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Author Topic: Wood or Plastic  (Read 2772 times)

thunderchild

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Wood or Plastic
« on: May 17, 2010, 01:39:38 PM »

Good Day All

I'm currently building a 1/72 scale model of a Bathurst Class Corvette, 31" LOA, 5.1" Beam, approx weight to waterline is 2.2 kgs.

I have to watch the overall weight of the boat, The question is size for size which is lighter and stronger, Ply or Plastic.

Thanks
Richard
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DickyD

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Re: Wood or Plastic
« Reply #1 on: May 17, 2010, 01:44:22 PM »

I would say as the plastic will be a lot thinner I would go for plastic.
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Netleyned

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Re: Wood or Plastic
« Reply #2 on: May 17, 2010, 04:15:41 PM »

Using plastic will also save paint weight as opposed to ply which will need a lot more filling and sealing


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Colin Bishop

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Re: Wood or Plastic
« Reply #3 on: May 17, 2010, 04:59:37 PM »

Plywood needs more finishing but strength for strength it is thinner and lighter. I replaced the 1mm plastic deck on my Deans Medea kit with 1mm birch ply which was around half the weight of the plastic.

It comes down to what you prefer working with really. I like the traditional materials even if they do take a bit more work but styrene is obviously quicker to work with and easier in some respects. I don't think the weight of sealer on ply makes much difference as most of it evaporates anyway and both plastic and ply still need a top finish of paint.

Colin
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Netleyned

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Re: Wood or Plastic
« Reply #4 on: May 17, 2010, 05:19:37 PM »

Plywood needs more finishing but strength for stength it is thinner and lighter. I replaced the 1mm plastic deck on my Deans Medea kit with 1mm birch ply which was around half the weight of the plastic.

It comes down to what you prefer working with really. I like the traditional materials even if they do take a bit more work but styrene is obviously quicker to work with and easier in some respects. I don't think the weight of sealer on ply makes much difference as most of it evaporates anyway and both plastic and ply still need a top finish of paint.

Colin

Thats us told Dicky  >>:-( >>:-( >>:-( :embarrassed: :embarrassed:


Ned
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Colin Bishop

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Re: Wood or Plastic
« Reply #5 on: May 17, 2010, 05:47:25 PM »

Not at all Guys! It's just that my Deans kit has the same issues as Richard's Bathurst. 30 inches long, 4.5 wide and weighs 1.7kg. With a model that small weight is something you need to watch very carefully indeed. As it was, I did use the plastic in the kit to build the superstructure sides but got a bit worried about the weight and used plywood for the top. 0.5mm ply, (1/64th) is a lovely material to work with and takes a superb finish when sealed and it's plenty strong enough with a bit of balsa strip backing.

I'm not saying that the original kit materials would not have worked but the more structural weight you can shave off, the more leeway you have with the interior fittings, batteries and motor etc. When you are building larger models you can use plastic of a decent thickness and the weight isn't usually too much of an issue.

Very thin plastic is a bit delicate and needs bracing to preserve its shape over flat panels. I personally think that its also more prone to going brittle over time but that's just my opinion.

Just horses for courses really.

Colin
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DickyD

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Re: Wood or Plastic
« Reply #6 on: May 17, 2010, 06:06:29 PM »

Er hmmm, scuse me.



Deans HMS Amethyst, Scale 1/96  Length 958m  Beam 114mm  Sailing weight 3.1kgs  all plastic, no wood, sails like a dream.
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Colin Bishop

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Re: Wood or Plastic
« Reply #7 on: May 17, 2010, 06:43:49 PM »

That's a HUGE model Richard - and very, very nice. Congratulations,

Colin
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thunderchild

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Re: Wood or Plastic
« Reply #8 on: May 19, 2010, 01:06:48 PM »

Good Day Guys

That gives me lots to think about, I'm still undecided on wood or plastic.

I've weighed the boat (hull, esc/receiver/servo, 2 motors/shafts, 1 battery (6v 3.2 ah), deck fittings and the weight comes in at just over 1.8 kgs. Not much left to play with.

I'm still looking for a supplier of both who can give me a weight to work with (not much luck on that front yet).



Hopefully, all going well, it should look like the one above (built my Mark from Task Force 72).

