The boats, with their gear and the sledges beneath them, weighed each more than a ton.
The cutter was smaller than the whaler, but weighed more and was a much more strongly built boat.

The whaler was mounted on the sledge part of the Girling tractor forward and two sledges amidships and aft.

These sledges were strengthened with cross-timbers and shortened oars fore and aft.

The cutter was mounted on the aero-sledge.

The sledges were the point of weakness.