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 Post subject: Sliding seats
PostPosted: Tue Mar 25, 2008 4:28 pm 
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Joined: Fri Aug 01, 2003 2:26 pm
Posts: 164
One of the hardest parts of building a good IC is the sliding seat.
I have done a design for a US style seat that can be laser or CNC cut out of a sheet of 3mm plywood , 2040 long X 100mm deep X450 wide.
Vee shaped in cross section with a 7250mm radius.
The whole thing slides together with intersecting slots in bulkheads and beams and should deliver a very stiff seat for about 7kg.
One sheet of plywood and some carbon fiber and running two pieces of timber through a table saw does it
I have this available a s a DXF file that I will happily send to anyone who wants it.
Send me your email because I doubt I can put a DXF file up on this forum.
SHC

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 Post subject: Re: Sliding seats
PostPosted: Tue Mar 25, 2008 7:03 pm 
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If I've done the configuration right you should be able to attach DXF files now.

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 Post subject: Re: Sliding seats
PostPosted: Thu Mar 27, 2008 1:01 am 
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Actually I have to do a bit of rework to this design. When I did the final nesting of parts I realized to my chagrin that they didn't all fit on a single piece of plywood.
"Sh.t oh dear!" as my mother used to say.
So I have to play around a bit, but mostly it gives me a chance to use different thickness wood which is probably a good thing.
SHC

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 Post subject: Re: Sliding seats
PostPosted: Fri Mar 28, 2008 10:01 am 
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Sounds good Steve,
Please keep me informed. Just about to start on the seat and carriage.


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 Post subject: Re: Sliding seats
PostPosted: Thu May 15, 2008 4:11 pm 
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Joined: Fri Aug 01, 2003 2:26 pm
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[img]
Attachment:
seat%20construction.jpg
[/img]
The first of the laser cut seat is being assembled this week.
There are some small details that aren't quite right. It is easy to correct the files and try again, it is really close.
The photo shows the general idea. It happens pretty fast and is very nifty.
More as it happens.
SHC


Attachments:
seat construction.jpg
seat construction.jpg [ 163.41 KB | Viewed 17083 times ]

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 Post subject: Re: Sliding seats
PostPosted: Tue Jun 10, 2008 6:42 pm 
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First seat finished at 7.5 kg and broke first day.
I was trying to see if the plies of unidirectional carbon fiber in the top fore and aft edges and on the bottom center line were necessary, and I conclude that they are.
There was no evidence of a fabrication flaw or damage caused by poor fit in tha carriage.
My vast bulk may have had something to do with it, but I take that into account when I design stuff. If I can break it it isn't strong enough.
What I had been thinking is:
On the top edges, 75mm strip of 900g/m^2 uni folded such that it forms 3 layers 25mm wide.
On center line at the bottom a 150mm wide strip of 900g/m^2 uni folded up to form a 50mm wide band.
I like folding up strips rather than making multiple cuts because I think it makes a neater job and because you lose the fewest fibers this way.
You will finish the edges the standard way with a ply of +/- 45 degree cloth after this.
SHC

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 Post subject: Re: Sliding seats
PostPosted: Wed Jun 11, 2008 8:20 am 
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Location: United Kingdom
Steve Clark wrote:
First seat finished at 7.5 kg and broke first day.

Sucking eggs, I know, but did you figure out the failure mechanism? Always something for the rest of use to learn from that sort of thing:-) I also wonder if you could get away wihout either the top or bottom strips, just have one... I fully appreciate though that there are limits in how many times you want to break test seats - I'm not volunteering to join in the development program...:-)


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 Post subject: Re: Sliding seats
PostPosted: Thu Jun 12, 2008 12:14 am 
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I guess I am still swinging for the fences trying to keep the seats really light. A bit better than a KG lighter than what was minimum weight.
I could not find anything that looked obviously wrong. Often on other seat breaks it becomes pretty clear that either there was a fabrication issue or that there was something wrong with the way the seat was fit into the carriage that resulted in the death of the part.
I built a seat to these general scantlings over 25 years ago, and it lasted a good long time. It may even still be in service for all I know What was different is that that seat had 4 12mm square stringers top and bottom instead of the three plywood webs. The cross sectional area of those stringers instead of the plywood may have been the difference.
You don't usually like to add a bit of carbon fiber because it is so much stiffer than the wood, it will take all the stress. So if you don't put enough there to do the whole job it will break first, then the seat will pack it in. So what I have called out is the same uni as is in the composite seats. Given that even these break now and then, it isn't over generous. Once again, maybe I am being too aggressive, or heavy.
SHC

