Ship and cargo characteristics have a significant influence on the application of ship weather routing. Ship size, speed capability, and type of cargo are important considerations in the route selection process prior to sailing and the surveillance procedure while underway. A ship's characteristics identify

Generally, ships with higher speed capability and less cargo encumbrances will have shorter routes and be better able to maintain near normal SOA's than ships with lower speed capability or cargoes. Some routes are unique because of the type of ship or cargo. Avoiding one element of weather to reduce pounding or rolling may be of prime importance. For example, a 20 knot ship with a heavy deck cargo may be severely hampered in its ability to maintain a 20 knot SOA in any seas exceeding moderate head or beam seas because of the possibility of damage resulting from the deck load's characteristics. A similar ship with a stable cargo under the deck is not as vulnerable and may be able to maintain the 20 knot SOA in conditions which would drastically slow the deck-loaded vessel. In towing operations, a tug is more vulnerable to adverse weather and sea conditions, not only in consideration of the tow, but also because of its already limited speed capability. Its slow speed adds to the difficulty of avoiding adverse weather and sea conditions.

Ship performance curves (speed curves) are used to estimate the ship's SOA while transiting the forecast sea states. The curves indicate the effect of head, beam, and nofollowing seas of various significant wave heights on the ship's speed. Figure below is a performance curve prepared for an 18 knot vessel.

With the speed curves it is possible to determine just how costly a diversion will be in terms of the required distance and time. A diversion may not be necessary where the duration of the adverse conditions is limited. In this case, it may be better to ride out the weather and seas knowing that a diversion, even if able to maintain the normal SOA, will not overcome the increased distance and time required.

At other times, the diversion track is less costly because it avoids an area of adverse weather and sea conditions, while being able to maintain normal SOA even though the distance to destination is increased. Based on input data for environmental conditions and ship's behavior, route selection and surveillance techniques seek to achieve the optimum balance between time, distance, and acceptable environmental and seakeeping conditions. Although speed performance curves are an aid to the ship routing agency, the response by mariners to deteriorating weather and sea conditions is not uniform. Some reduce speed voluntarily or change heading sooner than others when unfavorable conditions are encountered. Certain waves with characteristics such that the ship's bow and stern are in successive crests and troughs present special problems for the mariner. Being nearly equal to the ship's length, such wavelengths may induce very dangerous stresses. The degree of hogging and sagging and the associated danger may be more apparent to the mariner than to the ship routing agency. Therefore, adjustment in course and speed for a more favorable ride may be initiated by the commanding officer or master when this situation is encountered.

• Zone Time In Celestial Navigation - 2009-04-21 - 01:09:16
• Some common local winds are listed by local name - 2009-04-21 - 12:35:43
• Wind Patterns - Modifications of the General Circulation - 2009-04-21 - 05:46:03
• Maneuvering to Avoid the Storm Center - 2009-04-21 - 05:03:03
• Weather Routing - Benefits - 2009-04-19 - 07:35:50
• Weather Routing - Communications - 2009-04-19 - 07:25:17
• Weather Routing - Southern Hemisphere Routing - 2009-04-19 - 07:21:29
• Weather Routing - Types of Recommendations and Advisories - 2009-04-19 - 07:16:12
• Special Weather and Environmental Considerations - 2009-04-19 - 07:06:59
• Weather Routing - Synoptic Weather Considerations - 2009-04-19 - 06:15:22

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