Are composite boats made in autoclaves better?
Stelph
have brought out a new design of single called the ST1, the main
difference being it is made in an autoclave rather than the X1 and S1
composite boats which appear to be made in vacum bags
http://www.staempfli-boats.ch/boats/composit/index_en.html
They are boat heated to 130 degrees centigrade but the Autoclave boats
are put under 6 bar of pressure and the composite boats are,
supposidly, in a vacumm. Does the autoclave process produce a stifffer/
tougher boat?
Out of interest, the only other autoclave boat manufacturer I have
found are Lola-Aylings, the other top manufactures fo carbon boats
(e.g. Fillipi and Empacher) seem to use the composite method..
row...@gmail.com
Henning Lippke
> http://www.staempfli-boats.ch/boats/composit/index_en.html
There are some stories around about the extraordinary impact resistance
of the new ST1. Can anyone add more?
Gareth Gruenbaum
I saw one in Eton at the World Champs.
It looked good, and it was as they say, "impact insensitive".
In fact, at Melch's insistence we were all giving it a good kickin',
and it was fine.
This is because it is single skin, so gives, and in fact it gives a
huge amount.
I think you really could drop it and watch it bounce.
One thing I cannot say though is how stiff it is through the water, or
around the cockpit/rigger interface.
I'm surprised we haven't heard more about it.
Perhaps we will see some this summer.
regards
Gareth
Bob Miller
further detail, but in the interim, from wikipedia:
quote
A vacuum bag is a bag made of strong rubber-coated fabric, open at one
end, and used to bond or laminate materials. The item to be laminated is
placed inside the bag, the open end is sealed, and air is drawn out with
a vacuum pump. As a result, uniform pressure approaching one atmosphere
is applied to the surfaces of the object inside the bag, holding parts
together while the adhesive cures. The entire bag may be placed in a
temperature-controlled oven, oil bath or water bath and gently heated to
accelerate curing.
Laminating of flat objects can be performed more efficiently in a heated
laminating press, but when the objects are curved or have irregular
shapes, a vacuum bag works better.
end quote
In addition to holding parts together it also ensures more uniform resin
penetration.
I'm pretty sure composite materials are always vacuum-bagged before
being autoclaved but vacuum-bagging can also be done stand-alone.
I doubt that the only difference is the use of an autoclave in the
production process. The autoclave probably allows for different
construction and fiber layering etc.
Bob Miller
rami...@dogstardreams.com
Stelph <ste...@hotmail.com> wrote in
news:1178873578....@o5g2000hsb.googlegroups.com:
Charles Carroll
single actually 12,000 US dollars?
This is about $2,000 more than Empacher is asking for one of its single
racing shells. Can anyone explain what justifies the cost? Is it in the
material? Or the labor?
ben
I'm not a physicist, but as a former molecular biologist can tell you
that an autoclave is certainly the best way to ensure that your boat
is not contaminated by any living organisms.
On the other hand, I once tried to to autoclave my 15 year old never-
washed hockey elbow pads to get rid of some of the deep down smell.
Unfortunately it killed a lot of whatever kind of 15 year old foam was
in there and they were useless afterwards.
Robin
> I'm not a physicist, but as a former molecular biologist can tell you
> that an autoclave is certainly the best way to ensure that your boat
> is not contaminated by any living organisms.
I think you need to be a bit more specific about your 'living
organisms' to avoid accusations of inhumanity :) ..
as a current molecular biologist - based for rowing purposes at Dundee
UBC's barn - I should point out that this is probably *not* the best
way to prevent or cure the perennial problem of wrens nesting in the
shoes of your boat(s) during the summer. Autoclaved wrens may feature
at some stage on a "Fat Duck" in Bray menu, but would probably elicit
bad PR in rowing circles.
Going back to the topic in question - does anyone know whether
Fluidesigns are autoclaved, being single skin carbon like the
Staempfli?
Walter Martindale
sterilize (sterilise?) things like surgical instruments. Surely an
autoclave big enough and hot enough for a boat would be a very expensive
pressure cooker to build and run. Do the composite materials in a
racing shell take well to the temperatures in an autoclave? Or is my
understanding of an autoclave too narrow?
