Operating in Fog

Chris Riley by Chris Riley Updated on August 13, 2019. In nauticalknowhow

Rules of Thumb
and other quick boating tips:

Operating in Fog
Hose Guards
Kitty Litter
Coat Hanger
Paint & Varnish
Estimating Distance
“Pencil” Radar
Navigating by Eye
Piloting by Echo
Wake Crossing
Changing oil
Accident Reports

The Original
Rule of Thumb

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Operating in Fog

Objects may seem larger than they appear…

When operating in fog be aware that visibility can drop drastically. When visibility is between 30 and 150 yards objects, including other boats, may appear twice as large as normal. The illusion also tends to make you think that they are approaching at a much faster rate than they actually are.

Steering a straight line without a compass…

Many a small recreational boat owner will find themselves steering in fog without a compass. With no compass and with no reference points because of limited visibility, even the best helmsman will tend to steer in circles.

To steer a straight course, attach a light line high on the bow or from the mast and drag a drogue, cushion, or anything that can create resistance over the stern. Keep the line centered where it passes over the stern and you will steer a straight line.

Actions to take in fog…

If you see a fog bank approaching or fog starting to form be sure to fix your position by any and all means necessary, including electronically or by bearings. If possible, anchor and wait out the fog in an area which is too shallow for large ships to operate. Don’t forget to ring your bell for 5 seconds every minute while at anchor. Post as many lookouts as you have onboard and listen intently for the sounds of other vessels. If you hear a vessel approaching, sound the optional one short – one prolonged – one short blast to notify them of your presence.

Hose Guards

Don’t throw away that old hose. Cut a piece about a foot long, split is and put it around your dock lines and anchor lines where they pass through the chocks to prevent chaffing.

Kitty Litter Below

When you put your boat up for a period of time put a few boxes of kitty litter below. It will absorb moisture, reduce mildew, and eliminate odors.

The Handy Coat Hanger

Always have a metal coat hanger in your tool kit. It can be used to:

  • free hose blockages

  • hook something in an inaccessible area

  • used to replace a cotter pin

  • used as a temporary tie down

  • free blocked limber holes

When is Weight Not Weight? – The Matter of Tonnage –

Tonnage in boats and large vessels or ships has several meanings depending on what the term is referring to. It can at times be weight and at times be volume. The origin of the word in its maritime sense was the tun, a large cask in which wine was transported. The measurement of an old sailing ship was in tunnage, or the number of tuns of wine that could be carried. Following are the most commonly used definitions:

Gross tonnage is based on a vessels volume and represents the total enclosed space or internal capacity for transporting cargo. A gross ton represents 100 cubic feet.

Net tonnage is gross tonnage less the volume of spaces that will not hold cargo. In pleasure boats these spaces would be the engine compartment, helm station, etc. Net tonnage is also called registered tonnage. In order to document a vessel with the USCG it has to be a minimum of 5 net tons.

Displacement tonnage deals with weight in long tons which equal 2,240 pounds each. This is the actual weight of the boat. This can be calculated by finding the total volume of the boat below the waterline expressed in cubic feet. Divide this number by 35. (35 cubic feet of seawater weigh one long ton)

Deadweight tonnage is to displacement tonnage what net tonnage is to gross tonnage. Deadweight tonnage represents a boats cargo capacity in weight or long tons.

Off-Season Maintenance – Paint and Varnish

The off-season in many parts of the country can be used to maintain, upgrade or plan for the fun of the upcoming spring and summer boating season. A few “Rules of Thumb” that come to mind may help you with your winter activities.

Need a new coat of paint? In order to estimate how much paint to purchase use the following formulas. (Measurements should be in feet and your answers will be in square feet to cover). You then need to refer to the manufacturer’s brochures or the paint can itself to see how much paint is required to cover the square footage area.

  • Bottom Paint: Use the Load Waterline Length (LWL) times the beam times the draft.
    For full keel boats multiple this figure by .75. For lighter boats with less keel multiply this figure by .50.
    Example: LWL = 30  Beam = 10  Draft = 5   30 X 10 X 5 = 1500 X .75 = 1125 sq. feet to cover for a full keel boat.
  • Decks: Overall length of deck times the beam times .75. (subtract area of cockpit and deck structures)
    Example: Deck length = 34  Beam = 10  34 X 10 X .75 = 255 square feet
  • Topsides: Overall length plus beam time 2 times the average freeboard.
    Example: Overall length = 36  Beam = 12  Avg. Freeboard = 5  36 + 12 X 10 = 480 sq. feet.

