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PostPosted: Sat Feb 23, 2013 4:18 pm 
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Location: Sarasota,Key West FL
CaptnChaos (Jim)
Here is a pic of the setup just before installation with 5/16 hose.

Image

Here is the 5/16 hose in place, notice that it does not sit against the bottom of the hull, it actually clings to the underside of the seal.
Image

After thinking about it I thought that the seals might get pushed out a little too much (possibly damaging them), so I replaced the 5/16OD tubing with 1/4" OD tubing, the hatch actually goes all the way down completely now (there was a small gap between the hull and the seal with the 5/16 tubing.

Here is the 1/4" dia tubing installed.
Image

Here is a pic of side sitting all the way down with the quarter in tubing.
Image

I have not tested the 1/4" dia tubing, next time I go out in rough water I will take both along and do so sea trials.
Both of the other seals (original seals) are compression seals, being held down by the bungy, if the hull flexes at all, gaps are created allowing water to get in. With the addition of a third pinch type seal, that sandwiches between the side wall of the of the hatch, and the side wall of the hatch opening, this pinch seal should remain sealed, even when the hull flex's. At least thats my theory and I'm sticking to it. There should be no maintainence at all, and it should last for years (all for about $2 bucks) .
Hope this helps
Bob


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PostPosted: Sat Feb 23, 2013 7:26 pm 
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As they say, a picture is worth a thousand words. Thanks for posting Bob. Looks like the TI hatch is somewhat different than the AI.

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PostPosted: Sun Feb 24, 2013 2:14 am 
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tonystott wrote:
Thomas, surely Hobie has now sorted out your problem under warranty? I think everyone agreed that the problem you have/had with your hull was extremely abnormal, confirmed by Hobie's decision to correct it under warranty.
Well, not excatly. My dealer pointed out the problem when she was visiting Hobie US, and so far (so good) she got the message that it was a Hobie problem, not mine. I will make some efforts to correct the problem as I see it. If I don't succeed, I will raise the warranty issue. So I follow this tread with great interest.


fusioneng wrote:
Kal-P-Dal's problem, which was unique ( a defective hull), should have been addressed by Hobie as a separate kind of unrelated not typical issue.
I don't think it is unique at all. Hobie does not make just ONE kayak wrong. (I think as Chekika, most AI's haven't been tested in the right conditions where the leaks appear!) I have not recived any information from Hobie about WHAT is wrong with my hull. When my dealer was visiting Hobie USA they found at least one other kayak with the same fault, enought out of the tolerance to see the problem. I have confidence to think I can fix the big issue. Wich leaves me at same point where you are, trying to find a solution to get the front hatch completely water tight.

So I will stand with my point of view, the front hatch is not designed to meet the "normal" conditions sailing an AI.
And no, I will not accept water inside the hull. I see that as a fault and will try to fix it. Other kayaks have water tight hatch covers, it is not impossible to make. Even the two small 8" hatch covers could be better designed. No water dripping, not so sensitive to sand / dirt.

br thomas


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PostPosted: Sun Feb 24, 2013 2:50 am 
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Sorry Thomas, but I can't help thinking that you are not in a hurry to solve your leakage problems, which must have arisen about a year ago by now. Why on earth haven't you simply presented the problem to Hobie, who have already acknowledged that it is a warranty issue?

Good luck with your belief that the inside of your hull should remain bone dry. There is no design on earth that will make a hatch 100% watertight when it is less than 3cm above calm water level, unless of course you only use the hatch when the hull is out of the water.

