Roll Stabilization Tanks
 

Anyone here have any experience with roll stabilization tanks -
designing, building, tuning, etc. ?

I'm talking about passive roll stabilization using port and starboard
water tanks connected by a "slosh" tunnel. If sized properly the
water sloshing between the tanks will be out of phase with the roll
period and dampen the motion, even at anchor.

Roll Stabilization Tanks
 

Wayne.B wrote:
Anyone here have any experience with roll stabilization tanks -
designing, building, tuning, etc. ?

I'm talking about passive roll stabilization using port and starboard
water tanks connected by a "slosh" tunnel. If sized properly the
water sloshing between the tanks will be out of phase with the roll
period and dampen the motion, even at anchor.

The "slosh" tunnel would need to be as big as the tanks, diameter-wise, and
a huge amount of water would be needed to have any effect whatsoever. If you
don't believe me. take an overweight friend sailing and get him to lose
weight by leaping from side to side in phase with the roll, always moving to
the "up" side. He/she would need to weigh in at around 500lbs if you can
find such a person.

If this system worked the QM2 would use it instead of spending $millions on
stabilisiers.

DP

Roll Stabilization Tanks
 

On Sun, 30 Dec 2007 09:41:10 GMT, "Dennis Pogson"
wrote:

Wayne.B wrote:
Anyone here have any experience with roll stabilization tanks -
designing, building, tuning, etc. ?

Undoubtedly not.

I'm talking about passive roll stabilization using port and starboard
water tanks connected by a "slosh" tunnel. If sized properly the
water sloshing between the tanks will be out of phase with the roll
period and dampen the motion, even at anchor.

Yes, this has been known to work, at least somewhat.

The "slosh" tunnel would need to be as big as the tanks, diameter-wise, and

Absolutely not.

a huge amount of water would be needed to have any effect whatsoever.

It does take fairly large tanks, the one big drawback to the idea.

If you
don't believe me. take an overweight friend sailing and get him to lose
weight by leaping from side to side in phase with the roll, always moving to
the "up" side. He/she would need to weigh in at around 500lbs if you can
find such a person.

I can't find a way to comment on that utter nonsense.

If this system worked the QM2 would use it instead of spending $millions on
stabilisiers.

What they have is better and they use it. This does not mean that an
arrangement of tanks cannot work at all.

Casady

DP

Roll Stabilization Tanks
 

Richard Casady wrote:
On Sun, 30 Dec 2007 09:41:10 GMT, "Dennis Pogson"
wrote:


Wayne.B wrote:

Anyone here have any experience with roll stabilization tanks -
designing, building, tuning, etc. ?


Undoubtedly not.


I'm talking about passive roll stabilization using port and starboard
water tanks connected by a "slosh" tunnel. If sized properly the
water sloshing between the tanks will be out of phase with the roll
period and dampen the motion, even at anchor.


Yes, this has been known to work, at least somewhat.

The "slosh" tunnel would need to be as big as the tanks, diameter-wise, and


Absolutely not.


a huge amount of water would be needed to have any effect whatsoever.


It does take fairly large tanks, the one big drawback to the idea.


If you
don't believe me. take an overweight friend sailing and get him to lose
weight by leaping from side to side in phase with the roll, always moving to
the "up" side. He/she would need to weigh in at around 500lbs if you can
find such a person.


I can't find a way to comment on that utter nonsense.

If this system worked the QM2 would use it instead of spending $millions on
stabilisiers.


What they have is better and they use it. This does not mean that an
arrangement of tanks cannot work at all.

Casady

DP




I doubt it will work passively.
Control of the phase is most important - and won't coincide with the
roll.

Think great big powerful pumps?

Roll Stabilization Tanks
 

On Sun, 30 Dec 2007 00:20:52 -0500, Wayne.B
wrote:

Anyone here have any experience with roll stabilization tanks -
designing, building, tuning, etc. ?

I'm talking about passive roll stabilization using port and starboard
water tanks connected by a "slosh" tunnel. If sized properly the
water sloshing between the tanks will be out of phase with the roll
period and dampen the motion, even at anchor.

I thinks its about the same principle as skyscraper passive sway
stabilizers. A moveable mass tuned to the same period as the sway
(roll) frequency, that moves out of phase with the sway or roll,
damping it. Come to think of it, there's the pendulum crankshaft
damper used in light aero engines to damp torsional vibrations - an
engine killer.

