Creating Plans

[Alistair Musgrove 1Participant @alistairmusgrove1]

I would like to plan and build a small replica (RC) of an existing yacht – ex BT Challenge Clipper.

My idea is to draw the plans build a plug, and create a mould to build further on, eventually resulting in a replica of the existing yacht, that would be fully "sail-able" and operated under Radio Control.

I have an understanding of the design process for "full size" yachts, so my question is how to downscale this?

Do all the same calculations that apply to yacht design also apply to model boats or should the plans be drawn under a different approach?

Thanks in Advance

Alistair

[Alistair Musgrove 1Participant @alistairmusgrove1]

Plans based an a full size yacht

[Colin BishopModerator @colinbishop34627]

The biggest thing to take account of is that when scaling down the hull displacement will reduce by the cube root but the sail area only by the square root so the model will not be able to carry so much sail proportionately as the full size prototype in typical wind conditions. The conventional means of offsetting this to some extent (apart from carrying less sail) is to extend the keel, model Thames barges for example are often fitted with a false keel for sailing.

Colin

[Alistair Musgrove 1Participant @alistairmusgrove1]

Great start and thanks for the heads up here. SO with the exception of the above, does this mean the measurements would be essentially the "full size " measurements scaled down to the model?

Or am I missing something more complicated?

[Colin BishopModerator @colinbishop34627]

If you scale down then you scale down proportionately but then you have to take into account the effects I have mentioned. I am not a model yachting expert myself I'm afraid although I have owned a couple of small yachts. However, if your full size yacht has a fin keel then you can look at extending it downwards. If it has a bulb on the end then you can make provision for altering the weight by experimentation to see what works best. As in full size practice, model yacht design can be quite a technical subject if you are looking for best performance but more forgiving if you are just wanting to build something that will sail nicely.

A quick look online shows that the Clipper 70s have fin and bulb keels so I guess that will give you the options you need. Other members may have other ideas but my inclination would be to build the hull exactly to scale but make provision for attaching differing lengths of keel. The weight of the bulb will be dictated by how much is needed to bring the hull to its design waterline with the full rig and sails up and the operating gear aboard. The depth at which it is carried will obviously influence the righting moment it will exert in opposition to the press of the sails. If you make the fin of aluminium then its weight won't complicate matters further!

The fore and aft length of the fin will also have an effect on performance and of course leeway but I couldn't even try to guess at what that might be so experimentation with different fins is probably the way to go. If you incorporate a mounting plate on the bottom of the hull with bolt attachments it should be simple to try out different combinations quite easily.

Colin

 

Edited By Colin Bishop, Website Editor on 17/06/2016 17:14:41

[Alistair Musgrove 1Participant @alistairmusgrove1]

Thank you for the responses. I guess I will give it a go and see how it works out.

Alistair

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