Question: What would cause a boat's bow to dig into waves?
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.
The wreck was examined and videotaped by remotely operated underwater vehicles and by divers from a Norwegian company, Rockwater A/S, contracted for the investigation work.
The official report indicated that the locks on the bow door had failed from the strain of the waves and the door had separated from the rest of the vessel, pulling ajar the ramp behind it.
The bow visor and ramp had been torn off at points that would not trigger an "open" or "unlatched" warning on the bridge, as is the case in normal operation or failure of the latches.
The bridge was also situated too far back on the ferry for the visor to be seen from there.
While there was video monitoring of the inner ramp, the monitor on the bridge was not visible from the conning station.
The bow visor was under-designed for the conditions "Estonia" was operating in (the ferry was designed for coastal waters, not open regions like the Baltic Sea), and the visor's overhang focused the impact on a small area.
The first metallic bang was believed to be the sound of the visor's lower locking mechanism failing, and subsequent noises were the visor 'flapping' against the hull as the other locks failed, before tearing free and exposing the bow ramp.
The subsequent failure of the bow ramp allowed water into the vehicle deck, which was listed as the main cause of the capsizing and sinking: RORO ferries with their wide vehicle decks are particularly vulnerable to capsizing if the car deck is even slightly flooded because of free surface effect: the fluid's swilling motion across such a large area hampers the boat's ability to right itself after rolling with a wave.
The report was critical of the crew's actions, particularly for failing to reduce speed before investigating the noises emanating from the bow, and for being unaware that the list was being caused by water entering the vehicle deck.
There were also general criticisms of the delays in sounding the alarm, the passivity of the crew and the lack of guidance from the bridge.
Recommendations for modifications to be applied to similar ships included separation of the condition sensors from the latch and hinge mechanisms. 
The restoration of the boat was supervised by marine architect Alan L. Bates (now Captain Bates), whose book, "Str.
Belle of Louisville", (1964) remains a primary source on the history of the boat and the crews who worked on her.
Prior to the auction, the boat's hull had been condemned as unfit by the U. S. Coast Guard: concrete patches had added much weight to the oft-damaged hull, as had generations of accumulated modifications to the decks and fittings within her superstructure.
These were stripped and repaired in dry dock or removed by volunteers.
What remained was cleaned, surface prepared, supplied with new finish carpentry, and painted in a style consistent with the boat's early 20th-century origins.
Captain Clarke "Doc" Hawley, had worked aboard the boat during her "Avalon" days.
He had salvaged the brass nameplates from the ends of the two massive cylinders in order to prevent them from being sold for scrap, and now he returned them to the boat.
Hawley had also, before the auction, at his own cost hired an assistant to drain the boat's water-filled fittings for winter, so that they would not freeze and burst.
This meant that the mechanical restoration of the boat was now possible, at far less cost than had extensive refitting of ruined pipe work been necessary.
Various of her workings, though not her engine and drive train, had been stripped and sold in separate lots at auction, including the boat's original steam calliope.
Volunteers donated materials which could be adapted to use.
Some of them, such as brass steam-powered bilge clearing pumps known as siphons, were cannibalized from steamboats sunken long-ago, whose hulls could still be seen and dived at low water.
Some missing components were custom-fabricated by local foundries in a style copied from photographs of the boat in her earlier days.
The degree of preservation was considerable, and the boat is still piloted with a 19th-century skill set, though now with the assistance of modern communications.
Although authentic to its core, the boat has occasionally seen improvements not part of the original restoration.
The compressed-air driven calliope which replaced the missing original proved unsatisfying, and was ultimately replaced with the true steam calliope which the boat uses today, audible for many blocks in the surrounding Downtown Louisville area when the boat is readying to depart.
The new calliope was built by Morecraft Manufacturing of Peru, Indiana and installed in 1988.
The instrument is a reproduction of the Nichol instrument that the boat carried when named "Avalon".
The ship's bow was also redesigned by Bates in the late 1960s, to make the boat a better contender in the Great Steamboat Race: the original, blunter bow at maximum speeds showed the tendency for waves to break over it. 
"Havock" was launched first, on 12 August 1893.
Her sea trials on 28 October 1893 were successful, her top speed indicating that she was capable of keeping up with battleships.
However, her bow torpedo tube proved to be useless as the ship would usually outrun her own torpedo.
It also tended to cause the bows to dig into the sea, resulting in a very wet turtleback.
As such it (and later, the turtleback) was absent in later destroyers.
"Havock" "behaved well" on trials.
It was noted that "Hornet" "steers readily and well" but her coal consumption trial revealed that she used considerably more fuel than her sister. 
A ship moving over the surface of undisturbed water sets up waves emanating mainly from the bow and stern of the ship.
The waves created by the ship consist of divergent and transverse waves.
The divergent waves are observed as the wake of a ship with a series of diagonal or oblique crests moving outwardly from the point of disturbance.
These waves were first studied by Lord Kelvin, who found that regardless of the speed of the ship, they were always contained in the 19 degree (each side) symmetric wedge following the ship.
The divergent waves do not cause much resistance against the ships forward motion.
However, the transverse waves appear as troughs and crests along the length of a ship and constitute the major part of the wave-making resistance of a ship.
The energy associated with the transverse wave system travels at one half the phase velocity or the group velocity of the waves.
The prime mover of the vessel must put additional energy into the system in order to overcome this expense of energy.
The relationship between the velocity of ships and that of the transverse waves can be found by equating the wave celerity and the ship’s velocity.