| 摘要 |
A tide ruler is disclosed for use with a tidal stream atlas. The ruler comprises, along its top and bottom edges, a series of hourly increments for a given estimated boat speed. The ruler can be overlayed onto the intended tidal stream atlas, and the width of the hour markers on the top and bottom edges of the tide ruler represent the distance travelled in an hour for the estimated boat speed. The passage of the boat may therefore be estimated on the tidal atlas for a given hour, and the rate and direction of a tide for that hour may be identified from the tidal atlas. The information may be used to calculate a true course to steer for the entire passage. The ruler may provide a means of identifying the rate and direction of tide for four different boat speeds (see figures 2 & 3). The ruler may also include, on a side edge, a means for verifying the device is of the correct scale to be used on a particular page of a tidal stream atlas (see figure 4). |
