One for the thinkers....

So here is the question.
OK, two actually, but related.

Does water in the bucket alter the waterline of the craft?

And, does a couple of litres sloshing around in the bucket alter the acceleration of the ski?

What I'm particularly talking about here is water that equals the height of the water outside of the ski, not a completely swamped bucket that has yet to equal itself with the outside level.

So really the ultimate question is:

Does a small amount of water in the bucket slow you down versus a
dry bucket?
Or is the lovely sucking venturi noise the only benefit to a dry bucket apart from warm toes in the winter?

You should rename this thread 'One for people with too much time on their hands'

Its been a while since my high school physics, but If the water in the bucket is at waterline, then the entire craft is displacing a tiny bit less water, and your boat will sit a tiny bit lower in the water. So you will have more wetted surface and go slower. And be a little more stable.

The slosh effect: water in the bucket is horrible when you're trying to surf, turn, not fall over or do anything except cool off your gonads.

Speaking of gonads, has anyone else experimented with pissing into your footwell on long runs? I've been practicing quite seriously in preparation for Molokai. The other day I was able to totally drain my bladder on a single bump and that's probably the best thing I will ever accomplish as a paddler...

patrickswitz wrote: Speaking of gonads, has anyone else experimented with pissing into your footwell on long runs? I've been practicing quite seriously in preparation for Molokai. The other day I was able to totally drain my bladder on a single bump and that's probably the best thing I will ever accomplish as a paddler...

The quality of this forum has jumped massively in one post, love your work mate!!

I've tried taking a snake's hiss while paddling, can't do it. Back in the day when I used to do a lot of marathon racing, I was guilty of priming my foot pump on the start line with the aforementioned liquid.

Its been a while since my high school physics, but If the water in the bucket is at waterline, then the entire craft is displacing a tiny bit less water, and your boat will sit a tiny bit lower in the water. So you will have more wetted surface and go slower. And be a little more stable.

How can it change displacement?
Unless you have a sealing bailer like a V12, the craft should feel no weight from the water in the bucket.
The water is free to move in and out of the bailer.

The boat is not holding the water, merely being surrounded by it.

Rightarmbad wrote:

Its been a while since my high school physics, but If the water in the bucket is at waterline, then the entire craft is displacing a tiny bit less water, and your boat will sit a tiny bit lower in the water. So you will have more wetted surface and go slower. And be a little more stable.

How can it change displacement?
Unless you have a sealing bailer like a V12, the craft should feel no weight from the water in the bucket.
The water is free to move in and out of the bailer.

The boat is not holding the water, merely being surrounded by it.

Why ask a question and then shoot down the answer

Why not put a hypothesis forward and ask for comment?

Sorry RAB, but the water is not free to move in and out of the bailer. All bailers drain at some rate that retains some water for a minute or two. Once the bucket is dry, or as dry as design allows, the boat is at its ideal. Until then you are dragging the water with you that same as if you were carrying it in your hydro pack.

cheers,
Tom

I'm thinking "why are you paddling a bucket?"

Here's a thought experiment which I believe will validate my opinion as being triumphant: Assume my empty V12 is sitting motionless next to the dock here in Honolulu, bailer open without the swinging gate in place. There's only a tiny bit of water collecting in the footwell because the ski is sitting high in the water. Now Oscar Chalupsky finishes his 11th beer, grabs one last cold one for the road and jumps in my ski to go for a paddle. Immediately the footwell has a few inches of water, since the ski is now sitting very low. Oscar, being somewhat buzzed, closes the bailer before leaving, trapping the water in the footwell.

If he then were to decide he didn't want to drink the 12th beer after all, and placed it back on the dock, then the ski would lighten up a tiny bit, and there would be a teeny bit less wetted surface, and Oscar would go faster. Alternatively, Oscar might decide to drink the beer, but then make up for it by scooping 12 ounces of water out of the footwell, which would lighten up the boat by the same amount.

If RAB's theory were correct, scooping water out of the footwell wouldn't affect the weight of the whole rig, which seems absurd. I believe the error lies in the belief that with an open bailer, the water somehow doesn't press down on the bottom of the footwell anymore, that the weight of the water is somehow neutralized by having a connection with all those free molecules of water cavorting around in the ocean. Wrong! Water pressure is still water pressure, and if you have 1 inch of water in your footwell, each square inch of footwell surface has a cubic inch of water weighing it down, regardless of whether the bailer is open or not.

Although I believe my argument will withstand the most scathing of attacks, I sincerely hope that someone will prove me wrong, because if they do, it means I can pour a case of beer into my footwell at the beginning of the race, drink it up through my hydro tube, and piss it back into the footwell, all without affecting the quality of my ride.... En Garde!!!

I don't do the Hypo thingy and don't drink and paddle. But my boat is sluggish until the foot well drains.

So patrick, lets use a standard open type bailer, as the V12 seals and is different.
Lets make the bailer really big.
Would you now agree that water in the bucket will not change the waterline?

