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    Re: Traverse boards
    From: George Huxtable
    Date: 1998 Oct 31, 18:42 EST

            I am glad that Rick Emerson has drawn attention to traverse boards,
    which were used by watchkeepers for hundreds of years to record course and
    distance travelled in each of the eight half-hour periods between bells in
    a four-hour watch. Their main virtue was that they could be used by men who
    were quite illiterate, as most seafarers were.
            First, I feel the need to question a part of Rick's mailing, which
    I do not understand. He describes well the compass-rose section of a
    traverse board as follows-
    >The compass rose follows this concept albeit with a different layout.
    >Here the arrows of a 16 or 32 point compass are carved into the
    >board.  On each arrow, a row of 8 holes is drilled in a line (forget a
    >drawing of that here!) so as to make 8 concentric rings of 16 or 32
    >holes each.
            This is fine. But then he goes on to state-
    >To make a record of the boat's heading, the
    >whole board is turned so that the arrow for due north matches the
    >north arrow on the boat's compass and a peg is set into a hole on the
    >arrow closest to the boat's heading.  For example, if the boat is
    >sailing due west, looking down on the compass, north is at the 3
    >o'clock position and the row of holes for west lies at 12 o'clock.
            This seems over-complicated, and indeed wrong. Surely, it's all a
    lot simpler; you simply put a peg into one of the radial holes on the
    board's compass rose that corresponds to your present compass course as
    shown on the steering compass. No need to lay the traverse board down
    horizontally and align it with the North. It can simply be left hanging,
    near the compass, from a hook, for which a hole is provided at the top of
    the board..
            Having got that over with, I can now come to the question that
    really interests me, about how various traverse boards were used in
    practice. In all traverse boards that I have seen, or have seen pictured,
    the compass-rose section follows Rick's description precisely. However,
    there's great variety in the rectangular section below the compass rose,
    which was used to record speeds. One might expect the number of columns of
    holes for speed to vary, for traverse boards used with different vessels in
    different trades, because there's no reason to provide more holes than the
    maximum speed the vessel is capable of. But there seems more to it than
    that...
            Eve Taylor's "The Haven-Finding Art" (1971), plate XII,  and Peter
    Kemp's "Oxford Companion to Ships and the Sea" (1976), (entry for "traverse
    board") both reproduce the same picture of a sixteenth-century traverse
    board found in the Hebridean island of Barra in 1844. The rectangular
    section of this board is indeed rather similar to the one described by
    Rick, with four rows of holes. The numbering is by no means clear in the
    illustration, but instead of the two blocks of 7 columns as Rick describes,
    it appears to show on the left a block of holes marked 1 to 8, on the right
    a block marked 1 to 9. Between them are two additional columns, each with
    four holes, which might perhaps be marked "1/4" and "1/2" (the clarity is
    poor). The compass-card uses a letter "O" to mark its Eastern point, so the
    board is presumably not of British origin.
            Next, I have a post-card from the Netherlands Historic Maritime
    Museum in Amsterdam, of a traverse board in their collection. The compass
    rose section shows the usual arrangement of radial lines, each with eight
    radiating peg-holes, just as Rick describes. The rectangular speed section,
    however, is rather different. To the left is a block of 12 columns of
    peg-holes, in four rows. These columns are marked 1 to 12. To the right is
    a block of 6 columns of holes, and these columns are not marked at all.
    Again, these holes are in four rows, and the rows are marked "1/4", "1/2",
    "3/4", and "1". Presumably, then, this is intended to be used for vessels
    which can reach 12, or perhaps 13, knots.
            J.E.D.Williams, in "From Sails to Satellites" (1992), on page 31,
    shows another traverse board, described as "c.1800, German or
    Scandinavian". Again the upper part shows 32 radial directions, each with 8
    radiating holes; the standard layout. The rectangular section underneath
    shows 4 rows of holes, in 15 columns, the columns being marked 1 to 12,
    then "1/4", "1/2" "3/4".
            It's apparent that one can record a precise speed, by pegging
    together an integer speed plus one or more fractions, using multiple pegs
    strung together.
            At last we come to my problem, that of trying to understand just
    how a traverse board was used. In a watch, there will be 8 directions and 8
    speeds to be pegged out. For each of the half-hour periods, it's necessary
    to associate together the course for that period and the speed for that
    same period, in order to get the correct vector sum over the whole watch.
    Rick has described a procedure in which the eight directions could be
    pegged out in a defined order, moving successively out from the inner ring,
    and the speeds could be recorded in a similar way,in a defined sequence of
    8 places on the board, from the start of the watch to the end. That can be
    done if there is a set of eight such positions for each speed, as there is
    for the board Rick describes.
            However, in the case of the other traverse boards I have referred
    to above, there can be 8 entries for each of the directions, but for some,
    or all, of the speed values there are less than 8, commonly 4, peg
    positions available. Of course, it's unlikely that in all the 8 half-hour
    periods in a watch, the speed will be exactly the same, but that's not the
    point. The point is, how do you associate each of the 8 measured courses,
    individually, with its corresponding speed, of the 8 measured speeds, when
    you have only 4 holes for each speed?
            Perhaps the string or strings have a more important function than
    Rick describes ("so the pegs wouldn't get lost"). One way of linking
    together a course, for a particular half-hour period, with the speed for
    that same period would be to arrange that each peg marking the course is
    linked by a string to the peg or pegs marking the speed. However, in most
    of the traverse boards I have seen, or seen pictured, this doesn't seem
    possible, as they have two separate bundles of 8 strings, with pegs. One
    bundle emerges from the centre of the compass rose, presumably for marking
    the directions. The other bundle of strings and pegs pops out from just
    above, or within, the rectangular section devoted to recording the speeds.
    The two bundles are quite separate.
            The board shown in Williams' book is strung quite differently, and
    gives a clue to another possible method of use. In this case, a single
    string emerges from the centre of the board's compass rose, carrying 8 pegs
    strung in sequence, and two other strings emerge from the zone for
    recording speed, each carrying four pegs, strung in a similar way. This
    would allow pegs to be chosen in order of their sequence along the string
    from one end, and pegged into the compass rose according to the course for
    each half-hour. Similarly, integer speeds in knots could be recorded in
    order using pegs from another string, and fractional knots, in the same
    way, from a third string. This scheme would allow speeds to be recorded at
    less frequent intervals (say four speeds, at one-hour intervals) than the
    half-hourly recording of course, but still allow the sequencing of these
    measurements to be preserved.
            Perhaps there have been changes in the method of use of a traverse
    board, reflecting changes in the measurement of ship's speed. Until the
    sixteenth century, speed was estimated largely by guesswork of the
    watchkeeper. Guessing, though inaccurate, was quick and easy, so it could
    be done often, once every half-hour perhaps, when the course was pegged.
    When the log, line, and glass were gradually introduced for measuring
    speed, this operation, though much more accurate, became more of a palaver,
    involving at least two of the hands, and presumably was carried out less
    often. Lecky's "Wrinkles ..." (1917 edn) states that the interval between
    streamings of the log was usually two hours, which implies that there would
    be only two recordings of the speed in each watch.
            I suppose that the strings which linked the pegs are the parts of
    the board system most vulnerable to decay, and conceivably the pegs may
    have been restrung in a museum conservation process, in each case. If so,
    are the reconstructions incorrect, perhaps? Any suggestions, from those who
    know more about the history of navigational instruments than I do?
            George Huxtable
    ------------------------------
    george{at}XXX.XXX
    George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    Tel, or fax, to 01865 820222 or (int.) +44 1865 820222.
    ------------------------------
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