knee tube or under the deck bag?

Hi. Building on the thread a few days on knee tubes, I"m trying to figure out how to best create space in the cockpit. Between a fiberglass knee tube and a northwater under-deck bag, what would the pros and cons to each be? I’m leaning toward the knee tube, not sure why, I guess it just seems it would be easier to access and is infinitely more durable. Thoughts? Thanks.

PS. Fadedred, if you read this, how did you install the bungees in your knee tube, that seems like a necessary feature. Can’t see in your pics though how you installed that bottom loop. Thx.

I drilled three holes in the edge of the knee tube. One in the exact center (at the bottom) and one as high up the sides as to be before the bend that accepts the the glass to hold it to the deck.

the bungie is then threaded through as a double loom on the bottom

the one ends then follow the outside of the knee tube to the one of the other two holes …through the hole then through the loop made by pushing the bungie up through the center hole then through the other hole…then tie the two ends together.

I do it as one continious loop so that the height of the bungie covering the tube entrance can be adjusted by just pulling the bottom loom a little farther out or not

I tie the ends of the bungie with a water knot and do it on the outside of the knee tube not on the inside, usually high on one of the sides

The knee tubes I use are made and sold by Valley, but would be easy enough to produce with a litle glass and some time, I bough a few cheep so that’s what I use.

Best Wishes


Knee Tube for Pump
Having a day hatch in the boat, I chose the knee tube for the cockpit. My bilge pump resides there, so I have a clean deck. Made the tube by laying up fiberglass over a 3" mailing tube covered with plastic wrap. This size fits the foam float ring on a Beckson pump very nicely. I glassed it into the Explorer and it’s been working well.


I use the under deck bag
it works out fairly nicely for me. You can remove it when you don’t need it - which is nice. I like to keep my pump on top of the bag (between the bag and the deck). With that set up the pump does slide around a bit, but nothing unmanageable. The bag is not waterproof so I don’t carry anything I don’t want to get in it.

I am not sure of the capacity of knee tubes but the bag holds a lot (two thermoses, sunscreen, skullcap, snack bars, pogies/gloves, and rescue sling - as well as a pump on top and out of the way).

If you want to carry anything heavy in the bag I would use West Systems GFlex epoxy to secure the ‘discs’ in place. I tried using the North Water recommendations but the discs kept pulling loose when I put a thermos or two in the bag. I probably messed up the application process of Vynabond.

fewer chances for entrapment
with a knee tube, seems to me

(that said, I’ve got the Northwater bag; my boat is plastic)

knee brace
Knee tubes are very popular in ocean cockpited boats because it creates an excellent inner knee brace. Even in a keyhole, if done correctly, you’ll appreciate having something solid for your knee to rest against while edging or rolling.

I suppose I’ll go with a knee tube, and thanks much Roy for the detailed instructions, appreciate it.

under deck bag
I went the economical route. I have the clips and pads glued / screwed (depending on the boat)in 4 and soon to be 5 boats. the underdeck bag is great because I can keep things like cliff bars, gps, deck light, thermos, gloves, sunscreen and bug repellant and just switch from boat to boat, with a pump securely wedged in between the bag and the deck. I take mine out every year and spray it inside and out with water repellant which helps a bit but the zipper is not waterproof and things will get wet in there if you are doing wet exits or no skirt rolling.


Am considering a bag now, especially since REI has the northwater underdeck bag for 40 bucks right now. Paul, what kind of glue do you use to affix the discs?

on glass or wood boats marinetex works great. On the plastic boats I had to drill and screw with silicone washers.


West Systems GFlex epoxy
I used it on my glass boats and it worked great. If you buy the ‘starter’ kit it comes with instructions on how to use the epoxy on plastic boats as well.

im building a shearwater and i plan on installing an underdeck bag rather than making a tube that way i can take it out when im not using it

cap, wenley’s comments on his knee tube.

I’ve had bags in all my boats…
I use epoxy and micro fibers to hold the pads in wood or glass boats.

then there’s this

Under deck bag
The under deck bag is handy for small stuff that could fall out of a kneetube. I store my hand pump on top of the under deck bag, a grease pencil for my Deck Slates, sunscreen, and other small items.

The only improvement I wish Northwater would make in the underdeck bag is a small drain hole with a grommet.