Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 15-01-2009, 18:44   #1
Registered User
 
SailorBOI's Avatar

Join Date: Jan 2009
Location: Bay of Islands, New Zealand
Boat: Wish for a Ketch
Posts: 9
Challenge: Spotting Coral

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?
__________________

__________________
“A pessimist sees the difficulty in every opportunity;
an optimist sees the opportunity in every difficulty”
SailorBOI is offline   Reply With Quote
Old 15-01-2009, 20:44   #2
Moderator Emeritus
 
Pblais's Avatar

Join Date: Mar 2003
Location: Hayes, VA
Boat: Gozzard 36
Posts: 8,700
Images: 15
Send a message via Skype™ to Pblais
Quote:
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.
__________________

__________________
Paul Blais
s/v Bright Eyes Gozzard 36
37 15.7 N 76 28.9 W
Pblais is offline   Reply With Quote
Old 15-01-2009, 21:22   #3
Registered User

Join Date: Jun 2008
Location: Florida
Boat: C & C Landfall 38
Posts: 130
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.
__________________
iiii is offline   Reply With Quote
Old 15-01-2009, 21:28   #4
CF Adviser
 
Pelagic's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 6,895
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.
__________________
Pelagic is offline   Reply With Quote
Old 16-01-2009, 02:13   #5
Senior Cruiser
 
Talbot's Avatar

Cruisers Forum Supporter

Join Date: Jun 2004
Location: Brighton, UK
Boat: Privilege 37
Posts: 3,579
Images: 32
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!
__________________
"Be wary of strong drink. It can make you shoot at tax collectors - and miss."
Robert A Heinlein
Talbot is offline   Reply With Quote
Old 16-01-2009, 03:05   #6
Registered User

Join Date: Feb 2008
Location: Oz
Boat: Jarcat 5, 5m, Mandy
Posts: 419
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.
__________________
Robertcateran is offline   Reply With Quote
Old 16-01-2009, 09:00   #7
Senior Cruiser
 
starfish62's Avatar

Cruisers Forum Supporter

Join Date: Mar 2006
Location: Palm Beach, Florida
Boat: Gulfstar 44 Sloop
Posts: 647
Images: 4
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.
__________________
Starfish
starfish62 is offline   Reply With Quote
Old 16-01-2009, 19:17   #8
Registered User

Join Date: Sep 2007
Location: Cayuga Lake NY - or on the boat somewhere south of there
Boat: Caliber 40
Posts: 1,096
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
__________________
sck5 is offline   Reply With Quote
Old 18-01-2009, 12:25   #9
Registered User
 
SailorBOI's Avatar

Join Date: Jan 2009
Location: Bay of Islands, New Zealand
Boat: Wish for a Ketch
Posts: 9
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.
__________________
“A pessimist sees the difficulty in every opportunity;
an optimist sees the opportunity in every difficulty”
SailorBOI is offline   Reply With Quote
Old 18-01-2009, 13:22   #10
CF Adviser
Moderator Emeritus
 
Hud3's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: Virginia
Boat: Island Packet 380, now sold
Posts: 8,929
Images: 49
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.
__________________
Hud
Hud3 is offline   Reply With Quote
Old 18-01-2009, 15:43   #11
Registered User
 
Reefmagnet's Avatar

Join Date: May 2008
Location: puɐןsuǝǝnb 'ʎɐʞɔɐɯ
Boat: Nantucket Island 33
Posts: 2,737
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.
__________________
Reefmagnet is online now   Reply With Quote
Old 25-01-2009, 10:14   #12
Registered User
 
Amgine's Avatar

Join Date: Dec 2004
Location: Vancouver BC
Posts: 1,384
Images: 1
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.
__________________
Amgine
Blog

On the internet, nobody knows you're a dog anchored in a coral atoll.
Amgine is offline   Reply With Quote
Old 25-01-2009, 10:51   #13
Senior Cruiser
 
Jim Cate's Avatar

Cruisers Forum Supporter

Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 11,467
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
__________________

__________________
Jim Cate is offline   Reply With Quote
Reply

Tags
coral

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Challenge: Wake Up The Mechanics - Outboard Challenge Ex-Calif Challenges 37 04-04-2016 09:55
BVI Coral - Where'd it Go ? Scottie2 Atlantic & the Caribbean 28 29-07-2009 09:07
Challenge: A Real Challenge Solved by a Forum Member Soft Air Challenges 10 27-03-2009 09:59
Healthiest coral reefs hardest hit by climate change GordMay Off Topic Forum 33 11-05-2007 03:07
Caribbean coral suffers record die-off CaptainK Atlantic & the Caribbean 2 02-04-2006 10:31



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 05:22.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.