Understanding Ikan kepe-kepe 02/20/2012
KEPE – KEPE (Familia : CHAETODONTIDAE)
Ikan kepe-kepe atau butterflyfish merupakan ikan yang mempunyai warna mencolok. Umumnya berukuran kecil antara 12-22cm. Ikan ini aktif disiang hari (diurnal), sedangkan pada malam hari mereka bersembunyi diantara celah karang dan memperlihatkan warna yang berbeda dibandingkan saat siang.
Berdasarkan peranannya dalam pemantauan ekosistem terumbu karang Ikan familia Chaetodontidae ini termasuk ikan indicator, karena hidupnya sangat tergantung pada terumbu karang.
Berikut adalah gambar/foto ikan Chaetodontidae yang kami jumpai dalam suatu trip di Bali
How Much Lead Do You Need? 01/30/2012
It is very important to get your weighting right. For instance, if you have a problem at depth and your are too negative you can't get up. On the other hand if you dont have enough weight you can't stay down and complete a decompression stop when you are getting low on gas.
You weighting need to be a balance between these two extremes and when you get it right you have "a balanced rig". And it can't be calculated, it has to be adjusted in the water.
Weight changes during the diveThere are two things that will change your weighting during the dive.
Number one, that affects everybody, is the weight of the gas in your bottles. As you breath it down and the pressure drops your tanks will become lighter - more buoyant or less negative depending on their weight in the first place. In the graph above you will see the weight of 32% nitrox in a 12 liter 232 bar bottle. 1 kg is about 2.2 pounds and the size of the cylinder is similar to a 80 cuft bottle.
As you can see the difference between a full bottle and an empty one is almost 3 kg, about 6 lbs. If you were wearing doubles the difference would be doubled.
The second thing affects your weighting is material that will compress at depth, for instance neoprene drysuits or neoprene wetsuits. When you go deeper the bubbles inside the neoprene will compress and the lift (positive buoyancy) from the neoprene will decrease.
The graph is calculated using a 7 mil XL full neoprene suit just as an example but actual values may vary depending on neoprene quality, thickness and size of the suit. Precruched or compressed neoprene should show only very small amounts of compression.
As you can see the difference between being at 30m/100ft or at the surface is about 5kg / 12 lbs in this case.
Two opposite extremesSince we have the weight of the gas and suit compression that affects us during the dive we need to think about two opposite situations when we consider our weighting.
One is that we are at the end of our dive with virtually no gas in our tanksand we try to hold a decompression stop close to the surface. In this situation we are the most buoyant and we need to make sure we have enough lead to just stay down.
The other situation is at the beginning of the dive when we have full tanksand have just reached the bottom. Now we are the most negative and if we have a problem, like our wing doesn't work, we need to be able to swim the negative weight up. If that is not possible we need to have droppable weight that we can get rid off in order to be able to get up. For a nightmare scenario imagine jumping of a boat with your tank valve off quickly sinking to the bottom with no gas to breath or no gas to put in your wing.
Determining the right amount of weightOur weighting consist not only of lead but also of tanks, backplate, lights etc. Basically we need to figure out how much weight we need in total and then how much of that we need to be able to dump in an emergency.
Step one is to dump the gas in your tank so you have about 10-20 bar/150-300psi. Drop down to 3m / 10ft. You should be able to stay down but just barely. If you can't get down however, you need to add more weight.
When you are down below have you buddy check the amount of gas you have in your wings. The wings should be empty and if you have a drysuit it should just hold a comfortable amount of gas.
By looking at how much gas you have in your wings while neutral you can guesstimate how much more lead you need to remove. Each 10 cm (4 inch) cube of gas equals about 1kg (2.2lbs) of lead.
Now, if you have small weights on a weight belt you can take some of until you find the amount of weight so that you can just stay down.
If you have removed all possible weight and still are too heavy you could change from a stainless steel backplate into an aluminum one. That will be almost 3kg / 6 lbs less weight. If you have done that too you need use other tanks that are less negatively buoyant. That is actually the primary reason thatsteel tanks are not recommended for wetsuit diving because often they are simply too negative and there is no way to get the weighting right.
Determining the amount of droppable weightAfter we have figured out how much total weight we need, we need to figure out how much can be permanently attached and how much we need to be able to dump in an emergency.
With full tanks drop down to the bottom. If you have a shell drysuit the depth doesn't really matter but if you have a wetsuit or neoprene drysuit you should go deep enough so that the suit compression is significant. About 20-25m or 70-80ft should probably do the trick.
Now empty your wing completely and try to swim up. If you can't, you must drop enough weight until you can. And if you have nothing to remove, you need to reconfigure your gear.
Droppable weight could be in the form of a weightbelt but also a heavy light cannister could be considered as droppable weight. Most of the latest NiMh cannisters are not that negative though.
Using weight beltsUsually most non decompression divers use some form of droppable weight, like weight belts. The problem with doing decompression diving is that an accidental loss of the weight belt means that we wont be able to complete our decompression and could end up seriously hurt or dead. So a lot of technical divers, especially those diving shell drysuits, avoid using weight belts unless it'a absolutely neccessary.
If you use a thin wetsuit or shell drysuit with a single tank, you most likely don'tneed a weight belt to be able to reach the surface in an emergency. However at the surface you might not be able to gain positive buoyancy without dropping some weight. So consider having 2-4kg / 5-9lbs of your weight detachable or be prepared to remove your gear entirally and let it sink to the bottom.
If you feel any insecurity about whether you should dive with a weight belt or not I suggest using one. But if you have a large amount of lead consider putting some of it on your tank instead.
Stages and decobottlesWhen doing your weighting test you should not have any stages or decobottles on you. Because they are detachable they are not part of your weighting system.
