Hi Tim, 

i have built a wherry...but didn't think about using carbon fibre instead of e-glass. 

is there some particular thing you are trying to accomplish that is making you think of carbon fibre?   i have used it sparingly on small parts (skegs, reinforcing tabs).  the major challenge, from my perspective, is that carbon fibre is challenging to get a good light-weight application over large areas without the use of vacume bagging techology....which is complex and expensive to implement.

its also relatively expensive as a raw material compared to common fibreglass....so, at least for me, i use it where it's properties best match up to the problem that i am trying to solve.

h

   I have also built a (tandem) wherry and have been using carbon fiber cloth quite a bit. The chief advantage of CF is less weight for the same stiffness. Another reason  is that some people think that twill under resin looks pretty cool.

Much as I want to cover everything in CF, I'm not sure that a wherry is the best candidate. Being somewhat heavy, it's not on the cusp of 'can I carry it by myself?', so losing a few pounds won't matter much. Since it's heavily built (compared to say a shell) it won't gain from added stiffness. And the traditionalist aesthetic of a wooden wherry might be a bit at odds with CF's aerospace look. 

So since there aren't any good reasons to do it, let's get started! The easiest place to use CF would be in the decks and seats (10 mm Okume, total weight 10 lbs). You could replace the seats with thinner (3 mm) CF reinforced okoume and the decks with maybe just carbon alone, using the supplied pieces as patterns. Altogether that might drop the total weight by 5-10%. Textured black surfaces could look nice against a warm varnished hull and would match the black drop-in and oars.

I don't vacuum bag, but get about the same resin/fabric ratio (~0.8) by applying clamping pressure or just a heavy weight. This won't work  a hull, but it does for smaller, flat pieces.  Details on request.

CF is a little pricey at about $40/lb (about the cost of your epoxy), but  lots of scrap pieces big enough for these purposes can be had for $15/lb.   

https://compositeenvisions.com/9-clearance-materials-fabrics/?sort=featured&page=2 

I'm currently rehabbing a couple of veteran kayaks and I'll be reinforcing the hulls with CF/Kevlar cloth. If there's interest I can post how it goes.

My thinking for using carbon is just to save weight. I'm old and it will mostly be me and my wife carrying the boat, so every pound saved is helpful. I'm an experienced wood worker and have a full shop but this would be my first boat build but I have almost no experience using fiberglass and no experience with carbon. Is there much difference working with the two materials? I was thinking about using it on the bottom and on the inside.

My experience with carbon fiber is as a material for building masts. One thing to keep in mind is that glass is sturdier than carbon fiber. It's less brittle and abrades less. When CF breaks, it makes sharp splinters. I never use CF without covering it with at least a lightweight layer of glass to protect it from abrasion and to contain flying splinters in case of a catastrophic break.

Since epoxy cures to a formica-hard finish, it's reasonable to use CF without glass over it in low-abrasion, low stress areas as long as it's completely encapsulated.

One practical difference is knowing when the material is properly wet out. Glass turns transparent. Areas that aren't saturated stay white or translucent. CF doesn't do that. It's a shiny black when dry and a very slightly different shiny black when saturated. Laying up by hand I have to go very heavy on the epoxy, then squeeze out the excess. This is where vacuum infusion pays for itself. If you do a lot of pieces, it's worth the overhead it takes in tools and supplies because you'll make it up in lower epoxy costs. I don't, so I pay for epoxy instead.

It's possible to build a boat to much lighter than the design weight without using CF. Mostly it's a matter of controlling how much epoxy you use through technique, thinner fillets, lighter glass and lighter woods. Howard (hspira) has some really good posts on this forum on how he does this. He seems to be able to routinely know 10 lbs or more off the design weight of the boat. Try searching the forum for his posts.

Good luck,

Laszlo

if its a significant weight saving that you are looking for, the way on a boat like this that you would acheive it is to find a different coring material -- okoume on this boat is where most of the weight is....and the difference between carbon fibre and e-glass, is just not big enough x enough utilization to make a big difference or any difference and may actually cost you wieght if you can't properly control the epoxy.

while i don't have the figures, (perhaps CLC can supply), an important measurement you need is the number of square feet of the annapolis wherry hull and all its bulkheads/seats (you really need square feet for each thickness of okoume in the design).  you can then work out on a spreadsheet the weight for the boat associated with the wood, the glass and the epoxy  at its normal specs (e.g., 4mm okoume, 4 o glass, epoxy related to 4 oz glass).  you can then do 'what if' weight scenarios by swapping out the normal spec'd material for alternate core and glass approaches. 

this is basically how i begin an analysis of how i might 'lighten' up a design as lazlo describes above.

an interesting comparison is look at the weight of the Noank pulling boat which is similar-ish to a wherry but exectued in cedar strip https://www.clcboats.com/shop/boats/rowboats/Noank-Pulling-Boat.html .  the posted weight is 54 lbs for the Noank vs 65 for the wherry executed in cedar.  ( this is about the weight difference between a cubic foot of cedar and a cubic foot of okoume plywood)

anyway, the point i am making is that when i am building light, the approach begins with a bill of materials for a 'standard build' from which i can compute the weight.....and then use it to test out alternatives.....and then that is how i set my targets on what i am shooting for.   if the weight of your expected ingredients don't meet your goals, nothing you can do in the construction phase can improve on the situation.

give it a try and tell us what different recipes yield in terms of weight savings vs the standard build.

h

   btw....the noank pulling boat specs say it is 76 square feet https://www.guillemot-kayaks.com/guillemot/node/3983/details and its base layup is 1/4 cedar and its not clear from what i can find is its glassing schedule.

a petrel kayak (17 foot high performance kayak) only has 46 square feet if laid out flat...and a hull weight of 32 lbs using 1/4 inch cedar.

h

   (I don't no why my post before came up anonymous - this is from turnAround!)

I’ve given my AW a rough measure and can give you some weight estimates (assuming Okoume SPGR of 0.45) for it.

Hull strakes are about 63 sq ft of ¼ “ weighing about 34 lbs (52% of 65 lbs nominal total). Rails add 4 lbs (6%), while decks, seats, and frames are 10 mm thick and contribute about 11 lbs (17%).

Assuming half the total area (17 sq yards) is glassed with 6 oz cloth, the FG comes to 3 lbs (5%). The epoxy supplied in the kit weighs 14 lbs (21%). And then there’s  the bresthook, knees, varnish, paint, wood flour, and odd copper wires.

Clearly, FG isn’t the major culprit here. Wood components add up to 49 lbs. and as hspira suggests, substituting ¼” cedar (SPGR = 0.32) strakes for Okoume would save 10 lbs.

A couple of other thoughts: Skipping the seat planks (the tandem wherry doesn’t have them) would shave off 3 lbs, and the 4 labs decks  might be made a bit thinner.  And what about the 17 lbs  RoWIng drop-in? I’m working on a lighter design (here carbon fiber is useful), and if you’re that ambitious I think you can drop a few more pounds there. And by all means resist the temptation to add inwales!

Finally, just congratulate yourself if you have the discipline and technique to meet the nominal weight given by CLC- I doubt many do. My first timer-built AW single weighs in at 76 lbs., 10 lbs over- all excess epoxy.