Subject: SMML VOL 2739 Date: Sun, 30 Jan 2005 02:54:08 +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 VULKAN 2 Fore River Shipyard accident kills two 3 Re Salinity and buoyancy 4 Re Salinity & bouyancy ---------------------------------------------------------------------------- MODELLERS ---------------------------------------------------------------------------- 1) From "JB" Subject VULKAN Hello all, well it is the weekend again(here in the UK!)--thoughts turning to beer, pizza and modelshipping.. HMS FURIOUS's scars are healing well and idle thoughts peruse books for obscure ship inspiration..... I came across the following in a recent e-Bay book purchase... GERMAN WARSHIPS OF WW1( intro by Friedman) It is a CATAMARAN hulled salvage ship for Submarines called 'VULKAN' A genuine catamaran hulled salvage ship -the photos show a funnel on each hull with a massive gantry affair stradling the hulls. How cool a model would that be!!?? Has anyone any more photos/information/history/drawings/plans on this fascinating looking vessel? Googling in english and german brought scant refernces, mentions aplenty but no hard stuff! If ever I felt compelled to scractchbuild a ship this is the one! Have a GREAT MODELMAKING weekend! JIM BAUMANN ---------------------------------------------------------------------------- 2) From "Ouellette, Lawrence M" Subject Fore River Shipyard accident kills two Fore River Shipyard, Quincy, Massachusetts A portion of a partially demolished crane structure collapsed onto an adjacent building, killing two workers and injuring many others. http//www.patriotledger.com/articles/2005/01/28/news/news01.txt http//www.patriotledger.com/articles/2005/01/28/news/news02.txt http//www.patriotledger.com/articles/2005/01/28/news/news03.txt A photo gallery of the aftermath is available here http//www.southofboston.net/specialreports/ Click on the picture on the right side of the page for 26 more pictures. FYI, the building hit by the craneway is the old turret shop, and is on the opposite side of the shipyard from where the USS Salem is berthed. Larry Ouellette Volunteer, USS Salem (CA 139) United States Naval Shipbuilding Museum Quincy, Massachusetts, USA http//www.uss-salem.org/ ---------------------------------------------------------------------------- 3) From "Rick Nelson" Subject Re Salinity and buoyancy Gary hits on a problem the submarine community has to deal with constantly, depth control. However, the depth gauge (barometer) does not aggravate the problem. It all has to do with Hydrostatics. Barometers work on the principle of measuring force over a given area with the water at a given depth providing the force. With that said let's look at the forces involved in supporting the vessel and then forces involved with the barometer. First, buoyancy. Salinity affects buoyancy because it determines the density of the volume of water displaced by the vessel. Temperature will also affect density but to a much lesser degree. Pure water at 4 Degrees Centigrade is defined as having a Density of 1.0, a Volume of 1.0 relative, and a weight of 62.43 pounds per cu. ft.. (Lead has a density of 11.3 gm/cu cm) When the density of the water displaced equals the density of the vessel, the vessel is said to be at "neutral" buoyancy. When the density of the water displaced is greater than the density of the vessel, the vessel is said to be at "positive" buoyancy and it floats. And "lesser" produces a state of "negative" buoyancy and it sinks. According to Archimedes' principle "The fluid exerts on a body an upward force Fy, which is equal to the weight (mg) of the fluid originally occupying the boundary surface and whose line of action passes through the original center of gravity." In our case the boundary surface is the submarine's hull Volume (V). Fy = mg; (Fy)Force in the vertical axis equals (m)mass times (g)acceleration due to gravity m = dV; (m)mass = (d)density times (V)Volume w = dgV; (w)weight = (d)density times (g)gravity times (V)Volume This explains the principles by which a submarine surfaces and submerges. Assuming for the moment that the density (d) of the fluid (water) is constant, a submarine has the ability to change it's density by changing it's Volume. When a submarine is on the surface it's "boundary surface" V is at it's maximum because it's buoyancy tanks are dry. By being dry the submarine now has a much larger "boundary surface" V but it's weight (w) still remains the same. So if w = dgV is constant, and V increases, then d must decrease because g never changes. The submainres' density is less that that of the density of the water it is displacing by design. When a submarine wants to submerge it floods it's buoyancy tanks thus reducing it's "boundary surface" V but it's weight (w) still remains the same, therefore If w = dgV is still constant, and V decreases, then d must increase. Now the submarines density is greater than the density of the water it is displacing. The trick in submarining is to achieve "neutral" buoyancy by controlling the submarine's density when submerged to be equal to the density