Dynamic
Stability During a Change of Course
- Marc Nugent,
BSE, SA
Why Does My Boat Heal Outwards
in a Turn?
I first tried looking at this in a static drawing not
taking into account the centrifugal force created by the
turn of the vessel. The only thing I learned looking at it
in this approach was it had to due with the Centre of
Gravity or another force unseen in a static position.
Draw a dynamic diagram and look at the
different forces being applied:
2. Inner running
surface force (lift)
3. Outer running
surface force
Then you have to take into account the
static situation, such as CG, M (Metacenter), B (buoyancy),
and (RM) righting moment.
As you apply the rudder angle it creates an
outward force. Since the rudder is aft of the CG it wants
pivot the vessel, but due to the tracking and momentum of
the vessel it starts to create a curve. This is where you
start to generate a centrifugal force. We also created
another moment by the difference if forces between the outer
running surface and the inner. As the vessel heals inwards
the other pressure forces are going to be greater then the
inner pressure forces. Some people say the inner hull is
being "sucked down", but what is really happening, it is
just compensating for the much larger outer lifting forces.
So go back to that static situation. What
changed as the vessel is heeled over? The Buoyancy shifted
inward for one, which resulted in our RM. When the vessel
is stable or the angle of heel is not changing the moment
cases by the pressure forces is equal to the righting
moment. In a balanced position all forces and moments have
to sum up to zero.
Now if we move the CG up, the RM becomes
less. Assuming we are in a balanced state, meaning there is
no Roll, and we are at a constant angle of heal; As the
moment caused by the RM decreases the moment caused by the
pressure forces has to decrease as well.
Picture a transverse force on the CG, in
this case it is the Centrifugal Force. This will cause
a moment around the CG. When the CG is low you can see
it would want to cause the bottom of the hull to be pull
outward, like the forces from the rudder. Thus causing
a moment acting in a inward heel.
No if we move the CG up enough we should
find a position where the two forces equal and there is no
heal.
The higher the CG, the more the Centrifugal
Force will want to heal the vessel outward. Once the CG is
high enough to cause the vessel to heal outwards, we then
have to again balance the moments to obtain a consistent
heel angle throughout the turn.
To sum
it up, the lower the CG the more the vessel will want to
heel inwards. The higher the CG the more the vessel will
want to heel outwards. The more the vessel heals the more
the moment cause by the pressure forces, and RM have to make
up for it.
In the case of the Arcadia, the vessel has
rounded chines and it is more of a "proper speed" issue then
flaw or concern. More like the concern is, too much
power for that boat, which could be a design error. If the
vessel has hard chines, it becomes much more dangerous and
can roll or flip just like a truck going sideways down the
road. You see this in offshore and hydroplane boats where
the engines are large compared to the vessel, it raises the
CG relatively high, and Centrifugal Forces are large. At
slow speed the same offshore vessel will heal inwards though
a turn, where at high speeds it will heal outwards.
The vessel was a newer recreational lobster
style boat. In my opinion the vessel was outfitted
with too large of engine of the design of the hull. As
long as the owner is aware of the condition and operates the
vessel correctly there is no concern. There are many
vessels built today that are capable of higher rates of
speeds there which they were originally designed for.
This puts the responsibility on the operator and they should
be educated in how to operate their vessel correctly.
This a quick answer tot he original
questions. I am currently working on expanding the
answer to include my information and some diagrams.
Copywright 2007-2008 -
Manitou Boatworks & Engineering LLC
How Should I Prepare
for a Marine Survey?
- Society of
Accredited Marine Surveyors Time and additional expense can be saved by
preparing the
vessel for inspection and making her more accessible.
Arrange to present a clean, shipshape
boat, and have all papers and miscellaneous gear ready. If applicable,
you will need to make arrangements with the marina to haul the vessel
for bottom inspection, and retain a captain for sea trials. Lockers and
cabin areas should be cleared of all miscellaneous gear.
