Navigating underwater from boat dives

[Matthew Yung]

So me and a mate are planning a boat dive for cray hunting sometime this or next week. For me, this is a first as I've only ever done shore dives.
However, I'm a little lost to as how you would navigate underwater from diving off a boat. I mean, for shore diving its relatively straightforward; point you point the lubber line to the shore and line up the bezel with N. Whats more, you've got this huuuge chunk of land which is pretty darn hard not to miss.
For me, boat diving doesn't seem as intuitive. You've got this small boat floating in the middle of the sea, in which you can only see the anchor line and the hull if your underwater.

So my question is, how would you go about navigating underwater off a boat dive, especially since we won't always be swimming in a straight line? I've read a few articles from googling, but I'd like to hear some of your feedback as well

 

[Crass3000]

I would take a class in navagation. While it might not be convenient, it will give you more tools to work with. As with anything, practicing and you will get better into it. Also, if there is a current make sure you head into the current.

I also find heading down to the anchor and taking the exact depth helps in finding the boat -- the depth given by a depth finder can vary quite a bit from the depth at the anchor.

 

[AfterDark]

I use my compass, bottom features, such as large rock(s), sandy area etc, bottom contour and my depth gauge to nav from shore or boat. To really provide oneself with accurate nav kick counting is very useful. It’ll get you back in the general area of the boat; which will cut down on the surface swim.
Of course the easiest way is for the boat tender to follow your bubbles so when you come up the boat is right there. Buy a book on underwater nav and learn it, practice on land with the compass if you are not well versed in its use. Or like the last poster suggested take a course.

 

[farsidefan1]

For me underwater geography is the primary tool combined with some basic compass work. You may have heard the old axiom, wall to the right out and to the left on the return. It works - if there is a wall. I'm just not able to focus on counting kicks and diving let alone adjusting for currents, distractions to the right or left. I just lose track. First off I move very slow while diving so I'm not going terribly far from the takeoff point. If it's a wreck or a formation, well even easier to navigate. If I'm covering some ground I make it a habit of looking back every few minutes and memorize how it will or should look on the return trip. If I have a specific objective then the compass is my bible. But if I'm just tooling around exploring the look back technique works great, especially if combined with a slate to note specific features and an occasional compass check just so I know the general direction back. Then assuming you are not fighting major currents there is always the surface and let the boat come to you method (keep your smb handy along with some sound device). This last technique is sometimes of dubious value in rough water. Especially if your boat captain isn't an alert person. Oh, and tell me you do leave someone on the boat - please. Of course all this presumes we are not talking about a drift dive. Have fun and happy diving.

 

[merxlin]

It takes lots of practice, especially in low viz. It takes a combination of reading compass headings, time, depth, and a bit of natural instinct.

 

[TMHeimer]

Take the course, use the compass, carry a SMB (you may want/need to use it for the boat to find you/pick you up as planned). Probably don't go too far afield the first few times. And #1: Always remember where the anchor line was....

 

[bpotkin]

Nothing is better than swimming around for 45 minutes, then surfacing right next to the boat. And nothing is
worse than surfacing and finding you have a 150 yard surface swim against current. An invitation for a leg cramp! With
that being said, I like to follow the bow line and start out swimming against the current. Keeping the compass on your
arm is a great way to keep track of your heading. Trying to keep track of where the sand is vrs. where the kelp is, works well.
Rather than counting kicks, tank pressure also works. Keeping track of depth can be helpful.
Basically a combination of all of the above.

 

[TSandM]

If you can follow some type of bottom structure, it isn't too bad. Follow the anchor line to the bottom, and make note of the lie of the anchor, including structures, depth, and how the chain is lying. If you can follow structure in a given direction, then you turn around and follow it back, making sure you end up at the same depth where you found the anchor.

Where it gets dicey is where there is no structure, or it's chaotic and the bottom has no significant slope. Then you can't use structure OR depth as a good clue. If you are in still water, you can try the best you can to get back to the anchor line, but you may surface to an annoying swim. If you are in rough water or current, you can be in trouble if you surface too far from the boat. It's my opinion that, in those conditions, there should be a tender on the boat who can come and pick you up if necessary. (That's ALWAYS a good idea, anyway.)

 

[Searcaigh]

As others have mentioned above, learn to use your instruments ... depth gauge, SPG, compass and watch as well as underwater landmarks

Take a refresher in navigation and carry an SMB

 

[Steve_C]

What they said about navigation.

In low viz. Run a line with a reel. In low viz it is really easy to swim right pass the anchor even if you are good with a compass.

When you first get down do not swim off. Make a circuit or two of the anchor area so that if you are not using a reel you can recognize the anchor area before you see the anchor when returning.

I like to plan the dive so that I return to the anchor area with a bit of extra air left. Nice margin if the anchor is hard to find. Always something to see if you find it quickly.

Look for the gloom. If you are diving some place shallow (like under 40 ft) there will usually be a darkened area under the boat that is noticable much further away than the anchor line.