Rules of thumb - SailNet Community
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post #1 of 17 Old 05-06-2014 Thread Starter
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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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post #2 of 17 Old 05-06-2014
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Re: Rules of thumb

Hahaha...........My rule of thumb for the wife: Just double the days I say I would be home on a delivery.
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post #3 of 17 Old 05-06-2014
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Re: Rules of thumb

I would add the rule of three's. "Any project an owner attempts on a boat will cost three times as much and take three times as long to complete as the original estimate. In the course of working on the project three other projects will be added to the ‘thing to do’ list each having its own Rule of Three’s. Any attempt to incorporate the Rule of Three’s into your project’s estimates will result in a further tripling of your original estimate."
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post #4 of 17 Old 05-07-2014
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Re: Rules of thumb

The time to reef is when you start thinking about the best time to reef.
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post #5 of 17 Old 05-07-2014
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Re: Rules of thumb

Best rule of thumb?
"A rule of thumb is the best way to improperly remember what you have to do."

The reef one is a personal pet peeve. It grates on me like someone saying "deja' vu all over again."

How about this one:
"You aren't sinking until you are taking on water faster than you can pump it out."
Wait that's a truism.

Another one that's a pet peeve...
"Happiest 2 days of a boat owners life is the day they buy their boat and the day they sell their boat." - I can't figure this one out... I've been sad to sell each of my boats, but at the same time have looked forward to the next boat.

Good ones?
"Red Right Returning."
"Big boat has right of way."
"Hull speed = 1.34 * SQRT(LWL)" roughly.
"Horsepower is inversely proportional to IQ."
"It's not the boat it's the sailor." Usually said when boat "x" wins a race.

"Rum Line" a 1982, S2 7.9 - Production boat limit tester, blue-water bucket owner, with wine taste on a beer budget.
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post #6 of 17 Old 05-07-2014
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Re: Rules of thumb

Quote:
Originally Posted by SHNOOL View Post
Best rule of thumb?
"A rule of thumb is the best way to improperly remember what you have to do."

SNIP

Good ones?
"Red Right Returning."
That one will get you into trouble because it simply is not true everywhere, even in the US.

Quote:
"Big boat has right of way."
Always observe the tonnage rule.

Quote:
"Horsepower is inversely proportional to IQ."


Quote:
"It's not the boat it's the sailor." Usually said when boat "x" wins a race.
OTOH, Sometimes it IS the boat, as when boat "y" wins.


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post #7 of 17 Old 05-07-2014
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Re: Rules of thumb

"Yeah and red sky at night/morning" doesn't really mean anything either... So "Red Right Returning" is about as accurate...

If you'll note none of the ones I gave are ever always true. Glad to see I made my point

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post #8 of 17 Old 05-07-2014
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Re: Rules of thumb

When wielding a hammer, always keep your thumbs out of the way.

"If a man must be obsessed by something, I suppose a boat is as good as anything, perhaps a bit better than most." --- E.B. White
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post #9 of 17 Old 05-07-2014
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Re: Rules of thumb

I remember a similar thread in the past.

My contribution was 'Explore on a rising tide.'
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post #10 of 17 Old 05-08-2014
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Re: Rules of thumb

These are more memory aids

The cardinal (buoy) rules

Western women are wasp waisted, while eastern ladies are elegantly elongated equatorially.

_______________________________

Correcting a compass

Can dead men vote twice at elections.

_____________________________________

Uncorrecting a compass

True virgins make dull company at weddings.

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Colregs rule 18 and some others

An over night room for sale plus snacks (and whisky)

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This is a rule of thumb for going those passes with lots of current

0-3 knots either side of slack- any time
3-6 knots either side of slack - 30 minutes
6 and more - 15 minutes and getting shorter.
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