Scope, All Chain Rode and Breaking Strength

[thinwater]

Originally Posted by Panope

I'll toss in another data point.

-20kt Breeze.
-2.5 mile fetch.
-wave height 1' (occasional 2')
-15,000lb boat.
-3/8" all chain rode with NO snubber.
-4:1 scope (depth 20' + 4' bow roller, 100' rode)

Average load appeared to be about 175lbs.
Very brief peak loads (twice) = 300 lbs.

I've used that scale! It is one of those in my stable.


I looked up my old data, and it is very similar to what I got with a 34-foot, 9,000 pound catamaran, no snubber. Less weight, more windage, same result (peak and approximate range). With a snubber the loads were lower.



I'd suggest testing close behind a breakwater or low spit, with a LONG snubber (like 100 feet of nylon, or just nylon rode), to get a wind-only load (no yawing, please). Hopefully the wind will be steady and the readings steady. The result should be less than 1/2, or even less.

[thinwater]

Originally Posted by cr180

Fat margin of safety for WHAT wind speed? It matters. 10 knots of wind or 80 knots of wind?

In previous editions ABYC stated a wind speed, but it was taken out of context so often they removed it. The working load values were not changed.

[sv_pelagia]

Originally Posted by Breaking Waves

perhaps you do - we did not.

we spent a month gunkholing around Prince Rupert, then a month around queen charlotte, and then a year around Vancouver/Vancouver Island.

I can only remember once we anchored somewhat deep - in Princess Louisa, where we used a shore tie and then the public dock emptied and we move to it to make walks easier.

We never skipped anyplace we wanted to see because of depth. I will comment that we do by choice prefer to spend some time exploring really nice anchorages rather than quickly skipping between less good ones.

Perhaps you prefer not to sneak into little coves and not to shore tie. That's fine, all good, but it is a choice to anchor deep and one certainly does not need to 'often anchor in +50' there.

Lovely area, one of our favorites.

No question, there are shallower anchorages. Many many wonderful ones. And yes, we hate stern ties (especially Gulf Islands and Desolation Sound, where stern ties can be dictated by large crowds), as so often one ends up being sideways to the wind, putting a strain on both anchor and stern tie. Certainly, however, sometimes a stern tie keeps one safely (and completely) out of the wind. ).

Having said the above, in over 20 years of cruising BC bottom to top (including 3x to Haida Gwaii), we probably find ouselves anchored in <30' depths (at high tide) less than 20-30% of the time, and 50' or greater (again, at high tide) >30% time. That's what I meant by "often".

But each to their own experience and preference. We like the option to anchor deeper -- also allows us to get away from some crowded anchorages -- indeed, this year we increased our anchor rode to 400'.

[Breaking Waves]

Originally Posted by sv_pelagia

and 50' or greater (again, at high tide) >30% time. That's what I meant by "often".

Out of curiosity - what are your 3 favorites 'do not miss' anchorages where you need to anchor greater than 50' (lat/longs would help me find them). I'm curious what we missed

[Kelkara]

Originally Posted by Breaking Waves

Perhaps you prefer not to sneak into little coves and not to shore tie. That's fine, all good, but it is a choice to anchor deep and one certainly does not need to 'often anchor in +50' there.

Well I'm glad to hear it's possible ... but for someone new to the area I'd certainly recommend that they carry enough rode to anchor in 50+ft, it will open up 100s of possible anchorages to easy anchoring. I very rarely anchor in less than 30ft, and sometimes my stern is swinging so close to rocks I can almost touch them from the cockpit.

As a single-hander I *HATE* using a shore tie, since it requires leaving the boat swinging unattended in a space that is necessarily too small for the boat to swing while going ashore to tie off. So yes, I do look for places that I can just drop the hook and swing to make anchoring easy ... but so far only twice have I backed out of an anchorage because I wouldn't be comfortable without a shore tie.

And since you mentioned Prince Rupert, with 25ft tides the number of shallow anchorages is dramatically reduced up there, being prepared to go deep really opens up options ... and going north into Alaska the anchorages seemed to get deeper and the tides bigger, I occasionally used all 400ft of rode.

[Kelkara]

Originally Posted by Breaking Waves

Out of curiosity - what are your 3 favorites 'do not miss' anchorages where you need to anchor greater than 50' (lat/longs would help me find them). I'm curious what we missed

It's not about "do not miss" for me ... it's about going from A to B and wanting somewhere to anchor on the overnights between ... very often the conveniently located anchorages are deep. I want to be able to drop the hook quickly when I arrive as the sun goes down, and pick it up again without fuss in the morning before leaving, and without having to deviate several miles off route to get there. 50ft is only 15m with 5m tides you have to be inside the 10m depth contour, on many parts of the coast that doesn't leave a lot of area which still has good holding.

But I can certainly think of a couple of "do not miss" deep places in Alaska for you:
The Pack Creek Bear Sanctuary - anchorage in 15 fathoms (+tide)
Glacier Bay - Several anchorages 15+ fathoms (again tides of 20+ ft) - sure there are a few shallow anchorages, but you'll be limiting yourself.

