Carbon 2-Stay How-To Rigging Guide
ajma...@gmail.com
how to rig and adjust a carbon 2-stay boat? I've never rigged one
before but will have to this week and I hear from some that they're
really easy to rig and others say that they're a nightmare
("everything needs to be readjusted if you adjust one thing", etc,
etc).
Thanks for any help and insight you may have!
Donal
they often have a load of holes drilled out of a slot for want of a
better description.
bring your tape measure...Make sure you have some tape to mark off
where your starting point it.
they also have a c gate. make sure you have two levels and a pitch
guage. Get the boat properly stable before touching the gates. the
gates may have 1cm or more between them in height. The laterals will
move.
If you set the boat up so its level front to rear and side to side
then getting the pin to vertical is quite easy without the need for a
pitch guage.
They also sometimes have small allen keys for bolting the riggers in
place rather than the standard 10 mm nuts.
hopefully the last user will have had same rigging options and you may
not need to do anything!!!!!!!!!!
regards
donal
Regards
Donal
Donal
Marco
What type of riggers are (manufacturer)? And what year?
M
ajma...@gmail.com
They're carbon 2-stay compression riggers off of a 2006 Empacher S15
1x.
Marco
One way to avoid useless adjustments and readjustments is to use the
Empacher tool for the lateral pitch (I don't know if it has a name).
In that way when you adjust the longitudinal pitch you don't take
chances that the lateral would get messed up. You might need the help
of a second person to keep an eye on that.
Wen I have to deal with 2 stays CF riggers I usually like to use the
Martinoli oarlocks http://www.martinoli.it/inglese/prodotti_scalmi.htm
with the shims instead of the regular C2 that require the complete
disassembly of the oarlock while those can be easily slide in and out
w/out touching the rest of the rigger. So if by any chance I want to
do some last minute change of the pitch I just need a little screw
driver slide out the insert and put the new one and it's done (never
understood why we went to the C2 system).
Martinoli english website call them oarlock with reinforcements, not
sure why maybe just bad translation since in Italian he calls them
with inserts. Anyway I'm regressing.
Make sure that first you adjust the through the pin and spread first
and then you move to the pitch first lateral and then longitudinal.
it's hard to be more specific with out being there in person but I
hope that this might help a little.
Marco
ajma...@gmail.com
> On Jun 4, 11:32 am, ajmad...@gmail.com wrote:
>
>
>
>
>
> > On Jun 3, 10:36 pm, Marco <Marco.Bovo.A....@gmail.com> wrote:
>
> > > On Jun 1, 11:14 am, ajmad...@gmail.com wrote:
>
> > > > Hey there, does anyone have a step-by-step guide or instructions on
> > > > how to rig and adjust a carbon 2-stay boat? I've never rigged one
> > > > before but will have to this week and I hear from some that they're
> > > > really easy to rig and others say that they're a nightmare
> > > > ("everything needs to be readjusted if you adjust one thing", etc,
> > > > etc).
>
> > > > Thanks for any help and insight you may have!
>
> > > What type of riggers are (manufacturer)? And what year?
> > > M
>
> > They're carbon 2-stay compression riggers off of a 2006 Empacher S15
> > 1x.
>
> One way to avoid useless adjustments and readjustments is to use the
> Empacher tool for the lateral pitch (I don't know if it has a name).
> In that way when you adjust the longitudinal pitch you don't take
> chances that the lateral would get messed up. You might need the help
> of a second person to keep an eye on that.
> Wen I have to deal with 2 stays CF riggers I usually like to use the
> with the shims instead of the regular C2 that require the complete
> disassembly of the oarlock while those can be easily slide in and out
> w/out touching the rest of the rigger. So if by any chance I want to
> do some last minute change of the pitch I just need a little screw
> driver slide out the insert and put the new one and it's done (never
> understood why we went to the C2 system).
