Designing to Steve Clark's proposed new rules

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Phil Stevenson
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Post by Phil Stevenson » Thu Oct 27, 2005 10:15 pm

While the IC class stalwarts and administration consider what direction they wish to take, and consequently whether, or when, they will change their rules, it is obvious from many postings on the relevant threads that there are quite a few people already thinking up design ideas around the rules proposed by Steve Clark.

If we keep all these ideas together on this thread and separate the If/why/when discussion from the what would I build qestions, then the consequent discussion might lead to some very interesting boats even if the IC movement do not in the end participate.

So why not post design ideas here and leave the other threads to their orginal subjects
Design perfection is achieved, not when there is nothing else to add but when there is nothing else which can be taken away.

Phil Stevenson
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Post by Phil Stevenson » Thu Oct 27, 2005 10:28 pm

Here is some of the design discussion so far copied from other threads :
Jim C 27 September
They (the proposed rules)don't look too bad, coming from Cherubs, which in the UK are notorious for fiddling with rules. The challenge you've got with any "box" rule is establishing a satisfactory balance.

On the one hand, if the rule is too tight, then you can end up with a boat that is frustrating to design, because the rules are forcing you to a shape that you would otherwise avoid. This is why the proposal to "float" the rise of floor measurement along the hull length is such a good idea.

On the other hand, if the rules are too loose, then you have problems with the boats maybe becoming too tricky to sail or so disparate in shape and size that the race is over before the start - you know Fred will win if its light and Sarah will win if its breezy.

So the rule set needs to define the general shape and size of boat, and it needs to give a reasonable balance between performance and ease of sailing.

The sail area and max seat length define the major parameters of power etc. Modest sail area is IMHO a GOOD THING - much more interesting to have a boat that gains its performance from elegeant design than brute force.

Things like requiring a seat, the pointy stern and so on ensure that what we are building is a Sailing Canoe with that tremendous history.
The rise of floor rule is to ensure a reasonable compromise between speed and stability.

There's one thing in the rule set I'm a little unsure of. I'm thinking that there might be advantages in not requiring the "line of greatest beam" to be a fair and continous curve, because it might be easier to organise support for shrouds if the topsides could flare out locally. Where I m I haven't got a graphics program handy, but this might give the idea of what I'm talking about.

Basically I think it would be a pity if the rule set forced you to goto an unstayed rig.

But on the whole I reckon that rule set is a pretty good compromise and should make for interesting and fun boats.

Andy P 27 September
The torsional loads on the hull are exactly the same for unstayed rigs and rigs with shrouds. The biggest difference between unstayed and unstayed is the huge point loads on the hull caused by tension ( shrouds ) and compression ( mast ) loads from a stayed rig. These loads increase as the hull gets narrower. The hull is actually loaded less with unstayed rig - but the rig is consequently a bit more wobbly. - is this slow or fast? ( good or bad ? )

I have considered deck level spreaders ( like open 60 ) to allow shrouds , low rig tension on a stayed mast, but this is contrary to the rule of 'no outriggers', and also a safety hazard!

Wing bumps as Jim suggests might help the mast support, but might be very slow ( and ugly ) in waves, also adding rule complication.

The moth type wings are very efficient in structure - low shroud tension, lots of support, but at ~ 1800mm shroud base, also triangulated at ~ 700mm above keel.
The IC however is a narrow / no wing / seat device, and the intention is to keep it distinct from moths and other winged things ?

I would agree that you need a balance between narrowness of hullform that might need unstayed rig, and a wider hull ( ie at present beam ) that can use shrouds. - You take your choice.


Karl W 28 September

Steve -I'll ask George or Bill but it seems to me you're shortening the shroud leverarm by about 5", or 25% from the current 39" beam (let's call it 40 to simplify calculations). Since the seat length is the same, the max torque load stays the same on the whole program (unless you eat lots of bacon). So for a 70kg sailor, the max static torque put on the hull by the sailor on the end of the seat is is 1461 Nm, if we take the leverarm at 7ft, or 2.13m (belly button fully hiked). Dynamically it's more than this, but proportionately the increase stays the same whatever figure you use for the seat length/sailor wt. The shroud has the job of counteracting this torque with whatever leverarm you give it. Since torque - Force x leverarm, if max torque remains constant (sailor on end of seat defines upper limit) but leverarm (on shroud plate) goes down by a factor of .25, then force on shroud goes up by .25. The actual numbers are a bit different, but when I assume the current leverarm for the shroud plate is 20" from centerline, and the new boat has 15", the load on the new shroud is 25% greater. In my example the static shroud load goes up from 2864N to 3844N, or the equivalent of 292kg to 392kg. Mast step load goes up similarly. Shouldn't be a problem to build to this, but it does dial in 100kg more load on the mast in compression, so mast/step/shroud/chainplate all have to be up to spec.The Moth plan appeals to me, even if the chainplates are over the water, because it greatly reduces the compression in the mast, allowing for lighter masts. Deck-stepped spreaders are a similar idea. Sure they can get caught on things and it's not streamlined, but either setup would allow us to directly transplant existing rigs into new boats by giving them a similar staying base, which is probably desirable.I don't know much about computing torsional loading on hulls, but intuitively it would seem to also follow a rule of linear increase with decreasing diameter. What this means in terms of extra laminate I have no idea.

