The Higgins mufflers were located, three each on either side of the boat, adjacent to the engine compartment and the Packard engines, partially submerged and incorporating a closable flap at the rear outlet to alternatively direct the exhaust under water for quiet running or, under full power, the flap would be opened to allow full exhaust outlet to the stern direction.
The top part of the muffler was connected through the hull, above the waterline, with a flexible metal pipe travelling upward, through the strengthening ply bracing and then back down and diectly to the engine exhaust manifolds. As the three engines were V12's each with dual exhaust manifolds, the wing engines exhausted to their respective port and starboard sides and the two side manifolds of the center engine exhausted to their respective side.
There appears to be two different versions of the mufflers which are very similar in appearance, however the later war boats appear to have a longer underwater tail by about 9 inches more than the early war boats, this can be seen, even in photographs of boats in the water as the forward two mufflers being further apart than in the early boats.
(c) copyright 2019 - 2020 John Drain