Underwater Navigation
 

Perhaps there are other things to be discussed also, but I was watching something this morning that made me wonder how I should adjust for current while navigating underwater. Assume no equipment other than a compass.

Porpoise occasionally. See where you are heading and adjust the compass heading accordingly. :lifter Example: if you see you are headed 100 M to the right of the target, adjust the compass to 100 M to the left. A porpoise is a very brief surfacing to see where you are heading. Subs have periscopes. :D

Let's assume this is either not possible or not desired for some reason.

Off set navigation
 

As with anything, it's speed, distance and direction. Underwater a swimmer is limited in distance but it all works the same under and above water. The navy has tide charts that you use to figure the direction and speed of the current. You take the target's location, back out the distance and direction you'll be swimming/boating and then move the drop off point upstream into the current the required distance. When you are dropped off you are not swimming/boating for the target. You are moving on a compass heading. The current drifts you into the target.

The key is time. Too fast and you hit short of the target, too slow and you hit way long of the target. This is where practice comes in. A team can spend a great amount of time working out loads and doing speed/time runs all for one run into the beach.

Pete

Of course in the new age we have GPS. Now you could just say "Go thata' way."

Get as close to the bottom as possible, where there is less current.
Also, you are able to have some type of land mark (ie reef, rock(s), wreck. Once past that landmark on your heading, pick up another, and leapfrog your way.

But being by the bottom is the best.

Night Ops
 

Underwater infiltration has been covered in the SFUWO thread. Underwater operations are mainly conducted at night because you have to be dropped off by some type of transport. Night allows the transport to bring you in close enough to complete the infiltration underwater.

Night distance swims under water are all characterized by the same thing "You can't see shit" not even your buddy. You have to depend on your compass and swim out the timed course. The east coast and gulf area allow most divers to hug the bottom but that does not work on a lot of islands in out of the way places. Also the deaper you go the more air you use per breath. Shallow = longer range.

Now we can get into harbor operations where we need kick counts, a multi legged course planned with more care than the D-day operation, stop watches and a whole lot more but I'll let the Navy keep that and I'll stick with my day job.

That's why guys like Terry and me say let the SEALS keep it.

But even in civilian diving a diver must be aware of currents and how fast they run or have a real good safty plan. Getting down current from your boat can get you in deep trouble in more ways than one.

Just thinking off the top of my head here.

Pete

This works just fine in AO's that have good visability; however, in areas that have limited visability (Like 6 to 8 ft.) it doesn't work to well. Have you ever done any work in Lk. Union Sdiver? :eek:

:D

RL - Tides and currents do not affect the combat diver - at least that's what they told me in Key West. Pete has given you the "textbook solution". It's properly referred to as a compensated launch point. Porpoising (QRQ30's suggestion) is also (properly) referred to as a tactical peek. Definitely not the school solution if you're trying to pass the CDQC but it is the most accurate. Unfortunately, it requires considerable practice to do it effectively - without compromising yourself. Sdiver hit it on the head for the average diver who will not be conducting tactical infiltrations over extended distances. Stay on the bottom (if possible) and fin hard. Observe the natural environment to determine actual current (grass, sand ripples, etc) and swag a (minute) compensated heading into the direction the current is coming from. If you have a good swimming pace and excellent technique you can be very accurate with practice. I would need to know more about what caused you to ask the question to give you a better answer. The type of swimming we are used to from combat diver training - bury your nose in the TAC board and swim like mad until your head hits the beach - is (almost) never required in the real world. True tactical underwater navigation with compass and stopwatch (extended distances with doglegs) is something of a lost art at least in the SF diving community. Even the SEALS are exploring high tech solutions to the problem. And most recreational divers have a hard enough time with buoyancy control without task loading a navigational problem. FWIW - Peregrino

Pete:

When I dive, I rarely am infiltrating to a target. Usually reconning an area around the boat, then returning to the boat. I always start into the current, but the question is how to adjust the number of kicks when going into the current, and when going with it. When the current is sideways, adjustments also need to be made.

