Lewmar Epsilon

[Neeves]

Jonathan, have a look at the estimated holding power listed on the Viking website. If any figures will convince you these should, given your close association.

The increase in weight from the smallest Viking 5 model to the next size up is 53%, but the estimated holding power jumps by 80%.

The next model up increases in weight by 83%, but the estimated holding power increases by 111%.

The next model up increases in weight by 33%, but the estimated holding power increases by 37%.

The next model up increases in weight by 69%, but the estimated holding power increases by 23%.

The next model up increases in weight by 28% but the estimated holding power increases by 41%.

If we look at the total Viking range the largest anchor is 8 times heavier than the smallest anchor, but the larger anchor has 9 times the estimated holding ability according to the manufacturer.

Frankly I am skeptical of this manufacturer’s figures, particularly as there is no reference to the type of substrate or how these estimates were made, but nevertheless this manufacturer (like the other anchor manufacturers) believes that if you increase in anchor size by doubling the weight the estimated holding power doubles or more than doubles.

Do you have any data or test results or anything at all that supports your contention that if an anchor’s weight is increased by 60% the holding power will increase by 30% or 25%. If so, could you please post a link.

I'm not an anchor maker and unlike some I don't spruik specific anchors - if you want an answer to your question I suggest you contact Viking. As far as I know Viking test all their anchors for hold - in sand.

But one comment.

It is impossible for an anchor maker to accurately scale their anchors. Steel plate comes in specific thicknesses and when you scale an anchor the scaling of the plate needed might not 'fit' the available plate thickness.

I would not compare scaling using the smallest anchor as being an accurate copy of the largest - the issues of plate size are greatest with the smaller anchors. For example a 1,400 MPa steel from Bisalloy is available from 6mm and up - the smallest anchor might only demand 3mm plate. If you want a 2050MPa steel then the minimum size is 12mm - you can make a big anchor, because the fluke might be 12mm thick - but how do you make a smaller one. You could use a less strong steel - but then the fluke will need to be thicker - and the anchor will not have as good a hold - because greater fluke thickness resists penetration.

If money was no object you could have a range of steels with different tensile strengths and plate thicknesses to better accomodate scaling - but who is going to pay for the stock....


Its not easy being an anchor maker - and made worse in a war zone.

We have the same issues when we choose our sheets - we don't need the strength of thicker rope - but we do need the ability to handle it - so we oversize. You do exactly the same - but forget to extrapolate for an anchor maker.

Jonathan

 

[noelex]

This is another example of questionable data.

A 15kg Rocna has been consistently tested to hold 2,000kg in clean sand, in common with Spade, Excel, Epsilon, and Supreme

This is often repeated on this forum, but it is misleading and needs correcting.

This subject is a little off topic for this thread that should be about the Episilon anchor, but nevertheless it is an important subject, so I have started a new thread here:

The 2000 kg holding myth

 

[boomerangben]

I would be interested to see what (if any) correlation there is with perimeter of fluke. However I suspect holding is dependent on a mix of weight, area and perhaps perimeter. Let’s not forget that holding is entirely dependant on the structural failure of the soil that anchor is working on. Only by understanding soil mechanics can we get to the bottom of how anchor holding really works and what the relationship there is between anchor physical properties and holding power.

Edit: Consider digging up your garden: if you plunge a spade into the lawn and lever out a lump, the shape of the plug of soil is unlikely to be shape of the spade. The shape of the lump give the area of soil that has failed, which dictates (along with the strength of the soil) how hard it was to get the lump out. The bigger the area of soil failure, the harder it is to dig, or the better the anchor holds. Digging with a digging fork in undisturbed ground is not necessarily easier in proportion to the area of the tines vs spade area. Yes once you have broken the soil, the fork holds much less weight of soil, but the whole point of secure anchoring is not to allow the soil to fail. End edit

If we all knew what our vessels need in terms of holding power (balanced by the probability profile of conditions experienced) then we could choose an acceptable anchor. But with the mix of substrate variability, affordability, attitude to risk and environmental conditions, there is no one correct answer.

I would be interested to know what stresses are placed on anchors. I find it really hard to believe that high tensile (ie high cost) steel of more 355 grade is really needed for flukes, shanks perhaps a bit stronger but UTS of 2050MPa……. I would definitely not fancy paying for that

 

[Neeves]

I would be interested to see what (if any) correlation there is with perimeter of fluke. However I suspect holding is dependent on a mix of weight, area and perhaps perimeter. Let’s not forget that holding is entirely dependant on the structural failure of the soil that anchor is working on. Only by understanding soil mechanics can we get to the bottom of how anchor holding really works and what the relationship there is between anchor physical properties and holding power.

Edit: Consider digging up your garden: if you plunge a spade into the lawn and lever out a lump, the shape of the plug of soil is unlikely to be shape of the spade. The shape of the lump give the area of soil that has failed, which dictates (along with the strength of the soil) how hard it was to get the lump out. The bigger the area of soil failure, the harder it is to dig, or the better the anchor holds. Digging with a digging fork in undisturbed ground is not necessarily easier in proportion to the area of the tines vs spade area. Yes once you have broken the soil, the fork holds much less weight of soil, but the whole point of secure anchoring is not to allow the soil to fail. End edit

If we all knew what our vessels need in terms of holding power (balanced by the probability profile of conditions experienced) then we could choose an acceptable anchor. But with the mix of substrate variability, affordability, attitude to risk and environmental conditions, there is no one correct answer.

I would be interested to know what stresses are placed on anchors. I find it really hard to believe that high tensile (ie high cost) steel of more 355 grade is really needed for flukes, shanks perhaps a bit stronger but UTS of 2050MPa……. I would definitely not fancy paying for that

I used 2050MPa as an example - its the extreme I found. I'm not aware of anyone using it for an anchor. It would be difficult to work and need some pretty hefty kit if there was a need to bend/fold.

If you think of a Fortress, its effectively all fluke, or 2 flukes. Each fluke is strengthened along its length by the right angled fold down one side. You could engender strength in a plate by making the plate thicker - but a thick plate, like a thick shank, resists burial. Those side pieces do not contribute to hold. Knox has a flange underneath the fluke, and a similar right-angled flange to support the fluke. Viking and Odin, also all fluke, the fluke is simply a flat plate, very thin (comparable in thickness to a Fortress fluke) but given strength by using a HT steel. They could have used less strong steel and a flange welded down the centre, either side of the shank - but its extra metal that does not contribute to hold. Other anchors, like Spade and Excel have a ballast chamber that offers strength to the fluke - but the primary reason for the ballast is to encourage initial setting and the extra steel used for the chamber (and the ballast itself) does not contribute to hold. Rocna uses a thick steel fluke, some of the weight is for ballast some is to give the fluke strength.

The fluke needs to be strong enough to resist the shear strength of the seabed. You can strengthen by extra fillets of metal (no contribution to hold), thicker plate (resists seabed penetration) or stronger plate - maximises the size of the surface area/volume of the plate.

Jonathan