I had been following another thread and learned that folks have vented their dry compartments by drilling a small hole in each of the bulkheads. This sounds like a great idea and I plan to do it.
The original thread was discussing water leaks. This got me thinking. I am going to go ahead and vent as described. However, I have noted, similar to others, that after sitting in the sun removal of one of the hatches allows air to escape from the compartment, (I can hear it as I crack the hatch).
My question is spawned by the sound of the air comming out which indicates a higher pressure due likely to expansion from heat. If the dry compartment will hold a positive air pressure, then how in the heck does water get in?
Mark
I’ll take a stab at that
I don’t have holes in my bulkheads, but I have noticed on occasion that there was a very small amount of water (sometimes mere dampness) inside my rear hatch, despite the fact that my hatch cover went SSSSSSSSSSS when I loosened the knob and cracked the seal.
Two possibilities:
- If the hatch cover is on securely before paddling (as I’d hope it would be!), when the kayak enters cold water it could cause the air inside the hatch compartment to compress, allowing any water around the seal edges to be sucked inside. I don’t know what your hatch seals are, but mine are weatherstripping (4 pieces butted up end-to-end in a rectangle) and it is possible that a few drops of water around the outside could work their way in under that kind of suction.
When you get out of the water and, especially, if the kayak sits in heat while being transported, the air in the hatch compartment expands, giving you the impression it is watertight. But remember that the seals themselves may expand slightly in the heat, so at that point the thing IS airtight and watertight. But it may not have been when the kayak first got in the cold water.
In my case, I also gain 2000’ elevation when I get home. It is always VERY difficult to break the air seal there.
As for why the water only enters my rear hatch instead of both, maybe it’s because the front hatch cover sits higher up and is less prone to having water wash onto it. Also, I may have done a better job butting the weatherstrip joints. At any rate, the water in the rear hatch is less than a tablespoon’s worth, when there is any.
- If it’s only a tiny amount of water, that water might be the result of condensation, not leakage. I suspect this is the case in my kayak. The front of the kayak has more volume above waterline (higher foredeck), so its hatch may be less prone to condensation.
- Another (very bad) possibility is that the stern end of the kayak has a leak in it somewhere. I have checked it several times and can’t find any kind of break in the outer surface, so this does not appear to be the case. Also, if there were such a leak, water would ALWAYS be in the rear compartment, instead of only sometimes.
Hey Mark…
May I suggest that before you drill a hole in one of your bulkheads you cantact Phil and see what he says.
We have two QCC’s and there is no way I am drilling a hole in the bulkhead.
Even though my compartments leak, they don’t leak enough to fill with water, and if you drill a hole, you are just going to be inviting more water in if your cockpit is full of water or upside down.
I would rather stick with my little bit of water that comes in in an all day paddle with breaking waves over the bow and still know that I have a possible life saving air tight compartment.
Cheers,
JackL
Concern is more about blowing hatch off
Rather than the water in it concern, most past posts have had to do with the concern, legit or not of air pressure on a hot day blowing off the hatch lid. For most kayaks the opposing forces of cold water below cooling the compartment minimizes the expansive forces of heating the hatch cover and deck. If the hatch cover is blown off, this is no small matter, so many kayaks do have a PIN hole in their bulkheads you may not even know about. Definitely do not make a larger hole. A pin hole is not likely to swamp you as Jack is rightly conerned about. To each their own here as usual, but before making a hole, figure out why something is happening before applying any solution.
Pinhole won’t cause a leak
My husband put a pinhole in our bulkheads, and I can testify that it has not caused any kind of leak in the wettest of conditions. I am working fairly aggressively this spring on rolls, deeper braces and some sculling. Between missed rolls and water coming into the cockpit with the looser skirt I often use for practice ( helps mitigate my anxiety level), there has been lots of water available. My bulkheads have been bone dry every time.
But they never leaked before either - if a pinhole causes a leak I’d suspect that it was taking advantage of a pre-existing tendency thru some other entry point. As I understand it, QCC hatches have always had a tendency to leak (I paddle with a couple of people who have QCC’s, fairly new ones.)
As to the air being trapped - I don’t know physics well enough to come up with a brilliant explanation. But one thng that does occur to me is that air expands due to a lot of heat when the boat is sitting in the sun, while water seeping into a bulkhead is most likely to be an issue when the boat is in the water and the relative temperatures of the interior and the surrounding water are closer. The relative difference in pressure and the fact that water has the attribute of hydrostatic tension may be part of it.
The ladies are right
In many areas, the water temp is lower than the air temp, which means that negative pressure is created in a sealed compartment when you put the boat on the water, resulting in water being drawn in, either through the hatch or other seepage points.
Venting the bulkheads does not result in water leaking into the compartments when the cockpit is flooded. I’ve spend a fair amount of time in flooded boats with vented bulkheads (during rescue practice) and it’s never been a problem.
