Sea Otter Ballast

[Tom and Bex]

Here's a simple test;

 

start filling your boat with water.

 

It will get lower in the water, it's called sinking.

 

ballasting with water is exactly the same (except the idea is to stop before sinking)

 

I cannot believe that otherwise intelligent-seeming people can be arguing about this.

 

(that's my Meldrew moment for the day)

Yes but if you could then cut the bottom off and weld it back at the height of the water you would have less space inside but the boat would still sit at the same place in the water.

 

What I'm trying to say but obviously not very clearly is if you add say a 6" tank along the base of your boat and fill it with water then the boat is 6" lower in the water (lets ignore the weight of steel/aluminium for now) but the 6" lower is purely down to the 6" extra depth that is filled with water and the waterline would still be the same. I see how it works by adding stability but my understanding of ballast is that it is to add extra weight to the boat to make it more stable and lower down in the water but the sea otter ballast tanks seem to just be stability tanks and would have no effect on the how the boat sits in the water if they are there filled with water or not there at all.

 

Tom

[jelunga]

No - I am not buying the submarine explanation. A submarine's ballast tanks are INSIDE the hull and the only time they are exposed to the outside is when the are flooded or emptied. The Sea Otter ballast tank is permanently exposed to the outside and therefore can never be considered to be inside the hull. If it is not inside the hull it cannot contribute to the boat's density.

 

Because the Sea Otter tank is PERMANENTLY EXTERNAL to the hull it's contents cannot make any contribution to the overall density of the boat. When the boat is in the water the tank is permanently flooded, thus debunking the submarine explanation.

 

 

If a Sea Otter were to heel over at a frightening angle thus lifting the ballast tank clear of the water then for a few seconds before the tank begins to drain the tank will have a ballasting effect - but that is extreme and unlikely!

 

 

Sorry, you are wrong about sub ballast tanks. These are outside the pressure hull,nd when empty give buoyancy to the boat. To submerge they are filled with water to the required level, the submarine loses buoyancy and gains weight and sinks.

 

 

I do not know the seat otter system, but from the description given, it would act mainly as a stabilising ballast for rolling and pitching. If the tanksallow water to be partially restrained below the water level it will act as ballast.

[Grace and Favour]

That is not making sense for me - if you put water INSIDE the hull then yes, the density of the boat will increase and the boat will sit lower in the water. But the Sea Otter has a flood-able chamber OUTSIDE the hull. That chamber never provided any buoyancy to begin with.

 

If you hang lead weights off the bottom of the hull that will lower it in the water, but if you hang a 1500kg AIR WEIGHT of water off the bottom of the hull it will have no effect - because 1500kg air weight water weighs nothing when it is in water. It seems to me that the only ballast added is the weight of the chamber structure, because aluminium does weigh something in water - but not a lot!

 

If water in water was weightless - - it would rise to the surface - and float away skywards, together with any air that may be present

[Guest]

Yes but if you could then cut the bottom off and weld it back at the height of the water you would have less space inside but the boat would still sit at the same place in the water.

 

What I'm trying to say but obviously not very clearly is if you add say a 6" tank along the base of your boat and fill it with water then the boat is 6" lower in the water (lets ignore the weight of steel/aluminium for now) but the 6" lower is purely down to the 6" extra depth that is filled with water and the waterline would still be the same. I see how it works by adding stability but my understanding of ballast is that it is to add extra weight to the boat to make it more stable and lower down in the water but the sea otter ballast tanks seem to just be stability tanks and would have no effect on the how the boat sits in the water if they are there filled with water or not there at all.

 

Tom

 

Has anybody stopped to think that it actually works and that is why Sea Otter employ the system.....

Edited August 1, 2012 by The Dog House

[Bat & Frog]

Just out of interest, is it possible to get to the inside of the water ballast tank to black it etc? If not, isn't it more suseptable to rust and corrosion?

 

I believe sea otters are aluminium so rust not a problem and once surface corrosion has formed its fairly stable (unless of course you fill the ballast tanks with air then it becomes unstable )

 

My understanding is that the water is not ballast as it weighs the same as water outside, but displacement material. This forces air from regions where not required and allows the boat to sit lower in the water allowing for better control and stability.

 

Oh 10 post since started writing, must learn to use 2 fingers !

