Sail to Prop - directly downwind

something to help visualize the concepts of faster than the wind directly downwind vessels.

Category:

Science & Technology

Tags:

• fttwddw
• wind
• directly
• down
• sail
• propeller
• ddw
• prop

[axelerat3d]

@chrismasterith

Nope - iceboats, sailboats, sailcarts all can beat the wind downwind (just not directly). Their downwind speed component can be significantly faster than then the wind. This is generally accepted as a fact and proven over and over again.

just to be clear= A boat can beat a floating balloon to the downwind marker.

[eyytee]

chrismasterith: "the windward component of the sailboat velocity never exceeds the actual wind velocity"

This is a common misconception. This animation shows how the air can push a boat forward, which already has a windward velocity component greater that wind-speed:

watch?v=63hvQABLOaE

The same for the prop-blade:

watch?v=vVMqa7Mft0k

[planetofthescums]

@axelerat3d I am constantly looking for ways to help you explain this to people. I don't know how far I plan on taking on this mission, but I will take the time to re-read your comments, resources, and make sure I am not in error before I take up your time again.

[planetofthescums]

@axelerat3d I don't know what leverage even means buddy. I am just getting started on the discussion.

You seem to be speaking on many points which we agree and I am starting to see this from your perspective.

But if you want to bow out I won't hesitate to say good luck and thanks for the discussion, it won't hurt me to leave this as it is.

[planetofthescums]

@axelerat3d If you are on a cart DDWFTTW when wind appears to stop around you, then the air behind the prop appears to move back with velocity opposite the acceleration of the cart.

When you sail you do not force the wind to move in an opposing direction, Sitting on the boat the relative wind hits the sail from the side and appears to blow backwards as well.

You said the aerodynamics don't change so the prop is, from perspective sitting in the cart, at any speed is pushing air backwards.

[axelerat3d]

@planetofthescums

Ok I will finally stop for good. I am not name dropping or confusing on purpose. You seem to constantly complain and suggest that somehow my way of communicating is wrong. Yet fail to see that ypu are the one doing the insulting.

And guess what the rolling friction + air/ground speed difference on the DDW cart is exactly the same thing as the cart on treadmill.

[planetofthescums]

@axelerat3d No we can't simply ignore the fact this is a treadmill, things which could theoretically stop the wind would not stop a treadmill. This treadmill experiment was designed to prove a point and it was made. Rolling friction causes forward propulsion.

[planetofthescums]

@axelerat3d I know, the change in velocity could be any amount if you are given enough wind. Why bring leverage into it. That seems kind of counter-intuitive; just another name-drop?

[planetofthescums]

@axelerat3d The only reason a boat zigzags is to get to an exact destination, this couldn't possible improve speed in any way, turning parallel to the wind where it has negative relative wind speed..

[axelerat3d]

Even minimal change in wind speed can accelerate the boat as long as enough air is affected. Affect big mass of air just by tiny bit and it ads up to a lot if the system can use the leverage.

Treadmill is analogous to the sailcart. Sure there is power source in the t-mill but we can ignore that just like we ignore the fact that earth is spinning - ground travels quite a bit but from my point of reference its irrelevant. What is relevant is difference of speed between air and perceived ground.

[axelerat3d]

@planetofthescums by constant tack I meant condition similar to a boat being for example in starboard tack. Basically traveling at an angle in relation to the wind Boat does it by changing tacks (zig zagging) propeller blade does this by nature as it has the similar effect as the sideways movement coming from the spinning.

Air doesn't need to reverse just slow down (of course from some point of reference this might look like reversing) .

[planetofthescums]

@axelerat3d The "tack description" is the description you gave as the as 'constant tack' OR "air being tacked".

I mean, when a boat is tacking in the wind, the wind is tacked.

The keel is in a normal position, along the the length of the boat. Sorry, bad grammar, short sentences.

Negative velocity, this means the whatever the wind speed is initially, that at final, once the boat is travelling faster than wind in the direction of the wind, the sail has forced the wind to change direction.