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Old 05-06-2014
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davidpm davidpm is offline
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Rules of thumb

As we all know rules of thumb are often misleading.
They are also useful. If you have no other information at least they give you an order of magnitude sanity check.

What rules of thumb do you know of.

I'll start us out with a few

If you are carrying a chain and nylon rode the chain should be at least a long as your boat.

If you are replacing your jib sheets they will probably be about 1.5 times your boat length.

If you are figuring fresh water usage you can figure from 1 quart to 1 gal per person.

If you are figuring diesel fuel you can figure about .5 gal per 10 hp used.

If you have a cross current you have to steer up current to fetch a mark. To figure how many degrees figure out how many minutes it takes you to go a mile at your current speed. At 3 knots that would be 20 minutes. Multiply that times the current to get the number of degrees necessary to steer up current. So if your speed was 3 knots and the current was 1.5 knots, steer up-current 30 degrees.

Nylon rode diameter is 1/8" of rope diameter for every 9' of boat length.

Any adjustment to the above rules of thumb.

More importantly what other rules of thumb do you have?
The lesson from the Icarus story is not about human failing.
It is a lesson about the limitations of wax as an adhesive.
If you have an engineering problem solve it.

Last edited by davidpm; 05-06-2014 at 11:37 PM.
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