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 Post subject: Re: Sliding seats
PostPosted: Sat Oct 11, 2008 4:12 pm 
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Joined: Fri Jan 11, 2008 12:01 pm
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Location: Essex, Maldon
Hi Guys
What sort off weight are getting down to with the seat as I was thinking
Of building a new one for IC166 this winter have just weighed the current
One and it is coming out at 10.8kg

regards
Adrian

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 Post subject: Re: Sliding seats
PostPosted: Sat Oct 11, 2008 5:57 pm 
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Joined: Fri Jul 18, 2003 7:53 am
Posts: 142
Location: Emsworth Hants United Kingdom
The lightest I make seats at is 8kg & that's for helm weights up to 90kg. Pushing the limits of this very high stressed bit of kit can have catastrophic results as I'm sure many have found out. Incorrect choice of materials, bad desighn, bad workmanship or under engineering will all show up in the finished item so concider every aspect before you start & try not to copromise, it'll show. Good building.


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 Post subject: Re: Sliding seats
PostPosted: Sat Oct 11, 2008 7:36 pm 
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Joined: Tue Jul 15, 2003 11:02 pm
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Location: Australia
adrianM wrote:
Hi Guys
What sort off weight are getting down to with the seat as I was thinking
Of building a new one for IC166 this winter have just weighed the current
One and it is coming out at 10.8kg

regards
Adrian


At the 2008 Worlds, weights ranged from 6.4kg to 12kg
http://www.internationalcanoe.yachting. ... suring.pdf

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 Post subject: Re: Sliding seats
PostPosted: Mon Oct 13, 2008 1:44 am 
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Location: USA
My new seat weighs in at 6kg unrigged and unpainted. It's only had a couple of windy sessions with 90kg sailors so I don't know yet how it will stand up. It could probably use another layer of 200gm carbon on the top for dent resistance

The mold is made with tile board and, used carefully, is probably good for a dozen seats. The shape is pretty much a copy of Steve Clark's.

The structure relies heavily on a 'I' beam spar on the center. At the part of the seat over the weather gunwale the load from the I beam is transfered directly down to the center of the carriage at the gunwale rather than out to the fore and aft carriage rails. Since my carriage rolls on wheels this means a bunch of wheels under the I beam to take the downward load.

Anyone who is careful, has done a little epoxy and carbon work and knows how to vacuum bag could build this without too much trouble. It's the details that get you though and unless you are a risk taker I wouldn't advise trying to build something lighter than 7-8kg's first time.

Today's farm girl powered test:


Attachments:
IC test 124.JPG
IC test 124.JPG [ 201.35 KB | Viewed 16176 times ]
IC2 024.JPG
IC2 024.JPG [ 99.79 KB | Viewed 16168 times ]
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 Post subject: Re: Sliding seats
PostPosted: Wed Dec 08, 2010 5:53 am 
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Joined: Sun Feb 07, 2010 1:30 pm
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Location: De Rust, South Africa
Chris, Steve

Can you possibly send me your DXF files for the sliding seat?

Thanks!

Jan Theron
http://www.kanoefabrik.com


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 Post subject: Re: Sliding seats
PostPosted: Mon Aug 22, 2016 11:50 am 
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Joined: Mon Sep 22, 2003 7:28 pm
Posts: 235
Location: United Kingdom
Been thinking about sliding seats, what widths do people make them?
My current one is 400mm wide, I see from this thread that Steve Clark's is 450mm, 500mm is max, what is the best?
I think possibly it may depend on sailing conditions.... my 400mm seems great where I sail with variable wind but in Richmond it seemed very narrow.

Alistair

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 Post subject: Re: Sliding seats
PostPosted: Mon Aug 22, 2016 4:37 pm 
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Joined: Thu Oct 02, 2014 11:41 am
Posts: 28
The seat on GBR 311 is wedge-shaped, 380mm wide, and has a square leading edge 68mm deep. My experience is that it provides zero uplift when you touch down / go in to windward. Instant death, really, if like me you're slow to get inboard. It's narrow enough to encourage wrapping your legs around the slide when off the end, which legend used to have it was potentially bone-breaking, though I've never hurt myself going into a wave in that position.

I sailed on one of Steve Clark's seats - essentially a shallow vee with a flat centre, and presumably 450 wide - when I chartered US249 last month. This gave me a bounce on touchdown, though I felt that the shape might also keep you on the surface, rather than release upwards with ease. Sitting out is only practical with toes in straps and heels in the seat notches, which works well when the tension in the straps is right. I found the main downside to the width was the simple discomfort of planting your feet to either side of the slide in light air, when you want to have them on / in the hull rather than on the slide.

These are entirely subjective observations. It would be interesting to know if any work has been done in towing tanks or similar on seat shapes with a view to finding out how to maximise lift.

Perham
GBR 311


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