beware the bullseye

[serenility]

The sun through a bullseye caused an aerosol to explode and set fire to a very nice tug in Wigrams today. I gather that due to quick and heroic work by marina staff getting the gas bottles off and towing the boat to a berth where the fire service could fight the fire saved it from being completely gutted. Cover your bullseyes or paint the inside with whitewash etc. to prevent the sun through a magnifying glass effect.

[Bobbybass]

The sun through a bullseye caused an aerosol to explode and set fire to a very nice tug in Wigrams today. I gather that due to quick and heroic work by marina staff getting the gas bottles off and towing the boat to a berth where the fire service could fight the fire saved it from being completely gutted. Cover your bullseyes or paint the inside with whitewash etc. to prevent the sun through a magnifying glass effect.

 

This nearly happened to me last week. The bullseye is original and has been on the boat for 13 years with no problems.

Along comes me...... I'm fed up with getting woken up in the morning and I put velcro pads under it and at night fix a cardboard cover onto it.

This worked well ...and then last week we returned to the boat to find the smell of smouldering and a hole in the cardboard !!

I have now purchased a pound shop wok to cover it from the outside.

Lucky escape !

 

Bob

[blackrose]

I've heard similar stories so many times that I can't help thinking bullseyes are stupid things to have on boats. Why would anyone install a magnifying glass in their roof and then have to cover it up? Ridiculous!

 

There are other shaped prisms available - you don't need to choose a lens shaped piece of glass that will focus the sunlight and set fire to your boat.

Edited May 27, 2010 by blackrose

[Grace and Favour]

I've heard similar stories so many times that I can't help thinking bullseyes are stupid things to have on boats. Why would anyone install a magnifying glass in their roof and then have to cover it up? Ridiculous!

 

There are other shaped prisms available - you don't need to choose a lens shaped piece of glass that will focus the sunlight and set fire to your boat.

Shucks - - You old traditionalist you!

 

 

Bulls eyes were used because they were the cheapest piece of glass one could buy at the time . . .

Edited May 27, 2010 by Grace & Favour

[blackrose]

Shucks - - You old traditionalist you!

 

 

Bulls eyes were used because they were the cheapest piece of glass one could buy at the time . . .

 

A false economy if it burns your boat down!

 

Edit: It just goes to show that despite what some like to think, the old ways were not always the best ways.

Edited May 27, 2010 by blackrose

[Christine]

A bit off topic but our local optician nearly burned his shop down after his window display of magnifying glasses caused a fire.

[frangar]

We have a bullseye on our boat. Having played with a bit of paper it seems that the light is focussed about 2" below the lens...meaning there is nothing to burn where that is...the liner is in brass...maybe more modern ones have a different focal point??? I like our bullseye cos u can see if it's sunny before u get up! Oh & it's right for a boatmans cabin. I think maybe the problem lies more the design of modern bullseyes.

 

Cheers

 

Gareth

[Natalie Graham]

A bit off topic but our local optician nearly burned his shop down after his window display of magnifying glasses caused a fire.

 

We had a barbecue display set up in the greenhouse of the garden centre and the lighters started exploding in the sun.

[Dovetail]

Its not just boats that suffer with bullseyes causing fires it was popular to have one in the front door of houses (I lived in one once how quaint) and they caused fires to and on a similar note discarded bottles in dry grass.

[Derek R.]

The Sun gives us light and warmth, we just need to be aware of some of the dangers and adapt to them.

 

A Bulls Eye is domed to prevent vision through and maintain privacy as well as give a lot of light for its size - though it need not be domed for the latter. Almost all working boats from the first cabins on, had Bulls Eyes. Not very many suffered conflagration, partly I suspect due to the focal point being away from flammable woodwork, and where there was a perceived problem, one trick was to paint a small circle on the underside of the glass in the middle to break the concentration of light rays.

 

Post 1960 Bulls Eyes are quite a bit smaller, and focal points are different. With more woodwork fitted in cruisers in the form of partitions etc., there's a real danger, and the Wigram's incident is not the first. No need to go 'ape' over them though, the solution is simple - but needs to be applied.

 

I was at a steam fair once, and amongst the exhibits was a very nicely restored Velocette with sidecar. The bike had a bar end mirror of with convex shaped glass. The Sun was bright, and a focal point from the mirror concentrated a small area of light onto the upholstery of the chair in the sidecar - it was beginning to smoke! The handlebars were turned, and the owner sought out!

 

At one place of work, we had a weather station on a rooftop. Part of the apparatus was a Sunshine recorder measuring the hours of Sunshine through the day. This was a non-mechanical device using a glass to concentrate the Suns rays onto a curved piece of green card mounted at focal point of the glass. As the Sun moved around the sky - or more correctly - the Earth turned, a line was scorched into the card which was calibrated in hours and quarter hours, no Sun - no scorch-mark.

 

Derek

[carlt]

You can always replace the lens type glass with a "grapefruit squeezer" which scatters the light.

[DHutch]

We have a bullseye on our boat. Having played with a bit of paper it seems that the light is focussed about 2" below the lens...meaning there is nothing to burn where that is...the liner is in brass...maybe more modern ones have a different focal point???

Its quite possible. Along with modern ones perhaps being more accurately manufactured resulting in far less scatter, or less thought being put as to where they are placed.

 

But as said, if the focal point is close to the lens, and away from objects, there should be no issue and the light well distributed. If not, you are going to have the issues seen here.

