Subject: SMML VOL 2741 Date: Tue, 01 Feb 2005 02:10:06 +1100 The Ship Modelling Mailing List (SMML) is proudly sponsored by SANDLE http//sandlehobbies.com For infomation on how to Post to SMML and Unsubscribe from SMML http//smmlonline.com/aboutsmml/rules.html ---------------------------------------------------------------------------- MODELLERS INDEX 1 Salinity and bouyancy 2 Re Salinity and bouyancy 3 Re Salinity and bouyancy 4 Recommended Airbrushes? ---------------------------------------------------------------------------- MODELLERS ---------------------------------------------------------------------------- 1) From KELVIN MOK Subject Salinity and bouyancy > From "Rick Nelson" >> Hull compression is a very demonstrable phenomena ............effect on the Volumetric change of the sub. << Thanks for the great stuff on submarine bouyancy. There is one argument I miss though. Air is higly compressible and therefore has a much smaller volume at depth than at the surface. Thus when diving wouldn't the rate of dive increase with depth as the voulme of air gets smaller and therefore the sub's bouyancy decreases? Ergo there will be a need to top up air to the dive tanks to control the rate of dive. Likewise when rising from the depths the air would expand and increase the sub's bouyancy. Wouldn't there be a necessity to vent the air to control the rate of rise? ---------------------------------------------------------------------------- 2) From Kdg345@aol.com Subject Re Salinity and bouyancy I understand the discussions on salinity etc. but, I would like to hear more on how it relates to the Plimsol marks on a ship. I would like to add Plimsol marks on my model of an AKA. I am pretty sure the Plimsol marks show the extremes of ship loading requirements but, what salinity and temperatures define these marks? Ken Groom ---------------------------------------------------------------------------- 3) From Reynold.Oh@defence.gov.au Subject Re Salinity and bouyancy Hi SMMLies, 1. Apologies for initiating the highly-technical discussion(s) on the salinity of seawater and diving submarines. 2. SALINITY. Fresh water floats on top of sea water. Salty water floats on top of saltier water. I saw in a Discovery Chanel program, that a bathysphere (really deep-diving submarine) discovered pools of brine (really salty water) on a rocky sea floor. The old Time/Life book on "The Sea" contained a diagram that claimed that U-Boats exploited the difference in salinity between the Mediterranean Sea and the Atlantic Ocean. The Med seawater was/is saltier (= denser) than the Atlantic's. Why? Because it is a (relatively) large, warm, shallow body of water, so it looses a lot of water (as pure freshwater) into the sky by evaporation, leaving the salt behind. So, in the Straits of Gibraltar (between the Pillars of Hercules) there was/is a surface current that flowed into the Med., while at the same time, there was/is a deep under-current of saltier water that flowed out of the Med. Apparently (& I can't confirm this) U-Boats would exploit these currents to quietly enter (or leave) the Med. Nor can I confirm if the submarines of other nationalities used the same idea. 3. TEMPERATURE. All oceanographers (& submariners) know that the surface water of the sea is warm when compared with the deeper water (which is quite cold), and that the demarcation between the two temperature layers is quite marked - as marked as the difference between a thick layer of mist on the sea, and the seawater itself. This demarcation is known as the THERMOCLINE. The depth of the thermocline varies from 150mr - 600mr. Modern submarine skippers know that the thermocline will reflect a lot of sound. Sound from above (eg, searchers SONAR) is reflected back up, and sound from below (eg, fast submarine noise) is reflected back down. So they can hide under the thermocline. But it also prevents them from listening to activity above it, so they must raise their submarine (slowly) above the thermocline, do a quick listen, then duck back under it (again, slowly). Why slowly? If they did it at speed, the submarine would be deafened by its own noise, and sub-hunters would hear them anyway. Ducking under the thermocline (then doing a sharp turn) is a good submariners tactic used immediately after launching torpedoes &/or missiles. The sub-hunters counter is to send a listening device (sonar-bouy or helicopter-mounted dipping sonar) below the thermocline. With sonabouys, you can place some above AND below the thermocline in the same drop. And this is why submaine skippers, & hunters, know that their trade is a big deadly cat-and-mouse game. 4. I believe that sounds produced in the water, above the thermocline (eg, ships propellers or a submarine) can also be reflected down by the surface of the sea. So sounds can travel by zig-zagging along between the two layers - like a ball travelling down a hallway by bouncing off each wall in turn. This creates zones far around the noisy item where it can be heard. George, out. TX ends......................... ---------------------------------------------------------------------------- 4) From "Andy Airlie" Subject Recommended Airbrushes? Hello all, Does anyone have recommendations on airbrushes primarily suitable for sparaying fine detail? I use a Tamiya Sprayworks purely for large area coverage and manual brushing for detail/camo schemes. I'm looking to find a suitable airbrush to speed up this process for 1/700 scale ships and I'm sure the vast array of talent among the group has tried most of them and can recommend some ! Best wishes, Andy Airlie ---------------------------------------------------------------------------- Check out the SMML site for the List Rules, Reviews, Articles, Backissues, Member's models & Reference Pictures at http//smmlonline.com ---------------------------------------------------------------------------- End of Volume