Who is Richard Macfarlane? Here is his anchoring advice...

[rslifkin]

Originally Posted by Pete7

Its the bit "over factory recommendations" that I am not sure about. During the winter lock down I have been watching Steve Goodwin's videos on anchors setting as I suspect have many with interest. What I was interested in is not the absolute holding power, but the holding achieved in average conditions that he was able to replicate pull after pull. As he noted in one review, the holding power is approaching the load a yacht would see in a TS, if this was an appropriate size of anchor. Rocna size the anchor for 50 knots of wind, that will do for me, but happy to accept others might want larger for a particular reason, a cat for example.




Leading on from the numbers Steve Goodwin was seeing, this made wonder about dropping from 45m of 8mm chain down to 6mm chain. Minimum breaking loads (MBL) for G40/43 is about 4.4T for 8mm and 2.4T for 6mm. If the maximum load generated by an anchor is 1000kgs, why not 6mm chain and then have 60m for 20% less weight than 45m of 8mm chain? The only thing stopping me is a change of windlass is needed as 6mm Gypys aren't available for mine.

Pete

In my mind, the reason to go bigger isn't for more holding power under decent conditions (unless you want to go through a hurricane). But going bigger means you have a better shot at having enough holding power in a crap bottom. And in a good bottom, you have more excess holding power, meaning you can afford to give up more with shorter scope, so you can anchor in a tighter spot if the conditions are at least halfway decent.


A bigger / heavier anchor should also do a better job of pushing through weeds and other crap, so it might be able to set well in a spot where a small anchor can't.

[Pete7]

Yes I can see that has merit.

I went back and watched the video again so edited my post. This all happened in no more that 25 knots and could have been a difficult spot to anchor, though the beach does look very sandy and they all chose the same spot.

Pete

[OneKoolCat]

I am trying to digest the discussion so please excuse my ignorance I have been l living with it for years.

Aren't the catenary curve calculations describing the the curve of the chain under its own weight with no external force acting on it? When setting the anchor I see the chain straighten out and then when I drop power it relaxes into a catenary.

My dad always said the scope let out is so when the wind straightens out your rode your anchor can still bite. As the forces acting upon your boat increase that chain approaches a straight line. Yeah, I probably let out too much chain.

[boat driver]

you all bored? arguing over historical variables that there is no correct answer?
The system: anchor, chain, nylon line, snubber, windless are all part of the program.
Short stay for calm weather, make for a longer stay when weather kicks up. Then shorten back when weather passes. You all staying in them big anchorages have the pleasure of taking up space, but in narrow and smaller anchorages the system must ADEPT.
The biggest focus on a properly set anchor is simply reducing the surging. If your vessel sails a great deal, try a hammerhead more, if it rides up and back, try a stern short anchor or heavy chain, if it needs more rode and less space, try moving the lead back 15% from one side of the bow. Be amazed how that will reduce sailing and other surging issues. Last , to much anchor out can potentially exceed the strength of the chain during an event that the anchor should have pulled out.
Sometimes dragging the vessel is a designed method of riding out a storm when conditions dictate (particularly in a running seaway)

[rslifkin]

Originally Posted by boat driver

Last , to much anchor out can potentially exceed the strength of the chain during an event that the anchor should have pulled out.

If that happens, the chain is undersized for the boat. Basically, you have to look at the worst conditions you're designing for and size the chain to the expected loads the boat will place on it in those conditions. It doesn't matter if the anchor can hold 10 times that under good conditions if the boat will never pull hard enough to hurt the chain.

[Mike OReilly]

I didn't realize anyone was arguing. The main point of my little graph was to show that in the depth range most people anchor in most of the time, all the approaches provide similar rode-length answers; not identical, but similar.

They're all just simple rules of thumb, and seem to give a reasonable number. It's not like there's only one right answer here.

[DocHolliday]

Originally Posted by OneKoolCat

...Aren't the catenary curve calculations describing the the curve of the chain under its own weight with no external force acting on it? When setting the anchor I see the chain straighten out and then when I drop power it relaxes into a catenary.

As a practical matter, the chain / cable / wire / rope becomes roughly "straight", but according to the math and physics, a flexible horizontal element always follows a catenary, however flat. That's because gravity always is pulling the element downward....there are equations to calc a cathenary with applied linear force.

[Kim Klaka]

Originally Posted by UFO

Thought I'd throw the cat among the pigeons on a slow day


"The traditional chain scope calculation, using a simple multiplier, is not correct due to the curvature of the chain. 15m (50ft) plus double the depth is better calculation. But always put out more chain in challenging conditions."

To answer the question in the title "Who is Richard Macfarlane?":
Richard is a mechanical engineer who established the boatbuilding and design company Windrush Catamarans in Western Australia in the 1970s. He and I conducted some anchor trials last year, the results of which have been published in
Klaka K. (2020) “The Loads on Yacht Anchor Rodes”. International Journal of Maritime Engineering v162 part A4 pp 453-459.
There is also a Youtube video of a joint presentation Richard and I did last year, viewable at

https://www.youtube.com/watch?v=KVV0...3GpnEj&index=3

[Searles]

Chain in the locker never saved a boat,more is always better ,within reason , plus of course you will also carry at least one spare anchor and rode ,even if only going out over night .⚓️⛵️

[UFO]

Originally Posted by Kim Klaka

To answer the question in the title "Who is Richard Macfarlane?":
Richard is a mechanical engineer who established the boatbuilding and design company Windrush Catamarans in Western Australia in the 1970s. He and I conducted some anchor trials last year, the results of which have been published in
Klaka K. (2020) “The Loads on Yacht Anchor Rodes”. International Journal of Maritime Engineering v162 part A4 pp 453-459.
There is also a Youtube video of a joint presentation Richard and I did last year, viewable at

Thanks for the info

[Chotu]

Including the catenary is a mistake.

Catenary is at maximum with no wind or current.

When you need the anchor to really work, the catenary is almost zero.

[Lodesman]

Originally Posted by OneKoolCat

Aren't the catenary curve calculations describing the the curve of the chain under its own weight with no external force acting on it?

Originally Posted by Chotu

Catenary is at maximum with no wind or current.

Under its own weight alone, the chain hangs straight down and the remainder of chain horizontal on the sea-floor. There is no catenary at all in this condition.

[Lodesman]

Originally Posted by longjonsilver

However what he didn't say is that the chain is the poorest use of the weight - lighter chain and heavier anchor is my belief....

What do you base this on? Empirical testing? Pet theory? I'd like to hear the logic behind this.

[barnakiel]

Because so few boats today use rubber chain, the calculation must be reverse-engineered.


Say we have 30 meters of chain. Minus 15, divided by two : our maximum anchorage depth is 7 meters.


Roger roger?


barnakiel

[Chotu]

Originally Posted by Lodesman

Under its own weight alone, the chain hangs straight down and the remainder of chain horizontal on the sea-floor. There is no catenary at all in this condition.

Figured i didn’t need to explain this in excruciating detail. Of course, it’s the cruisers forum, so people will always get it wrong.

“No wind or current” is a relative term in my post. Not an absolute term.

Duh. Of course is there is absolutely zero force the chain if it is dangling. Who would think otherwise??? Why would we even be discussing that condition?

I’ll just copy and paste my post back in here:


Including the catenary is a mistake.

Catenary is at maximum with RELATIVELY no wind or current.

When you need the anchor to really work, the catenary is almost zero.

Which was the point!!!!