Final plea for help - leak detection in Adventure

FOUND!

I appreciate everyone's suggestions, and finally had a couple days to try to debug in earnest.

First I lined the hull with newspapers and duct tape and pedaled around a saltwater inlet (crazy boat traffic w/Memorial Day weekend!), and narrowed the leak to somewhere in the middle of the boat. It was choppy enough I couldn't rule out the center hatch, so I duct-taped that and repeated the test. This time I narrowed to either the drive well area or base of the tube for the sail mast.

I flipped the boat and studied the hull carefully. At each of these areas, where the white plastic plug is, appeared a hairline crack or deep scratch. I took some Gorilla<tm> tape, and covered each area with a piece or two. Pedaled around: no water. Pulled the first piece of tape off (over the area for the mast), and no water. Pulled the second piece, in front of the drive well, and: water!!

So there's a crack just as the forward part of the drive well. As Stobbo said, above, it's amazing how much water can intrude from an almost invisible crack - clearly the force of the pedaling opens the area. Quite honestly, I'm also really annoyed at the dealer's repair person who told me he 'water-tested' the boat, and it was dry as a bone. No freakin' way.

What's the best way to repair? I'm not sure how long I'd trust a piece of Gorilla tape.

Nice catch! I had a similar crack a few years ago. While it is theoretically possible you could plastic weld the crack, I came to the conclusion my hull was "totaled". Cracks below the water line are just very difficult to recover from.

You may need to talk to your dealer about seeing if you could get a hull-only replacement from Hobie.

Here was my experience:
https://www.hobie.com/forums/viewtopic.php?f=75&t=55184

Something I thought about doing if I ever did develop a crack in my drivewell. Never had a drivewell go bad since about 2007, over many boats, so I never got a chance to try the idea out.
One thing I found out is ge clear silicone sticks to the hull fairly well if you prep the polyethylene beforehand. What I do is I clean the area I want to fix with bestest rubber cement thinner, ( available at Home depot). The stuff is heptane, (heptane melts pretty much all plastics including polyethylene). What I do is place damp towels, (dampened with heptane) over the repair area and let it soak for a little while, ( this kind of softens the surface of the plastic). I then remove the towels and let it dry, I then spray a thin coat of Krylon for plastics clear coat spray paint over the entire repair area, (the active ingredient in krylon for plastics is heptane). The spray paint bonds amazingly well to the polyethylene.
Next get a new tube of clear ge silicone caulk, (not silicone 2, thats the wrong stuff). Now on the inside of the hull coat the entire area around the drivewell, (around where the leak is) so the entire area is coated with 1/8” to 1/4” thick silicone, you want it to extend at least three inches away from repair area. It’s fairly easy to trowel around and smooth out, if you place some saran wrap, ( or really thin cloth) over the silicone while spreading it around, ( the stuff is really sticky). Doesn’t need to look nice. It can take few days to dry btw.

Keep in mind doing this does nothing to repair the crack itself, ( once the crack is there, it’s near impossible to fix). However having a crack, and having a water leak are two different problems. If you have a crack, you can still use the boat, but if you have a water leak, the boat fills up with water and you drown, ( an exaggeration obviously).
Think about it the same as repairing a tear in a vinyl pool liner in your swimming pool. Get a tear in the liner you have two choices, either replace the entire liner, of just put a patch over the hole, ( in the case of the mirage drive leak, the patch is on the inside of the hull, ( who cares, it’s on the inside, even if it looks like crap it doesn’t matter)).
Once patched, the mirage drive will not leak water even if the crack gets much worse, (which could take years to become un-usable).
It’s one thing to have a crack, it’s another thing entirely to have a leak, with a crack the boat is still usable, with a leak it’s not.
We have had many high speed crashes with our boats, and there are dings, cracks all over the boats, for example we had an AMA fall off the trailer, and the tire rubbed a huge swirly in the side of the AMA, (oops), it didn’t leak water so we didn’t do anything to try and repair, yea it looks like crap, but I’m not about to spend $600 bucks for a new AMA just because I screwed up, as long as it still works, ( ie,,, doesn’t leak), I continue to us it, ( that happened like 4 yrs ago).
Kind of like getting a dinger on your car, ( most of us just live with it).

