the weigth of the resin used to encapsulate the wood could make the weight
difference of the wood negligeable. it depends on the resin-to-wood ratio
you are using and that depends on whether the design is using the wood or
the resin for the structural stength.

you have to put a minimum thickness of resin on the wood to effectively
encapsulate it. the required thickness depends to some extent on the
rigidity of the hull. if its a light racing dingy the hull is subject
to large deforming stresses, particularly twist from the mast. if the
resin is too thin it will scratch and crack and let in water and there
goes your wood core.

I don't know of any formulae for resolving the above tradeoffs.

here in Ontario native white cedar (arbor vitae) is used because it lasts
in fresh water. (I don't think it is related to European cedars.) Salt
water is not so much a problem for wood because salt inhibits the
growth of wood rot. look at www.cedarboats.com for varnished cedar-on-oak
work boats used by professional fishing guides.

finally, if the boat is not kept in the water and is protected from rain
then rot is not a concern. However I've seen many retired racing dingys
anchored off summer cottages with the transom flaps left open to keep
them from filling up and sinking, where rot would be a problem for a wood
core boat if it were not well "encapsulated"

Glenn Ashmore ) writes:
Sorry. I was thinking on this side of the pond where solid okoume is
very rare and expensive. In that case okoume could be an option. Just
be sure to encapsulate it extremely well in epoxy because it is rated as
non-durable. Once rot starts it will spread very quickly.

You will not have a problem with strength. Okoume is about equal to
cedar in bending strength and stiffness and slightly better in impact
resistance and crush strength.

Weight will be a consideration with cedar running about 370 Kg/M and
okoume averaging 450 Kg/M. Also okoume is hard on tool sharpness.

Leo wrote:

"Jim Conlin" wrote:

Perhaps I misunderstood the original question. Was it about plywood or

solid okoume?

It is solid okoumè.

I know cedar is better: lighter and more durable .
In Italy (I think so in all the Europe) western red cedar is 1,200 Euro x
cube meter (sorry, metric, but ratio is the same), much more expensive than
Okoumè.
Therefore, red cedar I found has high weight, similar to okoumè:
450kg/cu.meter (again, see the ratio).
Cedar should be1/5 less heavy on weight to be good.
For that I'm asking about.

Alternative could be Spruce, light as cedar but I think less durable than
okoumè.
In any case wood will be 'encapsulated' in coatings, as Ron says, as a core.
My doubts are on strength of these different woods.

Plywood-lapstrake could be a good solution, but I need a smooth round bilge
for a modern 19' racer.

What do You think about?

Ciao
Leo



Backyard Renegade wrote:


"Ron Magen" wrote:

However, plywood is the material for 'glued lapstrake' construction.

I did struggle with the post I made because of this and other
possibilities, that I why I said, "for strip building (as we know
it)".


As
Okoume is supposedly prone to rot, this would probably do the job if

it was

'encapsulated'. That is, epoxy, cloth, & finish on the outside with a

few

coats of a quality exterior primer and finish paint on the inside. Or
several coats of a UV Varnish . . . and keep them maintained.

I get lot's of guys who have me deliver S+T boats clear coated cause
the Okoume and Mahogany look so nice, I wonder how long they will stay
clear though;-)
Scotty


"Backyard Renegade" wrote:


Any kind of plywood is not good for strip building (as we know it).
The properties of the plywood make it difficult if not impossible to
bend the strips in such a manner as to follow the lines of a hull.
Scotty from SmallBoats.com




--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com



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I repost with some variations. I replied some hours ago but I don't see any
my message.

"Jim Conlin" wrote:

Perhaps I misunderstood the original question. Was it about plywood or
solid okoume?

It is solid okoumè.

I know that cedar is better: lighter and more durable .

In Italy, the North American Cedar is a very valuable wood, very difficult
to find and much more expensive than Okoumè (solid).

