Taking off Lines

I did this exercise for Model #4 of the Henry Huddleston Rogers collection at the US Naval Academy. The model purports to be that of a royal yacht of Charles II from the late 1600s. As such, there are no plans of the ship, nor does the ship still exist. Since we cannot know the dimensions of the actual vessel, the best that we can do is derive a set of plans, in a reasonably accurate manner, from the model that does exist. The curators graciously allowed me to take the model to a workroom where I took off the hull lines and took many photographs. Based on my table of offsets I developed a set of plans, which I then converted into a model.

An exploded view of the measuring device.

The completed device.
The calibrated probe.

To generate the table of offsets I invented a device consisting of two plastic grids, the kind that cover overhead fluorescent lights. These are 2' x 4' panels, with the square holes 5/8" on center. The two panels were held vertically and at about 2" distance from each other, with the grid holes lined up. A measuring rod was constructed that slid through the holes with little clearance on all sides, and a narrow soft plastic tip which would be the only thing to touch the model itself. The measuring rod had a ruler mounted on its top face in such a way that the tip of the measuring rod was the zero point of measurement.

The device aligned to the model and probe taking an offset.

To use, the model was set up on the work table and shimmed until precisely vertical. The grid fixture was set up exactly parallel to the centerline of the model and also precisely vertical. The distance from the rear face of the back grid to the centerline of the model was established at exactly 10" (although this is an arbitrary figure depending upon the size of the model). The measuring rod was slid through each pair of grid holes until the tip contacted the model. The reading on the ruler at the back edge of the rear grid was noted, and this dimension was subtracted from 10" to give the offset dimension at that location. If the measuring tip landed on a bare frame, there was no adjustment to this offset dimension was made. If it landed on a plank, carving or other object, an adjustment was made from an estimate of the thickness to the frame. By repeating the measurement for each grid location a table of offsets was derived with station lines, and waterlines, every 5/8" vertically and horizontally. Final adjustments to the table were made as the lines on the plans were faired.

For fitings which did not fall directly under the tip, photos were taken with the tip of the measuring rod touching the fitting in question, and copious notes of each was made. These were used later to locate various features such as wales, port wreaths, and other hull fittings. A separate series of photos was devoted to the numerous carvings, stern, beakhead bulkhead, and the break of the poop, as well as the lion figurehead.

The device worked so well that the curator at the Museum asked if he could make a copy. Rather than that, I donated it to the Museum, so long as I could re-use it in the future.

I wrote an article on the devise for the Nautical Research Journal (Vol 40, p128-131), which is more detailed than this note and has a number of additional photographs.

The advantages, as I see them, to this devise rather than a swing-arm devise, are these:

1. Ease of construction and minimal cost.
2. Each measurement is independent of the others, so errors do not add.
3. The model is touched by the soft tip in one spot at a time, without movement across the model which could scratch the finish.

If you decide to use this devise, or improve on it, feel free to contact me to discuss.

Note: In doing my historic research, it became clear that the model had been incorrectly identified by Henry B. Culver when he worked as model custodian and curator for Colonel Rogers. The model was initially identified as that of the Navy, a yacht from 1675, if I recall correctly. After reviewing the known dimensions of all of the yachts of Charles II, as well as numerous drawings and paintings by Willem Van de Velde the Elder and Willem Van de Velde the Younger from the National Maritime Museum and the Boymans Museum, it was obviously not the Navy. From the dimensions taken from the model a ratio of length to breadth was derived, which was then compared to the same derivative from the known ship dimensions. Those yachts whose ratios closely matched those of the model were further examined in the documentary and pictorial record. On that basis, although there are some significant discrepancies, the model was identified as the Henrietta yacht of 1679. This conclusion was accepted and the identification and documentation of the model has been changed by the Naval Academy Museum.
{Dan Pariser}

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