80# Manson Supreme Surprise!

[foggysail]

Last week Wifey and I took our 40' Silverton Aftcabin, completely canvas enclosed powerboat to Cuttyhunk, a small island off the coast of Massachusetts. I was in a hurry to get the anchor down and set, dropped out about 50-60 feet of 5/16 chain where the water depth is about 6' at low tide, about 10' at the high.

My 80# MS has performed above expectations since I installed it last year so I put only one engine in reverse and tugged until it set. That I know is not the right way to set an anchor but the anchor is soooo reliable, I though at the time it was good enough. With that, I set my GPS as always so I could monitor any position changes.

Where I anchor at Cutty, virtually nobody else does. It is an area most fear as shallow but that is another story. What Cutty does have is a proliferation of ell grass, most 4-5' tall! It was a nice day and a better early evening, the type stories are written about.

Things changed later along with the wind moving to out of the NE blowing a steady 25K with gust over 30. I checked the GPS around midnight, it looked like we had slipped about 60' that I think occurred with the wind change. The mulitple plotted lines on the GPS indicated if we had slipped, we were then holding.

I checked several times during the night and early morning hours and indeed, we were moving, not much but moving. Maybe a total of 75' but we were limited to how far the boat could slip because of a moored sailboat along with a large, moored floating fishing bait box. At eight AM it was time to move after slipping about 125' as measured on the GPS. Some fun lifting the anchor and trying to control the boat in the heavy wind and well over 2' harbor chop.

We moved to one of the nearby pilings and spend the next two days listening to the howling wind and the slapping chop on the boat's hull.

Now I have an uncertainty factor.... did the anchor slip because I failed to properly set it? With the huge wind load my boat has, why did not the anchor set itself rather than just continually slip? The bottom below the ell grass is pure heavy mud.

[rebel heart]

Originally Posted by foggysail

ell grass, most 4-5' tall!

I've heard bad results from eel grass like that, no personal experience though. Did you have a bunch of mud on it when you pulled it up?

[tamicatana]

If I understand, you set at 5:1 (at high tide). Then the wind came up, and you didn't add more scope. In a blow I'd think it best to be at 7:1 or more.

That, based on the information given, sounds like it may have been your problem - not enough scope for windage and conditions

[rebel heart]

5:1 all chain in 25-30 knots seem more than enough.

[Tim R.]

Originally Posted by tamicatana

If I understand, you set at 5:1 (at high tide). Then the wind came up, and you didn't add more scope. In a blow I'd think it best to be at 7:1 or more.

That, based on the information given, sounds like it may have been your problem - not enough scope for windage and conditions

Actually less than 5:1 at high. What is the distance from the surface to the anchor roller? Let's assume 5' and 60' of chain. That would be 4:1. Gets a little more scary if only 50' of chain and 6' at the roller; just over 3:1.

how much was your bow moving vertically in that 2' chop? I bet the chain was taught so the weight of it was useless and the bow at it's highest reduced your scope even more. The bow bobbing up and down at a potential 3:1 scope or even 4:1 scope would be too much for most any anchor in that blow and your high windage. Your anchor was probably set below the grass bed but never bit into the mud because of the limited scope.

[foggysail]

Originally Posted by rebel heart

I've heard bad results from eel grass like that, no personal experience though. Did you have a bunch of mud on it when you pulled it up?

Yes, it was covered with heavy mud. I left the mud on the anchor until we returned to the dock. I tried washing it off with a hose until I resorted to using a boat hook or waste a lot of water and time washing it. There was NO grass on it though.

[Suijin]

A thick bed of five foot eel grass is hard to set in, and the solution is to set the anchor hard and to confirm that it is properly set by putting adequate load on it to test the set. The anchor dragged and the logical conclusion is that it was never fully set. You were probably just dragging it over the grass bed the whole time, perhaps only hitting mud at the end of your drag. Additional scope always helps, but if an anchor is not set properly then it is of limited benefit.

I've had experiences in that area with eel grass where it took me several tries to set the anchor, sometimes including moving a bit to find more favorable holding ground.

