Anchoring Stern-to in a Storm

[Dockhead]

Have we come to any conclusions about this? I recall it was much discussed over the years.

The problem with lying to an anchor in a really bad storm is that the center of aerodynamic pressure of your boat with the sails down is ahead of the boats center of gravity as well as the boat's keel. That means that wind pressure tends to make the boat's head fall off -- tends to blow the bow off. It means that being anchored bow-to is inherently unstable in a strong wind.

That's the same principle which explains why it can be hard to get your boat's head through the wind when it's really blowing. And why backing up into a strong wind is the best way to maneuvre in close quarters and strong wind. Your boat will back into a strong wind with stability, because the wind will not blow the stern around like it does the bow. That's because the center of pressure is behind your keel, when you're backing up, so the effect of wind when backing upwind is just to keep you on course, not blow you off.

Apparently that's the same principle that makes a boat yaw at anchor in a strong wind. This yawing can break your anchor rode or snubbers or bridle in a really bad storm. There are many accounts of boats anchored in hurricanes yawing wildly, and being knocked on their beam ends at the end of every yaw, putting huge stresses on the ground tackle.

So someone recommended anchoring stern-to in such conditions, claiming that the boat will lie stably like that.

Has anyone actually tried this out in anger? Any thoughts?

[skipmac]

Have you read the writeup by Don Jordan, developer of the Jordan Series Drogue?

Jordan Series Drogue - Mooring and Anchoring

[boatman61]

Originally Posted by Dockhead

Have we come to any conclusions about this? I recall it was much discussed over the years.

The problem with lying to an anchor in a really bad storm is that the center of aerodynamic pressure of your boat with the sails down is ahead of the boats center of gravity as well as the boat's keel. That means that wind pressure tends to make the boat's head fall off -- tends to blow the bow off. It means that being anchored bow-to is inherently unstable in a strong wind.

That's the same principle which explains why it can be hard to get your boat's head through the wind when it's really blowing. And why backing up into a strong wind is the best way to maneuvre in close quarters and strong wind. Your boat will back into a strong wind with stability, because the wind will not blow the stern around like it does the bow. That's because the center of pressure is behind your keel, when you're backing up, so the effect of wind when backing upwind is just to keep you on course, not blow you off.

Apparently that's the same principle that makes a boat yaw at anchor in a strong wind. This yawing can break your anchor rode or snubbers or bridle in a really bad storm. There are many accounts of boats anchored in hurricanes yawing wildly, and being knocked on their beam ends at the end of every yaw, putting huge stresses on the ground tackle.

So someone recommended anchoring stern-to in such conditions, claiming that the boat will lie stably like that.

Has anyone actually tried this out in anger? Any thoughts?

A reasonable assumption.. till you look at the problems..

1/ No boat is set up with fittings strong enough to take the loads...

2/ Great until the waves start then the blunt stern will add to the loads as the waves smack up against it... also there's the likelyhood that they'll start flooding your cockpit.... as for those with a canoe stern... would that not yaw as well..

Maybe someone knows better...

[Dockhead]

Originally Posted by skipmac

Have you read the writeup by Don Jordan, developer of the Jordan Series Drogue?

Jordan Series Drogue - Mooring and Anchoring

Indeed, that's one of my main sources of information. I find it totally convincing, but the purpose of this thread is to find out whether others have confirmed any of this theory in practice.

[Dockhead]

Originally Posted by boatman61

A reasonable assumption.. till you look at the problems..

1/ No boat is set up with fittings strong enough to take the loads...

2/ Great until the waves start then the blunt stern will add to the loads as the waves smack up against it... also there's the likelyhood that they'll start flooding your cockpit.... as for those with a canoe stern... would that not yaw as well..

Maybe someone knows better...

I'm particularly interested in these questions -- practical experience.

As to fittings -- it might be worthwhile to create them for this purpose. You need them anyway in order to use a Jordan series drogue.

As to waves -- interested in people's experience. I suppose different boats will suffer from this to different degrees -- big center cockpit boats probably least susceptible.

[rtbates]

that's my quote about the subject to Mr Jordan..

I've only used it in winds upward of 25-35kts and the difference was amassing....

A Cape Dory's wineglass stern has no issues with wind waves from astern that I felt... Waves were only a few feet though....


All of Seraph's cleats are through bolted with 1/4 alum backing plates... They'll handle the load....

