Posted by Ed Kiser on July 28, 2003 at 04:42:59 from 205.188.208.8 user Kisered.
In "We Didn't Mean To Go To Sea," the rising tide caused the
anchor to drag, and in fact as the Goblin shifted into the deeper
part of the channel, the anchor line hung vertically, with the
anchor dangling free of the bottom.
In properly anchoring a boat like this, there is the proper
procedure of paying out enough of the anchor line so that its
scope is around eight times the depth, thus permitting the
tugging on the anchor there on the bottom to be essentially a
horizontal force, thus permitting its flukes to properly dig in
and take hold.
The question I have is, there in the harbour of Lowestoft, just
how much depth does high tide add to the depth of its lowest
tidal point?
Let me make some guesses here, for the sake of helping the
description of the situation. Assume the Goblin at low tide on
the shelf was anchored in eight feet of water (pure guess). To
get a scope of proper length, considering the eight feet of
water, and about four feet from deck top to the surface (another
guess) means that the anchor, if hanging straight down, would be
twelve feet below the deck. Now, to allow for a proper scope of
eight times that, this would require ninety-six feet of anchor
line to be paid out before snubbing that line fast with the
anchor on the bottom, with the boat drifting backwards, laying
the line on the bottom for a part of its length. Now assume the
tide comes in and adds five feet to the depth (another wild
guess). This makes the depth from deck to bottom to be 17 feet
at high tide. It would seem, that with the original scope of
ninety-six being originally paid out, although a part of that
line that was originally lying on the bottom will now be lifted,
there is still enough line to allow the anchor to be pulled
horizontally.
In the story, we see that the anchor was dragging, indicating
that a good part of the direction of the force applied to the
anchor by its line was not horizontal, but was considerably
upward, thus causing it to lose its grab on the bottom.
It seems to me that one of two things must have occurred (or
perhaps a combination of both). Jim Brading, in spite of all of
his great reputation as a sailor, when he originally anchored the
boat, did not lay out a length of anchor line of sufficient
scope, even for the current depth of low tide. Or, the high tide
added considerably more to the depth than I have guessed at in my
example above.
The other difficulty the Goblin had was when the bitter end of
the anchor line was reached, it did not seem to be sufficiently
belayed to the ship, with the resultant loss of the anchor and
its line.
I realize of course that Jim's intention was to be away from his
ship for only a brief time, so he did not figure on much of a
tidal change to the depth during that time. However, I feel with
the insufficient scope of anchor line, and its lack of being
properly terminated firmly to the boat, puts the responsibility
squarely on Jim. With all the teaching that Jim gave to John,
and thank goodness he taught him as much as he did, the proper
anchoring of the Goblin was not a well taught lesson.
But then, if Jim had properly anchored his ship, we would not
have had that much of a story.
I still feel that of the twelve books, this one would make the
best movie, if you could get four youngsters with enough stomach
to handle it.
My own experience with anchoring a boat involves a ten foot flat
bottom aluminum jon boat, used for fishing, powered by a paddle
and electric trolling motor, in the Swamp called the Florida
Everglades whose max depth is about 6 feet (usually much
shallower) using an anchor that most people would call a cinder
block with a ten foot length of closeline attached to it,
belayed to a cleat on the gunwale. Maybe not very professional
or high-tech, but it seems to serve my purposes.
Ed Kiser, South Florida