Re: [bolger] Aluminum Laminate for Center Board
> Somewhere I read about using aluminumWhich alloy of aluminum you are using
> Ben
matters, as there are many differences.
I have used 6061 and it seems to
not noticeably corrode, it is strong,
and works with standard woodworking
tools. Scrape pieces of 6061 are
available on eBay, which is where
I bought mine.
Maybe someone more expert than
me can explain.
Instead of screws you can use aluminum rivets, to avoid the dissimilar
metals problem. I wouldn't skip the mechanical fasteners, even with the "wet
sanding" through the epoxy. I haven't had good luck epoxying big pieces of
metal to wood, even with wet sanding.
metals problem. I wouldn't skip the mechanical fasteners, even with the "wet
sanding" through the epoxy. I haven't had good luck epoxying big pieces of
metal to wood, even with wet sanding.
On Tue, 10 Aug 2004 15:38:27 +0200, Juan wrote:
> Aluminium and epoxy are not a straightforward match.
> ...
> For your purposes it may be better to sandwich the parts with
> countersunk screws. You may have problems with electrolysis though.
--
John <jkohnen@...>
http://www.boat-links.com/
Missionaries, my Dear! Don't you realize that missionaries are the divinely
provided food for destitute cannibals? Whenever they are on the brink of
starvation, Heaven in its infinite mercy send them a nice plump missionary.
<Oscar Wilde>
A couple years ago I glued a "skid plate" onto the bow of my Diablo.
I had some scrap aluminum, 1/8" (weighs about the same as 3/4 ply).
Using a cordless skil saw, I cut it into an inverted Y shape - about
3/4 inch wide running a foot or so up the stem, and continuing,
wider, along the bottom, to almost a foot back.
To glue it on, I followed Juan's advice, coating the metal with
UNMIXED epoxy resin, and using a grinder to wet-sand the aluminum.
Messy, but not too bad to clean up. This gave plenty of time to mix
a batch of glue, and spread it on both the boat bottom and the metal
surface. I "worked" the glue into the sanded metal to assure there
was no plain resin left.
We now regularly land by banging up on a ledge, providing time to
raise the motor and get forward, even in wind or current. Air
temperature ranges from well below 0F to 90F, water temp from the
20's to the 60's. The aluminum is wearing, but no signs of
delamination or thermal problems.
Curtis
juan negron wrote:
I had some scrap aluminum, 1/8" (weighs about the same as 3/4 ply).
Using a cordless skil saw, I cut it into an inverted Y shape - about
3/4 inch wide running a foot or so up the stem, and continuing,
wider, along the bottom, to almost a foot back.
To glue it on, I followed Juan's advice, coating the metal with
UNMIXED epoxy resin, and using a grinder to wet-sand the aluminum.
Messy, but not too bad to clean up. This gave plenty of time to mix
a batch of glue, and spread it on both the boat bottom and the metal
surface. I "worked" the glue into the sanded metal to assure there
was no plain resin left.
We now regularly land by banging up on a ledge, providing time to
raise the motor and get forward, even in wind or current. Air
temperature ranges from well below 0F to 90F, water temp from the
20's to the 60's. The aluminum is wearing, but no signs of
delamination or thermal problems.
Curtis
juan negron wrote:
>Coat thethe
> surface of the aluminium with epoxy, and with good gloves on, sand
> aluminium with a coarse grain emery cloth THROUGH the liquid epoxy.epoxy,
> This way bare, bright, non-oxidized aluminium is exposed to the
> without contact with air, and without a chance for the oxide layerto form.
>it
> The oxide layer forms very quickly, as soon as you sand aluminium,
> starts to oxidize in contact with air. This oxide layer is whatmakes
> aluminium impervious to so many agents; but it also works to prevent
> adhesion of so many things, including epoxy.
>
I suggested 5/8" because it would be roughly the same wt as the
laminate proposed. It's not possible to make an accurate comparison
because we don't know the density of the wood that would be used.
A problem with a steel, or aluminum or laminated board is that,
instead of breaking, it can bend. Then it's impossible to retract;
this would be a real problem with a trailerable boat, for example.
PCB's Wolftrap is a 30' x 10' aluminum yawl (or a ketch, depending on
definitions). Its centreboard is drawn slightly thinner than the
3/8" al. keel bottom. The board could be steel, of course. There must
be an engineer in the group who can tell us whether 3/8" mild-steel
plate is more or less resistant to bending (beyond the point of
elasticity) than 5/8" marine al. plate.
The drawing also seems to show what I suppose is plywood sheathing
(about 5/8") on the inside of the c/b case.
Howard
laminate proposed. It's not possible to make an accurate comparison
because we don't know the density of the wood that would be used.
A problem with a steel, or aluminum or laminated board is that,
instead of breaking, it can bend. Then it's impossible to retract;
this would be a real problem with a trailerable boat, for example.