Thanks to the Molecular Biologists present and past for an 'injection'
of humour (Ben, stay away with that needle - oh, wait, there's 15,000 km
between us).
Walter
Jonny
>
> Does the autoclave process produce a stifffer/tougher boat?
My understanding is that using an autoclave or 'oven' is more about
quality control and speed of production.
If you can control the curing time and make it consistent (with a
consistent temperature and pressure) then every boat that you make
using that set up will be very similar. It is possible to acheive good
results without it, but it requires more skill and some luck with the
weather. If the weather is not ideal, then your curing times will
alter.
Vacuum bagging aids the even distribution of the resin and a good
bond. The pressure in an autoclave is helping to achieve the same
things.
I know that Sykes and Prime (Geelong AUS) both have ovens that are
similar to those used in the car painting business. Lads at Sykes
wouldn't tell me the temperature they used, but said you could walk in
while it was happening and be ok for a bit (so I'm guessing not hotter
than 60deg C). KIRS (NZ) used to have a slogan that said "we don't
just make 'em, we bake 'em".
I suspect that Carl will probably correct us all very soon!
Chris Kerr
Further to this - how do they account for the thermal expansion/contraction
when the boat is taken out of the oven? Carbon fibre IIRC has a very
anisotropic thermal expansion and I would have thought this would pose a
problem.
JY
>
> - Show quoted text -
I have a little experience in making composite materials ceramic,
metallic and plastic (but not boats):
Apart from controlling and accelerating the curing process by cooking
the boat, you can use epoxies that are stronger than ordinary ambient
drying ones. Done properly this should make the production process
faster, more repeatable and the product better. The sort of
temperatures we are talking about, I would have thought the best
technology would be a heated mould, either electrically traced or
(better IMHO) a traced tube with hot oil pumped around it. This is
what Janousek does (did). Large ovens are expensive and difficult to
acheive a decent temperature uniformity. I think the word autoclave is
rather being mis-used today. Some marketing guru probably got his
thesaurus out because 'oven' or 'cooker' didn't sound high tech
enough!
One of the slightly counter-intuitive factors when making a composite
material is that you do not want too good a bond between the fiber and
the matrix. This is because when you do get damage, you want the fiber
to stay intact and pull out of the matrix, rather than fracture along
with the matrix. The difference in thermal expansion coefficients
between fiber and matrix may therefore be a good thing rather than
bad, although with such modest curing temperature and a pretty elastic
matrix, I doubt it is significant.
J Flory
As yet ANOTHER molecular biologist on this ng, I decided it would be
wise to ask a composites engineer and learned the following:
Optimum curing depends on various factors including the resin/catalyst
system being used and the thickness of the item being made. One
adjusts the temperature, the temperature profile over time, and the
pressure to smoosh out excess resin, eliminate voids, achieve good
adhesion between layers, etc. The temperature profile is important
because as the resin cures it becomes more viscous so more pressure
would be needed to smoosh out the excess. For most liquids viscosity
decreases as temperature increases, so initially heating should make
the resin flow more easily. It becomes a race between flow and
curing. Complicating this is the fact that the curing is an
exothermic reaction (generates heat).
He suggested "Smart Autoclave Cure of Composites" by P. R. Ciriscioli
and G. S. Springer for more accurate info (perhaps because he's one of
the authors ;) ).
To clarify a few things:
Almost all shells made today are "composites" of fibers (carbon,
kevlar, fiberglass, ..) enmeshed in a polymer network made by using a
catalyst to encourage a monomer resin to polymerize into long chains
and networks around the fibers.
AFAIK all builders of composite shells use vacuum bagging to squeeze
out excess resin and compress the layers together as noted above.
This applies a pressure of 1 atmosphere (=1 bar, =14.4 psi). Those
using autoclaves put the vacuum bagged item inside and apply
additional pressure, in this case 6 atmospheres total. Yes we are so
used to thinking of steam autoclaves that we don't think of
pressurized ovens as autoclaves. One big enough for an 8 could be
expensive - another reason for sectional 8's!
The original catalyst/resin systems cured at room temperature, perhaps
with a mild heating (postcure) at the end to finish off the process.
