Chapter 2 N38143 Dry systems Dry exhaust systems are most commonly used with engines which are keel cooled and are used for environmental reasons in some areas. This arrangement is particularly useful for commercial or pleasure craft operating in heavily silted water with debris and with radiator cooled engines. Dry exhaust systems for marine installations need careful design to minimise the disadvantages of enclosing components that are at a high temperature in confined spaces. A typical system is shown in (F).
The first part of a dry system should include flexible connections (F2) to permit movement between the engine and the fixed part of the exhaust except the 415GM and 422GM which have a simple flange (F1) for the customer to connect to. Connections of the stainless steel bellows type are suitable, but care must be taken to ensure that they are only required to accommodate movements that do not involve twisting the ends of the bellows relative to each other. Fitting a second bellows (F4) 90 degrees to the first will achieve this.The bellows and elbows should be covered with fire blankets (F3). The remainder of the exhaust system should be well insulated to avoid fire risk.
If there is a long exhaust run which gains height as it leaves the exhaust manifold, it may be necessary to incorporate a trap to collect condensate and allow it to be drained. Bellows should be in an unstrained condition when installed, so that the full bellows movement is available to absorb expansion and engine movement. Page Minimum bore of the exhaust pipe 415GM 40mm (1.6ins) 422GM 422TGM 700GM 4GM 60mm (2.4ins) 4TGM 4.4GM 4.4TGM 4.4TWGM 76mm (3ins) 4.4TW2GM 6TG2AM 6TWGM