Anchor Geekdom

Panope

Super Anarchist
1,446
609
Port Townsend, WA
Great info, Steve. I plan to have my boat on the hard for some (extensive) glass work in the next 12 months or so and will happily lend you my 85# Mantus if you want to test it.
Thanks Istream. I am very interested in testing your Mantus. Panope will be going on the hard as well for a few months so we had better act fast (before Thanksgiving) unless we wait until spring.

Your Mantus is so large and high holding power that Panope may be unable to properly set the anchor. Some theorize that this is a problem so a test would be good.

Steve

 

Norse Horse

Super Anarchist
4,987
546
The Rock
Norse, I guess it was a Lewmar "Delta" that you lost? I'd like to test one as they do have a less than stellar reputation.

Steve
Yes, this one here.

I also read that Mark Bay in Nanaimo is closed to anchoring to protect the seabed, Pacific Yachting reported that. Seems more like people preferring to anchor rather than sit on a mooring 50 ft from the next mooring, or pay 12.50.

Delta_Galv1-900x450.jpg


 
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IStream

Super Anarchist
10,795
2,976
Great info, Steve. I plan to have my boat on the hard for some (extensive) glass work in the next 12 months or so and will happily lend you my 85# Mantus if you want to test it.
Thanks Istream. I am very interested in testing your Mantus. Panope will be going on the hard as well for a few months so we had better act fast (before Thanksgiving) unless we wait until spring.
Your Mantus is so large and high holding power that Panope may be unable to properly set the anchor. Some theorize that this is a problem so a test would be good.

Steve
Hi Steve,

My girl's not going on the hard before year-end, I'm thinking closer to next Thanksgiving. I'd be surprised if Panope had trouble getting a good set with my Mantus but there's no substitute for data so we shall see...

 

Ishmael

Yes, we have no bananas
50,948
11,248
Fuctifino
Norse, I guess it was a Lewmar "Delta" that you lost? I'd like to test one as they do have a less than stellar reputation.

Steve
I have been using Deltas with no problem for a couple of decades. They might not have the instant set of a newer design, but mine have been very dependable. I'd be interested to see the tests if you can find one.

 
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Steve, invaluable work here. I notice you use 3000 rpm on the backdown to determine that a test anchor is truly holding ( boat no longer moving). What do you think the equivalent windspeed would be?

I imagine the equivalent it would be different for each boat because of displacement, freeboard etc but it would be comforting to contemplate when lying awake while laying to anchor that for example, at 25 kts true one is only testing the set to the equivalent of 2000 rpms, and therefore there is still half of the successful holding power 'remaining'.

 

RKoch

Super Anarchist
14,865
346
da 'burg
IIRC, you can get about 10lbs of thrust per horsepower. I don't know the HP of Steves motor, or the size of his boat, but as a wild guess I'd say the 3000 rpm might be equivilent to 10-12 knots of wind. The force on an anchor and rode increases as the square of the wind velocity....thus, when it breezes up you need some serious ground tackle.

This is a pretty informative thread, thanks, Steve, for the great videos.

 

kimbottles

Super Anarchist
8,055
783
PNW
IIRC, you can get about 10lbs of thrust per horsepower. I don't know the HP of Steves motor, or the size of his boat, but as a wild guess I'd say the 3000 rpm might be equivilent to 10-12 knots of wind. The force on an anchor and rode increases as the square of the wind velocity....thus, when it breezes up you need some serious ground tackle.

This is a pretty informative thread, thanks, Steve, for the great videos.
Steve has 39hp in Panope
Edit: 40hp

 
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Panope

Super Anarchist
1,446
609
Port Townsend, WA
Cwinsor,

I recently had the opportunity to test the engines ability to "back" into strong wind in a recent gale. It was blowing steadily in the upper 30's and with a 3 foot chop (couple miles of fetch) I was able to hold the boat stationary at about 3000 RPM. The engine redlines at 3,800 RPM (it will achieve that) and is rated at 40 horsepower. I use a 18" diameter, fixed pitch three blade propeller and like all fixed props, it makes only about half as much thrust in reverse as when in forward gear.

The limited ability of our modestly powered sailboats to back down on the anchor, is a big reason why I like to give the anchor some "momentum based" yanking. It is only a short duration pull but I have to believe that the forces are much higher than what the engine alone can produce.

Steve

 

Panope

Super Anarchist
1,446
609
Port Townsend, WA
I'll add that when turned around and facing into that same gale force wind, the boat was able to bash along at just under 5 knots at 3,000 RPM.

Steve

 
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RKoch

Super Anarchist
14,865
346
da 'burg
IIRC, you can get about 10lbs of thrust per horsepower. I don't know the HP of Steves motor, or the size of his boat, but as a wild guess I'd say the 3000 rpm might be equivilent to 10-12 knots of wind. The force on an anchor and rode increases as the square of the wind velocity....thus, when it breezes up you need some serious ground tackle.

This is a pretty informative thread, thanks, Steve, for the great videos.
Steve has 39hp in Panope
Edit: 40hp
OK. That equals about 400 lbs of thrust, which would be about 20-25 knots of wind, assuming his boat is about 40'. If the wind doubled, the load on anchor will quadruple...1600 lbs.
Here is an interesting formula I found in an old book:

Lbs of pull = k AV^2

V is the wind velocity in MPH, A is the frontal area of the boat (beam times height of cabintop), and k is a shape factor... .0055 for an average sloop, .0035 for an average powerboat. More masts and rigging use a higher constant, more streamlining use a lower one. If the boat tends to tack at anchor, might want to use LOA times cabin height for A to account for the greater load.

