Sorry if this is a dumb question but does a stern anchor typically have to have the same scope as the primary anchor ?
Stern anchoring
- Thread starter circa1971la
- Start date
Never a dumb question.
Yes. The anchor doesn't know where it is tied. There my be many cases where it requires less. There are two cases where it might require quite a lot:
- The bottom is sloping up towards the shore. The steeper the slope, the more scope is required to get the same angle with the bottom.
- You have bow and stern anchors (Bahamian moor) and the wind may come from the side. In that case, the force on both anchors may become extreme. You really want to avoid this case.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,913
It is a regular condition when an anchor is set that the boat sits down wind, down current.
A second anchor from the stern is often set to hold the boat in alignment with the prevailing winds/currents and unable to swing as the currents or winds reverse direction due to natural obstacles or other boats.
Since the current/winds reverse direction you will want the same holding power (scope & bower) capabilities on both the bow and stern anchoring systems. In such cases what started as the primary will reverse priority with the secondary as the current or winds change.
A second anchor from the stern is often set to hold the boat in alignment with the prevailing winds/currents and unable to swing as the currents or winds reverse direction due to natural obstacles or other boats.
Since the current/winds reverse direction you will want the same holding power (scope & bower) capabilities on both the bow and stern anchoring systems. In such cases what started as the primary will reverse priority with the secondary as the current or winds change.
You want them both the same and adequate for the depth and conditions.
Anchoring off an Island in the Canadian Thousand Island National Park, I went with a short scope on the stern anchor in deeper water to keep us off a shore. Strong winds dragged the anchor. When I started to raise it, the resistance was remarkable, even after it broke free. Turns out while dragging, the anchor had hooked the crotch of a good sized tree! Although the tree was waterlogged, it was buoyant enough to allow me to raise it until the tree started to clear the water - then it was impossible. Luckily, the anchor was close enough to the surface that I managed to rig a trip line, and pull it out of the crotch. But I will never use an anchor with inadequate scope again!
Anchoring off an Island in the Canadian Thousand Island National Park, I went with a short scope on the stern anchor in deeper water to keep us off a shore. Strong winds dragged the anchor. When I started to raise it, the resistance was remarkable, even after it broke free. Turns out while dragging, the anchor had hooked the crotch of a good sized tree! Although the tree was waterlogged, it was buoyant enough to allow me to raise it until the tree started to clear the water - then it was impossible. Luckily, the anchor was close enough to the surface that I managed to rig a trip line, and pull it out of the crotch. But I will never use an anchor with inadequate scope again!
Just to clarify, I think what people are saying is that the stern anchor needs the same scope as the bow anchor in terms of rode angle or depth-to-run ratio. In many cases you'll be stern-toward-shore so the water will be shallower, meaning you don't need as much line out to get the same scope ratio. But you still need that ratio for the anchor to hold properly.
Keep on mind that a sailboat is designed for wind on the head. When stern anchoring the rudder and fin keel lead. This may cause adverse effects in a current. As far as above the water, the mast and stays actually might improve riding at anchor. Think about your particular boat's design.
-Will
-Will
I think it depends on why you are putting a stern anchor out. I often used one in very light conditions to stop the boat from roaming. In that case I used a small anchor with less rode.
If I remember correctly, a Bahamian moor involves two anchors, both secured at the bow with one leading forward, and the other leading aft. The boat is free to rotate as the tide reverses. I used this technique many times on the East Coast in areas with sufficient swing room. At other times, such as a creek without swinging room, I have used a bow anchor and a stern anchor. Both techniques have their advantages and disadvantages, but what they have in common is that they require constant vigilance to avoid fouling anchor rodes on the keel or rudder.
Typically, I’d say yes. But it depends on what is its expected function. If you are anchored in the lee of some elevation not far back from shallow water or sheer rock face, you might choose to set a stern anchor. The reason: so that if the wind reverses and blows from 180 deg your heading you won’t blow into the shallows and go aground. In that case the stern set should have the same holding power, or greater, as the bower set. Yes, scope is one important parameter but also the type and size of the stern anchor. You’d be surprised what some newbies will deploy for a stern anchor to spend the night maybe 4 or 5 boat lengths from a hard grounding if the wind gets up. And its not always newbies. 
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Never have nor ever will deploy a stern anchor. Much rather let the boat settle in with either the wind or current while at anchor. Much less pressure on the anchoring system especially when those conditions abeam. Having the boat sashaying about in a blow provides me with a good tell. Ditto a stern tie except in calm conditions.
I don’t like ‘em much either. However, when cruising the northern California Channel Islands some skippers want to shelter under, and very close to, a headland, big rock, or ridge, etc., in the big winds that sometimes blow rather than return to harbor. We often see big seas running out there as well. Clearly, the nearer that you are to good shelter, the less exposed. Basically, a stern hook is needed to anchor safely under close shelter. I’ve seen boats with three anchors set out to moor the boat safely among rocks and shoals. But more commonly a stern anchor is set to keep the bow oriented to the seas even if only low “waves” or wavelets. When the wind dies off at night the boat can rock very uncomfortably if lying abeam to them. Lots of pounding if they arrive under the stern, etc. I use one when I see the need or advantage. That’s why I carry three sets of ground tackle when visiting those islands.
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I can’t imagine such a situation that wouldn’t expose the boat and crew to unpleasant and possibly dangerous conditions. Waves wrap around headlands and I would not want to get close enough to a rock headland that it requires a stern anchor to hold the boat off it.
That situation is not at all unusual at any of the channel islands in the Southern California bight.