[foggysail]

No doubt about it guys, if I was doing it over I would let out more chain during the initial setting. I would also pull hard using both engines to make sure the anchor buried deeply. The bow is as mentioned about 5' off the water... so is the bow roller. So now the scope at high tide is as mentioned 50/15 to 60/15 or about 4. But remember, the boat slipped slowly during the entire night which means it also slipped at low tide where the scope was better.

All in all, the slippage total was not catastrophic. I dared not let out more scope before we moved to a piling because that risked putting the boat in harm's way. Incidentally... TowBoatUS pulled 2 boats off the beach that morning.

[tamicatana]

so there it is... make sure of a good set, and be sure to include height off the water when calculating scope, and be generous with the scope if there's any doubt

[foggysail]

Originally Posted by tamicatana

so there it is... make sure of a good set, and be sure to include height off the water when calculating scope, and be generous with the scope if there's any doubt

GEEZ, HOW RIGHT YOUR ARE!!!

[Tim R.]

Another quick point is that just because the anchor came up covered in mud does not mean it was in the mud the entire time it was dragging.

[noelex 77]

It is unusual to drag slowly like that, apart from soft mud.


25k is about the stage where the chain will slowly drag through thick weed. You mention a "wind shift" is it possible the the boat moved, but the anchor stayed in one position? The anchor covered in mud suggest it reached the substrate below.

With 60 feet of chain and a 40 foot boat (with the GPS aerial near the back) a 180 degree wind shift will produce almost a 200 foot movement on the GPS, less than the 125 feet you mention

In thick weed and 25k this movement will be slow. You don't mention the degree of wind shift so its only a possibility.

A photo of the GPS trace would help.

[Cheechako]

sounds like mud over clay with eel grass... bad combo for any anchor. A true 5:1 scope should have been good, but if blowing hard I woiuld have put more ot to 7:1 or so.... even if not moving...

think of it this way: If you had a lessor anchor, wouldy ou have been slipping like a freight train? The new anchors are reportedly "improvements" ...in some conditions anyway... but there is no golden fleece... anchoring is more about knowing your anchor's limitation , whatever it's make, the bottom, and being ready to change with the wind...

[foggysail]

Originally Posted by noelex 77

It is unusual to drag slowly like that, apart from soft mud.


25k is about the stage where the chain will slowly drag through thick weed. You mention a "wind shift" is it possible the the boat moved, but the anchor stayed in one position? The anchor covered in mud suggest it reached the substrate below.

With 60 feet of chain and a 40 foot boat (with the GPS aerial near the back) a 180 degree wind shift will produce almost a 200 foot movement on the GPS.

In thick weed and 25k this movement will be slow. You don't mention the degree of wind shift so its only a possibility.

A photo of the GPS trace would help.

Yeah, and I had a camera onboard but no picture taken at the time. I just got the GPS location set and am charging the camera battery and of course, I don't have the usb cable for it. Tonight I will try to attach a picture but there are buts. For example, because the boat is not at the location the GPS does not give an offset reading to show the distances. I might be able to get a distance guess from the lat/lon.

The GPS is located about 25 ft from the bow.

And yes the movement was slow. I noted that the boat seemed to slip right after the wind change. I first checked the GPS around midnight, we moved the boat sometime around 8-8:30AM. The wind change looking at the GPS was about 180 degrees.

[foggysail]

Originally Posted by Cheechako

sounds like mud over clay with eel grass... bad combo for any anchor. A true 5:1 scope should have been good, but if blowing hard I woiuld have put more ot to 7:1 or so.... even if not moving...

think of it this way: If you had a lessor anchor, wouldy ou have been slipping like a freight train? The new anchors are reportedly "improvements" ...in some conditions anyway... but there is no golden fleece... anchoring is more about knowing your anchor's limitation , whatever it's make, the bottom, and being ready to change with the wind...

IT DID SLIP but overall, the slippage was slow, over a period exceeding 8 hours. If I had one of my Deltas (sold the 55 but still have a like new 88), I think the boat would have moved smartly and quickly, far cry from over 8 hours.