Reducing scale of plans

[Andy BarkerParticipant @andybarker11470]

Hello to everyone.

I have plans for Brave Borderer by Ken Hards, had them about 50 years.

The plans make an MTB of 36 inches, however I want to reduce the size to 18 inches. I have a scanner so scanning the plans and reducing size isn't an issue. the problem is sizing the timber.

The keel and bulkheads are from 3/16 ply, the inwales and chines from 3/8 balsa.

Should these sizes be reduced, the model would be for display only.

I used to design, build and fly control line aircraft so am used to working with balsa, all be it 50+ years ago.

Any help much appreciated.

[Andy BarkerParticipant @andybarker11470]

want to reduce scale of plans by 50%

[Dave Cooper 6Participant @davecooper6]

Hi Andy and welcome to the forum.

After you've reduced the plans by 50%, does the model still 'look right'. It may not, strangely, this to do with the relationship of linear measurements, areas and volumes…..

If you have 3D CAD, it will help you visualise this. For the timber sizing, again I would go with what looks right. Perhaps make up a few small pieces – to scale, and see how they look. You could also build a scale hull in, say, card first (old cereal packets are good for this).

Good hunting,

Dave

[fredParticipant @fred20856]

Vic Smeeds "Mistral" was a cabin cruiser 18 inches long

Used 1/8 balsa for keel and bulkheads
Chines were 2 of 1/16 x 1/8 laminated or 1/8 x 1/8 nicked and steamed

Made a strong working model

[Andy BarkerParticipant @andybarker11470]

Dave thanks for that. Think it should be OK at the reduced size but think, as you say may be worth making a mock up first of the hull. I want to use the hull as a base and then do a bit more work to make the cabin and deck furniture more like the real vosper/thornicroft. A scale model, but no quite.

Fred, thanks had wondered about 1/8 ply for the keel. Never thought of using 2x 1/16 for the chines. At lot easier.

I suppose I now have to bite the bullet and spend some time on the PC.

[Ray Wood 3Participant @raywood3]

Hi Andy,

The Brave Borderer has one of the most attractive bows of any MTB you may consider using balsa block or Styro foam to form the flared concave bow below the chine and above ?

At 18" long for a static model you really don't need ply keel or bulkheads, balsa would be fine

Regards Ray

[Andy BarkerParticipant @andybarker11470]

Thanks Ray, whilst I'm familiar with airplanes it's my first attempt at a boat. I like the hull lines as well but not keen on having just 4 torpedoes stuck on the side, photos of the actual MTBs all show launch tubes.

I note from some of your photos that you build the hull upside down. Is this the norm or your preferred way of building? Looking like I have a lot to learn 😀

[Ray Wood 3Participant @raywood3]

Hi Andy,

Yes most of my builds are on a board inverted as they have shear on the deck line and that's the easiest way to achieve it, that said if you have a flat deck build straight on the deck as my baby MTB Ferret which is 15" long as a comparison it's in front of the 1/24th scale version, It's slightly wider on the beam for stability and runs well

I'm also a flyer, can't wait for the weather to warm up so I can get out on the slope & field, where are you based ??

Regards Ray

[Andy BarkerParticipant @andybarker11470]

Hi Ray

Launch tubes (excellent), looks so much better. Will try to build upside down, makes sense after what you've said, so much to learn and not yet put a knife to balsa . Have found a company who can reduce the original plans by 50% so will make things easier.

I live up in Yorkshire near Selby. may sound daft but once Id flown a plane a couple of times, got bored and wanted to start building again.

Once I get started will try to keep a diary.

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