How can I build an underwater tunnel?

EDIT: After using @Nick’s method I have completed the tunnel. While the effort was indeed worth it, I think unless sponges come to SSP…next time I’ll build a bridge. Next thing is a station…but that’s another question.

Here’s a picture of the finished product (the sandy island in the middle is what I was stood on in the picture below). enter image description here.

Bonus Picture:
enter image description here

I am attempting my first underwater MineCart tunnel and am having difficulty with the optimal (and easiest) method for building it. I’ve read this thread and have tried the “build walkway, drop sand in” method. I’ve looked at using doors and signs but this will probably leave me with a large amount of doors that I won’t use (and don’t want to dispose of). I’ve also though about damming the entire section off but that’s probably a little excessive.

A tunnel cross section would be: enter image description here

So far, I have got this far (1/4 of the distance) and have realised I am going to have to sort the current out as well: enter image description here

Answer

I think the underwater tunnel concept is pretty cool but I never gave it a try until this post reminded me about it. After spending too much time dropping sand and picking it up again, I think I came up with a decent method to make underwater walkways in the least amount of time.

So, find a way down to the level you want to work at and make one tiny section of your walkway. You can use sand or dig some nice stairs since you’ll probably want to start above the water level. When you have your first section, place two doors and then block off the top two blocks:

Double doors, underwater

The water won’t flow through the doors, so you can peek out to the other side and place two ground blocks, then build around with glass and duck back into the doors for a breath. I generally do this for four blocks at a time before placing another set of doors. Here’s an artificially brightened shot of a half-built section of tunnel. You can see the doors and the air behind them, and two slices of tunnel with floor and glass placed already.

It's really dark underwater

After you finish a section and place your new doors, removing the water blocks from this section with sand is easy as it’s only 4x3x2 and you only have to place two sand blocks per column (n-1 of the walkway height) to clear out all the water. At this point, you can remove the old double doors (and glass padding on top) behind you and repeat from the set in front of you.

And the best part about this method? No currents if you make your top glass layer at least 1 block below the surface!

Look, ma, no currents!

To conclude; build using this method for the following benefits:

  • build straight, corners, crosses, etc
  • only four doors needed
  • deal minimally with swimming or fighting currents
  • don’t having to place a million sand blocks and clean them up later
  • no bucketing around with current clean-up

Attribution
Source : Link , Question Author : tombull89 , Answer Author : authenticgeek

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