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Old 30-10-2020, 14:40   #1
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Odd little question

Help settle a bet - a week's worth of coffee rides on it

Checking how the shrinkwrapping was coming along, my wife and i noticed a few inches of water between the wood stringers in the bilge. With temps below zero it will soon turn to ice.

I thought the ice will find the least path of resistance and climb upwards without pressure on the stringers or bilge floor. My wife feels the ice will expand uniformly with equal pressure on the stringers and floor.

Cant see this causing damage to the stringers, but.....enquiring minds must know lol.
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Old 30-10-2020, 15:03   #2
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Re: Odd little question

I'd say it depends on how fast the freeze is, and also the shape and angle of the bilge. If it's 90 or less, or if the water is confined between the stringers, I'd be worried. If it is a sloped bilge with plenty of expansion space, then I'd be less concerned.



To be certain of no problem I always dump some antifreeze into the bilge. That way it can't freeze hard, no matter what.
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Old 30-10-2020, 15:07   #3
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Re: Odd little question

I would worry more about small gaps where the water has gotten between the stringers and the bilge floor. I don't know if it will damage the wood but I would pour a gallon or two of -50 or -100 anti-freeze down there.


Though maybe its too late for all that now. How about a small heater for the night.
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Old 30-10-2020, 16:01   #4
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Re: Odd little question

In most cases water freezes from the top. (say in pond)


The frozen top layer then holds a lid on the lower layers that freeze and push sidewise more than upwards.


Another story - water freezes and THEN STARTS to expand (the ice expands as temperatures drop). No matter how it freezes - it will be pushing sidewise on the stringers.


As noted - if there is a distinct V shape - the ice will detach at a point from the surface and pop up.


A boat for the ice is always built in V - the ice pushes her out and up at a point.



Years living in a country with icy winters .... brrrrr ;-)))



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Old 30-10-2020, 16:16   #5
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Re: Odd little question

FWIW and AFAIK, maximun expansion occurs at -4C
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Old 30-10-2020, 18:10   #6
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Re: Odd little question

Hmm, so for sure I will drop some antifreeze in there as cheap insurance. I'm guessing I pay for coffee but worth it for the info and that tip
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Old 30-10-2020, 19:15   #7
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Re: Odd little question

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FWIW and AFAIK, maximun expansion occurs at -4C

I think you may be confusing that with maximum density of water which occurs at +4C. Ice at constant pressure increase in density with decreasing temperature.
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Old 30-10-2020, 19:31   #8
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Re: Odd little question

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I think you may be confusing that with maximum density of water which occurs at +4C. Ice at constant pressure increase in density with decreasing temperature.
Probably!!!

Thanks for the correction
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Old 31-10-2020, 02:34   #9
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Re: Odd little question

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Originally Posted by barnakiel View Post
In most cases water freezes from the top. (say in pond) ...
... water freezes and THEN STARTS to expand (the ice expands as temperatures drop). No matter how it freezes - it will be pushing sidewise on the stringers...
This is really complicated! I look forward to hearing from someone, who really understand the physics.

“Regular” ice, (the version we were familiar with, before we learned about the other 14 kinds), is capable of applying massive amounts of force, when it freezes and expands. This is due to a very unique trait of water, mainly, that it is less dense as a solid, than as a liquid.
This density disparity is due to how the molecules of water react upon freezing; water molecules join together, in a rigid hexagonal structure, which leaves a small, but nonetheless significant gap, between the atoms, that wasn’t there, when the water was liquid. Water reaches its densest point at 4 degrees Celsius. Any cooler or hotter and it begins to expand. (as Wotname noted)


The surface of the liquid will freeze first. There are two reasons for this. First, water at 0 C has lower density than water at 4 C, so "cold water rises to the top". And since the coldest water will freeze first, freezing will start with a film on the surface.

However, once all the liquid reaches a temperature of 0 C, any location where water can lose the heat of fusion, can (in principle) become ice.

If the walls (hull) are sufficiently conductive, eventually the water adjacent to the walls will freeze more rapidly than the water below the ice at the surface (as the layer of ice gets thicker it starts to act as an insulator). And once you have a region of ice "on all sides of the container", the increase of volume that accompanies further freezing will result in isostatic increase in pressure, inside the "ice pressure vessel".

In principle this will result in pressure in all directions - and since the ice at the top will typically be thicker (and therefore stiffer) you can imagine more pressure will be applied laterally.
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Old 31-10-2020, 02:41   #10
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Re: Odd little question

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Hmm, so for sure I will drop some antifreeze in there as cheap insurance. I'm guessing I pay for coffee but worth it for the info and that tip
Sounds like you could use a couple hot chocolates as well!
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Old 31-10-2020, 03:28   #11
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Re: Odd little question

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Hmm, so for sure I will drop some antifreeze in there as cheap insurance. I'm guessing I pay for coffee but worth it for the info and that tip
And you should pump. / sponge as much water out as you can first. Maybe that will be enough.
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Old 31-10-2020, 06:51   #12
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Re: Odd little question

I would agree on the pump/sponge the last bit of water out, but also add in the antifreeze as a precaution. I once visited my boat to find the winter cover had collapsed under the weight of snow from a 2' snowstorm that rolled through. I must have pumped 200 gallons by hand out of the bilge one afternoon, what a mess. I would try and find where any water intrusion might come from and remedy that as well.
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Old 10-11-2020, 09:34   #13
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Re: Odd little question

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I would agree on the pump/sponge the last bit of water out, but also add in the antifreeze as a precaution. I once visited my boat to find the winter cover had collapsed under the weight of snow from a 2' snowstorm that rolled through. I must have pumped 200 gallons by hand out of the bilge one afternoon, what a mess. I would try and find where any water intrusion might come from and remedy that as well.
I agree 1000%

When I had to winterize, part of my checklist was:

a. Pull the bottom plug(s). If you do not have a bottom plug, consider having one installed
b. Clean out the bilge with Dawn (or similar) and hot water. Make sure the bilge smells sweet.
c. Reinstall the plug. No need to tighten.
d. Pour antifreeze in all forward bilge access points in the boat (could be under a bunk, the anchor locker, shower pan, who knows? Wait to see the antifreeze reaches the stern. Once you see the "right" color, you know that there is at a minimum, antifreeze in those areas that you cannot see.
e. Allow antifreeze to run out of all bilge pumps, even the emergency pump.
f. Pull the plug again and just lay it down in the bilge for the winter. If you're forgetful, put a sticky note on the dash to remind you to reinstall the plug before launching.
g. With a wet vac, vacuum out as much water as you can find. Stick the hose over the little hole that leads forward so you can suck out whatever water might be forward of the engine room bulkhead.

You're done with the bilge. It should be dry, and whatever liquid that's left should be antifreeze. With the plug out, if water does leak into the boat, it should drain out.

If you have access to electricity, buy a temperature activated plug. Plug in a lamp or light socket that has a 100 watt bulb. The 100 watt bulb will provide enough heat in the bilge to stop ice from forming. It will also burn off moisture.
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Old 10-11-2020, 10:06   #14
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Re: Odd little question

If I had a fully balsa cored hull like the OP, I wouldn't care which direction the ice expanded, I'd just want it out of my bilge.
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Old 10-11-2020, 12:29   #15
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Re: Odd little question

Thx everyone for all the thoughtful replies, and yes she now has a bone dry bilge, winterized systems, a taste of the pink stuff left over the bilge surface, and is snuggled under shrinkwrap to sleep for the winter.
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