Brian Whatcott Altus OK

Roll Stabilization Tanks
 

In article , Richard Casady wrote:
On Sun, 30 Dec 2007 09:41:10 GMT, "Dennis Pogson"
wrote:

[snip]

If this system worked the QM2 would use it instead of spending $millions on
stabilisiers.

What they have is better and they use it. This does not mean that an
arrangement of tanks cannot work at all.

Surely the water wouldn't slosh until the boat started to heel, and then
it would slosh to the lower side aggravating the situation rather than
helping it. Then, as the wave passed, and the boat was prepared to
return to upright, the water would be slow to slosh back 'up-hill' - it
would counter the mass of the keel. Wouldn't that possibly put a boat at
a potentially bad angle to the next wave?

Justin.

--
Justin C, by the sea.

Roll Stabilization Tanks
 

In article , Roger Long wrote:
[snip]

The last ones I was involved with were on a fleet of longliners. The tanks
were tuned by adjusting the level and designed to be about 20% full. After
the vessels were in operation, they were found full to the top on all of the
vessels and they were damn near about to capsize in some loading conditions.
The less stability a vessel has, the slower the roll. The slowest roll
possible is to just lay over and stay there. The captains found that the
boat just got more and more comfortable and rolled slower and slower as they
filled the tanks. They didn't understand the dynamic and the peril they
were exposing themselves to.

Sounds like the principle that makes a metronome work as it does. With
the weight low, the beat/tick is more frequent, the low COG righting
itself almost immediately it moves away from upright. Conversely, with
the weight high up, the beat/tick is much less frequent, but the
momentum of the 'roll' carries a long way passed upright before forces
kick in to bring it back upright.

I agree, it certainly doesn't sound like something you'd want to
over-use on a boat.

Justin.

--
Justin C, by the sea.

Roll Stabilization Tanks
 

Wayne.B wrote in
:

Anyone here have any experience with roll stabilization tanks -
designing, building, tuning, etc. ?

I'm talking about passive roll stabilization using port and starboard
water tanks connected by a "slosh" tunnel. If sized properly the
water sloshing between the tanks will be out of phase with the roll
period and dampen the motion, even at anchor.

Basically what you're talking about are "Flume" Stabilizers.
John J. McMullen (the company) was at one time the principal designer.
You might try going to them to see if they are still using them and if
there have been any advances.
No pumps are needed, other than for filling and installation; high up is
generally better for better results; you generally need to be aware of
stability (waddahey, you're basically making "free surface" work for you in
a positive way; the system works the same at all speeds, but EG you have
to roll for the system to work (sometimes that first roll can be a
doozy)..... etc.

otn

Roll Stabilization Tanks
 

On Dec 30, 4:37 am, "Roger Long" wrote:
....
The required size is a function of the vessel's stability so, if you have a
vessel with the stability I hope you have, the tanks will be huge ...

Unlike Roger, I'm not a naval architect and I don't have any
experience with this. Still, I suppose a boat with low initial
stability but with adequate stability at high angles might benefit
from smaller tanks. I can imagine a case where a ballasted sailboat
has been converted to a pure motor boat where even a few hundred
pounds of ballast in anti-roll tanks might make the boat at least as
comfortable as it was before the mast was removed. On paper, anti-
roll tanks seem like a reasonable alternative for some types of slow
speed vessels that require additional stabilization and that are
operating in somewhat protected waters. The costs are noise, weight,
difficulty of installation, reduced stability and a limited range of
effectiveness. There was a good article discussing active and passive
stability devices on smaller vessels in Professional Boat Builder in
'04.

-- Tom.

Roll Stabilization Tanks
 

otnmbrd wrote:
Wayne.B wrote in
:

Anyone here have any experience with roll stabilization tanks -
designing, building, tuning, etc. ?

I'm talking about passive roll stabilization using port and starboard
water tanks connected by a "slosh" tunnel. If sized properly the
water sloshing between the tanks will be out of phase with the roll
period and dampen the motion, even at anchor.

Basically what you're talking about are "Flume" Stabilizers.
John J. McMullen (the company) was at one time the principal designer.
You might try going to them to see if they are still using them and if
there have been any advances.
No pumps are needed, other than for filling and installation; high
up is generally better for better results; you generally need to be
aware of stability (waddahey, you're basically making "free surface"
work for you in a positive way; the system works the same at all
speeds, but EG you have to roll for the system to work (sometimes
that first roll can be a doozy)..... etc.

otn

Googling for "water ballasted yachts" brings up a whole plethora of stuff,
including forum discussions. The consensus seems to be that the roll period
is too short to move a volume of water that would make any difference to
lateral stability, and pumping requires a huge amount of energy.

