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Discussion Starter · #1 · (Edited)
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?
 

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Jnoiur Mebemr
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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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Freedom isn't free
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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.
 

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Swab
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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.

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

"Horsepower is inversely proportional to IQ."
:cool:

"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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Freedom isn't free
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"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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These are more memory aids

The cardinal (buoy) rules

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

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Correcting a compass

Can dead men vote twice at elections.

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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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Never drive over birds standing in the water.
 
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When will "red right returning" get you into trouble in IALA System B?

Local rules of buoyage (AKA the upstream rules)

- returning from seaward
- moving toward to the headwaters of a river
- entering a harbour
- travelling in the same direction of the flood current.

These can be superseded by the General Direction of Buoyage which is clockwise around continents.
 

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With respect to chart colours

Sail on the white stuff, anchor on the blue stuff, drink on the brown stuff.
 

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If you'll note none of the ones I gave are ever always true. Glad to see I made my point
That's why they are called "rules of thumb" instead of "facts". :D
 

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A good rule of thumb when anchoring: 5 to 7 times the depth of the water at high tide and if you have to go out to 10 times the depth it is time to find another anchorage.
Plus an anchor light isn't all that bright so light your boat up like a christmas tree to be easier to be seen.
 
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