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Author Topic: HMS Intrepid, 1:96 scale Sirmar semi-kit  (Read 25928 times)

Dave Cook

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #25 on: March 14, 2016, 06:31:07 PM »

Great stuff Edmund.keep us updated
Dave :-))
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warspite

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #26 on: March 14, 2016, 08:44:15 PM »

Does filling the cavity with water to the required level and then pouring it into a measured container not allow you to calculate the volume, the length of the profile and its thickness and any profiles and vertical skin then is added as these are easily calculated.
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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #27 on: March 14, 2016, 09:07:21 PM »

Does filling the cavity with water to the required level and then pouring it into a measured container not allow you to calculate the volume, the length of the profile and its thickness and any profiles and vertical skin then is added as these are easily calculated.


Absolutely!  Archimedes' eureka moment!  I had calculated that 2 litres would be required to flood the dock, but having built the dock with all its complex curves it is very difficult to judge what its volume was.  So I poured a 2 litre lemonade bottle of water into the ballast tank and hey presto it all disappears into the tank no problem.  In fact it seemed to fill the tank to just over the floor of the dock, so the full ballast tank volume would probably be about three litres. 


Now I need to filll the tank with the ship floating and see exactly what amount of water will flood the dock to the right level.  Hopefully if the level in the ballast tank is higher than the dock level water, one can put an overflow in to prevent overfilling the ballast tank.  If the level is lower I might need some buoyancy added to the ballast tank in the form of polystyrene foam to decrease its volume.  Otherwise there is the danger of becoming a submarine!

Edmund

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #28 on: March 17, 2016, 09:18:46 PM »

After consideration I decided to have a second ballast tank at the bow and pump water between them instead of pumping from the pond.  There are perhaps two advantages to this.  First that some of the ballast of the Intrepid can be dumped in the pond before return home, making transport a little easier.  Second one won't need as much ballast transferred into the tanks as there will be a fulcrum effect between bow and stern.  Bow goes up and stern gows down.  So another bath test and see just what is needed.  I have installed two 12volt acquired from China fish tank pumps.  They only pump in one direction but are submersable if needed, but I discover that as they are of impeller type it means that when not active you can pump water straight throuh them.  So one at each end of the connecting pipe.


So two litres of water in the forward ballast tank, and a couple of large 12v batteries for ballast.  All nicely trimmed.  Then pump for approximately one minute and the dock drops gently into the water with it filling through the drain holes while the bow rises correspondingly. Trimming is going to have to be carefully done.  Stop pumping but the dock still fills gently.  So the amount of ballast needed to lower the dock enough to flood it seems to be around about 1 litre of water.


Rudders are now fitted with clevises and flexible bike brake cables through to the main hold.  I'll get a phptograph once I have fitted the servos in place.

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #29 on: March 18, 2016, 01:18:24 AM »

Edmund....not dampening your thoughts %)....and displaceable water ballast can be a great advantage :-))

One point for consideration is the need is to use water baffles in the tank...this will greatly assist in a large volume of water being thrown from one side of a partially full/empty tank in any violent >>:-(  manner...which can cause temporary instability

Derek
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Edmund

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #30 on: March 18, 2016, 11:32:21 PM »

Quite right Derek!


I thought a bath sponge in the wide bit of the forward ballast tank would dampen the movement of the water, if that is the right word!  The rear ballast tank doesn't need the baffle as the ship shouldn't be on the move if this one is full of water and then the dock also acts as a sort of baffle to prevent the water sloshing around.


It's the anchor that's taxing my mind at the moment.  Winding in is easy but it is the paying out without tangling that is more of a problem.  All is ok while the weight of the anchor is on the chain but as soon as it hits the floor of the workshop the chain doesn't have enough weight to keep paying out.....  What to do?

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #31 on: March 19, 2016, 12:11:42 PM »

The anchor.....  this has been a headache!  It will be necessary to have an operating anchor that holds the ship in some way while assault operations happen from the stern, with dock flooding and landing craft setting off so I have tried a variety of self stopping winches etc with a mixed bag of results.

The main issue is tangled chain and not feeding through the hawse pipe effectively.  But sometimes it is the simplest solution that is the best.

Apologies for the mucky interior of the ship in the photo - work in progress and this is the hidden bits that no one is ever meant to see!!  But it shows a solution which is seeming to work.  Anyway it has been dropping and raising an anchor and chain to the workshop floor all morning without any problems.

