Challenge: Spotting Coral

[SailorBOI]

Ok, I've done a search to see if this has already been discussed, and from what I can tell, it either hasn't been, or not specifically. I'd like to invite anyone to share their experiences regarding navigation in and through channels around coral reefs, and in comparison, other typical rocks and coastlines. Most of my own experience has been with normally dark rocks, often seaweed-clad and more often than not, in murky waters. Judging the depth of such I have found harder than coral heads in clear waters which may or may not make sense to some. I know that where possible, it makes sense to avoid going over the top of coral that you're "sure" is below the draft of your vessel, however being able to judge the depth of each obstacle is essential in my mind.
One memory I have with the only experience I've had with coral, is that when we arrived at Middleton reef not long after midday, I found the coral heads quite easy to spot and judge the depth of either being above or below the 7' draft of the ketch (Kanani). However, leaving at first light about 4 days later, I recall it not being so easy to judge the depth below the surface. I can't recall if I discussed it with Wayne at the time, but I wonder now if it has anything to do with the refraction of light at the different times of the day? Or is it that the farther below the coral, the harder it is to judge the depth?
Comments/experience anyone?
Also, is a greater surface area rock easier to judge the depth on than a coral pinnacle?

[Pblais]

I wonder now if it has anything to do with the refraction of light at the different times of the day? Or is it that the farther below the coral, the harder it is to judge the depth?

Light has everything to do with it. Coral is also not the same color all over the world. At different light levels, sun angles to the horizon, cloud cover, your height above the water, turbidity, and the sea state will effect how it appears to your eye.

Practice over time helps to refine your visual accuracy at predicting depth. A thumping sound as you hit the bottom provides audio feedback. Gaining elevation above the water helps greatly. The additon of rat lines and a crows nest is advised.

[iiii]

Navigating though coral heads in the Bahamas is pretty easy; my wife usually takes a position just forward of the mast and give directions. These include left, right and MORE LEFT and MORE RIGHT, depending on how close we get.

[Pelagic]

When you have high light behind you and clear water, color is the key. Anything with brown tinges can be shallow as the reds wash out at deeper depths.

[Talbot]

This obviously becomes a significant problem for the single-hander.

Has anyone sited a colour camera up the mast and used the advantage of that height in order to spot the dreaded coral!

[Robertcateran]

with a remote autopilot, you can steer from nice and high up the mast. I recall seeing a boat with a wheel up the mast.

[starfish62]

The light makes a huge difference. Between 10 and 2 was my target window. Cloud cover and/or low light makes things too sketchy. I've laid offshore overnight rather than trying to run into an unfamiliar cut. Having said that, when I went into Beveridge Reef I sailed around a lot of bommies that I subsequently dove on and discovered that they were in 30 feet of water. The water clarity made a big difference in my perception of their depth, but that water was almost uniquely clear. We could identify species of sharks at night by moonlight in that water.

[sck5]

i am just back from sailing the offshore reefs and cays in Belize. It is all about water color which you can see best when the sun is high and even better if it is behind you. We had somebody stand at the bow and give directions in places where it was necessary but saw people who just sailed through them looking from the helm. It seemed possible to do but eyes up front were better.

We practiced by guessing the depth we were in and then asking the helm what the depth finder said. You can get pretty good after a while

[SailorBOI]

Thanks guys - those are all really good replies IMHO. I had not thought too much of colour, yet indeed if all coral of the particular reef being navigated was the same, this could also help in judging the depth. I'd like to think we don't rely on audio feedback however! Prefer to avoid such myself.
Thanks again.

[Hud3]

Besides having good light, i.e., having the sun high and preferably behind you, polarized sunglasses really help you see what's out there. The colors that you see really do vary pretty much with depth. Here's a little ditty to help you remember, "Brown, brown, you'll run aground; white, white, you might you might; green, green, nice and clean; blue, blue, go on through."

Sck5's suggestion to practice using the depth finder is a good one. Slow down, and don't get yourself into a spot that you can't easily recover from if you happen to misjudge. You'll get the hang of it pretty quickly.

[Reefmagnet]

My preferred approach is to use polarised glasses and come in to the anchorage with no cloud cover and with the sun > 30 deg. above the horizon and no wind disturbed water, ideally with a lookout placed at the bow. These conditions don't always exist when entering an unfamiliar anchorage, however.

Fortunately, bommies only grow to about LAT height. If you know the tidal information for the area and it has sufficient range then you can use the tides to float over the top of the reef then use the depth sounder to determine the bottom composition.

[Amgine]

I recall Lee Graham rigged a single-line remote steering system to con from the bow. It's pretty easy to do with a tiller - add bungees from the tiller to one side of the cockpit, and a line to a turning block on the other side. A moderate pull on the line keeps the tiller amidships, slacking or more tension brings the tiller to one side or the other.

But I wouldn't want to be so far from the reverse.

[Jim Cate]

Polarized sunglasses, getting up a little higher, traveling between 10 & 2 all on days with good sun, help. In addition, we've found
that sometimes there are hidden bommies in murky water, and
for that, we have a forward looking depth sounder, which has
kept us off a reef we had no other way of seeing. We had previously touched one time when it was overcast on arrival
from an overnight passage where there were no markers. The
clouds in the sky were mirrored on the smooth water, and fortunately we were going very slowly. In addition, we carry
cheap "walkie-talkie" headsets which we use to communicate
with someone at distance from the helmsman. Also useful for
stress-free anchor drills, communicating with the skipper when
he's working at the masthead, and so on. We put sponge over
the microphone to cut down on wind noise. Too bad they're not
water-proof, too; then we rely on hand signals.
(Signed) Ann Cate, s/v Insatiable II