This required that one use "wet layup", involving mixing resin and
catalyst, saturating sheets of fiber material with the mix, applying
to a mold, and then vacuum bagging, etc.
Then someone got the clever idea of using machines to meter precise
amounts of resin/catalyst onto sheets of fiber. To prevent this from
curing immediately, they used a catalyst/resin system that cured only
at elevated temperature. The resulting material is called "prepreg".
It is much faster to apply to a mold and speeds up the process so that
the mold can be re-used sooner, but it is available in fewer weights
and types of fiber, must be stored refrigerated and even then has a
limited shelf life (because it cures slowly at lower temps), and
requires an oven to cure it and stronger molds that will not distort
when heated.
Empacher, Filippi, BBG (I think) use wet layup. Fluidesign uses wet
layup but with an aviation system that cures at high temperature.
Vespoli, Resolute, Hudson, van Dusen and Stampfli use prepreg.
I've visited Vespoli, van Dusen, Resolute, and Fluidesign, saw their
ovens, and stupidly neglected to check which ones were autoclaves.
Fluidesign tells me that their oven is not an autoclave and that very
few manufacturers use autoclaves. I suspect Vespoli may not have
autoclaves because their molds were bolted to the concrete floor and
ovens were set over them by an overhead crane system.
Most manufacturers incorporate a core of Nomex hexagonal mesh (looks
like cardboard sliced end-on) into the center of their hull layers to
act as a "stiffener". Stampfli (on this boat) and Fluidesign use
coreless construction, aka "single layer" though they actually have
multiple layers of fiber reinforcement in them. The absence of a
core makes their hulls flexible locally, rather like Grahm King's
wooden boats, even though their overall hull strength is fine. FD
uses wet layup because they use fiber weights that are not available
in prepreg. They may add extra layers or some core material to the
midsection of their hulls, I'm not sure.
It would be very interesting to know why Stampfli uses 6 bar on a
coreless boat. One would think that the coreless hull would be
thinner so less pressure would be needed than for their cored boats.
Carl
Why would I do that?
To make an effective laminate requires a curable resin, controllable
pressure & an appropriate (in time & temperature) curing cycle.
The bonding resin can come in a number of forms:
1. Liquid, which you mix up from 2 or more reactive components, plus
fillers as appropriate to modify the physical characteristics. The
resulting resin may cure well over time at room temperature but normally
requires heat to achieve acceptable cure rates and optimum properties.
2. Resin film - a part-cured, tacky material, impregnated by the
supplier into a lightweight "carrier" fabric. This normally has to be
stored in a freezer to prevent premature cure, but even so has a limited
shelf life. It will only cure satisfactorily if heated to & held at a
stipulated temperature (or made to follow a stipulated temperature/time
cycle) which allows it to liquefy, flow & properly wet the materials to
be bonded.
3. Pre-impregnated fabric - really a variant on 2 above, in which the
bonding resin has been infused into the reinforcing fabric by the supplier.
When you make a laminate, especially a large one like a boat or part of
an aircraft, you need to have an adequately long "open time" before
pressure must be applied & the heating cycle begun. The resin must
remain curable (not have started to "go off") during this period
In nearly every case, the pressure required to ensure intimate contact &
conformity to the mould is achieved by applying vacuum. At sea level,
atmospheric pressure is ~1kgf/cm^2 or 14.7lbf/in^2, & when you consider
applying that much pressure over the entire surface of a boat that's an
awful lot of force (1kgf/cm^2 = 10 tonnes/sq m). Yet simply by
enclosing your laminate & its mould in a flexible, impermeable bag &
sucking out the air with a vacuum pump, you can easily achieve >90% of
that pressure as atmospheric pressure outside presses against the
reduced pressure inside. In this case, of course, it owes nothing to
fluid-dynamic lift ;)
Sometimes even such a pressure difference is insufficient to achieve
good compaction of the laminate, or too much vacuum may cause a resin
component to boil off. In such cases, you may use less vacuum & put the
whole moulding into a pressure chamber. Pressure chambers are costly &,
unless properly designed & maintained, can be dangerous (compressed air,
even if only at 1 atmosphere above normal, can do a lot of harm if a
vessel ruptures) so are subject to inspection regimes which increase costs
Then you need to apply heat. This either requires internal (steam,
thermal fluid or electrical) heating of the mould - a very economical &
effective process, but making for costly tooling - or external heating
in the form of a heated enclosure or oven.
