Roll Stabilization Tanks

"Roger Long" <strider.DeleteThis@maine.rr.com> wrote in
news:4778232b$0$24307$4c368faf@roadrunner.com:

> "Wayne.B" <waynebatrecdotboats.DeleteThis@hotmail.com> 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)
 >> Stay informed about: Roll Stabilization Tanks 

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.

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. 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.

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. 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 you
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.

--
Roger Long
 >> Stay informed about: Roll Stabilization Tanks 

Peggie Hall wrote:
> Roger Long wrote:
>> "Richard Casady" <richardcasady.DeleteThis@earthlink.net> wrote
>>
>>>>> Anyone here have any experience with roll stabilization tanks -
>>>>> designing, building, tuning, etc. ?
>>> Undoubtedly not.
>>
>> Actually, Yes.
>
> Roger, how does this differ from water ballasted sailboats (not that I
> completely understand how THAT works either)?
>
Peggy,

Water ballast these days most commonly comes in two types:

Straight ballast (ala McGregor) most often used in small boats to
replace solid fixed ballast - like lead. This is a single tank in the
bottom of the boat that has to be filled nearly full to prevent the
effects that the free surface would cause.

Active ballast systems are used on many of the Vende Globe around the
world boats but not that others in a normal sailor's world. These have
two tanks and the high tank is dumped into the low tank just before
coming about (so it will be on the new high side). This makes for some
interesting times. Most have powered pumps to move the ballast water,
but these are much slower and use valuable power. Movable water
ballast is allowed under the current racing rules, but there are also
knockdown recovery rules that make active water ballast problematic.

I will leave this discussion here unless someone really wants to know a
great deal more.

Matt Colie
 >> Stay informed about: Roll Stabilization Tanks 

On Mon, 31 Dec 2007 07:58:13 -0500, "Roger Long"
<strider RemoveThis @maine.rr.com> 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.
 >> Stay informed about: Roll Stabilization Tanks 

On Sun, 30 Dec 2007 23:53:18 -0500, Wayne.B
<waynebatrecdotboats.RemoveThis@hotmail.com> wrote:

>On Sun, 30 Dec 2007 20:53:17 -0600, Brian Whatcott
><betwys1.RemoveThis@sbcglobal.net> 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
 >> Stay informed about: Roll Stabilization Tanks 

On Mon, 31 Dec 2007 10:36:35 -0500, Wayne.B
<waynebatrecdotboats.RemoveThis@hotmail.com> 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
 >> Stay informed about: Roll Stabilization Tanks 

Thanks, Matt!

Peggie

Matt Colie wrote:
>> Roger, how does this differ from water ballasted sailboats (not that I
>> completely understand how THAT works either)?
>>
> Peggy,
>
> Water ballast these days most commonly comes in two types:
>
> Straight ballast (ala McGregor) most often used in small boats to
> replace solid fixed ballast - like lead. This is a single tank in the
> bottom of the boat that has to be filled nearly full to prevent the
> effects that the free surface would cause.
>
> Active ballast systems are used on many of the Vende Globe around the
> world boats but not that others in a normal sailor's world. These have
> two tanks and the high tank is dumped into the low tank just before
> coming about (so it will be on the new high side). This makes for some
> interesting times. Most have powered pumps to move the ballast water,
> but these are much slower and use valuable power. Movable water
> ballast is allowed under the current racing rules, but there are also
> knockdown recovery rules that make active water ballast problematic.
>
> I will leave this discussion here unless someone really wants to know a
> great deal more.
>
> Matt Colie


--
Peggie
----------
Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"
http://shop.sailboatowners.com/boat_odors/
 >> Stay informed about: Roll Stabilization Tanks