That's a possible technique that I had not considered. One difficulty I see with some boats I have already built is that it has two datum surfaces which would need to be constructed flat - the deck and sub-deck. A couple of recent boats - the OSA missile boat and the Elco PTB - have had complex curves on the deck, an 'S' shape longitudinally together with camber, and this technique might make it hard to shape the deck in this way.

For these boats I used the sub-deck as a datum and built the deck curves with different height bulkheads. But where the prototype does not have a complex deck this would no longer be a problem, of course...

Your corvette also has another complexity - effectively a second chine line above the first!

Good morning DG,

In this instance building from the underside of the deck you could actually have more cut outs in the sub deck making it a lot easier to seal the inside of the hull.

Another way to make this model would be a module build then using the grain of the wood in different directions could make it easier to form the curves with out making the build complicated.

Martin555.

"....Yes, that way you assemble the bulkheads to the underside of the deck section then attach the deck section to the sub deck then add the keel to the bottom of the bulkheads and sub deck.
If that makes sense...."

Ah, that certainly makes sense. It is, in fact, the way the Terrier is assembled. See Illustrations 1, 2 and 3 on this sheet: http://eezebilt.tk/Terins.pdf

I had tried something like this approach on the Tamar (which, constructionally, is a close copy of the Terrier) but have never thought of using it on a bigger boat....

I suppose you could call it a sub assembly DG,.

Martin555.

Yes, that way you assemble the bulkheads to the underside of the deck section then attach the deck section to the sub deck then add the keel to the bottom of the bulkheads and sub deck.
If that makes sense.

Martin555.

"..you could attach the other bulkheads to a part section of the main deck .."

Ah - so you would develop the bow in sections? An interesting idea...

"...as you are designing developable surface boats.."

Nice boat, and thanks for the reference.

It's true that EeZeBilts are 'developable surface', in that the hulls are all made with flat materials which may be twisted but not distorted. Clever use of grain allows quite a lot of curves where necessary, and in fact you can distort balsa to an extent - the decks of the bigger craft are often slightly dome-shaped in length AND breadth. This is simply achieved by pinning the thin deck over a strong former...

Of great interest would be techniques for overlapping and butt joints. This is always tricky when skinning...

Yes but if you had a bulkhead at the end of the sub deck then you could attach the other bulkheads to a part section of the main deck then that should prevent it from twisting out of shape.

Martin555.

My perspective drawing is poor - but do you mean something like this?

If so, you will find that twisting is the enemy of internally jigged boats, and there would be a danger of the front bulkhead being out of true with the subdeck and keel.

In fact, the keel is the key component in 'traditional' boat building - the sub-deck is the key reference in EeZeBilts...

DG, as you are designing developable surface boats I thought this might be of interest. Not sure if the Shellbacks library is still selling (disappeared for a while but seems to be back) but there are lots of nice designs on the site, (many with developable surface building methods.) Edson I Schock did a lot of work back in the late 30s to 60s on developable surface design (Naval Architect) and produced many small boat designs which could be transferred to the Eze Built boats.
His booklet on developable surfaces may be available from the ShellBack site (I will check to see if it is still a kosher site, had no problems buying before) and might make useful reading. My 15 ft 'Sharron Potts' daysailer is one of his designs from the early 50s and is built using this method, (it is shown on the ShellBack site where I purchased the original reproduced plans)
John B

Hi DG,
If the sub deck was ended before the upward curve.
Then the keel strip attached to the under side of the sub deck
Bulkheads can then be added to the centre keel section that will end up being joined to the main deck.

Build out from centre instead of building up and down!

Spacers from balsa could be inserted between the bulkheads for strength.
Hopefully this makes a bit of sense.

It seems to be hard to keep on the topic on this thread.... still, back to the design.

Making a simple box with a bulkhead cross-section is straightforward enough. But what do you do when the box has to come to a point? In particular, when the chine has to curve upward?

Well, on some of the small original EeZeBilts the sub-deck just continued straight, giving a straight chine line - like the Mermaid and Cresta - fig 14. But there are a number of techniques to give a more realistic shape. Fig 15 shows the simplest - just bend the sub-deck up. When the hull is skinned the sharp angle gets sanded away and blended smoother by the balsa skin. You can even do a reflex curve - as in the Crash Tender - fig 16.

If the boat is a bit too big to blend a sharp angle, you can add a curved former as in fig17 - this is done in the Sea Princess. And finally, you can simply curve the sub-deck if it is narrow enough. This is what we will try for the Corvette - fig 18.