Edited August 1, 2012 by Bat & Frog

[WJM]

Here is a test then - if a diver got under a floating Sea Otter and cut the ballast tank off the hull it would make (almost) no difference to the boat. The boat would not rise up in the water (ignoring the very minimal weight of the removed aluminium). That proves that the water has no weight when it is in water. So it cannot be described as ballast.

 

If water in water was weightless - - it would rise to the surface - and float away skywards, together with any air that may be present

 

 

Water in water is weightless, if you throw a glass of water in the river it neither sinks nor floats

 

- water in air is not.

 

Sorry, you are wrong about sub ballast tanks. These are outside the pressure hull,nd when empty give buoyancy to the boat. To submerge they are filled with water to the required level, the submarine loses buoyancy and gains weight and sinks.

 

 

I do not know the seat otter system, but from the description given, it would act mainly as a stabilising ballast for rolling and pitching. If the tanksallow water to be partially restrained below the water level it will act as ballast.

 

 

The Sea Otter tank is PERMANENTLY OPEN to the water - this is completely different from a submarine

Edited August 1, 2012 by WJM

[Grace and Favour]

Here is a test then - if a diver got under a floating Sea Otter and cut the ballast tank off the hull it would make (almost) no difference to the boat. The boat would not rise up in the water (ignoring the very minimal weight of the removed aluminium). That proves that the water has no weight when it is in water. So it cannot be described as ballast.

 

 

 

 

Water in water is weightless, if you throw a glass of water in the river it neither sinks nor floats

 

- water in air is not.

 

 

 

 

The Sea Otter tank is PERMANENTLY OPEN to the water - this is completely different from a submarine

 

A litre of water weighs 1Kg (at sea level) - it also weighs the same 1 foot lower than sea level in the sea- - that you may not have a method of weighing it makes no difference - it still weighs a kilo

Edited August 1, 2012 by Grace & Favour

[Chris Pink]

Yes but if you could then cut the bottom off and weld it back at the height of the water you would have less space inside but the boat would still sit at the same place in the water.

 

What I'm trying to say but obviously not very clearly is if you add say a 6" tank along the base of your boat and fill it with water then the boat is 6" lower in the water (lets ignore the weight of steel/aluminium for now) but the 6" lower is purely down to the 6" extra depth that is filled with water and the waterline would still be the same. I see how it works by adding stability but my understanding of ballast is that it is to add extra weight to the boat to make it more stable and lower down in the water but the sea otter ballast tanks seem to just be stability tanks and would have no effect on the how the boat sits in the water if they are there filled with water or not there at all.

 

Tom

 

But nobody cuts the bottom off a sea otter!!!

 

What is going on here? April 1st.

 

Instead of all that complicated "cut the bottom off", put a tank inside your boat (like the one the sea otter has), fill it with water and watch your boat go down in the water.

 

What on earth is so difficult to understand?

 

 

(incidentally you're wrong about your first statement, your boat would be lower in the water as it is displacing a lower volume of water)

 

 

 

..

Edited August 1, 2012 by Chris Pink

[Davidss]

I take some reassurance from the fact that understanding how a construction technique works is NOT a prerequisite of that construction technique giving the benefits the designer wanted.

 

Only one person needs to understand how a system works, the designer.

It doesn't stop working just because 3, 30, or 300 people don't understand how the system works.

 

Which is good news, because there are a lot of people who don't understand how an infernal combustion engine works, but without them we would all be knee deep, or higher, in horse shit.

 

I think this is one thread I'm going to ignore from now on :-)

[Chris Pink]

 

 

The Sea Otter tank is PERMANENTLY OPEN to the water - this is completely different from a submarine

 

Will you answer my initial question please;

 

If you cut a hole in your boat it will sink, ie it will be lower in the water. If you cut a hole in a sea otter it will be lower in the water (hang on you don't have to, they've already done it)

[WJM]

The tank on the Sea Otter is EXTERNAL TO THE BOAT - ie It is not inside the boat, it is outside, it is not contained within the hull, it is not part of the floatation, buoyancy, density. It is permanently isolated from the hull and it is permanently connected to the surrounding water. Therefore it cannot be ballast, can it? - ballast must be INSIDE the hull.

 

 

And Chris - there is no hole in a Sea Otter's hull - just a strange structure welded to the outside.

Edited August 1, 2012 by WJM

[Gibbo]

This thread is hilarious.

[Mac of Cygnet]

This thread is hilarious.

 

It's actually making me want to scream "No, no, NO!"

