![collision regulations annex 1 paragraph 2(a)(ii)](/web/20071224093339im_/http://www.tc.gc.ca/marinesafety/TP/TP1861/images/annex1_p2b.gif)
1. To find the Angle C (with the aid of the Ships drawing)
Horrizontal distance
CL + LH + HF = CF
Vertical heights ![spacer](/web/20071224093339im_/http://www.tc.gc.ca/marinesafety/TP/TP1861/images/h-spacer-sm.gif)
DE + EF = DF
Tan C = ![bh over cf](/web/20071224093339im_/http://www.tc.gc.ca/marinesafety/TP/TP1861/images/distance_and_height.gif)
2. To find BH (The height where the dotted line crosses the
formast
Tan C = ![bh over ch](/web/20071224093339im_/http://www.tc.gc.ca/marinesafety/TP/TP1861/images/to_fing_bh.gif)
^BH = CH x Tan C
3. To find height of B above A (with the aid of the Ship’s drawing)
AB = BH - AH
WL is waterline with maximum trim by the stern.
C is 1000 metres ahead of the vessel’s stem.
A is the foremast light; D is the mainmast light.
CD produced cuts the foremast at B; for the foremast light to be seen from C distinctly separate from and below the mainmast light, it must be placed a minimum distance of about 0.5m below B at position A.