[sv_pelagia]

Originally Posted by Breaking Waves

Out of curiosity - what are your 3 favorites 'do not miss' anchorages where you need to anchor greater than 50' (lat/longs would help me find them). I'm curious what we missed

What the others say....

As noted, it's not just about "favourite" anchorages. Deeper anchorages may be your only choice for the day. Or, a deeper anchorage might turn out to be a potentially "nice" anchorage to try out. Importantly, all it takes sometime is a couple other boats to necessitate deeper anchoring.

Here's several deeper anchorages (south to north) we've found ourselves in over the years - - not necessarily our favourites! All depths at max high tide.

Clam Bay (Thetis/Penelakut Islands): gets crowded, so anchoring in 47' quite common (USED to be a regular/favourite place, but in Summer often too busy... going even deeper than 47' helps)

Douglas Bay/Forward Harbour: if you come after 2-4 other boats, you will be anchoring in 65-80 ft. Gets busy in Summer.

OBrien Bay, Simoon Sound: tried Simoon for first time this year. Turned out somewhat shallower (43') and popular McIntosh Bay was packed. We went further in to Obrien where we anchored in about 75' (only 1 other boat)

Codville Lagoon. A favourite. About 70-80'

Quigley Cove, Laredo Inlet: 70-80'

Fifer Cove, Laredo Inlet: 80'

Nettle Bay/Lowe Inlet: about 80' (less if no other boats in front of falls)

Murchison Island, Haida Gwaii (near Hotsprings). Only 2 mooring buoys, so 79' to anchor if 2 others already there (quite common)

Sorry, but too much work to provide lat/long. If you're a regular cruiser in BC, the above should be familiar.

[cr180]

Originally Posted by thinwater

The blog post you refer to is just that. A blog post, a 5-minute sound bite. I've written many articles and a book on the topic, so that was certainly the short version.

Well ... maybe you should not use a short snubber in shallow water. This is ... obvious. Maybe some of these locations are simply not safe harbors and can't be made so. Once upon a time I used a short snubber with all chain, and it only took one afternoon at 20 knots to make me splice up something more suitable for that evening.

In fact, I sail the Chesapeake Bay, most commonly anchor in 6-8 feet, and the regular bridle I use is generally greater than the water depth (18-foot legs). If you think about it, most catamaran bridles will reach the bottom when anchored shallow. It's not a big deal and it is what you must do if you want a bridle long enough to damp yawing. If I expect a bumpy ride I use a long bridle does not anchor to the bows, it anchors to either the stern cleats or midships cleats, giving me about 45 feet of snubber. The routing around the bow and chafe gear take some thought, but it's not hard.

No, there are not always trees. Yes, we get fierce thunderstorms here, as good as anywhere. Most of my testing was off beaches with on-shore winds and at least 5 miles of fetch. I tested wind-only loads behind a low breakwater, but all of the rode tension results were fully exposed to wind and long fetch waves, and were still many times less than ABYC H-40 Table 1. The ONLY way I could reach the ABYC values was:

• Shallow water (just short of breaking, often 5-7 feet).
• All chain, no snubber (I used a Dyneema bridle to mount the load cell).
• Long fetch (typically 8 miles).

In other words, worst case, an unseamanlike way to anchor, and a mistake. The boat will be snatching violently at the chain. It should be obvious that something is wrong, and not just the weather. Otherwise, the results were 2-5 times less.

But many of my readers are Chesapeake Bay area, and you can always find a sheltered spot. Fetch (waves) are often more important than waves, and anchoring with on shore winds in an exposed area will ALWAYS be a serious matter, something sailors try hard to avoid. Most anchoring tragedies result from those conditions.

The ABYC numbers have not changed for at least 40 years because they work. Chains don't break and equipment built to that standard holds up. Anchors dragging is not related. If you want to anchor in the "worst case" locations and use a short snubber, yes, you are in the market for larger gear.

Thinwater, thanks for weighing in. First, appreciate your work. Yes understand the blog was a snap shot and am interested in learning more about the test set up and methodology; is that info in your book? If so, am happy to buy it.

That said, do you stand behind the data published in your blog? I will not dispute the data. Especially the fact the loads were significantly reduced by adding elasticity to the rode either by a longer chain in deeper water adding catenary or by a longer snubber or by nylon rode instead of chain.

Where I challenge you is about your conclusions about the real world. You are viewing the world through a Chesapeake Bay prism. I have cruised the Bay as well. But ask you to trust me when I say that the Bahamas deserve another prism. To denigrate fellow sailors as exhibiting poor seamanship because they anchor off a lee shore in settled weather in 7’ of water in the Bahamas and have an unexpected 60 knot squal materialize in the middle of the night with a wind shift now making it an open anchorage with breaking waves (could easily be 5 nm fetch) as exhibiting poor seamanship deserves reconsideration.

Think you get the picture. If you anchor enough days in the Bahamas, 100 to 200 days a year for many of us, the squally weather will find you. Shouldn’t you be prepared?

Shallow water in the Bahamas is what it is. And all chain rode is a debate for another day. In your blog, you recognize larger boats choose all chain rode to be retrieved by the windlass gypsy and I’ll add a Bruce Van Sant truism that in the tropics if the coral or rocks don’t get your nylon rode, then surely the broken rum bottles will. So all chain for many of us is a given.

