Can you use any kind of plywood for boatbuilding ort does it have to be
marine ply? Surely if you are planning on glassing and painting a plywood
hull it wouldn't really matter?

exterior AB (ABX) is often used, depending on the design and what is called for
in the bill of materials by the designer

Marine BS1088 or similar standard ply will get you better quality
plywood with no voids between the plys. Marine ply, Okuome specifically,
is lighter than what you can get at the Home Depot. So if you're
building a small boat like a canoe where weight is a concern, it's a
nice option to go with.

--
Matt Langenfeld
JEM Watercraft
http://www.jemwatercraft.com/

Mike wrote:
Can you use any kind of plywood for boatbuilding ort does it have to be
marine ply? Surely if you are planning on glassing and painting a plywood
hull it wouldn't really matter?

Given the same quality of construction, in many situations marine plywood
will last longer and require less maintenance, but you pay more for it. So
there's a cost vs longevity tradeoff. For example if you are buildign a
large boat which will be in the water all the time, or a small boat which
is left outside on a trailer, and you want ot pass the boat on to your
children's children, then marine plywood would be cost effective.
If you are building a small boat like a canoe or kayak which is only
in the water a few days a year and is stored indoors, say hanging from a
garage ceiling, the rest of the time, then marine plywood would not likely
be cost effective. As a rule of thumb a marine plywood boat will last 25
years while a non-marine plywood boat will last 10-15. On larger boats
where weight isn't so improtant, at least 3 layers of "fibreglass" on the
hull turns a plywood boat into a "fibreglass" boat and can increase its
lifespan, with ocassional resurfacing, indefinitely.

Exterior grade meranti (or lauan) weighs the same as marine grade okume
(half a pound per square foot for the 1/5 inch plywood commonly used on
small boats). Here in Ottawa the meranti is $14 a sheet while the okumne
is $50. Meratni is stable unlike exterior grade douglas fir plywood which
swells and shrinks with changes in heat and humidity and developes surface
cracks (called "checks") on the surface which spoils the appearance,
especially if stored outside in the sun. Fir plywood pretty well has to be
covered in moderately thick fibreglass to stop the checking.

I'd avoid the virola underlayment sold at Home Deopt in this area. It is
the grey sapwood, not the white heart wood, and does not last. I tried it
on a small boat (Delta on my website) and have had to do more maintenance
than on the two lauan boats I have. Meranti has replaced lauan in this
area. The quality is much better, no edge voids and both sides smooth.
If selecting meranti try to get sheets without any surface splits filled
with wood filler.
--
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I think Okuome is much lighter.

William R. Watt wrote:
Exterior grade meranti (or lauan) weighs the same as marine grade okume

Meranti is about 25% heavier than Okoume but considerably less expensive and
a good bit stiffer and more impact resistant. I use okoume when weight is
at a premium and meranti when strength and price are more important.

It is hard to tell the difference between BS1088 and 6566 other than price.
1088 has thinner plys when you get past 5/8" and the face veneers are a bit
thicker.

1/4" ACX has 3 plys and may have voids, face plugs on the A side and open
knots on the C side. 1088 and 6566 have 5 plys and clear faces.

"Matt Langenfeld" wrote in message
k.net...
I think Okuome is much lighter.

William R. Watt wrote:
Exterior grade meranti (or lauan) weighs the same as marine grade
okume

In "New Plywood Boats" TF Jones gives the weight of 5mm okume marine
plywood as 1/2 pound per square foot, which is the same weight as lauan
underlayment which I think is 5.22mm. They may not be the same thickness
but would be substituted for each other in small boats.

In "Dingy Building" Richard Creagh-Osboren gives the following weights for
boatbuiding timber, not plywood, but probalby close enough ..

okume 25 lb/cu ft
lauan 37 lb/cu ft
meranti 25-45 lb/cu ft

I thought meranti was a type of lauan but I was wrong. Like lauan, meranti
seems to be a species of tree with different varieties used, two mentioned
by Creagh-Osborne are Borneo red Sereya and Oba Suluk. Confusing for the
boatbuilder.

For comparison, douglas fir is 33 lb/cu ft

the above weights are within a pound of what is listed in "Skene's
Elements" for the one's given in Skene's. not all are there.
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http://www.worldpanel.com/Marineplywoods.htm

Scroll down to the 2nd chart. I've used their products and found their
published information to be accurate.



William R. Watt wrote:
In "New Plywood Boats" TF Jones gives the weight of 5mm okume marine
plywood as 1/2 pound per square foot, which is the same weight as lauan
underlayment which I think is 5.22mm. They may not be the same thickness
but would be substituted for each other in small boats.

In "Dingy Building" Richard Creagh-Osboren gives the following weights for
boatbuiding timber, not plywood, but probalby close enough ..

okume 25 lb/cu ft
lauan 37 lb/cu ft
meranti 25-45 lb/cu ft

I thought meranti was a type of lauan but I was wrong. Like lauan, meranti
seems to be a species of tree with different varieties used, two mentioned
by Creagh-Osborne are Borneo red Sereya and Oba Suluk. Confusing for the
boatbuilder.

For comparison, douglas fir is 33 lb/cu ft

the above weights are within a pound of what is listed in "Skene's
Elements" for the one's given in Skene's. not all are there.
--
------------------------------------------------------------------------------
William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
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Meranti...

Use it if you will. But remember that your boat is contributing to
deforestation in Borneo. Your pleasure... will be at someone's cost.

Nicholas


"William R. Watt" wrote in message
...

In "New Plywood Boats" TF Jones gives the weight of 5mm okume marine
plywood as 1/2 pound per square foot, which is the same weight as lauan
underlayment which I think is 5.22mm. They may not be the same thickness
but would be substituted for each other in small boats.

In "Dingy Building" Richard Creagh-Osboren gives the following weights for
boatbuiding timber, not plywood, but probalby close enough ..

okume 25 lb/cu ft
lauan 37 lb/cu ft
meranti 25-45 lb/cu ft

I thought meranti was a type of lauan but I was wrong. Like lauan, meranti
seems to be a species of tree with different varieties used, two mentioned
by Creagh-Osborne are Borneo red Sereya and Oba Suluk. Confusing for the
boatbuilder.

For comparison, douglas fir is 33 lb/cu ft

the above weights are within a pound of what is listed in "Skene's
Elements" for the one's given in Skene's. not all are there.
--
------------------------------------------------------------------------------
William R Watt National Capital FreeNet Ottawa's free community
network
homepage: www.ncf.ca/~ag384/top.htm
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"Nicholas B" wrote in message
...
Meranti...

Use it if you will. But remember that your boat is contributing to
deforestation in Borneo. Your pleasure... will be at someone's cost.

Nicholas

Well, you have a few alternatives. Meranti is just another name of a high
grade of Luan. At least luan is a fast growing family of species and is
rapidly being planted all around SE Asia. Then there is Okoume which comes
almost exclusively from Gabon. The Dutch, Israeli and Chinese logging
operations there are opening up primeval forest to settlement and are only
giving lip service to replanting. Mahogany is impossible to get any more.
There is always spruce and fir but the Shrub is opening up our national
forests to strip that out so that the oil companies can start drilling.
That leaves Southern yellow pine which makes a very poor and heavy boat
building wood.

So if you want to be an ecco-boatbuilder it boils down to using a vastly
inferior domestic pine plywood, a slightly better spruce and rip up our own
National Forests, a good light boat in okoume and help destroy the forests
in Gabon or use luan/meranti and let some SE Asians make an honest living
planting and harvesting trees.