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Supplies
Drill: Almost any pneumatic air drill seems to work. We have mostly used Shinano models, but a $40 Husky H4310 3/8 in. Reversible Power Drill Air from Amazon worked just as well. The advantage of the Shinano drills are that you can buy three different models with varying speed/torque: the 5100A spins the fastest, but has the lowest torque - it is great for short cores or starting new holes, but struggles for cores deeper than about a meter. The 5500 spins the slowest but has the most torque - it is great for drilling long cores as it does not slow down very much even with multiple extension rods attached. The 5300A is in the middle and works decently well in all circumstances. Buying all three Shinano models will cost several hundred dollars though, and the advantage over a single $40 drill is pretty minor.
Bits: Most diamond wet core bits (typically used for drilling concrete) work well. With some trial and error, we have settled on the Lackmond Pro-VTB bits, but cheaper bits work almost as well. We use 2-1/2" bits as these will give you a 5 cm diameter core, which seems to be a good balance between getting enough material to nicely visualize growth bands and not leaving an unnecessarily large hole in the coral.
Adapters: Typically, core bits will come with 1-1/4"-7 threads. We use one adapter to go from 1-1/4"-7M threads to 5/8"-11F threads, and then another adapter to go down to 3/8" triangle that fits most handheld air drills.
Extenders: The bits described above are typically only 35 cm long. To drill longer cores, you need extenders. We use these, which fit between the two adapters listed above. This is convenient because you don't need to loosen the drill chuck to add the extender. However, a very large wrench is needed to grip the 1-1/4"-7 adapter. We typically add one extension rod on from the very start, so the initial setup is: core bit -> 1-1/4"-7M threads to 5/8"-11F threads adapter -> extension rod -> 5/8"-11F threads to3/8" triangle adapter -> drill. This makes the start of coring a bit awkward, but also means that it is not necessary to use wrenches underwater to add an extension rod until you have already drilled an ~80 cm core.
Air fittings: Most of the drills have a 1/4" NPT inlet, so we use these fittings. It is best to put the male side of the quick disconnect on the bottom of the drill because this allows you to disconnect the hose without draining air. To connect to the regulator (see below), we use a barbed fitting like this - we cut the SCUBA hose coming from the regulator, heat it in hot water, push it over the barbs, and seal it with a small stainless hose clamp.
Regulator: Any SCUBA first stage works. We use this one since it is cheap, and we use a yolk-DIN adapter if using yolk tanks.
Extension hoses: We use SCUBA Hookah hoses like this to enable up to ~50 meters of hose. This is optional, but it can make things easier to keep the SCUBA tanks on the boat and just run the hoses with the drill on the end into the water. Alternatively, bring the tanks underwater with you and then a short SCUBA hose will be sufficient.
Core extractor: Not necessary (see Methods below)
*a note on maintenance: none of this equipment is meant to go in seawater. After each time in the water, everything should be thoroughly cleaned with WD-40. The drills need to be cleaned especially well - run the drill in air to push out the water, then spray WD-40 into the inlet fitting and spin again.
Bits: Most diamond wet core bits (typically used for drilling concrete) work well. With some trial and error, we have settled on the Lackmond Pro-VTB bits, but cheaper bits work almost as well. We use 2-1/2" bits as these will give you a 5 cm diameter core, which seems to be a good balance between getting enough material to nicely visualize growth bands and not leaving an unnecessarily large hole in the coral.
Adapters: Typically, core bits will come with 1-1/4"-7 threads. We use one adapter to go from 1-1/4"-7M threads to 5/8"-11F threads, and then another adapter to go down to 3/8" triangle that fits most handheld air drills.
Extenders: The bits described above are typically only 35 cm long. To drill longer cores, you need extenders. We use these, which fit between the two adapters listed above. This is convenient because you don't need to loosen the drill chuck to add the extender. However, a very large wrench is needed to grip the 1-1/4"-7 adapter. We typically add one extension rod on from the very start, so the initial setup is: core bit -> 1-1/4"-7M threads to 5/8"-11F threads adapter -> extension rod -> 5/8"-11F threads to3/8" triangle adapter -> drill. This makes the start of coring a bit awkward, but also means that it is not necessary to use wrenches underwater to add an extension rod until you have already drilled an ~80 cm core.
Air fittings: Most of the drills have a 1/4" NPT inlet, so we use these fittings. It is best to put the male side of the quick disconnect on the bottom of the drill because this allows you to disconnect the hose without draining air. To connect to the regulator (see below), we use a barbed fitting like this - we cut the SCUBA hose coming from the regulator, heat it in hot water, push it over the barbs, and seal it with a small stainless hose clamp.
Regulator: Any SCUBA first stage works. We use this one since it is cheap, and we use a yolk-DIN adapter if using yolk tanks.
Extension hoses: We use SCUBA Hookah hoses like this to enable up to ~50 meters of hose. This is optional, but it can make things easier to keep the SCUBA tanks on the boat and just run the hoses with the drill on the end into the water. Alternatively, bring the tanks underwater with you and then a short SCUBA hose will be sufficient.
Core extractor: Not necessary (see Methods below)
*a note on maintenance: none of this equipment is meant to go in seawater. After each time in the water, everything should be thoroughly cleaned with WD-40. The drills need to be cleaned especially well - run the drill in air to push out the water, then spray WD-40 into the inlet fitting and spin again.
Method
Starting new holes: some people have custom-built tools to hold the bit in place, but this is not really necessary. It's usually fairly easy to just hold the bit by hand (wear gloves!), and start spinning the drill. Alternatively, just get a short piece of PVC pipe that is wider than the drill bit, and have one diver hold the PVC piper while the other starts the drill.
