04 Environmental Conditions

What are environmental conditions, how do they affect our work and how to deal with it?

May 19, 2021 www.seacamel.com 1 Module Summary

– Wind Conditions – Tables and – Wind force (Scale of Beaufort) – Tides and quay heights – Wind force (Scale of Beaufort) – Simple method to calculate the tide – Wind force (Scale of Beaufort) – Weather restricted operations (DNV) – Wind pressure and wind load – Weather restricted operations. The α-factor (DNV) – Wind gradient. – Tropical storm avoidance flow chart (float-over). – Finding the allowable wind speed for cranes using – OPLIM Operational environmental limiting criteria. a diagram – Water force (slamming, tide, current) – Calculating the allowable wind speed (1) – Storm at Borgholm Dolphin, North Jan 10, – Calculating the allowable wind speed (2) 2015 – Waves and – Significant wave – Longitudinal bending moments – Current – Loop Currents ( Currents) – Checking the weather yourself. – Location, heading and speed of a vessel. – Tide, what is causing it?

May 19, 2021 www.seacamel.com 2 Environmental conditions

Environmental conditions are natural phenomena which contribute to structural stress and strain, impose operational limitations/restrictions or navigational considerations. Phenomena of general importance are; –wind, –waves/swell –currents and tide. –soil conditions –ice and snow, –temperature, –fouling, –visibility/fog, –heavy rain, and –earthquake.

May 19, 2021 www.seacamel.com 3 Wind Conditions

Roughly we consider 3 types of wind Mean wind – The average wind velocity within a specified time interval. – Reference height 10 [m]. Gust wind – Average wind speed during a specified time interval less than one minute. 1 minute sustained wind. Squalls. – Squalls are strong winds characterised by a sudden onset, duration of the order of 10-60 minutes, and then a rather sudden decrease in speed. Squalls are caused by advancing cold air and are associated with active weather Example: such as thunderstorms. From N 20% force 5 Their formation is related From NE 68% force 4 to atmospheric instability Calms 1% and is subject to seasonality. Atlas of Pilot Charts per month and area can be found at http://msi.nga.mil/ May 19, 2021 www.seacamel.com 4 Wind force (Scale of Beaufort)

Beaufort number Description Wind speed Sea conditions Land conditions photo

< 1.1 km/h 0 m < 0.7 mph 0 Calm Flat. Calm. Smoke rises vertically. < 0.6 knot 0 ft < 0.3 m/s 1.1–5.5 km/h 0–0.2 m 0.7–3.4 mph Smoke drift indicates wind 1 Light air Ripples without crests. direction. Leaves and wind 0.6–3 knot vanes are stationary. 0–1 ft 0.3–1.5 m/s 5.5–11.9 km/h 0.2–0.5 m 3.4–7.4 mph Small wavelets. Crests Wind felt on exposed skin. 2 Light breeze of glassy appearance, Leaves rustle. Wind vanes 3–6.4 knot not breaking begin to move. 1–2 ft 1.5–3.3 m/s 11.9–19.7 km/h 0.5–1 m Large wavelets. Crests Leaves and small twigs Gentle 7.4–12.2 mph begin to break; constantly moving, light flags 3 breeze 6.4–10.6 knot scattered whitecaps extended. 2–3.5 ft 3.3–5.5 m/s 19.7–28.7 km/h 1–2 m Small waves with Dust and loose paper Moderate 12.2–17.9 mph breaking crests. raised. Small branches 4 breeze Fairly frequent 10.6–15.5 knot begin to move. 3.5–6 ft whitecaps. 5.5–8 m/s May 19, 2021 www.seacamel.com 5 Wind force (Scale of Beaufort)

28.7–38.8 km/h 2–3 m 17.9–24.1 mph Moderate waves of Branches of a Fresh some length. Many moderate size move. 5 15.5–21 knot breeze whitecaps. Small Small trees in leaf 6–9 ft amounts of spray. begin to sway. 8–10.8 m/s

38.8–49.9 km/h Large branches in 3–4 m Long waves begin to 24.1–31 mph motion. Whistling heard form. White foam crests Strong 21–26.9 knot in overhead wires. 6 are very frequent. Some breeze Umbrella use becomes airborne spray is 9–13 ft difficult. Empty plastic 10.8–13.9 m/s present. bins tip over.

