[ytupnorth]

I recently purchased a 16' NRS cataraft with hypalon tubes. The thing looks pretty new, in near mint shape, and the price was right. Model 1116. serial no WS108672C404. Got it home and noticed many small 3-5 mm 'blebs' on the underside of both tubes. They are raised vessicles, very near to the surface, just under the surface of the outer black rubbery surface of the long protective patch on the underside of each tube. When pierced, they contain water. What's the deal? They occur nowhere else on the otherwise spotless tubes. Anyone know what causes this.

I really don't think they compromise any structural integrity, but they sure are ugly and not too hydrodynamic. I figure I'll have to grind them offand sand down the whole long patch, then apply a couple layers of flex-tough. Just seems strange to have to do to seemingly new tubes. Anyone know what causes this? Ill try to post a picture when I can.

 

[theBoatPeople]

I am pretty sure that nothing actually "caused" this to happen, but rather it was something there from the git-go.
Whenever an inflatable maker adheres a large, wide patch onto a tube, especially in areas where there are compound curves, it is impossible to not get a few small air pockets trapped underneath. This would happen whether the material was reinforced, or unreinforced gum rubber.

At the boat factories, most of the time there are larger bubbles in wear pads than what you are seeing here, and they are dealt with using a pin to release as much of the trapped air as possible. These pinholes or some degree of porosity in the gum rubber may account for the water in them.

We sell few NRS hypalon boats and don't have any pony in the race, but this can and does happen with bottom chafers on every brand of inflatable. Anything this small won't affect the performance of the tubes, though larger crinkles maybe could.

I don't know the details of NRS's serial numbers that well, but it looks like your tubes could be nine years old. If they are in good shape otherwise I would not worry about small bubbles at all. A better reason to apply liquid urethane to the bottom of any NRS hypalon boat would be to overcome their natural tendency to stick on rocks, something they tend to excel at.

 

[ytupnorth]

@theboatpeople-
thanks for the reply and the information. I think you're right and that the tubes are from '04 which is pretty amazing considering (aside from these 'blisters') they look brand new. I bought the boat from a bible camp in willow, AK who were just using it as a lake platform, apparently.
The thing is, the 'blisters' are not under the botton wear pad, theyre on top of the pad between the pad and the outer black 'paint' layer.
Im planning on urethaning the bottom (good point about avoiding rock 'stickiness') so it'll probably take care of the bubbles by grinding them off during prep anyway.
We'll see how it goes.