Sunday, March 30, 2008

Small Boats (Crossing a Bar)

" The boat above made it"

" This boat did not"

Most navigable entrances have a bar, A BAR ENTRANCE CAN BE VERY DANGEROUS. Whenever a bar is to be crossed extra precautions need to be taken to minimise the risk to your boat and crew. Regardless of the vessel type the conditions at the bar must be examined before committing the craft to either enter or exit. The combined effects of tide, swell and wind need to
be assessed. A run out tide against either wind and / or swell can produce waves so big that an entry or exit is a bad idea, even when there are just small waves. Waves not running perpendicular to the required course can also make the situation worse. A narrow entry / exit channel gives less room to manoeuvre and smaller margins for errors in judgment. Not being familiar by the skipper and crew also makes for higher risks. Sometimes familiarity can be detrimental to making good decisions because of overconfidence and an attitude that the home bar has no fears. There will usually be a strong desire among the crew to either get home or get out which could easily be detrimental to making wise decisions in marginal conditions. IF IN DOUBT STAY OUT DO NOT ATTEMPT TO CROSS. Some precautions should be taken when crossing a bar.

Standard Precautions :
Check appropriate weather forecasts.
Call the Coast Guard for the latest bar conditions and tell them your intentions.
Secure all loose items.
Have everybody don life jackets.
Close and secure all hatches.
Brief all crew on emergency drills.
Determine the wave pattern before committing the boat.
Don't cross a bar with another boat.
Do not cross if the bar is breaking.
Spend as little time as possible on or near a bar.
Cross about 1-2 hours before high tide, but keep in mind this can very.
Before crossing try and time the series of bigger waves.

General Considerations:
There are two basic things, the entry and the exit, and there are quite marked differences in the techniques that should be used for a safe bar crossing. An important technique common to all craft is to keep the boat perpendicular to the wave fronts, especially when the waves are either large or steep. For an Exit the main decision is whether the boat can be controlled as it travels against and through the waves, especially as it falls off the top into the trough. Two conflicting requirements arise, the need to have the boat go over each crest slowly against the need to minimise the time spent on the bar. Judgment and experience are a must. Further consideration becomes necessary in marginal conditions,for the return will the bar allow a safe crossing and, if not, what are your other choices. Can the boat be positioned safely close enough to the bar to observe the wave pattern on and just outside the bar? Is the navigable channel wide enough to allow the boat to travel at right angles to the wave fronts?

For an Entry the technique depends primarily on the type of craft and whether it has the capability to travel at or above the speed of the waves. This can usually be achieved in runabouts, and in most other powered craft capable of 15Kts or better. Such craft should be held on the back of the wave once committed, using extreme caution to stop the boat getting on the forward face of the wave. A sailing vessel with a fixed deep keel will normally not be able to keep pace with a wave. These vessels should use most or all power to minimise the time spent in the danger zone and reduce the risk of broaching. When on the face of the wave the rudder use becomes critical to keep the boat as straight as possible and perpendicular to the wave. This problem for slower boats usually makes an entry much more hazardous than an exit. All skippers should only commit the boat at the end of the large waves of a set, in marginal conditions this will involve considerable time holding the boat in a safe position from where the wave pattern can be best seen.