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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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  #1  
Old 01-05-2009
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Anchoring for Hurricane - Shallow Water, Wing Keel

Where I live in NC, we frequently get hurricanes. The water in the river/bay at this point is shallow (10-14 ft.), 1-2 mile fetch in bay, 40 miles in river, storm surges on order of 8-9 ft., and winds now down to 70-80 mph, with significantly higher gusts at this point inland (although there is one storm on record of 105 mph locally). There are four large marinas on our creek and preparation for such storms is roughly 1/3 anchor out, 1/3 get marinas to haul out boats (but land is low lying), 1/3 stay at marinas. In the many past storms (over my 32 years on the creek), there are success and failure stories for each strategy and none seems superior. My previous and current stategy is to stay at the pier as long as I can tie the boat up appropriately....meaning 26 1/2" nylon lines tied to 8 tie points on the boat and to 11 tie points on the pier/pilings. On the open fetch side, because the 3 adjacent private slips are not in use during the storm (trailer boats pulled out), I tie across these slips, adjusting lines to accommodate the surge and the short choppy waves we get over the shallow bottom (6 ft. within the slip area), and adjust lines so loading is well distributed amoung the various lines. My concerns are not pulling the pier down (would be my expense), chafing of lines, line stretch allowing boat to get out of position in slip, and the action of my mast and that of the Pearson 323 in adjacent shoreward slip (the boats seem to have similar rolling/heeling characteristics). This techique has worked in past, but if I can't get to tie across the vacant slips or someone nearby appears to present a special hazard, then I would anchor out in the river/bay (going up a creek is not practical because of draft/depth issues. Anchoring out is dangerous ... lots of boats, soft bottom --- one boat in our marina got $80K of damage when another boat dragged down on it).

I have observed in past storms that some boats get one or more anchor lines wrapped around the keel and wind up presenting a broadside to the waves and wind, usually resulting in dragging ashore. Wing keels such as the one on my Catalina 320 present a special challenge to this issue, as the wings will act as scoops to pick up and hold a slack anchor rode if one is presented to it. In these storms, the wind will come from the east, veer to the north, and wind up coming from the west as the storm moves by. What seems to be the most recommended way to anchor with two (or more) anchors is to set the two anchors 45 degrees either side of the direction from where maximum wind/waves are expected. But, if you plot this out, you will see that as the boat swings, one anchor takes the load and the rode of the other one goes slack. Using nylon rodes in combination with the turbulent wave action over the shallow bottom, the rode is certain to be swept back towards the boat. In the storms, while the wind ultimately moves as above, locally variations in the wind will cause the boat to move about and there is a really good chance that the wing keel will snag the slack anchor rode, loading up the anchors excessively. While going to a chain rode might help this issue, there are reasons to stay with the current anchor, chain, nylon rode combination.

After thinking a lot about this issue, below is what I propose to do. It's a bit different and I would appreciate input/comment from experienced forum members -- if there are problems, then what and why, and what would be your proposal?

The center anchor would be a 43 lb. Danforth/West Marine, 20 ft. chain, 200 ft. 5/8 in. nylon rode laid in direction of maximum fetch/wind (more or less north). Either side at a 7 degree spread would be the other anchors...33 lb. Bruce to the east, 15 ft. chain, 200 ft. 1/2 in. nylon, 22 lb. Danforth to west, 15 ft. chain, 200 ft. 1/2 in. nylon. Thus, initial wind is a side loading situation from the east, with wind increasing to maximum in north region, where anchors are properly oriented with storm for maximum resistence, and finally side loading from the west as the wind, now decreasing as the storm moves past. In principle, this is how the wind should work, but in at least one storm, the maximum wind actually came from the southwest due to cyclonic conditions locally. The lines would be coupled at the boat with a swivel, with backup jumper lines around the swivel in case it failed, and tie points to three different cleats on the boat with chafe protection. The narrow spread assures that, as the boat swings about locally, it never gets enough slack to wrap the keel, and at the height of the storm forces, all three anchors are working together and oriented in best direction relative to maximum wind and maximum waves. One downside, is that this arrangement maximizes the swing area and requires significant separation from other boats. Bottom will be sand or mud. These are the anchors that will be used .... other types are not to be considered at this time.

Sorry for the long post, but the details need to be considered to give a considered opinion. Now, your comments on this proposal please. Thanks.
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Old 01-05-2009
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3 anchors close together - trouble. Only one holds the load, yet the load can shift

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Multiple anchor rigs (Rocna Knowledge Base)
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Old 01-05-2009
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Agree....there is a reason BoatUS pays half the cost for haulout for their insureds!!
The only situation where I would stay in the water in a substantial hurricane would be where I could tie into a web of lines in a small channel or mangroves or do the same within a marina to fixed and solid pilings...not to cleats in wood!
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pdqaltair,

Thanks for your reply. If I had primary and secondary anchors on chain, the system proposed in Jetsam looks attractive and minimizes the swing (reducing the possibility of contact with other boats that might drag into the larger swing area of my proposal).