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PostPosted: Sun Feb 24, 2013 7:37 am 
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thomas:
I agree with you 100%, It is the design of the hatch itself that is very very bad.
I own a very successful product design engineering firm (my day job), and my hobby is kayaking and sailing, so my interest here is only because it's fun for me, I have no connection with Hobiecat company at all.
And to be fair I can look at pretty much any design of any product and giggle at why in the heck did they do this or that, so I'm not knocking Hobie in particular here, as a whole they are better than most.
However the design of the hatch seals on all of their hatches on all of their kayaks (including the AI/TI) makes me laugh (LOL, or LMAO), as they have been making the same mistake for many years over and over again, shooting themselves in the foot again and again with every fix/improvement they make to the hatch design on all their boats. They are forcing themselves to try and manufacture a product to un-realistic tolerances when there is no reason neccessary (driving cost up ("which affects me")).
The simple fix I discribed earlier should help on your hatch cover also, at least until Hobie fixes your boat (which they should do). I made a picture showing why below (the underlying engineering).
In picture 1, this is showing the current design as it's supposed to work with two compression/butt (static) seals pressing against a flat surface. This type of seal is fine on something that you know is going to be flat everytime and doesn't move (like a canning jar lid), and can be easily manufactured to high precision. As an example a 1 gallon paint can lid uses two pinch type dynamic seals to seal the paint can, because a static compression seal would not work, and would be un-realistic to manufacture.
The hatch seal Hobie has can probably withstand a variation in flatness over the entire surface, ie.... flatness of both the hull and the hull lip being maintained within a manufacturing tolerance of around 1/16 of an inch (as long as it doesn't move). This also requires that the lid be manufactured to similar tolerances. To be honest, this is un-realistic in any type of plastics (especially rotomolding). Even auto manufacturers using stamped metal on door seals cannot hold these kind of tolerances.
Pic 2 shows the problem you are having, with a gap in the center, allowing water to flow freely into the hull.
Pic 3 shows the addition of a simple piece of tubing around the hatch, this adds the type of seal that should have been used in the first place ( a pinch type dynamic seal).
Pic 4 show that even if the hull is bent, or the cover is ill fitting, or the hull flexes (which it does in the waves) the water seal is maintained.

Basically you cannot use a static compression seal on something like this (engineering 101), please refer to any seal design guide.

Hobies hatch design is not my problem, I only came up with a simple fix to help my friend Jim so he can stay dry next week doing the EC challenge, and I'm not about to tell Hobie how to design their boats, but I do like to use them.

Bob
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PostPosted: Sun Feb 24, 2013 8:12 am 
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I was of course referring to the twist and seal hatches, which do not appear to suffer from any design issues unlike the forward hatch (eg the seal pulling down into the tapered housing seems to be quite efficient). The location, so close to water level, is however a different issue..

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PostPosted: Sun Feb 24, 2013 10:40 am 
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I made a 1/4" seal like yours Bob. Thank you very much for sharing your engineering experience. Not sure how it will work, as the AI hatch may be a little different than the TI, but it won't hurt. And I just couldn't replace the original hobie bottom 2 piece glued seal with the new seal since it just didn't feel right to do that.

Today is the final day for making any boat modifications around here. This morning when I showed the wife Dogs Life's flag and his go pro camera above the top of the mast, she gave me one of those looks and said "don't even think about it". :lol:

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PostPosted: Sun Feb 24, 2013 1:30 pm 
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Excellent info on seals Bob. 8)
It seems like Keith's solution with it's large cross section combines both pinch and compression types into one.


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PostPosted: Sun Feb 24, 2013 1:32 pm 
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tonystott wrote:
Sorry Thomas, but I can't help thinking that you are not in a hurry to solve your leakage problems, which must have arisen about a year ago by now. Why on earth haven't you simply presented the problem to Hobie, who have already acknowledged that it is a warranty issue?
Well, in Sweden there is a lot of ice covering the water this time of the year so there is no hurry yet. Normal season is from beginning of may until end of september. I did my last trip with my "old" 2010 Adventure Kayak and participated in a race about 28 miles long, took me 7 hours and 7 minutes (no sailing!). Lots of rain that day. That was 2012-10-20. Ice will go away about beginning of april or at best middle of mars. I hope to be on water beginning of may. So thats my deadline.

tonystott wrote:
Good luck with your belief that the inside of your hull should remain bone dry. There is no design on earth that will make a hatch 100% watertight when it is less than 3cm above calm water level, unless of course you only use the hatch when the hull is out of the water.
There are in fact bone dry kayaks. How do they make it? Why can't I try? Is it really to much to ask for? As long as we talk about inside hull. :D

@fusioneng
Thanks for your post! I will try your solution. It could work.

best regards
thomas


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PostPosted: Sun Feb 24, 2013 2:32 pm 
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tonystott wrote:
There is no design on earth that will make a hatch 100% watertight when it is less than 3cm above calm water level, unless of course you only use the hatch when the hull is out of the water.

Tony, I think there are many hatch covers that are essentially 100% leak proof. The round hatch covers on Valley Sea Kayaks and similar ones by Current Designs kayaks do not leak. And, then, in all modesty, I will put forth my own DIY Hobie front hatch seal:
Image

This seal absolutely did not leak a drop during my recent 6-day camping trip with the winds of 15-20 mph, gusting to 28 mph, for the first 3 days. I was fully loaded (probably had 125-150# gear, and, myself--200#) You can be sure my hull top was very close to water level. That picture was taken on the 6th day. Those are my tent poles fully exposed if any water would come in that hatch. I treat my poles with the highest care since they will be trashed by any saltwater contact. I was fully confident to leave them under that hatch cover, with that seal.