[Chris Pink]

The tank on the Sea Otter is EXTERNAL TO THE BOAT - ie It is not inside the boat, it is outside, it is not contained within the hull, it is not part of the floatation, buoyancy, density. It is permanently isolated from the hull and it is permanently connected to the surrounding water. Therefore it cannot be ballast, can it? - ballast must be INSIDE the hull.

 

 

And Chris - there is no hole in a Sea Otter's hull - just a strange structure welded to the outside.

 

Gosh. Not connected to the hull? Just follows the boat along like an obedient puppy?

 

Of course it's inside the hull - by definition. If you have a hole in your boat it will be "permanently connected to the surrounding water".

 

Go on, try it. Cut a hole in your hull. According to you your boat won't sink. You'll be fine.

 

 

 

..

Edited August 1, 2012 by Chris Pink

[DaveC]

Try this. Take the top off your weed hatch. Pour into the resulting hole a gallon or two of water (or a couple of hundred gallons if you like). Does the boat sit any deeper in the water?

 

Dave

[WJM]

This could run and run - but clearly many people are failing to see the complexity of the system. Many are seeing the Sea Otter's tank as no different to the regular domestic water tank. That tank is within the hull and that does have a ballasting effect. Those that see these two tanks as no different have no understanding of the topic.

[billS]

Here is a test then - if a diver got under a floating Sea Otter and cut the ballast tank off the hull it would make (almost) no difference to the boat. The boat would not rise up in the water (ignoring the very minimal weight of the removed aluminium). That proves that the water has no weight when it is in water. So it cannot be described as ballast.

 

 

Before the diver arrived, the hull had sufficient underwater profile for stability and steerage. After the diver has done his work, the cabin roof is the same height above the water, but you are blowing around like a leaf.

[Guest]

The tank on the Sea Otter is EXTERNAL TO THE BOAT - ie It is not inside the boat, it is outside, it is not contained within the hull, it is not part of the floatation, buoyancy, density. It is permanently isolated from the hull and it is permanently connected to the surrounding water. Therefore it cannot be ballast, can it? - ballast must be INSIDE the hull.

 

 

And Chris - there is no hole in a Sea Otter's hull - just a strange structure welded to the outside.

 

So you are either stupid or just a mickey taking troll...

 

which is it?

[Gibbo]

I'm amazed at how much confusion is being caused by such a simple matter.

[Mac of Cygnet]

This could run and run - but clearly many people are failing to see the complexity of the system. Many are seeing the Sea Otter's tank as no different to the regular domestic water tank. That tank is within the hull and that does have a ballasting effect. Those that see these two tanks as no different have no understanding of the topic.

 

Right. Let's say your regular domestic water tank is under the floor - it has a ballasting effect, as you say. Now connect the water tank to the outside of the boat through a skin fitting, thus placing it in contact with the water ouside. NOTHING WOULD CHANGE. The effect on the boat is just the same. The ballasting effect is just the same. That is how a Sea Otter works.

 

For God's sake!

[Guest]

I'm amazed at how much confusion is being caused by such a simple matter.

 

The intentionally confused will always be confused...

[bargemast]

If you watch the video in post#18, you see that it takes a long time for the water to empty out of this ballasttank, which means that the weight of the water in the tank added to the weight of the boat, so the boat will have more draft with the tank full than empty.

 

If the tank was a bottomless tank WJM's reasoning would be reasonable, which it isn't now.

 

Peter.

[bizzard]

Submarines are trimmed at periscope depth by juggling water around with pumps between their external trim water tanks which are separate from the huge external diving and surfacing main water ballast tanks.

[Nightwatch]

Is ballast and stability the same thing?

 

Does the water in a Sea Otter stability tank cause stability or make it sit deeper into the water which in turn causes the boat to be more stable?

 

 

Martyn

Edited August 1, 2012 by Nightwatch

[WJM]

Right. Let's say your regular domestic water tank is under the floor - it has a ballasting effect, as you say. Now connect the water tank to the outside of the boat through a skin fitting, thus placing it in contact with the water ouside. NOTHING WOULD CHANGE. The effect on the boat is just the same. The ballasting effect is just the same. That is how a Sea Otter works.

 

 

If the surface of the water tank is lower than the water line (which in both cases it is) and you connect it simultaneously to the canal and inside the hull then water will pour into the boat until equilibrium is achieved - on the bottom of the canal! A lot changes!