The "Rule of Twelfths" is a rule-of-thumb that we use frequently to decide if a location is safe to anchor or if a passage is safe to do. It only takes a few minutes and does not need tidal curves or templates. All you need is the tidal range and High Water height.

We use the Rule to decide the best passage north from Dublin to Skerries where we get a surprise in the night.

http://www.saltylass.co.uk/rule-of-tw...

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Morning Sun - Nicolai Heidlas
Royalty Free Music from HookSounds
http://www.hooksounds.com

Closed Captions (CC):
our anchor alarm went off because we got

down to half a meter under the keel our

winch seized today so sir pebble 'is

having to sort it all out aren't you Bev

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today's passage is up to scary's where

there's an anchor it's just here however

it's a bit of an interesting passage

because we would ideally like to go

between these two islands rather than

going it-- and rind and back in because

it would save us time

the problem is these two islands are

linked by spit and the water depth on

either side is about 10 meters but the

water depth on the spit is charted three

meters and at some points here about

half a meter right into the mid channel

and that's the chart of depths they may

be wrong it could be shallower it could

be deeper but I would like to go through

there the tide isn't particularly high

today and so I'm going to use the rule

of twelfths to decide whether or not I

need to go through here or rind here and

it's a very simple rule and it can be

used in anywhere where you've got a nice

tidal flow so this is a title chart for

Dublin and as you can see it's a lovely

smooth curve and it goes from low water

to high water to low water and it's nice

and smooth by some places in the UK and

Ireland half bumpy curves and if they do

the route of twelfths won't work but if

you're in a place where you've got a

nice regular tide twice a day the ruler

twelfths can quite literally save the

bottom of your boat

so my title height today is 3.6 meters

and I've got my twelve one twelve to

twelve three twelve my high water is

eleven thirty and it is four meters so

why states each are I subtract off some

of these

in sequence so for the first star I

subtract off 112 that's three point

seven meters because it is four minus

point three the next star I subtracted

off to twelve which is point six the

next star my subtracted off 3/12 just

point nine

then I do another 3:12 so that is there

1.3 I do another two twelve sixteen

thirty which is not 2.7 yeah I'm gonna

do one twelve not seventeen thirty which

is not nigh this differs this is no

water this differs from the low water

figure because I approximated it's

actually three and a half meters I did

three point six to make Mareth

meticulous simple otherwise out of a

heard lots of fractions so these are the

tidal heights at various times through

the day and the root of 12 uses the

pattern one two three three two one one

twelve 212 312 312 212 112 and that's

the pattern for doing it so that's spit

of scary's which is half a meter of

depth and spit and the keel depth of

this boat is one and a half meters and I

like to have an extra 1 meter of safety

margin so I need at least two and a half

meters okay we're gonna ignore the

little the little mess-up me it there so

I need at least two and a half meters of

depth I've got half a meter on the spit

so I need at least two meters of tide to

go through that gap safely which means

if I arrived by 1430 I can go through

the gap safely if I arrived 1530 I can't

go through the gap safely and I have to

go around the islands ideally I would

like to arrive much earlier but this

area here this might cut off below this

point I must go around the islands and

that's what I use the Riddler 12th today

oh dear we're approaching what we hope

will be our Anchorage for the night and

there's yet another Martello tower the

plan is to go between these two islands

and then turn in and go behind that

village over there

it's got another March avatar you'll

note and then we should be able to park

there it's noted for being a good

Anchorage so that's what we're hoping

today it does get shallow between these

two islands but we've done our

calculations and we should have about a

meter under the keel and let's go very

slow it's not for a huge distance and we

hope we'll be okay it's a great feature

so what are you doing

and that's the reason Gaynor is hanging

fenders on a boat hundreds of yards from

other boats in the middle of a marine

field a lot of things have cockpit a

Falls this is this is what we were we're

left so we're gonna be eating up here

today upon the open the deck with our

little cockpit table meanwhile dinner is

in progress toasters as you do our wind

sees today so so pebble ease having to

sort it all out aren't you Bev yep very

gently ease it up yeah so

ha so even when you're in the middle of

a rather nice Anchorage all right well

I'm taking more of your hands to be

honest but anyway he went you into

rather nice Anchorage or in mooring at

the moment you still have jobs to do

don't you bad Beverly's job is

progressing and we can now start seeing

the winch and what she's going to do

with this now it's just going to take it

all apart and clean it I'm not showing a

face cuz it's a picture even when you

are on your boat there's always stuff to

do Bev sorted out the winch which is

good

and I I'm now going to do the end came

off so we're going to do a little yeah

so basically we

together so not really good so we moved

it and we've actually anchored this time

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