Therefore, red cedar I found has high weight, similar to okoumè:
450kg/cu.meter (sorry,metric, but ratio is the same).
Cedar should be1/5 less heavy to be good.
For that I'm asking about.

Alternative could be Spruce, light as cedar but less durable than
okoumè.
In any case wood will be 'encapsulated' in coatings, as Ron says.
My doubts are on strength of these different woods.

Plywood-lapstrake could be a good solution, but I need a smooth round bilge
for a modern 19' racer.

Ciao
Leo

"Leo" wrote in message ...
"Jim Conlin" wrote:
Perhaps I misunderstood the original question. Was it about plywood or
solid okoume?

It is solid okoumè.


OOOps.. disreguard anything I said, I know nothing about solid okoume...
Scotty

"P.C." wrote in message . dk...
Hi

"Backyard Renegade" skrev i en meddelelse
om...
"Leo" wrote in message
...

Any kind of plywood is not good for strip building (as we know it).
The properties of the plywood make it difficult if not impossible to
bend the strips in such a manner as to follow the lines of a hull.
Scotty from SmallBoats.com

I do not agrea, -------- with my software I can prove different and acturly
already proven that any form can be unfolded from double curve surfaces
into maneagable strips forming the exact boat form.

------------- I already done this with true Lapstrake hulls, that is much
more difficult than smooth-hull designs, so ofcaurse Plywood strips can be
plottet full-size.
The way strip planking is done, already minimise the foults ,but sure you
can't rely on the free software avaible, as to work around the troubles you
reconise hands-on building , you need software that acturly work and a lot
of hands-on experience building.

How do you explain that I can project a true Lapstrake hull , unfold the
planking ,keelworks and building jig, and have the whole lot go together
within 2 cm . of the original plans, --------- you se while building the
measures are exact, and only when the hull leave the jig, the forces in the
wood will make _any_ wooden hull move slightly out of measure, this can not
be avoided.

The hardwood I used are more rigid than any Plywood, and even then I build
small boats without steaming and my experience after building a lot of
tradisional round bottom boats is, that with the right software, breaking up
double curved surfaces into strips of single curves forming the actural
shape, you can form any shape, ----------- shapes more advanced than boat
hulls.

----------- Just want to say that I produced lots of plywood boats even
Lapstrake with planks much wider than what you can do with wood, and before
I decided to drop glued Lapstrake to replace the glue with flexible
polyurethane mastic, these glued Lapstrake hulls was not more difficult than
strip planking.

http://groups.yahoo.com/group/Cyber-Boat/

P.C.

All irrelevant as he is not talking about lapstrake boats here but
strippers. Furthermore, I assumed he was talking about the plywood
commonly reffered to as okoume, and the origional poster was talking
about solid wood which I know nothing about.

I'm sorry. I too jumped to the conclusion the poster was refering to
plywood not solid wood. DUH!
Any reasonably light weight soft wood that in compatible with epoxy
would be suitable.


Leo wrote:
Hi to all, I'm newsbie.

It could be possible to use okoume (gaboon) instead of Red Western Cedar in
strip-planking?
advandages/disadvantages?

Thank's to all

Ciao
Leo

"Leo" wrote:
Hi to all, I'm newsbie.

It could be possible to use okoume (gaboon) instead of
Red Western Cedar in strip-planking?
advandages/disadvantages?

Sorry. I was not clear, not thinking that, in the "other side of the pond"
(as Glenn says... eh,eh,eh :-)), solid okuomè could be a rare exotic wood.
Here it is a valuable exotic wood but not so rare.

Ciao
Leo

I think that two or three hands of resin coating, with fairing and a good
cycle of polyurethane paints, will give wood the enaugh protection versus
rot.
Not sure that more resin will give boat more strenght, being the wood
structural. Rigidity is ensured longitudinally from wood strips and
transversally from bulkheads . Anyhow, two external layers of biaxial
reinforcement could be useful for stiffness.

The original projet is for a GRP-sandwich 19' cabin sailboat, displacement
800 kg, net weight about 500 kg, 200kg of ballast.

