Reply to: Since we're doing dumb physics/maths questions...

[xoggoth]

I'd go with the stick it in the water pointing backwards idea but how far are a few batteries going to take you anyway? Probably best to chuck them overboard and reduce the pointless weight.

[TimberWolf]

It's outside the scenario - this is a pure physics problem rather than a lateral thinking one - but yes in reality that would be quite effective, if rather tiring. You're translating biological (chemical) energy into kinetic energy to move the sail, effectively 'rowing' the boat with a 'paddle' in the air.

All forms of propulsion will boil down to the same basic principle and that is throwing mass (or rather momentum) in the direction opposite you want to travel. You can do this using little mass and lots of energy (e.g. light) or using a more mass and less energy. Fans are more on the high energy side because they are quite small and push relatively little air out at high speed. Wings (and sails) are better because they push on more air. Rowing an oar in water for instance is going to be more energy efficient than rowing in air, unless you have a huge oar.

[Sockpuppet]

Feck all your high powered physics malarky.

If it were me and I wasn't allowed to point it at myself I would.

Stick it on the front and mount it backwards at a 45 degree angle pointing it towards the mast.

This will provide backwards thrust from the fan and also will allow the sail form as an aero foil and generate motion from that effect.

The sail will have drag but not 1:1 with the air pushed so it'll move the boat.

[d000hg]

It's outside the scenario - this is a pure physics problem rather than a lateral thinking one - but yes in reality that would be quite effective, if rather tiring. You're translating biological (chemical) energy into kinetic energy to move the sail, effectively 'rowing' the boat with a 'paddle' in the air.

[TimberWolf]

Put it on the back (stern) of the boat, pointing backwards (astern) so it pushes air out behind the boat. Additionally, take the sail down.

It's because of Newton's 3rd law, but I won't spoil the thread completely by explaining the reasoning just yet.

I'm wondering whether you could power the boat with the sail, not least because the fan will be carp. I'm not a boating person, but I'm imagining a triangular sort of shape of sail that's pivoted on one corner. If that's swung to and fro, it will push the boat backwards. Just keep flapping, and use the steery thing (tiller?) too.

[d000hg]

Put it on the back (stern) of the boat, pointing backwards (astern) so it pushes air out behind the boat. Additionally, take the sail down.

It's because of Newton's 3rd law, but I won't spoil the thread completely by explaining the reasoning just yet.

[original PM]

given my previous lack of success with these damn questions I should leave well alone but I am glutton for punishment so here goes.

1) You could in effect use it to blow wind into the sail - I cannot see a problem with this. So point it foward.

2) It may be more efficent to point it back wards - either above the water so it acts like a hovercraft/swamp boat fan - but these tend to be quite large - so you may have more joy pointing it backwards in the water so it acts as a propeller.

3) I am sure the Benoulli principle will work also

As to which is going to be the best of the 3 options - I would go for using it as a propeller!

Come on someone come up with the correct answer to put me out of my misery!

[Advocate]

Electric music's rubbish, I'd chuck the fan overboard!

[NotAllThere]

Oh this should be a fun thread, because I actually tested this, (in a Physics laboratory no less,) so know the answer.

So, while the rest of us give our neurons a work out, and go to the effort of working it out from first pricinples, you just go an try it in a physics lab. Lazy git.

[scooterscot]

There's a reason I'm not an IT contractor - yes - these guys are on the tip of the sword there's no way I could wrestle with that kind of intellect.

[Grinder]

In the water, use it as a prop.

err *cough*

How about into the water?

[minestrone]

In the water, use it as a prop.

[Grinder]

Let me throw something in here (just to stir it up a bit more) - a helicopter works doesn't it? It has no sail underneath the rotor blades. If it did, it would not fly.

[threaded]

Out the aft (assuming you want to go forwards).

I guess the obvious answer is to point it at the sail, but that can't work as the sail is attached to the boat, and the fan is (effectively) attatched to the boat too. The best thing you can do with the sail is take it down to remove any drag.

Couple of clues:

The air isn't attached to anything is it?

You are best leaving the sail up.

[Menelaus]

Bernoulli - WHS above.