I have little chain and lots of nylon (I realize that chain, while expensive, is cheap comparied to cost of boat). In my proposal, all three of the nylon rodes would be stretching at all times in the wind (wet nylon will stretch about 40% before breaking), absorbing shock and surges. Since all are extended (stretched), wouldn't the load be gently automatically shifted from one to the other as the boat swings, and by having the anchors close together, all three anchors would be carrying some load at all times, but none would at any time be taking the full load on a single anchor as in other techiques. Am I missing something here?
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Old 01-06-2009
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Quote:
Originally Posted by camaraderie View Post
Agree....there is a reason BoatUS pays half the cost for haulout for their insureds!!
The only situation where I would stay in the water in a substantial hurricane would be where I could tie into a web of lines in a small channel or mangroves or do the same within a marina to fixed and solid pilings...not to cleats in wood!
A significant number (~1/3) of boats locally haul out. At time of Hurricane Floyd, my new C320 was being commissioned...bottom paint on but not yet in the water when that storm hit. The yards are low lying and it came within ~ 1 ft. of floating off the blocks as evidenced by the high water debris mark on the fresh bottom. Several of the boats pulled for the storm or which were already in the yard for work toppled or came off the stands.

My pier is piling type construction and I prefer to be there in the level of storms that we get, provided I have that spider web of lines (26 of them in my case..all good condition lines, tied to the pilings, with all lines and attachment points redundant). I agree with you on the cleats in wood piers, and while I use all available pilings and pier cleats (for redundancy), I've seen, in prior storms, cleats being pulled out from both pier and some boats. Additional caution on pier cleats is that when the water comes over the pier in the storms (storm surge), the water action around the cleats will untie lines unless the line tails are tied back to the line with half hitches. Our pier has just been rebuilt and pier cleats are large, with large bolts and backing plates thru double 2 x 10 stringers, so they are a little less a concern now. Also, the pier/pilings act as a buffer against anchored boats that drag (it collects one or two each storm). Dock walkers sometimes make comments about all the lines I have put on before the storm hits (and it does look like overkill), but when winds get over 40-50 mph and while you can still get on the pier, you begin to think maybe I should have added some more. It's always worked in the past, so this is my preference. As to the boats in the marina who tie with fewer lines (sometimes no choice given adjacent boats in slips), some survive ok, but lots get damaged in the storms.

I am terrified at the thought of anchoring out given our soft bottom and the way that some people anchor. There's a boat double anchored off the marina now that has drug anchors 4 different times in moderate blows in the last year. If two boats get together in a bad storm, they will beat each other horribly. My questions regarding the anchoring technique were because if I see the pier situation become untenable due to something happening within the marina, then I would have to anchor. As the two working marinas have limited lifting and yard capacity, boats wanting to ride out the storm on blocks have to prepay annually whether they get pulled or not. Most boats that anchor out do so in the creek just off the marinas or out in the relatively small adjacent bay. There are so many anchored in soft bottoms in so many anchoring styles during hurricanes, that I think I will take one old skipper's advice. He said he anchored his boat in the river (even though it has long fetches in two directions (SE, NW). Rather than anchoring in the creek or the bay where he has a good chance of becoming a "boat sandwich" (two or more boats banging together), he went up the river to where there were no other boats and anchored. If I have to anchor, I think I will do likewise.
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Another Option

The 320 isn't overly heavy or difficult to haul. The mast isn't unmanageable either. Have you considered a trailor and the other options having one might provide? There may even be a self loader available for that model with that shallow keel that would allow you to avoid travel lift charges....and may help pay for itself in decreased dry storage cost, if you haul out at all.

It sounds like even if you have a secure multi anchor system set up, you would not be able to control the other boats and stuff flying around such a confined space.

Good luck!

121 Guy
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Old 01-06-2009
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You won't be getting 40% stretch at your working loads.

Quote:
Originally Posted by NCC320 View Post
pdqaltair,

Thanks for your reply. If I had primary and secondary anchors on chain, the system proposed in Jetsam looks attractive and minimizes the swing (reducing the possibility of contact with other boats that might drag into the larger swing area of my proposal).

I have little chain and lots of nylon (I realize that chain, while expensive, is cheap comparied to cost of boat). In my proposal, all three of the nylon rodes would be stretching at all times in the wind (wet nylon will stretch about 40% before breaking), absorbing shock and surges. Since all are extended (stretched), wouldn't the load be gently automatically shifted from one to the other as the boat swings, and by having the anchors close together, all three anchors would be carrying some load at all times, but none would at any time be taking the full load on a single anchor as in other techiques. Am I missing something here?
5,000-10,000 pound ropes don't break at their limit in storms - they break from chafe. They don't even fail at knots, which would typically be 50% of line strength. I doubt you will see over 20-30% of breaking force, and thus only 15-20% elongation. At that point, a rope that is stretched 5% vs one that is stretched 20%... they won't share the load well. But you do have a point.

If it was me and I had to anchor out, I would find the tiniest cove I could, way at the head of some creek, and get lines to trees on one side, and have my anchors spread on the other. The lines would connect on the river bottom to prevent fouling, and I would have chain for the final connection (chafe and twist).
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Old 02-19-2009
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We anchored during Floyd(1999) as far up the Aligator River,as far as we dared ,well off the ICW round a few bends to where it narrowed.Put out 2 CQR's positioned for expected winds with danforth to current wind.Stripped the boat of all canvas including sail took dog for last pee partially sank dinghy with water then waited. Fun!!
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Old 02-19-2009
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One other point—you really need to check what your insurance policy says about named storms.
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Old 02-20-2009
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If I had a boat in a place where there were "frequent hurricanes" (and even if I didn't have a boat) I'd move to another location.

And that's not a flippant comment - I really would move away.

Having said that, I live in a city surrounded by 24 volcanoes. Go figure. Somehow they're not as scary.
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