Videos of Anchors Setting

[Panope]

Here is the Fortress FX-16 at the sand/gravel site with 2.5 to 1 scope.

The anchor struggled to initially set and then failed to re-set on the course reversal test. The anchor became heavily fouled with vegetation, a small tree and various rocks including one rock that was jambed between the flukes.

Steve

Video #50

https://www.youtube.com/watch?v=czN9jHW5lAU

[cwyckham]

I love my Fortress and will have a Fortress on every boat that I ever buy. They are the ultimate kedge/stern anchor.

However, that video really illustrates why Danforth style anchors don't make a good bower anchor for regular use. They can foul and go from great holding to no holding very quickly. I've had it happen and so have 2 friends of mine all within the last 2 years on the PNW which typically has pretty good holding.

[Panope]

Chris, The Fortress is a keeper for me too.

Cheers,

Steve

[Hydra]

Video #49 shows the Fortress anchor "planing" after being dropped: it goes down slower than the chain and takes some time to reach the bottom. Then, it wouldn't be effective as a "brake", e.g. in case of engine failure.

For this reason, my own Fortress anchor is stowed in a locker, not to be deployed instantly.

Alain

[Panope]

Alain,

Note that my latest "side view" camera mount is quite large and presents a lot of hydrodynamic drag as the anchor is free falling.

Here is one of my earlier videos where I am still using the much smaller and more simple "down view" camera set up. The Idea for the test was to simulate an "emergency stop" using the 10 pound Fortress anchor. Boat was motoring ahead at a steady 3.6 knots. Rode consisted of nylon and only 12 feet of 5/16" chain.

I actually had to work hard to delay the anchor from contacting the seabed so as to demonstrate weather or not it would set "on the fly". I did this by paying out rode slowly. Tossing the rode overboard all at once would have had the anchor reach the bottom much sooner.

Certainly, at some speed of perhaps 5 knots or more, the anchor may "fly" indefinitely if the slack in the rode was taken out prior to the anchor reaching the bottom.

Then again, I am not sure if any anchor will reliably set if first contact with the bottom occurs at 5+ knots. I does sound like the makings of an interesting video, however.

Steve

https://www.youtube.com/watch?v=qtD4DBjjE0w

[Fortress]

Originally Posted by cwyckham

I love my Fortress and will have a Fortress on every boat that I ever buy. They are the ultimate kedge/stern anchor.

However, that video really illustrates why Danforth style anchors don't make a good bower anchor for regular use. They can foul and go from great holding to no holding very quickly. I've had it happen and so have 2 friends of mine all within the last 2 years on the PNW which typically has pretty good holding.

Of course, I very respectfully disagree. This test was using only a 10 lb anchor and with a 2.5:1 scope, which is quite a vertical pull and the anchor is only capable of burying minimally into the bottom.

Yes, debris can get stuck between the shank and fluke, and render these parts immovable and in the open position.....but then the Danforth / Fortress type becomes just like other anchors which also have immovable parts.

Brian

[Hydra]

Steve,
I didn't remember video #8. It shows that at 3.6kts, an FX16 anchor needs 3:1 scope to reach the bottom.

Yes, I would like to see the same test at 5kts! But I'm not sure it would be safe: if the anchors sets suddenly, the kinetic energy of the boat has to go somewhere. What is the energy absorption capability of the rode?

Alain

[cwyckham]

Originally Posted by Fortress

Of course, I very respectfully disagree. This test was using only a 10 lb anchor and with a 2.5:1 scope, which is quite a vertical pull and the anchor is only capable of burying minimally into the bottom.

Yes, debris can get stuck between the shank and fluke, and render these parts immovable and in the open position.....but then the Danforth / Fortress type becomes just like other anchors which also have immovable parts.

Brian

The test was an intentional torture test designed to push anchors to their limits. I don't really care if an anchor held or not in these conditions. The concern is more in the picking up of detritus and jamming. It's an inherent part of the design. I think the tree probably held the anchor up at an angle so it couldn't re-set.

I have to disagree with the idea that jamming open is fine and then the anchor is like other anchors. This is not the case if it's jammed and on its back. It isn't designed to turn over and will never set. Also, I find it's often the rode that jams or tangles in the anchor when the anchor hasn't been fully buried. The pull on the anchor is then all wrong and it won't set.

