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

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

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

"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.



--
------------------------------------------------------------------------------
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

Ok for "stripper" construction :-)
Substance is the same.
We have not yet an acceptable italian translation ;-).

Centerboard slot and deck stepped mast are always risk areas, where loads
are very high.
That's true on every small sailboat, specially in homebuilding, whichever
material or technique You use.

As You know, Polyester has not high adhesive properties on wood.
In the the early 1980's there was a low knowledge of epoxies.
Now the risks of crash, leaking or delamination are a bit reduced

Ciao
Leo

"William R. Watt" wrote :

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.



--
--------------------------------------------------------------------------
----
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