Learn how to back down a rowing boat.
Timestamps
00:45 Struggling to learn how to back the boat
Blades up or blades down when backing? 
Different countries do this differently - UK is blades down and NZ is blades up.
Blades down rationale - the oar spoon is curved and you want the curve to grip the water and push it backwards. Blades up rationale - the oar has pitch on it from the oarlock tilts the blade - this makes the oar go the wrong way and may cause the oar to dive into the water.
My personal view is don’t turn your blades upside down (they are angled and the diving (being sucked down) you experienced is because the pitch / angle of the spoon is designed for the oar the right way up (not upside down).
It's simpler to leave the oar blades up - because it's always the same whether rowing normally or backing.
04:00 How to learn backing down
Two videos you can use to learn shared lower down.
1 - Start by sitting legs straight and arms straight with oars square and under the water surface. Scullers ensure your hands are nested tightly. Sweep rowers ensure the boat is level by having upward pressure on your thumbs. This shows the height the handle needs to be at to keep the boat level
2 - Begin with rowing in place. This is only moving your arms just pulling the handles towards you and pushing them away without taking the oars out of the water. Keep the handles at the same height throughout. Don't take the oars out of the water. Get the feeling of backing down.
Notice that your handle height is key to getting this right. Diving or sucking down into the water happens when your handles go too high.
3 - Now progress to backing down with arms and body rowing in place first
4 - Then start backing down arms only; arms and body; then go to half slide and longer to full slide.
09:00 Counter-feather the oars
5 - Keep the oars on the surface when they are not being used to back the boat. Remember to counter-feather your blades and run the tip of the oar along the water surface when they are out of the water in between backing strokes. Keeping them on the surface means you maintain the boat set/balance. This gives you a point of reference as to where horizontal is to keep the boat level - it shows you how high to have your handles when the oars are out of the water. 
Remember the catch when backing down starts with the oars next to your body. It may help to learn counter-feathering one side at a time. You can hold the boat level with just one oar.
11:20 two videos to teach you backing down skill
Here’s a video about improving your backing skills https://www.youtube.com/watch?v=B4CODkUdEGc
And another about turning the boat which demonstrates the counter-feathered oar https://youtu.be/ThTrg1N6Obg
A final recommendation - get confident backing with good pressure. Try practicing 100 meters of backing down each time you go rowing.

Backing down

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