Here is a little info from the Submarine Torpedo Fire Control Manual about how to figure out the correct height to measure with the stadimeter (or in this case the graticule's)
Basicaly count the number of decks and multiply them with 8 ft. (or 2.5 meters) then measure the same decks with the graticule's you know have an estimated height of the decks and a graticule count and can then calculate the distance the usual way. Say there are 3 visible decks above the deck you then measure with the graticule from deck to the top of the 3rd deck.
Estimated real height is 3x2.5 meters
Graticules says fx. 50 (in x6 zoom)
range is then :
7.5M x 1000 / 50 * 4
= 1500 meters
The method can also be used to "check" a stadimeter reading of range for gross errors.
Quote:
(g) When radar ranges cannot be obtained the Approach Officer must rely upon his ability to correctly estimate the height of the funnel or masthead, or other prominent mark on the ship's structure above the water line. If the target ship can be properly identified an accurate value may be obtained from intelligence information supplied the ship. If this is not available the
following procedure will he of assistance:
(1) Count or estimate the number of decks that are seen above the main deck.
(2) Add to this figure the approximate number of deck heights equal to the observed freeboard.
(3) Multiply the total by eight to determine the height of the top of the bridge structure above the visible waterline.
(4) Using height of bridge structure above the visible waterline as a yardstick, approximate the masthead height. The masthead heights of merchant ships are on the average about 2.1 times the bridge height (above waterline). A masthead height which appears to be shorter than normal will be about 1.7 to 1.8 times the bridge height, while one which appears to be higher than normal is approximately 2.2 to 23 times the bridge height.
(5) Funnel heights may be estimated by approximating the number of deck heights of the funnel which is seen above the top of the bridge structure and adding this height to the bridge structure height.
(6) At extreme ranges it must be remembered that the waterline is below the horizon. This necessitates estimating the position of the waterline.
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Quote:
(h) The following points should be kept in mind in height determination:
(1) Masthead heights may be purposely altered by the enemy to cause inaccuracies in periscope ranges.
(2) Tops of masts may be camouflaged in such a manner as to be invisible under average visibility conditions at any except short ranges.
(3) Funnel height is normally sufficient to insure that the smoke which is blown in the direction of the bridge by a tail wind will pass well over the bridge.
(4) Coal burners require taller funnels to insure adequate draft.
(5) Funnels of modern vessels having forced draft do not require as tall a funnel as older vessels without forced draft.
(6) Diesel propelled ships require no draft. Funnels are normally short, are not required, and generally have such dimensions as to provide a good appearance on the ship.
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Quote:
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Regardless of the methods employed by the individual Approach Officer, skill in estimating masthead heights, and ability to obtain accurate ranges can be acquired and maintain only by constant practice. Even when radar ranges are available daring an approach the Approach Officer should also obtain telemeter ranges as a means of improving and maintaining his skill.
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