Designing to Steve Clark's proposed new rules

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Phil Stevenson
Posts: 202
Joined: Wed Sep 07, 2005 9:54 pm
Location: Australia

Post by Phil Stevenson » Sun Aug 13, 2006 11:14 pm

IC AUS 21
I am very pleased with the performance so far.

As Christian says it was very fast in the light conditions, but he borrowed Seth's boat on Sunday and in one race with a reasonable 10kt breeze (feet on gunwale at least)he stayed right with me to the top mark. But on the square the big main just ran away. In fact down some of the runs I was passing some of the cats and skiffs, maybe they were sailing angles and getting out of the streaks of wind.

The canoe seems to slide ever so easilly and stay with the gust longer than most boats would.

We had two races in sub 5kts and two in maybe 10kts. In the second light one the wind switched 180 deg and filled in a little making a work back to the finish (shortenned for everyone to one lap.) In this race I led at the mark and was beaten back to the finish by only one A cat. Since there was less than 5kts at the start I did not really get too far away with my 1min start from the middle skiffs or 2 min start from the big skiffs and cats, so for me that was the best the canoe went all weekend. I had a small lead at the mark from a F18, F16 and two As and had enough speed up wind to hold off all but one.

I expect for next year the IC yardstick will drop and we will be in the next division, but at least this may be an indication of the performance gain possible with Steves new rule boats.

On the down side, My son Andrew had a ride after the regatta and with slightly more pressure he went further out than I had and the twin tube plank/seat failed. The bottom of the tube crushed at the windward gunwale. I thought I had copied the proven Skate design but maybe I missed some internal doublers or timber cores were it goes over the gunwale. I will check with some skate people before I rebuild.

The sail is still a little full but the stiffer mast since two weeks ago is much better and the leach holds up well, at least as far out on the seat as I have been (maybe feet a foot off the gunwale.)

I will now endeavour to complete the build story with details of the rig etc and get it posted so anyone else can do something similar. It will not be a complete "how to" but rather enough info for a competant builder to understand what I did and use the shape/design and/or ideas learned.

Phil S
Design perfection is achieved, not when there is nothing else to add but when there is nothing else which can be taken away.
http://philscanoes.blogspot.com/

Mal Smith
Posts: 79
Joined: Mon Dec 20, 2004 1:42 am
Location: Australia

Post by Mal Smith » Mon Aug 14, 2006 2:18 am

Phil,

The Skate, being wider, will have lower point loading at the gunwhale. Even if the skates don't use doublers or cores in the seat tubes, you might have to. The skate planks may be just on the limit.

Mal Smith.
AUS019

sfrosh
Posts: 24
Joined: Mon Jun 13, 2005 8:42 am
Location: Australia

Post by sfrosh » Mon Aug 14, 2006 7:29 am

Phil, quite a while ago I made a guess/prediction that a relatively low tech construction 750mm wide 50kg IC could be as much as 10% quicker around a course, than the traditional all carbon Nethercott IC. In a separate posting while discussing rigs I made on opinion that the sail if concentrated in mainsail only would on balance be cheaper, easier to sail and generally quicker than main and jib.
It is still early days but you have shown a glimpse of the potential that the new direction, (i.e. the DC) could fulfill.
As far as the failure of the aluminium tubing goes, was the loading concentrated on a very small area? What was the wall thickness?
Maybe these two factors were the main culprits.

Phil Stevenson
Posts: 202
Joined: Wed Sep 07, 2005 9:54 pm
Location: Australia

Post by Phil Stevenson » Mon Aug 14, 2006 8:57 am

I used to fantasise about a 16ft long moth, but was reluctant to build one as I detest people who start new classes every few years (and we end up with too many classes and poor fleets in all of them)

The IC/DC rules allowed me to live something like that fantasy within an existing class. And I did not see any point in doing it unless it was faster than the existing boats, so while I hoped it would be fast I am delighted that so far it seems to be so.

The plank was made from two 50mm x 1.6mm wt curved tubes spaced 450mm apart and the gap filled with 50mm thick styrene foam. The lot was then coated with 100gsm glass and epoxy.

The Skate crew plank is 3m long, mine is 2.4m, so I figured the bending moment was no problem. They have some big crews too. But the skate is about 1100mm wide and my rails are maybe only 750, so the windward bearing loads are about 20% bigger than the skate. Just as Mal said.

I had a good look at the broken bits today. The plank was not even fully extended (about 150 mm short) and there was evidence of some dints in the tubes at the fully extended bearing point, so I probably went close to a failure even before I passed the bpoat over to Andrew.

One thing I changed from the skate pattern last week was to remove the rippled rubber strips from the gunwales and replace them with alloy strips. This was to allow the seat/plank to slide through much more easilly, but it also removed all softening of the bearing area and would have contibuted to the failure. I will find some wider nylon strips for next time.

I have decided to make a new plank the same way (because it is too hard to get enough carbon to make a high tech one, and I do not need to save any more weight.), but I will add some internal strength to the tubes for about 500m about the gunwale bearing area.