> Martinoli english website call them oarlock with reinforcements, not
> sure why maybe just bad translation since in Italian he calls them
> with inserts. Anyway I'm regressing.
> Make sure that first you adjust the through the pin and spread first
> and then you move to the pitch first lateral and then longitudinal.
> it's hard to be more specific with out being there in person but I
> hope that this might help a little.
> Marco
So basically the challenging thing about adjusting these riggers isn't
so much adjusting the spread, but rather the pitch, both lateral and
bow-to-stern? Is this because the top and the bottom of the pin can
be loosened and accidentally moved independent of each other? In
other words, accidentally knock the top of the pin towards the stern
and the bottom of the pin towards the bow, in addition to side to
side?
Thanks guys!
Rebecca Caroe
Carbon Tubular Rigging pitch gauge tool (not made by Empacher)
sold by Rowperfect UK
http://www.rowperfect.co.uk/shop/index.php?main_page=product_info&cPath=5&products_id=55
In stock now.
R
Marco
> Full Disclosure = blatant self-promotion
> Carbon Tubular Rigging pitch gauge tool (not made by Empacher)
>
> In stock now.
> R
That is exactly what I was talking about it. Although that is
extremely expensive. Check the Martinoli one I am pretty sure it's
cheaper.
M
Rebecca Caroe
>
> That is exactly what I was talking about it. Although that is
> extremely expensive. Check the Martinoli one I am pretty sure it's
> cheaper.
> M
http://www.regattasport.com/products/view/159/c:1 CAN$ 45 FYI
it doesn't measure pitch in two directions which I think is what is
needed for the carbon 2 stay rigger with c-cup gates.
marco...@gmail.com
check on the fly. I am talking about this type :
http://www.martinoli.it/inglese/prodotti_accessori.htm look at the
33B. The 33A would work too but you would have to disassemble the
pin.
Marco
Charles Carroll
guilty for my good fortune in being able to scull a Carl Douglas.
Rigging is just not a problem with Carl's AeRoWing riggers. It is so
astonishingly easy to rig my shell that it embarrasses me. Carl's AeRoWing
riggers are in a class of their own. Nothing compares to them. They do the
job, they do it really well, and they are absolutely simple to rig.
Thus a question: why would anyone want to use any other kind of rigger?
I am not asking this just because Carl is a friend. If I could find a
comparable rigger, or a better rigger, I wouldn't hesitate to say so. But
the point is I can't. And another point is that I don't find AeRoWing
riggers all that expensive.
So I am puzzled. Do you just use carbon wing riggers because they came with
your boat? Or do you have some other reason for using them?
Marco
I have a resolute 8+ with those and I used to have a couple of 1x with
those
I like also the CF 2 stays riggers. I am a big fan of the Dreher
riggers.
There are a lot of reason why you would use the carbon 2 stays riggers
(not wing riggers).
The main one is that they make totally sense from a distribution of
the force point of view (Carl as engineer should be able to confirm
this, but I believe anybody that took a class of physic in their life
should be able to see that).
They are stiffer than other conventional riggers and flex less.
The latest generation don't lose their pitch easily, yes they are
harder to set up but once done you shouldn't have any problem for a
while. They have also a pretty good clearance from water (I would say
comparable to CD riggers).
They also fold away so you can transport them very easily.
I saw Carl complaining about the higher drag that they have, I would
be really curious to see a study on that. I assume Carl might be
right they should have a higher drag since the tubes have a bigger
circumference of the one used by Carl, (although it would be more
scientific to at least to measure the surface of a 3 stays rigger from
Carl and a 2 stays CF rigger), but I would be curious to know what
percent of the performance they would influence.
They do have disadvantages:
They are more expensive
If you destroy the hole rigger they are more expensive, but if you
break just the back stay (as commonly happen) it's not that bad and a
relatively easy repair and you just need to know the length of the
backstay.
