PART II - Special Characteristics Merchant Vessels and what you need to know to ensure your safety!

1. Typical Speeds of various Merchant vessels while operating
2. Horsepower to weight ratio and other factors on how it affects stopping distances
3. Turning diameters of various vessels at typical operating speed
4. Harbor (Dockside) maneuvering.
5. Ships radars in high seas and various weather conditions
6. Watch keeping and lookouts aboard vessels.
   ¤ Sleeping & fatigue while on watch
   ¤ Incompetent personnel
   ¤ Nobody is on the bridge!!!
   ¤ Single-man watches

1. Most merchant vessels often travel at a faster speed that you may think and will be on top of you before you know it. For a land-lubbers analogy, don't pull out in front of a truck moving at a high rate of speed towards a red light when you have a green light, the truck may not be able to stop in time. Typical operational speeds are as follows in open waters:

2. Horsepower to weight ratio. This ratio determines how fast a boat can accelerate, stop or otherwise maneuver. The higher the ratio, the more responsive the vessel is to stopping in an emergency.

On an off-shore racing boat, the horse power to weight ration can be up to several thousand horse power per ton. On a typical recreational power boat, the horse power ratio can be up to several hundred per ton. On a typical sailboat with an auxiliary motor typically there are a few horse power per ton. On most merchant ships the horse power ratio is usually significantly less than one horse power per ton. These numbers have been rounded for illustration purposes but are typical of each type of vessel.

These numbers are typical and can vary from vessel to vessel some having higher number and others having lower power to weight ratios. As one can plainly see that the 22' sailboat's auxiliary engine has 150 times (15,000%) more stopping power per ton than a large tanker, and is even higher for most motor boats

Another factor that will effect stopping distances is how fast the ship can reverse its thrust. On a military ship going from full ahead to full astern on a variable pitch screw takes around 18 seconds. On a steam turbine ship with a fixed pitch screw about a minute and a half. On a slow speed diesel directly coupled to the fixed pitched screw up to 3 minutes.

Ship's engine are generally too massive and powerful to use a transmission that you would find in a typical yacht (it would be torn to bits by the forces involved) so these are the typical configurations and maneuvering characteristics that are not conducive to being reversed quickly in an emergency situation from full ahead to full astern. Please keep this in mind before placing a merchant ship in such a situation.

Also ship's engine rooms are fully manned in most inland water ways where frequent maneuvering is required and the above procedures require a fully manned engine room. However, in the open sea, engine rooms are either minimally manned or not manned at all so such procedures are impractical 999 out of 1000 times while a ship is in the open sea, it will choose to alter course rather than change speed to avoid collision.

3. The turning diameter and stopping distances are measured in miles, it is not easy for a vessel of several hundred thousand tons to get out of your way (even if you have the right of way). These distances vary from ship to ship but average is 1 mile diameter turning diameter with a hard over rudder, and two miles to stop, some of the larger tankers you can multiply these numbers two or three times, and on smaller vessels these numbers are decreased. It is a lot easier for you to move out of his way that it is for him to move out of your way.

I am using the above listed types of vessels for comparisons from a full speed situation. Again these numbers are typical and have been rounded for illustration purposes.

* these boats are capable of a tighter turning diameter at slower speeds, but at high speed if they use hard over rudder they are subject to flipping.

 

4. Harbor (Dockside) maneuvering.  Once again, maneuvering around ships that are either approaching or leaving a dock require that yachters exercise special consideration.  Most ships are massive in weight.  As a result they have a lot of inertia, even at very slow speeds, and require enormous amounts of power and time to change speed as little as half a foot per second or 1/4 knot (typical speeds used in docking).  

Some of the older ships and many of the newer ships have their own bow and stern thrusters, however, many ship's do not have these thrusters, and utilize tug boats in docking and undocking.

I have personally witnessed a small ski boat passing between a large tanker and dock.  Fortunately the ski boat accelerated out before he and his passengers got crushed.  Yachters should always stay away from ships that are approaching a dock -- especially between a dock and the ship or if the ship has several tugs around it.

