hello everyone and welcome to nautical Academy in today's video I will show you how to determine the ship's under keal clearance also known as UKC let us start under Keel clearance or what we call UKC is the vertical distance between the vessel's Keel and the seabed in calculating the ship's UKC always follow the company policies and guidelines this is the form that I used in my previous company to determine the ships UKC I will use this procedure in today's video this procedure May differ if you are in a different company just check the company SMS or safety management system manual for the procedure and minimum UKC requirements to find the UKC we need the depth this refers to the depth of the water then the height of Tide the vessel's draft the ship squat swell and the category of zone of confidence or cat sock the company policy requires that the minimum UKC should be greater than 10% of the ship's draft throughout the transit let us deal with this one by one starting with the depth of the water the numbers that you can see in this chart represent the depth measurements that indicate the water depth in meters at specific locations for this specific location the depth of the water is 23 M here is 18.1 M and in this location the depth of the water is 12.3 M let us assume that you are making a passage plan and your ship will pass through TSS south of gser upon checking 12.3 M will be the lowest depth sounding that your ship will be passing through the entire Transit this is our recommended Lane because this Lane is a deep water route and intended for deep draft V vessel here it's stated that vessel with a draft of 16.50 M and greater are considered deep draft in some TSS with deep water route vessels with draft 15 M and greater will be considered deep draft vessel let us assume that our vessel has a lesser draft so this is the recommended Lane since 12.3 m is the lowest depth we will calculate our UKC using this depth the depth ings that you can see in the chart are based on the lowest astronomical tide or L A lowest astronomical tide refers to the lowest level that astronomical tides are predicted to reach under average meteorological conditions over an extended period it is essentially the lowest tide level that can be expected due to the gravitational influences it means that the 12.3 M depth sounding will increase due to high tide and it can be 13 M or 14 15 M or more depending on the height of the tide which can be found in the title tables for now we will leave this height of Tide blank we will see if the ship can pass a 12.3 M water depth without relying on the high tide to comply with the minimum UKC requirements let us proceed to the vessel's draft we have the different aspects of a ship's draft the static draft and the dynamic draft static draft refers to the draft of a ship when it is stationary at rest in the water or dead in the water Dynamic draft on the other hand takes into account the dynamic effects on the draft of a ship when it is in motion it includes factors such as the influence of waves ship speed Squat and the ship's response to sea conditions the draft that we will be using in this calculation is the static draft and we will take the ship's deepest draft let us assume that the ship's deepest static draft is 7.50 M the value of the ship's draft squat swell and zone of confidence will be subtracted from the depth of the water to find the ships UKC the only value that will be added from depth is the height of the Tide next we will proceed to the ship squat to determine the squat we can use a squat calculation table or software or we can calculate it manually in this video we will calculate the squat manually I have made a separate video on how to calculate the ship squat kindly check the link in the description the formula to calculate the ship squat is squat in open Waters is equal to the block coefficient times the squar of the ship speed relative to the water divided by 100 the answer will be in meters for confined Waters the formula is squat in confined Waters is equal to the the block coefficient time the squar of the ship speed relative to the water / 100 * 2 where CB is the ship's block coefficient v stands for the ship's speed relative to the water let us assume that the ship's trim is 1.0 M by the stern her speed is 11 knots and her block coefficient at a given draft is 0.845 let us solve this example using these formulas for Squat and open Waters it is equal to the block coefficient which is 0.845 0 * 11^ 2 which is the ship speed relative to the water divided by 100 the squat in open Waters is 1.02 M for the squat in confined Waters we will just multiply the squat in open Waters by two so we have 1.02 M * 2 the squat in confined Waters is 2.04 M since the ship is trimmed by the stern at her static draft the squat will take place on the AFT and there will be an increase in the ship's trim aft due to the squat an increase in the trim will be a decrease in the ship's under keal clearance that is