Scaling down a boat to make USV

Let's Make Robots
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I have been dealing with asects of theis for a while and this is my latest idea. Build a small plywood boat downsized to be a platform for robotics testing. I bought a "partially built kit" on eBay that turned out to be an abandoned upgrade of a hobby grade boat. It's a 15" V narrow plastic V-Hull and I am concerned about it being to close to max with a decent battery and gear in it. But the upgrade in process inculded a good servo steered rudder and through hull prop hardware. The supplied motor is marginal but workable. I have a brushed ESC with 5v BEC.

I have built small boats (but big enough for actual people) before from plywood and plans so I can handle that part okay, but what I am concerned about is what makes sense as a good platform and how well scaling works. I am toying with the idea of going with something like this:

http://www.duckworksbbs.com/plans/lewis/duckskiff/index.htm

adjusted to an 18" length. My idea is to have a sealed compartment for electroconis as well as a full deck. I might go with a scow insead for extar bouancy, but I don't like giving up the handling and seaworthiness. I want to be able to test a sonar unit that has a decent sized transducer, base and battery (I have a 14v LiPo for it, not expecting to launch a heavy SLA).

This is a blog. because I am going to start on this pretty soon and will be back adding ifo.

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Carrying capacity of model

Hi Arbarnhart,

 

To find the carrying capacity of the model take the length at water line, max beam at waterline and the draught all in inches.  If you multiply all these together and then multiply by 0.0363 and the ‘block coefficient’ (BC) this gives you the all up weight of the model in lbs to float on the water line. 

lwl x beam x draught x 0.0363 x bc = weight in Lb. 

In my hazy memory I seem to remember that the bc is usually in the range of 0.3-0.6.  Although for a square barge it would be 1.

This was one of the very first programs I wrote (around 1975!) doing my computer course at school linked to a computer at the local TAFE by 300 baud modem  and teletype machine (no screen!)  If you look up block coefficient on the web you should find a number suitable for your hull type.

Hope this helps to choose your hull.

 

Pete