Can anyone tell me what size float bag I need to fill the stern of a WS Tsunami 145?
Yes, the boat has bulkheads, but being a Duralite the hull flexes enough to sometimes blow the seal and start a leak. I’ve resealed the stern once already, but there’s a small leak again. 
I only use the boat for day-trips, so I don’t care if the bag wipes out any possibility of using the stern hatch, in fact a longer bag would be a plus. If it’s long enough it may help to isolate the day hatch by creating a second bulkhead, of sorts, just behind the day hatch lid.
-T
Not sure, but you can measure.
Here’s instructions that I followed when I made a couple of sets of floatbags:
http://blackdogkayaks.com/forum/YaBB.pl?num=1149782415
As for blowing out the hatch, I think the “normal” solution is to drill a small hole in the middle of the bulkhead. This lets the pressure equalize in the compartments.
“Blow Out”.
Perhaps I should have used a different term, as “Blow Out” doesn’t really describe it well…
Due to the extra thin skin on the Duralite line, they have a tendency to flex enough to pull the hull away from the bulkhead, causing a leak.
Generally this happens when the boat is on the roof rack, that’s why I recently replaced my Hully Rollers with J-Racks, but it can also happen when beaching on rocks and the like (over time).
I’m going to measure the stern hatch tomorrow, I just haven’t been finding a lot of size-detail on the Internet kayak sites lately, and my local shop doesn’t have any float bags stock. =(
are you looking for
a typical rectangular/cylindrical bag or a wedge-shaped one? a 15L bag will fit with room to spare, depending what you put in it.
I have a Duralite and haven’t had that problem, have you considered cutting a new bulkhead that fits tighter? you could use the existing one as a template and make it just a little larger.
you could just fill it with
packing peanuts
Bulkhead replacement
I actually tried making a slightly larger bulkhead using the very technique you mention, but I didn’t have the correct tool (a band-saw) for the job, so it didn’t work out too well.
I ended up just putting the old bulkhead back in and using more sealant. The leak is considerably smaller so now I’m just going to back it up with a float bag and call it even. 
Coping Saw
It’s a shame to have problems on such a nice boat. You don’t have to use a bandsaw for cutting bulkheads. If you are willing to try again, a coping saw works well. They are inexpensive and available at any hardware store. Handy to have around for cutting new baseboards or window moldings.
Since water will still leak into the compartment even with a float bag it’ll always be a problem unless you fix the leaking bulkhead. A coping saw will cost less than a float bag.
I found the perfect bag
– Last Updated: Sep-26-10 9:56 PM EST –
just by chance in the 50% off bin of my local outfitter, Aquan Sports.
It's actually a canoe float-bag and it measures 52" long by 27" wide. When inflated it fits perfectly from the stern to just behind the day-hatch.
That's the spot where Wilderness Systems *SHOULD* have put a second bulkhead. :(
(I finally have a functional day-hatch!).
I only use the boat for day-trips, so losing the bulk of the rear compartment is no biggie. I still have the large bow compartment for extra stuff.