A couple other tidbits in the book... The holding power of an anchor is proportional to the area of the flukes, and to the depth they bury. This is a cubic function, same as weight. Thus, when comparing similar anchors of different weights the holding power is proportional to the weight...ie: a 20lb Danforth will hold twice the load of a 10 lb Danforth. This can't be used to compare differing anchor types.

Also, the holding power of a traditional yachtsmans anchor (Herreshoff or Luke) is only about 7 times the weight. Modern burying anchors hold far more per pound. I don't think a Luke type anchor as a storm hook is worth the weight necessary to hold in a blow. It would require a massive anchor.

 
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Norse Horse

Super Anarchist
4,987
546
The Rock
I was drooling over the S100 tonight and wondered how the aluminum version would be at 26 lbs.https://www.spadeanchorusa.com/product/spade-a-aluminum-a100

I gave my Lewmar some real workouts and it held me all night so I should say some nice things about it too.

I tried anchoring it east of Potlatch in Howe Sound in what amounted to underwater talus. After 3 tries I got it to hook in the large marbles and spent the night there, well protected from the night's outflows. Given proper scope, it was dependable but in a tight anchorage with 15-20 winds and some real tide shifts, like Mark Bay, it does not sit well on a short scope without an all chain rode.

 

buchhla

Member
302
0
Seattle, Wa
I have a 20KG Lewmar delta on my boat down in Seattle you would be welcome to borrow for a test... I would love to see a Rocna vs Manson test as well. We had a 20KG Rocna on our 35' boat while we cruised from Seattle to NZ and were very happy with it. I have lots of anecdotal evidence of where we had problems, though of of those cases would be hard to recreate.

Your abrupt direction change with force is a good test though as one of the times we had an issue was when we were anchored with about 4.x:1 in about 75' of water with a nice normal 10-15 kt trades predicted a unpredicted storm came though and blew 55+ for a few hours about 120 degrees different than what was predicted. So gentle direction change due to a wind shift or current is not the only use case... :)

 
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eric e

Super Anarchist
6,396
9
nz.akl
thanks for the videos!

interesting to see that anchor "flying" in the stern emergency brake test

have read that smaller bruce anchors are heavy and hydro-dynamically stable enough to work as drouges when trying to slow down a little in deep water gale force winds

if you do end up with a load cell it would be interesting to see if that's true and/or how effective they are

though i guess i could simply toss mine off the stern and seen what happens to boat speed

 
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DDW

Super Anarchist
6,321
1,012
I was drooling over the S100 tonight and wondered how the aluminum version would be at 26 lbs.https://www.spadeanchorusa.com/product/spade-a-aluminum-a100
We twisted the shank off of an aluminum one with a mild jerk out in Carriacuo. As people have said, the shanks are fabricated from three pieces of plate. In this case the welds failed, and examination of the welding showed incomplete penetration. I would stay away from the aluminum one, or treat it carefully.

 

Panope

Super Anarchist
1,446
609
Port Townsend, WA
I have a 20KG Lewmar delta on my boat down in Seattle you would be welcome to borrow for a test... I would love to see a Rocna vs Manson test as well. We had a 20KG Rocna on our 35' boat while we cruised from Seattle to NZ and were very happy with it. I have lots of anecdotal evidence of where we had problems, though of of those cases would be hard to recreate.

Your abrupt direction change with force is a good test though as one of the times we had an issue was when we were anchored with about 4.x:1 in about 75' of water with a nice normal 10-15 kt trades predicted a unpredicted storm came though and blew 55+ for a few hours about 120 degrees different than what was predicted. So gentle direction change due to a wind shift or current is not the only use case... :)
buchhla, Thanks. I would very much like to test a Delta. I had been planning on storing the boat on the hard for couple months but this testing is ramping up to the point that I may not haul. It looks like Anchor Right of Australia will be sending a SARCA.

My work brings me to Boeing field frequently by airplane. I keep a car there so perhaps we can meet for an anchor hand-off.

Steve

 

Panope

Super Anarchist
1,446
609
Port Townsend, WA
I have found two new testing areas that have seabeds with different composition than the previous area.

Let's call the first location "Point Hudson". The tidal current runs at least 3 knots here and the resulting seabed is a sandy/rock combination. The navigation chart shows the symbol "RKY" here.

I attached the rode to the "Rock Slot" of the 45 pound Manson Supreme as I was not sure of the size of the rock and was worried the anchor may become lodged between larger rock. As it turned out, no large rock was present.

However, the chain did travel to the "tripping" position of the rock slot twice during the following set with somewhat unfavorable consequences.

Steve




 

Panope

Super Anarchist
1,446
609
Port Townsend, WA
Same area as yesterdays test area (Point Hudson - a sand and rock combination).

The Manson's rode was attached to the normal position and it dug in and stayed dug in through multiple "reversals"

The Spade leaped into the seabed and stayed deeply buried. Because a strong current was running, I had to retrieve the anchor incrementally as I was alone and could not operate the boat and the windlass simultaneously.

This provided a look at four different (decreasing) scopes. Even at as little as 1.7 to 1, the anchor was still making some holding power.

I was so impressed by this performance, I sent Spade Anchor a check. I am now a Spade owner.

Steve




 
Impressive results. I wonder what % of Manson users actually employ the rock slot, and under what conditions. If in practice it is almost always being used at the single point of attachment then it would appear to be a toss up between it and the spade. Related question - what windlass are you using? I understand it is manual, so you have gotten a good workout over the last 21 tests. I am seeking to upgrade and am torn between the simplicity of reinstalling another manual vs the ability to quickly up anchor short-handed with a powered windlass, either to re-do a failed set or because conditions require.

The dragging of the spade in the current/wind conditions you experienced while you had to belay and return to the helm and drive the boat forward multiple times to relieve strain gives me pause... But maybe that is a nice problem to have because it indicates such a good holding anchor?

 
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