Saturday, June 27, 2015

Northern BC Coast and Deep Anchoring

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.

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.

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