a hardness test strip at every new marina and record it in the laundry log.
- On soft RO water, cut detergent dose — often by 30-50 percent against the bottle instruction.
- On hard water, do not simply add more detergent; add a builder/water softener or the excess surfactant just makes more lime soap.
- Excess foam cushions the mechanical action and stops the wash from working; a foaming machine cleans worse, not better.
Bleach: oxygen versus chlorine
| Oxygen bleach (sodium percarbonate, hydrogen peroxide) | Chlorine bleach (sodium hypochlorite) | |
|---|---|---|
| Action | Releases oxygen; oxidises colour bodies gently | Powerfully oxidising, strips chromophores fast |
| Safe on | Cotton, linen, most synthetics, most colours (test first) | White cotton and linen only |
| Never on | Wool/silk if strongly alkaline; check pH | Wool, silk, cashmere, elastane, most colours |
| Temperature | Needs 40-60 C to activate properly (or an activator like TAED) | Works cold |
| Damage mode | Slow, mild fibre weakening | Yellows and dissolves protein fibres, destroys elastane, thins cotton, permanently strips dye |
Chlorine bleach yellows and weakens protein fibres. The yellowing is not dirt — it is chemical damage to the keratin/fibroin, and it is irreversible. On a yacht, chlorine bleach belongs to hard-surface hygiene, not to guest laundry.
Oxygen bleach is the yacht default: soak whites and white cotton table linen in warm oxygen bleach solution rather than reaching for hypochlorite.
Onboard Notes
- Bunkered dock water can carry iron. Iron plus oxygen bleach equals orange spotting on white linen; filter, or wash whites on watermaker water only.
- Never mix chlorine bleach with acidic products (some rust removers, some limescale removers) — that releases chlorine gas in a small, poorly ventilated space.
- Whites that are grey are usually overdosed and under-rinsed, not under-bleached. Fix the dose and the rinse before you fix anything else.
- Log tank source and hardness; when a batch of laundry goes wrong, the water is the first thing to check.