Videos of Anchors Setting

[noelex 77]

At average depths and scopes, yawing has little impact on the chain angle to the anchor.

Most boat GPS units are located close to the stern, which greatly exaggerates the apparant swing radius due to yaw. The anchor chain is led from the bow and the lateral movement is only small in this location. The change of angle at the anchor end from the boat yawing is only very small. If you get a chance dive and take a look.

The boat will tend to yaw when exposed to stronger gusts and this is when the anchor is under the most force especially as the yaw induces a higher drag coefficient. For this reason is worthwhile minimising the yaw, but unless you are anchored in shallow water do not be concerned that the anchor will experience a significant change in direction of pull.

Below is typical plot corrected for the bow position (rather than stern). Note how the yacht is yawing at a very significant angle but the angle of the anchor chain is completely unchanged. The anchor will not be experiencing any sideways pull despite the yaw.

[wsmurdoch]

John H. Knox did some work with anchors dragging slowly which he called "ploughing" that seems to look into the same mode of dragging that Panope is investigating with the UHMWPE rode and cycles of pulling and resting.
https://static1.squarespace.com/stat...Owner-2002.pdf
page 8, "Holding Power and Speed of Drag".

[Panope]

Originally Posted by fugue137

Hi Steve!

Stretching a spring increases tension. So with a stretchy rode, I believe that whenever the tension on your gauge is decreasing, then the anchor is moving... as long as anything hygroscopic (e.g. nylon) is saturated.

And as long as the boat isn't coming down off a wave... more below...

"a bit" is right! I'd like to try to put a number on that... somebody please check my math!!

My apologies---I've forgotten what size dyneema you're running.

3/8"

Just guessing wildly (and using only 1 significant figure), you might get up to around 5% of breaking strength? At 5%, dyneema might stretch 0.2%. In 50 m of line,

120 meters is typical

that's 10 cm of stretch between full load and zero load, so probably half of that between the peaks and troughs you're seeing. The timescale of the spring's response will be quick for the side attached to the test anchor and slower on the deadman side due to inertia and fluid mechanics of the test boat. If you take in 2 cm of line on 50 m of 10-mm dyneema, you increase the force on the anchor by 100 kg.

I'd expect a boat like that (~10 m^2 waterline area?) to sink 1 cm for every 100 kg of load

Yes, I guesstimated 500 pounds per inch

(given my ballpark estimates, close enough to 800 kg of tension at 8:1). Is that about right? That's equivalent to around 1 mm rode elongation. The inertial and fluid damping will be high, so I'm thinking the timescale will be seconds, but I'm not sure how that will affect the measurement...

Incidentally, a ground swell of 10 cm should change the tension at the anchors (still assuming 50 m of 10mm dyneema) by 50 kg. This may make it difficult to get good readings at any of your ocean test sites.

All my test sites are inland and protected from ocean swell. In the small wind chop, the bow lifts (mostly) in unison with the stern lowering. Impossible to know how much the "total" boat is moving up or down


Yes, that's a very good point and reminder. Just---the above reasoning is me wondering whether this protocol tends to measure dynamic drag rather than holding power. They may be similar (identical?) in seabeds that don't compact? I don't know.


Thank you! Obviously I'm pretty excited about your work. Keep it up!!

There is no stopping now!

Steve

[Panope]

Picked up another Bruce to add to the other 4. I Should be able to settle the "Bruce scaling" theory once and for all.

50kg/110lb. ($150, Craigslist)

Weather looks good for testing tomorrow.

Was a real struggle loading on to the roller.

[Uncle Bob]

Originally Posted by Panope

Picked up another Bruce to add to the other 4. I Should be able to settle the "Bruce scaling" theory once and for all.

50kg/110lb. ($150, Craigslist)

Weather looks good for testing tomorrow.

Was a real struggle loading on to the roller.

Now that will get some chuckles down at the ramp.

[Panope]

Originally Posted by Uncle Bob

Now that will get some chuckles down at the ramp.

Their expressions might be more interesting than the anchor test!

[Panope]

https://www.youtube.com/watch?v=R666LAqB1IM

[Pelagic]

I don't know if Steve has ever tested a "Quick Link" or Boomerang bar on seabed anchor performance .

Curious when you have a 180° breakout and recovery, if it helps or hinders?