You should also use bottles that will be slightly negative when full and slightly positive when empty. That means aluminum tanks are the DIR choice in most cases.
If you have a problem and are too heavy you can give some of your negative bottles to you buddy. If you are too positive you can dump them because if they are that positive they are also empty. They will end up on the surface - get them another day.
ConclusionGet your weighting right and you will be in a much better position to handle emergencies, like wing failures and other problems. Also not carrying more weight than neccessary means it will be easier for you to control your bouyancy because you don't have to fill and dump as much gas from your wings during the dive.
Remember though that you need to do this all over again when you change something in your configuration like tanks, primary light or drysuit underwear.
Also keep in mind that most of the things on this site relates to DIR diving as we use specific equipment and procedures. Not all of the logic and arguments will apply if you change some parts. If you want to use fancy words you could say that DIR is a holistic approach.
How to Clear a Scuba Mask of Water 12/24/2011
I was kneeling on a shallow water platform during my open water course when my diving instructor floated up to me and signaled me to put a little water in my scuba mask. Forgetting the predive briefing, I glared at him in annoyance. My mask was fine. Why would I want to let water in to a perfectly sealed, water tight scuba mask?
Although it may be counterintuitive to purposefully let water into a well-sealed mask, the mask clearing skill is one of the most important skills of the open water course. Leaky masks are not fun, but every scuba diver will find water in his mask at some point in his diving career (usually sooner rather than later). He will need to be able to efficiently get the water out without surfacing and without panicking. With a little practice, mask clearing becomes easy and automatic. Here's how to clear your mask of water.
Step 1: Relax
If this is the first time you have tried to clear a mask of water, take a moment to relax, slow your breathing rate, and review the steps of mask clearing in your mind. It is normal to be nervous about clearing your mask for the first time, but if you work through the skill step by step you should have no problems. You can even do a “dry run” by practicing the steps of mask clearing without adding any water to the mask until you are confident. When you are calm and ready to begin the skill, signal to your instructor that you are “okay” and about to begin.
Step 2: Allow Water to Enter the Mask
Before you can practice clearing water from your mask, you need to let some water into it. Allow a small amount of water to trickle into the mask in a controlled manner. It is no fun to suddenly find yourself with a completely flooded mask!
The instructor in the photo demonstrates one method of controlling the flow of water as it enters the mask. She pinches the upper mask skirt, letting just a tiny amount of water to trickle in. This method of adding water to the mask works well because it exposes divers to the sensation of water flowing over or near their eyes; something that may happen on a dive.
An alternate method of putting water in the mask is to gently lift the bottom of the mask away from your face. Water will slowly enter the mask because it has to displace the air already in the mask. This method does not allow as much control of the flow of water entering the mask.
Do you wear contact lenses or have very sensitive eyes? Don't worry, it is perfectly fine to close your eyes during this skill.
Step 3: Breathe Past the Water in Your Mask
If this is your first time practicing clearing your mask, fill it to just below eye level. Take a moment to relax and get used to the sensation of water in the mask. Practice breathing in and out using your mouth only, or breathe in your mouth and out your nose. If you feel water entering your nostrils, breathe out your nose, tilt your head down, and look at the floor. This traps air bubbles in your nose and prevents water from flowing in. See, there is nothing scary about it!
Step 4: Exhale Through Your Nose
Start by holding the top of the mask frame firmly against your forehead. You can do this with one hand placed in the center of the mask frame, or a finger on each upper edge. When you are ready, look down to keep water out of your nose and take a deep breath from the regulator. Begin exhaling slowly but forcefully through your nose, then tilt your head up while continuing to exhale. If you have difficulty exhaling from your nose, it helps to imagine that you have some extra sticky, nasty boogers up your nostrils that you need to blow out. Focus on your imaginary boogers and blooooow.
Your exhalation should last at least a few seconds. As a goal, try to breathe out your nose for a minimum of five seconds. Air from your nose bubbles upwards and fills the mask, forcing the water out the bottom. It is important to maintain firm pressure on the upper frame of the mask, or the exhaled air will simply escape from the top of the mask. Remember to look upwards while exhaling, otherwise the air will just flow out the bottom and sides of the mask.
Before you finish exhaling, look back down towards the floor. By doing this any water remaining in the mask will not flow up into your nose.
Step 5: Repeat
On a first attempt, you may not be able to completely clear a mask of water with only one breath. Don't worry. If water remains in the mask, look down at the floor and take a few moments to catch your breath. Repeat the exhalation step, focusing on breathing out your nose slowly, holding the mask firmly against your forehead, and looking up. It may take a few iterations to get the last few drops of water out, and that's okay.
If you wear contacts or have sensitive eyes, you may still have your eyes closed during this stage. Once you think you have cleared the water out of the mask, open your eyes slowly. Your instructor may tap you gently to let you know the skill is finished. It is normal to feel that your face is still wet – it is! You just had water in your mask and you haven't had a chance to let it dry yet. Don't worry, any water on your face will dry in a few moments.
Step 7: Congratulations
Good job! Now you know how to clear your mask of water. Practice this skill until it becomes automatic and comfortable. Once you are an expert at mask clearing, try the exercise in a variety of positions. You can even clear your mask while maintaining a proper, horizontal swimming position.
This skill has another application. If a mask fogs up during a dive (click here to learn more about foggy masks), you can clear the fog from the mask lens using the mask clearing skill. Simply allow a small amount of water to drip into the mask, then tilt your head down so that the water flows down into the mask lens. Shake you head gently side to side so that the water contacts all parts of the mask lens, then clear the mask normally. Presto! Now you can enjoy a clear view of the underwater world during every part of the dive.
By Natalie Gibb, About.com Guide