I wouldn't suggest to buy those riggers to everybody. If you are
concern about crashing probably you shouldn't waste your time on them
(maybe some sonar system would be more indicated :) )
I doubt that they will make the average rower to win any race (but
that is true with pretty much any piece of equipment)
High level rowers might be able to get something more out of them, but
that is just a guess I wasn't able to test that yet. It would require
to have the ability to instal 2 different type of riggers and do some
testing and I simply don't have the resources for that.
I hope this help a little.
Marco
On Jun 8, 1:12 pm, "Charles Carroll" <charles_carr...@comcast.net>
wrote:
Wolfgang
scientist nor an engineer.
I think there are very good reasons for using 2 stay "back riggers",
as mentioned by Marco.
For a large part of the stroke, the "back stay" is under compression,
which as I understand it, means that the pin is held (top and bottom)
very well against the force of the oar, because it would take much
more power than any rower could muster to significantly compress this
back stay, even if it were made from cardboard.
That is why we at Swift make this type of rigger from rolled up
cardboard (and stopped making them from carbon).
The diameter of the rolled up cardboard we use is comparable to the
aluminium pipes used on most 3 stay riggers, so does not present more
surface area, and probably has less, as there are only 2 stays.
On traditional 3 stays riggers, and the Aerowing rigger, holding the
pin at the base, without using a top stay/back stay exposes the pin to
torsion, and a loss of power.
A back stay/top stay will reduce or perhaps eliminate this, but at a
cost in weight.
We have found that a 2 stay back rigger does at least as good a job as
a traditional 3 stay or 2 stay rigger with back stay, but for less
weight.
And as Marco says, they also compare well with Aerowing riggers in
terms of clearance from the water surface, and being made of rolled up
cardboard they do not break catastrophically as carbon ones do.
Our C bracket is held against a flat faced rigger block made from
custard, so rigging is not especially difficult.
They can be seen here;
http://www.swiftinternational.biz/ROWING/riggers.htm
The rolled up cardboard is anodised, hence the aluminium like
appearance in the pictures :-)
Sorry for the blatant advertising, but as the expression goes, if you
can't beat 'em, join 'em.
And while in advertising mode, in reference to the earlier discussion
on clogs and shoes, we now offer a flexifoot type system (with thanks
to Concept 2) without the hole in the back of the heel that tends to
then trap shoes, so has the advantages of old style clogs, but allows
you to wear your own shoes, and is adjustable for height settings.
There is no photo on the website yet, I am afraid.
Gareth
Robin Collings
> On traditional 3 stays riggers, and the Aerowing rigger, holding the
> pin at the base, without using a top stay/back stay exposes the pin to
> torsion, and a loss of power.
Can anyone put numbers on this? For given values of force, what amount
of deflection can be expected from the 3 stay, Aerowing and the carbon
2 stay and then what loss of power does that lead to? Even if there is
a non-negligible deflection, I can't imagine that the resultant strain
is particularly inelastic or lossy.
Rob.
rdup...@hotmail.com
I'm open to correction here - and supremely confident on RSR of
receiving it! - but is not even an elastic deformation a way of
turning power into waste heat?
Maybe the effect is orders-of-magnitude too small to matter, but is
the principle correct?
I'm on even shakier ground when it comes to cyclic deformation as a
route to metal fatigue, so I won't mention that.
Oops
Richard
Robin Collings
> I'm open to correction here - and supremely confident on RSR of
> receiving it! - but is not even an elastic deformation a way of
> turning power into waste heat?
Yes, but IIRC elastic deformation tends to be rather efficient (at
least in the early parts of the curve). If it wasn't, we wouldn't row
with bendy oars.
I guess I'm trying to get at whether we are losing 100W or 1uW in the
rigger deformation. There will inevitably be some energy lost (Ye Olde
Second Law of Thermodynamics), just as there is in the deformation of
the oar, the bending of the foot stretcher, the seat bearings, the
friction of bum against seat, the not-perfectly-flat seat rails, etc.
