Hi Robert

ROBERT M. Wrote:
-------------------------------------------------------
> When the boat launches torpedoes, the breech doors
> are wide open, allowing seawater to flood the tubes.
> The flooded seawater weighs more than the launched torpedo,
> correct?

Well, in case of german U-Boats, torpedoes were launched by
means of piston (to avoid air escape). So during whole launch
the space after torpedo was not filled with sea water. After
some while, torpedo room crew vented the tube, piston was back
and torpedo tube was filled with water. But for some time, the
torpedo tube was empty, filled only with air. That's why
the trim maintaining actions had to be taken.
As far as I know, on US subs, the whole procedure was automatic,
but german tubes (until type XXI) had to be manual serviced.

> So how does the u-boat broach? IMO, the boat was very
> light, out of trim well before the torpedo launches.
> And the CO could have slowed his advance during
> launches.

Well, it could be, but I think, that U-Boat was cruising slow
before launch - when taking periscope bearigns - to avoid
wake and perisope vibrations, so rapid change of speed
rahter did not occur.

> U.S. boats have a WRT (water round
> torpedo) tank to take care of this
> excess water, which allows them to reload the
> tubes. When the tube is ready to
> launch a torpedo, seawater is blown from the WRT
> tank to the torpedo tube, in order
> to equalize the tube with sea pressure so the
> outer doors can be opened. This is
> how trim is maintained during launches.

How torpedo tubes on US subs worked can be read here:
[www.maritime.org]
As I've writen before, the US tubes were far more
automatic, than german. The counterpart of WRT tank
was Torpedozelle (torpedo compensating tank). The operations
were almost the same, but initiated by crew, not by
automatic gears.

--
Regards
Maciek


[www.tvre.org]