| Powerful typhoon slams into Japan
“…TOKYO – A powerful typhoon slammed into Japan on Thursday, damaging buildings and roads, halting train service and canceling hundreds of flights as it swept across the country. One man died and dozens were reported injured. The storm flooded roads and homes, toppled trees and power lines and heavily damaged some buildings….”
This was our first time to go through a typhoon at the marina, so we didn’t know how protected (sheltered from the wind) we would be. The good news is that we are VERY well protected. All three boats made it through the storm without damage. The winds at our boats were not that bad. We had sustained winds at 40 knots, with gusts to 57 knots. The direction of the wind also helped. The winds were on Grey Pearl and Seabird’s stern, and were pushing me off the dock.
A few weeks back, when we were in the Yokohama marina, my boat, Sans Souci, was in the opposite situation. We had tied down the boat for an approaching typhoon, and were feeling good about how well we were tied. As the winds topped 27 knots, I heard a knock-knock-knock on the side of the boat. It was the harbormaster, and he asked if I could move the boat. The typhoon was going to be pushing Sans Souci into the dock, and he was afraid that Sans Souci’s 120 tons of weight were going to smash his dock. I couldn’t believe he wanted me to move the boat in high wind, with a typhoon coming, and grumbled a bit, but knew he was right. Luckily the wind dropped, and I had no trouble moving the boat. Even better, the typhoon made a turn and never came ashore.
Over the past couple of days, as I was watching Typhoon Melor gain strength, and realized that it was going to score a direct hit, I resolved myself that there would be some damage. When we left Japan I was confident that typhoons were over for the season, and yet put plenty of lines on anyhow. I counted the docklines as we left the marina for the last time, and I had 12 lines holding Sans Souci to the dock, most of which were 1 1/8” double-braid, thick heavy dock line. I had also put out far more fenders than were necessary. I wasn’t worried about the boat going anywhere, but did think we would lose some of our canvas covers, and perhaps some of the equipment on the radar arch.
However, thanks to being in an extremely well-protected marina we were sheltered from the heaviest winds. In the days prior to the typhoon striking, Steven and Carol Argosy added additional lines and fenders to all three GSSR boats, for which I thank them immensely. With a little luck Steven will send some pictures from during the typhoon, and if so, I’ll send them out.
And, on a different topic, last night, Roberta and I had dinner with Scott and Teri Strickland…
Scott and Teri crossed the Atlantic with us back in 2004, as part of the Nordhavn Atlantic Rally. Recently, and sadly, they sold their Nordhavn 47. Many of you will remember this picture from the end of the Atlantic Rally, where Teri listed on a rally T-Shirt all of the seasickness medications she took, and joked about selling the boat:
It seems like there have been a number of highly visible drop-outs amongst Nordhavn cruisers this year. A few months back, a Nordhavn 40 owner, Scott Bulger, who has been a very active writer about cruising, sold his boat, after cruising all the way from Seattle to Maine. Circumnavigators, Eric and Christi Grab, who just took their Nordhavn 43, Kosmos, around the world, announced they would be selling their boat.
I think in all three of these cases, selling the boat, after a few years cruising, was always the plan. I remember Scott Strickland’s and my first conversation where he said he had negotiated a deal with Teri to cruise for three years, then buy a house in Minnesota and settle down. Instead, they’ve cruised most of the world over the past five years.
I was curious to see whether or not they regretted selling the boat. And in fact, they are. It’s tough to leave a life of world exploration and go back to being a ‘civilian.’ Both of them are missing their boat, and it wouldn’t surprise me if they are back to cruising within a few years. I asked their favorite cruising destinations, and they said: Turkey and Croatia. I asked where they would go if they ever bought another boat. Scott didn’t hesitate before saying, “Across the Pacific.”
And, of course, when guys get together, and have a couple glasses of wine, the conversation always turns to…
You guessed it, Anchoring.