The surveyor should never be asked to
prepare a boat for inspection. The surveyor may request minor
dismantling of interior ceilings, headliners, flooring, etc. in order to
gain access to the suspected areas. Random removal and examination of
below-the-waterline fasteners on wood boats may be required. Any
dismantling and re-installation of parts should be performed by
qualified personnel and is the responsibility of the person ordering the
survey.
Written authorization from the owner may
be needed to board and/or to remove part of the vessel.
How Do I
Choose a Marine Surveyor?
- Society of Accredited Marine Surveyors Anyone
can title him or herself as a Marine Surveyor and start a business.
Certain marine surveyors are permitted to use a designation denoting
membership in accrediting organizations that require members to meet
strict professional, technical and ethical standards.
Surveyors should provide you with a
professionally prepared report that can be accepted by your bank and/or
insurance company. Talk with prospective surveyors and ask questions!
What does the survey include and what type of reporting format is used?
Do they use ABYC, NFPA and USCG standards in their surveys? How much
will the inspection cost? How long will the on-board inspection take?
A thorough inspection will not be rushed
and will depend on the type of survey required based on vessel size,
equipment and on-board systems. There may be additional services
available such as engine surveys, oil analysis, galvanic and stray
current corrosion testing, ultrasonic testing, moisture testing and
other non-destructive tests. There may be additional charges for these
and other services.
Well conducted surveys can provide good
information on the vessels' condition, but they are not guarantees. The
surveyor reports the condition in accessible areas only as it exists at
the time of inspection.
Why should you have a vessel surveyed?
Most insurance companies and banks will require them on older vessels.
They will need to know her condition and fair market value in order to
finance and/or underwrite the vessel. Knowing her condition and fair
market value before you purchase is also important. However, the most
important reason to survey your vessel is for the safety of the
passengers and crew.
Salvage or
tow? You need to know
- David S. Yetman
You might be surprised to learn that salvage operations aren’t just
for wrecks
The engine is dead, in spite of your best efforts to revive it, and the
wind is pushing you toward an ominous-looking rocky shore. In
desperation you deploy the anchor, and it holds at last. But the depth
alarm is sounding and you are so close to the hazard that you can see
the grain in the rocks. After tightening the straps of your PFD and
rechecking the security of the anchor rode on its cleat, you contact the
local towing service on channel 16 and nervously wait for help. Although
it may be the farthest thing from your mind at the moment, when it’s all
over will you end up paying for a tow or be presented with a much higher
salvage bill? From a legal standpoint, the answer is not etched in
stone. Because of a fortunate lack of first-hand experience, most boat
owners are blissfully unaware of the laws that regulate such events.
Those who subscribe to a towing service, like Sea Tow or TowBoatU.S.,
contentedly assume that they don’t have to worry about such things since
they’re “covered.” Others take comfort in the knowledge that their boat
insurance policy provides reimbursement for towing expenses. And most —
if they consider it at all — think “salvage” only applies to spectacular
wrecks and commercial vessels.
Think again. It would be convenient if the difference between towing and
salvage could be determined by a simple set of cut-and-dried rules, but
it cannot. In fact, many of the day-to-day services provided by towboat
operators could rightfully be construed as salvage under maritime law.
Let’s look at the details.
Salvage
The legal definition of salvage is saving a boat or its cargo to
preserve some or all of its value. To stand up in court, the act of
salvaging has to pass three tests:
1. The boat has to be in peril.
2. The salvage effort has to be voluntary (more on that later).
3. The project has to be successful in whole or in part.
It doesn’t take much out of the ordinary to put a boat in danger. Being
dead in the water, drifting toward some peril, taking on water,
suffering a fuel leak or simply being lost in fog can reasonably qualify
as endangering the boat. And the danger doesn’t always have to be
immediate or imminent. If a logical expectation of future peril can be
shown, then the rules of salvage can apply.