Keith

Image

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PostPosted: Sun Feb 24, 2013 2:51 pm 
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Keith, I have no doubt that your new hatch seal can keep water out 100%, unless you open it while sailing. This was my point to Thomas, that it is unrealistic to expect the interior of the hull to remain bone dry, unless you leave all hatches completely closed while at sea.

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PostPosted: Sun Feb 24, 2013 5:21 pm 
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Bow Hatches, I guess it is my time to jump into this issue.

It may be close to impossible to design the perfect seal for a boat that flexes and has many manufacturing variations due to the rotomold process. But, where and how you shape the hatch should be the starting point.

The design of the hatch should protect the seal from the direct impact of the rushing water. I have watched how the water runs over the bow for many hours. My boat now has ~2000 miles under her keel. On a slight heel as the water runs by the hull the bungee cut-out scoops water, hydraulically forcing the water into the hatch groove. This is a formula for a seal failure.

Image

Not the best picture. I have closed down the the opening by welding in a plate that covers the slot leaving just enough to remove the bungee. Water still drains. The hatch gap is reduced with foam tape. Top of the gap is also covered. It does not have to be 100% watertight, just has to reduce the pressure on the seals. The strip in front of the hatch splits the water as it flows over the bow.

Image

With the watertight bulkhead installed just aft of the mast and a little silicone grease on the gasket I can get almost a perfect seal. When cold water hits the hull the warm air in the bow compartment shrinks down and pulls a vacuum. As long as there is no sand under the gaskets and the seal does not beak vacuum I have problems lifting up the hatch. This is OK since the only time I open the front hatch is to remove my camping gear...

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PostPosted: Sun Feb 24, 2013 7:25 pm 
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I own a bunch of mirage boats including the AI, and not one of them has ever had a water tight hull. Above one gallon in an AI seems a bit excessive, but Hawaii heavy wind sails push a lot of water around. Anyway, I just think the boats can't ever expected to be water tight completely, you can only do the best you can to keep the myriad of holes in this boat water tight. I've done a number of expeditions with mirage Hobies and I always put everything in drybags inside the hull, never could count on anything to stay dry in there.

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AI x2 Revo x2 Outback Oasis Pursuit Odyssey Bravo

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PostPosted: Mon Feb 25, 2013 1:59 am 
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Dog, thanks for reposting your approach here. That unique solution is not for everyone, but adds useful info to the discussion. We'd love to see more details as soon as you're able.

Your's is maybe the only real attempt made to seal and pressurize the kayak hull (part of it). I wonder if that's ever going to be feasible on a production boat, or desirable for most of us (such as those who want to haul gear/rods, etc or run electronics through the hull). It's clearly nice to have in an expedition kayak, though.

As long as Hobie hulls are porous, the focus for the rest of us remains on how best to displace air with air (and not with water).

Simple stuff like a better design of the front hatch, keeping the overall ride drier, routing the rudder controls outside the boat (seal the rear tubes) and adding a vent that wont catch water would be great places to start.

And not that hard for the company to do, it seems to me.

Good luck and "Stay thirsty my friend",..


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PostPosted: Mon Feb 25, 2013 2:17 am 
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tonystott wrote:
Keith, I have no doubt that your new hatch seal can keep water out 100%, unless you open it while sailing. This was my point to Thomas, that it is unrealistic to expect the interior of the hull to remain bone dry, unless you leave all hatches completely closed while at sea.
Sorry I didn't get that. Missunderstanding. The hatch in middle is the only possible hatch to access when in fast sailing conditions. With lots of gear and heavy loaded, it is not a god idea to open it. You are quite right! But it can be done. I have a "Sea to Summit" water tight bag with bottom cut away and mounted between hull and hatch. If I open the middle hatch there is a limited volume where leaking water collects. I can grab the bag opening and pull it up. Now it is possible to reach through the bag (when opened) and get things inside hull. It is also possible to pump out water from inside hull without getting more water in. Even in very rough conditions.

@DogsLife
Thanks for a very interesting post and your ideas. With your milage under the keel, I suspect all is well tested.
BTW in standard kayaks there is often a very small hole (1 millimeter) drilled in bulkheads to let air flow between water tight compartments. This is just to prevent both popping hatch covers and difficulties to open hatches. The hole should be placed where water normally can't reach, even with kayak upside down.

@NOHUHU
Yes I'm totally with you on your statement, but it could well end with DogsLife's solutions. Just because there is no other way.

I understand several accept some water inside hull. I will do what I can to keep the water in sea (where I need it to travel in!). But thats just me...(and some others too...)

best regards
thomas


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