pressure relief hole in bulkhead?

I need to drill a hole in the bulkheads of my kayak for pressure relief. I have soft hatch covers (on an NDK Pilgrim) and yesterday in our almost-100-degree heat I saw the covers bulging upward.

So the questions are:

1 Should I use the very smallest-diameter drill bit? Or is there some optimum size?

2 Do I need some backing where I drill? I won’t be able to hold a backing block but perhaps I could apply a piece of duct tape – if that is necessary to prevent damage to the fiberglass bulkhead at the site of the hole.

Any advice? Thanks!

G in NC

We did that
Different NDK boats but the same problem. Some manufacturers do this for you, but that’s another story.

Husband did it and he just used a quite small bit, about 2/3 of the way up and centered. I don’t think he used any backing, but then he is a bigger person. Some of this may come down to how solidly you can hold the drill. Can’t see how it’d hurt to put some duct tape down first. Very fast though, and yes the boat is bone dry.

I can’t say the same for the Vela, but the really really huge real oval hatch cover is the source of the problem. Not the teeny hole in the bulkhead.

It’s pretty surprising how thin the fiberglass in these boats actually is, although they do hold up quite well. I’ve done some repair and other work to my NDK over the years, and it won’t take more than a second or two with a very small drill bit to get right through.

One trick I’ve heard is to use a small piece of Gore-Tex cloth repair tape over the hole - since it’s waterproof and breathable, it’ll do the trick. Some of the P&H boats have a one-way valve of sorts to take care of this as well. But even just leaving the hole open shouldn’t cause any real problem.

my concern . . .
is whether drilling a hole unsupported will cause spiderweb cracking of the fiberglass bulkhead radiating out from the hole. Maybe not. Maybe I just get out the littlest drill bit and make that hole 2/3 the way up from the bottom.

Thanks for replies.


Duct tape
on both sides of where you drill the hole is a good idea to prevent the cracking you mention. After removing the tape you can put a tiny dab of epoxy on the hole to seal the edges/fibers (don’t re-plug the hole though!).

use a variable speed drill
And build speed slowly and with a sharp bit. It will be fine with a tiny bit.

I’m glad my hatches leak :slight_smile:

Ryan L.

i had the same problemwith my Dirago
But my bulkhead is close-cell foam so I took a straw from a WD-40 can (those computer air cans also work) and twisted as I shoved it through the foam.

Then cut it flush.

So long as the hole/straw is close to the top, water never enters and the air flows safely.

OK, got it . . .
sharp drill bit, start slow, after covering both sides of bulkhead with a bit of tape. (I see no reason to remove it afterwards, actually.) Thanks!


Dremel tool
I needed to use one for its small size and easier access compared with a regular drill/driver.

Use a tiny bit for it, which is easy to get.

And be careful because the rpms are very high so it will get the job done FAST.

I just recently drilled some in two …
different QCC bulkheads for the same reason.

I used a 1/16 " bit and drilled them half way up.

Just use an electric drill with a sharp bit and go for it. There is no need for any special prep.

Jack L

air exhange hole in bulkhead
1/16 hole halfway up is what we recommend. If you were to drill it at the top of the bulkhead, should you capsize and spend more time with the kayak upside down that you bargain for before you right the craft, water will siphon in to the rear or front hatch. So halfway up the wall is best and having duct tape on both sides can prevent flaving from the drill bit if it’s duller than you think. Actually, the fact that the hatch cover is pushing out is a good sign that the hatch plate and the bulkhead is very well done and anyone reading your post that thinks you might have a poorly made kayak should know to the contrary.

Don’t worry
This is over analysis to the max.

Use a a bit about the thickness of a paper clip. Drill a hole in the center of each bulkhead and forget it. You boat is not going to explode in pieces. You’re done.

Jay, two thumbs up! (nm)

Another thank you…
…for not making a mountain out of a mole hill (or the Grand Canyon out of the entrance to an ant hill.)

Yes, I know it’s a scary thing to take a drill to the bulkhead of a $3K plus kayak, but many of us have done it and not hit davy jones’ locker yet.

I do like the idea, though, of putting a bit of duct tape on either side of where you’re going to drill, though.

it won’t
think of the fiberglass cloth bulkhead as stiff cloth. You put a needle hole into cloth and the cloth doesn’t unravel. Fiberglass isn’t a solid material ready to shatter, it’s cloth stiffened with resin.

I wouldn’t bother
Just take your hatch covers off when you aren’t on the water, and ‘burp’ them as needed.

I know a lot of people drill holes, but I wouldn’t compromise my waterproof hatches.

What about while driving?
I wouldn’t drive with covers off - and this is the time when I expect the compartments to get the hottest, with no water to help keep things cool. An elevated compartment pressure will play much more havoc on your boat than a little bitty hole in the bulkhead.

If the air in the compartment increases from 70 to 100 degrees F, this corresponds to an approx 6% increase in absolute temperature. The corresponding pressure rise is also 6% (pV = nRT, so pressure rise is proportional to temperature rise at constant volume). If the volume increases at the same time, the pressure rise will be lessened, but not eliminated.

A 5% increase in atmospheric pressure is about 0.7 psi. Over the area of a bulkhead (estimated as an 18" circle), this gives a 180 pound internal force trying to blow out the bulkhead. A 50 degree temp increase gives a force over 300 pounds. That type of force cycling on a bulkhead has got to be bad for business.

Meanwhile, a 1/16" hole, which will continuously equalize air pressure, is structurally insignificant in a FG matrix as was pointed out above. It will admit a near-zero amount of water, due to the oddities of fluid mechanics at small scales. To test this, put a 1/16" hole in a closed milk jug and hold it under water - not much happens.

I would just drill the holes - I’m not sure how duct tape is supposed to help, I wouldn’t bother.

Thanks for the math … I like that !
Be happy the hatches seal, thats good and just ram the tiny hole though … Not going to hurt anything.

Think about all the holes for the outfitting stuff + no need to seal anything either.

I have seen foam cored boats delam and others with blown out seams from pressure differentials. This was from sea level going to about 9000’ and back down.

I drive with covers off all the time
if I am going long distances the kayak goes deck down in case it rains.

My avoidance about drilling holes isn’t about structural damage. It is about keeping water out when surfing, rolling, doing rescues, having fun and messing about. Nothing quite a nice as throwing clothes and keys in the day hatch for a surf session and when you stop 3 hours later everything is still dry.

It’s not an issue
If fiberglass was so fragile that drilling a tiny hole in it caused it to fracture, you wouldn’t be able to make boats out of it.

I use a 1/32" bit and it goes through quickly with no issues. If you don’t have anything that small, a 1/16" bit will be fine. That’s the smallest size you find in a typical drill bit set.