Rigid Hull Inflatable Boats (RIBs) have many advantages. They don’t mark a boat’s hull when alongside, they have sufficient buoyancy to stay afloat when completely full of water, and they are sold in large enough quantities that pricing is competitive. They have lots of downsides as well and the demise of most inflatables is slow deflation that rarely poses a safety risk but can positively drive owners crazy. It can be challenging to chase down the source of a slow leak but pumping the boat up every second day is annoying as well. Many of these boats just get replaced. It turns out they really aren’t all that difficult to repair—the real challenge is finding the source of the leak. This one was easy to find.
Two weeks ago, we were underway at speed in moderate seas and the boat was fully inflated when it suddenly tilted to the right. I look down and the entire right side tube had just gone flat. Even more unusual, the tube quickly was vacuuming down to the shape of the fiberglass boat in which the tube was glued. It was exactly what you would see if you put a vacuum on the tube and removed all the air. I’ve never seen anything like it.
I asked Jennifer to go the opposite corner as I slowed down to investigate. As I slowed, the boat tilted toward the deflated tube since there was now no buoyancy in that side of the boat. The good news is that medium-sized ribs and above have three flotation chambers and are assured to stay floating if one chamber is out of commission. As we slowed, I realized two things: 1) the boat would float fine in flat water on two chambers, but in rough water it would certainly be swamped and 2) on plane was the safest operating mode for the boat under these conditions.
I shifted over to the far left side of the tender, with Jennifer as far forward and left as was safe, and brought the tender back to full speed doing a slow 180 degree turn back to Dirona. It was looking like we would make it. In fact, the boat leaned quite a bit right, but otherwise seemed to be doing fine. However, It was clear that if we were in heavy seas the boat would not be safe with only two flotation chambers full. It’s disappointing to see one of the key reasons I really like RIBs turn out to not really be correct.
As we arrived back at Dirona, the tender settled into the water far deeper than it had so far. Jennifer hooked up the lifting harness and I ran up to the boat deck to lower the crane. As soon as we got the tender on the crane, we had it fully under control so the time pressure was off. But the tender must have weighed in at something close to 1,200 lbs, nearing double its normal weight.
Ironically, the Longhope RNLI lifeboat Helen Comrie was operating nearby with a film crew on board. We were glad not to need their assistance and end up becoming part of the documentary.
As the crane slowly lifted the tender, water poured out of the damaged tube and we could see what had happened.
Rather than starting to leak slowly, a 6-8-inch seam had failed at the same time over its entire length. Because the failed seam was so large, the air was gone nearly instantly. And, since the seam was at the back of the boat, the speed of the boat formed a vacuum and sucked that tube down flat against the hull. Once we stopped, the flotation chamber quickly filled with water. We drained the tens of gallons out of the tube as it hung from the crane and, once the tender had gotten light enough to safely lift without overloading our crane, we brought it up onto the boat deck.
We used a wet/dry vacuum to get the last of the water out of the tube and started the drying process in preparation for repairing the seam the next day. Technically we do have a backup “micro-tender” that we use when we need to land in surf where the 800lb tender isn’t safe or when we have a crane or primary tender failure. We were far from stranded, but the micro-tender is just over 7ft long and powered by a 2.3hp engine, whereas the main tender is a comfortable and dry 12ft with a 40hp outboard capable of 30 MPH. The primary tender is usually the best choice, so we wanted to get it back operational.
The most sensible answer is to replace the tender since it’s now more than 8 years old (about 6 months older than Dirona) and has 550 hours of operation. We run it in difficult conditions, with some very heavy loads, and it’s exposed to a lot of sun. There are numerous reasons why replacing the boat is probably the right answer. However, replacement isn’t a quick option in the Orkney Island group north of the Scottish mainland.
We will replace the boat as quickly as we can, but needed a few more weeks or months out of it so we got to work on the repair. After waiting a day, the heavy winds so common in Northern Scotland had dried it thoroughly so we were ready to get started. We first carefully rotary wire brushed using a Dremel the surfaces of the entire length of the failed seam. This cleaned off any old glue residue and ensured that the surface was roughed up adequately and ready for glue. Then we cleaned the surfaces with MEK (wearing gloves) to ensure the surfaces were clean. Then we applied Bostick Hypalon inflatable boat glue to both sides, let the glue partially set and become tacky, and then quickly brought the two surfaces together exactly where they needed to be. We applied pressure against a metal bowl pushed up against the hull of the boat to get the appropriate curve to seal against. We then left the boat for 24 hours for the glue to cure.
Rain began to fall soon after we started work, so we rigged a large patio umbrella to cover the work area. Ideally gluing is best done between 65 and 75 °F (18 to 24 °C) with humidity below 70% and ideally at 40%. With the temperature at 54°F (12°C) and near 100% humidity we missed both by quite a large margin, but there’s not much we could do about it.
The next morning we pumped the tender up tightly and checked for leaks using sprayed soapy water. We found another wear point underneath, near the failed seam, where the boat was leaking fairly heavily. It may have happened due to the flapping of the deflated tube after the failure Everything else all the way around the boat looked good and was well-sealed.
We deflated the boat and cut a patch to more than cover the additional leak we found. Then we prepared both the boat and the patched surfaces again using the rotary wire wheel and MEK. Finally, we applied the glue and once it was tacky and partly set, we pushed the patch onto the location we were patching.
The large seam we had fixed the previous day was well sealed up and looked good but, since a large seam failure can be dangerous, we wanted to add an additional large patch over the entire area. We cut it to fit, used the same preparation and gluing technique, and applied the patch.
We gave the tender another 24 hours to cure and then again pumped it up over-full and checked for leaks. It was rock solid. We then launched the tender and put it back into work. Twelve days have passed now and the tender hasn’t leaked the tiniest amount. It’s looking great.
However, we still want to replace the tender so we’ve been shopping for an AB Alumina 12ALX with a Yamaha 30 BETL, and it’s looking like the AB shipment won’t arrive until right around the time we leave the UK. We’ll keep shopping, and will investigate shipping a boat from the US, but it’s looking like we will need to make the current boat last a bit longer at this point.
Update 2018-05-18: We eventually did buy a new tender, but it wasn’t an an AB Alumina 12ALX with a Yamaha 30. Read more at New Tender for Dirona