And while Andrew was breaking my boat I really enjoyed the ride back downwind taking
his place in the 12 under big rig and kite, something I had not done since about 1975.

Now as well as making a new plank I have to finish my foiling moth rebuild.
Design perfection is achieved, not when there is nothing else to add but when there is nothing else which can be taken away.
http://philscanoes.blogspot.com/

Steve Clark
Posts: 165
Joined: Fri Aug 01, 2003 2:26 pm

Post by Steve Clark » Mon Aug 14, 2006 12:40 pm

Broken bits on a new toy are such a drag.
I was investigating building an alloy tube seat along Skate lines, and as I had a pile of 60mmx 1.6mm 6061 t6 drawn tubes (astute observers will recognize these as Radial Lowers) Alloy numbers are different in different places, but 6061 is a pretty good alloy and they had been drawn, so by rights these should have been been stronger/stiffer than any 50mm tube with the same wall thickness.
I tested them by building a simple jig and standing on the far end. Thus duplicating the IC seat loading. It wasn't even close. The tube packed it in instantly. As two of these beauties would have been heavier than the published weight of a Skate seat, I went back to putting carbon fiber into the mold.
I guess there are things that work in Australia that don't work elsewhere or there is a lot going on inside those seats that isn't obvious from the outside. And It makes me think that the weights are understated.
It may a good idea to think about plywood skins on either side of the foam.
SHC
Beatings will continue until morale improves

Andy P
Posts: 97
Joined: Thu Sep 08, 2005 9:31 pm

Post by Andy P » Mon Aug 14, 2006 8:59 pm

Launched at last... only about 3 knots of wind today vs 30kts yesterday.
It was a bit slippery - needs more non-slip, and maybe some push foot blocks on the hull centreline.
But also slippery in the water - sailed along very nicely in very little wind. The wake off the back reminds me of a rowing scull.
It felt nicely reactive to sheeting upwind, but was quite stable downwind - nothing like a moth wobbliness in no wind.
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I will have to get used to standing up to tack and gybe, and not try to squeeze under the very low boom.
The T foil adjuster worked OK - the forefoot either out or jsut in the water, with maybe 100mm of ride-height difference at the transom.

Next sail at Ullswater, and some practice for the nationals!

Phil Stevenson
Posts: 202
Joined: Wed Sep 07, 2005 9:54 pm
Location: Australia

Post by Phil Stevenson » Mon Aug 14, 2006 10:16 pm

Andy,
It looks very good, but I see your difficulty with the low boom. How is forward visibility? You certainly got better aspect ratio than I did with your deck sweeper.
They certainly are a lot nicer to sail downwind in the light stuff than a narrow moth, but slip along at least as well as the lighter moths.

Steve,
My seat weighed 7kg but it was wider than the skate's, and I made the styrene foam full depth where they only use a 20mm PVC at half thickness. I also may have used heavier glass. So maybe they get down to 5.5kg but I doubt any lighter. That would be for the skippers 2.4m plank, not the crew's 3m one. I think your idea of ply on the botom may be good value. I have another sheet of ply and wil check what weight it will add. In any case I think I will use some internal timber or sleaves as well, at least near the windward gunwale.

Your 60mm tubes would have added almost a kg but probably because of the larger dia they were more susceptible to dinting and hence buckling. The L Radial mast gets a sleave at deck level but they still occassionally fail there too. I can get 50 x 2mm but that would also add almost a kg. I have some thinking and calculating to do before starting again.

The joys of development.
Phil S
Design perfection is achieved, not when there is nothing else to add but when there is nothing else which can be taken away.
http://philscanoes.blogspot.com/

Steve Clark
Posts: 165
Joined: Fri Aug 01, 2003 2:26 pm

Post by Steve Clark » Mon Aug 14, 2006 11:31 pm

Andy, sure looks nice. Over the years I foound the critical dimension on boom height was the distance from my heel to knee. If I can get knee under the boom with my foot on centerline everything is happy. If not, it just makes life difficult.
Phil, the problem was that the tube didn't dent or buckle because it was nicely supported in a round chock. It just bent.
And I know all about sleeves in Radial Lowers and exactly how frequently they bend...
A ply seat could be the default choice. They have been around for years and are pretty easy to construct. 3mm ply with a central rib hangs out pretty well. With a layer of Kevlar, it's pretty indestructable. I suspect that if you glued it to your EPS foam you would get an improvement in stiffness and strength that might solve the whole problem.
I think you will decide you need foot holes as well. I started out without them too.
SHC
Beatings will continue until morale improves

Phil Stevenson
Posts: 202
Joined: Wed Sep 07, 2005 9:54 pm
Location: Australia

Post by Phil Stevenson » Tue Aug 15, 2006 3:17 am

I spoke to the guy who makes the skate planks and found out they have a sleave which doubles the wall thickness over a considerable length. Their boats are are also 1.2m wide so the bearing loads are even less than I calculated.

All bad judgment on my part.