Drilling: Pretty simple, just hold down the trigger. It's best to keep the drill spinning as much as possible - in other words, don't let up on the trigger. When the drill is spinning, it will keep the coral dust away from the bottom of the bit, but as soon as you stop drilling, all that dust settles on the bottom and slows down the drilling once you restart. It's not usually necessary to push down while drilling, the weight of the drill and extension rod(s) is usually sufficient, but you can push down a little bit as long as you are not causing the drill to slow down or stop.
Breaking off core pieces: Once you fill the core barrel, you need to break off that piece of core to continue drilling. The first piece is easy, as you can gently nudge it with a dive knife or the teeth of the bit until it breaks and then just pull it out with your fingers. After this, breaking off pieces down in the hole is a bit trickier. We assemble separate extension rods into essential a long pipe that reaches to the bottom of the hole. Just wiggling this around will break off the piece of core down in the hole.
Removing core sections from down in the hole: A lot of people buy or design extractors to grip broken-off pieces of core and pull them from the bottom of the hole. This is totally unnecessary. The drill bit (or at least, the Lackmond one that we use) has a tight enough seal around the core that if you push it over a broken-off piece of core down in the hole and lift it up, suction will pull the piece of core straight out of the hole.
Swapping tanks: This is a lot easier if you have a long hose and leave the tanks on the boat (assuming the boat can anchor close enough). Then, just have someone on the boat turn off the air and switch to a fresh tank when one runs low (we usually switch around 800-1000 PSI). If you bring tanks underwater, you just need to have a method to keep track of the tanks. We make small pieces of rope about 1 meter in length and with a loop on each end. We use the loop to make a quick slip knot, and tie one end to the tank valve. Underwater, the other end is tied off on anything we can find (usually a dead-coral knob). Full tanks will rest on the bottom, but become buoyant with empty. So when one tank runs low, take off the regulator and put it on a new tank, but make sure the old tank is secured. Switching the regulator underwater is fine, it won't break it, but don't use this regulator for breathing. Also, make sure to have a plan for how to bring the empty tanks to the surface. We bring 6-8 tanks underwater at a time, and it's not safe for a diver to bring these all to the surface. If you are shallow enough to just let each tank reach the surface while holding the end of the lines, that is fine. Otherwise, if you are deeper, it is best to have a snorkeler available to collect the tanks, and the divers just release them from the bottom at the end of the dive for the snorkeler to gather.
Plugging the hole: Either use pre-made cement plugs or coral rubble. If using plugs, you just need to measure (or trial and error) to find the right sized cup and how much to fill it to make a plug that just barely fits into the hole made by the bit you are using. You don't want to plug sticking more than 1 cm out the top of the hole, or it will take the coral a longer time to recover. You may use underwater epoxy to secure the plugs in place, but this doesn't seem necessary.
Drilling: Pretty simple, just hold down the trigger. It's best to keep the drill spinning as much as possible - in other words, don't let up on the trigger. When the drill is spinning, it will keep the coral dust away from the bottom of the bit, but as soon as you stop drilling, all that dust settles on the bottom and slows down the drilling once you restart. It's not usually necessary to push down while drilling, the weight of the drill and extension rod(s) is usually sufficient, but you can push down a little bit as long as you are not causing the drill to slow down or stop.
Breaking off core pieces: Once you fill the core barrel, you need to break off that piece of core to continue drilling. The first piece is easy, as you can gently nudge it with a dive knife or the teeth of the bit until it breaks and then just pull it out with your fingers. After this, breaking off pieces down in the hole is a bit trickier. We assemble separate extension rods into essential a long pipe that reaches to the bottom of the hole. Just wiggling this around will break off the piece of core down in the hole.
Removing core sections from down in the hole: A lot of people buy or design extractors to grip broken-off pieces of core and pull them from the bottom of the hole. This is totally unnecessary. The drill bit (or at least, the Lackmond one that we use) has a tight enough seal around the core that if you push it over a broken-off piece of core down in the hole and lift it up, suction will pull the piece of core straight out of the hole.
Swapping tanks: This is a lot easier if you have a long hose and leave the tanks on the boat (assuming the boat can anchor close enough). Then, just have someone on the boat turn off the air and switch to a fresh tank when one runs low (we usually switch around 800-1000 PSI). If you bring tanks underwater, you just need to have a method to keep track of the tanks. We make small pieces of rope about 1 meter in length and with a loop on each end. We use the loop to make a quick slip knot, and tie one end to the tank valve. Underwater, the other end is tied off on anything we can find (usually a dead-coral knob). Full tanks will rest on the bottom, but become buoyant with empty. So when one tank runs low, take off the regulator and put it on a new tank, but make sure the old tank is secured. Switching the regulator underwater is fine, it won't break it, but don't use this regulator for breathing. Also, make sure to have a plan for how to bring the empty tanks to the surface. We bring 6-8 tanks underwater at a time, and it's not safe for a diver to bring these all to the surface. If you are shallow enough to just let each tank reach the surface while holding the end of the lines, that is fine. Otherwise, if you are deeper, it is best to have a snorkeler available to collect the tanks, and the divers just release them from the bottom at the end of the dive for the snorkeler to gather.
Plugging the hole: Either use pre-made cement plugs or coral rubble. If using plugs, you just need to measure (or trial and error) to find the right sized cup and how much to fill it to make a plug that just barely fits into the hole made by the bit you are using. You don't want to plug sticking more than 1 cm out the top of the hole, or it will take the coral a longer time to recover. You may use underwater epoxy to secure the plugs in place, but this doesn't seem necessary.