I am not sure in wood thickness for strip planking: considering
reinforcements, I'm oriented in 1/2'' to save weight but maybe 3/4'' could
be better?

Ciao
Leo


"William R. Watt" wrote:

the weigth of the resin used to encapsulate the wood could make the weight
difference of the wood negligeable. it depends on the resin-to-wood ratio
you are using and that depends on whether the design is using the wood or
the resin for the structural stength.

you have to put a minimum thickness of resin on the wood to effectively
encapsulate it. the required thickness depends to some extent on the
rigidity of the hull. if its a light racing dingy the hull is subject
to large deforming stresses, particularly twist from the mast. if the
resin is too thin it will scratch and crack and let in water and there
goes your wood core.

I don't know of any formulae for resolving the above tradeoffs.

here in Ontario native white cedar (arbor vitae) is used because it lasts
in fresh water. (I don't think it is related to European cedars.) Salt
water is not so much a problem for wood because salt inhibits the
growth of wood rot. look at www.cedarboats.com for varnished cedar-on-oak
work boats used by professional fishing guides.

finally, if the boat is not kept in the water and is protected from rain
then rot is not a concern. However I've seen many retired racing dingys
anchored off summer cottages with the transom flaps left open to keep
them from filling up and sinking, where rot would be a problem for a wood
core boat if it were not well "encapsulated"

Glenn Ashmore ) writes:
Sorry. I was thinking on this side of the pond where solid okoume is
very rare and expensive. In that case okoume could be an option. Just
be sure to encapsulate it extremely well in epoxy because it is rated as
non-durable. Once rot starts it will spread very quickly.

You will not have a problem with strength. Okoume is about equal to
cedar in bending strength and stiffness and slightly better in impact
resistance and crush strength.

Weight will be a consideration with cedar running about 370 Kg/M and
okoume averaging 450 Kg/M. Also okoume is hard on tool sharpness.

Leo wrote:

"Jim Conlin" wrote:

Perhaps I misunderstood the original question. Was it about plywood or

solid okoume?

It is solid okoumè.

I know cedar is better: lighter and more durable .
In Italy (I think so in all the Europe) western red cedar is 1,200 Euro
x
cube meter (sorry, metric, but ratio is the same), much more expensive
than
Okoumè.
Therefore, red cedar I found has high weight, similar to okoumè:
450kg/cu.meter (again, see the ratio).
Cedar should be1/5 less heavy on weight to be good.
For that I'm asking about.

Alternative could be Spruce, light as cedar but I think less durable
than
okoumè.
In any case wood will be 'encapsulated' in coatings, as Ron says, as a
core.
My doubts are on strength of these different woods.

Plywood-lapstrake could be a good solution, but I need a smooth round
bilge
for a modern 19' racer.

What do You think about?

Ciao
Leo



Backyard Renegade wrote:


"Ron Magen" wrote:

However, plywood is the material for 'glued lapstrake' construction.

I did struggle with the post I made because of this and other
possibilities, that I why I said, "for strip building (as we know
it)".


As
Okoume is supposedly prone to rot, this would probably do the job if

it was

'encapsulated'. That is, epoxy, cloth, & finish on the outside with a

few

coats of a quality exterior primer and finish paint on the inside. Or
several coats of a UV Varnish . . . and keep them maintained.

I get lot's of guys who have me deliver S+T boats clear coated cause
the Okoume and Mahogany look so nice, I wonder how long they will stay
clear though;-)
Scotty


"Backyard Renegade" wrote:


Any kind of plywood is not good for strip building (as we know it).
The properties of the plywood make it difficult if not impossible to
bend the strips in such a manner as to follow the lines of a hull.
Scotty from SmallBoats.com




--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com



--
--------------------------------------------------------------------------
----
William R Watt National Capital FreeNet Ottawa's free community
network
homepage: www.ncf.ca/~ag384/top.htm
warning: non-freenet email must have "notspam" in subject or it's returned

Hi Leo.
Nice to find you also here :-)

In Italy, the North American Cedar is a very valuable wood, very difficult
to find and much more expensive than Okoumè (solid).
......
Alternative could be Spruce, light as cedar but less durable than
okoumè.

