Exterior ply for bulkheads nS&G kayak

[TK1]

Hi all,

I'm new here and just getting into building a Chesapeake 17 a my first kayak (but I have the next 4 or 5 planned ). This is the 'learning' kayak so I can gain knowledge on fiberglass, epoxy, building techniques, etc before I do a few more serious ones (also how I justify it to SWMBO - "I'll practice on this one so yours is nice and neat").

Anyway, I've read various comments on different ply being used, including luan and home interior/exterior ply to varying degrees. Seems like success has been had with all.

So (finally to the question), to (a) save some money and (b) to speed up the build as the marine ply dealer is quite a distance away...is there any reason not to use exterior-grade plywood for the bulkheads in my C17?*

The exterior is all marine ply, and I figure the bulkheads will be unseen, completely covered in epoxy, fiberglass filletted and just to give it shape, is there any reason not to use it (will be 6mm ply, 1 fore & 1 aft bulkhead).

Interested in opinions from those who've built more than 1/2 a kayak. Note, it will only really be used in lakes and rivers, not filled with hundreds of pounds of gear and in the surf or anything, although I may fit a sail one day.

Thanks,
Darren
Melbourne, Victoria

*(a) marine ply is really expensive here, and I don't need a whole sheet of 6mm; (b) it will be maybe a month before I can get to the marine ply place, and the local hardware store is 5 mins away and sells part sheets.

 

[hairymick]

G'day Darren,

So far, I have only used 3mm interior grade ply for the bulkheads and give them a very good penetrating coat of empoxy both sides.

Apart from holding the deck up, there is very little structural load on the bulkheads and it has worked well for me.

If you have a look at the factory, fibreglass sea kayaks, the bulkheads in them are paper thin. I see no, or very littleneed to go to any heavier ply than what the hull is made out of.

Exteror grade ply is mainly a hardwood type in this country and is comparitavely heavy.
Weight is the only reason I would hesitate to use it. It would certainly be strong enough.

 

[TK1]

Thanks Mick

Hope you had a good Aussie Day and got to enjoy a long weekend.

I hadn't thought of the weight difference in interior/exterior ply...I'll have to go to Bunnies and see what a piece of each weighs (ensuring the pieces are the same size :roll: ).

I thought 6mm was a bit overkill for a boat with 4mm hull, as I've seen others with 3 - 4mm bulkheads. Will ponder this overnight, but will probably go for normal ply for the bulkheads and give them a good soak in epoxy.

Thanks, will let you know how I go.

Regards,
Darren

 

[oldsparkey]

I don't know this for sure but it seams like it is true.

They say that a piece of plywood which is epoxy saturated increases in strength up to 4 times of the original strength. I do know a piece of plywood is easy to break but when epoxy saturated it is a hard sucker (if not almost impossible , you have to work at breaking it ) to break. Then put some fiberglass on each side and it will stand up to just about anything for boating.

The bulkheads in my kayaks are only epoxy saturated then varnished and they are strong.

Chuck.

 

[Kayak Jack]

TK1,

Bulkheads could almost be corrugated cardboard if soaked in epoxy, and maybe a layer of glass on one side. Use something thin & inexpensive.

The hull, on the other hand, deserves the very best you can obtain.

 

[TK1]

Thanks all,

I'm going with standard ply for the bulkheads, suitable encapsulated in epoxy.

As I thought, should be strong enough and not suffer any wear like the hull might.

Regards,
Darren

 

[Kayak Jack]

Darren, your "bulkhead" can be just a 2" ring around he inside of the boat for structural strength. Does not have to be a whole panel. If you are making cargo bays with hatches, then you may want an entire panel.