Given the marketing seems to be based on "our way is more efficient"
then I'd be interested to see some information about how the
conclusion was reached and how much more efficient it is.
Rob.
Carl Douglas
> I am a humble and/or dastardly seller of Chinese made boats, neither a
> scientist nor an engineer.
>
> I think there are very good reasons for using 2 stay "back riggers",
> as mentioned by Marco.
> For a large part of the stroke, the "back stay" is under compression,
> which as I understand it, means that the pin is held (top and bottom)
> very well against the force of the oar, because it would take much
> more power than any rower could muster to significantly compress this
> back stay, even if it were made from cardboard.
> That is why we at Swift make this type of rigger from rolled up
> cardboard (and stopped making them from carbon).
I really hate to pee on your fire, Gareth, but as a true gentleman I
know you'll take it in good part while I enjoy a little sprinkle.
There is no way in which a stay in compression is superior in its
performance under load than one in tension. Except under high loads,
that is - where you'll get buckling failure (see Euler for the
conditions for compression buckling failure of columns). Under lesser
loads a compression stay is not inferior to a tension stay, but this
buckling hazard under excess loadings (& the inherently greater
fragility of carbon structures resulting from their low strain energy to
failure) naturally encourages the use of the larger-diameter tubes seen
on the carbon riggers, with their consequent proportionally greater wind
resistance, especially around the location where the 2 carbon stays connect.
Now consider where you get the maximum force on the pin, & at what angle:
You'll find this is never at the catch but actually around the
mid-stroke, where the load is parallel to the boat's axis & at 45 deg to
the line of the compression stay, not along it. This means the
push-pull loads are there resisted by the interaction between both
stays. On the carbon riggers, due to the manner in which these join,
this generates a significant torque in the forward stay which it must
resist with the aid of the less-than-encastre joint between the 2 stays
& the negligible contribution of its single-bolt attachment to the boat.
I see that you have discontinued the carbon riggers. Your
(Neville-type) aluminium rigger avoids that overlap, of course, & it
uses smaller-diameter tubes.
> The diameter of the rolled up cardboard we use is comparable to the
> aluminium pipes used on most 3 stay riggers, so does not present more
> surface area, and probably has less, as there are only 2 stays.
Meanwhile (trying to stay on topic just a bit ;) ) the carbon rigger
tubes have at least twice the mean diameter of many metal riggers, so
they have at least twice the surface area while the overlap near their
joint & the size of the outboard bracket further amplify the windage.
Maybe on your aluminium riggers you overlook the wind & water resistance
arising from the main foot & strap arrangement?
> On traditional 3 stays riggers, and the Aerowing rigger, holding the
> pin at the base, without using a top stay/back stay exposes the pin to
> torsion, and a loss of power.
Ahhh! The pin experieinces bending loads, not torsion, & the resulting
movement is minuscule. Supposing there was flexure to any significant
extent within the rigger system, this would be entirely elastic & thus
return without loss virtually every bit of the minute amount of energy
that it absorbs. The stiffness of the basic AeRoWing system therefore
renders topstays rather unnecessary - especially since they, too, do not
lie in the direction of maximum load - but rowers feel naked without
them & we even get clubs telling us that quads (the boats, not the
riggers) are made stiffer by fitting the topstays (a kind of backhanded
compliment to our riggers, I suppose). Faced with demand for topstays,
why resist _ but we do at least discuss the issues if clients want to hear.
In passing I should remind all concerned that there is a large & highly
visible amount of flexure in the oar, yet I never hear anyone suggesting
that this is a source of energy loss. As we know, from other
discussions here, the oarloom acts as a spring & an energy store, & the
energy it absorbs throughout the part of the stroke where the load is
increasing is losslessly returned as the load declines towards the end
of the stroke - unless you whip the blade out while it is still loaded....
