Anchoring in Sand

[Dave M.]

I did a little testing of my Delta anchor in sand a few days ago. Basically, I took the anchor and threw it up on the beach, then used the boat to try and "set" it. So maybe the first issue I have is that I don't know what "set" means. Is the anchor in the following pictures set or not?

Anyway, I carried the anchor up on the sand and dropped it. Got back in the boat and tried to set the anchor so it would not pull through the sand. Here is a picture of the third try.

Here is a side shot of the anchor, I am pulling almost parallel to the sand.

And looking from behind, it was like a lemming headed for the sea. Maybe it is just too small, or maybe an anchor can't set above water level like this?

So I decided maybe the scope was too steep. So I decided to tie the anchor line off via the bow eye, just above the water line. I would have a scope of maybe 20:1 o something like that. Quite high. Ready to pull.

And after a few feet again...

And the rear view.

There is not a lot of chain on the rode, only about 15 feet. But I am pulling almost horizontal, so I don't think that is the issue. Maybe I am wrong. :huh: What I know is that I cannot trust this anchor to hold this boat in this sand again much of a breeze; at least not as presently configured.

 

[Sea Gull]

Your test seems valid except I don't don't how much reverse thrust you gave - was it realistic for the size anchor? Basically there are better anchors for sand Than the Delta. You should carry at least two different anchors for varying conditions.

There is a lot of interesting articles about how different achors hold and re-set in various bottom conditions. Here is one http://www.cruisersforum.com/forums/f90/ps-anchor-test-report-2383.html that you might find interesting.

 

[Presentation]

You did everything correct. If the anchor was in the water the sand would be saturated with water and the anchor would be driven deeper giving you the holding power you seek.

Because the sand was not submerged you need to get to the beach and manually burry the anchor for it to give you the high holding power.

 

[Hampton]

I think the problem is the angle of the beach. When you set the anchor on that kind of angle, it's exactly like the force it will receive when you are above the anchor trying to free it.

The whole purpose behind an anchor chain is to keep the angle between the anchor and the rode in line with the shank by weighting it down and holding on the ocean floor, which should keep everything all lined up.

In the pictures, it looks like you're trying to set the anchor on a 30 or 45 degree incline, which is like setting the anchor on bottom with very little, if any, scope.

 

[lorenbennett]

Even in sand if your setting your anchor on a rising bottom backing towards the shore line the anchor will continue to sink deeper and deeper in the sand. That along with the weight of water causing the sand to want to compact around the anchor will cause it to hold. When I am using the anchor to hold me on beach I just set a large rock on it to cause it to sink if pulled on. :thumbsup:

 

[Nehalennia II]

I think the problem is the angle of the beach. When you set the anchor on that kind of angle, it's exactly like the force it will receive when you are above the anchor trying to free it.

I think Hampton's Correct. As long as there is no force pulling it in the direction to release it it should continue to dig itself it. Was the test to see if you can anchor to stay on the beach or out in a bay or whereever?
I think your anchor's fine, just get it in a flat plane.

 

[Dave M.]

The angle of the sand at the water edge is quite shallow, although back 5 or 10 feet it is 45 degrees or so. I was trying to see why I can never get this anchor to hold. I am always dealing with this sand here. I would like to be able to carry the anchor to shore and have it hold, but I am more concerned about what it does in a few feet of water.

Regarding how much power I used, I should have made note of how many RPM the engine was running to pull the anchor along. I will guess about 1200, but that is just a guess.

I guess I need to repeat this test with more chain. There are very few places where I could put the anchor that has a flatter bottom than this. Actually, I can't think of any. So maybe more chain is the ticket. I have some 5/16 chain I use when lifting and moving stuff with the tractor. I could put on 25 or 50 feet of it. That would be a good test to try it.

Thanks for all the comments. Maybe I can make this work yet. I really would like to be able to use this anchor in the water, as it fits the bow chute. I have a Fortress I can carry ashore and set in the sand. I know it will hold there.

 

[lorenbennett]

Dave a couple of and spikes or a box anchor for shore line anchoring is the real ticket. Been in big wind like that and never a problem. :thumbsup:

 

[Nehalennia II]

Dave a couple of and spikes or a box anchor for shore line anchoring is the real ticket. Been in big wind like that and never a problem. :thumbsup:

Dave, that's why I asked. For normal anchoring where the anchor is beneath you your anchor should be fine. But for the river
I have seen the Sand Spike
It seems to work great.

 

[Dave M.]

