# Modelling forces acting on a sail

Hi all.

I'd like to create a basic model of the forces acting on a sail (wind sail, like a tail ship)

A couple of things I was thinking about:
1) can create a very simple model where wind is 'one' force acting on the a uniform body.
2) model wind as vectors. This is where I am a little confused on how to start.
3) adding in multiple sails.

Any pointers?

I'm not looking for someone to actually do the modelling for me, just a place to start. Like maybe some Wikipedia articles, etc.

Thanks
Chris

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## Answers and Replies

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Sails (proper sails that is) are airfoils so you need to study aeroplane wings.

Sails as most people think of them (e.g. Viking Longship) operate in the stalled condition and are very inefficient.

Thanks for the reply. I'm really looking for a starting point. I know that this would be a differential equation but after that I can't really see how it would be modeled.

This isn't a hw question. I'm looking at this out of interest. Its been a few years since I worked in differential equations and modelling math problems so any help or starting points are greatly appreciated.

Thanks

kjl
Do you really need to know exactly how the wind is pushing on the sails to such a fine degree? From your 3rd point (adding in multiple sails) it sounds like you are trying to design a craft of some sort, maybe?

In which case it seems more important to know how hard, and in what direction, the wind is pushing on the sail in total. At that broadest level, you can just draw the incoming wind vector, the outgoing (after interaction with sail) wind vector, and the difference between the two is the force vector applied to the sail (which will be divided - unequally I think - between the mast and wherever the main sheet connects with the boat)

So, it doesn't need to be so fine. It just a hobby/interesting project I've chosen.

I'm really trying to re-develop my modeling/simulation skills.

I was hoping someone who might have done something like this before could start me off.
Thanks