Sailing Navigation Secrets: Do You Know Your “Navigational Draft”?

Here is another sailing tip from our friend Capt. John at skippertips.com

Sailing navigation safety in my eyes means the navigator must keep enough water beneath the keel–at all stages of the tide. But that’s not all. Navigation aboard a small sailboat will always be a challenge, in particular in choppy or rough weather.

Use “navigational draft” to make a decision before you thread your way through shallow channels. Double your sailboat draft or use an even more conservative estimate for sailing safety. How many of these shoals would your sailboat’s “navigational draft” clear? Highlight dangers like these so that they stand out on your nautical chart. See more below.

You have your hands full to keep the position up to date, steer an accurate sailing course, and estimate factors of current and leeway. And besides all that–keep the sailboat keel clear of the seabed!

Why Use Navigational Draft?

Navigation aboard Coast Guard cutters began with awareness of the Captain’s standing orders for navigation safety. Navigational draft designated the least amount of water that the navigator was allowed to take the ship across at any given moment. In most cases, this was a minimum of 1½ times the ships aft draft.

On a 210 foot medium endurance cutter, an aft draft of 12-14 feet meant keeping her in water deeper than 18 to 21 feet. On 295 foot Barque Eagle (the USCG training tall ship), her 17′ draft required a navigational draft allowance of 25′.

Of course, some channels didn’t allow this much water. Like the day the Captain said he wanted our nav team to take him through a narrow channel on Bermuda’s eastern side. It was the first time the 295′ Eagle had ever attempted this tight passage. Successful it was, but your humble author’s pucker meter stayed pegged until we cleared the coral heads on both sides and were bound for sea.

Use This Five-Second Calculation for Sailing Safety

Sailing skippers must decide when and where to use a similar safety factor for their own sailboat draft. You could use navigational draft when you:

- Make landfall on an unfamiliar coastline.

- Decide whether to sail through an inlet or narrow pass.

- Navigate in thick fog or rough weather.

- Highlight shoals or depth curves on your nautical chart.

- Choose a safe anchorage in shallow-water cruising areas.

Use an even more generous safety factor of 2x loaded draft (boat fully provisioned with fuel, water, stores and crew). This will give you an extra margin of safety. If your draft isn’t an even number, round up before doubling.

Examples Below Include Sail and Power
(draft shown should be adjusted if loaded for cruising):

The Contessa 32 sloop carries a 5½’ draft. Round up to 6′ and double. She should stay in waters deeper than 12 feet at mean lower low water (or the low water sounding datum used in your area).

A Bertram 47 cruiser carries a 4′ 7″ draft. Round up to 5′ and double. She should stay in waters deeper than 10′ at mean lower low water (or the low water sounding datum used in your area).

Be aware that some charts, including those on your trusty electronic plotter, were last surveyed in the earlier part of the 20th century.

Popular cruising grounds in the Bahamas or Pacific islands might show soundings going back to the days of the tall ships. Find the survey date of the soundings in the title block area.

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Use these sailing tips to decide when to use navigational draft for sailing safety aboard your small sailboat. Keep your sailing crew or partner safe and sound–wherever in the world you choose to sail or cruise!

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