Reconstruction of the Hjortspringboat - Theoretical Performance and Initial Test Results.

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ISBSA 8, Session C_2


Niels Peter Fenger, Hans Lumbye-Hansen.


The present paper is the second of three papers dealing with the reconstruction of the Hjortspringboat. Of these three papers the two first are being presented at ISBSA 8, while the third one, reporting on the sailing performance of the boat, will be published in the autumn 1998.

Our predecessors 2500 years ago had the experience of building a line of still more refined boats by a team of boat building professionals. According to the characteristics of the trees at hand, each new boat would vary.
As the philosophy of the reconstruction was to build a boat as close as possible to newest interpretation of the excavated Hjortspringboat, and as we did not have any experience in boat design or manufacturing, we had to use modern theoretical tools.
The employment of these tools produced at the same time new knowledge as to the standard of boat building in the Celtic Iron Age, compared with modern standards of "similar" boats. Furthermore the prediction of the performance, compared with the tests, gives new knowledge regarding the validity of these theoretical tools.

A line plan of the boat, taken from Fr. Johannessens drawing was read into a computer.
From this computer program, shapes of the boat were printed out for use by the boat building group.
From the same program were calculated the volume of displacement and the wetted surface at different draughts (loads).
Through tests with the middle section of the boat (part of the wood training program), the center of gravity of the paddling crew and the boat was determined, and the static stability was calculated. The metacenter position is that close to the center of gravity, that the boat can't be characterized as being very stable.

As to hydrodynamics we calculated different shape coefficients.
Furthermore calculation of resistance and effective power versus speed was performed. The calculations shows, that 1500 watts (2 hp) is required in order to obtain a boat speed of 8 knots.

Paddle force and efficiency characteristics were calculated.

The stress and strain characteristics of the sewing material and the seam construction were determined by tests.

Some strength and elasticity characteristics of the boat were predicted.

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