What is the issue?Exhaust pipes are subject to taking water in through the exhaust outlet. IF this happens in quantity the exhaust system will backfill right up to and into the pistons. Exhausts should be as high above the waterline as possible but they are always vulnerable. Following waves can push water from behind into outlet pipes and they may go a long way under when heeling. Cruising boats are typically loaded more and so they go down a few inches on the waterline making them more vulnerable.
Why address this?Taking in a volume of water via the exhaust outlet will at best disable the engine. At worst, if it backfills into the pistons, it could cause untold damage.
How to address this?Fit a stainless steel swan neck at the exhaust outlet to stop water flowing back in and straight down into the engine as presented in figure 1.
This invidious little problem has a tendency to catch you out when you least expect it. It was only when we hove-to that this issue manifested itself upon our vessel. We noticed the boat slow to start after hoving to but paid little attention to it. It was only when a real blow came and we hove to for a night that we found the extent of the problem we had. At this stage it backfilled right back to the pistons. I believe we came within a hairs breadth of loosing our engine and perhaps even the boat itself in the dangerous waters we were sailing at the time.
Being at the part of the world I could not address this at the time, and a time in my circumnavigation budget, I resorted to hanging over the stern and tapping a bung into the exhaust from that point on. Literally at the merest possibility of backfilling I was over the stern.
The first thing I would do with a vessel now is check if it has a swan neck, if not I would set one in place. A stopper pipe helps for following seas and will help but not halt an inflow when the outlet dips below the waterline say in our example when hove to.
With thanks to:Michael Harpur, Yacht Obsession.
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