If your pressure vessel is also your oven, then it is called an
autoclave. The same term applies to biological sterilising devices as
to laminate curing pressure chambers & to any other heated
pressure-processing chamber.
Each method of lamination can produce top-quality laminates, & the
choice is based on a mix of tooling & production economics, the
characteristics of the materials you wish to bond, the qualities you
require in your laminate & a host of other factors. Thus, where very
long open times are required for the lay-up of a laminate (take a large
yacht or aircraft wing) then the ability to us very slow-curing pre-preg
systems which require very high temperatures to effect cure will lead to
an autoclaving process. On the other hand, if you need to use
particular types of resin formulation for reasons of aesthetics, yet can
work fast enough to close the laminate within an appropriate time, then
liquid resins with fillers & other additives may be the only answer.
Of course, there are many other ways to use these & other materials to
achieve fine laminates for particular uses, but that's for another time.
As ever, it's not just the process but also the quality of design,
workmanship & materials which go together to determine the quality of
the end result.
HTH -
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing low-drag Riggers/Advanced Accessories
Write: The Boathouse, Timsway, Chertsey Lane, Staines TW18 3JY, UK
Email: ca...@carldouglas.co.uk Tel: +44(0)1784-456344 Fax: -466550
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)
Robin
> I thought autoclaves used high temperature, high pressure, and steam to
> sterilize (sterilise?) things like surgical instruments. Surely an
> autoclave big enough and hot enough for a boat would be a very expensive
> pressure cooker to build and run.
They are used for things like Formula-1 car chassis monocoques,
aerospace components, and other stuff if I'm not mistaken - so objects
on that physical scale are clearly viable both from the perspective of
running them and also the thermal stability of the object being heated
- and then cooled (at defined rates) by the autoclave. Lola's (non-
rowing engineering division) website list details of their 5
autoclaves which range in length right up to 8 metres.
Our standard laboratory autoclaves range from things the size of a
large pressure cooker right up to ones used for glassware that you
could push a trolley-load of palettes into, and that's not a
particularly large one. Moreover, you can programme the heating and
cooling rates of these in order to best preserve biological media /
sterilised nutrient broths, and they are not particularly
sophisticated ones compared to what would be used by the boat /
aerospace companies.
J Flory
> They are used for things like Formula-1 car chassis monocoques,
> aerospace components, and other stuff if I'm not mistaken - so objects
> on that physical scale are clearly viable both from the perspective of
> running them and also the thermal stability of the object being heated
> - and then cooled (at defined rates) by the autoclave. Lola's (non-
> rowing engineering division) website list details of their 5
> autoclaves which range in length right up to 8 metres.
>
> Our standard laboratory autoclaves range from things the size of a
> large pressure cooker right up to ones used for glassware that you
> could push a trolley-load of palettes into, and that's not a
> particularly large one.
Interestingly, van Dusen makes up to 2x's so they must have a ca. 10m
autoclave. Their other products are flatwater racing kayaks, sailboat
booms and masts, and wind turbine blades (to run generators), all of
which are long narrow items. Which allows them to use the same
autoclave.
Stelph
time to reply!
As well as this discussion about autoclaves another thing I find
interesting about boat manufacture is the stiffness of the hulls, id
always thought that the stiffer the hull, the better the boat! (up to
a limit of course, extremly stiff boats would shatter if there was any
impact and I think i read somewhere that they would be very difficult
to sit)
One way i always tested the stiffness of a boat is to gently squeeze
the hull of the boat, for example near the bows, to see if theres any
give! Now hulls which have the nomex honeycomb (like empacher or
swift) have no give at all,but ive noticed that boats like Hudsen and
Fluiddesign are quite squidgy at the bows. Now i would have though
that this squidyness would mean the water would slightly deform the
boat as it passes through the water, resulting in lost energy and so
lost speed? But as both makes are thought to be very quick boats im
wondering where my logic has fallen down....