Jim C 28 Sep

As a clarification With the curve of the point of max beam, do you intend that to be a single convex curve from bow to stern, or could it be a complex curve. If you allow a complex curve with the ability to be concave in places you can draw a hull that flares out above the measurement point at shrouds (and seat, presumably a bit extra width at the seat anchorage does no harm either) but still has a slim foredeck at the bow for getting through waves.

Excuse the abysmal "sketches", I'm away from home and only have mspaint available.

Andy P 29 September
It might be better if the existing rigs and rig technology could be directly transplanted from the existing boats - to do this, the beam at the shrouds has to be the same as before. The advantage of new boats would be reducing the deck level beam fwd - this then would need mini flares/wings as Jim's sketch, to keep the styaing base the same.
So instead of the projection being a convex curve, this could read - continuous curve, and with a max beam of the existing ( 1m ish ).
This would then mean that you could have a narrow bow, but still get the spreader support for conventional masts with mini flares, and avoiding moth-type wings etc.

If the flares are at high level ( ie the top of the foredeck at max 560mm above keel), then the hullform could still be wavepiercing type.

Steve Clarke 27 Oct:
Arne and others:
I have been noodling away here on canoe designs under this proposal.
I have been looking at two threads, one is as quick and easy to build as I can make it and still have some elegance.
It is based on the very successful "Lust Puppet" designed by Bill Beaver but has some small changes to make it better under the new rule and look a bit different.
Seems to involve some 3mm plywood and a gig made up of cheap ply and some PVC pipe.
I realize that people will feel they need some guidance before setting off on a new hull shape, but there are simpler options than the Nethercott hull that will most likely be faster.
The second thing I am looking at is the more elegant design whichwill certainly involve a mold or two. Sometiomes I cant help myself.
I could probably get close to sticking some images up on this site, but Neil has to tell me what he can do, If not I can send DXF files to anyone who wants a gander.

Phil S 3 Oct
If you need deck width with narrow waterlines and no hollows look at the modern 12 ft skiff hull shape on
You could easilly stretch and push this shape and cut the back corners off to make a valid canoe complying to Steves proposed rules. The high sloping sides make these boats anazingly forgiving considering the rig size they carry. Remember until the last few years these were not even self draining boats, so the extra depth is probably not needed now

Phil S 26 Oct
Here is another option.

This article shows how to build a stressed ply moth. Several have been built from this article all around the world and have proven a cheap intoduction to the class. The fat version was not a very quick moth but shows how simply a hull can be formed, and has some potential for development and enlargment to make a valid Canoe to the proposed new rule.

Look at: and ... f_moth.pdf

Materials and paint for a moth hull is much less than $A500, so a Canoe sized version should not exceed $A1000

If the IC class decides to change the rule to allow it, I intend to make such a hull and then to provide a similar article for other potential IC builders.

There can be a lot of experiments in hull shape with cheap boats before anyone needs to build expensive molds.

Mal Smith 27 Oct
I've also been working on a design to suit the new rule. It is also a simlpe low cost plywood hull. The philosphy for this one is that it is a stitch and glue self jigging structure, also in 3mm ply, using closely spaced but lightweight frames (interlocking egg crate construction) to achieve panel stiffness. The panels will be fully developed and the parts could all be laser cut as an option. I've only done the (preliminary) bare hull shape at the moment as there is a fair bit of work in detailing the parts and I won't do that unless the rule change goes through. I could also post drawings of the hull shape if there is somewhere suitable on this site, or I could email PDF's or other formats to interested persons. One question, I'm designing for an all up weight of around 140kg (rigged boat plus helmsman). Does that sound fair?

Mal Smith
Design perfection is achieved, not when there is nothing else to add but when there is nothing else which can be taken away.

Karl Wittnebel
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Post by Karl Wittnebel » Fri Oct 28, 2005 3:46 pm


The Skate seats seem very cool, and I'd like to know how they wrap them.

The Skate seat carriages are also cool, as they are simple rails on the gunwales. While this works well on a skate, it seems that it would be more of a finger guillotine on an IC. The IC is a fair bit skinnier than a Skate, and when you grab the seat in a tack, you have less throw before you get to the gunwale. If there is a nice aluminim bar waiting for your fingers there, they will find a way to get under it. Fingers are funny that way. Maybe there is a way around this, but I'll let others conduct the on-the-water research.

Was talking to Rod Mincher the other day and he mentioned that as long as we're thinking about changing the hull shape, why not lengthen the hull? After all, waterline is king in displacement mode. I rather like the idea of an 18 or 19' canoe. Would make the reverse bow more practical, make the boat faster in light air, less prone to nosediving - many virtues. Just putting the idea out there.

Mal - 140kg seems a bit heavy, but then I am only 70kg. 90kg sailors would probably think your figure is perfect.

