Photogrammetry

We were aware that ‘Tassie Too’ a well-known 21footer that Tony had restored in the early 2000’s and now back in Tasmania run by the ‘Friends of Tassie Too’ had been digitally ‘surveyed’ and line drawings made using photogrammetry. 

With the assistance of Peter Higgs, the public officer of the ‘Tasmanian Wooden Boat Guild’ amongst many other duties, we received detailed instructions in the process of taking the photos need to produce the point cloud which is the basis of the final lines drawing. 

We first had to try and prop up 1820 back to its original shape. Without a shear plank and with the distortions from years of weathering it was a fun job with very few real reference points other than beam and overall length! It took most of the day to set the boat up and the light was fading. In the end had to come back the following weekend to complete the photos, in total 241 pictures were used.

Using the pictures taken of the boat Peter arranged to produce a set of line drawings.

From the lines drawing a set of frames were made with the intention of use them to rebuild 1820 on, after first constructing an ‘inner’ cold mould shell with veneer. This set of frames was made in the workshop whilst 1820 was still 200km away. 

When we actually got 1820 into the workshop we found the discrepancies between the jig and the actual boat too significant and decided to not use the jig. [The frames would make a very good sister boat to 1820 – maybe a project for the future? :-)]

I think the major cause for the discrepancies was the difficulty of ‘trueing up’ 1820 on the farm. At the farm we had concentrated on getting one side [the one with the least damage] of 1820 ‘true’. When we got her into the workshop we were able to do a much better job of propping the boat back into a ‘correct’ shape. Using plumb lines, and laser levels and careful propping the boat came back to a remarkably fair shape. The keel was straight, strong and true and the replaced transom, once the twist was removed, helped a lot with the shape. The picture shows 1820 partway through the trueing process. Several more cross beams going forward were added to assist in shaping the forward sections. A temporary and heavier shear plank was clamped to the frames allowing the boat to form a fair line. It was surprisingly easy to get the boat symmetrical which gave some confidence that we were close to the original shape.

Before we could finish setting the boat up correctly, we had to deal with the broken stem. It had broken in two, however luckily the break was sufficiently jagged that when the pieces were forced back together, they held the original shape. We could use this to make a new stem.

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