In Part B, Steering and Sailing Rules, Section 1 of the Coast Guard Navigation Rules, Rule 6 states that "Every vessel shall at all times proceed at a safe speed so that she can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and condition." Meaning... slow down in adverse conditions so that if you are in danger of collision, you can stop or turn away before it happens.
The Navigation Rules go on to state in Rule 6 to take into account the following factors when determining a safe speed:
Maintain a Proper Lookout
While this is not expressly stated in Rule 6, maintaining a proper lookout is Rule 5, and is a prerequisite of operating your vessel at a safe speed.State of Visibility
Take into account all visibility factors such as time of day, fog, wind-driven waves, rain, etc. If conditions are not perfectly clear, consider lowering your speed significantly. Do not go full speed at night or in the fog especially. There are a number of reasons for this, which I cover in my Live & Learn article - Slow Down at Night - that uses a real-life example to teach boaters safe boating practices.Traffic Density
The traffic density includes concentration of fishing vessels or any other vessels. If you are navigating high traffic areas, slowing down is imperative to avoid collision.The Manageability of the Vessel
The manageability of the vessel with special reference to stopping distance and turning ability in the prevailing conditions.
In other words, how manageable is your boat? If you have a large, cumbersome boat, it may take awhile to stop the vessel completely. It may also be difficult to turn the boat to avoid a collision.
For further reading on this subject, read my article Know Your Boat and Tips for Better Boat Driving Skills.
Background Lights at Night
At night, the presence of background light such as from shore lights or from back scatter from your boat's own lights can interfere with safe passage. It can be hard to see objects on the water if there is a reflection from shore, or if there is a reflection from your boat's running lights. Again, slowing down is a prudent action to take if you are near shore or any other type of background light.State of Sea Conditions and Navigational Hazards
The state of wind, sea and current, and the proximity of navigational hazards should be taken into consideration when determining a safe operating speed. It's a no-brainer that if the water is churned up, slowing down is necessary. But, this rule also applies when approaching a mooring or a navigational hazard. If you are going too fast to begin with, the wind, sea and current will exacerbate steering difficulties, possibly causing a collision.Draft
Taking into account the draft in relation to the available depth of water will help avoid running aground. If you are at a slower speed in shallow water, you may avoid running hard aground and damaging your vessel. A good rule of thumb is to operate your vessel at what I call clutch-ahead, in shallow water. This way, if your depth finder sounds the alarm, you can quickly come to a stop and reverse to avoid running aground.Vessels Operating with Radar
If you are operating your vessel with radar, Rule 6 goes on to give additional instructions for mariners to take into account when determining safe speed:
The characteristics, efficiency and limitations of the radar equipment;
Any constraints imposed by the radar range scale in use;
The effect on radar detection of the sea state, weather and other sources of interference;
The possibility that small vessels, ice and other floating objects may not be detected by radar at an adequate range;
The number, location and movement of vessels detected by radar;
The more exact assessment of visibility that may be possible when radar is used to determine the range of vessels or other objects in the vicinity.
