Two important design considerations for roll-on roll-off ferries should be a modest bow flare and drainage arrangements to remove water from the car deck. The pronounced bow flare seen on many ships results in very high localised stresses in heavy seas - if the flared bow is not an integral part of the hull structure, stresses generated might be sufficient to dislodge it.
It should be impossible for water to lie on the car deck. The stability of a ship is drastically reduced by any uncontained width of water, so the fitting of transverse bulkheads is not the whole answer. The car deck should perhaps sit on open-topped boxes connected to high-capacity emergency bilge pumps.
If a ship is driven too fast into heavy seas it may not be given time for its natural buoyancy to lift it over an approaching wave. This may not be quite so serious in a naval ship that has fine lines, but it is important in a squarer passenger ship.
J. B. LAIRD
Darley, North Yorkshire
The writer is a former naval architect and HM Inspector of the Health and Safety Executive.Reuse content