Slogging to Windward
AN MDO/HDO PLYWOOD UPDATE
can always be emailed to: firstname.lastname@example.org
we are, halfway through the year of two double aught one and well into the
summer TV rerun schedule. Before
getting into the heat of the meat of June’s column let me take a minute to
digress into an announcement or two:
own Ed Sasser, columnist extraordinary continues to work on one of my
designs, namely a Peanut 30’ houseboat.
If you want to take a peek at his project, click here to go to a
little page I’ve set up to monitor his progress:
expect that he’s much further along the road than these pictures show, but
getting photos from busy Ed is like pulling teeth. There’s also a link on this page to another that reproduces
Ed’s recent article in Boatbuilder Magazine recounting his adventure in
building (by his own admission) a slightly flawed Bolger Diablo.
unexpected announcement came from Bill Samson the world’s number one
Chebacco advocate that is; he’s decided to sell his Chebacco
“Sylvester”. The main
reason he wants to find a good home for his boat is because he wants to
build more boats and can’t justify keeping everything.
So, contact Bill if you’re interested in acquiring a well built and
scrupulously maintained Chebacco. mailto:email@example.com.
Never one to be idle though, Bill has recently built a baidarka and a
folding kayak. At the moment
he’s working on a boat that I drew for him.
It’s a stretched redesign (for stitch and glue) of William
Atkins’ Finkeldink, which I’ve called Peach Pie.
If you want to see Bill in his element slaving away on Peachy, click
on this link:
Chebacco News Link:
as some of you know, Jeff Gilbert has been very ill for the past few months,
but I just got email from him, and he seems to be back on his feet and
thinking about boats and boating again.
Now that Jeff is out of the hospital, he’s chartered a nice
powerboat (1951 36 ft. Halverson shown below) and is taking his parents on a
cruise. So, all the best to ya,
Jeff—continue getting better and have a nice boat ride!
you’re a member of one or several of the Yahoo mailing lists, or cruise
the Usenet in the boating venue’s you probably have noticed that certain
questions and subjects come up over and over from new readers and members.
One of those that often rear its head is a question about MDO and HDO
covered plywood, and it’s use as a boatbuilding material.
reason why I decided to address this subject is 1.) There is some new
information coming from the American Plywood Association, 2.) Simpson Timber
is offering a new product, and 3.) Since these columns are probably going to
be archived on Duckworks Web for awhile it should act as reference and
starting point for when those questions do appear on the lists.
4.) In the past I’ve spent many hours as a Consulting Industrial
Engineer in the Glue Room of various plywood mills making manufacturing
studies so have a good feel for the product.
and HDO are special use panels that were created by the plywood
manufacturers to do some specific jobs, but have also found acceptance and
interest among boatbuilders and in other crafts.
The initials MDO and HDO refer to either Medium Density Overlay or
High Density Overlay. The
overlay they’re talking about comes in the form of a phenolic (heat
activated) resin impregnated paper that is laminated to the faces of a
plywood panel during the manufacturing process.
Medium and High simply refer to the weight and thickness of the paper
panel face, but there are notable differences between these two as well.
MDO was created to satisfy the requirements of long lasting Interstate
Highway signs. It’s usually
produced to rigid specifications from very high grade materials and is
supposed to last almost indefinitely in extreme weather conditions with no
checking and with only a coating of paint (usually two-part epoxy) for
protection. The panel is
composed of fir cores and centers with the overlay over well-sanded
knot-free faces. Nowadays, the
faces are only fir, but in the past thin veneers of luan were used.
The reason for the luan faces was to create an even smoother surface,
which prevents the grain of the fir from telegraphing its pattern through to
the surface. The same process
is used for laminating fine-expensive wood veneer faces like teak over fir
plywood, but of course without the phenolic overlay.
surfaces of the MDO are waterproof, but stippled to readily accept and
retain paint. The overlay is
impossible to separate from the plywood, and if the edges are properly
sealed the panel will last practically forever.
is a good product to use for small boat hulls because if it’s used
properly, the edges sealed and seams taped, sheathing large areas of the
exterior may not be needed.
on the other hand up until recently, wasn’t a good material to use for
boatbuilding. While HDO is even
more indestructible than MDO, paint won’t stick to it and not much else
will either. The panel
construction process is the same, the paper is a heavy phenolic-coated paper
but the product is generally used to build concrete forms and molds.
The surface is made slick (I believe with a castor-oil based mold
release) so that the forms and panels can be used over and over again.
however, Simpson Timber has come up with an HDO product using a heavier
overlay, but designed to accept paint and reflective tape and is to be used
in similar applications as MDO. It’s
called “Highway HDO” and in addition, its heavier overlay contains a
greater percentage of resin for increased moisture resistance.
Whether MDO or the new HDO is for your small boat
project or not is something that I can’t know or recommend. It’s something you’ll have to decide, but it’s good to
know that products like this exist for those times you may have an
application where MDO or the new HDO offering would be just right.
you work and build with plywood, product knowledge is not only important,
but also comforting to have, and for this reason I can’t recommend the
following websites highly enough. There
are great product lists, specifications and product informational files that
can be downloaded in both word.doc and acrobat.pdf formats. They’re great resources and should answer any questions you
Plywood Association (APA) Home Page:
Timber Products Homepage: