Shipyard Memories #21: The Jig, Patterns, and Hull Glue Up

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Blog entry by shipwright posted 09-11-2011 01:11 AM 3745 reads 1 time favorited 11 comments Add to Favorites Watch
« Part 20: The Harbour Ferries: Stitch and Glue Construction. Part 21 of Shipyard Memories series Part 22: Closing Up the Hull »

As these boats are a little larger than the usual stitch and glue hull and because some of the bends are difficult, I chose to make a female jig in which to assemble the hulls.

This photo was taken when the jig was first built at my old yard in Coal Harbour B.C. It was disassembled and reassembled many times after that. The supports are the opposite of construction frames that you would build a hull outside of , taken from the boat’s lofting. Against the wall in the background you can see some long sheets of scarfed plywood and the pattern for 1/2 of the bottom leaning against them. (if your eyes are good)

In the next photo you can see the jig in the background. It’s over ten years old now and has had ten boats built in it. In the foreground one of the sides is being laid out with the side pattern. Both sides will come out of a single 4’ x 24’ sheet.

Here the two pieces of the bottom have been forced into place and clamped to the jig. The bend in the bow is extreme, although it may not appear so, and the pieces have been kerfed to facilitate the bend. To answer the question I know will be asked, no, the strength is not compromised appreciably because the kerfs will be filled with epoxy and the hull configuration there is very strong because of the angles and the glass chines.
What doesn’t show here is the pieces of tie wire used to pull the pieces tightly together along their length before application of the epoxy fillet. These are the “stitches” in the stitch and glue.

Now the bottom is in place and has been glassed together by first applying a smooth fillet of thickened epoxy followed, while the fillet is still wet, by a layer of 24 oz. triaxial fiberglass cloth and more epoxy. Doing it this way uses less epoxy and saves a lot of sanding of the fillets. The bow area has had the kerfs filled and the sides of the jig have been set up in anticipation of fitting the side panels.
On the right, you can see the two side pieces are being ‘glassed prior to assembly. It’s just easier that way.

A note about triaxial cloth.
This is a fiberglass material that consists of a layer of parallel strands of glass equal to 1/2 the thickness (12 oz), overlaid with two layers of parallel fibers laid at opposing 45 degree angles to the first layer. The layers are then sewn together.This material has a huge advantage over standard woven cloth or roving where the strands are at 90 degrees to each other because if you cut it into strips (we used 4” to 6” wide) across the heavy strands, the strip will when laid on a joint have all of it’s fibers crossing the joint. If you lay standard cloth or roving along a joint it will have 1/2 of it’s fibers running parallel to the joint and adding no strength. You can cut standard roving diagonally but it will become completely unstable and will likely fall apart.
Suffice to say that three layers of 18 oz. roving with half of it’s strands serving no purpose will give you 27 0z. of glass crossing the joint. The joint, because of the woven nature of the roving and the number of layers, will be 1/2” thick or better. That’s a lot of very expensive epoxy. A joint made with 24oz. triaxial cloth will have 24oz of glass crossing the joint and will be about 1/8” thick. It will be just as strong, way cheaper and more resiliant than the roving joint. Sorry to go on about that but it is a very important point.

The next one shows the sides cut out and scarfed for the joint to the round stern piece. They are quite narrow at the bow because there is a third piece that facilitates the steep bend as the bottom transitions to the stem.

The last one for this segment is a shot of the way the sides are attached to the bottom. After being placed into the jig, coaxed into their curvature and clamped into position, the adjacent edges are again stitched with tie wire through small drilled holes every foot or so as required to make a nice fair chine line. It’s worth saying here that the fits don’t have to be good. As long as you get a nice fair curve the odd 1/4” gap means exactly nothing. We used to call them “drywall boats” because close was good enough. I mean it, really. If you spend a lot of time making the joints fit perfectly the only thing you will accomplish is to take more time.
Once the joints are wired A fillet of thickened epoxy is applied as before and the triaxial cloth is laid on the fillet and more epoxy is massaged into it with a bondo spreader. That’s actually me this time. I guess Jim got hold of the camera.

I’ve had enough for now and I’m sure you have too so we’ll call it a day and next time we’ll finish up the hull with that round stern and roll it over.

Thanks for watching. Comments critiques and questions…. all good.


-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fibreglass trees.

11 comments so far

View SPalm's profile


5320 posts in 3906 days

#1 posted 09-11-2011 01:59 AM

Did you use Okoume ply or some other special marine type ply. It seems that you must have.

And how the heck did you come up with the original pattern? It is like a dress maker who just wraps and pins fabric around a make believe form? Using kraft paper or such?


-- -- I'm no rocket surgeon

View shipwright's profile


7992 posts in 2822 days

#2 posted 09-11-2011 02:07 AM

Thanks Steve.
We used marine Fir plywood, usually five ply but if three was all there was we used it too.
The second question would require a whole blog of it’s own. When people used to ask me questions like that I used to just say “magic”. Way easier than trying to explain it. Do a search on “lofting” or “lofting hull lines” and you should get the short answer the long answer involves experience and maybe a little “feel”.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fibreglass trees.

View lightweightladylefty's profile


3241 posts in 3737 days

#3 posted 09-11-2011 06:43 AM


I don’t think I’ll ever make a boat, but I always enjoy learning. This is extremely informative. Thanks for sharing.


-- Jesus is the ONLY reason for ANY season.

View TheHarr's profile


118 posts in 3563 days

#4 posted 09-11-2011 01:34 PM

Shipwright, very interesting article, I’m looking forward to the following issue. Please complete your story, it’s worth the effort.

-- The wood is good.

View Lee A. Jesberger's profile

Lee A. Jesberger

6859 posts in 4004 days

#5 posted 09-11-2011 04:20 PM

Hi Paul,

This is really interesting to see how this is done. I too, was curious to see what type of plywood you were using, but Paul took care of that.

You obviously are a master!

Very well written.


-- by Lee A. Jesberger

View sras's profile


4810 posts in 3154 days

#6 posted 09-11-2011 05:30 PM

This is my favorite blog series! Having built S&G and strip kayaks, it is really fun to see the process on a larger scale.

-- Steve - Impatience is Expensive

View BertFlores58's profile


1698 posts in 2946 days

#7 posted 09-11-2011 05:38 PM

Thanks for revealing all those secrets in you shipbuilding life. Hope I can catch up. You are so fast as a boat.
Just wondering… These methods and materials in it, are they still being done and available in stores?

-- Bert

View Bluepine38's profile


3379 posts in 3110 days

#8 posted 09-11-2011 06:19 PM

Very interesting and informative, makes me think I should build one for my daughter and her kids up at the
lake, but I do not think it would work as a ski boat, which is about all the kids are interested in. Thank you
for sharing.

-- As ever, Gus-the 79 yr young apprentice carpenter

View shipwright's profile


7992 posts in 2822 days

#9 posted 09-11-2011 06:45 PM

Thanks again to all. Bert, Yes as far as I know it’s all still available.
The last time I tried to get triaxial cloth, my supplier didn’t cary it anymore so I substituted a biaxial cloth which is the same but only has one diagonal layer. It works just as well as long as you get the correct weight.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fibreglass trees.

View BertFlores58's profile


1698 posts in 2946 days

#10 posted 09-12-2011 02:30 AM

Thanks Paul,
That’s a good news because most of the methods used now are epoxy bonds (Most use is Marine Epoxy) to plywood and it seems that cracking is always a problem. The cloth helps a lot on the flexibility and cracking problems. I ask you this because I am planning to make my own speaker housing (baffles) to make it a high density board plus the flexibility I want for the vibration. Thanks again,

-- Bert

View dbray45's profile


3320 posts in 2801 days

#11 posted 09-12-2011 07:56 PM

One of my relatives built a small boat and it seems to me that he used this methodology. Difference was that he would “shape” the wood first by wetting it, bending it, using ropes to keep the shape, and let it sit till it dried. Took him years to make a small sail boat.

This makes a whole lot more sense.

-- David in Damascus, MD

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