Anchor Right Australia introduces, the innovative Flip Link - Anchor Right Australia

Video
https://www.facebook.com/groups/sail...4162/?sfnsn=mo

[fxykty]

Originally Posted by Pelagic

I don't know if Steve has ever tested a "Quick Link" or Boomerang bar on seabed anchor performance .

Curious when you have a 180° breakout and recovery, if it helps or hinders?

Anchor Right Australia introduces, the innovative Flip Link - Anchor Right Australia

Video
https://www.facebook.com/groups/sail...4162/?sfnsn=mo

We recently bought a Sarca Excel and with the high shank and weighted tip I can’t imagine any situation where it wouldn’t flip itself to the correct position for sitting in the bow rollers. Same for our previous Spade. Perhaps they’re needed for a rollbar anchor such as their Super Sarca, and the other rollbar anchors? Why add another link to your rode if not absolutely necessary?

Another weird thing I’ve noticed with our chain. We have grooved bow rollers that keep the chain links aligned and we start out with no twists in the chain between the stored anchor and the windlass. But when we hoist the anchor the chain is often twisted early on the retrieve, then somehow comes straight again by the time the anchor comes up through the bow rollers. We have no swivel.

[Pelagic]

Originally Posted by fxykty

We recently bought a Sarca Excel and with the high shank and weighted tip I can’t imagine any situation where it wouldn’t flip itself to the correct position for sitting in the bow rollers. Same for our previous Spade. Perhaps they’re needed for a rollbar anchor such as their Super Sarca, and the other rollbar anchors? Why add another link to your rode if not absolutely necessary?

Another weird thing I’ve noticed with our chain. We have grooved bow rollers that keep the chain links aligned and we start out with no twists in the chain between the stored anchor and the windlass. But when we hoist the anchor the chain is often twisted early on the retrieve, then somehow comes straight again by the time the anchor comes up through the bow rollers. We have no swivel.

Simple reason for chain untwisting upon retrieval .
Once anchor is off the bottom, it spins and unwinds any twists that your gypsy kept pushing towards the anchor
I never use swivels for that reason

[rslifkin]

Originally Posted by fxykty

We recently bought a Sarca Excel and with the high shank and weighted tip I can’t imagine any situation where it wouldn’t flip itself to the correct position for sitting in the bow rollers. Same for our previous Spade. Perhaps they’re needed for a rollbar anchor such as their Super Sarca, and the other rollbar anchors? Why add another link to your rode if not absolutely necessary?

I have a similar thought. My Vulcan will self-orient just fine if it comes up sideways, but if it's perfectly backwards it won't flip. That might just be my roller setup though, where it would hit the underside of the pulpit before coming up enough to rotate. So if it comes up backwards, I just poke it with a boat hook right before pulling it onto the roller. That's enough to spin it sideways, then it can orient properly on its own.

[thinwater]

One of the most common reasons for the anchor coming up backwards is motoring forward during recovery. Most roll bar anchors strongly align with the water flow, which flips them fluke-aft. Either stop or drift back... or fight with twist.


I haven't used a swivel for many years and it always comes up right, in part because I don't motor forward until the anchor is clear of the water.

[rslifkin]

Originally Posted by thinwater

One of the most common reasons for the anchor coming up backwards is motoring forward during recovery. Most roll bar anchors strongly align with the water flow, which flips them fluke-aft. Either stop or drift back... or fight with twist.


I haven't used a swivel for many years and it always comes up right, in part because I don't motor forward until the anchor is clear of the water.

Agreed, that definitely makes a difference. In my case, it's not an issue if I'm only using chain, but once I get to the rope portion of my rode, it's hit or miss which way the chain will orient when the splice comes back in. So it's therefore a bit random which way the anchor will orient after feeding the splice through. Sometimes it's correct, sometimes it's backwards, sometimes it's sideways.

[Pelagic]

Originally Posted by thinwater

One of the most common reasons for the anchor coming up backwards is motoring forward during recovery. Most roll bar anchors strongly align with the water flow, which flips them fluke-aft. Either stop or drift back... or fight with twist.


I haven't used a swivel for many years and it always comes up right, in part because I don't motor forward until the anchor is clear of the water.

Interesting observation that I'd never thought about.

On Superyachts, my practice , if sea room allowed was to always slowly back away from point where anchor lifts from bottom in a slow curve until the stern finds the wind.

This helped in cleaning the mud off the ground tackle and kept the muddy high pressure spray from blowing on to white hull.

Without realizing, it also helped to align the anchor.

[Panope]

https://www.youtube.com/watch?v=OkNTM4LNXtc