Thanks guys! I think I read about the Sand Spikes on the other board, and then forgot about them.

 

[MLauman]

I think I'd be a little leery of that combination (of anchor type and bottom composite) based on the fact that your real-world anchoring attempts appear to give similar results. Why don't you try the Fortress in the exact same scenario and see what happens?

 

[Dave M.]

I will put testing the Fortress on my list. Will try and post pictures if relevant. Right now I am helping my daughter load up her stuff to move her and 4 kids to Colorado where her husband is working. Will be taking them as far as Boise, ID, on Wed.

After that, I will be free for boating stuff again. I hope!

I was thinking about this yesterday, and one question that occurred to me is "What do other boaters do?". Most are smaller boats, and they always beach the boat bow onto the beach. Larger boats tie off to a mooring bouy if they can find one. :smt013

 

[Asureyez]

Delta Anchor

It seems to me the Delta was doing what it is designed to do. The trouble would likley be the shore is sloping down and in the direction fo the pull, thus horizontal keeps getting lower than the flukes and the pull is lifting the back of the anchor before its set.

Aso the sand is fluffy as opposed to being a wet slog as would be encountered on a bottom.

In typical bottoms, course sand as you are showing, the Delta or plow type would dig into the bottom to the stock and then just sit there and you're hooked. As the rode works with wind or current powered drag on the boat the anchor will dig in more and moreas long as the stock is essentially horizontal to the pull and the bottom. If the bottom falls away the anchor will skip out and drag until a more favorable condition is encountered.

I don't thinka Danforth/Fortress would do any better in the given exercise.

 

[Dave M.]

Re: Delta Anchor

If the bottom falls away the anchor will skip out and drag until a more favorable condition is encountered.

That is just what I am afraid of! That might well be over the dam which is downstream 10 miles. :smt089

Here is a small clip from a chart. I would like to anchor somewhere on either side of the point that sticks up. This is sand, and the mapping is decades old, but still relatively valid. Soundings are in feet.

From off the point, it looks like the picture below from the boat. Here the transom depth sounder is reading about 70 feet. Looks like a piece of cake. Just head to the beach and drop anchor!

I move in a little, and to the right, which is downstream. Now I encounter the sandbar that is not really shown on the chart. It extends in a straight line from the right side edge of the point on the chart, where the river current has put it. Here I am in about 3 feet of water, and can move no farther starboard or towards the beach. Too shallow. I can wade from here and put an anchor out in the water on the port side, which is mostly 2 to 3 feet deep. But I am only about 60 feet from where the picture above was taken, and the water depth was 70 feet. The prevailing westerly wind would try and blow the boat and the anchor from the 2 or 3 feet of water into 70 feet of water. Bye-bye boat :smt013

In reality, I am already familiar with the location, and know I can only approach the beach from the right side of the point on as seen on the chart above. This is the side where the current is moving right to left, and the prevailing wind blows from the beach to the water. So here I am in the next picture below looking at the beach from the upstream side. Depth at transom is 40 feet. So from the beach out, it is a nice quick slope down to 40 or 60 feet. Or 80?

Next picture below, moving in a bit, here I am getting pretty close. Depth at transom is now about 14 feet. I am laying claim to this small strip of beach! There is no way I am going to drop the Delta anchor in that under water slope, I know it will not hold there. So I will put the bow in the sand, and try and tie off to a strong bush, or make the Fortress work on the beach. With these anchoring conditions, I won't trust an anchor I can't see. Throwing the Delta up in the brush might hold, I have not tried that.

I know. long post, but that is the scenario.

 

[Dave M.]

I also did an anchor test again, this time with about 20 more feet of chain, which weighed 20 pounds. So I am now testing with about 35 pounds of chain, maybe 35 feet or so. I did not measure the length, and I had two fairly short pieces included, the original chain. The chain weight is significant.

This time I am about a quarter mile down stream from the pictures in the above post. The water is shallow, and I can't get clear to the beach with the boat, but it is warm enough to wade. So again, I put the Delta anchor up on the beach, and pull. It sets quite a bit more securely this time. At about 1000 RPM, the anchor pulls out, then resets again down in the water. But does not set hard enough I can't pull it again with less than 1100 RPM. It did make a nice deep furrow. With more chain, I think it might work in a 25 MPH wind.

Then I took the Fortress and put it on the beach. It is an FX-11, which I think is comparable to the Delta 14 lb anchor in it recommended use. Like it says in one of the links that Sea Gull posted, it pulled about 3 feet while burying itself. It is in the sand, on the end of the chain there. Next to it is the furrow the Delta anchor made.