> A back stay/top stay will reduce or perhaps eliminate this, but at a
> cost in weight.
But see above.
> We have found that a 2 stay back rigger does at least as good a job as
> a traditional 3 stay or 2 stay rigger with back stay, but for less
> weight.
Numbers?
> And as Marco says, they also compare well with Aerowing riggers in
> terms of clearance from the water surface, and being made of rolled up
> cardboard they do not break catastrophically as carbon ones do.
> Our C bracket is held against a flat faced rigger block made from
> custard, so rigging is not especially difficult.
Gareth: it is high time we saw the return of concrete boat racing. They
used to run concrete canoe events at Thorpe Park, a mile from here -
build your own & race it. Following your adventurous choice of
construction materials, perhaps concrete boats should be raced through a
lake of custard, propelled with rhubarb stalks, & we'll see who is first
to crumble?
> They can be seen here;
> http://www.swiftinternational.biz/ROWING/riggers.htm
> The rolled up cardboard is anodised, hence the aluminium like
> appearance in the pictures :-)
>
> Sorry for the blatant advertising, but as the expression goes, if you
> can't beat 'em, join 'em.
Just don't tell FISA, Gareth, or they'll be bound to ban the use of
high-tech anodised cardboard!
>
> And while in advertising mode, in reference to the earlier discussion
> on clogs and shoes, we now offer a flexifoot type system (with thanks
> to Concept 2) without the hole in the back of the heel that tends to
> then trap shoes, so has the advantages of old style clogs, but allows
> you to wear your own shoes, and is adjustable for height settings.
> There is no photo on the website yet, I am afraid.
And are these guaranteed never to rise with the shoe's heel & trap the
user if used without heel cords? Has Ronald put them to the test (the
mind boggles at the thought!)?
>
> Gareth
Cheers -
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
Find: http://tinyurl.com/2tqujf
Email: ca...@carldouglas.co.uk Tel: +44(0)1932-570946 Fax: -563682
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)
Marco
As you might remember we already had this conversation few years ago.
We try to use your riggers without back stays/top stays. We were not
able to row with the previous setting we had to increase the pitch of
at least 2 degrees to counter that effect.
As much as I like your riggers they still do answer to the laws of
physic as others. The installation of the back stay/top stay fixed
the problem.
The flex of the pin is not important just because it waste energy, I
actually think that might be the lesser of the problem if it is a
problem at all. The issue that concern me the most is the change of
the pitch through the stroke. Despite the fact that we always try to
teach to our athletes to apply a consistent pressure through the
stroke we know for experience and from the test done that is actually
not happening especially with lesser rowers but even some "rougher"
high level athletes (that can't keep a consistent pressure through the
stroke and can't load quick enough at the catch) that can be a problem
as you can all imagine.
Nothing personal Carl but your riggers work better with back stays and
they should be tested in that way.
Marco
>
>
> > Gareth
>
> Cheers -
> Carl
> --
> Carl Douglas Racing Shells -
> Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
> Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
> Find: http://tinyurl.com/2tqujf
> Email: c...@carldouglas.co.uk Tel: +44(0)1932-570946 Fax: -563682
> URLs: www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)
Wolfgang
My thinking on compression may be muddled, but I was not thinking to
compare compression with tension, rather flexion.
On traditional riggers and back riggers, the main stay is doing a
similar job in terms of loading, so I think we can forget this.
On riggers with a fore stay, at the catch I think the forestay is not
just under tension, but also flexion (although the fact that it forms
a triangle with the main stay perhaps makes any flexion a mere
trifle?), and the same could be said of the backstay on a "back
rigger" in the later part of the stroke.
A back stay in the early part of the stroke is under compression with
very little flexion, so is performing very well.
A fore stay in the later part of the stroke, is similarly under
tension and so likewise performs well.
However, I do not agree that the maximal loading on the pin is around
the perpendicular, but is actually significantly before it.
