Towing a vessel - its more involved than you think!
By Wayne Spivak
National Press Corps / United States Coast Guard Auxiliary
This summer, my wife and I went to one of our favorite
haunts for dinner. It's a pleasant place to eat, and what makes it even more delightful is
that they not only have a mean coconut shrimp dish, but they are right on the water.
Sometimes we go by boat, other times by car, but in
either case, one of our pastimes when we eat at this restaurant is watching the boater's
passing by the eatery. We always get a good laugh while watching people try to dock their
boats at the restaurant. This is in part a result of the rather strong current that ebbs
and flows by the restaurant, and the strong winds that tend to blow.
If only people understood the physics involved in
docking a boat, and that speed or rather the lack of it, is a crucial factor in easy
docking, we wouldn't laugh as much. But this article is not about docking; maybe another
article will cover the techniques needed for an easy docking maneuver. This article is
about towing.
So what does my culinary tastes and entertainment values
have to do with towing? Well, while watching the boats and the waterfowl playing in the
estuary, I noticed a boat being towed by a Good Samaritan. What I saw v�s a v�, the tow
situation; caused those little hairs on the back of my neck to rise.
Good Samaritans
Let me start by saying I applaud people who are willing
to be Good Samaritans. I really do, otherwise why would I be involved with America's
Volunteer Lifesavers™, with the United States Coast Guard Auxiliary? But there is a
difference between being a good and good-hearted neighbor, and taking unnecessary risks
because of sheer ignorance.
This country is based on neighbor's helping neighbors.
It is the indomitable spirit of volunteerism that drives many of our social organizations,
our educational institutions and to some extent government service. It is for this reason
that many states have enacted legislation that protects the Good Samaritan from acts of
negligence.
Hippocrates gave some sage advice for medical
emergencies, and it works for all Good Samaritans: Primum non nocere.
"First of all, do no damage."
The English incorporated this advice into common law,
now called Tort Law. Today, we have two legal terms that apply to the Good Samaritan;
Negligence and Gross Negligence.
Negligence can be defined as "… a duty
to ensure that a persons actions do not cause harm to others." {Hippocrates code}
[Duhaime.org]
Gross negligence is "Any action or an
omission in reckless disregard of the consequences to the safety or property of another.
Sometimes referred to as "very great negligence" and it is more then just
neglect of ordinary care towards others or just inadvertence." [Duhaime.org]
So, by definition, it becomes imperative, that if you
are to offer assistance, offer only the assistance which you are capable of providing
safely.
Towing
Towing is not a simple procedure! There is a tremendous
amount of stress involved, and it affects both boats and the tow line you are using. I'm
talking about stress, as in forces, the types of forces you learned about in Physics
class. And, we're talking some major forces, enough, that a miscalculation could cause
someone's death.
What follows is meant to give the reader a basic
understanding why towing is dangerous. This article is insufficient to make the reader
prepared to tow any vessel of any size.
The Coast Guard and Coast Guard Auxiliary provide their
members with several different boat handling courses. Most of these courses contain
sections on towing.
As an Auxiliarist in the Boat Crew Program, you first
learn about towing in the Mission Oriented Operations chapters. Here you begin to learn
the methodology behind a tow, but very little of the theory. We're talking the
"how-to" under guidance of a Coxswain.
Auxiliary members would then refine the process of
towing, in the Coxswain program. Here more emphasis is placed on theory, so that the
Coxswain, who is in charge of the Auxiliary vessel (called a Facility) can make informed
decisions on whether to initiate the tow, and if the Coxswain feels confident that the tow
can be safely handled, what type of tow to undertake.
In the Auxiliary Operations course AUXSAR (Auxiliary
Search and Rescue); a sizeable portion of this course is about towing. This course
provides all the theoretical information about towing. The course material states
"Almost everything done during a tow is potentially hazardous; a successful tow is
one during which no damage is done to the engine(s) of the towing vessel, no damage is
sustained by either vessel, and no one sustains an injury."
Essentially, there are four factors that impact a towing
situation: the hull characteristics of boat doing the towing, the hull characteristics of
the boat being towed, the construction and diameter of the line used to tow the disabled
vessel, and the sea state (waves, wind, and current). With all the different makes and
models of vessels, as well as different line types, you can see that every tow is unique,
making towing as much an art as it is a science.