The winch is a 3mm rod which goes into a short brass tube in the bow as a bearing.  There is 2 metres of chain - more than enough for our pond which is hardly more that 60 cm deep. The 3mm rod is long enough to mean that the geared motor that powers it is the main hold of the ship so that maintenance is easy.  A short brass strap holds the motor in place.  The geared motor 1:60 gearing is attached to the rod with one of those rubber couplings that will slip if too much load is applied - such as anchor reaching hawse pipe and not being switched off, or caught on the bottom and not releasing.  The chain is attached to the rod with a bit of electrical insulating tape which again can slip if lots of load is applied.  And the whole thing can be withdrawn from under the deck by undoing one screw.  A servo operating two micro switches will operate the anchor by RC.

So I've been sending it up and down and even when it is only the weight of the chain taking the anchor out it seems to work without any tangles.  It does mean the anchor has to be lowered rather than let go, but at this small scale the anchor was not going to go easily by itself.  As for the winches visible on the deck - they will be static.

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #32 on: March 19, 2016, 08:18:31 PM »

Hullo Edmund............just thinking outside the model square

Real anchors are generally disconnected from the windlass clutch & free fall [however under some sort of overspeed brake] to the bottom.........to raise the anchor the clutch is re-engaged & the anchor slowly hauled in

You could consider modifying your anchor system to free fall via the disengaged windlass & having it as a single direction hauling in function

There are two reasons why in real life they function as above.....with the principal consideration being to get the anchor onto the seabed surface as quickly as possible to stabilise the position of the vessel.....this too is absolutely critical in an application such as the type of model vessel in your build....... Derek
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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #33 on: March 19, 2016, 09:22:22 PM »

How about a drive feed mechanism mounted right next to the hawse pipe and run from the same motor as the 3mm rod?

If two rubber tyred wheels are set just far enough apart that the chain is squeezed gently between them as they rotate then they would feed the chain in and out at the same time as the winch turns causing no sag or flops. Providing the drive to the wheels and cogs joining the whees together are the same size a simple plate gearbox could be made and no extra motors or servos need be fitted.

The mechanism could be made from Maccano wheels and cogs mounted in brass/aluminium plate carcasses.



The schematic shows:

1 Non specified hull profile with hawse pipe, winch rod and feed wheels.

1a shows suggested use of four meccano pullies with  rubber O ring tyres to grip chain that passes through gap between the four tyres.

2 shows the feed wheels in a simple plate carcass whose inner face could folow the shape of the inside hull.

2a and 3a show the feed wheels on their shafts with the gearbox at the other end. The winch shaft is not shown but you have that already

3 Shows the gear box that drives the wheels from the same motor as the winch shaft using three equal sized cogs and one small spur sheel to span the gap between two of them.

4 shows the cogs set in a simple carcass. The carcasses would not be difficult to make as the wheels and cogs would share common centers when marking out.

Just a thought.
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warspite

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #34 on: March 20, 2016, 11:11:25 AM »

I watched mighty ships some time ago and they showed a US navy ship searching for the wreck of a French ship given to the US in the American war of independence, carrying divers etc and searching predominetly for the bell.

In it they showed how they were centring the vessel so it didn't move, a 3 point anchorage port forward anchor dropped first at one point and then they repositioned to drop the starboard forward anchor and then reversed to drop the stern anchor, this meant they dropped a massive amount of chain but it held the vessel in a static position, in this case you would have to reverse it, the port and starboard anchors would have to come off the stern and then drop the forward anchor.

Otherwise wont she spin around any dropped anchor. Isnt the whole point that the chain holds the ship as that weighs more than the anchor, initially the weight of the anchor is the driving force to the bottom, then as the vessel reverses to pay out the chain this acts as the holding mechanism?.
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John W E

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #35 on: March 20, 2016, 11:42:52 AM »

Hi this link may help.  We had this conversation about raising and lowering anchors a while ago and there were a few threads on here showing various ways of doing this.    After a search this is the only link/thread I can find at the moment.   I do know there are several others.

http://www.modelboatmayhem.co.uk/forum/index.php/topic,7172.0.html
John
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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #36 on: March 20, 2016, 04:09:23 PM »

Thanks for all the ideas here guys.  Lots of food for thought.


Anchoring in a full scale ship does involve coming to an absolute stop, paying out the anchor and then gently reversing to let out more chain.  Then generally after stopping letting out the chain, to carry on going astern to see that the anchor is not going to drag.  The speed that the anchor hits the bottom is not important so, having brought the model ship to a stand still, one can pay out the chain until the anchor's on the ground and then reverse gently to pay out more chain.


I'd checked the links about working anchors and there were some good ideas in those which I had considered. 


Ian, I like your drawings, but thinking it through further there might not be the need for an anchor winch as well. Why not let the chain drop into a chain locker after passing through the motorised rubber rollers.  Only one needs to be powered, the other can be sprung against it, gently, to again allow for slippage should the chain catch or the anchor reach the hawse pipe.

