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Shipyard Memories #9: The Catboats: Framed Plywood Construction, Scarfing and Setup

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Blog entry by shipwright posted 12-07-2010 11:03 AM 4398 reads 1 time favorited 10 comments Add to Favorites Watch
« Part 8: The Smaug Blog: Wood Boatbuilding 101, Under Sail Part 9 of Shipyard Memories series Part 10: The Catboats: Framed Plywood Construction, Backbone and Structural Components »

Plywood construction probably presents the easiest method for an amateur to build a good boat, but it is also useful a useful construction for a professional shop wanting to satisfy a customer who doesn’t have a large budget. It is a straightforward process and the plans tend to be easy to follow but there are a few tricks of the trade which I will try to cover.

The two boats covered here are quite different sisters from the same plan. The first, “Catspaw” was built on spec in 1981 specifically to enter in a floating boat show in Vancouver and give me a venue to market my business of custom yacht construction. I used it as a sales office to show photos of other boats and to sit and talk to potential customers. I had a great time but didn’t sell anything (Anybody remember the economy in 1981?) so Catspaw became my boat for several years. I didn’t mind that a bit.

The second, “Sylvester” was built on contract for a customer who loved my boat but wanted many aesthetic and practical upgrades. These made what had been a very economical build (Catspaw) into a quite pricey but lovely little yacht.

This photo shows just about everything that you need to build a 19’ Catboat, from portholes and plywood to glue and oil lamps.

Here the bottom (3/4” fir ply) is being scarfed up. If you stack your pieces in a staggered pile at a 1:8 ratio, ie: 6” setback for 3/4” thickness, and then plane the slope, you can glue them together and achieve the same strength as if the plywood had been made up full length. In this photo the end scarf is being cut and the side scarf has already been done. This will render a single piece of 3/4” plywood that is 16’ long and 8’wide (minus scarf width). Another small bit scarfed on at the front end and the whole bottom will be done. The trick here is to keep an eye on the gluelines in the plywood as they will guide you to an even plane if you keep them straight.

In this one the bottom and one side have been rough shaped and epoxy sealed on the inside prior to fitting on the jig frame just visible on the left. Yes, that’s Smaug, of course, on the right.

Now the sides have been fitted and fastened to the transom. (I don’t have any photos of it but it’s just a boring flat piece of 3/4” plywood) The stem has yet to be fitted. The line down the length of the plywood is just a veneer joint in the sheets as they came from the factory, but the faint vertical line you can see is a scarf.

This is a scarf, seen from the edge on one of the bent sides (1/2” ply). It’s a perfectly fair curve and maintains full plywood strength. It’s a little hard to see but it travels back left from the seam you can see on the face of the plywood. The notches you can see here in the jig will have the permanent chine pieces fitted before the sides are finally fastened at the stem.

Last photo for now. Here the sides, chines and stem are fastened and glued and the bottom awaits. Notice that the sides have been planed down fair and ready for the bottom.
(We replaced 52 ribs and several other parts in the big powerboat in the background left. That was fun!)

Next time we’ll get her off the jig and have a look at the keel, centerboard case and cabin features.

As always Thanks for watching.

All comments, questions, and critiques are welcome.

Napaman, this one’s for you.

Paul

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/



10 comments so far

View Chip's profile

Chip

1904 posts in 2745 days


#1 posted 12-07-2010 11:23 AM

Thanks Paul. Terrific as always.

-- Better to say nothing and be thought the fool... then to speak and erase all doubt!

View sedcokid's profile

sedcokid

2675 posts in 2251 days


#2 posted 12-07-2010 03:44 PM

Paul that is amazing!

Thanks for sharing

-- Chuck Emery, Michigan,

View HalDougherty's profile

HalDougherty

1820 posts in 1890 days


#3 posted 12-07-2010 04:10 PM

Thanks for the details on constructing your yachts. Combining sailing and woodworking is the best of both disciplines. Here’s the most beautiful yacht I’ve ever seen that was constructed from wood. The owner’s bill to the yacht yard was over $40,000 a year for maintenance. I took these photos at Fried Dion’s yacht yard in Marblehead, MA.

http://www.first285.com/atlantic/1-395-373/t19.jpg

http://www.first285.com/atlantic/071101/t17.jpg

Here’s a few more wood crafted sailboats I photographed at the Royal Nova Scotia Yacht Squadron. We sailed from Marblehead, MA to Halifax, NS in 2001 as the first leg of our voyage to move a friends yacht from the US to Europe.

This boat was built in 1912 and has to be sailed from the dock because no engine was ever installed.

http://www.first285.com/atlantic/6-146-090/t12.jpg

This was another wood yacht that I thought was impressive enough to rate a photograph. I’d love to sail on a wood sailboat, but… I sure wouldn’t like to refinish all the brightwork.

http://www.first285.com/atlantic/6-146-090/t1.jpg

More photos and the story of the voyage can be found at:

http://www.first285.com/atlantic

I’m stuck on inland lakes for now… But my Beneteau First 285 is docked at Watts Bar Lake on the Tennessee River and it’s just a few days down the river to the Gulf of Mexico. Every dam below Knoxville, TN has locks and they open for everyone. Just pull up in any thing that floats and the lock keepers will open the gates and move you up or down the river.

-- Hal, Tennessee http://www.first285.com

View dbray45's profile

dbray45

2500 posts in 1429 days


#4 posted 12-07-2010 04:13 PM

I enjoy your work.

-- David in Damascus, MD

View sras's profile

sras

3835 posts in 1782 days


#5 posted 12-07-2010 05:23 PM

Having built a plywood kayak and a cedar strip one, these stories are very interesting. Already looking forward to the next chapter! Thanks for sharing.

-- Steve - Impatience is Expensive

View shipwright's profile (online now)

shipwright

4965 posts in 1451 days


#6 posted 12-07-2010 07:04 PM

Thank you all.
As with the “Smaug” post, I’m having a lot of fun here too. It’s pretty cool to look back and see what you could do when you were “just a kid”. Hal, I never built, nor wanted to build one of those really high finish boats. I took pride in building strong seaworthy vessels that could be afforded by “regular folks”. That’s not to say I don’t admire their work I just had different priorities. You will see as we go through here that maintenance on a well built wooden boat needn’t be any more than on any other kind.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

View Splinterman's profile

Splinterman

23058 posts in 2014 days


#7 posted 12-08-2010 09:06 AM

Hey Paul,
Cool ride so far…pics are great.

View Napaman's profile

Napaman

5346 posts in 2730 days


#8 posted 12-09-2010 07:34 AM

its really amazing how you cant (or barely) see the scarf line…

For plywood—-it looks like there was not jig? for scarfing? Do you just make sure the angle is equal? by hand?

-- Matt--Proud LJ since 2007

View shipwright's profile (online now)

shipwright

4965 posts in 1451 days


#9 posted 12-09-2010 07:59 AM

Matt,Just set the pieces up with the appropriate setback, mark a line the same distance back on the top sheet, and plane from that line to the feather edge on the bottom. Use a solid 3/4” sheet on the bottom to back up the feather edge. Keep an eye on the glue lines. They will guide you. I use a power plane to rough and a sander to finish. You’ll get the hang of it.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

View Napaman's profile

Napaman

5346 posts in 2730 days


#10 posted 12-10-2010 03:20 AM

ok…sounds good…I thought it would be much more complicated…thanks!

-- Matt--Proud LJ since 2007

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