49.9–61.8 km/h 4–5.5 m Sea heaps up. Some 31–38.4 mph foam from breaking High wind, 26.9–33.4 knot waves is blown into Whole trees in motion. moderate 7 streaks along wind Effort needed to walk gale, direction. Moderate against the wind. near gale 13–19 ft 13.9–17.2 m/s amounts of airborne spray.

61.8–74.6 km/h 5.5–7.5 m 38.4–46.3 mph Moderately high waves 33.4–40.3 knot with breaking crests Some twigs broken forming spindrift. Well- from trees. Cars veer Gale, 8 marked streaks of foam on road. Progress on fresh gale 18–25 ft are blown along wind foot is seriously 17.2–20.7 m/s direction. Considerable impeded. airborne spray.

May 19, 2021 www.seacamel.com 6 Wind force (Scale of Beaufort)

74.6–88.1 km/h 7–10 m High waves whose crests Some branches break 46.3-54.8 mph sometimes roll over. Dense off trees, and some 40.3–47.6 knot foam is blown along wind small trees blow over. 9 Strong gale direction. Large amounts of Construction/temporar 23–32 ft 20.7–24.5 m/s airborne spray may begin to y signs and barricades reduce visibility. blow over.

88.1–102.4 km/h Very high waves with 9–12.5 m 54.8–63.6 mph overhanging crests. Large patches of foam from wave 47.6–55.3 knot crests give the sea a white Trees are broken off or Storm 10 appearance. Considerable uprooted, structural whole gale 29–41 ft tumbling of waves with damage likely. 24.5–28.4 m/s heavy impact. Large amounts of airborne spray reduce visibility. 102.4–117.4 km/h Exceptionally high waves. 11.5–16 m 63.6–72.9 mph Very large patches of foam, driven before the wind, cover Widespread vegetation Violent 55.3–63.4 knot 11 much of the sea surface. and structural damage storm 37–52 ft Very large amounts of likely. 28.4–32.6 m/s airborne spray severely reduce visibility. ≥ 117.4 km/h ≥ 14 m ≥ 72.9 mph Huge waves. Sea is Severe widespread ≥ 63.4 knot completely white with foam damage to vegetation Hurricane 12 and spray. Air is filled with and structures. Debris force ≥ 46 ft driving spray, greatly and unsecured objects ≥ 32.6 m/s reducing visibility. are hurled about.

May 19, 2021 www.seacamel.com 7 Wind pressure and wind load

1 2 pressureP (wind ) = c d ´2 ´r ´ V were:

cd = drag coefficient 3 r air = 1.225 kg/m V = velocity m/s

Wind load (Fwind ) = Pwind ´ A were : A = projected area

Wind load on a building can be calculated as follows Height: 50 m Width: 4 m Wind: 10 m/s 1 2 Fwind= c d ´2 ´r ´ V ´ A 1 2 Fwind =1.05 ´2 ´ 1.225 ´ 10 ´ 50 ´ 4

Fwind = 12862.5 N

Fwind » 1.3 Ton

May 19, 2021 www.seacamel.com 8 Wind gradient.

At sea, we standard refer to the wind speed at 10m high.

May 19, 2021 www.seacamel.com 9 Finding the allowable wind speed for cranes using a diagram

If we know the surface area exposed to wind (AW) and the hoist load incl. lifting accessories and hook block (mH), we can read the maximum wind speed (Vmax) from a load chart. The surface area exposed to wind

(AW) equals the drag coefficient (cd) times the max projected surface area (Ap)

AW= c d ´ A P

projected surface

May 19, 2021 www.seacamel.com 10 Calculating the allowable wind speed (1)

