The following is what I learned about carving pumpkins underwater, for a crowd.
I should also point out that sk8ter20art posted a great video in his instructable carving a pumpkin underwater.
So hopefully I can add a few tips and tricks on top of what he's already gone over.
Please bear with me with pictures. I had a little more time day one to mess around. Day two the aquarium was understaffed and I had to help out with day to day chores while getting prepped to do my pumpkin. So there's no good set up shots for the second pumpkin. I was also solo on the first day, so there's no good in processing shots from that day. When you're underwater and on someone elses time, you kind of have to work with what you have. Hopefully everything makes sense though.
Step 1: Create Your Design
Also, remember where your pumpkin is going to go. I was carving for an aquarium, my signature batman symbol wouldn't really cut it in the underwater world.
For my first pumpkin, I decided to copy something someone else did. I did a google images search for "fish pumpkin" and on the first page I found a great Angler Fish.
For my second pumpkin, I did some research first. This specific aquarium has a lot of Seven Gill Sharks, and that's something a lot of people enjoy seeing. I decided I was going to try to figure out how to make a seven gill (since I couldn't find any designs online). I found a good greyscale image of a Seven Gill here. I pulled the photo into Photoshop, selected just the shark, and filled it with white (I planned on just taking the orange skin off of the pumpkin. I created a background layer and filled it with orange (to see what it'd look like on the pumpkin). I drew in a few extra details, and I was happy with my pumpkin pattern.
I've gone ahead and attached the photoshop file in case you'd like to see the process.
Step 2: Tools
A pencil, a roller (see step 3), or anything else you have on hand works really well in applying a pattern.
The regular run of the mill pumpkin saw is great for just about everything you may want to do. If you want to get super fancy, you might need a bigger kit...but one saw seemed plenty for my work.
Since I was going underwater, there's ropes and zipties attached to all of the tools. There's a couple of reasons for this.
First, I don't want to lose any of them.
Second, and far more important, I don't want any of the animals to try to eat them.
Step 3: Apply Your Design to Your Pumpkin
For the Angler Fish, I was copying from an image. The image I was looking at was on my phone. So I set my phone next to the pumpkin with the angler on it, and used a sharp pencil to poke just through the surface of the pumpkin. It created a nice fine line and I was able to see it quite clear underwater.
For the Seven Gill Shark, I used a roller (see step 2 here), and applied the design really slowly. the shark isn't too big, so I had to be really careful with my lines. The dots were a little hard to see underwater in certain places, but when you looked at the pumpkin straight on, it was all easy enough to find.
Step 4: Cut a Hole in Your Pumpkin
For my purposes, in the aquarium, one side of the pumpkin is always forward and the other side is always back. So cutting a hole in the back of the pumpkin made a lot of sense.
Even without all of the air in the pumpkin, they still like to float. When you cut pieces out, they'll float up. It's for this reason that I don't suggest cutting the top off of your pumpkin. If you cut the top off before you take it down, bring extra zip ties with you to reattach it to the pumpkin or it'll just float away.
If you want to show off, or you're not allowed to cut a hole, you can take a few stabs at your pumpkin. If you have more then one hole, you'll be able to get water to flow into it pretty well. The larger the holes, the quicker the flow, the smaller the hole, the more impressed everyone will be when you show it off at the bottom of the ocean, as they wonder how you got it down there.
Since this was being done in an aquarium, and we were going to be doing a lot of it, we didn't want the fish to get sick on pumpkin guts, so we de-gutted them before taking them down. When you go out, you can make your own choice. Fish will eat anything, but I'm not sure that pumpkins are the best thing for them.
Step 5: Take Your Pumpkin Underwater
Now, as I said before, even full of water, pumpkins still want to float. If you're deep enough, it's not going to be a problem, bit if you're shallower then sixty feet, it might be a bit difficult. That whole I put in the back of my pumpkin serves a good place to put a weight to hold my pumpkin down. Now, if you're doing this in the ocean, please don't leave lead weights lying around. Grab a decent sized rock from the shore, or one that's not being used at the bottom of the ocean. You can place this in your pumpkin and watch as it happily holds your pumpkin to the bottom of the sea. Now that you and your pumpkin are underwater, and no one wants to float away, we can get to the good part!
Step 6: Carve Your Pumpkin
When traveling, I tucked my saw into the wrist of my wetsuit. This way, I always knew where it was, and I could be sure none of the fish got a chance to nibble.
Now this is super important, always remember who you're carving for. If you're on the bottom with one other person and you're both just having fun for funs sake, then by all means hide your pumpkin till you're finish and have a game of who did the better job. But if you're at a place where people are going to be watching you, think of them when you decide how you carve. Don't put your whole body between them and the pumpkin. In fact, make sure they always have a clear line of sight at exactly what you're doing. Working upside down on a pumpkin isn't incredibly difficult, unless you're trying to freehand something, which I don't think you'd be doing for a crowd anyway, so yeah. Just to keep in mind.
There's a few techniques I found that worked.
The normal saw and cut is tried and true, and works just as well underwater as it does on land. I found myself working at an angle that would take out more of the inside then the outside. This way all of the floaties inside the pumpkin when you're cutting aren't as visible.
When trying to skin the pumpkin, if you place the numb of your saw about an eights of an inch into the pumpkin, and then lay the saw horizontal against the pumpkin, you can push the saw through the skin, and not through the pumpkin. It's kind of like putting a needle through the very outside of your skin to get out a splinter instead of jabbing the needle straight through your finger. A little finesse, and a little patience and this technique can work really well.
When you clear out an area with the nub, you can use the dull side of the saw and smooth out the ridges that it leaves behind. Think of it like a mom licking a finger and rubbing her kids cheek, but instead of a finger, it's the dull side of a saw and I don't recommend the licking.
Step 7: Some Safety Issues...
Your knife is your tool. Don't lose it. Not only would it be the end of your pumpkin carving, but fish swallow any and everything they can. Having a saw travel through any animals intestines is a horrible thing and you should do everything in your power not to let it happen.
Clean up after yourself. The ocean has enough trash in it and doesn't need your pumpkin. Carve it underwater, leave it there while you swim around, but gather it up when you leave. There's no need to start a trend of throwing pumpkins in the ocean. Everything that we cut in the aquarium that wasn't eaten by a fish was cleaned out. It's their home, try to leave it how you found it.
...okay, now for the final step...