A lighthouse mechanism

[BrockleyAndrew]

Following a site visit to Dungeness Old Lighthouse before it closed for winter I have been wondering if there is a good way to represent the lighthouse light. There are various questions, I realise.
Given that that the passenger services were few and limited, can one depict the lighthouse lit and train services together, passenger services finished at 5/6pm even in summer?

If you do try to depict the light, how to power the rotations and achieve the flashes of focused light.
Electronic simulations for Model lighthouses have a globe that is powered gradually up to a flash and then diminishing to portray the rotating lense. Old Dungeness lighthouse apparently gave a flash every ten seconds and had a 10 sided Fresnel lense first order optic. Web searches say the ten sided lense rotated once every 40 seconds but that doesn't fit with a 10 second flash....

So, you could do a single rotating beam on 10 second rotation or multiple lenses at slower speeds. The diameter at the the top of the lighthouse would be less than the base online info of 11metres.
I am in the first thinkings through of how to represent this. And am wondering how you might power/rotate a lense assembly that might be around 6-8cms diameter.

Happy new year all

Andrew

[Terry Bendall]

Given the scale, I would not bother with the rotating mechanism for the lens but use a flashing light. It is possible to by flashing Light Emmitting Diodes which just need a power supply. see https://www.amazon.co.uk/Flashing-White ... B00WX312IQ . The LEDs on that site flash twice per second but there may be other sources with different rates. Alternatively build a circuit which will have the ability for the rate of flashes to be adjusted. Such kits can be found on the internet for a few pounds and since they are based on printed circuit boards are not difficult to build. LEDs will be rather bright so you may need to put an additional resistor in theoutput side of the circuit to reduce the brightness. Alternatively a suitable circuit could be used to power a standard low voltage lamp say 3.5 or 6 volts.

If you really want to have a rotating lens, then a small geared motor such as those available from several suppliers, such as Squires, with the output shaft mounted vertically and the lens on top would do the job. Depending on the size of the tower the motor may have to be mounted at the base or even below baseboard level to give space to fit everything in and an extension to the shaft, or replace it with a longer piece of rod, would be needed.

Terry Bendall

[Jol Wilkinson]

Andrew,

the lenses probably had four elements at 90 degrees, hence four beams seen as one flash every 10 seconds.

Jol

[Will L]

Of course light house doesn't really flash, that is just an artefact depending on where the observer sees them from. As the view of a model lights house will be entirely unnatural, do you wish to see the rotating beams effect that exists in reality, or have it flash because we all "know" that's what light houses to do?

As an occasional visitor to the bird sanctuary by the South Stack lighthouse on Holyhead I can tell you that, when we were there at least, it was lit during the day, and that the beams it produces are narrow both horizontally (giving the flash effect when viewed from any distance), and vertically which means when you realtivly close to the light you can only see the flash if you are in the same horizontal plain as the beam (i.e level with the light). South Stack, being adjacent to Holyhead mountain, most day time visitors are well above the light and won't be aware that it is alight and flashing.

[Guy Rixon]

I'd make it as a light-weight rotating assembly of optical bits, with four beams, as Jol suggested, and mount it directly on the output shaft of an N20 gear-motor. No need for extra bearings or anything mechanically fancy.

Rather than mess about with real lenses, I'd model the visible bits of the full-size lens-assembly in plastic, then use pinholes in the hidden interior to collimate the beams. If a single pinhole doesn't pass enough light, I'd use two larger ones for each beam, spaced a little apart along the axis of the beam.

If the actual lamp needs to rotate, I'd run an LED off a battery. But it might be possible to mount the lamp on the roof of the model, poking down into the centre of the rotating bit.

[LesGros]

"Will L" wrote : Of course light house doesn't really flash, that is just an artefact depending on where the observer sees them from. As the view of a model lights house will be entirely unnatural, do you wish to see the rotating beams effect that exists in reality, or have it flash because we all "know" that's what light houses to do?

Will has described the viewpoint aspect perfectly.

For example: The Bell Rock lighthouse, halfway between Arbroath, and Fife Ness, has a shutter with six apertures. At ground level what is seen is a sequence of flashes. When viewed from above at two thousand feet, the light beams are clearly visible, the effect is like looking down at a gently rotating six-spoked cartwheel, the size of Saint Andrews bay.

On a dark night, with no visible horizon to the East with heavy cloud overcast; when orbiting above, the effect is mesmerizing; never was I more grateful for the Blind flying panel with duplicate artificial horizons; and miles to the West, the distant band of lights, of Dundee and Broughty Ferry.

[LesGros]

Terry mentioned electronics,
See: https://www.merg.org.uk

This example uses vero board.
PMP13 - Lighthouse Simulator - Kit Number: 813 - Simulates a variety of UK lighthouses or aircraft warning lights.

You will need to join the society, but it is a worthwhile investment, as many on here would testify.