A calculated maximum permissible wind Example explained according Liebherr: speed is given for every crane load chart in The load to be lifted weighs 65 t, has a cd- the load chart book. This is dependent on value of 1.4 and a projected surface area of the length of the boom and the crane 200 m². The surface area exposed to the configuration. Standard values from EN wind of 280 m². (1.4 x 200) 13000 have been used for the calculation. According to the Load reference value of 1.2 m²/ton. load chart, a The permissible wind speed can be maximum wind calculated with a single formula. For this the speed 11.1 m⁄s following data must first be collected: is permissible for this crane configuration. 1. 2 m2 / m VV= ´ H max maxTable A W The allowable maximum windspeed can now be calculated using following formulae. mH The hoist load incl. lifting accessories and hook block and any relevant portion of hoisting cable) m1.2 m2 / 65 t m V =11.1 ´ Vmax = 5.86 max s280 m 2 s AW The surface area exposed to wind

Vmax The maximum wind speed per the load chart liebherr-influence-of-wind-p403-e04-2017.pdf May 19, 2021 www.seacamel.com 11 Calculating the allowable wind speed (2)

Do we understand the formulae? The maximum wind speed from the manufacture is based on a standard area per ton ratio of 1.2 based on a drag coefficient cd of 1. If we have another area per ton ratio, we have to make a correction. First we calculate the surface area exposed or wind effective wind area which is: 2 AW= c d ´ A projected =1.4 ´ 200 = 280 m

That means that for this load, the area per ton ratio is: 280m2 m 2 = 4.31 65t t As this load has a relative high area, we need to reduce the wind speed. If the wind force would be linear with the wind speed, an area twice as big would mean that we should reduce the wind speed with 50%. However, the aerodynamic force depends on the square of the velocity, doubling the velocity will quadruple the lift and drag.

2 2 2 V ´1.2 VV´1.2 = ´ 4.31 Table Table max è Vmax = 4.31

11.12 ´ 1.2 m è V = = 5.86 4.31 s May 19, 2021 www.seacamel.com 12 Waves and swell

Waves Swell. Short period. Long period. Caused by the wind Distant storm from the past.

May 19, 2021 www.seacamel.com 13 Significant wave

The surface of the sea as we see it can be considered as a combination of numerous simple wave patterns that vary in: – Height – Period and – direction The , or

Hsig, is defined traditionally as the mean wave height (trough to crest) of the highest third of the waves (H1/3). Important to know is that: – the visually observed wave height is very close to the significant wave height and,, – the max wave height is about 2 times the significant wave height.

May 19, 2021 www.seacamel.com 14 Longitudinal bending moments

Hogging Sagging The changing wave pattern results in alternating When the wave tops are in way of the stern and stresses in the bottom and deck of the vessel. bow, the bending results to tension stresses in the When the top of the wave is amidships, the vessel bottom and compression stresses in the deck of will bend resulting to tension stresses in the deck the vessel. and compression stresses in the bottom of the Due to the change in the waterplane area, the vessel. stability increases. Due to the change in the waterplane area, the stability decreases.

May 19, 2021 www.seacamel.com 15 Current

Like wind is movement of air, current is movement of water.

Same formulas as for wind apply. Only ρseawater = 1025 kg/m3. Current can be caused by : – Tide – Wind – Rainfall – Melting water (rivers) – current,

Measured water levels at Astrakhan in the river Wolga during the year. In the winter, the river is frozen. Note the high water in spring due to melting water. This also means higher current speeds

May 19, 2021 www.seacamel.com 16 Loop Currents (Eddy Currents)

– Occur in the US gulf. – Like underwater hurricanes. They can measure 200 to 400 kilometres in diameter and extend down to a depth of 1000 meter and reaches flow speeds of 1.8 meters/second. – Not fully understood – They are named and monitored like hurricanes.

http://www.horizonmarine.com/

May 19, 2021 www.seacamel.com 17 Checking the weather yourself.

GRIB (GRIdded Binary or General Regularly-distributed Information in Binary form) is a data format used in meteorology to store weather data. They can contain a wide variety of information atmospheric and sea data. Many metocean offices publish this information for free. Freeware like www.zygrib.org can be used to download and visualize the information.

May 19, 2021 www.seacamel.com 18 Location, heading and speed of a vessel.

ww.marinetraffic.com May 19, 2021 www.seacamel.com 19 Tide, what is causing it?

