NEWB alert: Starting building a 1:120 Bismarck model from scratch

[John Menoche]

My nephew and his friend expressed interest in using my moderately equipped workshop and tools to work on an RC boat they want to build. They are both 13 with no safety training or experience. I thought, sure, but I'm going to be with you every step of the way.

The boat in question is a 1:120 scale replica of the German Battleship Bismarck. At this scale it is almost 7 foot long.

We're coming to having the hull finished, built of horizontal slices of stacked plywood. Once it is finished, we need to start working on propulsion. The Bismarck has (3) 3 blade screws. Two turn one way (LH), the remaining one, the other way (RH). If I were to scale them down proportionally from the 4.7m originals, this gives me 39mm (1.5") diameter. The question that is bother me is this; do the hydrodynamics scale proportionally? e.g. should I use larger than scale, faster RPM, lower/higher pitch to achieve decent movement in the water?

Also, might I be better served with a motor for each drive shaft or a by a common motor connected through belts/chains?

Thank you,
John

 

[Grimracer]

John,

A few here have built displacement hulls and maybe some are willing to help..

Never the less RC groups might be a better place to post on your project. Looks like a neat project.

https://www.rcgroups.com/forums/index.php

Kind Regards

Grim

 

[Hydro Junkie]

I would go with individual motors that run at lower speeds. To go with high speed motors could give you a battleship that planes out while running gears or belts/chains adds complexity and drag, something that's not good for battery life. After doing a lot of web searching, I found that the port and center prop turned counterclockwise and the starboard turned clockwise, when viewed from the stern as shown in this picture:
https://ww2db.com/images/ship_bismark27.jpg