A salvage effort is considered voluntary when the salvor has no contract
or obligation to participate. On the other hand, the owner of a boat or
the captain and members of a paid crew are assumed to have a contractual
obligation to do whatever is within their means to save the boat and its
cargo and preserve its value. As such, their efforts are not voluntary,
and they can make no claims to be compensated for their efforts,
successful or not.The effort is considered to be successful only if some
portion of the boat and cargo value is preserved and retrieved. If the
salvor irreparably damages or sinks the boat while trying to save it, he
or she is out of luck. “No cure, no pay” is the common phrase used by
people in the business, according to Nicholas Walsh, an attorney who
practices admiralty law in Portland, Maine.
A common misconception is that salvaging a boat means that the salvor
then owns it. The salvor has a right to place a lien on the boat to
ensure that the salvage award will be paid, but he or she doesn’t gain
title to the boat. Another surprise is the size of some awards, which
often seem excessive at first glance. Walsh cites a case where a boat
worth $300,000 was pulled off the rocks after suffering only $5,000 in
damage, and the salvor was awarded $25,000 for just three hours of work.
He explains that the courts have long recognized that salvors play a
vital maritime role that should be encouraged and rewarded, so the
expense of acquiring the expertise and maintaining the equipment that
makes salvage possible must be considered when granting awards.
Towing
Tow boat operators generally consider their standard assistance
offering or “covered service” to be disentangling props, delivering fuel
if you’ve run out, jump-starting a dead battery, towing you back to your
launch point or a repair facility in the case of a mechanical
malfunction, and refloating your boat in the case of a soft grounding.
Soft grounding is ambiguous and can be interpreted on a case-by-case
basis, but in general it means a situation where minimal effort — a
little extra pulling power, for example — is required to refloat your
boat in a low-water condition. If your boat is high and dry on shore or
teetering on a rock pile, you are beyond the definition of towing and
firmly in the realm of salvage.Sea Tow, for example, has a specific set
of six guidelines that are used to decide whether a grounding is a
covered service or a salvage operation, according to vice president of
operations Capt. Joseph Frohnhoefer III. For a covered service the
vessel must be:
1. in a safe, stable position
2. surrounded by water
3. not in the surf or the surf line
4. showing some movement (rocking, etc.)
5. able to be refloated by one towboat in 15 minutes or less
6. able to proceed under its own power after being refloated
If any one of these conditions isn’t met, it becomes a salvage
operation. In that event Sea Tow franchisees are strongly encouraged “to
inform the boater, whenever conditions are possible, if the service is
going to be a salvage before they begin working,” says Frohnhoefer.
“[But] in many cases,” he continues, “the events happen too fast for the
towboat captain and the owner to discuss or agree on a fee for the
salvage in advance.”BoatU.S. defines towing/ungrounding as any operation
not involving imminent peril to the boat or to a legally protected
marine environment, and one that requires just one tow vessel with lines
attached to a grounded or disabled boat to refloat or tow it, according
to Jerry Cardarelli, vice president of BoatU.S. Towing Services.He says
an operation would be considered salvage/ungrounding when there is
imminent peril to the boat or to a legally protected marine environment,
or risk to the salvage company. A salvage operation requires successful
rescue of a boat that is hard aground on rocks, coral or other material
that could significantly damage the hull; that is aground on a shoreline
exposed to hazards such as breaking surf, submerged or partially
submerged rocks, strong onshore winds (19 mph or greater) and may
require the use of swimmers exposed to these hazards; that is on land
(as in a hurricane or major catastrophe) where special equipment must be
used (cranes, barges, dredging equipment, etc.); or where multiple
vessels are required to tow the boat and refloat it at high tide.