why we will subtract the ship squat from the depth of the water since we will be passing shallow water we will take the value of squat in confined Waters so the ship squat is 2.04 M kindly check the link in the description on how to calculate the ship squat manually that video shows how to extract the value of the block coefficient at a given draft using a hydrostatic table next is the swell we can determine the value of the swell in that particular area through the weather forecast or weather routing let us assume that the information given from the weather routing in that particular area the swell is one 1 M so we will subtract 1 M from the depth of the water next is the category of zone of confidence known as katsock the zone of confidence is composed of six categories A1 A2 B C D and U with their corresponding symbols and the accuracy in position and depth starting with category A1 which is the most accurate down to category U which is unassessed I will not go deeper into the discussion of katsock let us focus on the depth accuracy since we are calculating the ship's UKC during our passage planning this is what you can see in the ectis monitor if we activate the zone of confidence in this ENC the symbols that look like an inverted triangle have six stars inside the category of zone of confidence is A1 in which the depth accuracy is equal to 0.50 m + 1% of the depth let us find the accuracy of 70 M depth sounding in this chart first we will determine the 1% of 70 M so 70 M * 01 is equal to 0.70 M then add 0.50 and 0.70 M the accuracy is 1.20 M this value is the zone of confidence margin this value will be subtracted from the depth to find the UKC if we subtract 1.20 M from 70 M depth sounding we will assume that the actual depth is 68.8 m not 70 M following the zone of confidence margin let us check another chart as you can see in this ENC we have different categories this area has only two stars so it belongs to category D here we have three stars this is category C and we have also category B with four four stars let us find the depth accuracy of this 38 M depth sounding in which the zone of confidence belongs to category C with only three stars to find the depth accuracy it is equal to 2.0 m + 5% of the depth we have 38 M * 5% is 1.9 m+ 2 m the margin is 3.9 M this is now the katsock value which will be subtracted to the depth to find the UKC if we subtract this from 38 M we will assume that the actual depth is 34.1 M instead of 38 M following the zone of confidence margin this is how we compute the depth accuracy using the cat sock in our etis in this chart in which our ship will pass a 12.3 M depth sounding let us assume that the zone of confidence is category A2 this may differ from the actual ENC you are using on board to calculate the depth accuracy first we will determine the 2% of 12.3 M so we will multiply it by 02 and that is equal to 0.25 M next we will add 1.0 M the accuracy is 1.25 M this is now the value of our cat sock which also be subtracted from the depth we will now subtract the vessel's draft squat swell and zone of Confidence from the depth of the water the ship's UKC when passing 12.3 M depth at a speed of 11 knots is 0.51 M to find the minimum UKC let us multiply the ship draft which is 7.50 M by 10% the minimum UKC should be greater than 0.75 m in this case we did not meet the minimum UKC requirement as stated in the company policy the big question is is there any way that we can still pass the intended traffic lane without using the traffic lane intended for deep draft vessels yes there are ways the primary option is to wait for the high tide check the height of the tide using your title tables you can use a hard copy or a digital form depending on the availability on board let us assume that the height of tide is 2.5 M during high tide by adding the height of Tide the ship's UKC now is 3.01 M which is four times greater than the required minimum UKC the next option is to reduce the ship speed by 1 half reducing the speed by 50% the ship sinkage due to squat is reduced by 1/4 or 25% the 25% of the ship squat which is 2.04 m is 0.51 M subtracting 0.51 m to the ship squat the remaining squat is 1.53 M by reducing the ship speed to 5.5 knots the new squat is 1.53 M and the ship's UKC is 1.02 m in this method we can still pass a 12.3 M depth sounding without waiting for the high tide and without violating the company policy for the minimum UKC requirements in this example we assume that the water density throughout the voyage is salt water if there is a change in water density when passing shallow water it should be considered in calculating the ship's UKC especially when passing from higher density to lower water density because the effect will be an increase in ship's draft due to sinkage if you are not familiar with this I made a separate video about the change in ship's draft due to a change in water density kindly check the link in the description 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