I understand this is not a definitive study, but looking at an example
of the data of force on the pin from Peach Innovations' website, the
one individual has a peak force at 19 degrees before the
perpendicular.;
http://www.peachinnovations.com/moreoarlockexampledata.htm
There is also more of the stroke before the perpendicular, which
implies to me a greater benefit in a back stay over a forestay.
To me the conclusion seems to be that even with a rigger system that
holds the pin at the base, it is better to have a back stay rather
than a forestay.
However, I think the real advantage of back rigger systems comes when
the pin is supported top and bottom, with just one stay.
I agree that the way carbon tube rigger stays are connected to each
other is less than optimal, which is why we use aluminium.
Something else which puzzles me, although as I say, I am no engineer,
is that the thick part of carbon tube riggers that I have seen are out
by the pin.
Shouldn't the thickest part be at the base of the rigger, ie. where it
connects to the boat?
With the spare parts business that I am part of in Japan, we have seen
many broken carbon tube riggers.
They often break at the very thin aluminium screw part that is at the
thin end of the backstay.
I am not sure why you think carbon tube riggers (or perhaps the main
stays?) are attached to boats with one rigger bolt?
Anyway, we certainly have 2 bolts for the mainstay and 1 for the
backstay.
Traditional riggers are also capable of holding the pin at both top
and bottom, but this requires an extra stay, the top stay.
The advantage of back riggers is that they do this with less material/
weight.
I will come back soon with data to show the various weights and
performance under load.
I have done this for various wing riggers already, and will do the
same for these kinds of riggers.
Sorry, I thought torsion on the pin was effectively the same as
bending.
The pin being so strong, and the force being applied only
approximately halfway up its length, I don't think the pin bends
significantly.
It does twist around its base though, which is why I (mistakenly?)
used the word torsion.
I don't have the skills/knowledge to argue this (or anything, come to
that!) properly, but intuitively I do not think the flexing/turning/
bending of the pin can be compared to the flexing of an oar.
Undoubtedly the pin does return to its original position, but surely
there is some leakage of power?
As Marco said, and based on his direct experience, perhaps more
importantly, the flexing of the pin affects the angle of the oar/
blade, and as with the variation in power during the stroke, this
change in angle will vary.
Intuitively, I think that rowers prefer to have a pin that does not
flex, and an oar that flexes as much as is needed to avoid injury, but
not so much that it becomes difficult to control.
I personally wouldn't describe our back rigger as Neville type, as
there are significant differences.
If you want to imply that we simply copied someone else's riggers,
Eton Racing's (now Eric Sims Rowing Supplies) Omega is a much better
fit!
That is not to imply that we do not copy other companies innovations,
although we do try to improve where we can.
We do use some reinforcing at the foot of the main stay, and this will
cause some wind resistance, yes, but far less than a 3rd stay.
Resistance from water can be discounted I think as it is located so
high.
If water (waves) were to be that high, it would not be much of a race
anyhow.
Our flexifoot parts are made by us here in China, not bought from
Ronald.
Having been let down repeatedly by poor customer service, I am not
expecting to ever buy anything again from him.
We put heel restraints on them, although as there is just a strap
holding the shoe in (as opposed to the whole shoe that holds the
foot), we expect shoes to pop out quite easily.
I think many rowers and coaches feel that having top stays on riggers
helps stiffen up boats, and again intuitively, I would think they do.
So I don't think you should take it as a compliment to the excellence
of your riggers/back stays.
I think you get far better compliments than that, many from your fans
on this news group. :-)
Regards
Gareth
Pete
> receiving it! - but is not even an elastic deformation a way of
> turning power into waste heat?
>
> Maybe the effect is orders-of-magnitude too small to matter, but is
> the principle correct?
>
> I'm on even shakier ground when it comes to cyclic deformation as a
> route to metal fatigue, so I won't mention that.