any help? :-)
Jonny
> One way i always tested the stiffness of a boat is to gently squeeze
> the hull of the boat, for example near the bows, to see if theres any
> give! Now hulls which have the nomex honeycomb (like empacher or
> swift) have no give at all,but ive noticed that boats like Hudsen and
> Fluiddesign are quite squidgy at the bows. Now i would have though
> that this squidyness would mean the water would slightly deform the
> boat as it passes through the water, resulting in lost energy and so
> lost speed? But as both makes are thought to be very quick boats im
> wondering where my logic has fallen down....
>
> any help? :-)
The water is not able to apply a point load like your finger does. I
would think that even though these boats are 'softer skinned' there
would be no deflection from normal water conditions. Perhaps a freak
wave or some wash might do something, but it is academic as the
conditions would be nasty enough to prevent rowing (ie you would have
to stop and ride out the wave).
Boyd
Dear All
I am happy to see that there is an interest in the technology of
rowing boats on Rec.Sport.Rowing. I have since 1998 working in the
composite industry for Janousek/Stampfli, Resolute, Subaru Rally Team,
Aston Martin Racing and now Formula 1 with Super Aguri F1 Team.
Most of the worlds Boat builders manufacture their boats using an oven
cure process which involves the use of either "wet-lay" or "pre-preg"
material and normally with a honeycomb or foam core. These boats are
cured in a vacuum bag with around 30psi of pressure as that is about
as much pressure as you can get with this process. This system
produces a good boat as long as there is the right amount of resin to
bond the core to the material either side. It also allows the boat
builder to hopefully build a light and stiff boat.
The use of an Autoclave has great advantages in that with the
additional pressure that it can exert the fibres will compress more
and therefore perform better. The disadvantage is that to make a boat
with honeycomb using all that pressure would leave the core flat as a
pancake. The other issue is the cost, to have a clave long enough for
a four which is the longest un-sectional boat would be hundreds of
thousands of pounds and while the aircraft and sailing industry has
the customer base to support the price, rowing doesn't as is shown
through our desire to buy cheap boats from the far east. You can
however build a boat in an Autoclave but only the outside skin or a
single skin boat would benefit.
Cored boats tend to be a better option as the process of putting
distance between the composite materials adds strength and not too
much weight and as we all no a single skin boat will flex as to add
enough material, carbon/glass or Kevlar to stop this would be to
expensive and probably make the boat to heavy.
To the best of my knowledge the following process are used in the
following boat builders
Empacher - Wet-layup using a Carbon / Glass / Kevlar mix and a core
oven cure
Fillippi - As above
BBG - As above
Pocock - As above
Dirgo - As above
Janousek/Stampfli (UK) - Pre-preg Carbon /Glass mix with honeycomb
core - oven cure
Resolute Racing Shells - Pre-preg Carbon with honeycomb core - oven
cure
Hudson - As above
Carl Douglas - Carl will I'm sure be better to explain
Chinese Boats - Mixture of Wet lay and pre-preg cored and un-cored -
oven cure
Vespoli - as above
Aylings - Pre-preg Autoclave on the small boat oven cured on the big
boats - cored
Van Dusen - Autoclaved - cored but only makes singles and doubles
Boat builders - I apologise if I have made any error, if I have please
let us know your process.
So the general feeling is the Pre-preg is better than Wet-lay up and
cored is better than single skin and Autoclave is better than oven
cure (if the design allows the process). At the end of the day you
should ask why the boat builder that you are about to give your /
clubs hard earned cash builds the way he dose, understand what you are
paying for - Technology - build quality - Hull shape - An image - A
colour .
Boyd
Carl
> Most of the worlds Boat builders manufacture their boats using an oven
> cure process which involves the use of either "wet-lay" or "pre-preg"
> material and normally with a honeycomb or foam core. These boats are
> cured in a vacuum bag with around 30psi of pressure as that is about
> as much pressure as you can get with this process.