When to Touch Up Varnish

The look of your brightwork says a lot about the pride of ownership that a boater has for his/her boat. A rule of thumb that you can use to tell if you need a touch up or a major overhaul of your brightwork is as follows:

Use a mild, soapy solution to wash thoroughly and get rid of all the grit and grime that has collected. (Hopefully, you do this more than once a season.) Rinse thoroughly with fresh water and dry. Take a towel and wet it thoroughly (make sure it is dripping). Drag the towel across the varnished surface. If the water that the towel leaves behind beads up the varnish is still in good condition. However, if the water that is left sheets or lies in flat streaks, you should plan on a light sanding and applying a couple of coats.

When A Varnish Touch Up Is Too Little Too Late

The only thing worse than going to the dentist is scraping varnish down to bare wood, sanding smooth and starting the arduous task of rebuilding 8 to 10 coats that will give you that “mirror” finish.

You can only patch the small abrasions and scratches so long until, ultimately, moisture has crept under the varnish and into the wood. This saturation of fresh and salt water will show up as dark patches under the still shiny finish. You will also notice lighter patches as the hot sun has glared down and has started to separate the varnish from the wood because of the moisture or perhaps the impact of dropping something on the varnish. It is at this point that you have no choice but to restore the integrity of the surface of your brightwork by scraping it down and starting anew.

Use the following as a step-by-step process to get brilliant brightwork consistently.

  1. I like to use a heatgun and scraper to remove the old varnish. This seems to go faster than sanding alone. In tight spaces you may have to just use sandpaper and lots of elbow grease. You should practice on a spare or out of sight piece to make sure you can control the scraper. Be careful not to make gouges in the wood.
  2. Once the varnish has been removed, sand the wood smooth using finer and finer grits of sandpaper. You may want to start with 80 grit to get all the rough areas and work up to 400 for that “babies bottom” smoothness.
  3. Before starting to apply varnish, make sure all sanding dust has been removed. Use a tack cloth dampened with a thinner that is recommended for the varnish you have selected. I lean toward varnishes with a high U/V rating. They tend to hold up longer in the sun.
  4. Stop! Don’t shake that varnish can, this is not paint. Shaking or even stirring will introduce bubbles which will show up on your brightwork. Most likely you don’t need to mix the varnish but if you feel obligated to make it move around the can while you watch, just swirl it slowly.
  5. Always filter the varnish by pouring from the can through a fine filter, or nylon stocking, into a small, clean container before applying each coat.
  6. For the first coat, thin the varnish with the compatible thinner 50/50. This will act as a sealer coat. Subsequent coats may be thinned if necessary to provide a good flowing viscosity.
  7. You may use a “real brush” or the disposable throw away foam brushes. Just make sure each is thoroughly clean and, if using a real brush, pull to remove any loose bristles or they will end up in your varnish work.
  8. Let the varnish flow on and only try to cover a small area at a time. Look for brush bristles, bubbles and holidays (spots that you missed) as you proceed.
  9. Make sure that each coat is completely dry before attempting to add another. Lightly sand with 400 grit paper between each coat.
  10. Repeat until you have 8 to 10 coats and that “mirror” finish that will be the envy of all at the marina.

Winterizing – A Quick Overview

Successful winterization focuses on preventing damage and corrosion by water and freezing weather. The most important rule to remember is to find everywhere water may be hiding. Wherever it hides, when it freezes and thaws it can severely damage that structure, pipe, tube or other object that contained it.

For more detailed information on winterization see BRRR – It’s Almost That Time Again – Winterizing Your Boat in the tips archive.

Another important rule is to protect your vessel from rain, snow, and frost while allowing a continuous stream of fresh air to flow through every nook and cranny. Good ventilation is just as important as roof or cover over the boat.