Sounds like you guys leave underwater recon missions to the SEALs . . .

Peregrino:

You hit the nail right on the head.

RL

Plan your dive and dive you plan. Each time you get in the water you are conducting a mission. Look at it that way. Take what you know about the local water conditions, your physical condition and what you want to do. Make your dive plan around that and then stick to it. Make sure you have a good backup/emergency plan. I knew a guy who ran a 200' drift line of the back of his boat with a small IB and tower at the end. If you drifted off the site you'd just surface and swim, aiming between the two boats. You'd hit the line somewhere inbetween and just pull yourself to the main boat. Each dive site has it;s own considerations.

All big commanders hate to turn down missions. They just love to say "Our guys can handle that". A few days later you'll find yourself with five other bone heads bouncing over some fair size waves in the middle of the night. You and all your gear inside a small inflated rubber boat. Not a light or star to be seen anywhere. The motor man is maintaining RPMs and compass bearing while cold seawater splashes over you. It's at this point that you ask yourself "Is that $175 a month really worth it?"

The good news is that a lot of the work we had to do in the old days has been replaced by drones. Drones? Did I just say we were replaced by drones. OK, in some areas only.

Pete

Times change -- vocabulary too I see..Not my solution but what we taught. Swimmers were allowed one porpoise within the first couple of minutes of the swim to assess their compass heading. On long swims they were allowed an addidional porpoise. Currents tend to be litoral or parallel to a beach. I have seen times when the curent will change direction by 180 deg in a swim. The "balls to the wall and kick like hell" is for training. Have you ever noticed how many run out of air on a 2000 M swim? Don't forget where that 80 lb rucksack comes from once you are ashore and ready to BEGIN your mission. You pulled it along with iyou. :lifter

Again as Pete said, for actual operations the visibility is at or near zero. It was always fun to reach down and grab the compass man's leg on a real dark night.. :D :D

RL - Happy to have been of service. My last job before I retired was writing the new SF Maritime Operations Manual. (FM3-05.212 replaces TC31-25) That gave me a unique perspective on your question. Don't get me wrong, I've enjoyed diving at gov't expense since 79, but there really aren't very many reasons to do it. What makes it worse is there aren't many commanders who understand the capabilities and limitations. With proper mission planning the only people who should get wet are (maybe) two scout swimmers reconning the BLS - and they can usually surface swim. (Damn - I'm going to be burned as a heretic!) The S(qu)EALs still have an underwater mission but they're also throwing money at the tech side of the underwater nav problem (with mixed success). Everything that goes on a dive mission must be considered expendable and the current "Buck Rogers" stuff is way too expensive for that. The most cost effective solution right now is underwater GPS but that still requires floating an antenna which is a compromise risk. There are some other minor details but none important here. Bottom line - proper mission planning will probably show that underwater ops have a very limited utility. 95+ % of missions assigned to SCUBA teams can probably be done with standard MAROPS techniques and nobody has to breath compressed air (for anything except the lobster dive - after all, got to party when the mission is done). Just my soapbox. Peregrino

I've been reading a history of the SEALs, and learned that the principal purpose of starting the UDTs was to recon and clear beaches prior to invasions in WWII. This still is a core mission of the SEALs, although apparently they are focused on other tasks at the moment.

Sounds like SF water teams are not trying to duplicate that capability, and are focused more on water infils.

Compass man
 

I see all dive buddies are the same all over the world. That leg would draw up faster than you could pull you hand back :eek: Then again, if it was your leg you thought some big ass damn sea eel just latched on.

Pete

Our planning range was 2,250 PSI at 15' was good for 2,000 meters. You should hit your reserve just before you hit the beach. 100 lps per 100 meters. Some of those steel 72s did hit the beach with some big dimples pulled up from the bottom and some guys had to buddy breathe the last 50 metes or so. That was only for in shape guys. I'd probably do 1,000 lps per 100 meters now. Oh well