I recommend staying at least 300 feet away from ships that are maneuvering around harbors and various other berthing areas.

5.  Ships radars in high seas and various weather conditions.  While radars allow ships to see other ships much easier in foul weather, many types of foul weather has a tendency to mask radar signatures of smaller and medium sized vessels.

What obscures radar the most is a heavy rain shower.  Just as there is complete visual 'white out' conditions during a heavy rain storm, even large ships are obscured in radar.  Localized rain, appears as big blotches on the screen.  For light to moderate amounts of rain filters on the radar can be set to optimize the picture and see medium to large size targets.  However, for all but the lightest of rain, the automatic acquisition on radars will not work, and most plots have to be made manually.

If there are small localized showers, I would suggest staying away from them (unless you have a need for fresh water) if you are going to be passing close to a ship while out at sea, or stay away from channels typically used by ships and tugs in inland waters during any kind of heavy rain conditions with restricted visibility as the chances of them seeing you in sufficient time have been reduced.

High seas will also create a lot of clutter on a ship's radar screen as each wave is sending its own reflection back to the ship, in 15 and 20 foot seas (5 - 6 m) small boats can be lost in 'clutter' up to six miles from the ship on a properly tuned radar.  

I have noticed a lot of junior mates as well as a few captains, do not know how to properly tune a radar.  Even the USCG in Prince William sound during the Exxon Valdez grounding did NOT have their radar tuned correctly.  For example the USCG could not see a super tanker on its tracking station -- perhaps one of the easiest  targets to track on radar.  From my own personal observations, I have noted that roughly 1/3 of professionals who are supposed to know how to operate radar, do not do it correctly.

Where radar is most useful, is in fog which usually is also associated with fairly calm conditions.  Fog has a relative low density, and radar is not hampered, nor are there any significant waves to reflect radar back at the ship.  Occasionally rain is accompanied by fog.  Under these circumstances make sure you have a good radar reflector properly rigged as discussed in part I

6.  Watch keeping and lookouts aboard vessels.  All ships are required by law to maintain a proper lookout.  However, on the high seas, where law enforcement isn't around, these laws are broken predominately by foreign flag (and some US flag) ships just as frequently as people break the speed limit either intentionally or unintentionally.

¤ Sleeping & fatigue while on watch -- for the exception of tankers in US waters who are now governed by OPA 90 (Oil Pollution Act of 1990), many mariners work in excess of 16 hours per day while in port.  After working long hours in port (often in foul weather), and then leaving port practically exhausted, the majority of mariners are operating at less than full attention.  On several occasions I have found myself nodding off while standing a bridge watch late in the evening.

¤ Incompetent personnel -- Even though STCW 95 is supposed to eliminate incompetent personnel, many 3rd world  countries have been rumored to rubber stamp the documents of their mariners.  Even though it is becoming less prevalent, many mariners, still lack knowledge of the basics such as the rules of the road or rudimentary English necessary for communication on the high seas.  I suggest that you stay clear of any merchant vessel that you have not adequately communicated with.

¤ Nobody is on the bridge!!! -- believe it or not, I have observed on numerous occasions ship's where no one is on the bridge (through high powered binoculars on a ship failing to yield according to the Rules).  I have heard of many stories where the mate and the lookout go below to watch a movie or to play cards, especially on the open ocean.  When it becomes apparent that a ship is not taking appropriate action follow the rules of the road and take the necessary action to prevent a collision.  I usually at a very large distance (around 15 miles out) on the open ocean alter my course slightly to ensure sufficient berth for clearance to further reduce the chances collision, I suggest you may want to do the same.

¤ Single-man watches -- many countries are reducing the manning to one person on the bridge.  With fatigue, the necessary requirements (especially Montezuma's revenge), GMDSS operations (composing and sending messages), chart plotting attentions, the bridge watch will not have his/her eyes where they are supposed to be -- on where he/she is going.  Always, operate your vessel in a defensive manner, much like driving down the highway next to a junker.  Even though on many occasions I knew I had the right of way, I will give way if I have doubt as to the others ability on the high seas.

© 1997-2003 Jan K. Genemans