Every sport or hobby has its mavens of minutiae, like the baseball fan who can recite the Brooklyn Dodger lineup of 1948 or the political wonk who knows eight ways to stop a filibuster. Well, boating has guys like that too, and I’m one of them. I’ve been collecting nautical trivia since I was a kid. It’s an obsession, and a good one too, since I’ve found that many of these little esoteric facts have helped me get more out of my time on the water, and impressed a few friends along the way.
Head Off Trouble
Telling guests that using too much toilet paper will clog the plumbing is not enough. Be specific. Tests show that six squares at a time is the maximum.
You use approximately a gallon of gasoline per hour at wide-open throttle for every 10 horsepower. Not super accurate, but surprisingly close.
Keep It on the Plate
Avoid “round” food, ones that roll around on the plate. Choose hamburgers over hot dogs, niblets over corn on the cob and mashed over baked potatoes. And always square off your meatballs.
You know the weight of your passengers, and maybe the gear. What about the sloshy stuff in the boat? It adds up fast.
1 gallon of fresh water = 8.3 pounds
1 gallon of diesel fuel = 7.1 pounds
1 gallon of gasoline = 6.6 pounds
The absolute minimum berth width that any normal human will be comfortable with. The length should be 4 inches longer than your height.
Approximate fuel consumption at cruising speed can be estimated as follows:
Diesel - 5.3 gallons per hour per 100 hp
Gasoline - 7.8 gallons per hour per 100 hp
Number of hours you can expect a gas marine engine to typically last before needing major overhauls. A diesel lasts about 5,000 hours. No hourly figures exist for outboards, but 10 to 15 years in salt water is common.
It Never Stops
To calculate how much it will cost to keep a boat going, figure to pay from 2 percent to 5 percent of the original cost (new) per year in maintenance.
Sound of Silence
The most effective sound insulation is layers of foam core to reduce low-frequency sounds, thin sheets of lead to cut down on higher-frequency noises and Mylar or aluminum foil sheathing to protect the insulation from heat. Look for a minimum combined thickness of one inch.
Many engine compartments, and the engines in them, are starved for fresh air. Increasing a 3-inch round vent to 4 inches almost doubles its volume.
For every foot of draft in fresh water, your boat will rise almost one-quarter inch when immersed in salt water. A boat drawing three feet on Lake Huron will draw only 2 feet 11¼ inches in the Atlantic Ocean.
Quick and Dirty Method
For small, lightweight runabouts of 24 feet and less, use the 1:25 rule. For every 25 pounds of weight (including engine, gear, fuel and crew) you’ll need approximately one horsepower to get on plane and cruise at a reasonable speed.
Hanging by a Thread
The length of a bolt is correct for the job if at least two threads are exposed past the nut after tightening — the first couple of threads do not have full strength.
Thunder, and the storm that comes with it, is nearby if it crashes and bangs. It is far off if it rumbles like timpani, and very far away if you see only the lightning but hear nothing.
When barometric pressure starts falling, foul weather is approaching. The barometer falling 0.1 inch or more per hour says that a major storm is close.
When atmospheric pressure increases, the sea level is slightly lowered in the highpressure cell. When pressure is lower, the sea level is slightly higher. The changes are only in inches and fractions of inches.
Approximate number of statute miles a cold front moves in a day (more in winter, less in summer). Warm fronts move approximately 200 statute miles a day.
Avoid a storm’s center by tracking its movements in relation to your course by putting your back to the wind and pointing to the left; that’s where the center of the storm lies.
Rule of 1/12
Tides do not rise or fall at an even rate. Divide the tide’s range by 12. A change of 1/12 occurs in the first hour, 2/12 in the second hour, 3/12 in the third hour, 3/12 in the fourth hour, 2/12 in the fifth hour and 1/12 in the sixth.
The Weather Clock
If you’re in the Northern Hemisphere as you face the wind, and it changes in a clockwise direction, it is generally an indicator that fair weather is on the way. Counterclockwise movement means just the opposite.
Navigation by Estimation
The attention span of the average helmsman working at peak efficiency is 30 minutes, dropping off considerably until four hours, after which he is more a danger than a helping hand.
In a crossing situation with another boat at night, note the other vessel’s position relative to a low star. If the boat and star don’t separate, take evasive action.
Give ’Em the Fingers
The “three-finger rule” says that when an object, such as a lighthouse or tower, appears as tall as three fingers held sideways at arm’s length, it’s about 10 times as far away as it is tall. If the chart says the lighthouse you see is 150 feet tall, when it appears “three fingers” tall you’re about 1,500 feet or a quarter of a nautical mile away from it.
Since sound travels at a known speed, you can tell how far off an object is by timing your echo. Every second of delay equals 200 yards. Use this in fog or at night against cliffs, buildings or even large ships.
Go to the Light
White navigational lights appear first when approaching a shore at night. Red and green lights have about three-quarters of the range of white ones.
Rule of Thumb
Nautical legend has it that the phrase “rule of thumb” came when ship masters never allowed themselves to get closer to an obstacle than the width of their thumb on a chart.
Edge of the Earth
Distances over the water seem greater than on land. When standing eight feet above the waterline, as you might in the cockpit of a cruiser, the horizon is barely 3¼ miles away. At six feet up, it’s only 2½ miles.
A statute mile is the distance a Roman soldier covered in a thousand (mille in Latin) steps, which is now 5,280 feet. By convention, statute miles are used with charts of inland waters and the Intracoastal Waterway. A nautical mile is 6,076 feet, which corresponds to one minute of latitude, and so makes navigation computations easier.
On most planing boats, stow heavy gear to maintain a center of gravity on plane that's about 60 percent of the boat’s waterline length aft of the bow.
Discharge time for the average fire extinguisher. So aim at the base of the fire and get as close in as you can before discharging. Better yet, carry two or three.
Bow and stern lines should be as long as the boat, spring lines 1.25 times the length. This will accommodate even the most extreme tidal ranges.
The eye splices in your dock lines should be at least two feet long to make them easier to place over a piling and to put less strain on the splice.
Allow one inch of cleat horn length for each one-sixteenth inch of rope diameter. This provides enough room for the rope to make a gentle curve without pinching, which weakens the line.
Hey, Big Fender
How big a fender do you need? A good guide is one inch of diameter for every five feet of overall length. A 25-foot boat needs at least a 5-inchdiameter fender.