Thank you for your help.
Richard



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John W E

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Re: Wood or Plastic
« Reply #9 on: May 19, 2010, 01:14:42 PM »

Hi Richard
have a look at this build its 95% made from wood  :-))
http://www.modelboatmayhem.co.uk/forum/index.php?topic=15073.0
aye

John e
bluebird
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Colin Bishop

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Re: Wood or Plastic
« Reply #10 on: May 19, 2010, 01:19:44 PM »

Quote
I've weighed the boat (hull, esc/receiver/servo, 2 motors/shafts, 1 battery (6v 3.2 ah), deck fittings and the weight comes in at just over 1.8 kgs. Not much left to play with.

Weight distribuition is equally important. You may keep within the overall weight allowance but if too much of it is too high you will have an unstable model which is why you need a safety margin if possible so you can add a bit of ballast low down.

Colin
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malcolmfrary

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Re: Wood or Plastic
« Reply #11 on: May 19, 2010, 01:21:16 PM »

Colin said "Horses for courses" and he was right.
For the homebuilt hull with a large percentage of flat, or flat-ish, area, ply has the strength to weight needed, and doesn't need anything like the bracing that plastic needs.  If someone has moulded it in plastic, that's a totally different case because the built-in double curves add a lot of rigidity..
For the superstructure, sheet styrene is fine, but some of the larger structures might well be both stronger and lighter done in ply.
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DickyD

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Re: Wood or Plastic
« Reply #12 on: May 19, 2010, 01:26:02 PM »

Hi Richard

Just a thought, my 1:72 scale corvette has lead sheet in the bottom of the hull and a 7.2V battery pack.

That keeps the overall weight down and the centre of gravity really low.

Its made of plastic by the way.

Sails in high seas and high winds.

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thunderchild

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Re: Wood or Plastic
« Reply #13 on: May 19, 2010, 01:36:01 PM »

Good Day John

What a lovely build, thats the way I usually build my boats, but this one is a semi kit (my first, and a training model, my next is going to be HMAS Perth (modified Leander Cruiser 1940) at 2.3m LOA with a beam of 240mm and a build weight of 18.6 kgs (what luxury, heaps of room to play with), fibreglass hull, and fittings. I've had no control over the hull construction, my fun now is to fill it up and finish it off.

Richard

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thunderchild

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Re: Wood or Plastic
« Reply #14 on: May 19, 2010, 01:40:07 PM »

Good Day Richard

So far all my weight is in the running gear, motors/shafts, battery and electrics, all low down in the hull, I don't have anything above the deck line.

Richard
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DickyD

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Re: Wood or Plastic
« Reply #15 on: May 19, 2010, 01:55:36 PM »

Is it a lead acid battery you are using? If so a battery pack is lighter and flatter and if put in the bottom of the hull will lower the centre of gravity.
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Colin Bishop

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Re: Wood or Plastic
« Reply #16 on: May 19, 2010, 02:00:44 PM »

It can be surprising how superstructure weight can build up stealthily with the structures and fittings etc. Even full time designers were not exempt. During the years of the international naval treaties between the wars many ships suffered from 'attempting too much on the displacement' and were overweight and unstable as a result - the Japanese especially. In earlier Victorian times even the Royal Yachr Victoria and Albert suffered from overweight fittings and almost capsized when launched: http://en.wikipedia.org/wiki/HMY_Victoria_and_Albert_III Big liners suffered from excess topweight too such as the German Imperator which was nicknamed Limperator as she was rarely seen on an even keel.

I have seen too many 'crank' models in my time not to be very careful about weight considerations. As an old friend once told me, the trick is to 'add lightness'. Good advice!

Colin
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thunderchild

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Re: Wood or Plastic
« Reply #17 on: May 19, 2010, 02:29:22 PM »

Good Day All

Yes, the battery is a lead acid type, lying on its side in the bottom of the hull (one weighs in at 600 grams, had two, now got a spare). I haven't had much to do with battery packs, never tried them, how much lighter are they and will they give me the same running time as a lead acid type (the motors are Graupner Speed 500E running at 6 volts).

Colin, luckily the Bathurst Corvettes haven't got much on the upper decks (a bit like the Bangor Class Minesweepers), so most of the weight is within the hull, its the deck and super structure weights that i need to keep light (I can't lighten up the hull or running gear, with maybe the exception of the battery), to keep the boat at the right waterline.

Richard
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