Rules of Thumb

To Bail or Not to Bail:

• An average depth of 1 inch of water 8 inches wide for 20 feet long in an OC6 canoe is 1.15 cubic feet or 75 lbs.
• An average depth of 2 inch of water 10 wide by 25 feet in an OC6 canoe is 3.33 cubic feet or 206 lbs.
• An average depth of 3 inches of water 12" wide in 30 feet of an OC6 canoe is 7.5 cubic feet and weighs 465 lb, more than the empty weight of an empty OC6 canoe without its occupants.

Weight of Water

• 62 lbs per Cubic Foot
• 10 lbs per Imperial Gallon
• 1 cubic metre of water weighs 1 metric tonne

General

There is a 50% chance of (insert condition here)

Paddle Weight

Every ounce of paddle weight is a major consideration when you consider 60 strokes a minute for a one hour race makes 3600 strokes.  The math reveals lifting an extra 225 pounds per hour of paddling for EACH extra ounce in your paddle. A four hour paddle means an extra 900 lbs.  No wonder I am tired at the end of a long Sunday paddle.

Canoe Weight

A standard weight established for composite Hawaiian racing canoes (6 man va'a) is 400 pounds.  Many dugout or other construction type of wood canoes may be lighter, or possibly even heavier, than this. Many carbon fibre OC1 and single va'a weigh as little as 20 pounds.

Wind

In the Northern Hemisphere, wind and currents are deflected toward the right; in the Southern Hemisphere they are deflected to the left

Northern Hemisphere rules of thumb. Opposite for the Southern Hemisphere

• If you are looking at the wind, the low is on your right (Buys Ballot's Law)
• If the wind direction doesn't change as the pressure drops, the storm is coming straight at you.
• If the wind veers (CW rotation), the storm is passing west of you. 
• If the wind backs, (CCW rotation) the storm is passing east of you.

Apparent wind: 

The best way to determine the effective direction of wind on a canoe is to feel the wind direction on your head.  This is the apparent wind on the boat and takes into account the boat's speed.  Watching the water will only give you the cardinal wind direction. Often, sailboats use an apparent wind indicator on the top of the mast because it is the apparent wind direction that is critical to the incident angle on their sails.  What may look like a 'for sure' wind direction may be off by some degrees when the boat speed is taken into account.

In zero wind, the face will feel a 12 km wind when the boat is travelling 12 km per hour. When the wind feels still while the boat is at speed, the wind is from behind you at the same speed as your boat.

Waves

The highest expected wave is equal to twice the significant wave height. This kind of height would be observed in about 1 out of every 3000 waves.

If an average wave period is known, the frequency of observing the highest expected wave can be obtained by multiplying 3000, or any other number of waves, by the wave period. If the average wave period is 10 seconds, then a wave two times as high as the significant wave height will be observed on average every 30,000 seconds, or about 8.3 hours. 

Wave height is limited by wave steepness: deep water waves (those in an area where the ocean depth is greater than half the wavelength) begin to break when their height to length ratio exceeds 1:7.  

Waves begin to 'feel the bottom', slow down and get higher and steeper when the depth is less than 1/4 of their length.

Northern hemisphere storms create the steepest waves in their South East quadrant.{footnote}Fred Dobson-Oceanwaves at http://www.cpshalifax.com/PDF_Files/oceanwaves-dobson.pdf{/footnote}

Determining Tide Height ~ Rule of Twelfths

There are two methods of calculating tidal height and water depth, one makes use of a 'tidal curve' and is preferred where you need to be as accurate as possible. The second method is known as the 'Rule of Twelfths' and can be easily calculated.{footnote}UKDivers.net{/footnote}

The level of water does not rise or fall at a constant rate throughout the 6 hour duration of a rising or falling tide, but the amount by which it will do so can be estimated mentally by means of the following rough guide:

• 1st hours rise or fall = 1/12 of Range
• 2nd hours rise or fall = 2/12 of Range
• 3rd hours rise or fall = 3/12 of Range
• 4th hours rise or fall = 3/12 of Range
• 5th hours rise or fall = 2/12 of Range
• 6th hours rise or fall = 1/12 of Range

Assume that after looking at the relevant tide tables, a party plan to dive a wreck at 4pm. The tidal range is 6 meters and the depth at low water (1 pm) is 10m. 

Each twelfth would = 0.5m ( tidal range / 12 = 0.5m) 

Estimating Distance at Sea

Here are a couple of distance estimators:

You're in to less than a mile from shore when you can discern individual trees.

You can see individual windows in a house just inside two miles

When the junction of beach and water becomes indistinct, you're about 3 miles off