South Pacific anchoring: dealing with bommies

We wondered a lot about anchoring among coral reefs before taking off from Mexico… and we’ve heard the question a few times since going through the experience ourselves. Jamie put together this response. 
South Pacific anchorages add a new dimension to parking the boat. Coral heads snag anchors, tangle and abrade anchor chain, and chew up nylon rode. This is not helpful to the common illusion of what South Pacific cruising is supposed to be like; nor is it good for living coral, in my view the most spectacular of all living things.
contemplating
Perfect example of an anchorage with a minefield of coral heads
First, it’s important for the uninitiated South Pacific cruiser to understand the difference between boobies and bommies. The former refers to what you saw at Isla Isabella and hope to see in French Polynesia. The later is the common reference to coral heads (derived the Australian Aboriginal word bomboras, loosely meaning isolated reef). So while the meanings of both words share a certain aesthetic beauty, bommies differ in that they can wreck your boat.
Among bommies, the “floating chain” anchoring technique is not new. It’s also not well known or practiced. It does reduce coral damage caused by anchor gear; and minimizes anchor chain on coral macramé events. The basic concept is to attach floats, usually boat fenders, to anchor chain thereby keeping sections of the chain above bommies.
keeping chain off coral
A rough idea from the deck of how the float system we use works.
Technique notes from Totem:
  1. We measure anchoring depth as being from the bottom to the bow roller.
  2. Scope: commonly 4:1 but varies widely based on local variables.
  3. Floats (boat fenders are perfect): we used fender measuring approx 8” x 30”. Occasionally we used larger fenders (12” x 32”) in deep anchorages or around very tall bommies.
  4. Attaching fenders to chain:  use about 2’-ish of line between chain and float. Tie to chain with a rolling hitch or clove hitch AND with an extra half hitch to “lock” it, as current/chain/boat movements keep the fenders working.
  5. Safety: mind the finger/toes/etc once the float is tied and more chain is let out! Make sure the float will not foul on the way over the side.
  6. Anchor drop: pick a clear spot to drop anchor (very challenging sometimes). The anchor drags before setting (varies with type), so account for drag distance as well.
  7. 1st float: about 1.5 x anchoring depth
  8. Additional floats: Very loosely, spacing equals 1 x anchoring depth. Amount varies with how much or little you want to control anchor chain droop between floats.
  9. Setting the anchor and use of snubber is no different than without floats.
  10. Communication:  Is a must, especially when windy/choppy. When attaching the first float it is incumbent on the person at the wheel/engine controls to keep the boat from sliding backwards much – or you’ll find the unset anchor will end up on or to close to a bommies.
  11. Hauling anchor: The cautions mentioned above are especially true when raising the anchor in rough conditions – fingers/toes/boat position. It’s also a good idea to take advantage of the clear water and get a good picture of the section of chain that is on the bottom because floats don’t eliminate minor bommie wrapping. Slowly motor forward in the direction of the chain to reduce the chance of destroying coral and to reduce the chance of pulling the anchor back into coral, causing bigger problems.
The catenary question: catenary we all know is the curve in the chain rode between the two fixed ends. More curve means better holding because of a dominate shear force (horizontal on the anchor) instead of peel force (lifting anchor from bottom); and because the curve acts as a shock absorber (in conjunction with the snubber) so that a pitching bow doesn’t jerk the anchor out. Floats do affect the catenary. In the first case, the first float lifts the chain and thereby makes the pull on the anchor more vertical – less good. In our experience on Totem, this never once caused us to drag; although different anchors may yield different results (we have a 33kg Rocna). In the second case, the shock absorber affect is not affected by the floats because they do not cause the chain to be straight between the 2 fixed ends.
The opposite is true if you don’t use the float method. Because the chain will wrap around a bommie (more or less dramatically) the anchor pull angle parallels the bottom so holding is very good. The problem is that the effective scope is reduced to the distance from bommie to bow roller; thus reducing chain weight and catenary, reducing the shock absorber affect. In a bouncy anchorage this can cause shock loading that stresses the chain, bow roller and/or snubber. Also, chain wrapped on bommies wears through galvanizing very quickly, can cause loading perpendicular to the chain link (much weaker), and causes loud scraping sounds as the boat moves around.
So in terms of holding power, anchoring both with and without floats poses  issues to be aware of around bommies. The real benefit of the float method is that you are much less likely to delay your departure from an anchorage due to a need to untangle chain. This process can literally take hours or be demanding in rough conditions.  And you cause less damage, or no damage, to the living coral that we all want to see.
Pacific destintions where Totem used the float method:
  • Marquesas – Tahuata (Hanamoenoa Bay), Ua Huka (Haavei Bay), Nuka Hiva (Anaho Bay, Controller Bay)
  • Tuamotus – Makemo (all anchorages) Fakarava (all anchorages)
  • Societies – Moorea (Opunohu Bay), Huahine (all anchorages), Tahaa (Baie Hurepiti)
  • Cook Islands – Suwarrow (Anchorage Island)
  • Tonga – Vav’au group (Hunga, Kenutu, Vakaaeitu)
  • Fiji – Yasawa and Mamanuca groups
  • Vanuatu – NW side of Lelepa Island
  • New Caledonia – N side of Lifou Island in the Loyalty group