Of course, bending requires that the subdeck be fixed firmly in the appropriate curve. The keel will need to be cut to this curve, but that on its own won't fix the sub-deck. So we will add extra formers at the bow - marked in red on fig19. You can see that they create a tighter 'egg-box' shape where the skin needs more support, and I have picked the positions to provide a convenient depression where the anchor-winches are mounted. We can take the shape directly off the plan - you can see the shape at the bottom of the image.

Note that the edges of these support structures are all tapered - this spreads the stress across the whole structure and improves the stiffness...

Thank you for the information DG.

Martin555.

Only commented as most I met were mostly surly idiots - with no perceivable skills social or otherwise.

"...all very competent and skilled - sad thing about it was they were all emigrating...."

Atlas Shrugged...

"...Is there a standard length and width that is used for EeZeBuilt models ?..."

Balsa seems to come in nominal 3" and 4" widths (100mm), and either 18", 36" or 1m lengths.

I usually buy mine off ebay, though I have used SLEC in the past. The days of going to a model shop and selecting your own sheets of matching density are long gone. 😭 Though 4D is still underneath the arches near Tower Hill http://modelshop.co.uk/Shop/Raw-Materials/Wood-Sheet/Balsa/Item/Balsa-sheet-100-1000mm/ITM3977

If you are making any balsa model you need to be aware that the raw material is only readily available in the above sizes. so requiring a flat sheet 6" square is going to require a join or some other approach...

Wandering far off course but had to sing a song about youngsters - in 2008 (?) heard of an 18 year old at the Beaulieu Auto Jumble - at the Austin 7 stand - had rebuilt a Seven by himself aged 16 made a very good job of it but had to wait for his drivers licence ........ Only one local tyre shop in Bournemouth was able to fit and balance new tyres on my MG Midgets wire wheels - run by a youngster of 25 who devised the method of doing so with limited equipment. Met at least another three similar youngsters in UK - all very competent and skilled - sad thing about it was they were all emigrating because of the "Nanny State" and the "Elf & Saveless".

I use a VERY old copy of Ashlar-Vellum's DrawingBoard. It's no longer current - it ran on W95, and worked up to XP. Their current products are Graphite, Cobalt and Xenon.

This package has an interface designed by two people from the Xerox PARC research centre, where they developed the ideas of a mouse and windows which we use today. It is completely intuitive, and you need no training whatsoever to use it - it's just like sketching with a pencil on a pad.

Unfortunately, they maintain patents on the interface, which is probably why other products are more clumsy, and they sell to the professional market. Their cheapest package starts at £1.5k, so I'm not suggesting that anyone use it. But if anyone is in the market for a commercial high-end CAD package I would recommend that they take a look at that company...

Rhino 3D is a very good programme. Developed originally, like CATIA, for aircraft design and also used by boat companies. Used to be available for a certain number of free saves, a student version and the final fairly expensive version for commercial use.

Martin

I used one years ago called Rhinoceros, which boat builders were using. It is 3D and a lot of fun. Does rendering and has a library of std shapes (polygons, triangles, splines etc) which you can grab and contort into anything you want. Been meaning to see if it will work on my new computer, (I took it off an earlier machine as it took too much memory to run) and never put it back on the next machine. The machine I have now would run it no problem if it was compatable with 8.1 (must drag it out and try it) my older machine is on Vista so it may work, Used to work on 2000 but might be too old now which would be a shame.

I use Draftsight. It is a free copy similar to Autocad and runs almost exactly the same. It has been free for years but as of December this year, the basic 2d package will be about £80 per year. The new version 19 is also 3d capable. I will purchase this package for work and see how it looks. I currently use Visi for 3d but only as a viewer. Very expensive. I am told that One Cad can be a useful tool. I have not tried it.

Hi DG,
The last time I used Balsa wood was many years ago.
I have still got a small bundle of it at different sizes,thicknesses and
Widths.
Is there a standard length and width that is used for EeZeBuilt models ?

Martin555.