[NOTE: The following discussion is a bit techie. Those of you who aren’t boat geeks probably want to stop reading now]
Our discussion of the typhoon in Japan led Scott and I to talking about the high winds we’ve both seen while anchoring in the Med. Both of us have sat at anchor in winds over 50 knots, on more than one occasion. I asked what scope Scott normally puts out (the ratio of how much anchor rode to the depth of the water). The ‘official’ coast guard recommendation is for 7 to 1 in normal conditions, 5 to 1 in calm seas, and 10 to 1 in heavy weather. A 7 to 1 ration means that if you are in 30 feet of water, you would put out 7 times as much in chain (rode), or 210 feet. However, as with all things, situations vary, and it is wrong to use a hard and fast rule. Putting out 200 feet of anchor rode means you need a ‘swing circle’ of at least 400’, which isn’t always possible, or, necessary. In Alaska, we often had to anchor in deep water, sometimes water over 100’ deep. I carry only 400’ of anchor rode. Even if I had enough chain (rode) to put out 7 to 1 scope, there wouldn’t have been room for my boat to swing in the anchorages. Plus, there’s a lot of garbage on the bottom. The greater my swing circle, the greater the odds I’ll be wrapping my anchor chain around a log or boulder lying on the bottom.
Here’s some fun with math…
100’ of rode = 31,400 sq ft
200’ of rode = 125,600 sq ft
300’ of rode = 282,600 sq ft
400’ of rode = 502,400 sq ft
The table above shows the area, in square feet, inside the swing circle, based on how many feet of rode is out. It says that if you put out 100’ of anchor rode, then the circle formed by your boat pivoting around the anchor is 31,400 sq ft. However, if you double the amount of anchor rode, the square footage of the circle formed rises exponentially, to 125,600 sq ft — four times as large! If you put 300′ feet out, you now have nearly ten times as much square footage of bottom that you need to worry about. If the bottom is nice clean sand, this isn’t a big deal, but if the bottom is littered with crud, which can include rusted out cars, coral, trees and more – this can be a very important topic.
If you agree with the preceding paragraph, then there should be no more anchor rode out than it takes to hold the boat. Historically, I’ve always put out between 5 to 1 and 7 to 1. Scott mentioned that he regularly does 3 to 1, and in calm protected anchorages drops as little as 1.5 to 1 (meaning 45 feet of rode in 30 feet of water).
Scott’s a smart guy, and I like to think I’m a smart guy, and I also assume that the US Coast Guard is full of smart people. So, how can so many smart people see this issue so differently?
First off, let me say that putting out too little rode is a serious mistake. Snagging the rode on a log would be no fun, but it would be much worse to drag anchor on a windy night while sleeping. If the choice is to risk losing the anchor, or risk losing the boat, it’s an easy decision. In other words, this is a case where the right answer should be to err on the side of safety. Too much safety is not a bad thing. However, as I said earlier, dropping 7 to 1 isn’t always practical.
And, the needed ratio for safe anchoring can vary according to your anchor and your rode. There are many different kinds of materials used for anchor rode. I use heavy 1/2” high-test chain with a 250 lb Rocna anchor (which I’m in the process of upgrading to 325 lbs.) The chain is heavy and the anchor is heavy. My Nordhavn 68 has never dragged anchor, despite seeing some fairly tough anchoring conditions.
When I pushed Scott on how he was getting away with lower ratios, he surprised me by having a good analytical response to my question. Whereas I’ve always sought out anchorages with adequate swing room, Scott has put some effort into to quantifying how much space he really needs. This has all been a bit mysterious to me, so I was happy to hear someone with a good idea.
Scott has taken the time to set his anchor multiple times at the same location, each time putting out a different amount of rode. He then backs down on the anchor until the anchor drags. His contention is that all anchors will drag sooner or later, and it is just a matter of knowing what RPM it takes to cause the anchor to drag. For instance, let’s say that he puts out 300’ of chain, and discovers that the anchor drags at 2130 rpm, and then tries the same test with only 100’ of chain out, and the anchor drags at 2100 rpm. In other words, in this particular exercise, there was no material difference in the force required to drag the anchor, so why not go with the shorter amount of rode? It’s an interesting question, if true. Scott has tried this comparison and said that with his anchor, and his chain, he can’t see a material difference between a 3 to 1 scope, and a 5 to 1 scope or even 7 to 1 scope. If high winds are expected, and plenty of swing room is available, then it’s worth doing the longer scope, however, for Scott’s boat, under ‘normal’ conditions, why bother with putting unnecessary chain into the water?
Scott has actually taken this exercise a bit farther, and has correlated his engine rpm to the wind speed required to drag his anchor. For example, and I forget the exact RPMs he gave me, so don’t take this literally, he knows that if it takes 2,000 rpm to drag his anchor, he can sleep without worrying, up to 25 knots of wind.
