The next most extensive experience has been obtained in the British Navy with the Normand type, with more or less modification fitted in a considerable number of torpedo-boat destroyers by Messrs. Laird Bros, and the Clydebank Engineering Company, and this type of boiler has given satisfaction in all cases where the boiler tubes have been made of steel. In the Normand type, a drawing of which is shown in Figs. 61 and 62, there is the usual top cylinder with two lower water chambers. 

Yarrow boiler.

We come now to the Yarrow boiler (Figs. 65 and 66), which has been fitted in several British torpedo-boat destroyers, and many foreign ones. 

This boiler consists of a steam drum at the top, in the centre, with flat tube-plates at the lower end on each side, between which and the steam drum are a series of straight tubes which form the heating surface of the boiler. The tubes all deliver their steam to the steam drum below the water line. A small water chamber is  bolted to these lower tube-plates. The original boiler of this type fitted in No. 77 torpedo boat had external return water-tubes. In the torpedo-boat destroyer ‘Hornet,’ however, which was the next vessel fitted with these boilers in our Navy, these external return water tubes  were omitted.