My Ches 17LT is about completed - you might get away with using 6mm for the hull bottom and side panels, but I doubt very much indeed if you could get 6mm to conform to the heavily cambered deck profile.   I used 3mm here (4mm is recommended) and thought at the time that I'd prefer not to have been wrestling with 4mm!  But good luck.   And weight may come into it if that's a concern...

Wordsmith

Using 6mm ply would add to the weight of the boat.  That's one of the nice things about 3mm stitch and glue boats, they are lightweight.  Something to think about.

Wordsmith and Casey Wilkinson are both correct, in my opinion.

I've built a 17 LT pretty much to plans (I added a skeg), and can second Wordsmith's comment about bending the foredeck -- tough enough with 4 mm.  (Indeed, I also built a Ches. 14 with the 3 mm, and concur with Wordsmith's recommendation of the 3 mm for the LT 17.) 

By the way, I would add an additional deck support forward and aft, but then I think that's a good idea with the 4 mm, too.  I made mine from a single piece of 4 mm in a vertical orientation thwartwhips -- think of it as a partial bulkhead rather than a deck beam, and it may be easier to visualize -- with a 3 mm cap strip to spread the load on the deck.)

As Casey Wilkinson points out, the 6 mm would make the boat heavier, too.  As it is, I suspect most of us build them heavier than CLC tells us they can be built (I did!), so you really don't want the extra weight.  Besides, the hull is quite stiff and strong as designed; I don't think there's any need to beef up the structure.

I built a Mill Creek 13 usint 5.2mm for the entire hull below the deck.  You really will need to work hard to get the material to bend properly.  I really struggled with this on the nose.

For the deck I used mahogany "door skin" and it worked fine.

Good luck

I respectfully disagree with Jim C's suggestion about adding deck supprts. A 4mm deck is plenty stiff as designed. That double curve pre-stresses the deck and makes it too stiff to push in, especially with the deck glassed on the outside. If anyone manages to get that same curve with 6mm, it's gonna be so stiff that you could stand on it without deck supports. (In fact, I have a memory of CLC publishing a picture of someone doing just that with the 4mm deck).

So save yourselves the weight and trouble,

Laszlo

Re: Laszlo's comments about a deck support ....  I didn't express myself as clearly as I would  have liked, and he is right that the 4 mm is pretty strong as designed.

I added a skeg to my LT17, and found an arched support such as I describe was needed at the skeg case to maitain the deck camber -- cutting the slot in the deck for the skeg interrupted the woods tendency to arch correctly, and the support preserved the desired camber.  It also strengthened the deck, which is why I came to recommend the idea in general, and did so with little penalty in weight and little extra work, while intruding only minimally into the aft compartment. 

My comments about the additional deck supports in an LT17 were particularly prompted by Wordsmith's suggestion of using 3 mm for the LT17 deck.  I think the 3 mm would work, but I'd feel better adding the one additional support fore and aft.

I agree that there is less need for an additional deck support for the foredeck, as it has a more pronounced camber and is therefore stronger.

In any case, Laszlo is certainly correct in noting that these are good and strong hulls as designed.

Wordsmith here, adding a note about my Ches 17LT with 3mm deck.   As suggested above, I thought it would be useful - with minimal added weight - to put a 1" deep 4mm ply on-edge pre-epoxied 'beamlet' under the fore deck, about 620mm from the bow, and two others under the rather flatter aft deck in case I or someone else felt a need to clamber all over it at any time.   These aft beamlets were 3790 and 4468mm respectively from the bow (location of all of them just where it looked 'right').   The decks are now well-strengthened underneath at next to no extra weight, and they also promoted the desired camber to the decks.

I am currently anxiously and impatiently waiting for the first of two coats of paint on the hull to fully harden before cutting-back and applying the final coat - launch expected by month's end!

Cheers...

Wordsmith

OK, barrng any wood behavioral issues, the increased weight of an entire kayak of that heavy a wood will take a little off your top end in speed and make it a little slow to get up to your top speed. My WR180 is heavy  - I over fortefied it and frankly - to hell with 45lb. boats - lol. This baby is darned near an ice breaker.  Its a little slow to come up to speed - but I dont even notice it to tell you the truth. That said, i fear little in the way of underwater obstructions and never put myself in the vicinity of waves that could drop me on a rock for example.   This baby is monster tough. 

Pete

Hi

I'm just finishing building two Chesapeake 17s. I brought 1 kit with me from Australia which used 3.5mm on the hull and built the second from Philippine 5.5mm ply. Worse than being just thicker, the plys of the local ply is 0.5-4.5-0.5mm so you are bending laterally not longitudinally to the core's grain - its stiffer. To overcome this I soaked it overnight and then wrapped it around a 44 gallon drum using bits of wood and a few straps. Then over a few days I it wet down and slowly tightened the straps. Worked a treat and was easier to install than the second. One upside is the ply is $10 per sheet.

Had to use 6oz fibreglass too and though I aven't yet done a final weight comparison yet but its not noticibly heavier. It will still be lighter than the plastics I used in Australia and about the same as my wifes 5.3m fibreglass boat. Anyway we will mostly use them for long day trips and overnight trips so a couple of extra kgs won't matter.

Now I just have to psych myself into having it bump into coral reefs and loaded on and off of local ferries.

Mark 

4mm okuome = 12 lb. per sheet

6mm okoume = 20 lb. per sheet

Weight adds up fast. Once you have added excess weight at one stage any other weight adding ideas you have become prohibitive unless you are an NFL linebacker. 

Light weight in paddleboats seems very desireable and worth big money. Look at the price of a heavy rotomolded polyethylene hull and compare it to the premium required for same hull in very light Carbon/Kevlar. If the reduced weight wasn't worth something nobody would pop the extra $1500-$2000.

If that 6mm ply is burning a hole in your pocket buld a Cheap Canoe. Everybody has a use for one and the plans are free.