Exciting development!

[Mark Beard 1Participant @markbeard1]

Looking again, I think the Maplin part number for this cable is XR15R and is priced at £0.79 per meter. This will give you two conductors, an inner core and an outer screen, just like the real thing.

Mark.

 

PS 100m reel is £39.

Edited By Billysugger on 30/04/2011 13:01:16

[Bob Abell 2Participant @bobabell2]

Thank you, Mark

 

Sounds a little too good for the job?

 

Here`s the tricky bit……….What length of cable can get in 75 dia x 150 long?

 

Another concern is…..How do I rewind the cable after a dummy run?…….covered in toxic duck muck water!

I was hoping the have several drums of wire to avoid this problem

 

Just curious…………Bob

[Bob Abell 2Participant @bobabell2]

 

Two views of the stern showing the payout sheave

No authentic pictures seem to be available of this section

 

Dramatic view from sea level!
The cable shown is not to scale

 

[Mark Beard 1Participant @markbeard1]

Posted by Bob Abell on 30/04/2011 13:41:02:

What length of cable can get in 75 dia x 150 long?

 

Is the hold 150mm long, or do you have extra length to run the cable from the drum/spool to the paying out gear? Extra length would be good, even if not absolutely necessary.

[Bob Abell 2Participant @bobabell2]

Hello there, Mark

 

I`ve got about 32″ from the spool to the intermediate winch mech…….then about 12″ to the paying out sheave

 

Still would like to know how much wire is there in a drum 150 mm long X 75 mm dia?

 

Bob

[Mark Beard 1Participant @markbeard1]

Oh that’s excellent… working on it at the moment….

[Mark Beard 1Participant @markbeard1]

There are several ways to work this problem.

The obvious way is to have a drum on a spindle and take the cable off tangentially, spinning the drum as the cable is unwound. This makes winding and unwinding the drum easy, but has a couple of disadvantages: 1) the inertia of the drum will cause cable overrun within the hold as the ship slows down; and 2) extra beam is required for the cable take-off.

The less obvious way is based on the principle of wire-guided missiles (can your imagination stretch from those to the Great Eastern?). A tapered bobbin with the narrow end astern. The take-off point is aligned with the spool axis and is further aft still. The attached sketch shows that the take-off point must be aft of the point projected by the outer layer of cable on the spool, to prevent it from fouling on the inner layers.

The advantage to this scheme is low un-spooling resistance, negligible inertia and simple axial take-off gear. This comes at the cost of less simple re-winding and the need to incorporate some twist into the cable as it is re-wound to avoid it twisting up when it is un-spooled .

Is this anything like what you have in mind? While you think of a diplomatic answer, I’ll work out how much cable can be spooled this way.

Mark

[Mark Beard 1Participant @markbeard1]

Right:

 

The parameters I’m working to are 2mm cable diameter, minimum cable bend radius of 20mm and max radius of 35mm (to accommodate the 75mm diameter plus 2x cable radii plus 1.5mm clearance).

DRUM

The volume of the drum of wire is drum length x coil area

V = L x pi x (r2² – r1&#178

where V = the volume in cubic-mm
pi = 3,14159
r2 = the outer coil diameter in mm
r1 = the inner coil (former) diameter in mm

Cable length, assuming that the cable coils lie next to each other and occupy square secion places, is the volume divided by the square section across the cable diameter d, which is

CL = L x pi x (r2² – r1&#178 / d²

So, for a simple drum on a 40mm former and 70mm outer diameter (leaving the spandrel section below the deck, adjacent to the hull, for the take-off gear), gives

L = 150
r1 = 20
r2 = 30
d = 2

CL = 150 x 3.142 x (900 – 400) / 4
= 58,912mm
= 58.9 metres

SPOOL

For a tapered spool, the angle of taper is given by the minimum radius 20mm and the 750mm (30-inch) take-off distance. 20mm in 750mm is 4mm in 150mm, which gives the minimum taper. So design with a 5mm taper, giving the bobbin a tapering in radius from 20mm to 25mm (diameter 40mm to 50mm).

