A marine water-tube boiler employing an upper steam drum connected by banks of
inclined tubes to two lower waterdrums. All the tubes discharge below the water
level in the upper drum. Larges downcomers are mounted outside the furnace. The
furnace is placed between the lower waterdrums and the flue gases flows between
the tubes on both sides of the steam drum.
The main difference between the Normand boiler and the
Yarrowboiler is the external downcomers.