Too right Colin, you could make a model in the 60s for a few dollars, (balsa and bits were cheap). My present ST model is way over $200 so far, problem is you can't buy 200 mls of paint, resin etc, you have to buy 500 mls or perhaps 1L (most you'll never use again). Balsa's like buying gold etc etc (although our local Bunnings home depot has started selling balsa cheaper than the LHS so I'm buying up large while the going good!).
Talking of the LHS here, it's not local, it's a 60km round trip as there is only one in Auckland (about 1.58m people 1086 sq km) so it shows the decline in modeling here as well. There were around 10 shops in the 70s-80s.
We nearly lost this one as the SA guy who owned it, flew his homebuilt biplane into the sea off Auckland on purpose (domestic problems I think), which was a shame as he was a real nice knowledgeable guy (not only with models but electronics). Luckily his son and business partner kept it going and it's still the biggest in NZ. There are a few down south and in the South Island but all of them are expensive, as they are trying to make ends meet and propping up a dying hobby,
The Chinese have done us a favour with endless cheap bits and pieces but at the expense of our LHS s' We are lucky I suppose that balsa is still available, as schools and university projects require it, and it's increasingly found in art shops etc. My son did Leggo and Warcraft figures when he was younger but Playstation and internet soon took over.
It's a bit like when TV came out and everyone stopped conversing, now its 10 x worse, (how many times have you been talking to someone and you catch them glancing at their phone, or their phone rings and they answer it without excusing themselves. Unfortunately that's the way the world is now and there ain't nuttin' we can do about it. Like WQ said, a good war will re-set everything .

Can you imagine, all talking on their phones and taking selfies on the front line and facebooking about the conditions, (that would be both sides) !

Nuttin wrong with Metros, best handling car I ever had (apart from my Fiat 127) , only sold it a few years ago. Would have kept it but had too many cars. We only got the top of the range ones here, plus a few turbos.

Hi DG,
The CAD program that I have been messing with is Designspark.
I gave up it is easier and quicker for me to use paper and pencil, at least I don't lose my temper with that.

Martin555.

"....Back when I started modelling with my dad in 1955 kits could be bought for shillings, my aerokits fire boat was 35 shillings(£1.75)
Now the same kit is over £200. I can buy a car at the auctions for less...."

I had a look at a value-comparison site. Interesting data, because of course values of objects have all changed quite extensively in 50+ years. Computers and electronics, for instance have become much cheaper...

£1 15s (1.75) in 1955 can be compared to nowadays in lots of ways. For instance, against the Retail Price Index it's worth about £45.10p. So a model boat kit is about 5 times more expensive than it was, compared to things like food. But that's probably more of an indication that household necessities like food have actually become a lot cheaper.

In terms of average pay the value would be £109. So model boat kits are about twice their cost to an average worker. Though as the pay median shifts that may not be an ideal measurement. I think that big model boats were a bit of a costly hobby even then. I think that's a measure of the rarity of model boat kits - they are no longer a common item and so attract a higher price because of the inability to make volume savings.

In terms of value as part of GDP - the cost of the item seen as an asset of the country, that value would be £190. So not a lot of change there at all...

".........Well I have spent most of the afternoon trying to get my head around this CAD program.
Slowly losing my temper ..........."

Which one? I don't think there are any easy-to-use free 2-d drawing packages. I have just been trying NanoCAD, which seems to be the best of a bad bunch. There are video tutorials on the web, but they rarely seem to tell us simply how to draw lines and curves...

Well I have spent most of the afternoon trying to get my head around this CAD program.
Slowly losing my temper
So I decided to put the laptop away before I threw it out of the window.
Me and computers are definitely not the best of friends.
A lot easier with this iPad.

Martin555.

Problem with the modern world is its expensive.
Back when I started modelling with my dad in 1955 kits could be bought for shillings, my aerokits fire boat was 35 shillings(£1.75)
Now the same kit is over £200. I can buy a car at the auctions for less.
It's the money grabbing manufactures pricing us out of the world of modelling, even though it costs less to produce now than 40 years ago. Mostly done by computer controlled robotic lasers, even the packing is automated.
My 5 year old grandson is mad on lego, and is just getting started with mecanno, both my wife and I enjoy watching his modelling, and his imagination is a wonderful thing to see. He is also a keen boater with two rc boats of his own, and he is also leaning to control my large scale tugs.
I'm sure if we persevere he'll be a fine modeller of the future.
Cheers Colin.

"..... some young guys turned up with a new Kyosho Calmato.
............ ( they all turned up in flasher cars than mine)........"

Far too late, you see. You need to catch them at about the age 8-12, and then introduce them to the idea that they can create something on their own. Something you have built is always better than something you have bought - even if it's only a plank with a handkerchief sail, there's a bit of your soul in it. That's why we need simple kits that a child can make with the minimum of adult help, but which will still look like a real boat. You are much less likely to discard something you have spent a week or more on building...

Alas, yes. Although I heard some young car fans on the wireless today talking about Metros and other unwanted examples and they even talked of doing their own mechanicking! There are only 10 basic Metros left in the country.