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #37 on: March 20, 2016, 05:56:34 PM »

Hi Edmund
The main downfall really is that on a free falling anchor we rely on the weight of the anchor and gravity to draw the chain through the Hawser pipe for the initial start and at 1.96 scale there isn't much weight in the anchor - even it its made from pure lead.  The other drawback (if we were using scale chain is the actual size of it for its strength as well).  This is a problem I had a few year ago when I was trying to make working anchors for the Type 42 - I abandoned the idea due to the fact that I couldn't get enough weight in the anchors to draw the chain.   The other problem was that the scale chain at 1:96 was pretty weak and it tended to snap - if you tugged onto it with too much force - the links would part and judging by the approximate weight your model may be when ballasted up, she will put a fair strain on the chain.  Do you really need to anchor the vessel during docking procedures?  Surely on a calm day the model wont drift too far away and a good skipper will be able to keep his model under control while operations are under way.  Just some thoughts.


John
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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #38 on: March 20, 2016, 07:17:41 PM »

The main problem is as you say that at 1:96 scale even on a large warship like is the anchor is very small.  Mine is a scale anchor and probably an  overscale chain, and yet most of the solutions for worjing anchors are looking at much larger scales. 


I'm hoping that my solution might work.  It would be great to be able to hold Intrepid still on an anchor while the landing craft are operated by a separate transmitter, and not have to worry about whether the mother ship is floating off down the pond!   

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #39 on: March 20, 2016, 07:30:07 PM »

You also need to bear in mind that it isn't so much the anchor that holds a ship in place but the weight of the chain on the sea floor which provides the 'elasticity' to damp out jerking by catenary effect. The anchor anchors the chain rather than the ship. Both anchors and chain weigh a lot less underwater than they do on the surface which doesn't help matters.

Also, anchors need to 'set' in the sea floor by driving their flukes in, partly by weight and partly by the ship backing up. Whilst the size of a model anchor is scaled down, the nature of the 'sea bed' isn't so on a model it is more likely to drag unless it catches in something from which it might be hard to detach it!

So even if you can get the anchor on a model to drop properly it it is still likely to have problems in holding the boat.

Colin
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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #40 on: March 20, 2016, 07:32:39 PM »

Lots of weed in our pond! Alredy growing up fast!  A big problem but I'm sure the anchor will be hooking on to it!

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #41 on: March 20, 2016, 07:43:49 PM »

'Lots of weed in our pond! Alredy growing up fast!  A big problem but I'm sure the anchor will be hooking on to it!'

And when you press the button to raise the anchor you submerge the ship instead!

Colin
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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #42 on: March 20, 2016, 08:16:25 PM »

I'm wondering if the HMS Intrepid can lead our assault on the weed problem in our pond, pulling it up plant by plant from the bottom with its anchor!

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #43 on: March 20, 2016, 08:22:23 PM »

Hello
I used this winch .
http://www.dahmen.de/cat9166.html


john
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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #44 on: March 20, 2016, 09:19:08 PM »

That's very neat isn't it? Very nice! I like the video!

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #45 on: March 21, 2016, 07:45:23 PM »

If anchoring is a major problem, and an absolute must,  :} there is an extreme way of doing it, you build a submarine chamber both at the front and the rear, hidden under the deck, (the actual anchor chain is just for show and operates with the lowering of the following), in the chamber which rises to above the water line - obviously - a pulley system pays out a chain of suitable strength with a 5 kilo scales weight attached, being the same at both the bow and stern, it fixes the vessel in a relatively static zone, being hidden within the ship the weight is already under water and is lowered to the bottom with none the wiser  :}.
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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #46 on: March 21, 2016, 08:37:45 PM »

That is something I had considered as well!  A hidden but effective system straight through the bottom of the boat!  But there is something nice about seeing the anchor moving on its chain from a hawse pipe....

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #47 on: March 21, 2016, 08:52:42 PM »

So here we go with a little detail on the hull.  All the vents and pipes and drains from the flight deck.  Also the gangways along either side of the flight deck.  Fibre glass hulk turning into the beginnings of a warship. 

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #48 on: April 10, 2016, 04:04:23 PM »

Well it feels like a long time since I've posted anything or done anything for that matter!  Work in Italy and a holiday in Prague, where there were some fascinating paddle steamers ( but that's another story or post).

But I've been back a couple of days and done a little painting to the hull and finally she begins to look like a ship of the grey funnel line.

Coaming done round the main hatch as well but as yet no superstructure or details.  Next I think is the fitting of the servos and controls inside as they are all arrived now....

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Re: HMS Intrepid, 1:96 scale Sirmar semi-kit
« Reply #49 on: April 10, 2016, 06:44:15 PM »

Considering the complexity of the build you have made remarkable progress. Shes coming along well.
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