Our first Hobie we bought used, and it developed a crack in the drive well, and we ended up throwing the boat away, (boy were we mad). Everyone said it couldn’t be repaired and the boat was scrap, so we threw it away in 2007. Seriously if I had thought about it, and knowing what I know now, (about repairs), I would still be using that same exact boat, 11 yrs later), as long as it didn’t leak I would have kept using it cracks and all.
FE

I will add that while I was waiting for my hull replacement, I did a quick fix of filling the crack with silicone and covering it with Gorilla tape (on the boat's exterior). I expected to replace the tape on every trip, but after probably 50 miles or so of trips, the original tape held, and I had virtually no leaking. I figured it was a short-term solution, but it did hold well. I wouldn't have minded fixing it every couple of months as needed, but of course the risk is always the crack will grow.

If you do try a repair, welding a metal screen into the polyethylene sounded promising, as it adds extra strength, and might even prevent the crack from growing.

Keep in mind though, knowing how much water a small crack let into the boat, if the crack splits open more while on the water, you could quickly be in a dangerous situation.

Is the crack only on the bottom or does it extend around the lip to the inner side.

Rather than just plastic weld the crack itself also plastic weld a patch over it. It creates a bump on the underside but substantially reinforces the repair

IMO, this crack is not easily repairable, but it is fixable. Because it is under continuous pulsating stress, any weld or solid material will not be able to stabilize it. Recycle's tape suggestion may work out well though. I've been using packing tape on Hobie hull bottoms for years and applied clean, they stick, last 2 to 3 months. You would just need to keep an eye on it to make sure the tape doesn't split at the crack.

Fusioneng's silicone on the inside might work as well. It doesn't make a high bond, but may not need to since it can flex.

The best permanent repair option, IMO, is to locate the leak inside, form fit a plastic patch (no less than 1/8" thick for stability. By heating the patch material, you can form fit it to the hull. You would then epoxy it with either Scotchweld DP 8010, DP 8010NS (if you have to fill spaces) or Loctite 3035. These are industrial products that are specifically formulated for PE and will make a permanent bond as strong as the PE itself. Your success here will depend on whether the crack is in a flat enough spot to patch over. You can get these products from industrial supply houses like R.S. Hughes.

In any event, these fixes should get you back in operation for the foreseeable future.

Thanks, all!

I chatted with the repair/kayak person at my area dealer, and he's complete confident he can fix it -- he uses fiberglass tape, and some special flexible epoxy. We'll see -- shouldn't be too expensive; ~$50. Since the serial number ends in "10" I'm guessing my Adventure is a 2010 model? So it's older than I thought. Anyway, will drop the boat off this weekend. I'm just relieved to have finally found the d*mn leak.

This really is my favorite kayak of all the Hobies I own/have owned.

To keep a crack from getting longer, drill a small hole through the hull in front of the crack. A crack puts a large amount of stress on a very small area at the tip of the crack, which is why cracks tend to keep getting longer. If you drill a hole at or right in front of the tip of the crack, this stress will be spread over much of the circumference of the hole, and the crack won't get longer. Drilling a hole won't stop the crack if you drill it behind the tip of the crack, so it's better to drill the hole just in front of the tip of the crack. I have read a technical explanation of this stress issue someplace, but can't locate it.

If a drummer gets a crack in a cymbal, he or she can drill a hole in front of the crack to keep it from getting longer. They also have to saw along the length of the crack to widen it, so the edges of the crack won't buzz against each other. Doing these two things allows them to continue using a cracked cymbal.

Obviously you still need to seal both the crack and the hole to keep water from getting into your kayak.

If you develop a crack in a relatively flat area of the hull of your kayak, after drilling holes at the ends of the crack, you can seal the crack by gluing a patch made of raft repair fabric over the crack with vinyl glue, which adheres well to kayak plastic. If you glue the patch to the inside of your kayak, it won't be exposed to abrasion and getting snagged or peeled up. If you glue the patch to the outside of your kayak, you can protect it from getting snagged or peeled up by putting duct tape on top of it. You can't fully patch a crack which extends up into a drive well or a scupper hole with raft repair fabric.

