Snow!

[Iain_S]

I am sure somebody can do the maths, but with most openings in a narrowboat hull at least a foot above the waterline, you would need a colossal amount of snow to sink it! A mound of snow perhaps the same height as a the boat itself?

 

I was surprised to hear of the sinkings as well. I always thought that a foot of fresh snow was equivalent to an inch of rain. However, thinking about it, the density of snow must increase with the depth, due to the weigh of the snow on top compressing the stuff underneath. There was about two and a half feet of snow on the boats at Drumshoreland, and so I'd only have expected them to go down two and a half inches, or possibly up to five inches in the worst possible case of uneven loading (which wasn't the case, due to no thawing, and not much wind).

 

Experimental bucket of snow thawing out in kitchen to check the figures

 

Iain

[nb Innisfree]

I was surprised to hear of the sinkings as well. I always thought that a foot of fresh snow was equivalent to an inch of rain. However, thinking about it, the density of snow must increase with the depth, due to the weigh of the snow on top compressing the stuff underneath. There was about two and a half feet of snow on the boats at Drumshoreland, and so I'd only have expected them to go down two and a half inches, or possibly up to five inches in the worst possible case of uneven loading (which wasn't the case, due to no thawing, and not much wind).

 

Experimental bucket of snow thawing out in kitchen to check the figures

 

Iain

 

Just Googled it. Freshly fallen snow is 160kg per cu metre so 45' nb roof would be about 3.5 ton at that (unlikely) depth.

Edited December 10, 2010 by nb Innisfree

[Iain_S]

Just Googled it. Freshly fallen snow is 160kg per cu metre so 45' nb roof would be about 3.5 ton at that (unlikely) depth.

 

Which gives a density of 0.16 that of water (about twice what I thought )

 

I didn't measure the depth of snow, but it was several inches higher than the canopy, and certainly well over two feet. We had 22" in the back garden, before Monday, when we got another 6" or more.(No drifting) Possibly there wasn't as much as two and a half feet, but at least 2'4".

 

Anyhow, the density figures make sinking slightly more likely. Assuming 2'4" (28"), the boat would go down about four and a half inches with even coverage, and one side could go down more if the boat was constrained by tight ropes.

 

Still seems very difficult to sink a boat by piling snow on it, though.

Iain

[blackrose]

Nobody have a raw water cooled NB then ??

 

Most NBs aren't.

 

The only other need for seacocks would be on shower and sink outlets etc, but since it's recommended that they're at least 10" above the waterline not many NBs have them. I often see narrow boats with outlets very close to the waterline, so in those cases seacocks should have been fitted (but I bet most aren't).

 

In my opinion on a boat with a relatively shallow draught it's generally possible to get all outlets 10" above the waterline which is the simplest system, and it's a mistake to fit them lower. The problem often arises when people choose fixtures that are fashionable rather than practical. I knew a couple who were fitting out a sailaway and the woman insisted on a deep Butler style kitchen sink near the aft of the boat. The outlet ended up about 2" above the waterline. The other option would have been a pumped rather than a gravity drained sink, but that's more complicated than it needs to be.

 

Of course any water entering an outlet would need to rise up the pipe and over the side of a sink etc, before it could flood the boat, but this assumes that all the pipe connections are sound and this may not be the case if they have dipped below the waterline and are immersed in frozen water.

Edited December 11, 2010 by blackrose

[alan_fincher]

Most NBs aren't.

 

The only other need for seacocks would be on shower and sink outlets etc, but since it's recommended that they're at least 10" above the waterline not many NBs have them. I often see narrow boats with outlets very close to the waterline, so in those cases seacocks should have been fitted (but I bet most aren't).

Of course very many older narrow boats have air-cooled Lister diesels, often involving large holes in the hull side, where the air cooled trunking goes. Many of those would fail a 10" test.

 

I'm fairly certain that quite a few modern Liverpool Boat style NBs that have large ventilation holes in the hull sides by the engine bay would be fairly borderline too, but I've not taken a tape measure to any.

 

When I had a raw water cooled narrow boat it never occurred to me to turn off the cocks when the boat was unattended. The hoses and clips used look no more likely to fail to me than bits of out 70 plus years old hull!

 

I'm a cautious type, but would certainly not bother with cocks on our sink and basin drains, which would almost certainly fail a "10 inch" test. That said, being bronze flanged fittings, I think they are far more likely to get sheared off by boat use, than to actually manage to dip below water and for the hoses and clips attached to them to have to fail at the same time. (The prospect of a dual failure like this seems unlikely enough not to cause me to lose too much sleep at nights.)

[blackrose]

Of course very many older narrow boats have air-cooled Lister diesels, often involving large holes in the hull side, where the air cooled trunking goes. Many of those would fail a 10" test.

 

I'm fairly certain that quite a few modern Liverpool Boat style NBs that have large ventilation holes in the hull sides by the engine bay would be fairly borderline too, but I've not taken a tape measure to any.

 

I don't understand why any ventilation holes for air cooled or water cooled engines would need to be anywhere near the waterline? My Liverpool Boat's engine vents are located in the slightly angled top plank rather than the hull sides, and the bottom of the vents are 15" above the waterline.

Edited December 11, 2010 by blackrose