The pendulum-like swinging bulb keels fitted to the Open 60 and other
derivatives seem to provide much more resistance to heeling than any water
ballast gadgetry, increasing the resistance to heeling by as much as 55%,
according to one guy. This, plus the double-rudder (fore and aft), and
massive dagger boards either side, seem to provide much more stability than
moving water around inside the hull.

This said, the all carbon fibre 140 foot super-maxi, Mari Cha IV, was
launched in August 2003, the yacht weighs just 50 tonnes, and has a canting
keel with a 10 ton bulb, which can be swung + / - 40 degrees; and a water
ballast system.

Since she did the west-to-east crossing of the north Atlantic in 6 days
shortly after her launch, maybe there IS something in this water ballasting
after all! Perhaps it stops Mari Chai 1V from taking off and becoming a
flying machine!

Dennis.

Roll Stabilization Tanks
 

On Sun, 30 Dec 2007 19:29:48 GMT, "Dennis Pogson"
wrote:

maybe there IS something in this water ballasting
after all! Perhaps it stops Mari Chai 1V from taking off and becoming a
flying machine!

Water ballasting and water roll stabilization are two different
things.

Our boat is a Grand Banks 49 trawler displacing in the neighborhood of
60,000 lbs dry, 70,000 loaded. It has a substantial flybridge deck
located about 12 feet above the waterline, and about 12 feet wide.
Since we have frequently had a dozen people up there with no obvious
ill effects, I'm assuming we could also get away with several thousand
pounds of water, especially at anchor. The boat already has dynamic
roll stabilizers which are quite effective underway but are expensive
to maintain.

I'm aware of at least one other boat in this size range that is
successfully using water stabilization. They had their system
designed by a Naval Architect which is no doubt the right way to go
for guaranteed results. I was more interested in cobbling up
something cheap and dirty for some informal testing of the concept on
our boat. Key variables are tank size, tunnel size/shape, and
gallons/pounds of water.

Any suggestions for a starting point?

Roll Stabilization Tanks
 

On Sun, 30 Dec 2007 18:01:09 -0500, "Roger Long"
wrote:

Any suggestions for a starting point?

Yes, start by deciding whether you are willing to invest a lot in
construction and additional weight with it's attendant increase in fuel
consumption to make things just a little better. If it's worth it just to
reduce motion by 10 - 15 percent, you can probably do something.

Thanks, some interesting points there. Weight could largely turn out
to be a non-issue if used only at anchor or as a backup to the dynamic
stabilizer system (Naiads). It would be easy enough to pump some salt
water up into the tanks when I wanted to use them, and drain it back
out afterwards.

I was thinking of buying a couple of fiberglass dock boxes from West
Marine and cross connecting them with PVC pipes. The system could be
tuned by restricting flow or adding additional pipes. I have no idea
how to calculate optimal starting pipe size(s) however.

Just for the sake of argument, lets assume 400 total gallons and a
natural roll period of about 3 seconds. Given a 5 degree roll, most
of that water would have to flow to the downhill tank in about 1.5
seconds if I'm conceptualizing this correctly.

Roll Stabilization Tanks
 

"Roger Long" wrote in
:

"Wayne.B" wrote

Any suggestions for a starting point?

Yes, start by deciding whether you are willing to invest a lot in
construction and additional weight with it's attendant increase in
fuel consumption to make things just a little better. If it's worth
it just to reduce motion by 10 - 15 percent, you can probably do
something. Most people who are bothered by motion will still think
there is nearly as much rolling as there was before. If you want to
do something significant, it will need to be huge.

The tanks in the project I was involved with were a dodge around the
MacMullen patents. They were simply rectangular boxes and worked on
the principle that the shallow wave of water rolling from one end to
the other would break, retarding it's speed. Speed was adjusted to
tune to the vessel's natural rolling period by adjusting water depth.

In the MacMullen tanks, the speed of water is regulated by either an
hourglass shape or sometimes by two pipes installed vertically at the
middle to restrict the flow. Tuning is fixed at the construction
phase requiring careful calculations.

You could build the largest tank you think the boat can handle with a
removable panel in the middle of the top. Install two pipes of 2 - 3
inches diameter between the bottom and the removable panel. Then make
larger spools of different diameters. Fill the tank half full and
then experiment by inserting different spool sizes until it seems to
work. If the MacMullen patents are still in force, they might have an
issue with this if you start selling them.