I think that was a slip, Boyd, & that you meant ~30" of mercury, which
is all you can get under total vacuum when operating your shop at normal
atmospheric pressure
Cheers -
Carl
There are no meaningful data, nor theory, on which to base the popular
assumption that stiffer is better. Just to test that assumption, if you
will: would it be better for your boat to somewhat conform to a swell or
to be so stiff that it in effect does not flex in the slightest (of
course that's never going to be possible, but just suppose)? That said,
all boatbuilders accept that clients do judge boats by longitudinal
stiffness so they build them as stiff as they can.
Nor is panel stiffness (squidgyness) in any meaningful sense related to
longitudinal stiffness (boat bendability) at the stress levels
encountered in rowing shells. Provided a boat is designed such that it
in use it nowhere approaches local compressive stress levels which could
induce incipient panel buckling (Euler sorted out the maths for that),
it already has sufficient panel stiffness to resist its main service
loads.
Interestingly, the most common mode of initial failure of certain makes
of honeycomb-cored shells is by compressive buckling - the hull or deck
structure on the compression side during a bending load case (e.g. a
glancing impact or running up the bank) starts to buckle (wrinkle)
across each hollow cell of the honeycomb, depriving those cells of
compressive stiffness along the axis of the boat & thus initiating
collapse in the most compressed areas which spreads rapidly, allowing
increased bending on the tension side, local skin rupture & final fracture.
Also interesting is the fact that a hull with a more squidgy
characteristic can, if properly designed, be much more resistant to
perforation on impact, since it is able to yield, absorb the impact
energy & spring back. A stiffer panel with no more material in it
concentrates the impact very locally & is usually much easier to
puncture as a result.
Finally, water pressure on the surface of a shell is so slight as to
have no meaningful influence on hull shape for normal shells of all
types of construction.
HTH
Charles Carroll
> assumption that stiffer is better.
Carl,
I wish you had told me this when I was in Staines last summer and persuaded
you to grab the bow of one of your shells while I held on the stern. Then we
just kind of lifted the shell up and down.
Sandy asked what we were doing, and you smiled and said, "Charles is just
testing the shell for stiffness."
Now I feel like the proper fool. But what's new there?
I will, however, offer one comment. Of all the boats I have ever tested for
stiffness, none has been stiffer than the Carl Douglas we held in our hands
that Sunday morning.
Cordially,
Charles
paul_v...@hotmail.com
wrote:
More importantly, is a demonstratably stiff boat better at prying open
your wallet? [;o)
Cheers,
Paul Smith
tien...@wanadoo.nl
composite product is not very to the point. A composite is a product
of a man made fibre and a resin. The function of the resin is to keep
the fibres togeather. There is an optimal volume of fibre to resin. To
much and the strength (and stiffness) is dependent on the resin, to
little and the construction will not have enough bonding between the
fibres.
Choosing the manufacturing process depends more on the costs involved
than the quality of the end product. Wet lay up means that you should
control the application of resin carefully (by hand). Since this is
more easily done with a resin with a longer pot - life it can be
advantageous to do a post cure in an oven. Pre preg (Preimpregnated
material) need a higher temperature to harden. Also a high (or higher)
amount of pressure is needed to wet the fibres optimally and to get
all the air out. The advantage of a pre preg is that is is slightly
sticky and therefore can be placed on a mould - even against a wall.
This comes in handy when you need to place your fibre exactly where it
is needed. Or, you can do without when less weight is essential.
Honeycomb can be used in a product with pre preg and placed in an
autoclave. Only the pressure cannot be so great. The problem is here
that bonding the honeycomb to the skin is critical. Compare to bonding
two pieces of paper perpendicular to each other. Go for the closed
cell foam.
As to the stiffness of a rowing shell. Stiffer is better: you will not
put energy into deformation of the boat, but into propulsion of the
boat through the water. However, you will need to change your rowing
style. Very relaxed and as little vertical movement in the catch and
the finish as possible to minimise pushing the boat into and out of
the water.
Lastly the price of the stampfli single scull. Frankly you would be
out of your mind to pay euro 8770.86 for a single. Even Carl is
cheaper and his boats will last (and look reasonably well). But prices
should be around euro 4000 - 5000 for a single.
Hope this clears things up.
Eelco