How to Test Anchors?

[David M]

There are so many variables with anchoring that it is close to impossible to come up with a test that clearly defines which are the "best" anchors. What you clearly do not want is inferior metallurgy which is all you can definitely say about it.

You can drop the same exact anchor in the same place under the identical conditions with the same boat with the same rode with the same scope and get different results each time you drop the anchor....making testing results inconsistent.

Another factor is that the bottom is rarely homogeneous. This means that in many places you can drop the anchor 5 yards away and get different results.

The bottom line for me is to take anchor tests with a huge grain of salt.

[Adelie]

Originally Posted by capngeo

You wouldn't by chance work for the Federal Government would you?

Not a chance!!! Do you work for Wall Street?

I am a private construction inspector and a civil engineer.

The first gives me experience experience with materials testing, including soils, and testing apparatus. The second gives me a theoretical idea of what is going on with soils and it gives me an idea of the scope of the problem at hand.

This is a really big question, both in importance and in scope. That's why to really do good comparisons on anchors you would need a big set up.

I could see a much smaller setup for straight line testing, say 10x50x8, with fixed pulling equip. I could also see somewhat smaller basins with a shape that mimics the likely paths of an anchor. But to do a good job you are going to need a big setup.

The reality is that no one is ever going to do really good comparative testing like I described because the issue has too small a constituency for the Feds, too big a price tag for the NGO's like BoatUS, West Marine et al and the manufacturers don't have the money or the inclination to do testing that might put their products anywhere but at the top of the heap. This is just wishful thinking on my part, unless some individual or individuals with money and an interest comes along.

[zeehag]

i love engineerz but they tend to overthink easy stuff-- throw out that anchor, making certain the bitter end is tied to something other than yer foot, set it gooood, see if it drags. test done. ok did it work??-- pass...... if it didnt work-- fail, and sleep was lost, no sweat.

[Adelie]

Originally Posted by zeehag

i love engineerz but they tend to overthink easy stuff-- throw out that anchor, making certain the bitter end is tied to something other than yer foot, set it gooood, see if it drags. test done. ok did it work??-- pass...... if it didnt work-- fail, and sleep was lost, no sweat.

Is that the way you want the next plane you ride home to have been designed?

[GordMay]

Originally Posted by Adelie

... To prep the basin you would place 7' of the soil of your choice in it, then fill to the top with water. Now you have an underwater seabed. Air or water is pumped thru the pipes to thoroughly agitate the bottom. Now you have a uniform underwater seabed that can be recreated after each round of testing ...

Q: Wouldn’t that more likely result in aeration and air entrainment, than in agitation and mixing (to uniformity)?

[Auspicious]

Originally Posted by Adelie

Ahh, a man after my own heart, rigor in testing.

Thanks. I try. *grin*

Originally Posted by Adelie

The big problem I see is not the testing protocol, it is finding or creating repeatable conditions.

I agree that repeatability is important. To some extent that depends on the degree of homogeneity in the soil. I don't know what the horizontal and vertical variation is likely to be, thus one of the many reasons I'm looking for someone with expertise in saturated soils.

I like your idea of a known test site, but the cost provides a barrier to entry of my goal for anyone (pretty much) to contribute results. On the other hand, taking a number of cores and a step by step procedure for assessing characteristics would open up the opportunity for nearly anyone to do "certifiable" testing that can be compared to any other test. I'm quite out of my depth there, so I really do need the soils person.

Further, another real-world problem with your test-bed idea is that the uninformed will challenge the applicability of results. The rocks thrown at "theoretical" approaches--even if there is just a bit of analysis--is offputting.

[estarzinger]

Originally Posted by Auspicious

I agree that repeatability is important.

Since testing dynamic behavior will be essential for any "proper" test . .

We will need a wave making machine for the concrete testing tank.

And an oscillating (side to side and loading) rode driver - to simulate the dynamic wind behavior.

[Adelie]

Originally Posted by GordMay

Q: Wouldn’t that more likely result in aeration and air entrainment, than in agitation and mixing (to uniformity)?

Depends on the soil involved.

Gravels, no.
Sands, probably not.
Muds, seems likely.

In the case of mud it might be useful for the creation of a very soft mud. It may be that the passage of an anchor or the rode in front of it may disturb the mud enough to release the air and then you don't have the very soft mud that was the purpose of this test in the first place.

In the case that you want to get rid of the air the concrete vibrators would likely do the trick. It has occured to me that it may take several round with the vibrators to do the job. If the vibrators are automated that should be time consuming and a big user of electricity rather than a very daunting task.

I was just thinking it would be possible to 'plant' a bunch of polypro fibers in a small area of a tank to represent weeds for set testing. I don't know if it would be very representative but it would be worth a try.

[lancelot9898]

Originally Posted by estarzinger

We will need a wave making machine for the concrete testing tank.