PCB's Wolftrap is a 30' x 10' aluminum yawl (or a ketch, depending on
definitions). Its centreboard is drawn slightly thinner than the
3/8" al. keel bottom. The board could be steel, of course. There must
be an engineer in the group who can tell us whether 3/8" mild-steel
plate is more or less resistant to bending (beyond the point of
elasticity) than 5/8" marine al. plate.
The drawing also seems to show what I suppose is plywood sheathing
(about 5/8") on the inside of the c/b case.
Howard
--- Inbolger@yahoogroups.com, "bh100014" <ben.ho@s...> wrote:
> I assume a solid plate will be much heavier than aluminum/wood, but
> I will have to calculate the actual weights and compare the two
> approaches. I've seen solid galvanized iron CB's, but there the
> design is to also use it as sort of a swing keel, so the weight is
> intentional. The Chebacco's CB per plan is wood with lead, so I
> wouldn't want to have something much heavier than the designed
> weight. Also am not sure if 5/8" aluminum is solid enough that it
> won't bent when running aground with lateral speed.
>
> Ben
...
You may have problems with electrolysis though.
This should read:
I don't know if you may have problems with eletrolysis, though.
Juan.
You may have problems with electrolysis though.
This should read:
I don't know if you may have problems with eletrolysis, though.
Juan.
Have just come across Bolgers Watervan, very interesting boat. Is there
any specific info avaible on it?
any specific info avaible on it?
The plate will work fine but not alone. Use the 1/2 ply as cheeks to form the proper foil shape or you'll find the plate will stall out at slower speeds plus you'll get a lot less drag with a foil shape than just a flat plate.
You can attach the plywood cheeks with 1 inch self tapping screws and caulk for sealing since epoxy doesn't do well on aluminum. All you need to do is seal the seam, especially for a trailer boat. Sink the screws into the plywood and fair / seal with epoxy.
Jeff
You can attach the plywood cheeks with 1 inch self tapping screws and caulk for sealing since epoxy doesn't do well on aluminum. All you need to do is seal the seam, especially for a trailer boat. Sink the screws into the plywood and fair / seal with epoxy.
Jeff
----- Original Message -----
From: Howard Stephenson
To:bolger@yahoogroups.com
Sent: Monday, August 09, 2004 11:21 PM
Subject: [bolger] Re: Aluminum Laminate for Center Board
Wouldn't it easier just to make it out of solid plate aluminum, 5/8"
or so thick? It would weigh about the same as the laminated board you
are suggesting but would be a lot easier and cheaper to make and
avoid the potential problems.
Howard
--- Inbolger@yahoogroups.com, "bh100014" <ben.ho@s...> wrote:
> Somewhere I read about using aluminum as the core for a center
> board. Use a 1/4" aluminum sheet in the center, two sides of 0.5"
> marine ply. The combined weight is probably similar to an all-wood
> CB with lead-fill, and stronger. The aluminum edge also should
> handle the occasional grounding well. Heck, one can even connect a
> ground wire from the shrouds and use that as the lightning
grounding
> path. What I am not sure is how well does aluminum bond with marine
> plywood, using say epoxy. Will the different expansion coefficient
> cause the two material to eventually deliminate?
>
> Ben
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Aluminium and epoxy are not a straightforward match. To properly bond
aluminium with epoxy you should etch or prime the aluminium with a
specific primer or etch solution.
In my opinion, for coating purposes, priming is fine, but to get
structural bonding I would do the following:
This procedure is more complex, but in my opinion better. Coat the
surface of the aluminium with epoxy, and with good gloves on, sand the
aluminium with a coarse grain emery cloth THROUGH the liquid epoxy.
This way bare, bright, non-oxidized aluminium is exposed to the epoxy,
without contact with air, and without a chance for the oxide layer to
form.
The oxide layer forms very quickly, as soon as you sand aluminium, it
starts to oxidize in contact with air. This oxide layer is what makes
aluminium impervious to so many agents; but it also works to prevent
adhesion of so many things, including epoxy.
For your purposes it may be better to sandwich the parts with
countersunk screws. You may have problems with electrolysis though.
Juan.
aluminium with epoxy you should etch or prime the aluminium with a
specific primer or etch solution.
In my opinion, for coating purposes, priming is fine, but to get
structural bonding I would do the following:
This procedure is more complex, but in my opinion better. Coat the
surface of the aluminium with epoxy, and with good gloves on, sand the
aluminium with a coarse grain emery cloth THROUGH the liquid epoxy.
This way bare, bright, non-oxidized aluminium is exposed to the epoxy,
without contact with air, and without a chance for the oxide layer to
form.
The oxide layer forms very quickly, as soon as you sand aluminium, it
starts to oxidize in contact with air. This oxide layer is what makes
aluminium impervious to so many agents; but it also works to prevent
adhesion of so many things, including epoxy.
For your purposes it may be better to sandwich the parts with
countersunk screws. You may have problems with electrolysis though.
Juan.
> I assume a solid plate will be much heavierAs a general rule of thumb, I understand,
> than aluminum/wood,
> Ben
that [within reason] weight down low in a
sailboat is a good thing.