Well this scenario means Patrick can't drink his own piss... Bummer, that was the only reason I was following the thread.
Which reminds me, is urine heavier/more dense that water? That may alter the equation.
I somehow thought RAB's post #666 would be more ominous.

RAB: Water in the bucket would indeed change the waterline relative to a dry (plugged) bucket. What if your footwell were six feet long? Do you still think having six feet of your ski flooded to waterline wouldn't make it sit lower in the water? Water in the bucket displaces air, thus your whole rig gets heavier. I can't think of a simpler way to state it, but if someone with more than a chimpanzee-level understanding of physics can step in and set us straight I will happily go off to the corner and eat my banana...

Here's the thing- Topologically speaking, a ski with a footwell drain is equivalent to a life preserver ring, or a donut. You've got a big sealed ring with a hole in the middle in which the ocean is sloshing around. Explore this topological exercise: Make your drain bigger and bigger, until it achieves nearly the size of the ski. You've now got yourself a 21 foot long life preserver ring that is sitting very very low in the water, because it displaces far less water than it's surfski ancestor.

One more way to look at the problem: Inflate an inner tube and toss it in the water. Topologically and physics-wise, this is equivalent to a bailer-equipped ski. It's sitting pretty high on the water, but now you pull it out, glue a rubber sheet to enclose the "donut-hole", and toss it back it. Does it sit higher? Of course it does.

In reality, the amount of water that collects in a stationary ski as a result of the waterline equalizing is tiny. So in effect, that tiny amount of water displaces only a tiny amount of air, and the effect on waterline is marginal.

But real.

I believe it would make I difference. Here's my take on the topic

1. The bucket is full of water up to the waterline. At this point the bucket is neutrally buoyant.
2. You start paddling and the venturi's empty the bucket. At this point all the air in the bucket below the water line is now positively buoyant. Now being positively buoyant it is lifting the ski slightly, hence reducing the waterline

There's my two cents worth

Cheers
Mark

So ignoring waterline effects and open or closed bailers, does say 5 litres of water in the bucket effect the ability of the ski to accelerate and slow down with each paddle stroke?

Is the 'relatively free to move water' connected enough to the footwell to resist the movement the boat as it is paddled?

Rightarmband, A guy called Arcimedes figured all this out over 2000 years ago, hopefully you will have your eureka moment soon,just don't go running down the road naked.

This is far more complex than figuring out material densities.
That's why I asked people to think about it.

Here's a take on the question…

Yes, the water on the inside will sink the vessel further.

The long version:

When something floats it is in equilibrium, which means that the downward force it feels from gravity is being cancelled by an equal upward buoyant force it feels from the water.

Archimedes found out that the magnitude of the upward force on the object is equal to the weight of the water that is displaced by the object.

All the above, more succintly, for any floating object:

object's weight = buoyant force on the object = weight of water displaced by the object


Three illustrated examples (see attachment):

A. The cup-shaped object displaces water. The volume highlighted in red is equivalent to the volume of water displaced by the object. If the cup is floating and weights 100 pounds, then the water displaced by the cup also weights 100 pounds (by Archimedes).

B. Say we add additional weight to the cup. In order to compensate the added weight it needs to displace an additional volume of water to increase the buoyant force by an amount equivalent to the added weight. It thus sits lower while floating.

C. If the vessel has a hole, it ends up displacing less water when submerged to a certain level vs. an identical vessel without a hole. Less water displaced means less upward bouyant force (due to Archimedes). To compensate and still float, the vessel needs to sink some more in order to increase the buoyant force on it (by displacing more water). Actually, the additional bit it needs to displace (sink) is equivalent to the water volume that seeped in the vessel.

When equilibrium is reached, the weight of the water displaced by the volume shaded in red (i.e. the volume of water displaced by the vessel) is equal to the vessel's weight.

Where I get confused and it gets ugly real quick is if you want to study the actual dynamics of how the vessel fills with water when you open a hole (i.e. how fast it sinks, etc.). I think it depends on the size of the hole, the initial waterline level, and who knows how many other things.

Regarding the second question: the water in the bucket travels along with it, so it is added mass that needs to be accelerated along with the boat when you paddle.

Wetted surface should also increase due to the hull sitting lower in the water.

But it is not as simple as that.
The water in the bucket will initially feel no acceleration as it is free to move.

Hence the perceived sloshing forward and backward of the water in the bucket, it tries to stay at constant speed and the boat accelerates and decelerates around it.

With the only things to impart movement to the water, being drag on the inside of the bucket and and surfaces that face forward or backward that can prevent it staying where it wants to and pushing it forward or backward.

Otherwise you wouldn't get a lap full of water when you take off.

We are also not talking about water entering a hull here, only an open bucket.

So if you put 10 plastic cups taped together to form a raft and measure it's waterline; do you think that adding one more with the bottom removed will alter the waterline of the conglomerate, apart from the extra weight of the cup itself?