M

That's a bit heavy, not all young Earthlings are the same.
Some are a lot worse LOL!
Martin555.

Frankly these people are equally disposable in my view (but then I've never liked Earthlings). A good War would sort them out (he said, trying to sound like his Dad)

Martin

Problem is that we are all living in our past and the young ones today have too much other electronic stuff to play with. People can't go anywhere without a phone in their hands and using their spare time telling everybody what they had for lunch that day. I tried to get my son interested in planes but he was more interested in computers, (built his own big gaming computer with water cooled everything, fans and lights everywhere for around $4000 ) and he and his friends play games against people on the net from all round the world.
As WQ said they can buy anything off the net, so why spend all that time staying inside, building a model when you can buy a nice ready made one which you know will work. A good example of how they look at models was, - I was flying one of my planes one day when some young guys turned up with a new Kyosho Calmato.
They had no idea how to fly it so I tried to give them a few ideas (like taxi round for a start for a few hrs to get the hang of it on the ground) but no- straight off, full up elevator and into the ground. They all went running over with their phones, laughing and taking pictures. Made no difference the plane cost around $500 ( they all turned up in flasher cars than mine) and they just picked it up and threw it in the car, (could have been repaired quite easily but they were going to bin it.)
We had to make do, but young people just have so much choice and disposable income, they don't know what to buy next. You only have to look at how they treat a nice car these days, most just thrash them to death and buy another one. Everything is disposable today.

In the past I have spent a lot of money in my local model shop, but unfortunately that has now closed.
I like you DG try to encourage the new generation in to this hobby that is why as soon as I can I will try and design and build a simple modern boat for your site.

Maybe a more modern boat will appeal more to this new generation!

Martin555.

"...Model shops are shutting because anyone under 50 is likely to be so bloody useless that they wouldn't know balsa from styrene sheet, much less how to use it. So, they buy ready mades off the 'net. Ergo, another model shop goes bust...."

They are closing rapidly. Because they no longer have the customers to keep them going.

A lot of modelling blogs make a regular plea for the diminishing number of modellers to use the remaining shops more and more, but it doesn't seem to be stemming the tide. I prefer to address the problem at source, and try to make it as easy as possible for young kids to get into the hobby. If we have no new blood the skills will vanish very rapidly.

As far as I can see, there are no readily available starter kits for children to make R/C boats, which is why I try to push the plans on my web site. I hope that adults will be able to cut out the parts and create a 'kit' very much like the original die-cut ones that many of us started with, to give to a child as a present. Or perhaps a teacher will take some up for use in CDT classes - or whatever they call it nowadays...

Sounds like a nightmare place to live if you have a hobby!
I still use cellulose sanding sealer, but also have shellac type and use cellulose thinners for cleaning all my paints. I won't use water based crap for anything. All it does on wood stuff is raise the grain, the very thing you're trying to stop!
I use spirit based wood stains too. If nothing else I love the smell! So does my wife.

Model shops are shutting because anyone under 50 is likely to be so bloody useless that they wouldn't know balsa from styrene sheet, much less how to use it. So, they buy ready mades off the 'net. Ergo, another model shop goes bust.

I'm no help because, being a tight wad, I make everything I can and buy only things like props and batteries. And I could, if pressed, make the props, too. Lithium I've found a little more difficult to file

Martin

We are a bit "luckier" here - can still get dope, solvent based paints & varnishes . Only lead free of course - that's how far we have got with the "Elf & Safety" bit. I use water based varnish for our commercial stuff because there's no pong or fumes to contend with - do most varnishing at home at night . Boats still have good old solvent based stuff.
On the other hand virtually nothing for model boats is obtainable here - only stuff used in aircraft or cars - and that's only in the 5 big cities. Like the UK hobby shops seem to be a thing of the past. Toy shops & stationers have been closing at a rapid rate too - virtually none left.
Growing up in a small Rhodesian town the local "sports" shop also kept model boat & aircraft kits & bits - plus the local stationers & department stores had a limited amount of model bits & pieces.
Now you see the occasional plastic kit in a toy section of a supermarket and that's about it. Online shops still exist here - but the transport charges are very high and the prices ridiculous for anything imported as the exchange rate is really horrendous.
The external online shops like Hobby King are available but prices are high for us and postage/courier exorbitant plus parcels tend to get lost in transit. Then to add insult to injury customs are normally a big hassle and additional cost as well.