I assume a solid plate will be much heavier than aluminum/wood, but
I will have to calculate the actual weights and compare the two
approaches. I've seen solid galvanized iron CB's, but there the
design is to also use it as sort of a swing keel, so the weight is
intentional. The Chebacco's CB per plan is wood with lead, so I
wouldn't want to have something much heavier than the designed
weight. Also am not sure if 5/8" aluminum is solid enough that it
won't bent when running aground with lateral speed.
Ben
--- Inbolger@yahoogroups.com, "Howard Stephenson"
<stephensonhw@a...> wrote:
I will have to calculate the actual weights and compare the two
approaches. I've seen solid galvanized iron CB's, but there the
design is to also use it as sort of a swing keel, so the weight is
intentional. The Chebacco's CB per plan is wood with lead, so I
wouldn't want to have something much heavier than the designed
weight. Also am not sure if 5/8" aluminum is solid enough that it
won't bent when running aground with lateral speed.
Ben
--- Inbolger@yahoogroups.com, "Howard Stephenson"
<stephensonhw@a...> wrote:
> Wouldn't it easier just to make it out of solid plate aluminum,5/8"
> or so thick? It would weigh about the same as the laminated boardyou
> are suggesting but would be a lot easier and cheaper to make and0.5"
> avoid the potential problems.
>
> Howard
>
> --- Inbolger@yahoogroups.com, "bh100014" <ben.ho@s...> wrote:
> > Somewhere I read about using aluminum as the core for a center
> > board. Use a 1/4" aluminum sheet in the center, two sides of
> > marine ply. The combined weight is probably similar to an all-wood
> > CB with lead-fill, and stronger. The aluminum edge also shoulda
> > handle the occasional grounding well. Heck, one can even connect
> > ground wire from the shrouds and use that as the lightningmarine
> grounding
> > path. What I am not sure is how well does aluminum bond with
> > plywood, using say epoxy. Will the different expansioncoefficient
> > cause the two material to eventually deliminate?
> >
> > Ben
--- Inbolger@yahoogroups.com, "bh100014" <ben.ho@s...> wrote:
smash.
i would be inclined to drill some holes through the whole show and
plug them with some wood and epoxy dowels to hold the 2 wood sides
together in case of failure.
cheers paul
> Somewhere I read about using aluminum as the core for a centergrounding
> board. Use a 1/4" aluminum sheet in the center, two sides of 0.5"
> marine ply. The combined weight is probably similar to an all-wood
> CB with lead-fill, and stronger. The aluminum edge also should
> handle the occasional grounding well. Heck, one can even connect a
> ground wire from the shrouds and use that as the lightning
> path. What I am not sure is how well does aluminum bond with marineI think you should do 2 small test pieces . 1 to soak and 1 to
> plywood, using say epoxy. Will the different expansion coefficient
> cause the two material to eventually deliminate?
>
> Ben
smash.
i would be inclined to drill some holes through the whole show and
plug them with some wood and epoxy dowels to hold the 2 wood sides
together in case of failure.
cheers paul
Wouldn't it easier just to make it out of solid plate aluminum, 5/8"
or so thick? It would weigh about the same as the laminated board you
are suggesting but would be a lot easier and cheaper to make and
avoid the potential problems.
Howard
or so thick? It would weigh about the same as the laminated board you
are suggesting but would be a lot easier and cheaper to make and
avoid the potential problems.
Howard
--- Inbolger@yahoogroups.com, "bh100014" <ben.ho@s...> wrote:
> Somewhere I read about using aluminum as the core for a center
> board. Use a 1/4" aluminum sheet in the center, two sides of 0.5"
> marine ply. The combined weight is probably similar to an all-wood
> CB with lead-fill, and stronger. The aluminum edge also should
> handle the occasional grounding well. Heck, one can even connect a
> ground wire from the shrouds and use that as the lightning
grounding
> path. What I am not sure is how well does aluminum bond with marine
> plywood, using say epoxy. Will the different expansion coefficient
> cause the two material to eventually deliminate?
>
> Ben
Somewhere I read about using aluminum as the core for a center
board. Use a 1/4" aluminum sheet in the center, two sides of 0.5"
marine ply. The combined weight is probably similar to an all-wood
CB with lead-fill, and stronger. The aluminum edge also should
handle the occasional grounding well. Heck, one can even connect a
ground wire from the shrouds and use that as the lightning grounding
path. What I am not sure is how well does aluminum bond with marine
plywood, using say epoxy. Will the different expansion coefficient
cause the two material to eventually deliminate?
Ben
board. Use a 1/4" aluminum sheet in the center, two sides of 0.5"
marine ply. The combined weight is probably similar to an all-wood
CB with lead-fill, and stronger. The aluminum edge also should
handle the occasional grounding well. Heck, one can even connect a
ground wire from the shrouds and use that as the lightning grounding
path. What I am not sure is how well does aluminum bond with marine
plywood, using say epoxy. Will the different expansion coefficient
cause the two material to eventually deliminate?
Ben