Photos of Anchors Setting

[Robin3]

I have always set with 3 x the anticipated max depth at HW, then adjusted for special cases like more wind expected, etc. Our current 36 foot boat has a Yanmar 3GM30 27 Hp with a 3 blade fixed prop, bit like ocean girl's prior to that we had a bigger (41 footer)with a 4JHE 44Hp and we reversed that in using up to 2,500rpm but we also had a 3 bladed Brunton Autoprop on that boat which is self pitching ahead and astern the blades pivot to face the other way) and could stop the boat from 6kts in a boat' length in reverse if asked nicely so I would guess the 2,500 rpm we used was pulling pretty darn hard In both cases we had/have an all chain rode 10mm/3/8", now with a 45lb Delta, but only a 35lb delta on the previous 41footer, the 45lb on our curren tboat is sized up from choice and because even if I could afford the new gen stuff , it mostly wouldn't sit on our bow roller nicely.

[JPA Cate]

When you're talking about technique for setting, this may be a little off to the side of the purpose of the thread, but I have to agree about using shorter scope for the beginning stages of setting the hook. We let it out till it tries to grab then tug it a little, veer out more, more tugging, stronger. For our final setting, we're at 3 or more to 1, and it has to hold a half minute at max revs, which for us is 2200 rpm. We have dragged once with this technique, in sustained 50 knot puffs, from two different sides of the hill, so the boat was shearing around a lot. We put out our trusty 20# Danforth, and stopped dragging. When Jim got the anchors up, the mud on the two anchors was different, and he said that he thought where the Manson was was poorer holding. Which sort of suggests that if we'd anchored just that little distance different, we might not have dragged there.

Keep the pictures coming. We had a Bruce let go once on us, too. Neat to see it weed gathering. Sort of scary.

[thinwater]

Originally Posted by wsmurdoch

Like Brian, I have a Pacific Seacraft 34. It has a 3HM35F Yanmar engine turning a 17x10 2 blade fixed propeller. The transmission ratio is 2.14 in forward and 2.50 in reverse. The lower propeller speed in reverse really hurts the reverse thrust. With the engine turning at the same speed, the reversing prop pumps less water per unit of time and pumps it at a lower velocity. [F=d(mv)/dt and all that...] In addition the prop has a slight airfoil cross section, so in reverse it is like flying upside down without raising the airplane nose.

I own a 0-2000lb Dillon dynamometer and have measured my reverse bollard pull. I get 110lb at 2000rpm, 170lb at 2500rpm, 240lb at 3000rpm and 300lb at 3500rpm.

There are a couple of magazine articles where the reverse bollard pull of sailboats have been measured with different propellers.

www.flexofold.com/upload_dir/docs/Test_YachtingMonthly_low.pdf

www.propelspecialisten.dk/download/segeln_magazine_test_2008.pdf

https://books.google.com/books?id=yJ...20pull&f=false

They are great evening reads. It is hard to draw solid conclusions from the data as the all the props are not perfectly (or equally) matched to the engines, but there is still lots to learn.

Interesting. I was doing some similar testing and got 240# in reverse with twin 9.9 Yamaha high-thrust engines. Outboards are generally weak in reverse, though the Yamahas are better. Apparently your prop is weak in reverse too.

The next question is how does you 300# relate to wind load and rode load (they can be VERY different--I've been measuring those too--and the chain load can be as much as 4X higher). ABYC says 900# for a working anchor and 1800# for a storm anchor. I'll bet the wind load only is about 600# at 45 knots, and with surging, depending on your snubber, about twice that.

Also note that the chain is coming off the bottom near full setting power, or just a few hundred pounds. This is consistent with a resent magazine report. Clearly this depends on water depth, but it probably consistent across most boats, that the chain lifts and the catenary will vanish at about setting force, or something like a fresh breeze. In other words... when it starts to matter.

[wsmurdoch]

Originally Posted by thinwater

Apparently your prop is weak in reverse too.

