Difference of Speed over Ground (SOG) and Speed through Water (STW) | FleetMon's Vessel Tracking Help Desk (2024)

FAQs

Difference of Speed over Ground (SOG) and Speed through Water (STW) | FleetMon's Vessel Tracking Help Desk? ›

Speed over Ground (SOG) is the vessel's speed in one hour concerning the land or any other fixed object such as buoys. Speed through Water (STW) is the vessel's speed in one hour concerning the water or anything floating on water.

Speed Over the Ground (SOG) is the speed of the vessel relative to the surface of the earth. Speed Through Water (STW) is the speed of the vessel relative to the water. It is possible for the STW to be zero while the SOG is 5 knots, for example if the boat was drifting in a 5 knot current.

Speed over water is only required to be used for collision avoidance and not necessarily for navigation. By using speed over ground, a navigator is more aware of the situation than otherwise. For example, if the ship is drifting towards a danger, navigator will know it better if he has speed over ground in radar.

In general, STW is used for radar collision avoidance to provide a more accurate indication of the target's aspect and SOG is used for navigation.

SOG. Speed Over Ground. This differs from boat speed- so for example if your boat is stationary in the water, it may still be moving in relation to the land due to current and wind etc.

SOG = Speed over Ground - includes current forecast. COG = Course over Ground to the next waypoint.

Highlights. • Ship Speed Through Water (STW) is estimated from in-service measurements on the propeller shaft.

Water track or Course Through Water (CTW) is the direction of the yacht through the water derived from combining heading and leeway. Water track = HDG ± leeway . Course Over Ground (COG) is the path of the boat over the ground.

The squat effect is the hydrodynamic phenomenon by which a vessel moving through shallow water creates an area of reduced pressure that causes the ship to increase its draft and thereby be closer to the seabed than would otherwise be expected.

Since it was originally measured as the number of knots per unit time, speed over water traditionally uses the unit of “knots” to indicate speed. One knot (kt) = 1 nautical mile per hour = 1.15 mph = 1.85 kph.

What is the difference between ground stabilized and sea stabilized radar? ›

Where true target trails is selected, a sea stabilised display will indicate all targets' motion through the water. A ground stabilised display will indicate all targets' motion over the ground.

It is shown that speed through the water is the appropriate reference for avoiding collision on the high seas since it will produce a correct measure of the target-aspect information that is essential in determining legal collision avoidance manoeuvres.

AN/TPS-59. Developed for the U.S. Marine Corps to provide a mobile long-range surveillance radar capability. It is recognized as the world's most capable long-range ground-based radar for tactical ballistic missile defense with proven performance during live fire tests.

To find the speed over the ground (SOG) we go back to the diagram and measure the distance from the start point to the point where the water track meets the ground track. If this distance is 5.5M and we have constructed the diagram for one hour, the vessels SOG is 5.5Kn.

SOG was named in honor of a covert US Special Ops unit that fought in Vietnam. That unit was known as Military Assistance Command, Vietnam - Studies and Observations Group (MACV-SOG). Its existence once denied by the US Government, it wasn't until long after the war that the SOG story could even be told.

Course Over Ground is the actual direction of progress of a vessel, between two points, concerning the earth's surface. The vessel's "heading" may differ from the Course Over Ground (COG) due to the effects of wind, tide, and currents.

Speed over ground – 0.1 knot resolution from 0 to 102 knots. Position accuracy. Longitude – to 1/10000 minute and Latitude – to 1/10000 minute.

Course Made Good (CMG) - Is the course actually steered which includes the effect of current set (direction) & drift (speed), wind and leeway and helmsman errrors. Note we distinguish COG (course over ground) from cmg (course made good), as one being present dynamic value, and the other being past.

Standard Treatment Workflows (STWs)

Electro-technical Rating (ETR)

What does STW mean in contract? ›

Short-time Work Scheme (STW): The key objective of STW schemes is to provide support to companies to retain their employees in times of economic difficulties.

Remember that carat is a measure of weight, not size. CTTW stands for carat (CT) and total weight (TW). In a piece of jewelry that has more than one diamond, it's the weight of all the diamonds, added together.

You may see halo earrings that say "1 CTW", which means that all of the diamonds, both center and halo, in both of the earrings, add up to 1.00 Carat Total Weight.

COG, Course Over Ground, indicates the direction of the boat's heading relative to the land. Over ground means "in relation to the earth", see also the term SOG. Therefore, COG means the true direction free from the effects of sea currents.

The wave speed in shallow-water waves is related to water depth, rather than wave period as it is for deep water waves. The shallower the water, the slower is the wave speed.

Speed through water is the speed of the ship with respect to the water such as anything floating on water. A ship with her engine stopped in water with 2 knots currents will have zero speed through water but will have 2 knots speed over ground.

Theoretical displacement hull speed is calculated by the formula: velocity in knots = 1.35 x the square root of the waterline length in feet.

knot, in navigation, measure of speed at sea, equal to one nautical mile per hour (approximately 1.15 statute miles per hour). Thus, a ship moving at 20 knots is traveling as fast as a land vehicle at about 23 mph (37 km/hr).

log, also called maritime log, instrument for measuring the speed of a ship through water. The first practical log, developed about 1600, consisted of a pie-shaped log chip with a lead weight on its curved edge that caused it to float upright and resist towing.