I have read somewere that in NZ also Paulonia (or Paulownia) as been used.
Paulonia is known in Italy mainly for flowers, but it is a fast growing
tree, is really light (lighter that the best WRC) and is claimed to be
extremely durable in salt water.
It originates from Japan or China... I don't remember... but I know that it
exist one organization for paulonia wood promotion also in Italy....
You can try a googgle search....

Paolo Zini

"Paolo Zini" wrote:

Hi Leo.
Nice to find you also here :-)

Hi Paolo.
World is small, as we say ;-)

I have read somewere that in NZ also Paulonia (or Paulownia)
as been used.
Paulonia is known in Italy mainly for flowers, but it is a fast growing
tree, is really light (lighter that the best WRC) and is claimed to be
extremely durable in salt water.

This is a great notice. Paulownia seems to be a very adaptable tree for our
ambient.
It should be see if there are already grown plantations and if wood is on
sale.

It originates from Japan or China... I don't remember... but I know that
it
exist one organization for paulonia wood promotion also in Italy....
You can try a googgle search....

http://www.paulownia.it/
Thank You Paolo,
I will contact them

Ciao
Leo

"Leo" ) writes:
I am not sure in wood thickness for strip planking: considering
reinforcements, I'm oriented in 1/2'' to save weight but maybe 3/4'' could
be better?

people used to use the term "strip planking" to describe what you are
planning but now its used more widely for any very narrow planks, like the
thin planks used on canoes and kayaks, called "stripper" construction.

I owned a boat much like what you are describing, 3/4 x 3/4 "mahogany"
(probably luaun) strips, sheathed in fibreglass cloth and polyester resin,
21 ft long, moulded fibreglass deck and cabin. I bought it used. I didn't
trust my sailing ability enough to buy a new boat. I tried to estimate the
dispalcement from lookign at the waterline adn got about 1200 lb but
that's suspect. It had a flat steel plate centreboard weighing 75 lb. It
was not built to sail but to be used as a plug for a mould for a class of
fibreglass sailboats but the fibreglass prototype was too heavy and they
gave it up. too bad they did not do their calaclutions before wasting all
the time and money. the plug made a lovely light dispalcement sailboat and
of course the hull was faired to perfection.

This boat was a bit too lightly built and had stress lines in the hull
from bow sheer to the base of the mast support and the same to stern. It
leaked at the centerboard slot and that also might have been due to the
compressive forces on the mast not being routed properly. But then all
wooden centerboard boats leak, don't they? The mast pushed down and the
shrouds pulled up and it was too much for the light hull. I don't think it
altered the shape of the boat, and I don't know if it weakened the hull, but
the stress lines in the wooden hull were plain to see.

The choice of wood was fine. I can't claim any expertise but I do think
I'd favour the 3/4" strips and I'd check the routing of those compressive
forces the mast and shrouds transfer to the hull. The hull had been
bleached on the outside before the polyester resin was put on giving it a
light colour. The polyester bond was fine except where the water leaked at
the centreboard and the polyester was coming away. I had the loose
skin cut away, the slot sealed, and new polyester put on. The slot
actually stopped leaking for one whole season.

I had it in the early 1980's. It was my first sailboat. It was old and
cheap, mostly because nobody wanted a wooden boat. I knew nothing about
boatbuilding at the time. I had to replace one small piece of plank where
some Sunday sailor in a Laser II rammed his solid fibreglass bow into it.
(I was on starboard, he was on port, but I doubt he knew the difference
let alone the rules of the road.) I can't recall very well what I saw when
making that small repair, but I think the planks were edge nailed with no
adhesive or bedding between planks.

I liked the boat. I'd buy another strip planked boat.



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