In order to track down the potential damaging water, look for it in “p” traps under the sinks, sea cocks, holding tanks, strainers and any other place you can think of. You should physically remove as much water as you can and what can’t be removed should be treated with a good dose of antifreeze. Since antifreeze is not recommended for ingestion you may want to use a 50/50 solution of water and vodka for the drinking water lines. Be sure to remember to flush out the system prior to taking the first sip next spring.

As soon as you pull the boat out of the water for the winter, be sure to clean the hull immediately. If you wait until it dries you will have to struggle with the marine growth that would have otherwise rinsed right off.

What about the engine? Engine manufacturers all have their own specific instructions about winterizing and you should consult your owner’s manual. Some of the basics are:

  • Drain all raw-water systems.
  • Check the antifreeze in an enclosed cooling system and top it off.
  • Change the engine oil now, not at the beginning the season. You don’t want old oil, full of acids, eating away at your engine’s insides all winter.
  • Grease everything that can be greased.
  • Use fogging oil to spray into the air intake manifold so that it coats the piston heads and cylinder walls. (turning the engine over without starting it will make sure you get good coverage)
  • Check sacrificial zincs and replace them.
  • Plug all openings into the engine from the air intakes, exhaust system, breathers, and any other areas which could provide access to debris such as dust, insects and even small varmints. Don’t forget to post a warning at the ignition switch to remind you not to start the engine without removing the obstructions.

Take the batteries home with you and place on a non-conductive stand (two concrete blocks with a 2 X 6 bridge make a good stand) and provide a trickle charge to keep them “alive” over the winter. Don’t forget to check the battery water every couple of weeks during the winter.

Make a list of maintenance items which you can do over the winter. You know, those things that you should have done during the season but were too busy boating to take the time for.

Is It a Good Knot or Not – How Do Knots Affect Line Strength?

Knots must earn their worth aboard your boat. In order to be worth their salt they must:

  • Hold fast under all conditions
  • Come apart easily when you want them to

You must do your part with respect to knots. You should be able to tie them as automatically as you do your shoe laces. The reason that you don’t have to think about tying your shoes is something called “muscle memory”. The muscles in your fingers have been flexed in the same manner so often that your brain doesn’t have to send individual signals to all the muscles involved. The memory appears to actually lie in the muscles themselves.

Knots obviously introduce kinks into a line that can diminish its strength. Some knots introduce tighter kinks than others. A three-strand line that has been tied with a knot that causes a tight kink can lose up to 30 percent of its strength. This loss of strength can cause a line to part more quickly under strain.

The reduction of line strength varies with the knot. Some examples follow:

  • Anchor bend: 24 percent
  • Round turn and two half hitches: 30 – 35 percent
  • Timber hitch: 30 – 35 percent
  • Bowline: 40 percent
  • Sheet bend: 45 percent
  • Reef knot: 55 percent

See also: Marlinespike for Recreational Boaters

Estimating Distance Off

In clear weather, one can distinguish the shapes of tall houses, trees, lighthouses, etc. from about 8 miles offshore. The distance to the horizon however can be quite small. if, in a small boat, your eye is 5 feet above the water level, the distance to the horizon is only 2.5 miles away. Although the distance can be more accurately estimated using the formula

1.17 times the square root of your height of eye = Distance to the horizon in nautical miles

Some rules of thumb you can use are as follows:

  • A light-colored beach can be seen at approximately 4 miles offshore from the deck of a typical small boat.
  • Individual windows in buildings can be distinguished by day or night at about 2 miles off.
  • A large buoy is visible at 2 miles.
  • A small buoy is visible at 1.5 miles but color and shape will not be clear.
  • The shape of a small buoy can be distinguished at about 1 mile.
  • The color of a large buoy can be distinguished at about 1 mile.
  • A person is seen as a moving black dot without limbs at 1 mile.
  • Movement of a person’s legs or arms can be distinguished at about 400 yards.
  • Faces can be seen, but not necessarily recognizable, at 250 to 300 yards.