[grovenor-2685]

The relevant info from the kit instructions is,
The available patterns are:
Pattern, Lighthouses.
4 flashes every 5 secs, Flamborough, Lynmouth Foreland, Pendeen, Strumble Head
2 flashes every 30 secs, Alderney, Casquets, Nab Tower
2 flashes every 20 secs, Beachy Head, St Bees, Holy Isle
1 flash every 20 secs, Longstone, Mull of Galloway, Peninnis, Royal Sovereign
1 flash every 15 secs, Lowestoft, Lundy North, Sark, Turnberry, Wolf Rock
1 flash every 10 secs, Anvil Point, Crammag Head, Dungeness,Point Lynas, Southwold
1 flash every 5 secs, Cromer, Little Ross, Lundy South, Monkstone, Orfordness, South Bishop, St, Catherines, Trwyn Du
1 flash every sec, Aircraft warning lights
The lighthouse simulations should use a white LED, while a red LED is commonly used for aircraft warning lights.

NB The kit circuit flashes an LED, there are no rotating parts in the kit, but unless you want to watch the beams from above!

[davebradwell]

Ach, a simple flashing light just wouldn't be a finescale job and would likely drive you nuts eventually. Being above or below optimum height with a proper job would probably give a gentle throb rather than a bright flash so should be bearable even if baseboard height needs adjusting. I'm trying to remember my basic optical design but there's some vital details missing like position of the defining aperture. Remember you can't have a parallel beam, it's all to do with the etendue. Also you'd only see the beams in a smoke filled room. Suspect your biggest problem would be containing all the stray light that doesn't go through the correct route.

DaveB

[BrockleyAndrew]

Many thanks everyone for the advice and suggestions. Just for interest here are two photographs from the 1930s one showing the inside of the 10sided first order Fresnel lens and another showing the rotating beams.
I agree that that effect would be difficult to achieve, as pointed out it would need a smoke-filled room and the effect probably wouldn't scale down well anyway. I have bought some cheap small plastic Fresnel lenses 27mm diameter, mini magnifying glasses from an archaeological equipment supplier! I'm going to experiment a bit with cutting them into panels if I can.

Screenshot_20211110-165056__01.jpg

Screenshot_20211128-112900__01.jpg

[LesGros]

Andrew,
Interesting images.
I have a dust covered project; currently to be found in the compost of ideas papers in the back of a drawer. It is to model the reef, and aforementioned Bell Rock lighthouse, to be 3D printed at a suitable scale for placement in the distant dark back corner of a layout [Also yet to be built]

Given the constraints of MERG PMP 13, the simpler solution here would be to model with a rotating mask, spun to suit the required flash rate. It should be possible to contain the light in a closed cylinder.

In truth, at this point, it is mostly a thought exercise which piques my interest from time to time. Issues to be solved are: 1 Using Fusion 360 for reproducing the shape of the tower, from research of images in "Stevenson's Light houses, and online; 2 The detail of the reef, and at which state of tide (simplest would be with the landing stage covered at High tide);3 The representation of sea state, and at a distance for the scale to make sense.

Meanwhile, in the here and now, there is Garden landscaping to be completed; now in the twentieth year of a five year project. Being surrounded by trees means that many of the regeneration weeds now require the attention of a chain saw. Tempus Fugits

It is fortunate that we are in favour of the wild garden style; the local birdlife seems to approve too.

Happy Modelling Andrew, I suspect that your project will be finished long before mine comes to fruition.


Cheerydoo

[davebradwell]

Who said there were only 4 lenses, although it made sense at the time?

If you hold your lens at arms length and look at a LED through it, there is a distance from the LED when it appears to fill said lens. Suspect this is the effect you want and a larger light source would give a bigger viewing angle which would be beneficial. You would then have the top of lighthouse with a background glow and by bending your knees you could reach the right height for a flash, if you see what I mean!

It's a vital part of the model - same as the mill on Slattocks or the gasworks at Barrow Road.

DaveB

[Jol Wilkinson]

Who said there were only 4 lenses, although it made sense at the time?

If you hold your lens at arms length and look at a LED through it, there is a distance from the LED when it appears to fill said lens. Suspect this is the effect you want and a larger light source would give a bigger viewing angle which would be beneficial. You would then have the top of lighthouse with a background glow and by bending your knees you could reach the right height for a flash, if you see what I mean!

It's a vital part of the model - same as the mill on Slattocks or the gasworks at Barrow Road.

DaveB

Dave,

it was I.

The speed of rotation and the number of lenses will define the number of flashes. A slower speed and more lenses would give the desired 10 second flash but presumably there is an ideal flash period which will have an influence on both. I haven't found a definitive time for the length of the flash from an internet search but 2 secs has turned up a couple of times. Shorted periods seem to apply to fixed flashing lights (buoys, beacons, etc).

Jol

[grovenor-2685]

See my post above for a selection of lighthouse flash rates.

