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