of the water it displaces (Archimedes' principle). This is accomplished by controlling the total Volume of the submarine. Besides the buoyancy tanks which are either dry or flooded, there are reserve tanks whose sea water content can be varied on demand. It is the combination of the buoyancy tanks and these reserve tanks that make up the Volume of the submarine that can be changed. Ultimately with the buoyancy tanks fully flooded and some controlled amount of seawater in the reserves tanks the submarines' Volume can be adjusted to where it's density is equal to the density of the water it has displaced and achieve "neutral" buoyancy. This principle applies regardless of depth. The submarine operators must keep their density equal to the density of the water they have displaced. Control surfaces like the fairwater planes and the stern planes are limited in the variations from "neutral" buoyancy that they can overcome. However, seawater density can vary. As can be seen by the above equation for Force, if density of the seawater increases (more salt) the Force Fy increases and the submarine takes on a "positive" buoyancy, etc, etc. The operators would then flood the reserve tanks to diminish the submarines' overall Volume more to compensate for the rise in density. But the ocean is for the most part fairly homogeneous with regard to its' density but variations will be found near large sources of fresh water like river estuaries, icebergs, and deep running currents. The biggest density variation is the submarine itself. Consumables are depleted, GDU (Garbage Disposal Unit) weights are used, fresh water is made and consumed, sanitary tanks fill and are emptied, etc. Now, measuring depth. A depth gauge works on the principle of a barometer, where it measures "absolute" pressure as compared to "gauge" pressure. The basic equation for pressure is P = F/A; (P)Pressure = (F)Force divided by (A)Area If F = mg and, since m = dV the, mg = dgV, and then P = (dgV)/A (Note Weight and Force are both equal to dgV) and if (V)Volume = (h)height times (A)Area, then P = (dghA)/A P = dgh, and therefore h = P/dg We can derive a similar equation from Pt = Pa + dgh; (P)Pressure-total equals (Pa)Pressure-atmospheric plus (d)density time (g)gravity times (h)height (of the water surface) Since it is the (h)height of the water above the submarine that we are interested in, transposing this equation gives h = (Pt - Pa)/dg; (h)height equals [(P)Pressure-total minus (Pa)Pressure Atmospheric] divided by (d)density times (g)gravity In both final equations we can see two things 1) that height (h) will vary directly with pressure (P) and 2) that height will change inversely to density (d). This is good and this is why barometers will measure both depth and altitude. In measuring the depth below the ocean the primary contributor in the equations is pressure (P) since water cannot be compressed and density variation is a secondary factor. However, in measuring altitude the primary contributor is air density (d) and pressure variation is a secondary factor. The equations also show that for the submarine if the water density gets greater (more Salty) the height (h) will decrease. This actually tracks with what the submarine itself is doing. As it travels into more dense water it will rise also. Sorry I got so long winded but it gets complicated. Rick Nelson "Damn the Pressure, Six-Zero feet!" "Boomers Hide With Pride" ---------------------------------------------------------------------------- 4) From Ives100@aol.com Subject Re Salinity & bouyancy >> What I can't be sure of in my own mind is what happens in a fully immersed vessel; in a sub they must flood to near neutral buoyancy and control depth with the planes. I am assuming that even in those conditions, the sub would reach a depth where the apparent density of the water matched the depth they thought they wanted. But I could be wrong. << More complicated than that for submarines. First, there is not a smooth gradient of salt water. There are definite changes in temperature and salinity that form layers. Second, as a submarine dives, the hull shrinks, changing the displacement. A submarine near neutral buoyancy at 200 ft that planes down to 600 ft would find itself "too heavy", as its volume had decreased. It is a very dynamic situation, and the diving officers use trim tanks to try to balance out the submarine as close to neutral buoyancy at an ordered depth, and also fore and aft balance, and then use the planes and dynamic forces to control depth. Modern US submarines no longer have the numerous "saddle" tanks used for ballast control and/or fule storage that the WWII Fleet submarines had. Also eliminated was the negative and safety tanks of the fleet boats. Tanks are now at the bow and stern only. Tom Dougherty ---------------------------------------------------------------------------- Check out the SMML site for the List Rules, Reviews, Articles, Backissues, Member's models & Reference Pictures at http//smmlonline.com ---------------------------------------------------------------------------- End of Volume