Tumblehome and Gunwale

A distinctive feature of 1820 was its tumblehome sides, however other than at the transom this shape had been lost when the new timbers were steamed in.

Additionally 1820 had lost much of its sheerplanks so there was no clear sheerline to work from. A number of broken sections where recovered and with some detective work these were pieced together and clamped to the boat in the place they had originally come from. 

The final part of the puzzle was to get the correct curve of the gunwale from transom to stem looking at it from a plan view.

The task was to create a 3d shape with very few reference points which would still be authentic to the original. And then how to bend the timbers to this virtual line? Given the number of unknows decided to go step by step, first mark onto the timbers the best original sheer line we could, second bend the timbers to produce a tumble home shape, thirdly fit a new gunwale set to the sheer and symetrical and fair from a plan view. Final step is to connect everything together whilst making adjustments to produce a fair line.

To bend the timbers at the sheer line a series of adjustable jigs were made that produced the required curve. The amount of curve required decreased moving forward. The timbers had to be securely clamped to the jigs, steamed in situ and then epoxied to hold the new shape. 

The picture shows Tony adjusting clamps on a series of jigs to produce a consistent [decreasing as you moved forward] curve whilst the epoxy set them into shape.

This was done to all the timbers, slowly reducing the tumblehome over the length of the boat.

To produce the correct shape of the gunwale, battens were clamped both inside and outside of the timbers. The gunwale was adjusted to follow a fair sheer from transom to stem. The gunwale also needed to be twisted to lay flat to the steamed timbers. Some minimal chocking was required when the timbers were finally screwed into the beamshelf [gunwale].

The long sash clamps were used to help twist the beamshelf. A second batten was epoxied and screws to make the final beam shelf 38mm thick.

The final step was to lay a flexible batten over the timbers and with a grinder, fair some of the high points from where we hadn’t got the tumble home curve in the timbers 100% correct. It was very pleasing to find that when everything was brought securely together in the final position very little fairing was required. Cross beams were added to hold the correct shape. In the final checks for symmetry Tony and I decided +/- 2mm was an allowable tolerance – we had a symmetrical boat! Even the shear side to side was within tolerance. Very pleasing!

The final piece to add before we could turn the boat and start the re-planking was to fix stringers. These were screwed into each of the timbers, running almost the entire length of the boat. 

We now had a hull that was true and sufficiently stiff to both turn over and to remove several planks at a time without losing its shape.

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