Need help selecting rudder core foam
Bob Medico
I am about to rebuild the rudder on my Tartan 30 (recent purchase). The
rudder core has water in it and the the skin has delaminated in places.
I plan to open it up and remove the existing core and replace it. The
question is what is the best modern core material to use for this
purpose?
TIA
Bob Medico
@goeshere Thomas Bloomer
Tom Bloomer
Hartly, DE
"Bob Medico" <bob.m...@bmc.org> wrote in message
news:3C306064...@bmc.org...
Bob Medico
I found ETAFOAM at the Dow web site:
http://www.dow.com/perffoam/prod/ethafoam/index.htm
It appears that there are many different densities of ETAFOAM. What
would you suggest for this application?
TIA
Bob Medico
@goeshere Thomas Bloomer
http://www.dow.com/perffoam/prod/ethafoam/e_900hs.htm
Either of these will work. The 900hs will have better shear strength, but
less buoyancy. Of all the "floatation foams" available, Ethafoam is the
most resistant to water intrusion by a wide margin. Note that this is
polyETHELYNE not polyURETHANE or PVC (PolyVinlyChloride). You will not
find it used very often in the boating industry because it is very
expensive. But it is perfect for filling a large cavity like a fiberglass
rudder.
A less expensive alternative would be to rebuild the rudder and leave it
hollow with drain holes to allow the water to leak out when you store it for
the winter. The rudder is busted because the existing foam absorbed water
and expanded when it froze during winter storage . . . a very common flaw in
a lot of sail boats.
Tom Bloomer,
Hartly, DE
"Bob Medico" <bob.m...@bmc.org> wrote in message
news:3C30921C...@bmc.org...
Bob Medico
have asked in last post. I am planning to use epoxy resin. Will there be
any issues with this foam and epoxy resin? I imagine a thickening agent
should be used with the resin??
@goeshere Thomas Bloomer
it is polyethylene - so it really is not suitable for a core that requires
sheer strength to bond to the skin. Polyethylene is one of those plastics
that nothing sticks to unless it is "welded" to it. Try gluing a milk jug
with epoxy . . . it just peels off.
What you wind up with is a buoyant filler that does not absorb water. You
will have to allow for water to drain out somewhere because it will work its
way in between the fiberglass skin and the foam. When you rebuild the
rudder, build it so that it does not depend on the core for structural
strength - the Ethafoam is there for buoyancy only. If you think you can
get away with the reduced buoyancy, just build it hollow with no foam and
put drain holes in the top and bottom.
Originally the rudder was built with two-part expanding urethane foam poured
in like a Boston Whaler - so it really is not a structural core. I
suggested the higher density ethafoam because it will withstand flexing and
collapsing better, but you aren't likely going to find any adhesive will
stick to it. If you contact Dow, they may have a suggestion about some kind
of primer to promote a chemical bond with epoxy, but you will probably not
achieve a good mechanical bond.
Foam filled rudders SUCK!
Tom Bloomer,
Hartly, DE
"Bob Medico" <bob.m...@bmc.org> wrote in message
news:3C30A55A...@bmc.org...
Jim Conlin
ddinc
A rudder that size would need 6-8 lb/ft^2.
"Bob Medico" <bob.m...@bmc.org> wrote in message
news:3C306064...@bmc.org...
Rich Mechaber
3M came up with an adhesive for HDPE and other hard-to-bond plastics.
It's called ScotchWeld DP-8005. I've yet to find a supplier of small
quantities, though. Here's a link for more info.:
http://www.diy-boat.com/Pages/Archives/links/00_4/Glue.html
Rich Mechaber
Ron Thornton
What is the significance of bouyancy in a rudder? I assume you are
speaking of positive bouyancy.