So that leaves the snubber. Read with interest about you recommendation for a 35 to 50’ snubber taken back to the midship or stern cleat. For most of us to get that length would be the stern cleat. Understand the physics and how that adds elasticity resulting in lower loads. But here again, your prism of the real world is through the Chesapeake Bay experience. My real world experience is that for safety reasons, this is a very bad idea. Can you imagine having to go to the foredeck in the middle the night in 60 knot winds and a rolling and pitching sea only to trip on the snubber line on deck resulting in injury in a remote location. No sir, ain’t doin it. Doubt many other cruisers would either. Would rather pay for the heavier duty ground tackle. So again to imply that we cruisers would not consider a snubber line to the rear cleat as bad seamanship deserves reconsideration.

Where does this leave us? Your own 60 knot wind test data exceeds the currently published ABYC H-40 load chart storm anchor data by 50% for shallow water, all chain rode, and short snubber, the very configuration that hundreds of cruisers in the Bahamas currently experience. The chart is non-
Conservative because as you show in your blog, the ABCY storm values are based on 42 knots. By the way, your 40 knot data correlates well with the 42 knot chart Storm data. Therefore, not only is there not a large safety factor, but if you want to size your ground tackle for 60 knots, it is grossly non-conservative.

Said all that to say this. Thanks for your test data. Please allow me to draw a different conclusion on applying it to Bahamas cruising.

[cr180]

Originally Posted by Breaking Waves

The author of that is here @thinwater - you should discuss it with him.

but do note he says in the comments " In real world practice, I have never observed values higher than 1/3 of ABYC table 1." I believe that indicates that the 2nd table you are looking is attempting to explain/quantify the gap between wind load and the theoretical abyc numbers - the bottom row is calculated not measured - the real-world measured numbers are always lower than this. . . but ask him directly, no point in speculating when he is right here. (he has written a book on all this - might be worth your buying and reading if you are really interested).

I have measured anchoring loads up to 35 knts with a load cell and always found significantly less than abyc (that included situations where we had more fetch than I would have preferred). Never did over 35kts but have used 10mm climbing line for snubber thru cat 1 hurricane (47' boat), and its cover chafed on fairlead but did not break - says something about the loads.

honestly, if you are anchoring with significant fetch, in 60kts, with essentially all chain in shallow water and no snubber elasticity . . . well yea . . . (Note: there are definitely practical ways to get more snubber length/elasticity, like running it back along the deck to a stern cleat. There are also practical ways to reduce yawing, which can reduce loads significantly. You should honestly attempt to practice some seamanship here.)

Have responded to Thinwater. You can read my reply. Your comment about practicing some seamanship is a cheap shot. Will let others draw their own conclusion about who is practicing seamanship here.

[Cadence]

Isn't the whole discussion relevant to locale?

[Breaking Waves]

Originally Posted by Kelkara

It's not about "do not miss" for me ... it's about going from A to B and wanting somewhere to anchor on the overnights between ...

ah, ok, interesting, we don't 'anchor every night' on such cruising. If the next great place is more than a day away, and there is nothing I really like the looks of between, we typically just make the full hop. That perhaps explains a lot.





deep places in Alaska

Alaska we have not 'cruised' so I don't have any judgment there. I have only been there one time, going very very quickly thru as ice pilot on a superyacht. My old boat just finished a 10-week cruise to the Aleutians - I am a bit jealous of her

..........

[cr180]

Originally Posted by Cadence

Isn't the whole discussion relevant to locale?

Yes. Thanks, you are exactly right.

So we all must be carefully to provide posts that are based on local prisms and attempt to strongly lobby for universal application. Some actually attempt to intimidate those with a different opinion. I have been accused of practicing poor seamanship.

For us old timers, we can throw the BS flag, the problem is that the new cruisers will apply local info to wrong location. Results can be dramatically bad!

[cr180]

Originally Posted by thinwater

In previous editions ABYC stated a wind speed, but it was taken out of context so often they removed it. The working load values were not changed.

Thinwater. Thanks again for weighing in. Problem is as I pointed out in my reply to you earlier, that for many of us, we want ground tackle for 60 knots or more. So now the ABYC table does not address wind. Can only speculate why. But as I pointed out in a previous post, the H-40 standard is for building boats, not for sizing ground tackle for cruising boats. As I responded to you previously, dispute your claim that actual ground tackle loads are less than in the ABYC standard, so where does that leave cruisers?

[Cadence]

Originally Posted by cr180

Yes. Thanks, you are exactly right.

So we all must be carefully to provide posts that are based on local prisms and attempt to strongly lobby for universal application. Some actually attempt to intimidate those with a different opinion. I have been accused of practicing poor seamanship.

For us old timers, we can throw the BS flag, the problem is that the new cruisers will apply local info to wrong location. Results can be dramatically bad!

Some people read to many books and have never dropped a hook.

[Breaking Waves]

Originally Posted by Cadence

Some people read to many books and have never dropped a hook.

lol...