Pencil Radar

It is possible to use something as simple as a pencil to determine approximate distance off. In order to use pencil radar:

  • Locate an object that can be seen onshore which is shown on your chart with a charted height.
  • Hold a pencil up at arm’s length and site the top of the object with the tip of the pencil with one eye.
  • Switch eyes.
  • You should estimate the horizontal distance (HD) that the tip appears to have jumped relative to the known height of the object. For example, if you are spotting the top of a spire on a mountain (as shown on your chart at 600 feet), when you shift eyes the pencil appears to shift twice the horizontal distance as the height, you would have an estimated horizontal distance of 1200 feet.
  • Now you simply use the formula D (Distance Off in feet) = HD (in feet) X 10. In our example, if the spire was 600 feet and the horizontal distance (HD) is 1200 feet, the distance off the spire = 1200′ X 10 = 12,000′ or 2 approximately miles.

Navigating By Eye

When navigating in areas with uncharted coral reefs it is a good idea to wait until the sun is high and behind you – from 10AM to 4PM. (This is why charter companies encourage you to anchor no later than 4PM.) Height above deck is an advantage to the spotter and vision can be improved with polarized sunglasses. Calm, grey days are the most difficult when trying to look deep into the water. As a rule of thumb in reading the water:

  • Dark blue tones mean deep water, 20 fathoms or more.
  • The blue becomes lighter with decreasing depth, and the turquoise (green-blue) is a warning of shoaling. it is the color of the coral sand covering a flat expanse of reef with 4-6 feet of water coverage.
  • Dark brown indicates coral heads.
  • Brown or yellow indicates reefs with a depth of 3 or 4 feet over them.
  • Green-brown means a grassy bottom.
  • White means very shallow water.

How reliable are your distress signals?

Even if your pyrotechnic devices (flares) are within the expiration date printed on each flare, you can only presume that 50% of them will actually work properly.

This is a sensible rule of thumb for any small vessel venturing out of protected waters. The U.S. Coast Guard minimum requirements do not take into account the often damp and exposed stowage conditions of pyrotechnics on small vessels.

Although you can never know for sure whether the device will work properly until you try it, you can make some precautions to increase your odds. Start by checking your existing flares by pulling off the striker top. If you find beads of moisture inside, you can probably rest assured that they will not work. Next, place your NEW flares in a waterproof, zip lock container. If available put a packet of silica (the kind you find in electronic equipment boxes to absorb moisture) in the bag with the flares. More on Distress Signals

Piloting Using Echoes

As kids we all thought that echoes were fun and interesting but did you know you could use them in piloting? Note the time in seconds from a signal to the return echo from a cliff, iceberg, wharf, or moored freighter. Every second’s delay indicates a distance off of 1 cable, or 200 yards. Every 10 second’s delay indicates a distance off of 1 mile.

This rule could be useful in fog some day. A blank pistol shot produces a sharp echo, but the ship’s bell or horn will work as well. Even a loud hailer works in close quarters. The Rule of Thumb at work here is that sound travels about 1 mile in 5 seconds.

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“This is the first year that I will have to moor my boat off shore in a lake. Can you tell me how this is done and what to watch out for? My boat is a 25′ power boat.

Many things depend on how you are going to get to your boat on the mooring. If there is a launch that simply drops you off, that eliminates one variable. If, however, you have a dinghy to reach the mooring, is the dinghy left there while you boat, or do you pull it behind you? The most important thing to remember when using a dinghy is not to get the dinghy painter (line) fowled in the prop of the boat.

Departing from and retrieving a mooring is much like anchoring. When departing, make sure your engine is warmed thoroughly and check other boats around you. All the boats should be pointing into the wind and/or current, whichever is greater. Make sure when you drop the mooring that you have sufficient room to get under way and establish steering control before you are blown or pushed into other boats. Plan your departure path prior to dropping the mooring. Pull forward, into the wind or current, slowly until the mooring line is slack. I am assuming that the mooring line has a float on it so when dropped it is easy to pick up. If not, you should rig one. Once you are in a position to drop the mooring line, do so and back slowly, make your turn to a path that will lead out of the mooring area and slowly motor away.

When picking up a mooring, look at the other boats first. This will tell you the direction of wind or current, whichever is stronger. Approach slowly into the wind or current and shift to neutral when close enough to pick up the mooring line. (Don’t overshoot the mark and get the mooring line fouled in the prop.) Once the mooring line is retrieved, simply attach it securely to the bow and let the wind or current set the boat back on the mooring line.

You can find additional information on moorings and mooring procedures in Chapman Piloting and Small Boat Handling, the boater’s bible.