Southeastern Virginia, home of PETA
"People Eating Tasty Animals"
Nick White
goes here<snip.net> wrote something
......and in reply I say!:
>What you wind up with is a buoyant filler that does not absorb water. You
>will have to allow for water to drain out somewhere because it will work its
>way in between the fiberglass skin and the foam. When you rebuild the
>rudder, build it so that it does not depend on the core for structural
>strength - the Ethafoam is there for buoyancy only. If you think you can
>get away with the reduced buoyancy, just build it hollow with no foam and
>put drain holes in the top and bottom.
>
Actually, unless the whole rudder leaks badly, there will be more
bouyancy _without_ the foam. The foam simply adds weight. It is there
to hold the glass skins apart, and provide a shape for manufacure in a
one-off job.
Nick White --- HEAD:Hertz Music
(please remove ns from my header email address to reply)
....damn spam
!!
<")
_/ )
( )
_//- \__/
Nick White
wrote something
......and in reply I say!:
You are going to have to use glass with this, not just resin. The
whole strength of the thing is in the skins. The foam just spreads any
point loads and holds the skins apart for stiffness. In that case the
resin should be used as a layup resin, and very little if any
thickening will be needed. You should ask the manufacturer that you
choose.
You really need to look into rudder design, because there is a bit to
sort out. For instance, where there are attachments and point
loadings, use wood (ply) as a core because foam will simply compress.
Have thicker glass where you go from wood to foam, to prevent hard
spots. I would look at using double the weight of glass on the leading
edge, and probably the trailing edge. What weight of glass will be
enough for the blade you are looking at?
In the end you should probably NOT use ethafoam, because it is
polyethylene. I did some tests as a result of an argument about
adhering to foam "sausages" for stability on a kayak, and because the
foam has half-bubbles, the epoxy will "mechanically" stick to it at
least as strong as the foam itself.
But the preferred foams are PVC. Epoxy does not stick to this very
well as a smooth sheet either, but better than ethylene. Divinycell or
Airex are the two names that come to my out of date mind. Neither of
these will absord water worth a damn. What can happen is that water
may wick up between the glass an the foam, or through/along the glass
strands.
However, given that the original foam was probably extremely friable
urethane (crumbly green or brown stuff) then there was no real
structural need there anyway, except to hold the skins apart.
Evan Gatehouse & Diane Selkirk
Thomas Bloomer the @ goes here <bloomersnip.net> wrote in message
news:3c308...@news7.fast.net...
Bob,
Ethafoam is NOT a good idea for this application. It won't stick to
anything. Some people have suggested "all the foam does is keep the skins
apart." Well not really. To do that it has to have some shear strength. I
don't know what Ethafoam's shear strength is, but since Dow doesn't publish
it, I would question it's use here.
There are 2 ways you can do this repair:
The hard way:
(1) Split the skins open along the leading & trailing edges. Remove all the
old core. (check to see if the rudder stock and webs are still o.k.) Build
a new foam core from solid foam sheets. Shape it to suit. Re-glass with
new skins
You should use a foam core that is recognized for this type of marine
application. i.e. Divinycell, Airex, Herex, Corecell, etc etc.
The easier way for a amateur:
(2) Spli the skins open again. Remove old core again. Tab the webs to one
skin with glass/epoxy resin. Join up the two halves of the skins with a few
layers of biaxial cloth at 45 deg to the edges. Leave an opening at the top
of the rudder. Pour in some high density (8 lb/cu ft) pour-in-place
polyurethane foam. Do it in several batches. Trim off the excess foam that
flows out of the top pouring hold. Glass over the pouring hole.
--
Evan Gatehouse
Glenn Ashmore
--
Glenn Ashmore
I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Bob Medico
Thanks for the response. After reading all the other posts to my
question and doing other research I had already settled on your solution
#1 . I have already opened the rudder and removed all of the old foam
since I first posted my question. It was evident that the old core was
poured in by the way it had filled all of the intricate inside spaces.
