[PSUBS-MAILIST] G.L. Summary Stability & Buoyancy

[Phil Nuytten]

The minimum hatch to waterline measure applies to those submersibles ‘intended to be entered while afloat’ - 
Phil

From: Jon Wallace 
Sent: Thursday, December 05, 2013 7:33 AM
To: Personal Submersibles General Discussion 
Subject: Re: [PSUBS-MAILIST] G.L. Summary Stability & Buoyancy


I think the first sentence is key, "Submersibles will be assigned Class only after it has been demonstrated that their buoyancy and their static and dynamic stability in in tact condition is adequate FOR THE SERVICE INTENDED".  Some of the lack of specificity is because they can't conceive of every possible application.  They do however have quite a few specifics as you outlined.  Some of the testing won't apply (ie fuel load) and it's possible that a narrow scope of service might lower number of tests required.


On 12/5/2013 4:08 AM, Alan James wrote:


  I'm afraid there is nothing simple in this section. It is lacking in a lot of specifics.
  There are statements such as "shall generally meet the standard defined
  in the following unless special operational restrictions reflected in the class
  notification allow a lower level. & ...Depending on the type of submersible & the 
  operation area, the distance between the waterline in fully surfaced condition
  and the upper edge of entrance openings, air pipes,etc. which may be open
  for surfaced operation, has to be approved by G.L.
     ABS has a minimum distance from the waterline to the hatch opening of 30"
  whereas G.L. states; For surfaced; a minimum distance between metacentric height & center of gravity of 10cm. (4") And for submerged, a minimum distance between center of buoyancy & center of gravity of 5cm (2") (same as ABS). At no stage will G be above B. (including after dropping the drop weight)
  In the initial paper work sent before construction, a detailed analyses of stability is to
  be included.  This takes the form of analyzing the heeling levers of 10 different load cases in fresh & salt water, 6 on the surface & 4 submerged & at 6 different heeling
  angles. So looks like 120 calculations. Heeling forces from free liquid surfaces, turning circles, wind, ice loads, transference of equipment & personal & payloads from working devices have to be considered.
  There needs to be sufficient ballast to keep a minimum of 10% of the pressure
  hull out of the water. The draught line has to be marked on the hull. 
  When one major ballast tank is damaged the hatch has to be able to open without
  water coming in & the heeling angle shouldn't exceed 22,5 degrees.
  There is an operational in water test at the end of construction with evaluation
  of the center of gravity upon which the pre build calculations were based.
  Alan












   

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