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8 Responses to South Pacific anchoring: dealing with bommies

  1. Tony Hollingsworth March 14, 2011 at 6:19 pm #

    So glad to have met you Behan – and to see you still blogging! Catch up soon at coffee mornings.
    Tony

  2. Del Viento March 15, 2011 at 12:47 am #

    Behan, When we left on our first cruise, we carried a physical notebook I’d filled with clippings from Latitude 38 and articles from Cruising World containing info I knew would be useful to us along the way. This time, we will depart with a virtual notebook of mostly blog entries, many of which are from Totem. Thank you for this and your other “helpful info” posts.
    Michael of s/v Del Viento

  3. Andy & sonja Pulman March 15, 2011 at 5:19 am #

    Hi Folks, we are looking for info on the cost of sailing, we have “like many others” a plan & hope to get our catamaran in 7 months time as we will hopefully financially ok to get the boat & sail for about 3 to 5 years as we have put a side $40k as living expenditure after we pay for the boat, would you say this is an ok figure as every thing we read says between $10 & 15k for 2 people per year.
    We are great full for all info. welshdiver@hotmail.com

  4. Red Charlotte March 18, 2011 at 2:28 pm #

    Very helpful post. Thank you!

  5. SV Estrellita 5.10b March 29, 2011 at 6:26 am #

    Speaking of navigating coral heads…Does Totem have mast steps? I didn’t see any obvious ones in the photos and my memory is that IO doesn’t have any. Were you able to see clearly enough from the bow pulpit?

  6. Bruce Stewart October 23, 2015 at 8:43 am #

    Hi – was just reading your post on anchoring between bommies. I had head of the technique previously but was interested in you experience with the technique. I have one question. How do you set the anchor with this technique? Do you lay out the 4:1 scope and set the anchor as usual prior to hauling it back in to attach the bouys (unlikely) or do you set it with 1.5 x depth scope before attaching the first bouy? I note you have a 33kg Rocna which I understand sets very well and quickly, but I was surprised that any anchor could be set with 1.5 scope.

    My wife and I will be doing the coconut milk run across the pacific in the near future and, while we have a lot of experience anchoring amongst coral (we do live in Queensland), we are aware of the bommie-filled anchorages commonly found in the Pacific.

    Love your blog – a great reference for many a cruiser.

    Kind regards – Bruce Stewart

    • Behan October 27, 2015 at 2:05 pm #

      Hi Bruce- Fenders are tied AS the chain is let out, so it’s a stop-and-start process.
      So the first fender goes on at 1.5x anchoring depth, but there’s still a 2nd fender (or more) and then we have full scope (typical is 4:1) all out *before* we try to set that anchor. Def not trying to set in 1.5:1, that wouldn’t fly! I’ll check the post wording to make sure that’s clearer. We needed this technique a LOT in the Indian Ocean – notably Maldives – to be kind to coral.

  7. Bruce Stewart October 28, 2015 at 2:41 am #

    Thanks Behan – that clears things up and I can now visualise the technique as it is laid out. We will definitely put this technique to use. As Jamie notes, you are much less likely to delay your departure from an anchorage due to a need to untangle chain, not to mention not damaging coral in the process.

    Thanks for getting back to me on this – very much appreciated!

    best regards – Bruce S

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