Severe Wind & Rolling

This is an examination of the ability of the ship to withstand the combined effects of high winds and seas and is mandatory in all ships classed “Deep Sea” with somewhat reduced requirements for vessels under 24 metres (80ft) in length and coastal waters.

It is a three stage application of wind pressure and rolling acting perpendicular to the beam of the ship in the following sequence:

  • The ship is subjected to a wind of 54 knots with a maximum permissible angle of heel of 16 degrees or less depending on the minimum freeboard and beam of the ship
  • The ship is then subjected to a roll to windward due to wave action to a specified angle of heel.
  • The ship is then subjected to a wind gust of 61 knots.

The ship must have a specified reserve of dynamic stability to resist the above forces. The action of stabilizers cannot to be taken into account.

Ships with large windage area, low draft and low beam to draft ratios are particularly sensitive to these dynamics and many we see have doubtful ability to meet them.

Ordinary sail boats with ballast keels are innately suitable because of their ability to reduce their windage area at will. This perhaps explains their remarkable safety record.

Designers of commercial craft are all familiar with this requirement because in many craft it is a statutory regulation and is always considered in the early design stages.

It is Pacific Motoryachts view, and practice that any vessel designed for, and ultimately intended for ocean passages must and should be able to demonstrate its ability to meet the above criteria.

 

Last Updated (Sunday, 05 September 2010 23:37)