Instead of the wave making machine I think the most practical way of testing would be to take a given "generic" size sailboat out to a mooring and actually measure the loads on the rode under some severe conditions. That loading would represent the base case and could be duplicated with a test rig such that force vs time and direction(three dimension) could be applied time and time again to the various anchor designs in the test facility. Not only x-y directional changes could be applied but vertical direction could also be factored to account for wave surges.

[estarzinger]

Originally Posted by lancelot9898

Instead of the wave making machine I think the most practical way of testing would be to take a given "generic" size sailboat out to a mooring and actually measure the loads on the rode under some severe conditions. That loading would represent the base case and could be duplicated with a test rig such that force vs time and direction(three dimension) could be applied time and time again to the various anchor designs in the test facility. Not only x-y directional changes could be applied but vertical direction could also be factored to account for wave surges.

agreed, good idea. More repeatable and analytical.

But we will need some load vector data from 50kts in a roadstead anchorage!

[zeehag]

as every anchoring ground is different and every anchorage has differing conditions, WHY NOT TEST IN REAL CONDITIONS??/ contrived conditions are just that-- contrived, and nothing like reality-- what hurt is it to go out and test in a real situation....then you KNOW what it will do....LOL

[Hydra]

Originally Posted by zeehag

as every anchoring ground is different and every anchorage has differing conditions, WHY NOT TEST IN REAL CONDITIONS??/ contrived conditions are just that-- contrived, and nothing like reality-- what hurt is it to go out and test in a real situation....then you KNOW what it will do....LOL

Yes, you will know the performance of an anchor in these condition but how will you know the conditions themselves?

You would need some measuring equipment to know accurately the sea state (directional energy spectrum), the current/tidal stream (speed & direction), the wind on the surface and at mast height (speed and direction in lulls and gusts), and the mechanical properties of the sea bottom.

You would also need some detailed information on the yacht: hull form, rigging, weight, inertia...

Alain

[Adelie]

Originally Posted by estarzinger

Since testing dynamic behavior will be essential for any "proper" test . .

We will need a wave making machine for the concrete testing tank.

And an oscillating (side to side and loading) rode driver - to simulate the dynamic wind behavior.

I don't see the need for a wave-making machine. Anchors on the bottom would be mostly beyond the direct effect of waves. Secondarily the shallow water allows easier observation of what is happening, at least at the seabed surface.

That is not to say that waves don't have an effect, they do, indirectly by varying the magnitude of the load in the rode and the direction of pull.

Varying the load should be pretty easy, the only question would be can the load be varied fast enough to approximate real world conditions? That's a big research project in and of itself, lining up a large variety of boats, putting a load cell in line with the rode and waiting for a storm you you can test the magnitude and rate of load change. At the same time you are going to want to attach an instrument package to the rode need the anchor to measure angle to the seabed or to horizontal.

The harder part is varying direction. If you assume constant wind direction then you are only looking at the oscilation of the boat sailing back and forth on the rode and the plunging of the boat vertically. Since all the directions average out over time you could build a straightline basin 100x15x8, and have a set of winches with lines that pull snatchblocks hooked over the rode and pull left-right-up-downabout halfway between the anchor and the main rode winch. This should allow you to cycle the direction up to 10-20 degrees either way on a period of 1-2sec. That would be fast for horizontal occilations and slow for vertical. This would involve building much smaller than normal basins (ie cheaper) and a bit more equipment (a bit more $).

The really hard part is occilating movement with a general veer at the same time, this would involve using a big basin. Given that the test car is on a radiused track having the car move back and forth to simulate oscilations with a general trend in one direction to simulate veering would not seem like a problem and I would expect the car to able to move fast enough to approximate real world cycle times. The hard part is creating the vertical movement when all of the seabed around you needs to remain free of obstructions so the anchor can drag through undisturbed soil. I can see a number of solutions that would involve a fair bit more engineering and cost.

[Adelie]

Originally Posted by zeehag

as every anchoring ground is different and every anchorage has differing conditions, WHY NOT TEST IN REAL CONDITIONS??/ contrived conditions are just that-- contrived, and nothing like reality-- what hurt is it to go out and test in a real situation....then you KNOW what it will do....LOL

Actually the contrived conditions are similar to reality, if not exactly the same.

And you want to test in contrived conditions because no one is going to be able to afford to have 5 identical boats loaded just the same, laying to 5 different anchors sitting and waiting for storms to come along. This assumes that you have a big enough area of seafloor for 5 boats that you know is EXACTLY the same for each boat's anchor.

By using contrived conditions you can do two things, make sure each anchor experiences exactly the same bottom conditions and loading as the other anchors and you can get results a lot faster. If you can test 1 anchor a day, this week you can do 5 anchors in this soil type. Next week you can test the same 5 anchors in a different soil. And the week after, and the week after,..... The trick is making sure the contrived conditions are similar to real world conditions you would find in various places, that's why you use different soils and use a variety of ways to get the soils to settle into place before testing the anchors.

[boatman61]

Throw em in the water... if they sink they're okay....