from
Things I Wish I'd Known Before I Started Sailing


by John Vigor

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ENGINES, BLEEDING
Learn to bleed your diesel.

If you spend much time around boats, the chances are that sooner or later you’ll have to bleed a diesel. That is, you’ll have to purge the fuel system of air.

It might seem strange, but a small bubble of air can prevent a diesel engine from firing. That’s because fuel is injected into the cylinder under very high pressure. But air is compressible, so if air is present instead of fuel, the injector will never open and the engine will never start. To get rid of the air, you have to loosen the fittings at certain connections and physically pump the fuel through until all the air is forced out. It takes time and it can be messy.

Some diesel engines are supposedly self-bleeding. They have
electric fuel pumps that will circulate the fuel and send the air out, but even they might require you to crack the injector nuts from time to time.

You’ll find detailed instructions in the workshop manual for
your engine. Practice, because there may not be time to start learning when your engine quits.

TIP: Be cautious about running the engine when the boat is heeled under sail. The fuel can run to one side of the tank and the engine will suck in air.


L

LIES
People always lie about how fast their boats are

Always take sailors’ estimates of their boats’ speed with a dose of salt. They lie. Mostly not deliberately, although you probably know a couple who do. The trouble is that boat speed is very difficult to measure exactly.

Knotmeters are only as good as their calibration—often pure guesswork. GPS is notoriously unreliable for speeds and doesn’t account for current.

For accuracy, time your progress over a known distance. For example, to determine your maximum speed under power, find a measured nautical mile. Many are marked on large-scale charts, but you can also use landmarks to measure your own.

• On a calm day, time the boat in seconds between the marks.
• Divide the number of seconds into 3,600. The answer is your
speed in knots.
• Reverse your course and time the run between the marks.
Find the speed again.
• Average the two speeds. (Not the two times.) The result is
your true speed through the water.
• Steam at top speed as before, and calibrate your knotmeter.
• Repeat the speed trial in both directions to check the accuracy of your knotmeter and the distance log.

TIP: The measured course must be in water of about 30 feet or
deeper. Shallow water causes a drag and slows your boat.

 

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