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From: Mike Brasler (no email)
Date: Thu Jun 09 2005 - 04:19:30 EDT
Agree with you completely, Jeff!
I think that statistically most sinkings occur from a failure of a thru-hull
or pre-existing hull penetration than all other types of sinking.
These minimum standards already exist well defined in various maritime
standards authorities, Lloyds springs to mind already, so when one claims a
build according to Lloyds 100/A1 etc. then all the design details
automatically follow.
An example of one of these details is "Where cockpit drains pass through an
engine or machinery space, shuch drains shall be constructed of a material
that will remain rigid to 12" above waterline during and after a fully
destructive fire"
Now most rubber hoses will not burn where they are full of water, but if
they burn off above the water level, will they remain vertical, or flop over
and sink the boat? Suppose you could call it an automatic extinguisher.
Hell ours are steel all the way up to the cockpit floor.
IN our case we have a sea chest, and although individual takeoffs can be
isolated from the seachest, the whole shooting match can be shut with the 4"
ballvalve. There is a tapering 4" wooden bung nearby in case the whole
seachest breaks off, unlikely seeing that its scedule 180 316 stainless
tube.
The sea chest has an integral strainer with about 5 sq feet of filtration
area. The Thru hulls remaining, ie discharges, are all led to deck level
with vented loops before exiting.
All the hull perforations are led through "thickeners" where a 3/4" thick
flange is welded to the hull, then the hole is bored, and a tube end-welded
inside the bored hole. A ballvalve is bolted into the flanges utilising 4 of
the 8 threaded holes in the flange. The unused threads are filled with a
lanolin smeared nylon stud, so that if a bolt shears or strips, a 45 degree
rotation of the valve body will line up 4 new holes.
Now if all that sounds unusual for a yacht, it should not, it is perfecly
normal and, the de-facto standard in shipbuilding.
I have always wondered why the yachting industry is so different from the
shipbuilding industry???
OK mainy because of materials, SO when a steel yacht is built, why
construct it any differently from a ship. The design is important, our boat
is designed by Van de Stadt of Holland, and I have struggled to fault it. It
seems that safety was the highest priority, however, we have seen the same
boat, contructed in a backyard, and that vessel had bronze thru-hull skin
fittings with plastic hoses and gate valves. A recipe for disaster.
I too could not sleep on a boat where your flotation is dependant on hose
clamps and valves that were hidden or inaccessible.
Regards
Laura, Mike and Liz
http://www.seakin.com/gilana/default.htm
>From: "Jeff Smith" <>
>To:
>Subject: lv-ab: Thru hulls
>Date: Thu, 09 Jun 2005 00:53:49 +0000
>
>
>I have a fairly large sailboat I think. Two staterooms with queen beds,
>plus a large double and dining for 6.
>
>A great deal of thought was put into keeping her seaworthy, and two of the
>more obvious (to me at least) elements were:
>
>1) Keep the number of UNDERWATE HOLES in the boat to a minimum. Hence we
>have just just four. Strategically located to serve multiple purposes.
>
>2) Make damned sure that any HOLES in the boat that are underwater are
>REALLY easily accessible. That means, without tools and in a location where
>they can be felt for underwater should the need arise.
>
>I could never sleep on a boat whose thru hulls required tools to access, or
>where so numerous as to render figuring out which one to shut in an
>emergency (i.e sinking!) a crap shoot.
>
>Example: Somone I know well installed a watermaker. The intake thru hull
>was up near the bow. The water maker about 25 feet away from that thru
>hull. About 50 miles out to sea, in pounding waves the bilge pump alarm
>sounded. A fitting or hose (forget which now) near to the watermaker had
>failed. He rushed below and seeing substantial amount of water coming in,
>proceeded to shut the thru hulls in the vicinity of the watermaker. He had
>17 thru hulls, and managed to close 8 as the water continued to rise. It
>~finally~ occured to him that it might be the watermaker. He tore the
>forward cabin apart and ripped the plywood under the bed up by prying with
>a screwdriver in order to access the thru hull and shut it. No time was
>wasted undoing the four or six philips screws that held the panel in place.
>All this while being tossed about down below in the waves and heeling in
>the wind.
>
>By the time the leak was stopped, he had nearly a foot of water OVER the
>floorboards.
>
>His thru hulls were too numerous, and they were located badly, requiring
>tools to access some of them.
>
>I did not make the same mistake.
>
>Just my opinion. To each his/her own I suppose.
>
>Jeff
>
>
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