The material (1979) looked like cheap styrofoam of the kind that can be
ground to dust if dry. There was so much water in this foam that I
cannot imagine ever getting it dried out by any of the "drilling lots of
holes methods" that I have heard about. The post mortem also showed that
virtually all of the foam was no longer bonded to the skins. The only
area that was still stuck was at the extreme top of the rudder.
The skins are in pretty good shape, nearly quarter inch thick
everywhere. The post and horizontal webbing is all stainless steel with
the welds in excellent condition. I had learned that only the later
Tartan 30s had horizontal webbing of stainless steel. All the earlier
hulls had black iron welded to the stainless post which tended to rust
out.
Do you know of any good sources for the core materials that you
mentioned?
Thanks,
Bob Medico
Meindert Sprang
> Evan,
>
> Thanks for the response. After reading all the other posts to my
> question and doing other research I had already settled on your solution
> #1 . I have already opened the rudder and removed all of the old foam
> since I first posted my question. It was evident that the old core was
> poured in by the way it had filled all of the intricate inside spaces.
> The material (1979) looked like cheap styrofoam of the kind that can be
> ground to dust if dry. There was so much water in this foam that I
> cannot imagine ever getting it dried out by any of the "drilling lots of
> holes methods" that I have heard about. The post mortem also showed that
> virtually all of the foam was no longer bonded to the skins. The only
> area that was still stuck was at the extreme top of the rudder.
>
> The skins are in pretty good shape, nearly quarter inch thick
> everywhere. The post and horizontal webbing is all stainless steel with
> the welds in excellent condition. I had learned that only the later
> Tartan 30s had horizontal webbing of stainless steel. All the earlier
> hulls had black iron welded to the stainless post which tended to rust
> out.
Aren't you afraid that the new foam will also be ground to pulp over some
years? Often the forces from the steel webbing embedded in the foam are just
too high for the foam. Here in the Netherlands is a company that has
specialized in repairing/replacing rudders that are constructed that way.
They found that almost all rudders that are filled with foam, experience
this problem. Therefore this company 'copies' the shape of the old rudder
and makes a new one from 40mm thick plywood panels, were the webbing get
embedded in routed slots, filled with epoxy. The whole rudder is covered
with glass/epoxy.
Meindert
Nick White
<gash...@mindspring.com> wrote something
Aided no doubt by your own timely and helpful input.<g>
Nick White
<cei...@prodigy.net> wrote something
hmmm...as the "some people" referred to, I think, I would like to
correct the "quote". I said it spreads the load and holds the skins
apart. This means quite a bit more. It stops them collapsing together
under bending forces. But basically, yess, it keeps the sides apart
This applies especially in the case of a rudder, where the rudder
itself is a complete, sealed unit, and not just an edgeless board.
I also feel that, having tried it as I described, even ethafoam (or
ployethylene foam of some description) is probably better than
urethane, which has been used in many many glass sandwiches. Urethane
has almost no shear strength, and crumbles at the slightest movement.
Evan Gatehouse & Diane Selkirk
> Evan,
>
> The skins are in pretty good shape, nearly quarter inch thick
> everywhere. The post and horizontal webbing is all stainless steel with
> the welds in excellent condition. I had learned that only the later
> Tartan 30s had horizontal webbing of stainless steel. All the earlier
> hulls had black iron welded to the stainless post which tended to rust
> out.
>
> Do you know of any good sources for the core materials that you
> mentioned?
Are you sure you want to reshape a foam core and re-glass new skins? It
sure would be a lot easier to just keep the old skins and use pour in place
foam.
Dan Spurr, the ex-editor of Practical Sailor did a great article on this
method. (#2 method I described) You could contact PS for a reprint. It
would be well worth the small expense.
Don't forget that good rudder performance depends on a proper shape - how
are you going to get it right (take templates off the existing skins I
guess)?
Since the method used for your rudder lasted perhaps 20 years, maybe that's
the way to go for a repair? It may not last forever but it's not bad. It's
also the way most new rudders are still made.