Again, I love the anchor, own one and am an ardent fan. I just don't like using Danforth style anchors for a primary.

[Panope]

Originally Posted by Hydra

Steve,
I didn't remember video #8. It shows that at 3.6kts, an FX16 anchor needs 3:1 scope to reach the bottom.

Yes, I would like to see the same test at 5kts! But I'm not sure it would be safe: if the anchors sets suddenly, the kinetic energy of the boat has to go somewhere. What is the energy absorption capability of the rode?

Alain

Total rode length for that test was 90 feet with 78 feet of it being 9/16" nylon available to stretch and absorb the energy. From my vantage point on the boat, the "jerk" was much more gentle than the sudden stops felt during the tests at slower speed (2 knots) but using all chain.

Perhaps someone with more knowledge on the subject can do a rough physics calculation to determine how much 9/16" nylon is needed to protect itself from overloading during a 5 knot emergency stop test (boat weighs 15,000 pounds).

Steve

[Fortress]

Originally Posted by cwyckham

I have to disagree with the idea that jamming open is fine and then the anchor is like other anchors. This is not the case if it's jammed and on its back. It isn't designed to turn over and will never set.

You have a valid point. On a separate comparison note, during the Chesapeake Bay soft mud testing, it was theorized after extensive observation that a roll bar anchor needs a solid surface in order to roll over into the fluke downward position.

Other immovable, non-pivoting fluke type anchors can also sink into soft mud and not right themselves if they land upside down or on their sides.

By contrast, with a pivoting shank & flukes, the Danforth / Fortress type has no upside down position, which is a definite benefit, particularly in that type of bottom.

[Snowpetrel]

Originally Posted by Panope

Total rode length for that test was 90 feet with 78 feet of it being 9/16" nylon available to stretch and absorb the energy. From my vantage point on the boat, the "jerk" was much more gentle than the sudden stops felt during the tests at slower speed (2 knots) but using all chain.

Perhaps someone with more knowledge on the subject can do a rough physics calculation to determine how much 9/16" nylon is needed to protect itself from overloading during a 5 knot emergency stop test (boat weighs 15,000 pounds).

Steve

I don't assume I have more knowledge of physics than you Steve, but I'll give it a go since nobody else has stepped up.

Using some very very rusty physics and with the assistance of Wikipedia and google...

Convert to si units and round to make numbers easy.

Panope 7000kg
3.6 kn=1.8m/s
5.0 kn=2.6m/s
14mm nylon approx 4000kg=400000N


Stretch in nylon very approx
25% load=10% stretch
50% load=20% stretch
78 feet of nylon=24 meters

Assume Anchor sets instantly and holds all the load.

Ignore scope effects and any chain.

So the kinetic energy of Panope in the 3.6 knot example is

1/2*7000*1.8^2=11340 joules

Rode at 25%load gives 2.4m stretch assuming it stretches linearly.

So we get something like
1/2*10000N*2.4m=12000 joules, so the 3.6knot stop should have loaded the rope to less than 25% of break load, and probably much less, due to the anchor slipping, and setting.

At five knots the kinetic energy is more like
1/2*7000kg*2.6m/s^2=23660J

15% stretch gives us 1/2*15000N*3.6m=27000 joules, more than enough to stop her, but we are getting up towards 40% breaking strain. Too much for safety I think. Peak loads are around 1.5 tonnes

If we doubled the line length. Call it 50m, then we get back into the 25% of break zone.

1/2*10000N*5m=25000Joules, this should be enough to stop her, with maximum loads no more than the 3.6 knot test with 24 meters of rode. Peaks loads around 1 tonne.

These numbers SEEM reasonable to me, but it's late, and I haven't looked at any of this stuff for years, so any real experts better chip in with a yay or nay to my very simplified calculation. I would welcome any corrections.

Sent from my HTC_0PCV2 using Cruisers Sailing Forum mobile app

[Panope]

Thanks a lot SnowP,

I am more likely to do my critical engineering calculations with a hammer but in this case, the calculator was more appropriate. Your conclusion matches my gut feeling: the 9/16" nylon would probably survive the 5 knot test, but would be pushing it a bit. If I proceed with a 5 knot test, I'll use my 5/8" rode.