I will be adding 'stern chainplates' to handle the series drogue before sailing off.

[Tallswede]

It seems to me, you could be putting a lot of pressure on your rudder fittings also. Especially a vessel with a transom hung rudder. Waves hitting the transom could put some great force onto the fittings. Every boat being different, you would have to assess yours as to how it would handle these stresses.

Kevin

[boatman61]

Originally Posted by Dockhead

I'm particularly interested in these questions -- practical experience.

As to fittings -- it might be worthwhile to create them for this purpose. You need them anyway in order to use a Jordan series drogue.

As to waves -- interested in people's experience. I suppose different boats will suffer from this to different degrees -- big center cockpit boats probably least susceptible.

Anchorings a totally different thing to trailing a drogue.... one is designed to slow your rate of drift...
The other is to STOP any possible drift... loads would more than double...

[Dockhead]

Originally Posted by boatman61

Anchorings a totally different thing to trailing a drogue.... one is designed to slow your rate of drift...
The other is to STOP any possible drift... loads would more than double...

Yes, but double a given load is not a huge engineering difference. So if you're creating the strong points anyway, you just double their strength. I don't think this is a fatal problem to anchoring stern-to.

Also, remember, that if the theory actually works in practice, you will have dramatically less snatch loads than an ordinary anchor rode has to suffer.

I think experience with trailing drogues may also be relevant on the wave question. I understand that waves do not typically crash over the stern of boats trailing drogues. The waves lift them up and over. I wonder if this is true to boats anchored stern-to, also?

[sneuman]

Originally Posted by boatman61

A reasonable assumption.. till you look at the problems..

1/ No boat is set up with fittings strong enough to take the loads...

2/ Great until the waves start then the blunt stern will add to the loads as the waves smack up against it... also there's the likelyhood that they'll start flooding your cockpit.... as for those with a canoe stern... would that not yaw as well..

Maybe someone knows better...

Canoe stern/double enders exempted from #2?

[swagman]

If you've a canoe stern and a very strong rudder I am sure hanging backwards may feel ok. If you've any other style of boat I suspect not.

The design of all boats will find the greatest hull strength right on the bow; the aerodynamics flowing from the bow to aft is usually better than the other way around, and as is a simple matter to prevent yawing by hanging a drogue off ones anchor chain, why bother hanging backward?

Most modern designs hung from the stern would soon find the wave slop onto broad transoms driving the crew mad. It could certainly place greater wear onto a skeg or spade rudder.

Methinks this is all why most hang from the bow.

Cheers
JOHN

[Tallswede]

I think if I had a canoe sterned boat I would anchor it by the stern. I've anchored my little boats by the stern in protected spots and enjoyed not sailing around at anchor. If the waves pick up though, the slapping and pounding get old quick. LOL

Kevin

[Shrew]

I'm pretty sure that backing into the wind when slow-speed manuvering has nothing to do with the shape of the bow, stern or hull. Rather I believe it has to do with the location of the prop and the force being generated while under power.

Think of trying to drag a rope vs. trying to push a rope. I don't think this can be likened to anchoring bow into the wind or stern into the wind. While the bow may drift, it is still designed to ride up and over or through the waves, while the stern is decidedly not. Nor is the stern designed to take waves up over the transom, while the bow is designed to be able to be buried into a wave.

Ive' seen quite a few small boats get swamped anchoring and docking stern to, while those next to it, bow to ride it out just fine. Just a thought, but hey, what do I know.

[daddle]

The stern of most cruising boats is significantly overloaded. Plus some recent designs place much of the buoyancy far aft. These issues make taking seas on the stern problematic. Then there's the reverse transom and open transom of some boats....

[CarlF]

Jordan's stern-to mooring is intended for protected anchorages where wind loading (especially during a yaw) rather than wave action is the the principal source of stress. This is reasonable since it is far easier to find a wave protected anchorage than a wind protected anchorage.

Many of today's boats have woefully unsupported bow cleats - often installed in the middle of an unsupported piece of deck with no solid timber going to the keel or even a heavy cross member. If there are two cleats, they often are in the same piece of weak deck. By contrast, there's a lot of beefy places to attach cleats or strong points in the stern quarter of most boats where laminates for the hull and deck come together and the gunwale forms a natural I beam.

Better, most stern cleats don't need chocks to have a fair lead for a bridle - removing the single biggest risk of parting a line.


Carl