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Tilt/Trim: I understand the basic principle of these functions, but I am not familiar with when/how to use them. For example, I usually start off with tilt fully lowered. Then, after I gain speed to my desired cruising velocity, I’m not sure what will happen if I pull the tilt up. I notice my bow pull up sometimes. And, I cannot tell what trim is doing whatsoever. Please explain basic operating functions of these features.

The trim on outboards and inboard/outboards is used to balance the boat in various conditions. As you mention, you should start with the motor in the vertical, 90 degree angle, to the water’s surface. Once you are “on plane” you can adjust the trim down or up to balance or flatten the boat. Trimming will help compensate for different conditions, weight distribution, etc.

By trimming “down”, which puts the lower unit closer to the transom, the stern will be pushed up and the bow will plow. On the other hand, if you trim “up”, meaning that the lower unit is further from the transom, the stern is pushed down and the bow is pushed up.

In smooth water with the bow trimmed “up” slightly, you may get a little more speed. In rough water you may get a slightly smoother ride with the bow trimmed down slightly. Simply put, tilt is what the outboard/outboard-inboard does. Trim is the effect that it has on the boat. Trim is the horizontal adjustment of the boat which makes the bow and stern move up and down.

See also:

  • Tilt? Trim? What Those Trim Tabs Do
  • Tilt & Trim for Outboards and I/Os

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Wake crossing: When the lake begins to get more and more crowded over the course of the day, the water gets choppier and choppier. Is there a good method of crossing wakes without having to greatly drop speed? The only thing I’ve seen is to turn my direction to be almost parallel to the wake. This seems to be fine, but in tighter situations, this isn’t always an option. Slowing down works, but this doesn’t seem very feasible or enjoyable to the skier, if we are pulling a water skier. Will the jumping across wakes harm the boat hull, or will it be only uncomfortable to the occupants of the boat?

Depending on the size of the wake you are crossing, you may be forced to slow your speed to keep from pounding the bow of the boat or even leaving the water entirely. Both can do damage to the boat and/or your engine. The best way to handle wakes, if traffic allows, is as follows:

  • If you are approaching a wake caused by a boat coming in the opposite direction, approach with your bow at approximately a 45 degree angle to the oncoming wake. This will allow the bow to move up and over with a little roll and lessen the bow pounding. If the wake is large, you will need to slow your speed to keep from falling off the top of the oncoming wake.
  • If the vessel making the wake has passed you (going the same direction you are going) and if traffic allows, turn so that your stern is at a 45 degree angle to the approaching wake. This lets the wake roll under the stern and pick it up while keeping the motor in the water.
  • Keep an eye on your skier when making any of these maneuvers.

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To prevent spills into the bilge when you’re replacing your oil and fuel filters, line the area with newspapers, paper towels, or oilsorb pads. When changing the filter, wrap a plastic bag around it before breaking it free. Any spills will drain into the bag instead of the bilge. Be sure to dispose of oils and fuels at a proper disposal/recycling facility and remember that Federal Law prohibits discharge of these materials into the water- you could be fined.

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Did you ever find yourself aground and wonder how to get off? One method is kedging. Kedging is accomplished by setting an anchor back in the direction “where you were floating” and pulling yourself off with the anchor line. Of course this works best if you wrap the line around a winch and winch yourself off. Setting the anchor is easy if you have a dingy, however, if none is available and conditions permit (and only as a last resort) a good swimmer wearing a PFD can take the anchor out resting on another PFD or anything that floats. When he/she is out as far as the anchor rode will allow, let go the anchor and bring the float back. Always have the swimmer do this wearing a PFD so they do not get fatigued. Related info

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Accident Reporting – Federal and state laws require the reporting of any boating accident that involves a fatality, injuries requiring medical treatment beyond first aid or property damage over $2,000. Some states have lower property damage limits. “Accidents” include capsizing, falls overboard, collisions, fire, sinking/flooding, explosions, or disappearance and should be reported to your local boating authority. Related Info

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The original “Rule of Thumb” is thought to be the principle adopted by shipmasters to avoid dangers. They would never allow their vessel to approach a danger nearer than the distance that corresponded to a thumb’s width on the chart. On a large-scale chart with plenty of detail they could navigate closer to potential dangers than on a small-scale chart with less detail.




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