Most areas have a double tide. tidal bulge is caused by centrifugal forces 1. As masses attract each other, water is pulled towards the moon and the sun. Common axis of rotation → there is a bulge of water in the direction of the moon (and the sun) 2. Although it seems that the moon orbits around the earth, the actually orbit around each other. → The centrifugal force causes a bulge of water One tidal bulge is at the opposite side of the moon. caused by the pull of gravity. Land masses causing irregularities around the world. Some areas have no tide. (Amphidromic points)

http://earth.eo.esa.int/brat/html/appli/ocean/tides_en.html May 19, 2021 www.seacamel.com 20 Tide Tables and Tides – We have two Spring Tides a month. Predicted values. Measured values.

Neap Spring Neap Spring

2008-12-27 8:49 PM IST 1.21 meters High Tide 2008-12-28 3:13 AM IST 0.40 meters Low Tide 2008-12-28 6:29 AM IST Sunrise 2008-12-28 8:47 AM IST 0.93 meters High Tide 2008-12-28 2:42 PM IST 0.28 meters Low Tide 2008-12-28 5:51 PM IST Sunset 2008-12-28 9:20 PM IST 1.22 meters High Tide 2008-12-29 3:44 AM IST 0.38 meters Low Tide 2008-12-29 6:30 AM IST Sunrise 2008-12-29 9:21 AM IST 0.95 meters High Tide 2008-12-29 3:15 PM IST 0.28 meters Low Tide 2008-12-29 5:51 PM IST Sunset 2008-12-29 9:50 PM IST 1.23 meters High Tide 2008-12-30 4:15 AM IST 0.36 meters Low Tide 2008-12-30 6:30 AM IST Sunrise 2008-12-30 9:55 AM IST 0.95 meters High Tide 2008-12-30 3:48 PM IST 0.29 meters Low Tide 2008-12-30 5:52 PM IST Sunset Tide table 2008-12-30 10:21 PM IST 1.21 meters High Tide May 19, 2021 www.seacamel.com 21 Tides and quay heights

Always check Elevation of quay in relation to Chart Datum A tide table, sometimes called a tide chart, is used for tidal prediction and shows the daily times and height of High Water (HW) and Low Water (LW) for a particular location in relation to Chart Datum. The abbreviations may differ from country to country. The effect of wind and high or low pressure areas is not accounted for in these tables.

CD, Chart Datum, (datum for sounding Top of skid beam Top of quay reduction Chartered HAT / LAT: The highest/lowest level clearance that can be expected to occur under HAT meteorological conditions MHWS MHWS / MHWN: The average of the MHWN two successive high waters when the MSL range of the tide is at its greatest/least. MLWN MLWS / MLWN: The average of the MLWS CD ~ HAT two successive low waters during those periods of 24 hours when the range of the tide is at its greatest/least. MSL: The average observed height of Chartered the surface of the sea relative to a depth stated vertical datum.

May 19, 2021 www.seacamel.com 22 Simple method to calculate the tide

Rule of twelfths During first hour after high water (HW) the water drops 1/12th of the full range. During the second hour an additional 2/12th. During the third hour an additional 3/12th. During the fourth hour an additional 3/12th. During the fifth hour an additional 2/12th. During the sixth hour an additional 1/12th. Hence, two hours after the HW the water has fallen 3/12 of the full range. Q: If is 2.8m, what is rising 4hrs after low water? æ 1 2 3 3 ö 9 A: ç + + + ÷ ´ 2.8 = 2.8 = 2.1m è 12 12 12 12 ø 12

May 19, 2021 www.seacamel.com 23 Weather restricted operations (DNV)

Marine operations may either be weather restricted or as unrestricted. A weather restricted operation shall be of limited duration defined as:

TR = TPOP + TC where:

TR = Operation reference period

TPOP = Planned Operation Period

TC = Estimated maximum contingency time (An applied contingency time (TC) less than 6 hours is normally not acceptable)

OPLIM Operational environmental limiting criteria.