 

 

Daniel

[magnetman]

Its quite possible. Along with modern ones perhaps being more accurately manufactured resulting in far less scatter, or less thought being put as to where they are placed.

 

But as said, if the focal point is close to the lens, and away from objects, there should be no issue and the light well distributed. If not, you are going to have the issues seen here.

 

 

Daniel

 

and maybe it depends which way up it is fitted. I'm sure I've seen bullseyes with the dome facing upwards - surely this is wrong?

[Water Rat.]

A bit off topic but our local optician nearly burned his shop down after his window display of magnifying glasses caused a fire.

 

 

:lol: :lol: not funny really but you have to laugh at that.

 

Who has not used a magnifying glass to burn some thing??

 

edited for spolling

Edited May 28, 2010 by Water Rat.

[Derek R.]

and maybe it depends which way up it is fitted. I'm sure I've seen bullseyes with the dome facing upwards - surely this is wrong?

 

Dome up is correct, most are fitted that way. The other way round creates a recess, into which water will collect. Also, the angle of direct Sunlight has more to refract light through when the Sun is lower on the horizon.

 

Derek.

[Natalie Graham]

A Bulls Eye is domed to prevent vision through and maintain privacy as well as give a lot of light for its size -

 

A bull's eye is domed because it was the middle bit when glass for windows was spun before the invention of float glass. As Grace & Favour said earlier, they were the cheapest bit of glass you could get. The other properties you mention are incidental, there was no intention to design for those features.

Edited May 28, 2010 by Natalie Graham

[dave moore]

Hi all

I'm sure I've posted this before, but it seems to be a recurrent problem. Our bulls eye, mounted curve uppermost has also scorched the liner immediately below, a potential fire hazard. Years ago I disussed the problem with another Norton Canes boater/ customer, a scientist by profession who designed satellites (as I recall). His response was that the bulls eye would act as a condenser or focusing lens whichever way it was fitted. His solution was to add a piece of "frosted" perspex (similar to bathroom glass) below the bulls eye. I cut a 4" circle of the stuff and pushed it into place using silicone adhesive...10 years on, no further problems. The explanation was that the irregular suface of the frosted perspex dispersed the light rays, so disabling the focal properties of the bulls eye....Carl's juicer solution sounds a similar approach

Cheers

Dave

[Speedwheel]

A bull's eye is domed because it was the middle bit when glass for windows was spun before the invention of float glass. As Grace & Favour said earlier, they were the cheapest bit of glass you could get. The other properties you mention are incidental, there was no intention to design for those features.

 

Crown glass

 

Someone once told me that if you grind a very small section off the top of the dome, with a grinder or similar, it would stop this.

Edited May 28, 2010 by Speedwheel

[carlt]

Carl's juicer solution sounds a similar approach

Classic marine call them "Melon Decklights" but I prefer Grapefruit Squeezer.

 

Clicky

[Derek R.]

A bull's eye is domed because it was the middle bit when glass for windows was spun before the invention of float glass. As Grace & Favour said earlier, they were the cheapest bit of glass you could get. The other properties you mention are incidental, there was no intention to design for those features.

 

Granted, so perhaps I should have said: "A Bulls Eye is domed and prevents vision through, maintaining privacy as well as giving a lot of light for its size -"

 

As float glass was invented some time before narrow boat cabins were fitted with Bulls Eyes - why are they domed, and why not flat glass? What was the intention?

 

Derek

 

Classic marine call them "Melon Decklights" but I prefer Grapefruit Squeezer.

 

Clicky

 

I like that - but would do my head a further injury in a cabin!!

 

Derek

Edited May 28, 2010 by Derek R.

[Laurence Hogg]

Dome up is correct, most are fitted that way. The other way round creates a recess, into which water will collect. Also, the angle of direct Sunlight has more to refract light through when the Sun is lower on the horizon.

 

Derek.

 

Dome up is not correct.

All the original bulleyes (circular decklights) are meant to be fitted dome down, the casting frame was in two parts, a recessed base and a circular top plate, so the glass was sealed into the init and then fitted. Refer to any old catalogue from Simpson Lawrence or similar and you will find this is so. For some odd reason the GUCCCo specified the reverse fitting and thats where this came from. Nazeing glass at Ware supplied most of the decklights, inc the oblongs toblerone style and the orange squeezer ribbed circular etc. The GU co used their 8h014 as the 8 inch fitted to Yarwoods boats, these had a riplled flat side which I presume was to dissipate focus. Midland Chandlers purchased vast quantities of ex BR signal lamp lenses in the late 1980's from Reading signal works and sold them on as bulleyes, there were several near misses (two at Calcutt) where boats nearly caught fire, the focal length was short. I presume they have had these copied in the far east so the problem continues. It is difficult to prevent the heat coming through, I have seen white glass fitted under some which seems to do the trick, but the surrounding trim is what normally gets burnt first. The 8" bullseye was one of the few products we were wary of at Boatmans Cabin and always advised the buyers of the risk.

Edited May 28, 2010 by Laurence Hogg

[luctor et emergo]

Is there a reason why there would be a bull's eye fitted in the roof, but no porthole in the cabin wall?

[Laurence Hogg]

Is there a reason why there would be a bull's eye fitted in the roof, but no porthole in the cabin wall?

 

Some companies were reluctant to fit ports (deadlights) to their boats until very late on, FMC being the main company to note, opening deadlights were rare until the advent of the river class boats built in the late fifties.