My guess is that the results vary greatly based on: the type and weight of the rode, the anchor, and the bottom. In other words, Scott’s results may, or may not, be relevant to my boat. Thus, I’m not sure what to do with this information, and there’s no way I’m going to do similar testing with my boat. My policy is to not like to push the limits. Putting enough horsepower onto a well-set anchor, to drag it, is completely outside my thinking. It feels like a formula for breaking something; the windlass, the bow pulpit, a weak link in the chain, or, if anything goes wrong, hurting someone. This kind of testing strikes me as dangerous. I’m glad someone is doing it, but happy it isn’t me.
Indirectly, this whole discussion relates to another topic I was thinking about just a few weeks ago…
I wanted to buy a simple shackle to go into my chain rode. At the marine store, there were a wide array available, each at a different price, with a different holding capacity. I forget the specifics, but I saw a variety of shackles running from $10 to over a hundred dollars, each holding different weights. The rated capacities seemed to run from 1 ton to about 20 tons. My boat weighs 120 tons, which stumped me as to which shackle I should buy. It seemed obvious that I should buy the highest rated one. As they say, a chain is only as strong as the weakest link. However, I didn’t have the vaguest idea what kind of pressures my anchor rode sees during usage.
Last week, Ron Rogers, a reader of my blog, sent me this chart:
For each 100 sq. feet of boat area presented to the wind –
20 Kts = 136 Lbs.
40 Kts = 542 Lbs.
60 Kts = 1220 Lbs.
80 Kts = 2170 Lbs.
100 Kts = 3990 Lbs.
120 Kts = 4882 Lbs.
140 Kts = 6644 Lbs.
160 Kts = 8678 Lbs
180 Kts = 10984 Lbs.
This shows the pounds of pressure exerted against the boat under different wind conditions. Normally at anchor, your bow is pointing into the wind, so to compute the surface area, you multiply your beam times the height of the boat. This isn’t a particularly accurate way to accomplish this, but gets you into the ballpark. Sans Souci is 21 feet wide by about 45 feet tall, or around 945 sq ft of ‘windage’ when pointing bow-to the wind. For purposes of calculations, and to make the math easier, I’ll trim this by about 20% to 800 sq. ft. because the flybridge doesn’t present a solid surface to the wind. So, to apply the table above, I would multiply these values by eight (800 sq. ft. versus the 100 sq ft in the table.) Thus, in a 60 knot wind, there would be 1220 lbs, multiplied by eight, or around 10,000 lbs (5 tons) of pressure on my anchor rode. This is less than I would have expected, and might still indicate a shackle that can handle double or triple this stress. In a 60 knot wind, at anchor, the sea would be unsettled, and a solid chain rode, pulled taut and incapable of stretching, causes major spikes in stress on the rode and anchor. [Note: This brings up the whole topic of snubbing, which I’ll look at in some other blog…]
I was also curious to use this table to compute the pressure on my boat, if it were turned beam-to the wind. Let’s take the same example from the preceding paragraph, with 5 tons of pressure when the boat is pointed into the wind, and try turning my beam to the wind. Suddenly my windage (the ‘sail’ I’m presenting to the wind) represents the length of my boat multiplied by height, or 68 feet times 40 feet, or about 2,700 sq ft. This equates to about 32,000 pounds of pressure, or 16 tons. Ouch. This example is a bit extreme, but there are certainly times I have been maneuvering in tight marinas, in 15 to 25 knot winds, and discovered that when I turn the boat, I’m suddenly shoved sideways. It is critical to know where the wind is, and how strong it is, in these situations, and to remember that as the wind speed increases, the added impact is exponential, not straight line. Compare, in the table above, the force exerted against the boat at 20 knots, to the force at 60 knots. You have three times as much wind, but nearly 10 times as much pressure against the boat.
That’s it for today. Hopefully I haven’t put you to sleep with this discussion, but we spend a lot of time at anchor, and I’m always interested in learning anything that might make anchoring safer. As I look back over our years of boating, all three of my top ‘scary’ experiences occurred while at anchor.
Nordavn 68, Sans Souci
PS Steven and Carol Argosy (Seabird) emailed this morning their final update from this year’s GSSR cruising. It also includes a bit more information about the typhoon…