The distinguishing feature of the Herreshoff system of marine steam machinery is the safety
coil boiler which has been brought to great perfection and patented by the Herreshoff
Brothers. The boiler consists of a spiral coil made of iron tube arranged with proper spaces
between the coils for the escape of the products of combustion. The coil is made of conical
form and surrounds the combustion chamber presenting an effective heating surface to the fire.
The heated gases proceeding from this chamber are made to pass through the spaces of a flat
coil at the top which heats the feed water before its entrance to the boiler proper. The feed
water is forced in at the cooler end of the flat coil through which it passes to the top of
the main coil and descending is finally discharged into a vertical cylinder which is called
the separator and in which the steam and water discharged from the coil are divided the water
falling to the bottom the steam being taken from the top and passed through a super-heating
coil located above the main coil which completely dries and superheats the steam.
