A TradBoat Special

Building a Model Thames Barge

Frame Drawings and Station Lines

Frames are slices through the hull

Nearly every plan you come across will have on it a set of frame drawings.  These represent slices through the hull, rather like slices through a loaf.  Each frame drawing therefore shows the shape of the hull at that point.

          Half frame drawings

To save space on the plan only half of each frame is drawn - all that is needed really because it will be the same at each side.  By convention all frames aft of mid-ships are shown on the left hand side of the frame drawings, starting with the transom and looking forward..  Similarly  those frames forward of the mid-ships, are shown on the right hand side of the frame drawings staring with the bow frame and looking aft.  

When you come to use the drawings you can  make up a plan of a full size frame by  photo-copying the appropriate frame, then folding it at the centre line and cutting it out of the paper.  Unfold - and there is the frame at full size.  It's straight-forward in practice.

        How frames are numbered

Each frame is numbered or lettered and sometimes both.  Where both numbers and letters are used the letters usually refer to frames forward of midships, and the numbers to frames aft of  midships.  The purpose of these numbers or letters is to tell you where the frames are located along the the length of the vessel - they are the numbers of the "station lines". 

       So what are station lines ?

Station lines are drawn on the side view (elevation) and deck  (plan view) of the vessel, usually through both, and at right angles to the centre line.  These station lines mark the position of the frames from the frames plan, and are numbered or lettered in the same way.

        Frame drawings show the outside of the vessel

Frames are nearly always drawn to the outside of  the planking or plating of the vessel.  So they are too wide to be used as they are.  You will need to work out the thickness of the skin and deduct it from the width of the frame.  Again in practice this is fairly straight-forward. 

Example:  If the planking of the full size vessel is three inches thick, then this will be 1/8th of an inch thick at our scale So this is the amount that you will need to take off the drawing.  I found that the easiest way was to cut out the frame drawings first, but leave them folded. Then by using an instrument with two points - compasses or dividers will do, run one point around the edge of the drawing and score or draw a line1/8th inside the original drawing. 

Cut with a scalpel and unfold. You have a drawing of the correct size - that is to the inside of the planking.

        Mounting the actual frames

Pieces of paper have no noticeable thickness, but frames cut from plywood certainly do.  We said that the frames had to be mounted on the station lines so we have to choose whether to mount the front or the back of the actual frame on the line.  There is another convention:

All those frames forward of the centre frame are mounted so that the back of the frame lies on the station line.  For frames aft of the centre frame the reverse is true.  Of course the stempost and transom both have to be mounted "inside" the station line, otherwise the length of the vessel will be wrong.

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