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This is in response to an e-mail from Julian. The return address on
his e-mail is , hence the reply here. ----- Original Message ----- From: "Julian" To: Sent: Thursday, August 14, 2003 10:08 AM Subject: Fintry's sea chests Jim, I've been mulling over the merits of sea chests recently. Could you please tell me a little more about Fintry's sea chests. In particular, where are the openings in the hull, how large are the openings, and is there any clever shaping to the hull openings to minimise drag and/or increase water flow into them? I'm also interested to hear about any other aspects of the sea chest arangement that you think might be of interest. I think my design philosophy probably exhibits much of the "conservatism of the Royal Navy" so I'd love to know in more detail what they did. Thanks in advance, Julian Julian: If you go to our web site, you'll find a piping diagram: http://www.mvfintry.com/pix/piping800.png and lines drawing: http://www.mvfintry.com/pix/flines800.png If you're interested, I can send you bigger versions (ie, more legible) of either -- just say how big is OK. The originals are in AutoCAD, if any of those formats are helpful. The sea chests are at frame 8 and 17 (of 45 total, 20" spacing), so they are well aft of midships, but they are also well down under the hull, where there is little deadrise. This is a disadvantage when she is in very shallow water or sitting in a mud berth. Her sister, Amazon Hope (see link on site), which is way up the Amazon in Peru, has recently been modified to avoid this problem. (The drawings at the bottom of http://www.mvfintry.com/details.htm all show frame locations). The chests are just steel boxes welded to the inside of the hull, with grating holes in the hull plating -- no special shaping at all. They're maybe a foot square and 6" high and have two valves mounted on the top for seawater intake and weed clearance (if you look at the piping layout, valves M19, M20, and M21 allow you to inject pressure seawater into a seachest with the intake valve closed to blast away anything that might clog the chest. Obviously, this trick works only if you have more than one seachest.) On the intake side, there's a large (although not particularly fine) strainer with a valve on either side to isolate it for cleaning. All the piping is galvanized steel, which requires attention from time to time, but has the advantage that it won't burn and sink the boat in case of an engine room fire. The fundamental advantage of a sea chest system is minimum holes in the hull. On a smaller scale than Fintry, when we bought our Swan 57, Swee****er, she had ten seawater intakes (engine, genset, refrigeration, 3 air conditioners, 2 heads, washdown, watermaker) and ten intake seacocks. If you started flooding, you'd have to close ten seacocks, several of which were very difficult to reach, in order to eliminate a bad hose as the cause of the flooding. As part of the preparation for our circumnav, we put in one 2" seacock, and manifolded everything to it. On top of the seacock was a tee, with the manifold connected to the side and a pipe plug in the top (think of the tee on its side with the straight through part vertical). By closing the sea cock, removing the pipe plug, screwing in a three foot length of pipe (long enough to be above waterline), and opening the seacock, we could push a rod down through the pipe, the tee, the seacock, and the hull and clean the intake. All of this requires some care to get it big enough and to make sure that centrifugal pumps have a steady upward path so that air will move up and out even if the pump loses its prime. On Fintry that's easy -- the engine room is twenty feet square and nine feet high and things like air con that use centrifugal pumps can be racked well above the seachest. On Swee****er, it was much harder, as everything was fitted into fairly small spaces. You'd like the intake to be in a high pressure area on the hull (see your naval architect) and I'd probably put a clamshell aft of it to help things along unless I were racing. The clamshell should be clear of the rod-through-the-hull trick if you use it. Jim Woodward www.mvfintry.com |
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