[allanferguson]

Traditonally, lighthouses had an oil lamp surrounded by a set of lenses which rotated to give the desired characteristic. The mechanism was driven by a falling weight, which had to be wound back up every hour or so by the keeper on duty.
In more recent times the lamps have mostly become electric, as has also the rotating mechanism, which has made it possible for all lighthouses in Scotland to be unmanned. Most of the big lighthouses, instead of having rotating prisms, have an array of five or six sealed beam units (like car headlights) which rotates to give the desired characteristics.
The effect on the visible light is that the off/on is rather sharper, whereas the prisms did show a more gradual transition.
Also when the beam is rotating it will shine on ground or structures, if any, behind it, at the right height. We used to find our way home from dances in Kildonan by the beam from Pladda light Gp(3) 30 sec.
Small lights or beacons mostly had a simple on/off system (no rotation).
Since none of these lights would shine during daylight, there needs be, for model purposes, a certain suspension of disbelief --- but isn't that what modelling is about?
Another thought has struck me. What about the foghorn?

Allan F

[Julian Roberts]

Another thought has struck me. What about the foghorn?

Allan F

A believable depth of sound without enveloping the neighbourhood or whole exhibition hall might be a challenge!

[BrockleyAndrew]

I did wonder how long it would be before someone mentioned the foghorns! Tomorrow's World has an item about the most recent lighthouse at Dungeness, built when the nuclear power station blocked out the 1904 high Lighthouse. There is a piece about the new foghorn technology, multiple specifically aimed speakers. There is also information online about the historical foghorn installations at Dungeness, one of which is modelled on an American design. I was amused about the idea of modelling an annoying foghorn....

[Philip Hall]

I was amused about the idea of modelling an annoying foghorn....

It would make a change from annoying exhibition diesel depots with (far too loud) DCC sound!

Philip

[BrockleyAndrew]

Just to thank everyone again for their contributions to this thread. Sorry if I haven't replied to or thanked all. What I love about this hobby is the way it directs one to study historical areas one hasn't before considered and I always find personal reminiscences and technical help suggestions on this forum rewarding. I have, through this lighthouse deviation, looked up and found out much about gas lit lighthouses and Fresnel lenses. As ever with internet searching, while it is rewarding, it is a little scattergun and often sites are merely lifting their information from other sites without checking details. The Dungeness Old Lighthouse (No.4) is variously reported to be 150/140/163feet high and the flash interval is reported as 1 every ten seconds, but the pamphlet history of the lighthouse available in their shop has the lens assembly rotating every 40seconds which for the ten sided optic (which is still in place) would give 1 flash every 4 seconds. It also looks slightly suspicious that the 1 every 10 seconds appears in (the more famous) Lizard lighthouse references. Given that one of the advantages of rotating lenses was the opportunity to give them their own distinct patterns of flash I wonder if 1 in 10 was a first order Fresnel lense used in coastal lighthouses convention or if writers have just assumed a commonality. Lighthouse #3 at Dungeness is said to have had a rotating flash every 5 seconds.
The large first order Fresnel glass lense assemblies weighing over a ton were floated on a circular bath of mercury which the lighthouse keeper had to maintain and, even with a suppression later of engine oil on top, was a toxic vapour work hazard. The mercury allowed them to rotate by the clockwork mechanism.

Oh - on foghorns the Lighthouse history booklet by Edward Carpenter says that the 1930s Low Lighthouse and foghorn building, demolished to make way for Lighthouse #5 in 1959, gave a "deep burr sound of three blasts - the Morse R (.-.) - every two minutes.

[alan@york]

Surely you'll only need the foghorn in foggy conditions, to be accurate. Or is that covered as well by a fogging machine?
a@y

[Winander]

I am certain that lighthouses in the same general locality e.g. the Channel would all have different 'signatures' to assist mariners identifying where they were in extreme weather. This might be confirmed by establishing the location of the lighthouses with the same light pattern as listed in Keith's details of the MERG offering - I suspect you will find they are considerable distances apart.

As always, you research as diligently as possible to either get an accurate or the best representation of a model. Then wait for someone to try to prove you wrong, which, if you've researched properly, will be pretty hard to do. And rule 1 applies.

[Julian Roberts]

Sorry I'm getting a bit carried away by the modelling fantasies here! Fog - dry ice. Foghorn - tuba. To blow the fog away you may like some wind and thunder?...this is how they are modelled in the orchestra



Actually I'm still waiting for you to mention the surely greatest attraction there - the RHDR!!

[Guy Rixon]

The large first order Fresnel glass lense assemblies weighing over a ton were floated on a circular bath of mercury which the lighthouse keeper had to maintain and, even with a suppression later of engine oil on top, was a toxic vapour work hazard. The mercury allowed them to rotate by the clockwork mechanism.

The modern equivalent would be a hydrostatic bearing using pumped oil, but it's a more complex thing to maintain. These bearings can give superbly low friction; I've seen a 200-ton structure that could be pushed round by hand on its hydro bearing.

[BrockleyAndrew]

Oh the RDHR. To model the loop would take a lot of space and I haven't even engaged mentally as to what their comparative size is in 4mm.... I'm trying to ignore it even though I like it very much. Saw double headed steam the day I visited the lighthouse last year...

[Terry Bendall]

I haven't even engaged mentally as to what their comparative size is in 4mm....

The RH&D is ofcourse 15 inch gauge so in 4mm scale the track gauge would be 5mm. The prototype locos have shades of OO scale with the chassis about 1/4 full size but above the footplate they are 1/3 full size and are are of course scaled down full size locos. Try buuiding one of those in 4mm scale.

Terry Bendall