Most of the good stuff has gone now, most solvent based sanding sealers etc are waterbased now, (even car paints are going waterbased). Waterbased stuff just doesn't get the same results as the old paints etc (fade like mad down here in NZ sun) and are not much good if you don't want to wet your project, or later paint with acrylic enamel (solvent based) or enamel. On the other hand, I use painters (art) acrylic paints for some finishing work and interiors on the models. It's totally waterproof and you can mix any colour you like. I've used the metallics on the rudders and props on my HSL (even the boot topping stripe) and it's stuck really well, despite the props spinning at 15000 rpm max revs. I guess it can have a place on certain modelling jobs.
John B

In days gone by, I frequently used Valspar on my sailing dinghies, there was a good range of colours, it was nice to use, flowed on well and really dense colours. I liked it as much, if not more, than the proper marine and often overpriced paints. However that has been ruined by it becoming a 'mix any colour' water based paint which I have only seen in B & Q. I wouldn't even use it as an interior paint in my house leave alone a boat.

Nerys

Not used 2 pack as it's usually toxic. This was an enamel. The really good one was Rylard. Just remembered it. But in fact HRG is as good as the rest and way better than International. Best of all was made for us by Tim at Tramar coatings who used extra alkyd resins and much denser pigment. I used it on the restoration of our wooden boat and it was as good as new 5 years later when we sold it.

Martin

WQ, certainly sounds like your international is nothing like ours, (assuming it's Azko Nobel we're talking about) they paint super yachts with it here (2 pot paint) I've used it since I was a kid, never had a problem. We have another brand here Altex which is used for top end boats but their std cheaper polyurethane boat paint is rubbish. It's not even waterproof, as if you leave a damp cover on it for example it will blister.
I actually went to Altex here in Auckland and made a complaint to the manager and he denied there was anything wrong with it, wouldn't even accept my complaint, told me they paint super yachts with it (they don't, they use a top of the range 2 pot ). 2 friends had had the same problems,-blistering, not leveling off, ending up almost satin despite following instructions. Tried it one more time just to be sure with a new tin and it was just as crap.
They tell you not to use it below the waterline but it's rubbish above the waterline.
I will go back to International (dearer) but at least you can get a decent level gloss on it and it doesn't blister. Was the paint you were thinking of, Redux?

".......what about boring a 20mm hole in each section, pour plenty of the thin stuff in, swirl it around, pour the excess back into the container and repeat for each cavity........"

Some of the sections ARE 20mm in size. There may well be sections behind sections - to a depth of three or more. And having watertight sections is a useful safety feature when you have a thin balsa hull.

On the whole, using a syringe makes the whole process much less messy and more manageable. Balsa is easy for a needle to pass through. Just remember not to inject with a solvent which dissolves the glue... 😭

Jb,
I've tried painting canal narrow boats in international and watched other poor fools try too. No way. No density of pigment, took forever to dry, no coverage even after several coats. Absolute rubbish. Blakes was much better and another, beginning with R was best of all, but it's going back a bit now and I can't recall the name.
Martin

DG, what about boring a 20mm hole in each section, pour plenty of the thin stuff in, swirl it around, pour the excess back into the container and repeat for each cavity. They do it for house insulation (drill holes on the outside and fill with expanding foam) why not boats? You can always fill the holes later? (or just cover them with a carpet, matting etc)

"....and poured it into the hull and tipped it around, stood it on its' transom etc to get a good coverage all over......"

That won't be fully effective, of course, with an egg-box structure which is made of a lot of sealed cells. This is what I have tried... "Nurse! Another 10cc of Ronseal Wood Hardener!...".

WQ, Everdure or Norski are as good as each other (I used Norski on the ST) International is fine here, must be made differently up top. I recently restored a 45yr old 12 ft racing dinghy and used a local brand of sealer (same sort of thing) inside to toughen and seal the ply. I mixed about 1.5L and poured it into the hull and tipped it around, stood it on its' transom etc to get a good coverage all over. Won't rot for another 45yrs now.

I've often wondered about that, dg, but having always had access to Epoxy, I've always used that to reconstitute rotten window frames, etc. Sufficient to fool a surveyor, anyway

Martin

These all sound useful.

I have experimented with a number of hardeners in an effort to make balsa more durable at low cost - you can see what happened with my first attempt to inject cellulose sanding sealer into the sealed compartments of an egg-box structure when I was also using cellulose glue, and not thinking about where the solvent might go...

I have tried Z-Poxy, and Mouldcraft's SP106 - this is an epoxy finish used for surfboards - but the cost is still an issue.

Given that balsa is very absorbent, I wonder if the liquids designed to harden timber which is rotting might be useful?