The third link in my note is to a 1996 Cruising World article where they tested 12 propellers all turned by a Yanmar 3GM30F which is slightly smaller than my 3HM35F. On page 65 they list the average reverse thrust for the 12 propellers they tested as 123.3lb at the full throttle maximum rpm that the engine could reach with each propeller. The highest measured reverse thrust was 164lb. My 300lb reverse thrust at 3500rpm seems to be not so bad for a sailboat with a fixed 2 blade propeller.

The 7.5hp Johnson with a standard propeller on my Tanzer 22 gets a static thrust of 125lb in forward and 60lb in reverse.

[thinwater]

Originally Posted by wsmurdoch

The third link in my note is to a 1996 Cruising World article where they tested 12 propellers all turned by a Yanmar 3GM30F which is slightly smaller than my 3HM35F. On page 65 they list the average reverse thrust for the 12 propellers they tested as 123.3lb at the full throttle maximum rpm that the engine could reach with each propeller. The highest measured reverse thrust was 164lb. My 300lb reverse thrust at 3500rpm seems to be not so bad for a sailboat with a fixed 2 blade propeller.

The 7.5hp Johnson with a standard propeller on my Tanzer 22 gets a static thrust of 125lb in forward and 60lb in reverse.

True enough, for what it is.

[rgesner]

Noelex,

What camera gear are you using to take your photos and videos?

Thanks

[Seaworthy Lass]

Reply re setting

Originally Posted by Alan Mighty

Many thanks again, noelex, for your superb and pioneering work. You and your mermaid are fantastic. Your joint efforts are very worthy of a koala stamp of approval!

Your valuable video suggests, in that case at a scope of 3:1 with your Mantus on clean sand, that your engine was in reverse at significant rpm for 2 minutes 19 seconds (from 00:26 to 01:53 by my count).

I know you've mentioned in earlier posts that you set at close to your engine's max rpm. I'd be grateful if you could mention that rpm figure and especially if you could relate that the propeller power curve/shaft power curve to give a ballpark figure for shaft power.

Al

Thanks for the compliments Alan. Sorry for the delay responding. I have been super busy lately.

As I am at the engine controls when we anchor, I can answer your question. We have a two blade feathering Maxiprop and a 54hp Yanmah 4JH4AE. I usually give the engine 30 seconds in full reverse. That was all that was given in the video. The catenary disappeared well before then as we were in reasonably shallow water @3:1 so not much chain was out and we use 10mm chain so it is a little lighter than most cruising boats our size.

The time building up to full revs is variable and depends on wind strength. Calm conditions it takes longer. With no wind I need to apply idle reverse initially to actually make sure the chain is laid out in a straight line. Once it is all out I do not bump up the revs until until I receive a signal from the front that the chain is taut, then I very slowly increase. There was a slow increase of revs in the video, as there was little wind. Catenary was lost well before full revs were achieved.

At the other extreme, if it is blowing 20-30 knots, the chain has been laid out nearly straight by the time it is all out and the anchor is starting to dig in before I even start applying reverse. In fact, the anchor will even set quite happily on its own. I do apply the same amount of reverse though (and it can be done more quickly, as the anchor has already started to dig in) to ensure an extra good bury, which is reassuring to have in these conditions.

Anything in between wind wise takes an in between amount of time.

SWL

[noelex 77]

Originally Posted by rgesner

What camera gear are you using to take your photos and videos?

The camera is an Olympus TGi 2. It is waterproof down to 18m on its own, but I use it with an underwater housing that is waterproof to 40m. I don't dive deeper than 18m, (about 12m is my limit) so in theory the camera should be fine without the housing. Snorkelling most days in summer I think sooner or later there is likely to be poor seal on the camera door so the extra protection of the waterproof housing is good insurance.

[noelex 77]

This was a Bugel copy (it can be argued that there is no such thing as a genuine Bugel, but this term is commonly applied to the Wasi Bugel).

It was dropped in shallow water close to the beach by a cat in 3m @ 6:1. The sand gets better close to the beach with no rock or weed. Nevertheless, this anchor is doing a great job. Keep in mind that a Bugel copy is one of the very cheapest anchors you can buy. It is a very simple anchor to construct and is great value for money.

The precaution is that the copies can have very variable geometry and balance. You need to check it is made accurately.

The wind had swung around so the anchor was sitting directly under the boat, making the lighting for the photo difficult.

