If you notice a loss of pressure in an inflatable boat/dinghy while underway, how can you prevent or slow the loss? This is most important in full inflatables. Even if you are in shallow enough water to stand, and have your required personal flotation devices to keep the souls on board safe, you still want to save your engine (if you have one).
Depends where the hole is and how big it is, but:
First, determine if it's necessary to try and patch the hole in open water.
If you're close to shore, then go ashore and patch it there. If you're losing air faster than you could get back to shore, then you need to act quick.
Locate the the hole.
If you can't find the hole, then you can't stop the leak. A hole below the waterline will be given away by bubbles, a hole above the waterline should be audible. If you kill your engine you should be able to hear a large hole, a small one can be heard by sticking your ear against the hull. If you can't find the hole, then your only option is to replenish the air in the craft. Hopefully you have a pump on board and the inflation valve is one-way. If so, then you could try and pump air back into the craft as fast as it's leaking out. At the very least you could buy yourself some time to get closer to shore.
Stop the hole.
If you do locate the hole, you need to put something over it to stop the air loss. A small hole above the water can be plugged with a finger or patched with duck tape or a proper patch if you have one. A hole through the bottom could similarly be plugged or stopped from above, but if you have a hole below the waterline then you're going to have problems. A hole in a the bottom of a dingy isn't going to be so easily stopped. In a rigid boat you can push something under the hull and use water pressure to stop the leak (typically a sail/collision mat/tarp; in a smaller craft you could use a Gore-Tex jacket), but in an inflatable craft you have the issue of air escaping under pressure. Your best bet is going to be plugging it with something, if you can reach it.
In desperation, you may consider flipping the craft over so you can dress and patch the hole. After a patch is in place and cured, then you could put the craft right side up again, and replenish the lost air.
If you have multiple people one option is for one person to simply use their hand while others get you to safety ASAP.
This will not be at all a definitive answer, but here is one data point regarding getting to shore quickly rather than attempting repair:
Three friends and I chartered a six meter RHIB (rigid hulled inflatable boat, wasn’t a Zodiac brand but similar) with two large outboard engines for sport fishing off the coast of Mozambique, operated by two men who had the skills to launch off the beach through the surf. In the process of attempting to land a large dorado we somehow managed to gash one pontoon with a multi-barbed lure. The operator’s response was not to attempt a repair to the hull but rather to slow the leak by pressing on it hard with a bare hand, while running the engines full throttle to get us back to shore. We were a couple of KM offshore but we had calm seas and made it to the beach before any loss of stability, if I remember correctly they timed it so as to keep us on plane almost until we hit the sand, yet without a violent collision.
I welcome any comments as to whether this represents good or bad general practice (not whether it’s good practice for six humans to get their asses handed to them by a fish, but whether the subsequent response was the best that could be made of the situation).
Obviously the best result you will get by using a proper patch kit for inflatables, likely a vulcanising rubber patch similar to what you're using to fix bicycle tyres. If you know what your'e doing you can apply those to an inflated boat in a pinch - it being in the water makes it a bit more difficult, but not terribly so given the whole is above the water line.
Now, should you not have the proper repair kit at hand here are a bunch of improvised ways to plug the hole. Here is a list of what I have used in the past:
- Plug the hole with your finger. This will give you a good seal you might be awkward to get to shore. Mostly feasible if there are multiple people in the boat.
- Duct tape - works pretty well actually, best applied in long straps in a kind of 'star' pattern.
- In a pinch I have used a combination of chewing gum and the sticky wrappers around Coke PET bottles. This actually fixed a maybe 4x4mm hole well enough for us to finish a 2-3 hour river tour in an inflatable boat.
- Medical tape can work well - best in combination with something small and 'spongy' to plug the actual hole, with the tape adding pressure and holding it in place.
I have used all of the above to some success - most of them plugged the holes well enough that we could continue our 2-3 hour river trips with maybe one break for topping of air.
In case you're wondering what I'm doing to end up on broken inflatables so frequently... I live in Bern, where floating down the river in an inflatable boat is of the most beloved summer activities. :)