Home |
Search |
Today's Posts |
|
#1
|
|||
|
|||
To many pumps!!!
"Julian" wrote in message ...
SNIP There's no such thing as a new idea! I was considering a very similar mechanism of 2 sea chests and building in the facility to back-flush each sea chest if it became blocked. One thing that strikes me about the Fintry flushing arrangement however (if I have understood it correctly) is that, because it uses a seperate valve to inject water for clearing the seachest, it probably won't always clear a blockage in the mouth of the inlet valve (before the strainer) and might even make it worse. I was considering setting up each seachest with just one seacock leading to a strainer (like Fintry) but after the strainer then having a valve arrangement so that if the input becomes blocked the valves can be set to isolate the upstream water flow and allow water to be pumped out through the strainer and inlet to try to clear any obstruction that way. It seems to me that blasting water out through the inlet is the most effective way to clear any obstruction. Your concern is quite correct, but I think your solution just exchanges one problem for another. Your proposal tees the blast line to the inlet line outboard of the shutoff in the inlet. There is still a section of the inlet line between the tee and the inlet valve that can't be blasted. To some extent your concern is over an improbable event -- the grating in the hull plating has much smaller holes than the inlet line, so almost all of the time you'd be clearing either a plastic bag from the grating or mud from the chest. If I do it this way then I don't really see the need for a sea chest as such and the simpler "sea chest" of your earlier Swan 57 would seem sufficient, provided that the necessary calculations are done to ensure that the inlet size and placement is sufficient to provide adequate flow for everything manifolded off it. The advantage of the chest is that the first strainer is the small holes in the hull plating, so plastic bags don't get inside at all. SNIP That's a good idea. Actually, there is one other sea chest arrangement I have heard of that incorporates this, in a way it's like Fintry's seachest in that it's a foot share box welded (well, glassed, since it was fibreglass) to the hull, but instead of being 6 inches high like Fintry's, it was about 3 feet high so that it cleared the waterline, and the top was clear Lexan bolted on so that one could see any obstruction and unbolt an access panel to reach in (probably with a stick) to clear any obstruction. One drawback I see of a tall seachest like this is that it would compromise the effectiveness of using a back-blast of seawater from the other sea chest to clear an obstruction. Well, yes, you'd use the stick rather than blast. An advantage with this system is that you could use it as the manifold, putting a seacock on each pipe leading off it. While that means that you'd have to close all the seacocks to stop broken-hose-flooding, at least they'd all be in one maintainable and accessible place, rather than scattered around the boat. You've also got to find space for and construct a mission critical box three feet high. Using my philosophy of good engineering (carefully select everyone else's good ideas and blend them together to create the perfect result) my thinking right now is to fit 2 sea chests with each "sea chest" being in fact a simple large through-hull like your Swan 57, with your rather clever T arrangement and removable rodding-pipe as an emergency backup, but with appropriate valves upstream of the strainer to enable back-flushing through the inlet as the preferred method of clearing any blockage. If you have the space, looks good, although it violates KISS. I'd pick one or the other clearing method. I should add, that in our circumnav, roughly 33,000 miles, we never had an obstruction in the intake -- grass in the strainer that required cleaning eventually, yes, but a complete obstruction, no. Thus planning two different methods of clearing two intakes seems overkill to me. One further thing to consider. On Swee****er we located the graywater and blackwater discharges to port of the keel. (We used Lectra San, but a voyaging boat must be able to pump it overboard.) The one intake described above was to starboard. You don't want to be pumping your own waste back aboard -- there were places (Cairns, for example) where we were moored bow and stern in a reversing current, so half the time the current was moving from stern to bow. At least in places like that, I'd like the intake and discharges to be on oppostive sides of the boat. Jim Woodward www.mvfintry.com |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Mercruiser Power Steering Pumps?? | General | |||
Can a single 72 gal per hour fuel pump run two 392 cu inch motors? | General |