Cardarelli says salvage may include an emergency plug or patch or
pumping to stop significant water intrusion or to provide structural
support; dewatering a vessel that is completely sunk or swamped;
attachment of lift bags to raise or keep a vessel afloat or to secure it
against rocks or other damaging surfaces; or rescue of an unmanned
vessel in danger of grounding, collision or other imminent peril.If
possible, BoatU.S. will inform the skipper before beginning any work if
the operation is salvage, according to Cardarelli. However, if this
isn’t possible due to conditions or the fact that the boater isn’t
present, the tower will tell the skipper as soon as possible, he
says.Keep in mind that almost all towboat operators are independent
franchisees of the larger towing services but are not controlled by
them, so they are relatively free to establish their own terms and
practices.When there is time for a discussion, Sea Tow, like many towing
services, endorses the use of the standard U.S. Open Form Salvage
Agreement (MARSALV), which allows the parties to agree up front on
costs, payment issues and arbitration procedures in the event of a later
disagreement.
A common cause of confusion in the salvage vs. tow conundrum is that
almost any of the reasons you call a towboat for assistance can be
construed to mean that the boat is in some degree of peril and qualifies
for salvage. And the towboat operator is under no obligation to take on
the job, so his or her participation is voluntary by definition. And
it’s successful. The operator either remedies your problem and sends you
on your way, or tows you back to safety. Are you going to have to pay a
salvage claim? Probably not. And not because the towboat operator isn’t
legally entitled to lodge a salvage claim.Attorney Walsh offers a
succinct example. “If a boat is drifting in the harbor and you put a
line on it, has it been salvaged? Yes. Are you going to get much of an
award? No,” he says. “There’s no immediate peril [to the boat owner,
and] the boat wasn’t in significant peril.”The reason towboat operators
won’t lodge claims for salvage in such situations is purely economic in
nature. Contested salvage claims end up in arbitration or in court,
where salvage fees are set and awarded based on longstanding precedents
in admiralty law. The validity and the dollar amount of a salvage award
is determined by a wide range of factors, including how much danger was
involved, the risk to the salvor, the value of the property involved and
saved, and the salvor’s cost to do the job.
The relatively ordinary task of getting you on your way or towing you
back to safety may legally qualify for salvage, but in reality it
wouldn’t get far in court. Towboat operators are better off accepting
the normal towing fee, because it’s probably more than their lawyer
could win in court, and they have their reputations in the boating
community to consider as well.
Your role
There are several ways to help protect yourself and prevent unwelcome
surprises when towing is concerned. If you find yourself in a potential
salvage situation, always ask the towboat operator to define the task as
soon as he or she arrives on scene. Is it just a tow? If it’s something
more, be sure you know what he intends to do, all of the terms and
conditions under which the job will be done, how the cost will be
determined and what the terms of payment will be.
You also should be thoroughly familiar with the amount and limitations
of your towing insurance coverage long before you run into a problem.
Some subscription towing services may offer several levels of
reimbursement. If you regularly venture offshore, you should make sure
your limits are high enough to cover the longer two-way trip that a
service call might require. Call a local towing operator to get an idea
of the towing charges in your area. Check to see how much towing
coverage is included in your boat insurance policy. If it is
substantial, it could allow you to reduce the amount of subscription
coverage you sign up for, or provide a cushion for extraordinary
situations. If you have questions or need advice, talk to the agent who
sold you the policy.Cardarelli says BoatU.S. recommends that boaters
determine if their hull insurance policy will pay for a salvage, wreck
removal and environmental damage protection with no deductible and
without limiting payment to only a small percentage of the insured value
of the boat. That fine print is important, and many boaters overlook it
when buying insurance, he says.
Although it’s not just a towing or salvage issue, Walsh also brings up a
point many boat owners might not normally think about: the need to avoid
putting yourself “outside of coverage.” If you operate your vessel at a
time of year when it is supposed to be out of the water, or navigate in
waters beyond where you are covered geographically, your insurance
company can deny coverage under any provision of the policy. Those
limitations, and any others, will be clearly spelled out in the
policy.There are precious few silver linings in emergencies, but it
might be some comfort to know that in the event you find yourself in a
genuine salvage situation, most marine insurance companies are happy to
cover the cost of salvage, since it saves the expense of reimbursing you
for an even greater — or total — loss of the boat. If you properly
maintain your boat, practice good seamanship and enjoy a bit of good
luck, you might never go through the experience. But you should at least
know what to look for and expect
