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

Jim Woodward wrote:

.... in my defense I will point out that the Air Con pump is
almost certainly centrifugal (and, hence, non-PD) while the washdown
could be either, so my suggestion is OK.

Righto



Of course, in your praise of non-PD pumps, you don't mention that they
are unholy nuisances, prone to lose their prime at the slightest
provocation --

The times I've had this problem, it was tracable to a problem(s) with the system.
It's not inherently the nature of centrifugal pumps. However a lot of pumps suffer
from excessive casing clearance either due to wear or cheap manufacture; bad
suction piping runs or sharing a suction with another system & thus having to fight
for prime or being installed above the waterline or having air leaks in the suction
(choose one or all the above).

Having just repiped & remounted two pumps on our boat, and seen a lot of crummy
installations on OPBs lately, it seems like an epidemic. But industry and the
military don't have these problems often (and they pay more, too, hard as that is
to believe).


Jim Woodward wrote:

This is in response to an e-mail from Julian. The return address on

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

Thanks very much for your second post & links. I am considering installing sea
chests on our boat and this is very thought-provoking, useful material.

Fresh Breezes- Doug King

Julian:

Since I couldn't reply to your e-mail, I posted a response to this in
the original thread, "To Many Pumps"...

Jim

"Julian" wrote in message ...
"Jim Woodward" wrote in message m...
SNIP (Or why Fintry has
pressurized seawater available in volume from any of three sea chests
-- I love the conservatism of the Royal Navy, but that's another
story).
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.

Jim Woodward wrote:


Take a look at http://www.mvfintry.com/pix/manifoldbilges800.jpg
Every piece of pipe you see was custom welded and then galvanized
after welding. It won't burn, won't burst, and won't have hose clamp
failure.

DUDE! Galvanized? I'm impressed. You obviously spent a lot of time & money working out a good
engineering plant, did anybody suggest seamless SS piping just for laughs?


It will eventually rust through, but yearly inspections deal
with this -- rusting is obvious and slow. (We will, however, replace
most of it outside of the engine room with schedule 80 PVC).

Probably a smart move, although I've seen vibration cause trouble with PVC longevity, outside the
engineroom it shouldn't be an issue.



Whenever you get the chance, go aboard government and industrial boats
and make notes -- you'll learn a lot about really designing for
reliability and maintainability.

Thanks, that's where I cut my chops starting an embarassingly long time ago.


A trip to the Work Boat show in New
Orleans (early December) can be eye-opening for someone whose only
boating is on yachts.

Thanks for the tip, I have some friends in N'awlins we love to visit.

Fresh Breezes- Doug King

"Jim Woodward" wrote in message om...
This is in response to an e-mail from Julian. The return address on
his e-mail is , hence the reply here.


Jim,

Thanks so much for taking the time to explain both Fintry's and
your earlier Swan 57 sea chest set ups, and sorry about the email
address, I forgot that I'd recently changed it on my newsreader.
I have a few comments regarding your email below...

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 stuff on your website is perfectly legible thanks.


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.)

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.

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.


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.

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.

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.

Does anyone see any significant problem or improvement for the above?

- Julian

Just so there's no mistake here -- the galvanizing, etc. was done by
the builders to the Royal Navy spec thirty years ago. We're just
working within the framework (or should I say "maze" or maybe "rat's
nest") that we inherited. See the web site for more details.

You mentioned stainless -- do you have any thoughts about it? My
general feeling is "worried" when I think about stainless and hot
running salt water, or even cold stagnant salt water. I suspect that
the galvanized mild steel will last longer and fail more slowly (it
begins to weep), but I'm not a metallurgist.....

And, yes, PVC, even Scd 80, has its problems. We'll use it only for
bilge and freshwater suctions, not seawater, and not in the engine
room.

Jim Woodward
www.mvfintry.com

DSK wrote in message ...
Jim Woodward wrote:


Take a look at http://www.mvfintry.com/pix/manifoldbilges800.jpg
Every piece of pipe you see was custom welded and then galvanized
after welding. It won't burn, won't burst, and won't have hose clamp
failure.

DUDE! Galvanized? I'm impressed. You obviously spent a lot of time & money working out a good
engineering plant, did anybody suggest seamless SS piping just for laughs?


It will eventually rust through, but yearly inspections deal
with this -- rusting is obvious and slow. (We will, however, replace
most of it outside of the engine room with schedule 80 PVC).

Probably a smart move, although I've seen vibration cause trouble with PVC longevity, outside the
engineroom it shouldn't be an issue.



Whenever you get the chance, go aboard government and industrial boats
and make notes -- you'll learn a lot about really designing for
reliability and maintainability.

Thanks, that's where I cut my chops starting an embarassingly long time ago.


A trip to the Work Boat show in New
Orleans (early December) can be eye-opening for someone whose only
boating is on yachts.

Thanks for the tip, I have some friends in N'awlins we love to visit.

Fresh Breezes- Doug King

"Jim Woodward" wrote in message om...
SNIP
You mentioned stainless -- do you have any thoughts about it? My
general feeling is "worried" when I think about stainless and hot
running salt water, or even cold stagnant salt water. I suspect that
the galvanized mild steel will last longer and fail more slowly (it
begins to weep), but I'm not a metallurgist.....

Do you ever visit www.metalboatsociety.com? They have a set of
discussion forums and, since the emphasis is on metal, tend to discuss
such issues. In case you've not visited, it isn't at all obvious (at least
to me) as to how to go to the discussion forums. The way I get there
is to click on the "Search" link on the homepage and then click on
the "Metal Boat Society Forum Index" to get to the forum index.

- Julian.

"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

Jim Woodward wrote:

Just so there's no mistake here -- the galvanizing, etc. was done by
the builders to the Royal Navy spec thirty years ago. We're just
working within the framework (or should I say "maze" or maybe "rat's
nest") that we inherited.

It's kinda fun though. Isn't it amazing how you start out with a huge amount of space for absolutely
everything, and then you find that "everything" takes up more space than you thought? Having all valves
labelled is crucial.


See the web site for more details.

It's a great web site but many of the pictures have 'google' stamps instead of a picture.




You mentioned stainless -- do you have any thoughts about it?

Yep, it's way too friggin expensive and the electroformed pipe (rolled & welded instead of seamless) is
almost always fails along the joint. IMHO galvanised mild or hi-carbon steel is much better even if
neglected.



My
general feeling is "worried" when I think about stainless and hot
running salt water, or even cold stagnant salt water. I suspect that
the galvanized mild steel will last longer and fail more slowly (it
begins to weep), but I'm not a metallurgist.....

Also, you can spray on that "cold galvanise" rust inhibitor and do pretty well. Usually corrosion is
worst along joints & flanges. For places where you really want minimum corrosion and have money to
burn, monel is the way to go.

The boat looks really great, it's a huge project and the vessel has marvelous possibilities. We are
finding our 36 footer to be plenty enough work, though!

Fresh Breezes- Doug King