T&T: ART Roll reduction

[Dave Cooper]

<Ron wrote in part: Can you explain how the ART is different than this
example? I'm sure that it is.>

Absolutely no different. If you have a boat that doesn't have the stability
or would fail the normal inclination tests required for it's service area
then it will roll over even quicker with additional weight above the roll/
meta center.

Any boat that has paravanes is subject to the same issue. The weight of the
gear must not put the stability of the boat in danger. In fact if you
operate in icing areas then the weight of the gear plus the ice must be
accounted for. This is seldom done by any NA's.

In fact the development of ART was a direct result of the icing of the
paravanes on fishing fleet of Newfoundland and other Canadian waters by the
Marine Institute in St John's Newfoundland. The govt provided them a grant
for this research. We have just piggy backed on this.

So if you take an existing hull that has low numbers and add gear of any
type above the meta center then you have decreased the stability. It doesn't
matter what it is. Dinghy, cases of beer, people or an ART. You are inviting
trouble.

Any vessel that has cross connected tanks is in trouble if its stability
tests didn't take this into consideration. I'd give the NA an "F" on his
design for this little "oversight".

OTOH, if the design or the testing of a vessel shows it has adequate reserve
stability when all the possible weights are stacked on one side then he'd
get an "A".

Because of ART's design it doesn't conform to the normal free surface effect
unless you produce a constant heal as I had indicated. The usual dynamic of
the water that the boat sits in provides the energy for it to work.

Again the vessel must have the stability to accommodate an ART just as any
other added weight.

Using the saddle tank example you used and applying it to Swan Song.

Our saddle tanks are 500 gal each if we fill one and then the other we'd go
thru the worst case of your example. 500 gal on one side is ~3750 lbs. this
will produce a heel of about 4-5 degrees which is enough to cause the roll
tank to stack adding 1500 lbs to the low side. This is enough to produce 5-7
degrees of heel. We did this yesterday while fueling at the dock. Fill one
side then the other. No big thing for Swan Song...again it has plenty of
reserve stability.

Doing this on many boats would produce exactly the condition you describe.
Excessive heel; which will increase the danger of additional down flooding
if any vents/opening are submerged etc. Many things contribute to this
including a shifting load. Check the container ships that lose them on one
side an have extreme issues maintaining acceptable trim until they flood
compartments to trim the boats.
The car carrier last year that lost trim is another one.

I use to run day cruise boats up to 3000 passengers and always tried to
avoid anyone of the crew making announcements that would cause the
passengers to go to one side. The old Nantucket Ferry often would have one
screw flailing the air as they backed into Nantucket when they were full
with a bit of North wind and all the fares standing on the starboard side.
Very scary.


So to summarize:
1. The design of the boat and its stability determines whether it is a good
candidate for an ART or not.

2. Any NA could produce a ground up design that would accommodate an ART. A
telephone cal/email to Professor Donald Bass would get them started.

3. The boat buying public really isn't aware of ART so doesn't ask for it
from the NA.

4. Few NA's really are breaking new ground in actual designs for roll
reduction but trying to meet the customers requirements in order to stay in
business.

5. Roll reduction devices are generally considered "add ons" by most NA's
and thereby outside the normal design requirements.

Both Bob Phillips and I were fortunate to have boat designs that met the
basic requirements for an ART. I'm sure there are many more out there that
already meet them. Not as many however as don't meet them I suspect.

A simple test would be to ask 10000 lbs of people to stand on the gunnels of
your boat. If it heels slightly aka perhaps less than 15 degrees you may be
a candidate. If they get their feet wet you're not and if they need life
jackets keep that puppy in protected waters ;-)

Hope this helps explain it.

As always YMMV....
Dave & Nancy
Swan Song
Roughwater 58
Hawaii Passage '08/09