Differences Between S- and X-band Radar

S-band is on 2-4 GHz. X-band is 8-12 GHz. Another difference is physical size. X-band radar elements are typically spaced closer together than S-band.

What is sea stabilized and ground stabilized mode in radar? ›

To be sea-stabilized, your radar needs two key inputs: speed through the water, usually taken from your boat's paddlewheel log, and boat heading, usually taken from a fluxgate or satellite compass. By contrast, if your radar uses GPS speed over ground and course over ground, it's ground-stabilized.

There are 2 types of radars used on ships: X-band and S-band radars.

Ground stabilisation means that the display is referenced to the seabed by GNSS or through a twin-axis Doppler log. For sea stabilisation the display is referenced to the sea current that own ship is experiencing, typically based on SDME measurements.

Generally, due to operating frequency X band radar provides a clearer viewing screen and is used for target detection and collision avoidance. Whereas S-band radar gives better picture because it's radio waves can penetrate through fog particles and rain.

An average speed of within 0.5 knots (±0.257 meter/second) is normally acceptable, weather and safe navigation permitting.

How Deep Can GPR Penetrate? The depth of GPR depends on the application. For concrete scanning, the radar used can penetrate depths of 18-24”. For private utility locating needs on grass, soil, asphalt, or concrete, the type of antenna used can penetrate up to 8'.

Electromagnetic tracing (EM) is used to locate underground utility lines that hold a current. EM locators are known to perform well in a wide variety of soil types and conditions and are faster as well as more affordable than ground-penetrating radar (GPR) locators.

We recommend sticking with Level 3 radar when on the road chasing.

Speed over Ground (SOG) is the vessel's speed in one hour concerning the land or any other fixed object such as buoys. Speed through Water (STW) is the vessel's speed in one hour concerning the water or anything floating on water.

Boat's speed in still water = ½ (Downstream Speed + Upstream Speed) Downstream = (u+v)Km/hr.

Does tide affect speed through water? ›

It is important to realise that the speed through the water will always be different to the speed over the ground if there is a tidal stream. This is easy to imagine if the tide is travelling directly with or against the boat, but not so simple when it is travelling at right angles to it.

That is speed = distance ÷ time. Or to put it another way distance divided by speed will give you the time. Provided you know two of the inputs you can work out the third. For example if a car travels for 2 hours and covers 120 miles we can work out speed as 120 ÷ 2 = 60 miles per hour.

Choose how long the object is falling. In this example, we will use the time of 8 seconds. Calculate the final free fall speed (just before hitting the ground) with the formula: v = v₀ + gt = 0 + 9.80665 × 8 = 78.45 m/s.

Providing Tactical Operations. The Special Operations Group (SOG) is comprised of 10 officers who are specially trained in tactical operations.

Many of the military members of MAC-V SOG joined the CIA after their military service. The legacy of MAC-V SOG continues within SAC's Special Operations Group.

The two primary missions of MACV-SOG were direct action and reconnaissance. Hatchet teams were MACV SOG's primary raid force. They would conduct direct action missions and ambushes along the Ho Chi Minh Trail. Additionally, they could act as a quick reaction force for reconnaissance teams who were compromised.

It probably seems so much faster because water is significantly more dense than the air we breath, which is a fluid. With this in mind, the force required to push every water molecule out of your way as your swim is significantly more than air.

The term “knot”, in reference to currents, is defined as one nautical mile per hour and is used to measure speed. A nautical mile is slightly more than a standard mile. 1 nautical mile = 1.15 miles = 1.85 kilometers. 1 knot = 1.15 miles per hour = 1.85 kilometers per hour.

Since it was originally measured as the number of knots per unit time, speed over water traditionally uses the unit of “knots” to indicate speed. One knot (kt) = 1 nautical mile per hour = 1.15 mph = 1.85 kph.

Water temperature and pressure determine how far sound travels in the ocean. While sound moves at a much faster speed in the water than in air , the distance that sound waves travel is primarily dependent upon ocean temperature and pressure.

Are you faster underwater or on the surface? ›

First, swimmers who stay underwater for the full 15 metres will have faster starts, turns and overall race times. This effect is particularly strong in backstroke events, and when swimmers make the most of the final turn in a race (when swimmers usually surface quicker because they are growing tired).

When objects move through a fluid, such as air or water, the fluid exerts a frictional force on the moving object. The frictional force from a fluid is called a drag force. Friction drag force causes objects to slow down as they move through a fluid, such as air or water.

Nautical Miles

To put it another way, at 6,076 feet a nautical mile is longer than a statute mile, which has only 5,280 feet.

Slow Speed, Outside Channel – Maximum Speed Zone

They indicate that you should be traveling slowly, but highlight a specific speed (typically 25, 30, or 35 mph). However, unlike speed limits on the road that drivers tend to exceed with regularity, it's important you adhere to the posted speed limits.

Course Over Ground is the actual direction of progress of a vessel, between two points, concerning the earth's surface. The vessel's "heading" may differ from the Course Over Ground (COG) due to the effects of wind, tide, and currents.

In modern times, a knot is a unit of speed that ties directly into the global latitude and longitude coordinate system. Therefore, in the aviation and nautical worlds, knots are oftentimes used in place of MPH and KPH since they are easier to navigate with.