Looks like some plywood skins and timber cores in the tubes of the new one, until Carbon becomes more available at the old reasonable price.
Design perfection is achieved, not when there is nothing else to add but when there is nothing else which can be taken away.
http://philscanoes.blogspot.com/

Geoff Harman
Posts: 19
Joined: Sat Apr 29, 2006 9:58 am
Location: Australia

Post by Geoff Harman » Tue Aug 15, 2006 10:34 am

Phil - two 50 dia x 1.6 wall Al tubes rigidly tied together so load is taken equally by both will in the case of 750mm beam canoe have a deflection of 207mm and a stress of 246MPa assuming you weigh 80kg and are hiking with your bum over the end.
Design tensile stress of 6063 T5 al is 110Mpa. This will increase to 248 MPa if the tube is drawn.
Inserting secondary tubes of similar wall thickness will give 136Mpa and 115mm deflection - still too much.
For the Skate at 1200mm beam the stress is 101MPa and deflection is 63mm assuming the same load.
Using 60mm dia x 1.6mm wall 6061 T6, same load and beam, results in a stress of 167MPa and deflection of 114mm. Minimum design stress for this alloy is 240 MPa. While this appears to be o.k. local denting from the outboard support will result in the failure experienced by Steve.
I suspect there is quite a bit of UD glass in the Skate planks.
Geoff Harman

Phil Stevenson
Posts: 202
Joined: Wed Sep 07, 2005 9:54 pm
Location: Australia

Post by Phil Stevenson » Tue Aug 15, 2006 11:52 am

Geoff,
Thanks for the analysis I was too slack to do myself.

The skates are 1350 wide not 1200 as I said, so their numbers might just come out right. Max said they only have the sleaves but prefer to use drawn tube which is higher strength. The combined stresses at the gunwale plus G effects from waves would certainly increase stresses above your calculated BM figures.

I am going to see if I can get 50mm x 2mm wt square hollows which will have double the MoI of 50 x 3 round and also be more resistant to denting. Increase in weight would be about 1.5kg over the failed unit. Might also benefit from Steve's ply suggestion.

My analytical engineering skills are pretty rusty from little use lately, even these simple calcs were too much hassle, but I suffer as a consequence.
Design perfection is achieved, not when there is nothing else to add but when there is nothing else which can be taken away.
http://philscanoes.blogspot.com/

Paul Scott
Posts: 78
Joined: Sat Jan 31, 2004 5:56 am
Location: USA

Post by Paul Scott » Tue Aug 15, 2006 5:35 pm

These DIC's (that's a really terrible acronym, isn't it? How about D/IC's? Or ICD's?)look really great! Kudos, all!

Paul
"Exuberance is better than good taste" -Flaubert

Andy P
Posts: 97
Joined: Thu Sep 08, 2005 9:31 pm

Post by Andy P » Tue Aug 15, 2006 8:29 pm

My carbon/foam seat finished at 8.5 kg.

Strong enough so far ( ie with me sitting on the seat with feet on the gunwales ) which is not very far out yet.

The sail looks tall and narrow (ish ) but is only 10 sq m ( max 10.6 allowed ) - Definitely the low drag efficiency thing!

Maybe I should have gone for the more conventional dinghy boom, with a long foot and clearance to duck under, but the rest of the IC seem to manage OK stepping behind the sail with the mainsheet behind the seat.

Phil Stevenson
Posts: 202
Joined: Wed Sep 07, 2005 9:54 pm
Location: Australia

Post by Phil Stevenson » Wed Aug 16, 2006 4:20 am

I decided to make the boom high enough for a conventional boom vang, and also so I could sail it much the same as sailing my moth, hence less to learn. This made the luff shorter and hence the boom longer, so I had no chance of ducking round the back. But it does make the sail look very low aspect. Getting under on the tacks has not been a problem yet.

Plank reconstruction is in the design options phase. I did my own calculations and agree with Geoff. Based on load at time of failure (about 75% of full power)the hardening from pre bending of the tubes may have increased yield to about 115 mPa.

From what is readilly available I have to see if 60x 2mm tube will fit under the rail, otherwise 50.8 x 1.8 squ with something inside. The end weight should be just under 10kg, which is starting to look too chunky. I will have to start sourcing some carbon for a high tech #3.
Design perfection is achieved, not when there is nothing else to add but when there is nothing else which can be taken away.
http://philscanoes.blogspot.com/

sfrosh
Posts: 24
Joined: Mon Jun 13, 2005 8:42 am
Location: Australia

Post by sfrosh » Wed Aug 16, 2006 5:58 am

Phil, back when I was sailing Skates a long time back, we built the 10 ft. crew plank from one layer of ply with foot cutouts about 6 mm 5 ply I think, with red cedar square section timber beams laminated top and bottom on each side. It held the curve well with little deflection when sat on. Uni carbon 25mm tape is still easy to get, and although we didnt use it then it should work nicely on the upper surface of the cedar to improve stiffness. I realize that Skates have moved on from this method of construction but these planks were not all that heavy, and I never broke one, nor anyone I knew.
If nothing else at least it is a bit of history.:)

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