Bullseye Decklight

[NB Alnwick]

The bullseye glass fitted to our boat had domed surface uppermost but all logic suggests that it should be fitted with the flat surface at the top. Can anyone help with a definitive answer?

[Chris Pink]

No. They can't.

 

There are precisely two opinions both, apparently, equally weighted by traditional usage.

 

The two schools of thought are

 

dome up: to light working through locks in the dark

dome down: to make the cabin lighter.

 

it makes no difference to the focussing of the sun's rays.

 

so you could do what I do

 

one boat has it dome up

another has it dome down

[AJLintern]

I would think dome downward. The prism style decklights I've seen are pointy side down - would make quite a trip hazard to have them pointing out of the deck!

[Chris-B]

I have always fitted "dome" down.. but then I only copied other older boats

Chris-B

[alan_fincher]

Can anyone help with a definitive answer?

I doubt it.

 

I think you'd need to do a statistical survey to see which is most common, because it always feels about 50-50 to me.

 

On "Sickle" the restorers fitted it "dome up", but I don't think that means a lot.

[AJLintern]

Lots of discussion on this a year ago: http://www.canalworld.net/forums/index.php?showtopic=38171&st=0 A summary of which appears to confirm curved side down is the correct mounting method, though it'll still work the other way up. However the focal point will be sharper with curved side up, so still undesirable from a fire hazard point of view. So mount them downwards

[Laurence Hogg]

The bullseye glass fitted to our boat had domed surface uppermost but all logic suggests that it should be fitted with the flat surface at the top. Can anyone help with a definitive answer?

Hi, I supplied the bullseye for your boat to R W Davis when I was running the Boatmans Cabin Company and distributing our chandlery. It is a circular decklight glass ref No 8H-014 (made by Nazeing glassworks) and should be fitted dome down. It is designed to be used that way both for the spread of light and to be walked upon.

If it is complete it should have a brass frame which it sits in and a securing brass ring, the frame is set into the roof to hold the glass and the ring retains the glass. This is an identical system as used on the oblong "toblerone" shaped ones.

It should NOT be fitted dome up.

Edited May 30, 2012 by Laurence Hogg

[NB Alnwick]

Hi, I supplied the bullseye for your boat to R W Davis when I was running the Boatmans Cabin Company and distributing our chandlery. It is a circular decklight glass ref No 8H-014 (made by Nazeing glassworks) and should be fitted dome down. It is designed to be used that way both for the spread of light and to be walked upon.

If it is complete it should have a brass frame which it sits in and a securing brass ring, the frame is set into the roof to hold the glass and the ring retains the glass. This is an identical system as used on the oblong "toblerone" shaped ones.

It should NOT be fitted dome up.

 

Thank you for that - I had always assumed that, in keeping with boatbuilding tradition, decklights should always be mounted flat side up. The background information is also useful, although the original as supplied was never fitted over the boatman's cabin as intended. It was passed on to Geoff Towersey, who fitted out the main living quarters, and he fitted it to the hatch cover on the front 'tug' deck - dome side up! We are in the process of refurbishing the hatch (which was badly corroded) and have had to source a new bullseye glass from Midland Chandlers because the original had been cemented in place and was damaged during removal. The new glass will be re-fitted proud of the steel work using the original external frame that fits nicely. I don't know if this is the original frame - from the description above, I guess not and the retaining ring was no longer on the boat when we acquired it.

[micky44]

its not domed, the correct word is convex, and it should be fitted convexed side down.

[Bobbybass]

When I bought my boat..its was 12 years old..

Time enough...you would think...to iron out any problems..

One day...we left the bedding stacked slightly higher than normal...as we had been turning back the bed. When we returned...the bulls eye had nicely burnt a line across it...it was only a miracle that we did not catch fire !

 

I also recall...about 3 years ago...a boat at Napton...where the bulls eye had focussed the sun onto a can of spray left to one side of the cabin..and the boat was gutted..

I 'think'..(actually thoughts may vary)...there was talk of a BSS addition being made about bullseyes...at the time..?

 

Hmm..yes I recalled a conversation here :

 

http://www.canalworld.net/forums/index.php?showtopic=38171&st=20

 

I painted mine white...and white...it shall remain !!!

Edited June 1, 2012 by Bobbybass

[blackrose]

What about these ones? Sould they be fitted up or down for juicing oranges & grapefruits?

 

[NB Alnwick]

What about these ones? Sould they be fitted up or down for juicing oranges & grapefruits?

 

 

Prisms like this have been around since the days of wooden sailing ships - they are fitted with the pointy end facing downwards/inwards but mind your head!

[RLWP]

'You have a lathe, can you machine this? But it's a piece of glass Graham...'

