The exhaust flexible hose is led under the motor stringers to the riser and the transom.
The riser made from pipes and elbows.
Exhaust line can be made as flexible hose from the exhaust pipe to the transom port through any silencers, cooling elements etc. If the exhaust cooling from the engine is efficient enough and the engine is over the waterline, only the riser is needed to prevent the inflow of water to the exhaust line.
Later the green flexible hose has been changed to more rigid black widthstanding the high temperature. See newer posts (Mar/2017).