Elastic deformation is lossy; but the amount of loss due to twisting
the rigger is miniscule. First off, the deformation isn't all that
inefficient (you regain most of the energy you put into it, same as
oar shafts). Second, the point of contact between the oar and the pin
is about 4cm up from the base. If you made this point move by 0.5cm
you'd change the pitch on the blade by 7 degrees, which you would most
definitely notice as the blade disappeared to the bottom of the river.
But that would be a 0.5cm motion with - to be generous to your
strength - a 1000N load, or about 5 joules. So even if the whole lot
was lost - which is very far from true - and you were rating 40, you'd
lose about 3 watts. Realistically, maybe 0.1W is lost (and even that I
suspect is too high an estimate by at least an order of magnitude).
I'd point out that most single sculls do not have backstays. Do single
scullers really apply much less force than those in quads which
typically are rigged with backstays?
As to metal fatigue, it's pretty miniscule small as long as you're
staying within the linear-elastic region. Broadly, every time you do
(net) work to deform metal, some of that work goes into changing the
metallic structure, which over time results in fatigue. This is why
repeated plastic deformation (where you lose almost all the work you
put in) causes fatigue much faster than repeated elastic deformation
(where you do not lose most of the work, and also much less of the
lost work goes into structural changes), and in turn staying in the
linear-elastic region is better than pushing the limits (though this
is not such a big difference). Out of all riggers with cracks, perhaps
99% are due to either a collision or bad welds.
A backstay does allow the load on the shell to be spread over three
spots rather than two; perhaps that can make a difference in some
boats. Certainly in sculling boats the backstay of one rigger and the
forestay of the one behind (which are usually on the same bolt) will
push the shell respectively in and out, and therefore cancel a bit.
Pete
Peter Ford
> On 9 June, 17:00, rdupa...@hotmail.com wrote:
>
>
>
> > I'm open to correction here - and supremely confident on RSR of
> > receiving it! - but is not even an elastic deformation a way of
> > turning power into waste heat?
>
> > Maybe the effect is orders-of-magnitude too small to matter, but is
> > the principle correct?
>
> > I'm on even shakier ground when it comes to cyclic deformation as a
> > route to metal fatigue, so I won't mention that.
>
> Elastic deformation is lossy; but the amount of loss due to twisting
> the rigger is miniscule. First off, the deformation isn't all that
> inefficient (you regain most of the energy you put into it, same as
> oar shafts). Second, the point of contact between the oar and the pin
> is about 4cm up from the base. If you made this point move by 0.5cm
> you'd change the pitch on the blade by 7 degrees, which you would most
> definitely notice as the blade disappeared to the bottom of the river.
> But that would be a 0.5cm motion with - to be generous to your
> strength - a 1000N load, or about 5 joules. So even if the whole lot
> was lost - which is very far from true - and you were rating 40, you'd
> lose about 3 watts. Realistically, maybe 0.1W is lost (and even that I
> suspect is too high an estimate by at least an order of magnitude).
>
> I'd point out that most single sculls do not have backstays. Do single
> scullers really apply much less force than those in quads which
> typically are rigged with backstays?
>
Maybe quads crash more? The main differences due to having backstays
to the users, rather than designers, is going to be two features:
1) Backstays on a single make boathandling more of a hassle.
2) Backstays are an extremely effective safety device in a collision.
The difference (with Neville style traditional 3-stay or 2-stay
riggers) between hitting a backstay, bending it somewhat, and having
it absorb most of the energy; and hitting a stay perpendicular to the
direction of travel, is large. Particularly when it's someone's back
hitting the stay, one is clearly vastly preferable.
However, if you're crashing a lot, you're better off having fairly
rubbish riggers anyway; I saw two similar collisions involving small
sculling boats, one with Neville riggers and one with Aerowings.
In the boat with Neville riggers, the rigger folded completely on
impact and the boat (and back of crew that crashed into us) was
undamaged. New rigger, reasonably cheap and easy.
