My New Hatch Cover #1: Cold Molding a Curved Panel

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Blog entry by shipwright posted 05-15-2013 12:58 AM 6706 reads 0 times favorited 20 comments Add to Favorites Watch
no previous part Part 1 of My New Hatch Cover series Part 2: Cosmetic Veneering »

I just got Friendship back in the water for the summer last week and when I was getting her rigged at the dock someone ( OK me) sat on the acrylic top of the sliding hatch. This has been a weak point for seven years since I initially built her and it amazes me that it has taken this long to break it. Cutting to the chase, the replacement acrylic was going to cost $136 and wouldn’t be any stronger than it was before. I’ve never liked the plastic thing but it did give me a little more light inside. Verdict: Make a wooden top for her that you can stand on if you need to.

So here’s a shot you may have seen in another blog describing the new marquetry panels in the cabin doors. If you look closely you can also see the duct tape on the acrylic hatch cover. Oops!!

I decided to make the new cover the same way the hull is built, in cold molded cedar. This will produce a very strong yet light and quite thin curved panel. The hull itself is only about 5/8” thick so I’m thinking three layers of 1/8” each should provide the strength I need. Here is the light mold I made up to form it over. It’s not strong but will stay in shape if it is clamped down while applying the cedar.

With the 1/8” plywood skin in place I re-sawed some of my special old stock cedar into the 1/8” pieces I would need.

This is what I mean by “special old stock”. I count forty grains in the inch between 19 and 20. Maybe you will get a different count, but you have to agree this is special wood.

The first layer is applied with just a couple of brads at each end and the joints glued. (There’s waxed paper over the mold) Tape keeps the joints aligned for a few minutes while the glue tacks up.

The second layer is laid up at an opposing angle and stapled down with metal staples. These are removed after the glue has set.

I installed the third layer with plastic staples because I had them and it was such a PITA to remove all the metal ones. I didn’t use them on the second layer because they are 3/8” long and would have been a lot of work to sand off on the inside.

Once the glue has cured any unevenness is taken care of easily by a coarse sanding with a long block. You may notice that each of the layers arches across the curve rather than having one run parallel to the centerline and the other two arc across at 90 degrees. Having all the grain crossing the curve will make it stiffer. You may also notice that I’m using hot hide glue. (I wonder if this is still cold molding?) It is the cheapest and most convenient and I’m not worried about it getting wet because it will be epoxy sealed when complete. Also, it will have no “spring back” when it comes off the mold.

That’s about it for the structural part of replacing the acrylic piece. Next time I’ll get into the aesthetic part.

Thanks for looking in.


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

20 comments so far

View sras's profile


4808 posts in 3153 days

#1 posted 05-15-2013 01:07 AM

This is looking good!! I am interested to see what is next.

Are you thinking of any way of letting light in?

-- Steve - Impatience is Expensive

View gbear's profile


512 posts in 4123 days

#2 posted 05-15-2013 01:11 AM

That is “special” wood and with your layering system it ought to be very strong. I think you made the right call although you probably will miss the light from the acrylic top. Maybe you could incorporate a port hole in your hatch cover.
Whatever…I am so envious!! The Friendship is just so beautiful. Do you need an apprentice boat builder??

-- gbear, Carmichael, CA

View gfadvm's profile


14940 posts in 2714 days

#3 posted 05-15-2013 01:14 AM

That is a better “fit” than that plastic one! And you made it!

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

View shipwright's profile


7992 posts in 2821 days

#4 posted 05-15-2013 01:25 AM

The light isn’t really much of a big deal. I spend very little time in the cabin with the hatch closed, really only when it’s raining or when I’m sleeping. In either case the doors can be open. I also have a boom tent that would keep rain out of the hatch if it was open. No one is ever inside when sailing.

-- 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

#5 posted 05-15-2013 01:36 AM

Still in my doubtful mind is a question whether the hide glue will withstand the heat under the sun. Direct sunlight can melt asphalt roads down here (34 to 35 deg Celsius) tropics. Anyhow, the lesson I learned from you is how to crisscross laminates specially on a curve surface. I just wish to put it in practice. Thanks Paul.

