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[Bob K]

Andy:  That air pump looks really neat, and very compact too.  At 12 L/m that will blow the tanks very rapidly, and I would not need a pressure switch cut off if the bottom of the ballast tanks are open vented.  I will also need to think about interconnecting the two tanks with 3 mm tubes and fitting baffles to ensure it keeps on an even keel.  Thank you.

[Bob K]

Layout of internals:

I have found from previous builds that it is best to organise the internal layout before fitting bulkheads etc.  There is a lot going into this hull.  Murphy’s Law dictated that I am going to have to alter the ballast tank profiles to get vertical side walls with 100 mm between to fit the 6V 12AH SLA battery between, and allow space for the shafts and motors.  I was hoping that the mister outlet could be directly under the funnel, but . . .



Batteries
Three battery sets involved.  A big 6V 12Ah SLA for the low RPM motors, 12V for the air pump, and 24V for the mister.  For the later I have two 12V NiMh packs in series as it only needs around 1/2A for several hours running.  The 12V for the pump that Andy recommended (now on order) can also be fairly small.  Batteries as low in the hull as possible, final positions will be adjusted by bath-test ballasting, but will require waterproof cable glands between compartments.

Electronics
The electronics modules will be mounted on a removable internal panel, keeping them well away from motors and pump etc.  Mounting the 2.5” mylar cone speaker will need some thought due to very low freeboard.

I aim to operate the ballasting controls from one channel (stick).  A chunky servo sits at neutral.  Operate one way rudder-type linkages will open the Blagdon air valves, and in the other direction a cam + microswitch will turn on the air pump.
That should be interesting !

[Subculture]

Worth trying the pump on 6 volts, you may find it fast enough on the lower voltage, and it will save using another pack of batteries.

[Bob K]

Thanks for that suggestion Andy, I will try that when the pump arrives from the States.  Could make the battery recharging less complex too.


PS:  I took my wife out for dinner and a movie tonight.  The film was not a documentary on my latest ship build after all, but about aliens and spaceships.  However, it was a cracker and totally stopped me from thinking about boat wiring for over two hours.  

[Bob K]

H.M.S. Polyphemus (1881),  Smoke without fire

With space inside this 1.27 m hull I am adding some ‘first time’ special effects, bread-boarding the electrics to test them out before trialling the ballasted hull fit.  The size and shape of the side ballast tanks determines WTC space available between.

Smoke without Fire
A Victorian single funnelled ship really needs some serious smoke on the water.  After considering alternatives I opted for the MMB Foggy unit as this will be running inside a watertight chamber with ventilator inlet and ‘smoke’ outlet tubes.  No heat.  On 0.7 Amp and plain tap water, I ran it for over an hour without refilling.
However, the mister needs 24V (2 x 12V AA cell packs) plus 6V for the fan.


The Foggy Unit being run outdoors under natural wind conditions.  Does the job nicely.  There is also a version where the fan speed is varied by the throttle setting, but I’ll try the basic unit first as ships of this era made loads of smoke even when idling.  

See  http://www.marksmodelbits.com/

[Subculture]

You could always fit a switch mode booster to get your 24 volts- http://www.ebay.co.uk/itm/12V-to-24V-Step-up-DC-Power-Converter-Convertor-Module-/250874790943?pt=UK_Computing_LaptopAccessories_PowerSupplies&hash=item3a694d841f

[Bob K]

That does look a good idea Andy.  At the mo' I have two 12V 2600 mAh AA cell packs in series, and will try running the vacuum pump off the 6V main motors SLA as you suggested.  Not sure if the voltage step up involves converting to AC, stepping up then rectifying.  If so that big coil may radiate a lot of RF ?

I intend building a 'test jig' with two empty 2L lemonade bottles suitably ballasted and with bottom vents to gauge how fast the pump vents them, and how much 'pressure' may be generated before constructing the side ballast tank bulkheads.  Hopefully the worst case scenario will be huge amounts of air being vented from the bottom of the hull.  A good test for my Blagdon air valves too.

I am really looking forward to seeing how the ACTion P64 multi-cylinder steam engine sound module operates.  A lot of R&D in this project, but hugely enjoyable challenges.

Thinking ahead, I will need to find suitable gasket material for the screw down hatches, and blind nutserts.  I will search the Mayhem submarines section.

[Subculture]

It switches so it will be dirty, but should that matter with 2.4ghz? I think it's largely immune to such radiated interference, although there are others more knowledgeable than I on this. You could stick the thing inside a grounded steel case, that would deal with a lot of nasties (works for computer PSU's).