I mentioned stress before, as one of the many reasons
why you really need to learn how to tow a vessel before you actually just do it. There are
three types of forces that a tow boat, the towed boat and the lines that connect them,
undergo. These are: acceleration forces, steady forces and shock forces.
A brief definition will help you understand the dangers
involved.
Acceleration Forces is the stress placed on the
vessels and the towline during the time the towed and towing vessels are
dead-in-the-water, to the time they reach their maximum (constant) towing speed.
Steady Forces is the stress placed on the vessels
and the towline during the phase after maximum (constant) speed is reached. These forces
are just involved in pulling the towed vessel through smooth water at a constant speed.
Shock Forces occur because of the sea state.
Towing in calm, smooth water would produce little or no shock forces. Towing a vessel
where there are five foot waves, at 30 second intervals would produce considerable shock
forces. Just picture your boat slowing down and speeding up as it goes up and down waves.
The towed boat is doing the exact same thing. But, they probably are not in synch, so the
towline is being stretched and then goes slack, and then get pulled tightly again and
stretches.
An average size vessel towing a vessel of equal size
will, at a minimum, incur several hundred pounds of force, depending on the type of line
used, sea state, etc. While many lines may contain ratings for several thousand pounds of
force, those statistics are for brand new line. Lines that are well used, or that are
weathered, are probably capable of sustaining loads much smaller that what they are rated
for.
Deal Breakers - What Can Go Wrong, Usually Will
So great, now you know the factors that influence a tow
and some basics on what the forces are - so what? Without doing all the math and physics
involved, all you need to understand is this: Recreational vessels are often ill equipped
to handle the stresses of towing for a variety of reasons:
- While every piece of equipment has different breaking
characteristics, given enough stress, any part of this towing system could break, and
often with catastrophic results. If you must tow another vessel, examine its hardware
(cleats, bits, etc) as well as your own to make sure it is bolted through.. Never attempt
to tow another vessel using a "ski rope" or other lightweight line incapable of
sustaining the stresses outlined above. Under no circumstance should anyone stand directly
in line with the tow line, because if it were to break, it would "snap back"
like a rubber band, wreaking havoc with everything in its path.
- The cleats and deck fittings on most boats can only
accommodate smaller lines; which limits the amount of force they can take, and thus the
size of the vessel you an tow. How fast you tow another vessel can impact the forces
exerted.
- The pitch of most propellers on your average recreational
vessel is geared towards maximizing speed of the vessel, not torque. Using the average
propeller with a pitch of 19" or 21" results in a great deal of slip
(inefficient movement of water through the propeller), making towing inefficient and
stressful on an engine.
- The amount of power it takes to tow a vessel, if done
improperly could cause serious damage to one of the most expensive pieces of equipment in
your vessel - your engine(s)
- The average recreational vessel does not carry lines of
the length that may be necessary to minimize the shock forces by keeping the vessels
"in step" with one another. It is important to adjust the length of the tow line
to minimize the shock forces caused by wind, waves, and/or current.
- If the boat doing the towing is an outboard or an inboard/outboard, you
have another potential disaster - getting the towline caught in the prop of the tow
vessel. At the very least, this usually means cutting the tow line free from the prop, to
totally disabling the tow boat, resulting in the need for another potential tow.
Given the information above, I hope you can see that
there are a myriad number of things that can go wrong when towing another vessel. In any
case, if I was a professional gambler who was asked to bet on whether the average
recreational boater could tow another boat without incident, I would pass, as the odds
favor the house. The "house" here is the fact that you'll likely experience
damage to either the towed boat, the towing boat, or that someone on either vessel would
sustain an injury.
Being the Good Samaritan
I hope I've shown you that part of being the Good
Samaritan is learning when to just standby and when to act, at least when it comes to
towing. Under most circumstances, towing should be left to professionals especially if you
want to avoid the label of appearing grossly negligent.
Standing by, and waiting with the other vessel, is still
considered offering assistance, since should the situation worsen, you would be able to
provide help in sheltering the occupants of the other vessel. You can also provide
protection from other vessels, and help communicate with the Coast Guard.
If you want to learn how to tow a vessel, why not join
the Coast Guard or the Coast Guard Auxiliary. We'd be more than happy to teach you the
skills you need to be not only a better boater, but a trained lifesaver.
To find out how to join, contact your local Coast Guard
unit (visit www.uscg.mil for details), or visit the Coast Guard Auxiliary web site at www.cgaux.org and click on the Flotilla Finder link on the right side of the page.