You could also just build a big rectangular tank and try different
lesser amounts of water as was done on the long liners.

Whatever you do, as you are experimenting, bear in mind that getting
the tuning such that is it in phase with the vessel's natural roll
period will increase the roll by as much as the tank is capable of
reducing it. Could be exciting. Even with properly tuned tanks, there
will occasionally be sea that creates a roll just in tune with the
tank so that the vessel will take a larger roll than it would have
without the tank.

--
Roger Long

Most "Flume" Tanks I remember were more on the lines of a "U" shape layed
on it's side (tankers being the exception). At one point they were
looking at a system for yachts which would be installed on the
"flybridge" built into the shape around the upper steering station....
this had the advantage of reducing the size due to the fact that the
higher the tank, the greater the righting moment.
I don't know if any of these were ever installed, but you would have
expected a reduction of @50% of ROLLING (note: rolling, not roll angles).
As Roger is saying, trying to design one of these systems without knowing
the basic formula's they used could lead to some catastrophic results.

One final point: If the system could have easily been designed and built
to work effectively with a minimum loss of space, ease and safety of use,
and maintenance, we'd probably see a bunch of them out there...... we
don't.

The smallest boats I remember these being put on were some buoy tenders
and Tuna Clippers (built into the ramp for the seine boat on the stern)

Roll Stabilization Tanks
 

On Sun, 30 Dec 2007 20:28:13 -0500, Wayne.B
wrote:


I was thinking of buying a couple of fiberglass dock boxes from West
Marine and cross connecting them with PVC pipes. The system could be
tuned by restricting flow or adding additional pipes. I have no idea
how to calculate optimal starting pipe size(s) however.

Just for the sake of argument, lets assume 400 total gallons and a
natural roll period of about 3 seconds. Given a 5 degree roll, most
of that water would have to flow to the downhill tank in about 1.5
seconds if I'm conceptualizing this correctly.

My first shot, off the top: two 30 in diam smooth pipes

Brian W

Roll Stabilization Tanks
 

On Sun, 30 Dec 2007 20:53:17 -0600, Brian Whatcott
wrote:

Just for the sake of argument, lets assume 400 total gallons and a
natural roll period of about 3 seconds. Given a 5 degree roll, most
of that water would have to flow to the downhill tank in about 1.5
seconds if I'm conceptualizing this correctly.



My first shot, off the top: two 30 in diam smooth pipes


That's much too big of course. Can you take us through your
calculations? It would take a large rectangular tunnel to achieve
that much cross sectional flow area without creating an unworkable
obstruction on the flybridge.

Roll Stabilization Tanks
 

On Mon, 31 Dec 2007 07:58:13 -0500, "Roger Long"
wrote:

The tanks I've seen have the restriction at the middle, be it two vertical
pipes or a necking down of the width, about half of the cross section area
of the tanks themselves so you would be talking about pretty big pipes. The
time it takes for water to get all the way from one side to the other is the
issue so, if you are using pipes which are longer and restrict flow more,
they would be even larger.

Your roll period sounds improbably short. If your boat has a typical
trawler hull form, you would have sold her and moved to Kansas after just a
couple of trips if the roll period is that short. I'm curious what it is
and it is fairly easy to check.

On a very calm morning, slack the lines and push the boat off the dock.
Step on and off the boat or push up and down on something. You will see her
move just a little bit. Get into the rhythm and get her rolling as hard as
you can. You can set up an impressive roll on even a 100 foot boat this
way. Let go and time as many rolls as you can with a stopwatch before the
rolling stops. Sight a landmark such as the top of a rail stanchion against
the background to identify the end of the roll. A complete roll is from one
side, over to the other, and all the way back. I suspect your roll period
is actually 6 seconds.


It is definitely not as high as 6 seconds. I did this excercise a
while ago and recall that the actual number was between 3 and 4,
possibly closer to 4 but I don't remember the exact value.

4 seconds is a good roll period for a highly damped hull form such as the
Kingsbury with a flat beamy hull. When checking the roll period, the boat
will roll just once and pretty much flop back upright. There is no
carryover of motion.

That closely describes our boat, perhaps as a result of the full keel
and hard chines. There is some carry over of motion in flat water but
the amplitude is small and damps down quickly.

The roll period matches the period of waves found in
lighter winds. Resonant rolling is thus small in magnitude. When the waves
get big, the boat is no longer in tune and there is little rolling. The
number of times a hull rolls after you let it go during the roll test is a
measure of the amount of damping.