OPWF Forecasted (monitored) operation criteria. A weather restricted planned operational period must be shorter than 72 hours. If an operation takes longer, one should plan for safe HOLD points May 19, 2021 www.seacamel.com 24 Weather restricted operations. The α-factor (DNV)

As a weather forecast for 72h from now is less reliable then a forecast 6h from now, DNV builds in a factor to account for the uncertainty. The . (Offshore Standard DNV-OS-H101)

The α-factor gives a relation between the forecasted wave and the design wave. (Other factors can be applied when for example a meteorologist is on side.)

Q: For a design wave of 2m and a Planned Operational Period, TPOP = 36 hours, and we estimate and we estimate 6 hours contingency. What is the required weather window?

A: The duration of the window, TR , would be TPOP + TC = 36 + 6 = 42 hours. The max forecasted wave height during this period should be OPWF =0.71 ´ 2.0 m = 1.42 m

Note: Another α-factor can be applied if a project dedicated meteorologist is on site.

May 19, 2021 www.seacamel.com 25 Tropical storm avoidance flow chart (float-over).

No Receive weather forecast showing Forecast light weather for up comings 2 within design days and restricted conditions for limits? the upcoming week. Yes Docking HTV Prepare for ballasting undocking Alignment

Ballasting to 20% load transfer Recondition Low pressure fills up Mating and there is no longer Fitting of SSFDR columns Yes equipment. a risk of tropical storm Receive tropical storm forecast showing Low pressure Yes No no tropical storm expected that may hit No develops to South Korea or low pressure areas that tropical storm may develop to a tropical storm with 2 Ballast to 90% load transfer HTV with HULL days. sails for open waters and return when tropical Wait and monitor No Forecast complies storm has passed. development of low Low pressure fills up Yes with above Ballast to 20 % pressure area and there is no longer load transfer Yes a risk of tropical storm No Plastic Melting Reverse mating No operation tropical storm Ballast to 100 % load transfer and forecasted undock HTV point of no return Yes Unmoor SSFDR Yes Funnel of HTV Low pressure formed that installed No Tow SSFDR to SHI quay Start Welding and may develop in 2 days to a Yes complete to 35% tropical storm that may hit No South Korea Sail HTV to quay Moor SSFDR to SHI quay and wait for tropical storm to pass Weather forecast No remains within design limits Sail for open waters and return when Moor HTV to quay and wait for End of mating tropical storm has passed. tropical storm to pass operation

Yes Ballast to 100 % load transfer and undock HTV

May 19, 2021 www.seacamel.com 26 OPLIM Operational environmental limiting criteria.

Limiting operational environmental criteria (OPLIM) shall be established and clearly described in the marine operation manual.

The OPLIM shall not be taken greater than the minimum of: a) The environmental design criteria. b) Maximum wind and waves for safe working- (e.g. at vessel deck) or transfer conditions for personnel. c) Equipment (e.g. ROV and cranes) specified weather restrictions. Limiting weather conditions of diving system (if any). d) Limiting conditions for position keeping systems. e) Any limitations identified, e.g. in HAZID/HAZOP, based on operational experience with involved vessel(s), equipment, etc. f) Limiting weather conditions for carrying out identified contingency plans.

May 19, 2021 www.seacamel.com 27 Water force (slamming, tide, current)

The density of water, 1000 kg/m3 for fresh water and 1025kg/m3 for , is much larger than of air (1,293 kg/m3). More than 800 times heavier. The force that water can develop on a body is therefore many times larger than of air. When these loads are applied abruptly, we call this loads “slamming loads”. In a river with a strong current, the forces on the side of a barge can quickly rise to significant values. W can also make use of the “water force. Think of: – For Roll-on / Roll-off (RoRo) operations we deliberately make use of the force of water (tide) – tidal conditions, where a barge with cargo can be beached at high tide and ballasted aground. At low tide it is fixed aground.

LAW OF ARCHIMEDES The buoyant force on a floating body is also Bridge of vessel equivalent in magnitude to the weight of the “MICHELANGELO” 1966 floating object and is opposite in direction; The force of water May 19, 2021 www.seacamel.com 28 Storm at Borgholm Dolphin, North Sea Jan 10, 2015

Are we too stringent with our safety factors?

Storm at Borgholm Dolphin, North Sea Jan 10, 2015.

May 19, 2021 www.seacamel.com 29 index

May 19, 2021 www.seacamel.com 30