-- Bert

View Karson's profile


35125 posts in 4424 days

#6 posted 05-15-2013 01:46 AM

Paul: Are all the layers your special cedar.

And is the 1/8” plywood also glued into the sandwich? or is it just the holding the first layer of cedar that is edged glued?

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Southern Delaware soon moving to Virginia †

View Dan Lyke's profile

Dan Lyke

1520 posts in 4149 days

#7 posted 05-15-2013 02:27 AM

Cool, thanks for the details on the cold-molding: I’m formulating a plan to build a bathroom sink using that technique, and want to absorb all the details on the how-to that I can.

-- Dan Lyke, Petaluma California,

View longgone's profile


5688 posts in 3332 days

#8 posted 05-15-2013 03:33 AM

That will certainly last a lifetime and then some. Very good…

View grizzman's profile


7836 posts in 3327 days

#9 posted 05-15-2013 03:37 AM

what a fun project paul, its always great to learn new things from you, i wish i would have gone to a boat building class when younger , so i will enjoy seeing you show and tell…

-- GRIZZMAN ...[''''']

View Joe Lyddon's profile

Joe Lyddon

10117 posts in 4076 days

#10 posted 05-15-2013 04:02 AM

That’s quite a large piece… didn’t look that large before…
WOW… that is a real Project!

-- Have Fun! Joe Lyddon - Alta Loma, CA USA - Home: ... My Small Gallery:"

View shipwright's profile


7992 posts in 2821 days

#11 posted 05-15-2013 05:15 AM

Bert, Heat alone won’t hurt hide glue. It must be wet (not damp) as well. ............and I won’t be heading to the Philippines this year. :-)

Karson, The piece will be three layers of the 1/8” cedar (3/8” thick). It will be cosmetically veneered inside and out which will add another 1/8” but not much strength. The 1/8” plywood is just part of the form.

Dan, You can make almost any shape in the world by the cold molding process. A sink would be an interesting one. I did a bathtub in one of the 36’ sailboats I built in the 80’s. My best tip would be the S1 sealer. It is one of the former Industrial Formulators of Canada products now sold by System Three. I had the good fortune to know Jim Peters, the incredible chemist / founder of IFC and in my mind his products are still the best epoxies around. System Three bought them out several years ago.

Joe The cover is about 27” wide and 38 1/2” long.


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

View stefang's profile


15881 posts in 3358 days

#12 posted 05-15-2013 08:56 AM

Very interesting blog Paul. I have seen cold molding done in Wooden Boat mag. but never in enough detail to fully satisfy my curiosity. Thanks for showing us all the details.

-- Mike, an American living in Norway.

View SPalm's profile


5320 posts in 3905 days

#13 posted 05-15-2013 10:46 AM

Hey Paul. This is fascinating.

So the first layer of strips is just butt joint glued to itself and not the plywood? It seems that way, but wanted to check. Too bad that slow growth cedar won’t be seen – but I bet it is a treat to work with.

Yuck about removing staples – seems like there must be a better way of holding the strips in place. What are plastic staples?


-- -- I'm no rocket surgeon

View Lee A. Jesberger's profile

Lee A. Jesberger

6859 posts in 4003 days

#14 posted 05-15-2013 01:22 PM

Very nice write up, Paul.


-- by Lee A. Jesberger

View Bluepine38's profile


3379 posts in 3109 days

#15 posted 05-15-2013 01:54 PM

SPalm, we sold the raptor brand of plastic staples that were used when wrapping plastic tarps or covers on
log buildings or lumber being shipped. There is nothing quite as bad as having a nice piece of natural wood
finished and discovering a big rust stain caused by a metal staple someone missed. Paul just added one more
use for them. The metal staples holding those little tags on Trek or hardwood can also be a pain we could do

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

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