Steve

[cwyckham]

Originally Posted by Fortress

You have a valid point. On a separate comparison note, during the Chesapeake Bay soft mud testing, it was theorized after extensive observation that a roll bar anchor needs a solid surface in order to roll over into the fluke downward position.

Other immovable, non-pivoting fluke type anchors can also sink into soft mud and not right themselves if they land upside down or on their sides.

By contrast, with a pivoting shank & flukes, the Danforth / Fortress type has no upside down position, which is a definite benefit, particularly in that type of bottom.

Yes, interesting point. Very soft mud is certainly a situation where I would consider using a Danforth style anchor as a primary. Also in any situation where I knew there were both few rocks to jam the flukes, and I could guarantee that I would get full burial of the fluke with reverse power during setting.

I should restate that: I would consider using a Danforth style anchor any time that I could guarantee I could get the stock to bury and wouldn't jam the flukes. I'd still need to have other compelling reasons such as weight or space, though.

In the special case of very soft mud, then a Danforth styly would be my preference, based on your excellent data in those conditions and the virtual guarantee that I won't foul the anchor.

In all other cases, I prefer to carry it as a back-up and kedge/stern anchor only.

That's not such a bad thing. If 100% of kedges are Fortress and all the other brands battle it out for primary anchors, is that such a bad position to be in?

[Hydra]

Originally Posted by Snowpetrel

I don't assume I have more knowledge of physics than you Steve, but I'll give it a go since nobody else has stepped up.

Using some very very rusty physics and with the assistance of Wikipedia and google...

Convert to si units and round to make numbers easy.

Panope 7000kg
3.6 kn=1.8m/s
5.0 kn=2.6m/s
14mm nylon approx 4000kg=400000N


Stretch in nylon very approx
25% load=10% stretch
50% load=20% stretch
78 feet of nylon=24 meters

Assume Anchor sets instantly and holds all the load.

Ignore scope effects and any chain.

So the kinetic energy of Panope in the 3.6 knot example is

1/2*7000*1.8^2=11340 joules

Rode at 25%load gives 2.4m stretch assuming it stretches linearly.

So we get something like
1/2*10000N*2.4m=12000 joules, so the 3.6knot stop should have loaded the rope to less than 25% of break load, and probably much less, due to the anchor slipping, and setting.

At five knots the kinetic energy is more like
1/2*7000kg*2.6m/s^2=23660J

15% stretch gives us 1/2*15000N*3.6m=27000 joules, more than enough to stop her, but we are getting up towards 40% breaking strain. Too much for safety I think. Peak loads are around 1.5 tonnes

If we doubled the line length. Call it 50m, then we get back into the 25% of break zone.

1/2*10000N*5m=25000Joules, this should be enough to stop her, with maximum loads no more than the 3.6 knot test with 24 meters of rode. Peaks loads around 1 tonne.

I made a similar computation (was at work while Snowpetrel typed) and arrived at a similar result: 18m of 9/16" rode for 3.6kts initial speed and 34m for 5kts, neglecting the braking effect of hydrodynamic drag and assuming no thrust from the propeller, considering a linear stretch for Nylon and maximum admissible stress 30% of breaking.

If admissible stress 25% of breaking, I find 23.3m for 3.6kts.

Alain

[Fortress]

Originally Posted by cwyckham

Yes, interesting point. Very soft mud is certainly a situation where I would consider using a Danforth style anchor as a primary. Also in any situation where I knew there were both few rocks to jam the flukes, and I could guarantee that I would get full burial of the fluke with reverse power during setting.

I should restate that: I would consider using a Danforth style anchor any time that I could guarantee I could get the stock to bury and wouldn't jam the flukes. I'd still need to have other compelling reasons such as weight or space, though.

In the special case of very soft mud, then a Danforth styly would be my preference, based on your excellent data in those conditions and the virtual guarantee that I won't foul the anchor.

In all other cases, I prefer to carry it as a back-up and kedge/stern anchor only.

That's not such a bad thing. If 100% of kedges are Fortress and all the other brands battle it out for primary anchors, is that such a bad position to be in?

Chris,

No, its not, but let's also not forget about having a disassembled, stored below deck, at-the-ready, over-sized Fortress for deployment as the "ultimate storm anchor" when severe storm conditions are threatening!

Be safe,
Brian