Here is a side view. The beach is quite flat for a short distance here. By the way, when pulling the Fortess, I took the RPM up to 1400 in reverse. I stopped there, it was apparent the anchor was not going to come out with more RPM, without possibly breaking something first.

I dug down with my hands to find the end of the shank on the Fortress. It was a few inches under the sand surface.

 

[Dave M.]

So, you may be wondering which anchor is hanging off the bow of my boat. It is the Delta. It fits. And I am learning more about how to use it.

In one of the links that Sea Gull posted, they did some anchor tests. For a definition of 'set', they used the criterion that the anchor could withstand a pull of 200 lb horizontally and not move. These were the next larger size anchors, BTW. The anchors had sufficient chain that the pull was always horizontal, parallel to the flat bottom they somehow found (must be some other coast or something). There have been lots of comments about needing to use sufficient chain.

So, how much is enough? This was on my mind. My mental picture was of a chain, one end pulling horizontally on a point, from there curving upwards to the point the rode becomes line, then straight to the boat. Maybe there is no line, maybe it is all chain. Yes, assume that. It is chain, hanging from a point on the bow of the boat, connected at the other end to the anchor. Something is pulling on the boat to exert a pull of 200 lb on the anchor, which lifts the chain off the bottom, so it is horizontal at the anchor point only. And let's say the horizontal distance is 7 times the vertical distance.

That is when I realized what this is. It is a catenary. I figured someone had probably already figured them out, so found the link on the internet, and studied it a bit. It is not the full catenary as shown on the Wikipedia page, it is only the right half. But the left half is a mirror image, so it doesn't matter. The math still applies, you can start and end it anywhere.

So, with a bit of studying, I realized I was not going to solve for To. But I also realized I could use the 200 lb for To, and that the chain I had weighed about 1 lb/ft. So if I chose 'ft' as my unit length, I could easily find a. Then it's just a matter of making a spreadsheet, putting in a column for incremented values of 'x', and letting the spreadsheet find corresponding values of 'y'.

Then I made the weight per foot an entry in the spreadsheet too so I could see what happened when I changed it. So I played with different weight chains, and discovered that it is the total weight of the chain, not its length, that is important.

Here is some sample data. It is for 40 ft of 1 lb/ft chain, and a horizontal pull of 200 lb. It indicates I need a scope of 7:1 in order for the chain to just barely lay horizontal at the anchor. If the load increases, or the scope decreases, the chain will lift, and start to lift up on the anchor shank.

Note that the type or weight of the anchor is not relevant for this determination of the chain weight required and the scope required. The assumption in the chart is that the anchor is on a flat bottom, and will withstand a horizontal pull of 200 lb when set. The weight numbers scale, by the way. If you want to withstand 400 lb instead of 200 with the same scope, you need double the chain weight.


This modeling is telling me that I have been trying to use way too little chain on my Delta anchor, and that may be the real bottom line.

 

[Hampton]

Dude,

Just tie it to a tree.

 

[cr0ck1]

Dude,

Just tie it to a tree.

HAHAHAHAHAH>> LMAO!!!! :smt043

I have only been boating for a month now and anchor everytime i go out... ive learned that all you need is the BASIC anchor from the local marine store.. the claw type but not the small one the big one that cost aroung 40 bucks and it catches every time..


And if ever in doubt "Tie it to a TREE>> LOL"

 

[JeffM]

I may have missed your discussion of this, but can you drop anchor in the deeper water offshore and back into the beach, then set a Sand Spike or similar anchor into the shore (or tie it to a tree :grin: )? The drag on your Delta anchor would then be up-slope and you'd have a better bite into the sand.

Jeff

 

[Dave M.]

I may have missed your discussion of this, but can you drop anchor in the deeper water offshore and back into the beach, then set a Sand Spike or similar anchor into the shore (or tie it to a tree :grin: )? The drag on your Delta anchor would then be up-slope and you'd have a better bite into the sand.

Jeff

Jeff, that may be the best solution. I think with 35 ft of chain, the Fortress would hold. It did in the test I did above. I now have a much better understanding of how to know how much chain is needed.

Then I need to work out how I would do it in various wind conditions. For example, today the wind is supposed to be 20 to 30 MPH. It would be blowing away from shore, so would be blowing the boat away from shore when I was trying to set the anchor on shore. But that is manageable.

Tying to a tree is not a good option for me. In most cases I don't have enough line on board to reach the nearest tree.