[noelex 77]

This was a large Danforth style anchor (200 lbs?)

It was not doing well. It really was not set at all, just catching in the weed. The boat was slowly dragging backwards despite the light wind and large scope 11m @ 7:1.

Danforth style anchors do not do well in weed, but the fluke angle of this anchor looked wrong to me. Around 32° is the optimum fluke angle for most substrates. Up to 45° can be used in very soft substrates. The large fluke angle increases the holding power in very soft substrates, but if you try to use these large fluke angles on a normal or firm bottom the anchor will not work at all and the result is almost no holding power. This looked arround 40°-45° which is not appropriate for this bottom.

With the converse, of using too shallow a fluke angle in a very soft substrate, the anchor will work and set correctly, but the holding power will not be as high.

It is possible the fluke angle was made incorrectly, but it most likely there has been some internal wear and corrosion which has gradually increased the fluke angle, or maybe my impression of the fluke angle is wrong. Anyway, you can see the photo for yourself.

The stock was also slightly bent on this anchor, but I doubt that was having much effect.

[noelex 77]

This is another Rocna. It, too, was dropped by a catamaran close to the previous Rocna in post #1439. The net result is almost a carbon copy of that anchor. In fact the cats were the same model Lagoon 420s, although the Rocnas were one size different. This was a 33 kg (73 lb). The one in post #1439 was a Rocna 40 kg (88 lb).

Once again the set is poor by Rocna standards. There is quite a big of heaping up and the anchor has taken 6-7 feet to set.

[noelex 77]

This was a large Delta dropped in weed. It had been given very little force. It was sitting mostly above the surface , but it does look like the tip is trying to penetrate.

It would have been interesting to see this with a bit more force, but they left after a few hours. 10m @ 5:1

[noelex 77]

These couple of photos are to illustrate the chain rather than the anchor (it was the chain connected to the Rocna in post #1439).

People often discuss scope when anchoring. It is important to understand what is really important is the chain angle where it meets the shank. Scope is one very important factor in determining this, but it is not the only factor.

If they consider it all, many people underestimate the effect of bottom slope. This has been discussed in detail here:

http://www.cruisersforum.com/forums/...ng-137516.html

Another effect on the angle of pull at the anchor shank is local elevations of the chain caused typically by rock, debris. Here is an example of the chain being forced up by some rock associated with the weed bed. At the moment this is having little effect on the angle of pull right at the anchor shank where it counts. If the chain was pulled a little tighter as would be in slightly more wind the angle of the chain at the shank would be raised.

If the anchor was dropped (or moved) slightly more towards the rock the angle could become quite significant.

No matter how much scope was let out, the angle of the pull at the shank will not drop below the limit set by the rock.

Thus the boatowner might think in strong conditions by letting out 10:1 he was restricting the angle of pull at the shank to a bit over 5°. In reality local patches of rock may be creating a higher angle of pull reducing the potential holding power of the anchor significantly.

[nigel1]

I have been anchoring out frequently on the West Coast of Scotland, mainly in the Firth of Clyde area, and getting the scope right can be a challenge. A lot of the anchorages shoal steeply. If you put out sufficient scope to allow for the deep water, it will usually mean that if the boat drifts towards the shore, it will ground.

In these situations I tend to keep the scope short and rely on the anchor makers claims to high holding power , and the anchor alarm.

[noelex 77]

This was a Spade doing fantastically well in this difficult anchorage.

It was dropped by a large cat late in the day. We were having dinner in the taverna right on the beach so we had a ringside seat.

It was one of the most cautious anchor drops I have seen for a while. Not that there is anything wrong with that. The anchorage was reasonably busy so their first couple of drops were in weed. They put on plenty of reverse and the Spade failed to hold. They moved into shallower water and the next few drops were in sand, but they ended up too close to other boats.

They then came into very shallow water, dropped on a very long scope and tied the stern up to rocks on shore. They backed down very hard on the anchor, and together with the wind that was at right angles to the cat, there was quite a bit of force on the anchor.

This was the result photographed the next morning. What anchor? The spade is not a very tall anchor, so once the shank is under the substrate there is nothing to see, but this still a great result.