Suction from temperature changes
I’m pretty sure I notice this suction effect. With sun here and temps in the 80s - the deck (even though light) will be well over 100 degrees. The hull mid 70s (current water temps).
The air in the hatches will stabilize in temperature paddling flat water - but as soon as I take a water over the deck it is rapidly cooled. The air inside contracts and could be drawing in the small amount of water around the seals. Over time it adds up - but I usually have maybe a half cup at most.
The reason I think the suction plays a big part is when doing roll practice, whether I do two rolls or 50, I still end up with only the same amount. If it were a structural leak each roll should add more water - but I find the opposite happening. I think this is because the temperature is more stabilized by the frequent rolling so it does not have time to reheat in the sun and there are no sudden pressure changes.
Anyway, that’s why I think venting would help. I don’t think QCCs need to be vented to prevent pressure damage (as with Valley hatches) as the seal is not that aggressive.
Well, either that or waves are just sneaky and work their way under…
BTW - I don’t know about the rudder, but the stock QCC skeg setup leaks like a seive! When inverted, the water in the skeg box will run right into the aft compartment. Nothing to stop it. I get very little water there since I redid the skeg control and went all cable. Just a little from the stuff above - usually less than the front hatch now - sometimes none at all.
Several Points To Consider–
I had assumed that the air moving as I opened the hatches was a result of positive air pressure caused by heating the air and it expanding. As pointed out, what I hear could just as easily be the result of a vacuum within the compartment caused by cooler water temps allowing the air to reduce its pressure.
The rudder does not seem to leak on the QCCs. It has two SS brackets attached the the stern but they seem to be pretty well cauked. There are two fairleads for the cable which could possibly allow some water entry, but I have no evidence of this.
A very small pin hole in the bulkheads should not allow water entry and at the same time should allow air passage.
It the general consensous is that a change of air temp is causing a change of internal pressure then we would have to worry about that during storage as well as during use. I read somewhere to remove the hatches on your kayak during storage. I wonder if these are related? I have not been doing this.
I have only been shipping a small amount of water during use and am not really worried with the amount that I am getting.
All this said. I should have all the answers. I am a controls engineer and work with positive air pressure and vacuum every day. But… I dont really understand what is going on and will take a closer look.
Mark
Storage
I usually keep mine open so they air out - but I store it inside. If I forget it’s no big deal as I probably didn’t rinse them out (just wiped dry) and salt seems to inhibit mold. There’s not much to rust either.
Yours are different construction and gasket types than mine, but I’ve seen the newer ones and I’d guess you are hearing air come out on a post paddle inspection. Deck is usually up and in the light - so expanded air would be more likely - with contraction occurring only when cooler water hits the deck (wave and/or inverted). Suction would be intermittent and not happening when you were at the hatch to hear it.
Effect on yours could be different too, as it doesn’t have the little trough running all the way around that the pedestal gasket sits in like mine does. Yours has a vertical seal (that lacks any redundancy and relies 100% on the fit of the seal - but doesn’t have a moat of water).
QCC website still shows the old pedestal gasket setup:
http://www.qcckayaks.com/kayaks/construction.asp
Venting
Fill me in, please. Why would I want to vent my hatches?
Spoke with QCC today
– Last Updated: May-12-05 4:45 PM EST –
and here is the word: QCC has been venting the bulkheads for a few months now so no need to drill pinholes in bulkhead. Boy, am I relieved! Just wait 'till I need to start drilling holes in it for fishing rod holders, I will be a basket case.
With all the modifications I’ve done…
…to my 700, I’d still be very hesitant to cut holes like that.
Want to fish? Go get a nice used plastic SOT! Ultimate Florida fishing platforms.
Actually, I used to have one - that I got partly to fish from - but ended up liking paddling so much I never dropped a line.
The reason
I got the 400 instead of the 600 is to use it as a fishing platform. I know…a real compromise of speed and performance. But I can’t help it! I love to fish and paddle. Did the SOT thing over 10 years ago did not like it for long distance trips. It’s a great alternative for short distance fishing however.
Venting…
I just finished adding hatches and bulkheads to a wooden boat. Before I vented them they would be stuck shut after a paddle and I would have to pry them open… means good job though… GH
Watertight / Airtight
I’ve read all of the arguments for venting and they all sound logical and prudent. That being said I do not vent any of my bulkheads. I like to see that the integrity of the hatches are not compromised. During very hot air / cold water days I may cool the hull and burp the hatches but normally I prefer to watch the hatches bulge as things warm up and depress as things cool.
I’m my case the above opinions are in the context of rigid/glassed-in bulkheads so bulkhead failure is not a concern for me. Maybe I’ll change my tune once I actually have a failure attributable to the lack of venting but until then there are other more interesting things to ponder.
Venting a Surfski
Look at the little white/transparent tube between the bow and the cockpit:
http://community.webshots.com/photo/344423999/344427821mgEAwI
Regards,
Iceman
PS: The inside of the hull of a surfski and the bulklhead of a Kayak is the same…