Regarding watertight boxes, you don't need to bother with blind inserts for the bolts, use an o-ring sponge gasket for the seal and put the nuts and bolts on the outside of this seal (make sense?) then the bolts don't need to be sealed at all, and you can just use ordinary fittings. You could use wing nuts for easy tool free access.

Something else to consider is lock and seal boxes from tesco. These are watertight. Not so great for subs, becuase they're squishy, but would do the job here. only problem i can foresee is that these things are made from a plastic that doesn't take adhesives very well, so anything that passes through would need to be mechanically fastened or bonded in with a mastic sealer e.g. Sikaflex.

Regarding pump pressure- nothing to be concerned about. These pumps make about 15 psi maximum in the real world.

[Bob K]

It switches so it will be dirty, but should that matter with 2.4ghz?

I intended to use my 40 MHz F14 with the Multiplex Rx that was 'spare' from my sub project as the Rx will be below the waterline.  The main deck will run almost awash underway.    Hence my treating this as a surface running submarine.

Any waves are likely to wash over the deck when trimmed down so the six access hatches and fixings will need to be waterproof, yet be removable.  The space between the underside of the deck and the access hatches needs to allow for free flooding with scupper slots.
I was thinking along the lines of replicating the srew down hatches used on some of the Engel subs.

I have a selection of the nice Tesco boxes but can't get all my running gear in them.  Pity, they are really watertight.

[Bob K]

H.M.S. Polyphemus (1881),  Bulkheads

Next up are the bulkheads.  Two longitudinal ellipses for the ballast tanks, and five transverse for the six machinery compartments.  The ellipses were transcribed using mylar film from the side ballast fill lines, then transcribed onto 3 mm corrugated cardboard templates to test fit.  The side bulkheads had to be angled more upright to allow for a more practical 100mm compartment width.  This meant flat top edges need to be added.

Going from templates to 3 mm clear polystyrene will have to wait till payday as I will need a power jigsaw for the curves. 
This video clip was informative   http://www.youtube.com/watch?v=nh62xaTEmxw



Once the sides are fibre glassed in I can make up cardboard templates for the transverse bulkheads, then cut Marlon cellular copies to fibre glass in.  Care will need to be taken to ensure all top edges are level for the under deck.  I may utilise the long axial recess in the base of the hull to route wiring through brass tubes.  These can be sealed off with RTV after wiring.

• A:  Rudder
• B:  Motors
• C:  Main battery
• D:  Foggy mister unit
• E:  Other batteries and controls
• F:  Twin front rudders

[Subculture]

You can slice up polycarbonate with just about anything. It's more chewy than most plastics, so not brittle.

[Bob K]

I had some thought and tests on this.  The 3mm clear sheet is B&Q polystyrene for interior glazing, and very hard.  If I was cutting rectangles I could get away with repeated scoring with a Stanley knife and steel rule.  However the side bulkheads are long ellipses.  Fret saws will not do it due to frame getting in the way.  I may have no choice but to get a power jig saw and sandwich the material between two clamped sheets of wood.  At least I can cut both bulkheads together.  The other bulkheads will have profiled bottoms to suit the hull shape.

The more I get into boats, the more tools I seem to need !

[joppyuk1]

A fretsaw has its limitations but, have you considered a coping saw? You know, the one where the blade angle can be altered by twisting. Mine has about 6 inch clearance at maximum (90 degrees)  -  just been and measured, it's 170mm allowing for a couple of mm clearance. 

[Bob K]

Forgive me, but isn't a coping saw similar to a fret saw but usually with less 'throat' clearance in the frame?  My fret saw also has a revolvable blade but nowhere near man enough for the job.  Maybe worth looking into getting one with a very heavy duty frame, and scribe-cutting oversized rectangles first.  My thought on going for clear material was to be able to visually check water levels in the side tanks.

[Beagle1831]

I've had a similar problem cutting curves in clear sheet- it can be scored and snapped along the line as you described. I roughed out curves in short straight sections, making connecting cuts with a hacksaw from the edge of the plastic to the scored line to allow the excess to be snapped off in sections (if you see what I mean!?). Once I had the rough shape I then sanded down to the correct curve. Hope this helps! James

[joppyuk1]

Sorry, wasn't trying to mislead you. My fretsaw blade is fixed, hence reliance on coping saw for any saw cuts needed along any large length. If you'r adter oval shapes and cutting initial rectangles, would cutting the corners off as well help? thus starting with ovals .