Now because the take-off gear is axial, we can use almost the whole diameter available for the outer cable radius, so this will taper from 30mm to 35mm.

I don’t propose calculating the precise volume without knowing that this is the scheme to go for, but will estimate is by taking the average radii of the tapered spool and using the drum formula above.

So, for this approximation:

L = 150
r1 = 22.5
r2 = 32.5
d = 2

CL = 150 x 3.142 x (1056 – 506) / 4
= 64,804mm
= 64.8 metres

So, either way I reckon you’ll get around 60 metres in that volume, slightly more with the tapered spool. Is that enough?

[Mark Beard 1Participant @markbeard1]

Er, those smilies are supposed to be close brackets. Thanks forum software!

[Bob Abell 2Participant @bobabell2]

Wow! Mark!

You have been busy!

64 metres is disappointing!

Don’t fancy the tapered spool idea, as it wouldn’t look right in the hull….and it would twist the wire as it pulled off?

Prefer a parallel coil with a friction device resting on top……To prevent the drum overrunning

If that’s all the cable we’ve got, then we’ll have to live with it.

There is chance that single core cable could be made to work, with the earthing rods etc and an amplifier or something

I think a TV man is calling round, sometime next week and at least we make some progress, one way or the other.

Thank you very much for your assistance and tech stuff

Regards…..Bob

[Bob Abell 2Participant @bobabell2]

Latest pictures of the winch

Slightly oversize……..But needed to be very strong in case we have a snarl-up out to sea!

In which case the boat will stall with no damage done……Hopefully

 

Guess what I used for the pulley flanges?……….Pennies!

Edited By Bob Abell on 01/05/2011 09:47:12

[Mark Beard 1Participant @markbeard1]

Gosh Bob, you don’t hang about! That looks amazing.

[Mark Beard 1Participant @markbeard1]

Did you spot my error in the drum cable calculation? The outer diameter was 70mm so the radius should be 35 not 30mm. Too much of a late night I think!

 

L = 150
r1 = 20
r2 = 35
d = 2

CL = 150 x 3.142 x (1225 – 400) / 4
= 97,205mm

= 97 metres

 

Think it makes a big difference? It should do, as the volume is proportional to radius squared, so a small increase in radius makes a big difference in volume (hence length).

 

If you could increase the outer diameter to 92mm, then I reckon you’d get 200m of 2mm cable in. But that of course may be too much for the model, unless your size limit is for passing a drum through a hatch, and winding the cable in situe would allow for more cable?

[Bob Abell 2Participant @bobabell2]

Had a trial run with some handy two core stuff and it ran through ok

 

The winch in it`s final position. The cable travels down towards the drum via a length of plastic tubing…To get through the mass of assorted wires inside the hull and into a clear area and hopefully, will flex sideways as the cable comes of the 6″ wide drum

[Bob Abell 2Participant @bobabell2]

Looking at the archives again, Great Eastern`s max cable laying speed was 7 knots

 

This works out at 8 mph

 

The model is 1/100th scale and the model speed works out at 86″ per min

 

In other words…….one hull length per min……..1.44″ per second………Awfully slow!

 

It will be interesting to see what speed we get up to, the normal sailing speed is about 2 mph

 

Speaking to an electronic expert today, he reckons we can use fine earphone coaxial cable, and obtain a signal using computer on off signals?

This would make the cable drum size very practical

 

All good stuff!……Bob

[ashley needhamParticipant @ashleyneedham69188]

I like all the calculations…but

 

i think a practice run is needed first, using a.n.other boat and any old setup, using different types of wire….because…

 

The wire will not be heavy enough to sink straight away like the real stuff, although no doubt it WILL sink, and tension on the wire may cause an appreciable length to be strung out over the stern looking less than realistic. The paying out attachment at the stern looks very “period” but the realist in me would like to see a funnel at the front end to guide the wire through better than a simple `ole.

