Sink vs. Explode

The recreation of boating offers up many potential experiences, mostly fun but others that might fall into the “bad-day scenario”.  There is only one universally shared primary fear by all boaters, regardless of boat type (hint, it’s that sinking feeling) but there are a multitude of secondary bad-day scenarios that come to mind regularly for most of us who own and enjoy our pleasure craft.  I would venture to guess that blowing up an engine is a close second to sinking and from a purely financial standpoint, it can be just as devastating as the first.

Ironically, the two “events” – sinking and blowing up an engine – are very closely related in both the causes and safeguards one can take to avoid having either bad-day play out.  Given the natural laws that heavy, floating objects might just sink if given the opportunity, precautions must be taken where water can and will intentionally get through the hull and into the boat and that such opportunity be looked after regularly.  A busted hose, a clamp, or a failure at or near the seacock are at the top of the list among reasons a boat may sink, however, engines use these same seacocks, hoses and clamps to draw in raw, outside sea water to keep them cool, thereby being the main intentional ingress of sea water through the hull, generally in large volumes.

A responsible boater should know the state of all below waterline holes in the hull and that of the related end-to-end equipment connected to each.  The key to avoiding a sinking or a destructive event with one’s engine generally is sea water management and keeping it where it belongs.  Thru hulls and seacocks are the “holes” into the boat that are placed purposefully below the waterline to allow water in and out of the floating hull.  They generally have independent valves or fittings on them to shut out the flow of the when not needed or in use.  Many prudent boaters will intentionally close all seacocks as a final, precautionary step before stepping off a boat tied up at a dock or left on a mooring.  Equally prudent is to make certain that the ones that need to be re-opened to use on the boat are opened when one returns to allow water to flow through them when needed.  Many an engine has overheated and self-destructed because the raw water seacock was properly closed as a precautionary measure on the mooring but never re-opened when the engine was started up and subsequently run without cool water flowing to it.

Behind or inside the thru hull and seacock connections are propeller shaft seals, hoses, strainers, pumps, heads and sinks.  Regular inspection of these and all similar connections is critical.  Also, check for marine life that might have grown in and around your scoop strainer. An example of this, my friend’s engine sucked a piece of bull kelp blade through the scoop strainer and it went right into the water intake, so they had to shut the sea cock off and jam a fishing rod down the intake hose to push the kelp out. If an engine isn’t fitted with audible alarms indicating that it is overheating due to lack of cool water, one should pay particular attention to other less obvious visual clues:

*If visible, is water exiting the exhaust?

*Is water flowing through the raw water strainer?

*What does the temperature gauge indicate?

*Has the engine started making unusual sounds such as clicking or misfiring or is it simply losing power unexpectedly?

*Did the engine experience a loud pop followed by the discharge of a big cloud of white “smoke”?

While engines need a predictable flow of raw water to keep them cool, water flowing from the sea and through the engine is a closed system which works great as long as it stays sealed (i.e., a “closed” system) with uninhibited flow.  It doesn’t take long for dockside conversation to settle on someone’s catastrophic engine failure and the would-of-could-have-should-have post mortem analysis.  There is no doubt that every marina and yacht club has multiple members in recent history having experienced an overheated engine and similarly bad engine outcome due to either restricted flow or broken flow inside the boat.

Restricted flow generally is not due to a break in the line, but because of growth or a clog in the line outside the vessel before the cooling water has the opportunity to go from outside the hull to inside.  Barnacles, mussels and trash are the primary reasons a raw water system would which would lead to an overheating condition.  For some reason, barnacles, mussels and plastic bags are attracted like moths are to light at the raw water intake.  Generally, this is an out of sight out of mind problem because the intake isn’t easy to keep an eye on.  If a boat is left in the water either at dockside or on a mooring in freshwater or salt and the intake is not visible from above, it must be viewed regularly from below.  That means doing so personally with a diving mask, with a paid diver or by hauling out at least every 60 to 90 days.  This exercise presents a good opportunity to scrub other growth spots like the rudder and prop, replace anodes and to get a visual on everything else down below.  Also, the water paddle wheels and depth sounders generally benefit from a little attention below as well.

Once it is determined that the underwater, outside is clear, attention should focus on where that water goes once inside the vessel and that its flow is proper and predictable.  Sink, shower and head seacocks should remain closed while underway to avoid the risk of reverse siphoning.  When closed, they naturally fall into the “one less thing to worry about” category and they can remain closed even when their related equipment is used without causing a major issue.  It is worth mentioning that routinely opening and closing all seacocks is good practice and if they become too scary to turn due to corrosion or difficulty, they should be repaired or replaced.  While exercising them, it is a good time to take a deeper look at the related hose clamps and insuring that they are doubled up, tight and corrosion free.  Follow this by inspecting the attached hoses to make sure they are well fitted and they remain crack free and that there are no flow restricting bends or that they may be exposed to chafing or breakage.  Protruding wires are a sign that it is time to change a hose.  Next in line (on the engines raw water system) generally is the sea strainer followed by the engine’s raw water pump.  Again, for the sake of repetition, hoses should be traced from end-to-end to ensure that they have good purchase on their end fittings, there is no damage to the hoses, they have smooth curves and that all connections utilize two tight hose clamps in good order.   Higher quality raw water strainers allow one to visually inspect the flow of water into the strainer; look for bubbles or swirling on the sea side of the strainer which indicates that water is moving freely.  The engine’s raw water pump requires periodic inspection and maintenance.  There should be no sign of corrosion on this pump or directly below it, which would indicate that water is leaking from it.  Additionally, the pump’s impeller should be changed on an established schedule so that it doesn’t fail when the engine is running which too will lead to an overheating and possibly catastrophic condition.

Clearly not every worst-case boating scenario can be predicted but by making time for thorough inspections, planning maintenance on a schedule and adhering to repeatable and predictable patterns, fewer bad things are likely to happen when you make the time to enjoy your boat.  If you decide to play it ultra-safe and close all seacocks when the boat is not in use, do yourself a favor and attach the engine’s keys to the engine’s raw water seacock, thereby insuring that the engine will not be started with the water flow intentionally shut off.  The thanks you get will be the satisfaction that you know your boats systems, which in turn will lead to more predictable enjoyment by you and maybe fewer bad days on the horizon.


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