The biggest "rolling at anchor" isue we have ever had was in Bar
Harbor, Maine. At high tide the ocean swells surge over the
breakwater and really get things going. You also have the "Big Cat"
fast ferry coming in at night from Nova Scotia leaving a powerful
wake, not to mention the 40 ft lobster boats barreling in and out at
all hours.

6 - 8 seconds causes the boats natural period to match that of waves
typically experienced on the days when you decide to head for port or more
protected water. If the hull form isn't well damped, rolling can be heavy.
The stability the produces roll periods in this range will usually not have
a lot of inherent damping due to narrower beam and more rounded sections.
This is why your trawler needs those dynamic roll stabilizers.

An 8 - 10 second roll period means your boat could well be dangerous and
should have a full stability analysis, especially if freeboard is low.

It sounds like your issues are primarily at anchor. Before tanks, I would
try this.

Cut a sheet of 3/4 inch plywood into two of the largest equilateral
triangles you can. Drill holes in the corners and make a rope bridle so
they can be suspended flat by a length of rope about 50% longer than your
draft and freeboard combined. Weight the sheets so that they sink.

Yes, the old flopper stopper trick. I built a set for our old boat
and they were quite effective. On the Grand Banks they appear to be
undersized however, with 3x the displacement. Equilateral stoppers,
more than 4 ft on a side, would be quite bulky to stow and deploy.
I'll have to think about it. One trick that I did get some success
with was to leave the inflatable RIB dinghy over the side, half
suspended from the cargo boom. It allowed the boat to roll easily
towards the dinghy but provided 300 lbs of resistance going back the
other way. You could hear the dinghy splashing around at night
however so it was not a big hit with the admiral, and probably tough
on the mast rigging over the long term.

The
weights can be removable to facilitate storage. Concentrate the weight
towards one corner so that, when the sheets sink, the side away from the
weight is nearly floating. Hang these over the side made fast to your
midsheet cleats. When the boat rolls towards one of the paravanes, the
weight will pull it down edgewise and it will sink quickly. The other will
be pulled up flat with great water resistance. These will probably do a
better and quieter job at anchor than a tank.

On our old boat they provided about 50% damping which was a noticable
improvement from its deep-V "snap roll" characteristic.

Roll Stabilization Tanks
 

On Sun, 30 Dec 2007 23:53:18 -0500, Wayne.B
wrote:

On Sun, 30 Dec 2007 20:53:17 -0600, Brian Whatcott
wrote:

Just for the sake of argument, lets assume 400 total gallons and a
natural roll period of about 3 seconds. Given a 5 degree roll, most
of that water would have to flow to the downhill tank in about 1.5
seconds if I'm conceptualizing this correctly.



My first shot, off the top: two 30 in diam smooth pipes


That's much too big of course. Can you take us through your
calculations? It would take a large rectangular tunnel to achieve
that much cross sectional flow area without creating an unworkable
obstruction on the flybridge.

I looked up a table of flow rates for smooth pipes of various
diameters on Google and scaled to a flow rate of 12000 gal/min

Brian W

Roll Stabilization Tanks
 

On Mon, 31 Dec 2007 10:36:35 -0500, Wayne.B
wrote:


Yes, the old flopper stopper trick. I built a set for our old boat
and they were quite effective. On the Grand Banks they appear to be
undersized however, with 3x the displacement. Equilateral stoppers,
more than 4 ft on a side, would be quite bulky to stow and deploy.
I'll have to think about it. One trick that I did get some success
with was to leave the inflatable RIB dinghy over the side, half
suspended from the cargo boom. It allowed the boat to roll easily
towards the dinghy but provided 300 lbs of resistance going back the
other way. You could hear the dinghy splashing around at night
however so it was not a big hit with the admiral, and probably tough
on the mast rigging over the long term.

Since I began reading about "roll dampeners" I've wondered about the
stress on attachment points. Read a few accounts of flopper stoppers
breaking their cables, and it seems the forces are significant.
How do you judge what's too much stress for these setups?
Since cats are resistant to rolling I've pondered whether extendable
amas on strong poles - don't know what material - might be a solution.
Storage, cosmetics, and ease of deployment might be the big issues
with this, but less so on a bigger boat like yours than a smaller
boat. There are some interesting engineering questions about
flexibility of the poles, attachment points, ama buoyancy, etc, which
might be fun to work out. Sometimes I wish I were an engineer,
but I don't even do algebra. Still fun to Rube Goldberg it.

--Vic