Question: What is the adjustment of a boat's loading so as to change its fore-and-aft attitude in the water?
About the article "Sailing", section "Hull trim".

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Hull trim is the adjustment of a boat's loading so as to change its fore-and-aft attitude in the water.
In small boats, it is done by positioning the crew.
In larger boats the weight of a person has less effect on the hull trim, but it can be adjusted by shifting gear, fuel, water, or supplies.
Different hull trim efforts are required for different kinds of boats and different conditions.
Here are just a few examples: In a lightweight racing dinghy like a Thistle, the hull should be kept level, on its designed water line for best performance in all conditions.
In many small boats, weight too far aft can cause drag by submerging the transom, especially in light to moderate winds.
Weight too far forward can cause the bow to dig into the waves.
In heavy winds, a boat with its bow too low may capsize by pitching forward over its bow (pitch-pole) or dive under the waves (submarine).
On a run in heavy winds, the forces on the sails tend to drive a boat's bow down, so the crew weight is moved far aft.
Conventional wisdom dictates that the saddle should be positioned so that when the crankarms are horizontal and the feet are on the pedals the head of fibula of the forward leg is approximately above the pedal spindle in a vertical line.
However, several authors argue that there is no anatomical basis for this.
Furthermore, the relative position of saddle and bottom bracket varies between road racing, track and triathlon bicycles.
The range of adjustment differs for each saddle, and the comparison of saddles for increased ranges of adjustment can be confusing owing to their different shapes.
In comparing them, it is the range of adjustment of their "comfort points" that need considered, and because the matter is largely subjective, giving it proper attention is difficult to do.
The range of fore-aft adjustment for double-rail saddles rarely exceeds an inch or so, but advertisers claim that i-beam saddle designs can give up to 200% more adjustment range than some of these.
When the fore-aft adjustment range of the saddle needs "further" extension than the clamp affords, it may be possible to add a "saddle adjuster".
One such adjuster mounts on the existing saddle clamp and allows up to 40mm of "increase" or "decrease" in the fore-aft position of the saddle.
Another method for "increasing" the fore-aft adjustment is the swept-back seat post, where the seat post has a curve in it over the six inches or so before the saddle.
Because of the gentle sweep of the tube, the top part of the seat-post cannot fit within the seat-tube, so this solution is useful only for high seat positions. 
The longitudinal static stability of an aircraft is significantly influenced by the distance (moment arm or lever arm) between the centre of gravity (c.g.)
and the aerodynamic centre of the airplane.
The c.g.
is established by the design of the airplane and influenced by its loading, as by payload, passengers, etc.
The aerodynamic centre (a.c.) of the airplane can be located approximately by taking the algebraic sum of the plan-view areas fore and aft of the c.g.
multiplied by their blended moment arms and divided by their areas, in a manner analogous to the method of locating the c.g.
itself.
In conventional aircraft, this point is aft of, but close to, the one-quarter-chord point of the wing.
In unconventional aircraft, e.g.
the Quickie, it is between the two wings because the aft wing is so large.
The pitching moment at the a.c. is typically negative and constant.
The a.c. of an airplane typically does not change with loading or other changes; but the c.g.
does, as noted above.
If the c.g.
moves forward, the airplane becomes more stable (greater moment arm between the a.c. and the c.g.
), and if too far forward will cause the airplane to be difficult for the pilot to bring nose-up as for landing.
If the c.g.
is too far aft, the moment arm between it and the a.c. diminishes, reducing he inherent stability of the airplane and in the extreme going negative and rendering the airplane longitudinally unstable; see the diagram below.
Accordingly, the operating handbook for every airplane specifies the range over which the c.g.
is permitted to move.
Inside this range, the airplane is considered to be inherently stable, which is to say that it will self-correct longitudinal (pitch) disturbances without pilot input. 
A jibe can be a dangerous maneuver in a fore-and-aft rigged boat because, as the direction of the wind crosses the boat's centerline, the "old" leeward side of the mainsail and boom suddenly becomes the new windward side, and the sails are always fully filled by the wind.
The load on the sail and mainsheet can remain high throughout the maneuver, and if uncontrolled, the boom and mainsail can swing across the deck with high speed, striking and injuring anyone standing in the path of the boom or its tackle, as they sweep across the boat.
An uncontrolled boom slamming to the limit of its range may also put excessive stress on the rigging, and can break the boom or standing rigging, perhaps even bringing the mast down.
A jibe can also result in a sudden change in the direction of heeling, and can cause unexpected course changes due to the change in mainsail force changing from one side of the boat to the other.
Owing to the hazard associated with the accidental jibe, some designers are moving away from designs that require the use of booms.
There are also several designers that have placed the mast in the back of the boat in a configuration termed mast aft.
This enables them to greatly reduce the size of the boom or eliminate it completely. 
A fore-and-aft rig is a sailing rig consisting mainly of sails that are set along the line of the keel rather than perpendicular to it.
Such sails are described as fore-and-aft rigged.
Fore-and-aft rigged sails include staysails, bermuda rigged sails, gaff rigged sails, gaff sails, gunter rig, lateen sails, lugsails, the spanker sail on a square rig and crab claw sails.
Fore-and-aft rigs include:  Rigs with one mast: the proa, the catboat, the sloop, the cutter  Rigs with two masts: the ketch, the yawl  Rigs with two or more masts: the schooner Barques and barquentines are partially square rigged and partially fore-and-aft rigged.