Private boat diving at Isla San Benedicto

Isla San Benedicto, in the Revillagigedos group, is an amazing little island that offers some truly unforgettable diving. In February 2016 my wife and I, along with two guests, sailed our boat to the island and spent 2.5 weeks there; here is a detailed writeup of the trip. This was our first time in the Revillagigedos, and this post contains some information for anyone considering a similar trip.

– Benedicto is 220 nm from Cabo, pretty much downwind in the prevailing weather. Socorro is another 30 miles, and several other islands are further afield. We only visited Benedicto, though plan to return next year and see more of the archipelago. Visiting these islands requires a permit from SEMARNAT. We got our permit through Eco Naviera in La Paz, and other agencies can provide them as well. Our permit allowed us to stay at Benedicto for 20 days, and we paid one hundred dollars, in addition to the cost for national park passes (the same ones needed to visit Espiritu Santo).

– The island is three miles long, and the main anchorage is at the south end. The bottom varies across the anchorage, but in the northwestern part we had a sand bottom and good holding. Depending on conditions quite a bit of swell can enter the anchorage, but in our catamaran it was always comfortable. There is an anchorage on the east side of the island, though we never saw anyone there; it is far from the best diving and is exposed to the sometimes substantial wind swell coming from northers in the Sea of Cortez. We also investigated an anchorage halfway up the west side of the island, but never had an opportunity to use it. This is exposed to the pacific swell and has deeper water than the main anchorage, but in calm conditions would provide convenient access to the Boiler dive site.

– Take extreme care anchoring dinghys in areas with mantas. Manta rays are huge animals, up to 25′ across, and have eyes on the sides of their head and can’t see what is between their horns and about to enter their mouths. A few days after we arrived a manta got tangled in our dinghy’s anchor line while we were diving. Dealing with this was a horrible experience. Something similar happened to another boat in the anchorage on a previous trip, and it apparently happens to the commercial liveaboards sometimes — even if the operator is live boating their dinghys, some use buoys to mark dive sites. The best solution to this problem is clearly to not anchor the dinghy but to live boat it instead. We had four people aboard so were able to do this the rest of the trip, but if this isn’t an option I’ve included some thoughts on anchoring among mantas at the end of this post.

– We did almost all our diving at three sites on the island. The best is the Boiler, a pinnacle off the northwest portion of the island with a least depth of 15′ or so, dropping quickly to 120′ on all sides. The top of the Boiler is at 19N 19.800′ 110W 48.834′ (WGS84). Heavier swells break on the Boiler, which could have catastrophic results if it swamped or flipped a dinghy. Such swells were coming in about half the days we were on the island. The second dive site is the Canyon, near the main anchorage. This is a fairly large area which we didn’t explore all that well; we did most of our dives here starting at a small pinnacle with least depth of 15′ or so, whose top is at 19N 17.808′ 110W 48.427′. This pinnacle drops away to 60′ or so on all sides, quickly falling to much deeper water to the southeast. The third dive site is less of a spot and more of an area; we would dinghy around looking for groups of mantas at the surface, and then go diving or snorkeling with them. We would usually find them somewhere either close to the main anchorage or along the southwest coast of the island. We never saw commercial operators doing this, but it led to some of our best encounters with the mantas.

– There are a lot of critters at the island to see, but the stars are the manta rays. We saw rays nearly every day; they were always at the Boiler, often at the Canyon, and could usually be found by looking for them at the surface in the dinghy. They are amazing animals, sometimes playful and genuinely interested in divers, circling around and around to look at us. Besides mantas, there are a lot of white tip sharks on the reefs, which are fearful of divers, and many silky sharks in the top 20′ or so of the water column, which are usually wary of divers but sometimes got interested in us and caused us to abort one of our dives. Otherwise we saw dolphins, tuna, and many smaller fish and lobsters on the healthy reefs. Visibility ranged from 30′ to 60′, generally best at the Boiler.

– Few private boats visit these islands; the first week a family was in the anchorage with us, and for a few days a couple stopped by on their way back from Socorro. On the other hand, there are many liveaboards here. Most of the time there would be one or two liveaboards in the anchorage with us, and on every day where the Boiler was suitable for diving there would be at least one and usually two or three liveaboards anchored there. While this detracts from the island’s wild feeling and makes it tricky to dive the Boiler without running into a horde of other divers, the liveaboards provide an extra layer of safety and security that was quite welcome in this advanced, remote area.

Anchoring with Mantas

When the manta got tangled in our anchor line, I was underwater watching it happen. The line came between the manta’s horns and it reared up instinctively, catching the line, lifting the anchor off the bottom, and twisting the line around one of its horns as it took off in a panic, dragging the dinghy behind it, anchor dangling in the water. While we recovered the dinghy and the manta was alright, I want to do what I can to keep this from happening again to us or to other visitors. So to that end, here are some ideas about how to harden a dinghy anchor against mantas.

We heard later about tying strings to the dinghy’s anchor line every few feet, so that when the dinghy is anchored the strings sink down or float up and make the anchor line more visible to mantas. While doing this could help, this wouldn’t work for all angles of approach and doesn’t address the underlying problem, so I don’t feel this is enough on its own.

One reason the manta got tangled in our line was the lightness of the line — our rode was a typical nylon line with several feet of chain and an anchor at the end. I would be shocked if a manta could get tangled in or dislodge the primary rode on a private boat or liveaboard, especially an all chain rode. The line/chain would be too heavy and the manta, in rearing up, would not catch it and would be able to get away (mantas can only swim forward, but they frequently do cartwheels and other acrobatic maneuvers while feeding and traveling). Using a heavy all chain rode for a small dinghy seems pretty extreme and awkward to handle, but it should prevent tangling.

An alternative to chain that would weigh much less and should be easier to handle would be to run an ordinary nylon line through four foot sections of PVC pipe, with figure eight knots on the line between each pipe section so the pipes could not slide around. The line would still articulate and could be packaged up like a bundle of sticks, but it would be impossible for a manta to get tangled in it.

Tangling, however, is not the only issue. If the manta snags the anchor line it can just take off with the dinghy and anchor, even if it isn’t tangled. If you get back to the dinghy, start it, and motor out in front of the manta then the line will come off, but if you don’t have another dinghy or boat nearby to help you are in for a swim. Securing the anchor to the bottom by tying in to a boulder etc. would prevent this from happening.

I haven’t tried any of these ideas, as for the rest of the trip we used a live boat. The next time we visit these islands we will have an anchor that is ready for the mantas, however.

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