[Bob K]

That's a good idea James.  Start off with a scribe-scored rectangle then successively hacksaw short straight cuts to build up the curve before smoothing the contour.

Sorry Ian, my background is from Engineering.  My 'woodworking' knowledge is abysmal.  I tend to approach problems 'a la Brunel' (take a block of cast irion . . .) but without the big workshop machinery I was used to.  ie a nice heavy duty bandsaw   

[Bob K]

The internal bulkheads are taking some time, and head scratching to get the mechanics right.  

PM received asking “… if you drop the odd crumb of visual history in occasionally I'll love it” , so here is some more info on this strange warship.  At attack speed only the fore and flying decks remained ‘dry’, 18 kts was unprecedented in 1881.   This view from the aft quarter clearly shows the ultra low freeboard, side bulges, and propeller protecting docking booms


Note the two huge float-off life rafts amidships.

 

Armament  
Main armament of HMS Polyphemus was its five submerged torpedo tubes, a first for the Navy.  The ram was very much secondary armament.   The only other weapons carried were Nordenfelt four barrel 1 inch anti torpedo boat machine guns, carried in six rotating turrets on the flying deck.  A very early form of machine gun, it was operated by pulling a lever back and forth as this animation shows.  Yes, the turrets will rotate on the model, ganged together from underneath the deck.



http://www.youtube.com/watch?v=gu8GgzDiS90

[Norseman]

  ............ it was me
Thanks Bob

[victorian]

I intended to use my 40 MHz F14 with the Multiplex Rx that was 'spare' from my sub project as the Rx will be below the waterline.  The main deck will run almost awash underway. 

Some of the (very inexpensive) 2.4 Ghz Rx's have a socket for an extension antenna. For instance see http://robotbirds.com/catalog/product_info.php?products_id=6222. It's only the exposed part at the end that's active.

It would take a lot to persuade me back to 40 Mhz, especially with a unique model like this!

P.S. is it 'Poliffimus' or 'Poly - themus'? I'm still waiting to hear!

[unbuiltnautilus]

My vote goes on Poly-themus..

[Norseman]

http://en.wikipedia.org/wiki/HMS_Polyphemus_(1881)

[Bob K]

I will check into that 2.4 GHz Rx.  Thank you.  I had opted for 40 Mhz as I already had 'spares' from my submarine projects.

Pronunciation was Poly ‘ fi: mes .  In Greek mythology Polyphemus was the gigantic one-eyed son of Poseidon and Thoosa, one of the Cyclopes. His name means "much spoken of" or "famous".  Polyphemus plays a pivotal role in Homer's Odyssey.

To put this ship in historical context, she was laid down the year before the Zulu war of 1879, and launched three years before the ten month seige of Khartoum in which General Gordon died.  In the Sudan Nordenfelt rifle calibe machine guns were used at the corners of the British infantry square that held off the Dervish army at the battle of El Teb 1884.

Nice video clip shows these guns in action on a gunboat from the movie Khartoum. 
http://www.youtube.com/watch?v=sDkcG5whNQo&feature=related

[Bob K]

H.M.S. Polyphemus (1881),  Bulkheads

I wish I still had access to Pro/Engineer 3D software.  To have modelled the hull outline from plan sections it would then have been easy to make accurate movable vertical sections for bulkheads and generate all the volume and ballasting data.  With the big side bulges internal space is too restricted to use profile gauges.

So, back to the bath tub to replicate static ballasting, plus two part-filled 2 Litre plastic bottles to simulate additional pumped water ballast.   I need a constant 100 mm width for machinery spaces.  Two strips of ABS were fitted inside the hull equispaced about the keel line, then replicating the vertical bulkhead planes using a balsa frame to create card templates within.



Transverse bulkhead positions are set by positions of internal equipment when levelled on an even keel in the bath.  She will still need about an extra kilo of ballast, allowing for superstructure and electrics.  I plan on using an additional small 12V SLA battery just forward of the mister, which positions the mister outlet nicely under the funnel..



The card templates will then be used to define the clear plastic bulkhead outlines.  Getting this layout correct is essential before committing bulkheads in epoxy.  The trick is to have a level safe sailing waterline with tanks empty, and a level trimmed down attack mode waterline for millpond conditions with tanks full.  Wish me luck !   

[dreadnought72]

Looking good!

Definitely go for baffles in the tanks to reduce free surface/sloshing effects. Or else! 

Andy