Sight tube indicator

I used the led strip idea behind the site tube on my last boat and it worked okay but if all else fails you can follow Viv cox's link use the green ball and keep the other bits in the spares locker :)
 
I had the same requirement from the insurers to remove the permanently open sight tube on my diesel tank. It was simply a hose teed off the fuel take off at the bottom of the tank to a spigot at the top of the tank. I sealed off the top spigot and took a copper hose from the tee to a heating tank sight tube from BES. This had to be cut down to suit the installation and a breather hose taken from the top to a point well above the heeled waterline, but the critical point is that it has a momentary push to open valve at the base so that only a very small volume of fuel stands in it which could be released in a fire. It also came with a bead to float on the surface!

Actually if an engine room fire were intense enough to melt the sight tube, I guess it would only be a matter of seconds before the GRP tank would burn through.

Rob.
 
AntarcticPilot said:
The ideas like the diagonal strip or white paint behind the tube assume that the reading direction is normal to the tank wall. Sadly, it isn't on mine! The site-tube lives in a gap about 6 inches wide between the cockpit locker and the fuel tank, so the reading direction is parallel to the tank wall, and there's nothing behind it.

!
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To which the facetious answer would be : then put something behind it! :D
 
For a foolproof device you can't beat linking the fuel tank to the engine, when the engine stops it normally means fuel tank is empty and needs refilling.
 
I liked the diagonal striped backboard. Took me about 15 minutes to cut the ply and paint it with white and aquamarine stripes. Tested it with water in a clear plastic tube so I'll take it to the boat next time I visit. Haven't worked out yet how the refraction through a cylinder causes the stripes to reverse their tilt but I hope to get there.
 
reeac said:
I liked the diagonal striped backboard. Took me about 15 minutes to cut the ply and paint it with white and aquamarine stripes. Tested it with water in a clear plastic tube so I'll take it to the boat next time I visit. Haven't worked out yet how the refraction through a cylinder causes the stripes to reverse their tilt but I hope to get there.
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I was thinking about that on the train to London this morning (well you have to do something to pass the time) and I guess it's because the tube of water acts as a convex lens and inverts the image. No doubt this theory is complete baloney, as someone will delight in telling me.
 
parsifal said:
I was thinking about that on the train to London this morning (well you have to do something to pass the time) and I guess it's because the tube of water acts as a convex lens and inverts the image. No doubt this theory is complete baloney, as someone will delight in telling me.
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Not as simple as that, I'm afraid. Inverting the image will leave the stripes at the same angle.. Also it's a cylindrical lens, not the usual spherical one.
 
Think that I have it. Because it's a cylindrical lens there is no overall refraction in any vertical plane ....refraction occurs only in horizontal planes. Consider a stripe running from bottom left to top right. A ray coming from top right will enter the cylinder (the tube plus fuel) close to the right hand side as seen by the viewer and be refracted towards the left as it passes through due to the shape of the tube. A ray coming from the bottom right will enter close to the left hand side and be refracted towards the right as seen by the viewer. Neither ray will be refracted in a vertical direction so the first ray will be redirected from top right to top left whilst the ray coming from bottom left will be redirected to bottom right. These redirections will reverse the direction of the stripe. The centre point of the stripe will be opposite the centre line of the tube and a ray coming from that point towards the viewer will encounter perpendicular tube surfaces where it enters and exits ....hence no refraction so no movement of the image. Centre point stays put.
 
parsifal said:
I was thinking about that on the train to London this morning (well you have to do something to pass the time) and I guess it's because the tube of water acts as a convex lens and inverts the image. No doubt this theory is complete baloney, as someone will delight in telling me.
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Sorry to be such a bore about this, Parsifal, but reviewing my long winded answer, I can see that you were nearly correct about inverting the image. The cylindrical shape inverts the image from side to side but leaves it unaffected from top to bottom thus reversing the slope of the stripes. A spherical lens would invert about a vertical and also a horizontal axis leaving a final image identical with the original.
 
reeac said:
Sorry to be such a bore about this, Parsifal, but reviewing my long winded answer, I can see that you were nearly correct about inverting the image. The cylindrical shape inverts the image from side to side but leaves it unaffected from top to bottom thus reversing the slope of the stripes. A spherical lens would invert about a vertical and also a horizontal axis leaving a final image identical with the original.
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As Henry Royce is supposed to have said: "Nearly right is wrong"!

Your explanation makes it clear how it works.
 
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