June 10, 2015
The next major segment of our trip was the BC coast from the
end of Vancouver Island up to Prince Rupert near the US Alaskan Boarder. This stretch is another 250nm that
fronts the Queen Charlotte Sound and the Hecate Straight. Queen Charlotte Sound is open to the
ocean, and although Hecate Straight is somewhat shielded by the Queen Charlotte
Islands, it is still a very open segment of water and subject to some nasty
conditions. The good news is that
the coast is actually a collection of islands, inlets, and passages that allow
for an almost entirely inland and protected voyage. And to boot, it includes some beautiful destinations.
Our first stop out of Port McNeill was Allison Harbour which
is just barely past the end of Vancouver Island and not really even into Queen
Charlotte Sound. But it positioned
us well to make an early AM rounding of Cape Caution, which as the name
suggests can be a rough area. Allison
Harbour also made for an easy first day and was a spectacular, long channel
with great anchoring up at the end.
Allison Harbour |
June 11, 2015
Time for our first exposure to open ocean and to round Cape
Caution. Now bear in mind that
last fall we came the whole 1200nm up the west coast of the US out in the open
ocean, but all things are relative and calm water is always preferable to
rough.
It’s probably worth a brief side note on the daily weather pattern
in this area. Mornings tend to be
very calm, and around noon the wind picks up. To whatever extend it’s going to blow, it does so over the
afternoon. Often times from 3-6pm
it blows the most, but then it settles right down and the nights are typically
dead calm. In general we have
fallen into a pattern of getting going early in the AM and traveling while it’s
calmest with a goal of reaching our destination early afternoon.
The trip around Cape Caution was completely uneventful, and
we approached Penrose Island in the late morning. Our destination for the evening was Big Fry Pan, a secluded
anchorage shaped as its name suggests.
You enter through a very narrow channel where you can practically touch
the overhanging trees, then turn the corner and find yourself in a beautiful
enclosed cove. Once inside, it’s
hard to spot the exit and seems like you are in an enclosed pond.
Anchoring:
One good thing about this area with respect to navigation is
that it’s deep. The entrance
channel to Fry Pan, though narrow, was plenty deep. One bad thing about this area with respect to anchoring is
that it’s deep. Fry Pan is about
80’ deep, so a 3:1 scope is about 250’ of chain, and 5:1 is 400’ which is all
I’ve got. Putting out that much
chain takes some time.
We use the windlass both to deploy and retrieve the anchor,
and it runs at about 50’/min. So
paying out 250’ is a 5 minute operation.
It can take about 2 minutes
before the anchor even reaches the bottom, which is a critical time because
that’s when I need to remember to set the anchor alarms. The alarms create a boundary circle
centered on the anchor, and your boat should never venture outside the
circle. If it does, the alarms go
off.
Another complication that arises from deep anchoring is that
your swing space increases. A
simplistic formula is that your swing radius is the amount of chain that you
have out. It’s a simplified
formula for two reasons.
First, your rode doesn’t stretch horizontally from the
anchor to your boat. It descends
down at an angle towards the anchor on the sea bottom. If you draw out a triangle depicting
your horizontal distance from the anchor, depth to the anchor, and the rode as
the hypotenuse, you can see how it works.
The swing radius, assuming the rode is pulled perfectly tight and
straight, is the length of the rode times the cosine of the angle. If I can remember my trigonometry
correctly, which is not at all a certainty, it works out that the swing radius
is 95% or more of the rode length for scopes of 3:1 and higher. So, for all intents and purposes, the
same as the rode length, making this simplification pretty darn accurate.
The second simplification is that the boat’s swing radius actually
includes the length of the boat, not just the length of the rode. For a 65’ boat with 200’ of chain out,
that’s a significant difference and one that really needs to be taken into
consideration. So, the preferred
simplification is to assume that your swing radius is the length of your rode
plus the length of your boat. So
in our case, I would consider 200’ of chain to give us a 265’ swing radius.
You might be wondering why I’m going on about this now. Well, it’s because many of these
charming anchorages are small, so we really need to consider our required swing
space. And often times the areas that
are shallow enough to anchor are also too close to shore or shallow water once
you consider your swing space. And
then of course there is the tide.
50’ of water depth at low tide can be 70’ at high tide, and you need to
figure your scope based on high tide, not low. Yet you need to be sure you don’t swing too close to shallow
water when you have low tide and the shallows are closest to you.
Oh, and there is one more challenge that is exacerbated when
you have deep water and restricted swing room. The location where you set the anchor becomes more and more
important, and when you are waiting for 100’ of chain to pay out before the
anchor touches bottom, you need to be sure you haven’t drifted off your
intended location. I’ve started to
pre-deploy the anchor when in a deep location, positioning it 20’ or so above
the bottom while I slowly position the boat where I want the anchor set. Then when I start lowering it
again, I only need to hold position for 30 seconds or so before the anchor is
on the bottom. Then it’s a matter
of slowly drifting/powering down wind in an attempt to lay the chain out rather
than dumping it in a big pile.
Then, once you have the desired amount of chain laid out, gently back
down on it to set the anchor to ensure it’s dug into the bottom. This is the moment of truth where you
find out if you picked a good spot and the anchor digs in, or if you are on
rock ledge and the anchor just skips across it and you need to go through the
whole process again.
The temptation is to try setting the anchor with as little
chain out as possible. It can take
5 minutes to get the required length paid out, and if the anchor doesn’t set,
you just need to winch it all back in again and try somewhere else. But if you jump the gun and try to set
with too little scope, the pull angle of the chain is more up than horizontal,
and it tends to prevent the anchor from setting rather than encourage it. I’ve learned this the hard way.
So far our experience is that a 3:1 scope appears to work
fine in deep water as long as you can get a good bite on the bottom. With 300’ of chain in 100’ depth, there
is a significant amount of weight just in the chain itself… around 750lbs. As the boat pulls away from the
anchor, it’s lifting more and more of that chain off the bottom, and that
weight is pulling the boat back towards the anchor. That weight and the parabolic shape that the chain takes on
serves two key purposes. First, as
tension increases, more of the chain lifts off the bottom. But the part closest to the anchor is
the last to lift. This ensures
that the direction of pull at the anchor is horizontal in all but the most
extreme conditions, and that’s the angle where the anchor has the most holding
power. Second, the weight of
the chain cushions the force on both the boat and the anchor. The more the chain lifts, the harder
gravity pulls back, creating a spring-like action.
No comments:
Post a Comment
Make comments here