Scaling Up

[Tim CooperParticipant @timcooper90034]

Can someone offer advice on scaling up from plans?

Do you scale the materials used up by the same factor?

For example if I wanted to build a 20" Eezebilt PT Boat at 28" (x 1.4) do I amend the balsa thicknesses by the same factor?

I would assume I would but I have not tried it before.

Thanks

Tim

[Tim CooperParticipant @timcooper90034]

[Dave MilbournParticipant @davemilbourn48782]

Tim

That's not a bad place to start from, except you must realise that wood exactly 1.4 x as thick may well not be available. For example, if the original calls for 3/32" balsa then your re-scaled size would be 3/32" x 14/10. This results in 21/160". If you can find any of that listed anywhere then I really will eat plywood for breakfast! However, 20/160 = 1/8" which is the nearest standard size and happily just about identical to the calculated thickness. For the same increase in scale (x1.4) use 3/32" for 1/16" and 3/16" for 1/8". In practice it's never that critical, and you can always use something a bit too thick and sand it back.

Thought for the day:-
I was once told by a retired surgeon that one of the main differences between making model boats and performing abdominal surgery is that balsawood never grows to fill any gaps you might leave between cut parts, whereas human tissue rapidly will. Scary, isn't it?

Dave M

[Tim CooperParticipant @timcooper90034]

Thanks Dave

I will get the plans enlarged and then decide if to build the 20"" or the 28"" version. I quite like the idea of the 28"" version as there are 1/35 scale guns etc available.

Tim

[Dodgy Geezer 1Participant @dodgygeezer1]

In many cases the original parts are well over-strength, so you can use the same wood (though it never hurts to follow Dave's advice!)

There can, however, sometimes be problems with expanding the design. Longer runs of wood may need additional supports added – for instance see the Triton at the bottom of this page: **LINK**

I have not actually made a PT boat at 28", though I would like to give it a go – these items should make it look really good: **LINK**

**LINK**

The other issue is that making larger boats out of 1/16" balsa means that the boat is light, but the material is a closer approximation to the real-life structural strength! I was trying out some 'squadron formation' boating with a couple of the 20" ones on a rock-edged lake, and ended up knocking a small hole in each of their bows when I brought them in

So I would consider skinning a 28" job with 1/16" ply….

[Tim CooperParticipant @timcooper90034]

Thanks Dodgy

I have seen the Italieri kits and that prompted me to think about a 28 " version. I was thinking of using tissue and dope over the hull before painting, would that be as strong as ply?

Would a 28" benefit from twin motors?

I am hoping to build a normal sized Terrier first ( I built one in the 60's) to build my balsa skills again.

Tim

[Dodgy Geezer 1Participant @dodgygeezer1]

Tissue and dope would be strong – but ply would be stronger still.

I drove my boats onto rocks, so if you don't expect to do that then it's not a problem! But my original point was that a fibreglass hull hitting a log might leave a scratch, while a 1/16" balsa hull will get damaged like the full-size would if it hit a giant log….

Having said that, the effective 'double-hull' egg-box construction means that flooding is minimised, and it's easy to repair….

There isn't much space in a 20" version. You could probably get two motors in a 28" one, though three might be a squeeze! I was expecting some torque roll from my single motor (given how narrow the hull is), and was surprised to find there was little or none, so I would still go for a single motor at 28" – makes construction easier…

The Terrier is the obvious nostalgia boat for 1960s boys! I have an R/C one here, but it's only suitable for light-weather pond use. I'd make a smart one as an inside display piece. Here is a solid made-up one to give you some ideas…**LINK**

[harry smith 1Participant @harrysmith1]

Tim

As Dodgy said plywood is stronger and as for flooding areas I have the forward frames solid and the forward keel solid.

This gives you a number of separate areas that are sealed off from each other, without added weight.

One good size brushless motor about 1200-1500kv with around 500watts on 3S Lipo battery and a 2 blade 30mm prop will give the boat a bit of get up and go.

I have a 25 and 1/4" Sea Hornet with a B28-57-15L 1900kv 750watts,3S 2650mah battery and a 2 blade 30mm prop.

It is far over scale speed and dam quick!!!

Torque roll can be off set by having the battery across the hull and moving it a bit to the opposite of the prop torque direction also moving the battery forward or aft to get the balance point of the boat right.

A bit of bow down in the water to start and this will soon come up with power.

I scale up very easily by getting the copy shop to do it and I rescale the stringers and other timbers back to standard sizes.

[Dodgy Geezer 1Participant @dodgygeezer1]

The EezEbilt plans are not really plans in the traditional sense – but cutting lines to create the equivalent of the die-cut parts which came in the original box. There was no traditional plan included – just a set of line-drawing assembly instructions.

I emulate this by providing cutting lines on A4 .PDF files for your home printer, and a web-based build log. You should be able simply to specify the paper as A3, and then print out the larger image at home without paying for a copy shop – though you will have to tape a few pages together for the big parts.

One possible 'half-way house' when making an 'A3' sized EeZeBilt is to use 1/8" ply for the keel pieces. This will add quite a bit of strength even if the rest is balsa, and will stop you getting dents if you nose the boat into the side…

[Tim CooperParticipant @timcooper90034]

Thanks for the comments.

I like the idea to use ply for the keel and the ply skin. Maybe I would dope / tissue to fill the grain as well?

Not sure if I would go to brushless and Lipos, perhaps brushless and NiMh. The pond I use has stone slab sides so some slow control would be useful.

Dodgy, I have read that you use Radio link radios,; I have just (yesterday) received a Radio link AT9 for another boat. Not done more than stick some batteries in and look at the colour screen yet, but it seems well built, although I haven't taken the back off . I need to decide which bits of the 80 page manual to print off next, but there are some tutorials on the Net if I get stuck.

Tim

[Dodgy Geezer 1Participant @dodgygeezer1]

Posted by Tim Cooper on 18/08/2016 11:44:20:

Dodgy, I have read that you use Radio link radios,; I have just (yesterday) received a Radio link AT9 for another boat. Not done more than stick some batteries in and look at the colour screen yet, but it seems well built, although I haven't taken the back off . I need to decide which bits of the 80 page manual to print off next, but there are some tutorials on the Net if I get stuck.

Tim

Ah, the A9, Or the orange A10! Luxury!

I go for the bottom end of the market, with T4Us, and a recent purchase of the withdrawn T7Fs. They were going on Ebay for £20 a pop (+ £5 for postage), so I bought 3. The early cheap sets needed checking over for decent soldering, but these later ones look a lot better….

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