Bon appétit Rowen 👍😋
😎

Thanks Doug,
Some interesting potential motors there, much more food for thought.
Got so much to consider now!
Rowen

Hi Rowen,
18mm 3 blade sounds good👍
Here's a couple of mini motors for 3V
https://www.sol-expert-group.de/1-87-model-building/Motor-and-gear-units/Motors/Motor-M1068-3V::1091.html
https://www.sol-expert-group.de/1-87-model-building/Motor-and-gear-units/Motors/Motor-M2068::1092.html
and here the selection for various voltages up to 12V.

Here is a 3V Motraxx version that I buy at Conrad here in Munich.
(Sorry, I got mixed up with X-Track and Motraxx X-Drive before!😔)
https://www.conrad.de/de/p/motraxx-lff-k20wd-11608-u-min-233979.html
Here their selection of minimotors
https://www.conrad.de/de/o/mini-brushed-elektromotoren-1210014.html
Attached are a couple of pics of my load test and 'go machinery' selection for my 1:350 KGV and POW battleships, LoA 75cm, max beam 4.5cm, draught ca 2.5 - 3cm!
Cheers, Doug 😎

Hi Doug,
Have always done it your way before, but this time thought would try something more scientific! Am sure will end up doing as you suggest though.
Am intrigued by the small motors described. Do you have any links?
Was thinking of two brushless 18** outrunner drone motors driving 18mm 3 blade propellers.
Do you have any other suggestions?
Have no plastic magic experience so am trying to pick brains where I can.
Rowen

Hi Rowen,
I do plastic magic / small boat conversion, but I don't waste time with dubious formulae.
I take a more pragmatic approach 😉
As soon as I have the hull built (and waterproofed with EzeKote inside and out if wooden) I weigh it empty, and then do a Max Load Test by plonking it in the Domestic Test Tank Facility (🙄) and loading it down to the Deep Load Waterline, with lead shot or just water.
Weigh again, difference Loaded - Empty = Max Load capacity which must include-
Decks, Superstructure, fittings, drive train, electronics and battery.
Then I select possible motors, shafts - home made from 2mm silver steel and brass toob, ESC, RX, battery, weigh that lot and see what's left over for the decks and superstructure etc. If not enough usually the battery is the first to be reduced! BUILD LIGHT😉
Hope this helps.
BTW: If you fit two brushless in a hull that size you better give it wings and elevators as well!!
Two little (~180 size) should be more than enough.
Cheers, Doug 😎
PS If you're worried about stability; instead of a 'block' battery pack you can use individual cells (1.2V NiMh or 3.7V LiPo as appropriate for your electronics and motors) and lay them along the centre line at the bottom of the hull.
For the smallest of my 'Plastic Magics' and Mini boats I use Micro/Nano Rx, ESC and rudder servo and check that they can all work reliably from a single 3.7V LiPo cell.
There are also a lot of pretty powerful mini motors out there that run on 3V 😉
X-Track for example.

Trying to establish a target model weight for this project.
The vessel weights 100 tons and the scale is 1 :72. This gives, using the cube of scale theory, an estimated weight of about 10oz.
Which seems a little light.
Has anybody found a better conversion to determine a more accurate figure?

Interesting thought, have never fitted one to my larger planing hull models.
Will make provision for one during the build so can be added easily if necessary.
Thanks for the suggestion
Rowen

Thanks.
Had never considered using a plastic model conversion as a guide.
There are plenty of them out there, am sure can be pointed in the right direction.
Rowen

hi there

When you consider what some folk achieve when they can install all the electronics etc., in an Airfix model of the Air Sea Rescue Launch and MTB at 1:72 scale, I shouldn't think there would be much of a problem. I would think the height of the superstructure wouldn't create any unstability so therefore I dont think there would be any need to add a keel on or anything like that.

Look forward to seeing the build.

John

I believe you will need some sort of drop down removeable keel to sail your model especially as it has such a high superstructure and small draught.