Beam seas and rolling
Sea state · Power & sail
Seas on the beam make a boat roll hard, and a breaking wave on the beam can knock it down. Zigzag across the seas instead of running broadside, turn to meet any wave that looks like breaking, secure everything aboard, and use stabilizers or flopper-stoppers if you have them.
Safety first
- A breaking wave about as high as your boat is wide, striking broadside, can roll the boat. Don't get caught beam-on to breaking seas.
- People get thrown and hurt in heavy rolling. Move only when needed, keep one hand for yourself and one for the boat, and keep less experienced crew in the cockpit or cabin.
- Poles and lines for paravanes and flopper-stoppers carry very large loads in a sudden roll, such as a big wake. Rig them much stronger than normal sailing gear, keep hands clear when deploying or recovering, and light the poles at night in a crowded anchorage.
Don't run broadside
- Rolling is worst with the seas abeam. The USCG suggests crossing heavy swells at an angle of about 30 to 40 degrees in a zigzag, making each leg as long as you can, much as a sailboat tacks downwind.
- Running parallel to the seas, the boat lies on the slope of the wave: a 20-degree wave face means about 20 degrees of heel before any roll is added.
- If a wave looks likely to steepen or break, turn and meet it bow-on. The USCG stresses that squaring up to a threatening sea is never the wrong move.
- To turn across the seas, slow briefly, then put the helm hard over with a burst of power so you are beam-on for as short a time as possible. Twin-engine boats can split the throttles to pivot faster.
Securing the boat
- Before it gets rough, stow or lash loose gear, secure the galley, and close hatches, ports and doors. Loose weight thrown to one side reduces stability and can break windows or fittings.
- Water that only partly fills a space, such as bilge water or a flooded locker, sloshes from side to side and reduces stability. Keep bilges pumped and scuppers and deck drains clear.
- Water trapped on deck adds weight up high and can amplify rolling. Changing course or speed can reduce the water coming aboard.
Stabilizers and flopper-stoppers
- Fin stabilizers use fins below the waterline that change angle to push against each roll. They depend on water flowing past, so they work underway and do little at rest.
- Gyro stabilizers use a heavy spinning flywheel inside the hull and can work at rest, but they need space, strong mounting and electrical power.
- Paravanes ('birds' or 'fish') are towed from poles on each side and fly through the water at a slight downward angle, resisting each upward roll. They are for use underway.
- True flopper-stoppers are for use at anchor: hung from poles, they sink easily and resist being pulled up, which damps the roll when swell sets in from the side.
Sources (4)
higherlogicdownload.s3.amazonaws.com · northpacificyachts.com · cruisingworld.com · rya.org.uk
General guidance for recreational boaters, researched from the sources listed and written in our own words. Your equipment manuals, local knowledge, the Navigation Rules and a qualified instructor come first.