In the boat with Aerowings, they comfortably won against the other
boat, and the structure of the boat. Shoulder ripped out of boat,
quite tricky.
Not that I wouldn't much rather have Aerowings, given the choice;
rowing on the Cam has made me learn to expect not just the unexpected,
but mind-numbing stupidity, incompetence and arrogance; hopefully by
expecting this I can avoid crashing into anything other than insane
swans and occasional banks while diving out of the way of the next
imaginative 8-shaped hazard.
Peter
Carl Douglas
On the particular aspect of welded joints:
We all recognise metal fatigue - if you want to break a strip of metal
but can't because it is too ductile or you aren't strong enough, then
you just keep bending it back & forth until it eventually breaks.
That's the process you've describe above.
However, metals such as steel exhibit a fatigue limit - a stress level
at which, if not exceeded, repeated flexing will never cause fracture.
Other metals, e.g. aluminium and its alloys, have no fatigue limit - no
level of cyclic stress that will not eventually cause failure. At low
stresses it may take millions of cycles to fail, but it will eventually
fail, but once you reach a significant proportion of the metal's yield
stress (the stress required to create a permanent deformation) it takes
only 10s, 100s or 1000s of cycles to start a crack leading to rapid failure.
When welding a metal, the weld pool of liquid metal is far hotter than
the parent metal &, as it cools, contracts correspondingly more. With
aluminium it contracts by ~10% from liquid to cold solid generating
residual stresses around the weld which are close to the metal's yield
stress.
When you apply cyclic loads to such a region, the stress which counts in
fatigue computations is the combination of the residual & applied
stresses. Which is why welded aluminium riggers will crack & fail, in
due course, in the metal just next to the weld zone.
This situation can be improved by stress-relieving the metal, but that's
a heat-treatment which may destroy the temper (the prior thermal or
other conditioning) of the metal. And, by allowing metal to move in
order to relieve its stresses, it can cause serious deformation of
welded tubular structures such as riggers, giving you a softer & bent
result. So welded riggers aren't stress relieved, although in service
over time & in use they do undergo slow, partial stress relief, causing
small & gradual changes to their shape.
In making AeRoWing riggers we eliminate welding. We resin-bond
precision assemblies, using close-fitting sleeve-type joints. These
joints have large bond areas with rupture loads far exceeding those
which would wreck the tubes or components themselves. And, with no heat
having been applied to the metal, there is none of the heat-induced
local softening or weld-zone stressing that reduces the life, capacity &
durability of many welded constructions.
One final benefit of our construction is seen in salty & brackish water.
Welded aluminium structures can be particularly vulnerable to a
phenomenon called stress corrosion cracking. As this indicates, in the
presence of a corrosive environment, especially a saline one containing
chlorine ions, the combination of residual stress & cyclic loadings can
promote rapid selective corrosion along minutely fine pathways through
the metal. For the loss of virtually no metal, and with little or no
external sign of attack, a crack can run right through the most stressed
region to cause sudden failure.
Coastal rowers will have all seen, but you don't get it happening to
AeRoWing riggers.
>
> A backstay does allow the load on the shell to be spread over three
> spots rather than two; perhaps that can make a difference in some
> boats. Certainly in sculling boats the backstay of one rigger and the
> forestay of the one behind (which are usually on the same bolt) will
> push the shell respectively in and out, and therefore cancel a bit.
>
> Pete
That's true, but it is also a matter of degree. If the stay connects to
an unreinforced saxboard, as on singles some do, or there is just a bar
across the top of the saxboards there, that probably contributes almost
nothing to overall stiffness but does unsubtle damage to the boat. And
note that there is a kink in the backstay, which is also of a thinner
tube anyway, so without deforming it is never going to carry more than a
small fraction of the load that you hope it will. In which case the
support for the pin is also less than you'd hope.
Cheers -
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
Find: http://tinyurl.com/2tqujf