Would a custom anchor be an option?
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Hi All,
I've been designing a farm for a while and the anchors should be sized approximately 200lbs, my question is could I use custom cement or steel anchor somewhat shaped like an urchin. I attached an image with a rough sketch for reference. The depth of the site is between 25 and 40 feet and mostly sandy bottom with sporadic rock cropping. Would something like this have that kind of holding power?
Regards!
ruanr,
A lot of thought has gone into the design of present day anchors. There is no reason to ignore the progress that's been made in holding power vs. weight. What you are describing is basically a dead-weight anchor, the holding power of which is based on its underwater weight, less any upward pull from your anchor line, times some friction coefficient that depends on the material and the type of bottom.
200 ponds of concrete loses 43% of its weight when submerged. The friction coefficient of concrete on mud is approximately 0.70, so even if the pull is horizontal, you only have 80 pounds of holding
power. A block of steel loses less weight under water, but suffers from being more slippery.
You really need to look to shape to be efficient in holding power and that's where drag-embedment anchors come in. Present day anchor designs can provide 10 to 50 times their weight is holding power and when properly set, are a pretty dependable way to protect your farm investment. There are lots of options from yacht-type anchors to commercial-grade plow anchors. Here is one that has worked well on kelp farms. Check out: https://www.tendocean.com/prod...
Cliff cliff@cagoudey.com
@clifford_goudey - I like the idea of utilizing a steel anchor design, but since you're dealing with such a shallow depth, and the natural bottom is sandy/muddy bottom type, why not drive a steel pile or a timber pile 15' below the mudline and anchor your chain through the timber/steel pile? Just a thought.
Nathan,
I view 25-40 feet as fairly typical of East Coat site depths. Regardless, a steel or timber pile would probably work fine if you have the infrastructure to drive it to refusal in those depths. However, you need to be sure it is strong enough in bending to withstand the side loads.
Cliff
@ruanr_macedodonascimento -Hi, I needed something quick and dirty for a temporary job so I made this.. I wouldn't trust it for anything really important but it did the job for what I needed. 5 gallon bucket with 60# of concrete (as Cliff says, concrete loses 40+% of it's weight in water) plus about 50# of rocks in the bucket and 15' of 3/8 chain. I put two 4' pieces of rebar into the bucket so they stuck out on 4 sides similar to what you're looking for. It did the trick on the cobble substrate in swift current versus just the bucket that rolled around. Again, I would not use this for anything valuable or permanent
Mike,
Chain and a deadweight anchor seems an odd combination. Better to simply make the mass of concrete bigger and use a buoyant line, at least at the bottom. In that application, chain or sinking line is a sure-fire way to get things wrapped around the block at the change of tide.
Better to simply pour a stiff mix in a pile and embed a few links of very heavy chain that engage an X of rebar. Pour it on a bed of gravel or crushed rock so the lower surface is rough.
Getting a foothold in that bottom will be challenging. A lot depends on what's underneath that first layer of cobble. A driven pin may be the best alternative.
Cliff
Mike,
Chain and a deadweight anchor seems an odd combination. Better to simply make the mass of concrete bigger and use a buoyant line, at least at the bottom. In that application, chain or sinking line is a sure-fire way to get things wrapped around the block at the change of tide.
Better to simply pour a stiff mix in a pile and embed a few links of very heavy chain that engage an X of rebar. Pour it on a bed of gravel or crushed rock so the lower surface is rough.
Getting a foothold in that bottom will be challenging. A lot depends on what's underneath that first layer of cobble. A driven pin may be the best alternative.
Cliff
@clifford_goudey - I like the idea of utilizing a steel anchor design, but since you're dealing with such a shallow depth, and the natural bottom is sandy/muddy bottom type, why not drive a steel pile or a timber pile 15' below the mudline and anchor your chain through the timber/steel pile? Just a thought.
Nathan,
I view 25-40 feet as fairly typical of East Coat site depths. Regardless, a steel or timber pile would probably work fine if you have the infrastructure to drive it to refusal in those depths. However, you need to be sure it is strong enough in bending to withstand the side loads.
Cliff