Now I'm actually getting curious about the DIY approach, since it's a moderate hassle bring the boat to the dealership, waiting for it to get fixed, etc.

I'd like to see if the crack extends the other direction (into the well). What is that white plastic thing? A plug? Can it be safely removed/replaced? If so, how? Is it just pressure-fitted? Thx!

I received this response on another forum when I was discussing my hull failure:

"I had the same crack there as well. if hobie doesn't come through it can be fixed with an iron and plastic. Common milk jugs use the same type of plastic our boats are made out of. That white cap just pops out with a small flat head screwdriver. I then drilled a small hole at the other end of the crack to stop it from spreading further. Heated and layered plastic till it was built up good. This repair is going on 2 seasons and hasn't leaked yet."

Thanks again! I ordered a plastic welding kit, which comes with a bit of stainless mesh. So my plan is:
1) drill a tiny hole at the front of the crack, for stress relief, then embed a small piece of the mesh in the crack and build up with the iron.
2) Heat a piece of plastic to form fit the *inside* of the boat to cover the crack and fit around the 'nose' of the drive well....Then silicon(?) or otherwise glue the piece in.

The industrial PE adhesives like DP8010 are *expensive*. Silicon is a hell of a lot cheaper, but will it bond?

Anyway, hoping this combination repair will do the trick.

Personally, I would not imbed anything in the crack. I would have the mesh across the crack. The idea is to give the area linear strength, kind of lock things in place and prevent a new crack. The glue, melted plastic or whatever, just keeps it in place, gives it rigidity, and seals it. I would fill the crack with melted plastic, then build a sandwich over it of plastic, mesh and more plastic. Do that on both sides, if possible.

My welder kit from Amazon arrived last night, and that's basically what I did. First, drilled a small hole at the front of the crack. Then, cut a piece of the included mesh about 2" x 3/4" and placed that over the crack. I ran the iron over it, with no visible result at first, then it began to satisfyingly sink into the hull. I stopped when it was more or less flush, then began to 'weld' strips of plastic milk jug, over the mesh...

I will say the resulting repair is nothing pretty -- it looks like a horrible foot blister or something. But it does seem strong as hell.

While I had the milk jug handy, I cut out a palm-sized piece and used my heat gun to soften it to mold around the inside of the boat, covering the crack, and up over the 'nose' of the drive-well if that makes sense. (Actually I had to do this twice, because the heat gun will shrivel milk-jug to jelly in a heartbeat). So I have a form fitted inside patch, which I'll secure with silicone as an additional water barrier. We will see! I'll have a chance to test the kayak this weekend.

Keep us updated on the results!

STK:
Now you have the repair done, I'm wondering if there is something that can be done to remove the extreme point loading on that thin area where the front edge of the mirage drive slot, (the root cause of your failure). This is the highest point of stress on the entire boat. If you put a mask on, in your pool, (ok I had full scuba gear on, (lol)), and have someone pedal the boat above you, (with the boat either tied to something, or pointed into the side of the pool). When pedaling, you can easily see, (and feel) the hull flexing on every single pedal stroke, ( I strongly doubt anyone has ever tried this, lol everyone chases resultant failures, never root causes, (that's just human nature(). This is called a point load and I know of no un re-enforced plastic that can withstand that kind of load very long, (there is none). Dah we are scuba divers, so I use any excuse to dive, you can also just reach under the boat with your finger, and touch the spot while someone else is pedaling in the pool to test your fixes.
If you look at the front and rear of the mirage drive itself, (where it rests in the pocket) it has a narrow hard surface and two sharp edges.
There are a couple things that can be done, one being spread the point load over a larger area, the other being remove any load from that area altogether.

If you put your mirage drive into the slot and click it down, then rock it back and forth in the slot, with it rocked back measure the gap that is created in the front, (on most of our boats the gap ended up being around an eighth inch). If it's not enough gap, it's pretty easy remove the click and go clips, and shim up the bases a little bit to increase the gap. On one of our boats we had to make 1/16" thick shims under the click and go latches, (but that was one out of 8 boats, (actually one out of 12 mirage slots, because 4 of the boats were tandems). If you use plastic shims they don't rust, (however the shims under the click and go latches are a last resort, (don't do it if not needed)).

