On 6/24/2013 3:42 PM, Henry Baker wrote:
The front wheel of a bicycle travels more than the rear wheel, because it is the steering wheel. (The rear wheel track always points at the direction of tangent contact of the front wheel, more-or-less.)
I would imagine that since the rudder in a (prototypical) yacht is in the rear, that the rear end of a yacht travels further than the front end.
On submarines & some very large ships, they have front rudder-like steering apparatuses, as well, so perhaps they are more balanced.
If you look at air-to-air missiles, which also maneuver by fluid dynamic forces, you see all three placements. Some have the smaller movable fins at the front and then large fixed fins at the rear to keep stability. Some have the movable fins at the rear and fixed wings or narrow strakes just ahead along the after part of the body. And some had movable wings at the middle, near the center of gravity, with smaller fins at the rear for stability. Of course modern air-to-air missiles may have only marginal aerodynamic stability and rely on active controls for stable flight. Racing yachts are also designed to have only slight positive stability so that they will turn well. Normal yachts and ships probably have a large stability margin. But in almost any design the front is going to point inside the tangent to the turning circle because that's the way to be lateral force from the whole body, not just the movable fins. The only exception I know of were the older SPARROW air-to-air missiles which got all their lift from the movable wings located near the center of mass. They were designed this way so the radar wouldn't have to gimbal back and forth a lot as the wings moved; the body always just pointed along the velocity vector because of the fixed tail fins.
The real question is why boats stear from the rear (other than the fact that it is more comfortable for the captain to be there (not crashing up & down in the front), and perhaps it is the case that even with more modern technology, no one bothered to re-think where the best place to put the rudder would be.
Of course originally boats were steered with one of the oars (as you may still steer a canoe). It's hard to do this from the bow since you want the steering oar to trail behind the its pivot point; otherwise it's unstable. The reason the captain and the quarterdeck were at the rear was so he and the helmsman could easily see the sails and sailors while also being able to see the ship and it's relation to docks and buoys etc. On modern ships the quarterdeck is often well forward since the helmsman doesn't need to see the sails. Brent Meeker
A little-known 'turning point' in history took place right around the turn of the century 1900, when the rudder wheels started turning in the direction of the turn, instead of the reverse, which had been standard up until then. This change may have been done to make it consistent with those new-fangled automobiles. Many movies get this wheel direction/turning direction relationship of these older ships wrong.
http://en.wikipedia.org/wiki/Ship's_wheel
At 01:55 PM 6/24/2013, James Propp wrote:
Do the front and back of a yacht travel the same distance?
(Let's assume that the earth is flat for purposes of this problem.)
Here's a question that I think is equivalent: If a yacht travels in a circle, do the front and back ends of the yacht travel on circles of the same radius?
Jim Propp
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