DISPLACEMENT HULLS
Displacement hulls displace the same amount of water whether stationary or moving. We are indebted to an ancient Greek, Archimedes of Syracuse, for figuring out why floating bodies displace their own weight of the liquid in which they are floating.
Displacement hulls are supported by buoyancy and include big, round, bulbous hulls such as you see on Dutch Barges which also include elements of the Cathederal Hull to get them to plane at speed in open water. All canal boats use displacement and speed through the water is limited by their waterline length. It is total waste to put big horses into a displacement hull as its only effect is to increase the bow wave when the power is applied. A narrow boat is incapable of exceeding 4mph in the restriction ditch of a canal and this is best seen when approaching a bridge where you go in at whatever speed you like and exit at almost zero. Go figure. Most boaters don't. The ideal cruising speed in a canal boat is 2mph making almost no bow wave and optimising distance run against fuel burned.
Macho boaters do not know this and cause much aggro and bad feeling by setting up wash that wrecks canal banks, disturbs sediment, alarms wildlife, swamps nests in season. Their passage affects moored boats also in the displacement of their 20+tons of weight from before their boat to behind their boat especially in shallower reaches where water can not get UNDER the boat.
In plain language:
Go slow and stop rocking the boats
international code of signals uses
ROMEO YANKEE
Flat bottomed Cathedral hulls need less effort to get them on the plane, but because they have a larger flat surface area they are less comfortable in chop. They provide a very stable platform at slow speed which is a consideration when designing 9or buying!) a canal boat.
Displacement hulls displace the same amount of water whether stationary or moving. We are indebted to an ancient Greek, Archimedes of Syracuse, for figuring out why floating bodies displace their own weight of the liquid in which they are floating.
Displacement hulls are supported by buoyancy and include big, round, bulbous hulls such as you see on Dutch Barges which also include elements of the Cathederal Hull to get them to plane at speed in open water. All canal boats use displacement and speed through the water is limited by their waterline length. It is total waste to put big horses into a displacement hull as its only effect is to increase the bow wave when the power is applied. A narrow boat is incapable of exceeding 4mph in the restriction ditch of a canal and this is best seen when approaching a bridge where you go in at whatever speed you like and exit at almost zero. Go figure. Most boaters don't. The ideal cruising speed in a canal boat is 2mph making almost no bow wave and optimising distance run against fuel burned.
Macho boaters do not know this and cause much aggro and bad feeling by setting up wash that wrecks canal banks, disturbs sediment, alarms wildlife, swamps nests in season. Their passage affects moored boats also in the displacement of their 20+tons of weight from before their boat to behind their boat especially in shallower reaches where water can not get UNDER the boat.
In plain language:
Go slow and stop rocking the boats
international code of signals uses
ROMEO YANKEE
Flat bottomed Cathedral hulls need less effort to get them on the plane, but because they have a larger flat surface area they are less comfortable in chop. They provide a very stable platform at slow speed which is a consideration when designing 9or buying!) a canal boat.
DIRECTIONAL INSTABILITY
Pentargon is very skittish under way and the helm has to be constantly watched. Left to itself for even a few seconds it tends to steer itself and in an unpredictable manner. Its directional stability in calm weather and still water depend on many variables such as biased loading and trim. The water tank is far forward in the bow while the twin fuel tanks are low in the stern on each side of the engine. However this instability makes for a very manoeuvrable boat with very quick response. In 2023, while in dry dock, I found the [original 1973] lower rudder pin was eating away its pivot. A welded in rudder cup tightened up the steering no end but sea trials will have to wait til the boat is back in the water. WIP 20230425
A ship is directionally stable if deviation from a set course increases only while an external force is acting to cause the deviation. A directionally stable ship requires less energy expenditure by its steering gear in maintaining a set course. Left to its own devices it tends to 'steer itself'.
It is unstable if a course deviation happens in the absence of an external cause. A directionally unstable ship is easy to manoeuvre but the helm needs constant supervision to hold a course. A compromise between extremes is therefore desirable.
Pentargon is very skittish under way and the helm has to be constantly watched. Left to itself for even a few seconds it tends to steer itself and in an unpredictable manner. Its directional stability in calm weather and still water depend on many variables such as biased loading and trim. The water tank is far forward in the bow while the twin fuel tanks are low in the stern on each side of the engine. However this instability makes for a very manoeuvrable boat with very quick response. In 2023, while in dry dock, I found the [original 1973] lower rudder pin was eating away its pivot. A welded in rudder cup tightened up the steering no end but sea trials will have to wait til the boat is back in the water. WIP 20230425
A ship is directionally stable if deviation from a set course increases only while an external force is acting to cause the deviation. A directionally stable ship requires less energy expenditure by its steering gear in maintaining a set course. Left to its own devices it tends to 'steer itself'.
It is unstable if a course deviation happens in the absence of an external cause. A directionally unstable ship is easy to manoeuvre but the helm needs constant supervision to hold a course. A compromise between extremes is therefore desirable.
