Parents get help at BoatSafeKids

Chris Riley by Chris Riley Updated on August 9, 2019. In

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Parents get help at BoatSafeKids

dive_helmet.gif (8651 bytes) Frank writes: My son is reading 20,000 Leagues Under The Sea and asked me what distance a league is. Also, he wanted to know what the water pressure per square inch per foot of depth under water is. Your help would be greatly appreciated. A league is a measurement of length used in estimating sea distances. Its length varies among different nations. In Great Britain, France, the US and Spain the league has a recognized length of 6,075 yards. (5,554.9 meters)

As for the second part of your question, the water pressure increases the deeper you go. At the surface the atmospheric pressure is 14.7 PSI (pounds per square inch). For each foot of water depth the pressure increases by .445 PSI. You then have to add this to the atmospheric pressure to get the absolute pressure you are experiencing. In diving, each 33 feet adds an additional “atmosphere” or adds an additional 14.7 PSI to your body.

As an example, at a water depth of 33′ what would the pressure be?

33′ depth X .445 PSI/ft. = 14.685 (round to 14.7) you then must add this to the 14.7 atmospheric pressure and you get a total pressure of 29.4 or two atmospheres.

At 66′ of depth X .445 PSI/ft = 29.37 (round to 29.4) plus 14.7 atmospheric pressure gives you a total experienced pressure of 44.1 or 3 atmospheres.

Very good questions.

Capt. Matt

cruiseship.jpg (5037 bytes) Hi. My son, (11), and I have seen the movies, “TITANIC”, and, “SPEED II Cruise Controll”. He wants to know how fast say 17 “knots” is if he were traveling in a car (MPH). Can you answer or guide us to somewhere that could?

Thanking you in advance for your help in this matter, Jami & Josh

Statute miles are used to measure distance on land and on inland lakes, rivers and intracoastal waterways. Nautical miles are used to measure distances on the oceans of the world. If you assume the earth is perfectly round, (it is slightly flatter at the poles), there are 360 degrees around it at the equator. There are 60 minutes in each degree and each minute is one nautical mile. Doing the math, 60 minutes X 360 degrees = 21,600 nautical miles around the earth at the equator.

A statute mile is 5,280 feet in length.
A nautical mile is 6,076.11549… feet in length.

To convert distance use the following formulas:

statute miles x 1.15 = nautical miles

nautical miles x .87 = statute miles

To convert speed use the following formulas:

MPH X .87 = Knots
Knots X 1.15 = MPH

So… 17 knots would be approximately 19.5 MPH.

This is not completely accurate because of rounding but should suffice.


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