 

It may be that, although running the cable across the pond in one length is the aim, just thinking out loud…that “an amount” of cable could be layed, and then a sleeved weight placed over it, and laying continues..with “weight” stops, to ensure the ship has something to pull against without the cable rising in an unseemly manner, and keeping the rest down and in a straight line.

 

The stops in laying need not be televised of course, and the fact that the ship will have laid a continuous length will not be compromised.

 

Ashley just thinking around the practicalities.

[Bob Abell 2Participant @bobabell2]

Well it`s about time you chipped in!

 

Welcome aboard, Ashley!…….Always nice when an expert gets involved!

 

I am in the process of sorting some better cable guides on deck., there was going to be a bell mouth at the entrance to the sheave, but the hole is a little too low

 

As for the wire floating??????…..Not a chance, old chap!……Just tried it in the bath!

 

We know all about the tricks of the trade, but the first voyage will be a genuine cable laying exercise. If things turn bad, then the trickery will start!

 

Thanks for looking in……Your comments are always welcome

 

Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob, not suggesting that the wire will float, was more concerned about the aesthetics of the wire dropping into the oggy from behind the ship, or being under tension and having a fair amount being visibly pulled out the water.

 

Is it that the wire will be pulled off the spool by the ships forward motion, or fed over the stern by the motorized thingy? I suspect some tension will be required viz..pulling the cable, to prevent snarl up`s in deck.

 

Hence my suggestion for a mock up test rig/boat setup to test the operation and get “the look” right first. Photgraphic trickery will be of no use if the stuff isnt flowing out the back in the first instance….

 

Ashley

[Bob Abell 2Participant @bobabell2]

Me and Ducky or…Ducky and I……..will be carrying out a reliability test in a few days time, at Etherow lake, where we can study the situation

 

Just finalising the ship at the moment and waiting for the cable selection.

 

When GE is a reasonable distance from shore, the cable should be emerging from the stern sheave in a likeable manner, but the first 10 feet from shore could look a bit taut possibly……..Will be an interesting trial?

 

Bob

[Mark Beard 1Participant @markbeard1]

The screened cable I have sinks like a stone too, but that may not be the point. Since the model will be in water which is way too shallow, even allowing for scale, and is likely to be travelling faster than scale, and will be pulling against the drum, with a force much greater than scale, I envision the cable coming from the stern at a more shallow angle than the real cable laying operation. If that’s a bother, then a simple wire guide (with or without a pulley) below the waterline could ensure that the cable comes off the stern almost vertically, then trails at a shallower angle to the pond-bed unseen.

[Bob Abell 2Participant @bobabell2]

That`s a good idea there, Mark!…….About the concealed underwater eye

 

We`ll bear that in mind

 

We could move off in a series of stop/starts……to allow the cable to sag?

 

Bob

[Bob Abell 2Participant @bobabell2]

How`s this then?

Just the ticket!

 

Bob Chief Eng

[Bob Abell 2Participant @bobabell2]

Ahoy there, chaps!

 

Does anybody know if there are certain specific flags to be flown when cable laying?

 

Needs to be correct for the television viewers!

 

Bob

[DuckyParticipant @ducky]

Your certainly a stickler for detail Bob, I suppose its your engineering coming to the fore.

Nice to see you back into the modelling scene, its not been the same without your threads and comments. Looking foreward to the maiden voyage of your cable layer, hope its as exciting as the maiden voyage when it was first made, but not as exciting as the Deanie Deans At War when we were fighting the heavy wind and swells!.

[Bob Abell 2Participant @bobabell2]

Hello Ducky!

 

It`s about time you got involved again. You will be needed for the trials next week and also the TV event end of this month`ish……Can`t manage the big ship on my own!…..And besides….You know the ropes!

 

Bob

 

 

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