 

As part of his modification, Graham has cast a ring of West System resin around his bullseye to increase the thickness. Here is the bullseye as I got it:

 

 

There is about 7mm of resin on the top of the flange. The 'cracks' in the lens are actually cracks in the mould used to make it.

 

The problem was to hold it. First step was to use an offcut from Tawny Owl's rear seat:

 

 

I attached this to the faceplate, rough turned the outside then bored out a quarter inch deep recess in the face:

 

 

I carefully machined this recess until I could just hammer the lens in:

 

 

Just in case, I used the tailstock to hold the lens in place:

 

 

I have also removed the 'cracks' with a stone and then polished the lens with successive grades of wet and dry. Here is the finish machined lens with the flange reduced to 3/4" thick, the remaining spigot tidied up and polished and the lens polished

 

 

I'm very impressed with the West system resin, it machines well and polishes up to look like glass

 

Richard

[Mick_B]

Very impressive Richard... :clapping:

[Chris Pink]

 

 

There is about 7mm of resin on the top of the flange. The 'cracks' in the lens are actually cracks in the mould used to make it.

 

 

 

I have a bullseye with exactly the same 'crack' in it.

[RLWP]

I have a bullseye with exactly the same 'crack' in it.

 

Of course. There must be many of them

 

Richard

[NB Alnwick]

Richard has done a superb job that is well worth the five shillings that I promised him.

 

The idea of setting the glass in resin came about as a result of an accidental discovery. When fitting a prism light to one of Alnwick's new steel hatches, I had cut the hole slightly too large and to take up so I had the idea of filling the resultant gap with the West System resin that I had been using on the ply lining. The resin set nicely around the base of the prism sealing it to the steelwork and the ply lining. The seal has proved leakproof and the prism has never dripped condensation - yet others who have fitted these prism lights often complain of these problems. That is why our new bullseye is being set in resin.

 

I will report the result in due course . . .

[RLWP]

Five shillings and a packet of jelly babies as I remember it!

 

Richard

[Timleech]

It was common to fit them dome up, with no frame, in wooden cabins, easier to seal that way because no water needs to lie on the top.

 

Tim

[bizzard]

Good job that Richard. I have one dome up for the reason Tim states.

I once worked on an old Springer,the bedroom was midships with no windows at all but it had four of the oblong prisms and it was as bright in their as the dull day outside was.

[RLWP]

Good job that Richard. I have one dome up for the reason Tim states.

I once worked on an old Springer,the bedroom was midships with no windows at all but it had four of the oblong prisms and it was as bright in their as the dull day outside was.

 

Yes, those roof prisms are very good

 

Richard

[Chertsey]

Do you think the resin wheeze would help with Chertsey's bulls eye? It's fitted dome up and when we took it out (can't remember why, probably to shotblast the cabin top) we found that two pieces of the rim (hidden beneath the brass bezel) had broken off. We stuck it back together with silicone, put it back with plenty of sealant above and below, but it still leaks (in case anyone was wondering what the inverted pyrex mixing bowl on the roof was for). Do you think we could taki it out again, build up the edges with resin and get a better seal?

 

If a bulls eye has been fitted dome up, is it an easy matter to invert it? I'm an 'upper' by instinct but it does get a hammering from the heavily (in more than one sense of the word) modified slide.

[Timleech]

Looking on my back workshop shelves, among stuff that hasn't seen the light of day for years just in case there was still an old National big-end bearing lurking there (there wasn't), I found a long-forgotten circular deck light. The usual alternative to the bullseye is the dioptric prism, they have a series of annular ring prisms on the bottom. This one, though, has a whole lot of little pyramid prisms on the bottom. I don't think I've ever seen another one. Not much risk of starting a fire with one like that!

 

Tim

[Chris Pink]

I've got one of those, likewise lurking in a dusty place, I never thought it might be a roof light I simply thought it was a porthole for a bathroom!

 

I'm glad you described it so succinctly, my stab wouldn't have been so elegant.

[RLWP]

Do you think the resin wheeze would help with Chertsey's bulls eye? It's fitted dome up and when we took it out (can't remember why, probably to shotblast the cabin top) we found that two pieces of the rim (hidden beneath the brass bezel) had broken off. We stuck it back together with silicone, put it back with plenty of sealant above and below, but it still leaks (in case anyone was wondering what the inverted pyrex mixing bowl on the roof was for). Do you think we could taki it out again, build up the edges with resin and get a better seal?

 

If a bulls eye has been fitted dome up, is it an easy matter to invert it? I'm an 'upper' by instinct but it does get a hammering from the heavily (in more than one sense of the word) modified slide.

 

I think it would. The resin is pretty good stuff

 

Richard