I have used many different designs depending on the mood at the time, and what I have handy laying around the garage. We've been using Hobies since 2007, and have owned many of them, plus we use the daylights out of the things, (lol because we can in south florida and the keys year round), plus I'm kinda retired and have pretty much nothin else to do, so I play hard.

1. A thick piece of hard rubber (1/8"-3/16" thick, if you have enough play under the click and go clip). We just cut the rubber about 1" wide and glued it into the bottom of the slot. It worked ok, the bad spot in the center flexed much less.

2. I made a sandwich with .040" thick stainless shim stock (1/2" wide) glued between two pieces of hard rubber, (leather would also likely work). That worked a little better.

3. I also tried bondo, basically you spray the inside of the hull (the mirage drive slot area) with silicone or urethane release spray. Then gob some bondo body putty onto the front of the mirage drive, (big ole wad), then click the drive in place and let the bondo setup. Once dry the front of the mirage drive tang is the same exact shape as the slot in the hull. Of course the bondo sticks to the nylon mirage drive tang, (you can always sand it down a little so it drops in a little easier, and also fits in either mirage slot on our boat just in case we get the drives mixed up). If you ever sell the boat it's easy to chip the bondo off the drive. This worked great, and when testing in the pool there was no flex in the bad area, (it actually worked, (who knew, lol). We also did a version with a bike inner tube glued to the outside of the bondo, that also worked.

4: On one boat we bought some 1" wide 1/16" thick aluminum, (3 ft long at Lowes). And custom bent up a big flat bottom V shape. Basically start out by bending a flat bottom V in the middle, with fairly gentle curves in the lower corners. When your done you want the aluminum to follow the side walls of the mirage opening, (touching the walls), of course make sure the mirage drive still fits in. Now bend the ends so they lay across the top of the deck flat, you want the flat part around 3" long. I then sunk a couple screws into each leg on top of the deck to hold the aluminum piece in place. I then gobbed in silicone across the bottom of the slot and put the screws in. It looks like crap, but hey it works, when peddling in the pool there was no flex at the front of the mirage drive opening. However it's a lot of work to build, If you ever sell the boat you just remove the screws, pull the thing out, and fill the holes with your handy dandy Hobie welder.

Nothing needs to be done at the back of the mirage slot, there is no stress back there.

In other words there are a dozen ways to fix the issue, use any you wish, or do nothing at all, (your choice). In my case we pedaled all of our Hobies many miles most every week year round, (pedaling my boats was my main exercise program). I promised the wife in order to buy the darn boat in the first place, I committed to pedaling the boat 10-15 miles per week (year round), I even had to show her my GPS records every week as part of the deal. Our TI had a 100 mile per day range, and we regularly did 50-60 mile day trips, I always try to peddle 100% of the time, (that was my exercise program). Obviously the boats were souped up just a little. Let me make this perfectly clear, there was nothing written in our deal, how fast the boat traveled, ( a giant loophole in the agreement that I exploited heavily). BTW 15 miles at 2 mph is 8 hrs on the water in 95 degree sun, first few times out I suffered heat exposure, (boy did I get screwed in that deal I thought at the time, lol), so I modified the boat a little. Lets just say the stock boat was not quite as capable as I thought it was going to be, a rude awakening, from delusions of grandeur in April 2010 standing on the showroom floor workin out the deal with the wife, so I fixed all that.

Also I always used the huge Flex-90 eclipse fins on my boats over the last few years, (way more strain on everything). I highly suggest not using such fins without re-enforcing the mirage slot, (and many other mods). Plus your going to go thru a lot of cables, and wear out the drives quickly.

Obviously if you only take your boat out 2-3 times a year, and only go a couple miles, no need to do anything at all, we used our boats way more and way harder than the average bear.

This was just one of 50 mods made to all of our boats, to set them up for our use.

Hope this helps
FE