Sweet lordy-lord it’s Science of Diving (SoD) o’clock again!
The way I like to teach the SoD is taking all the technical information given by the manual & putting into practical application. We can use all the equations we want with all the measurements of depth, weight & volume given to us but sometimes we have to take into other factors, like the environment.
A question appears in the SoD final exam which reflects this thinking by suggesting the candidates have to “give it a go” when lifting an object from the bottom. The example I always use is bottom composition taken from the SSI Search & Recovery Specialty course.
If we have an object with the volume of 30 litres, weighing 70 Kgs & lying in 30 metres of sea water, we have information to theoretically calculate how much lift we require to surface the object. This helps with the practical application of lifting the object but doesn’t take into account other “real” factors; how is the object lying? What is the actual shape of the object? What are the water movement conditions? How long has the object been there? What type of bottom composition has the object been lying in?
So the subject of today’s Science-ame Street is the Mud Suction Factor (MSF). If the aforementioned object is sitting on a hard, rocky bottom with minimal water movement for a short amount of time it’s going to be an awful lot easier to lift than if it’s been lying in mud & heavy swell for a long period of time.
These factors have to be taken into account when lifting object & when we’re teaching our Divemaster, DiveCons or Search & Recovery students & Instructor candidates that sometimes they have to “suck it & see!”