Anyway:
The distributors/manufacturers who can tell you where to buy foam wherever
you are:
www.baltek.com for Airex & Herex foams
www.atc-chem.com for Corecell
www.diabgroup.com for Klegecell
Oh, and ignore that fellow who keeps insisting that polyurethane foams have
no shear strength and crumble at the slightest touch. Some may be friable
and crumble at the edges but lots of boats are built with these types of
foams - they do have shear strength sufficient for their application.
--
Evan Gatehouse
Nick White
<mhsp...@customware.nl> wrote something
Having thrashed about amongst the foam for a few postings I tend to
agree with you. Foam is nice and light, but in the end I wood prefer a
well-epoxied wood core.
>Aren't you afraid that the new foam will also be ground to pulp over some
>years? Often the forces from the steel webbing embedded in the foam are just
>too high for the foam. Here in the Netherlands is a company that has
>specialized in repairing/replacing rudders that are constructed that way.
>They found that almost all rudders that are filled with foam, experience
>this problem. Therefore this company 'copies' the shape of the old rudder
>and makes a new one from 40mm thick plywood panels, were the webbing get
>embedded in routed slots, filled with epoxy. The whole rudder is covered
>with glass/epoxy.
>
>Meindert
>
>
>
Nick White
<cei...@prodigy.net> wrote something
Diane
Since the chap who partners you in net address seems unwilling or
incapable of addressing me directly, perhaps we could use the
softening veils of your skirts to provide somewhere for him to cling
to, and from which he may actually feel safe enough to discuss our
disagreements concerning the matter at hand, beyond simple off- and
second-hand dismissal of my opinions on his part.
I try at all costs to avoid personal comments on the Web ngs, but his
niggling arse-pricking has really got my back up.
So here is my direct sally (as distinct from his indirect Diane).
Please let me know if his lordship deigns to reply.
LISTEN _FELLOW_!, Why the bloody hell don't you talk to _me_ if you
disagree with what I say? If you feel the need to discuss what I say,
at least have the decency to discuss it with me....pompous jerk.
My point (and I am addressing YOU, which you do not appear to have the
guts or whatever to do for me, is that while we are arguing about
whether epoxy will stick to ethylene foam, I still reckon that bonded,
it is probably stronger than urethane. Epoxy can stick to urethane
till it's blue in the face. If the urethane crumbles we have bugger
all shear strength, and away we go.
By way of evidence, I have a catamaran at home here that has a
urethane cored deck that has completely collapsed. And no I did not
build it. It's a Hobie. Once any delam started, even on a small area,
the whole lot just gave way under any impact or pressure, because a
bit of deck gave somewhat and the foam crumbled away inside, allowing
the deck to flex all over the place. If it had been built of better,
stronger, less friable foam, this would not have happened. As I said
(repeatedly, because cloth ears, cloth veiled, take some penetration)
I have watched epoxy stick to ethylene foam way past the failure point
of the foam itself, which is as it should be.
Hence I trust urethane foam little as a core. I will use _wood_ rather
than _any_ foam as a core in future. Have that out with the stripper
and S/G kayak designers. I have, and they support wood 100% for final
strength under stress.
I am willing to discuss it, but not be niggled at, jabbed from behind
and ignored, without reacting adversely.
>
>Oh, and ignore that fellow who keeps insisting that polyurethane foams have
>no shear strength and crumble at the slightest touch. Some may be friable
>and crumble at the edges but lots of boats are built with these types of
>foams - they do have shear strength sufficient for their application.
Jim Conlin
Bob Medico
Judging by the blackened, stinking foam inside I suspect that the rudder
had been in a failed condition for a while but can't prove for how many
years. The foam stank like the black mud at low tide in a Massachusetts
salt marsh (something that I am familiar with).
Evan Gatehouse & Diane Selkirk wrote:
>