Model Boat Mayhem

Technical, Techniques, Hints, and Tips => Other Technical Questions... => Topic started by: roylond on May 27, 2010, 08:45:38 pm

Title: Scratch Builds
Post by: roylond on May 27, 2010, 08:45:38 pm
Hello All scratchbuilders.
When building a plank on bulkhead model what is the thickness of the material used for the bulkheads and keel also do anyone use ply for these ?
Do you encounter any problems using ply instead of a grp premade hull which to me is not scratchbuilding.

Title: Re: Scratch Builds
Post by: longshanks on May 27, 2010, 09:55:54 pm
No problem using ply for bulkheads/keel. Thickness rather depends on what size boat your building.
Title: Re: Scratch Builds
Post by: hazmat on May 27, 2010, 10:08:03 pm
I only build in ply and balsa. Don't really see the point in ARTF or plastic hulls but as I'm as old as Moses so that's probably why!
Keels I use 1/4-3/8 inch (old money)  nearly all the time, bulkheads 3/32. Skins 1/16 lite ply or oak veneer.
Most of my hulls are 3-4 feet loa.
As for problems, all the time, but that's the fun. :} Working in wood is very forgiving so working round problems is generally easy. I seldom throw a hull away unlike my pal who seems to be unlucky working with glass or plastic hulls.
Good quality WPB ply is expensive as I only use 3 plus ply (layers).I get all my ply from the chandlers and postal.
Recently I've been playing with glass fibre as a hull covering but with not much success.(Wife has banned me from using poly resins in the house cause of the 'pong').
Planking I use copper 'tin tacks' (mail order) to fix to the bulkheads pushing the pins through the planks or skin using a modified hollow nail punch.
Adhesive is usually Cascamite (powered resin glue). DEAD slow but allows for plenty of tea breaks and pit stops. :embarrassed:(If you know what I mean)

Title: Re: Scratch Builds
Post by: tonyH on May 27, 2010, 10:15:10 pm
Ply is fine.

Thickness depends on the weight you can spare as much as anything else. For example, I've just finished a fast patrol boat with a 17lb displacement and I used some 9mm ply I had lying around but I'm now building a 5ft destroyer with a 9lb displacement and so 4mm was more suitable. Most of the force is taken across the face of the wood anyway, so strength is normally ample. It could be wise to seal the whole of the inside of the hull with a coat of paint or similar but many never seem to bother. As Paul said, Cascamite is great stuff but comes under another name now.

Hope this helps.

Title: Re: Scratch Builds
Post by: Peter Fitness on May 27, 2010, 11:18:53 pm
As Longshanks said, the thickness of material depends largely on the length of the model. I try to keep most of my models around a metre or less as storage is a problem, so I normally use 6mm ply for the frames / bulkheads, and 1.5mm ply cut into suitable width strips for the planking. I always coat both inside and outside the hull with fibreglass resin to waterproof it, before painting the outside, usually with spray cans.

Title: Re: Scratch Builds
Post by: Greggy1964 on May 28, 2010, 12:08:31 am
For me choice of bulkhead (shadow) material depends on the displacement of the finished model.

If you are going to end up adding lead ballast to bring the model down to water line you can afford to use thicker stuff like 3/8 or 1/2 ply, use good quality 2 good face exterior ply if you can and check for voids in the laminations as these can cause weaknesses in your frames.

The good thing with thicker bulkheads is that you have more gluing surface and somewhere to hang the planks with brass pins (or steel pins if you sink the heads into the planks and stop up the holes).

If weight is a premium I would go with 1/8 or 1/4 birch ply or thicker grades of hard balsa making 1" ring frames.

Plywood is OK for keels but your local builders merchant or timber mercant will buzz up a length of stick from some exotic hardwood used in door frames etc for just a few quid for exposed keels or ply is good if the keel is covered by planking ie as in a WW2 motor torpedo boat construction.

I have used both of the methods above in my current Master Hand Build found here on the forum :-))

For planking material you can get away with cheap pine but try to find stock that allows you to cut planks out quarter sawn (annular rings running front face of plank to back face of plank) as planks cut this way are stronger and are less prone to crushing and denting during collisions in the finished model

Choose pine boards free of knots of course.

I use this method to find planed finished boards and take them home and buzz them up into plank sizes on my cheap table top circular saw fitted with a tungsten tipped circular saw blade.

Daubing the interior of the hull with glass fibre resin and finishing the exterior of the hull in resin and fibreglass tissue will keep out the elements for the Sunday outings to the local pond as model boats are rarely kept on permanant moorings so this method of waterproofing will prove sufficient O0
Title: Re: Scratch Builds
Post by: John W E on May 28, 2010, 08:28:56 am
Hi roylond
If you have a look in the MASTERCLASS log at the builds of Whitehills lifeboat,Drifter Spashett,or the Blue Marlin  Scratch Builds, this will be more help to you

john e
Title: Re: Scratch Builds
Post by: roylond on May 28, 2010, 02:17:33 pm
Thanks to all who replied I have managed to convince my friend to get his hands dirty and get stuck in. I also convinced him that if all goes wrong he can always start again unlike a preformed hull which would be knackered and much less enjoyment in building everything himself.

Title: Re: Scratch Builds
Post by: vintagent on May 28, 2010, 08:10:53 pm
Ain't nothing beyond repair, but it's so nice to scratchbuild and this forum has a good share of them .  Well done and good luck to all.
Us old timers are here to advise and help whenever you like.

I would use 1/4" birch ply for buklheads and keels with 1/8" keel doublers, with the bevel filed on them. That gives you some land for the glue.  Cascamite's good enough for Mosquitos it's good enough for us, bur a good epoxy is quicker. Entirely up to you really.  Skin with either ply, if it's flat sections, or planks of mahogany, straight grain (preferably Oregon) pine or pear/cherry/lime.  All these are available from specialist timber suppliers of whom we have a few locally or they'll supply by mail order.  I would only use balsa if I were stuck AND covering it with veneers as final planking, in which case it is quite usable if you can find it in a regular density.

Birch ply is best, but a little pricey, but nowhere near as pricey as any of the kits these days which would have me collecting wild flowers if I weren't a scratchbuilder!
You can use cheapo Far Eastern so-called Best Ply, but you would have to cut it very carefully and then seal it thoroughly with WEST or similar epoxy treatments, first to stop it fraying and falling to bits and secondly to waterproof it or it will delaminate in no time.
DO NOT waste yur money on so-called Marine Ply. It isn't any more even if it has the 1086 mark on it.  I've seen it at the boat yrd where you could hide welding rods in the core gaps.  Disgraceful and should be investigated by the Trading standards.
No, stick to birch ply, but it'll still benefit from a sealing coat of epoxy before you paint the model inside and out. Then it's encapsulated and will outlast you!

My Aerokits Crash Tender is 47 years old and my Sea Urchin 51 and they both had cellulose varnish followed by oil paints used in and on them. They are still perfect!