I was out in LP last week and got my ass handed to me. Sure, it was the puffy Chesapeake Northwesterly, but still. I would recommend against skinny v-shaped sterns, whatever people do with the rest of the hull. Having said that, the boat is pretty fast all around considering it is twenty year-old plywood.

Steve if you send me some image files I will post them in the gallery on the US website.

Karl Wittnebel
NC USA 193 (Lust Puppet)

Steve Clark
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Post by Steve Clark » Fri Oct 28, 2005 9:06 pm

Yes Please don't put anything solid cross the top of the heel holes.
This was how it was done in the bad old days and there is a story of a German kid damn near bleeding to death after his heels had been cut off on an unexpected ride under the boom.
Chris Converse had such a bar on his first IC. He referred to it as the Veggie-matic in honor of the famous RonCo product. He used to tear beer cans in half as a demonstration followed by the classic "Isn't that amazing!"
But even before you get body parts involved, sheets and other stuff gets in there and jamb up the system.
Yes, Please don't do it.
Your old freind in canoing.
Uncle Boat
Beatings will continue until morale improves

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Post by jimc » Fri Oct 28, 2005 9:58 pm

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Karl Wittnebel</i>
why not lengthen the hull? <hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
A practical objection is that the boat would be to long to be able to do maintenance in the average european single garage. A philosophical one is that the length is as much part of the IC history as the fact that its canoe shaped. [Even as a class newcomer] I like the idea of returning to the pre one design rules with the tweak on weight much better than the idea of starting a whole new class.

Aprt from anything else, if we keep to basically the rule the Nethercott was designed to then the Nethwercotts will stay reasonably competitive for a good while - maybe a very long while if no-one manages a major improvement quickly. If we change the fundamental dimensions completely we'll never know if we've actually got something better...

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Christian AUS
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Post by Christian AUS » Thu Nov 10, 2005 9:09 pm

Four designs to the proposed rule, with designers descriptions, can be found at http://www.internationalcanoe.yachting. ... F13267%2F0
Good work, there are some very interesting concepts starting to appear (interestingly, 3 designs from Australia).

Now which designs will make the transition from paper to sailable hull?

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Post by RLM » Fri Nov 11, 2005 3:17 am

I sat down with Steve and Kim Clark at breakfast at Paul and Dawn Millers over the past weekend (thanks Dawn for the eggs and sausage!) in the typical stream of consciousness conversations I have with Steve. This time it covered IC design, quick building in ply, canting keels and patent litigation, and kids as they go off to college (and some other topics now lost to memory). I have been loath to post anything as I haven't been active in the IC's for several years now but Steve urged me to put a word in. Steve knows I have always pushed for an open rule in the IC hulls every since I got into the IC in the early 80's. I was the one to get the hull lines for Rossell's Slurp from Alan Hassell, that was drawn up by Bob Ames and then modified by Bill Beaver into Lust Puppet. I had Bob Ames draw up an Ames 1 design of which John Williamson built two and Bill Beaver and I worked on the pushed tolerance Nethercott - NoGo55. The only other person playing with IC design in the US at that time was Ted Causey; who came up with some interesting plywood designs not unlike some of the ones being drawn up now. To me the essence of the IC is a low horsepower, easily driven hull with loads of righting moment from the sliding seat - not the current skiff model of high downwind horsepower driven by racks on wider hulls. So I applaud Steve's effort to take a fresh look at the IC hull within the current constraints of rig and righting moment. As the class goes into the experiment phase, I think it would be good to have one hull built to a longer length - say 18'6" to see how it stacks up. I don't see why length should be off limits in this initial testing phase. For Jim Champ, the IC rule that Uffa and Douglas et al hammered out in the 1930's came from the B canoe class sailing divisions of both countries (both had different rules). If memory serves, the English B rule allowed canoes up to 20'. I don't think 17' was the maximum length allowed (just as the American 16X30 sailing canoes were not designed to the max length allowed by the B American rule). Ben Fuller may illuminate us on this if I have got my facts wrong.

Rod Mincher

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Christian AUS
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Post by Christian AUS » Fri Nov 11, 2005 5:05 am

I think the length gives us a box to work within, so I'm against mucking around with that aswell. Besides, I'd have to modify my trailer if we made the boats longer!

Paul Scott
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Post by Paul Scott » Fri Nov 11, 2005 2:57 pm

As long as you're tossing length around, I'd like to toss in the idea of an outer dimension box rule-something impressively wide, but still aesthetic, no moth style wings, no traps, with no inner box. I was messing around w/ design the other day, and using a light A cat hull, you could use a KEEL to get the thing up to the minimum weight! This what happens when one has actually read Ulysses, and reads the phrase "stream of conciousness". Now I'll have to shave..around a the a.m...or something....
"Exuberance is better than good taste" -Flaubert

Steve Clark
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Post by Steve Clark » Sun Nov 13, 2005 4:21 pm

MAx beam is set at 1070mm ( 42") which is quite wide. When you actually see a max beam boat ( Whitman Pheonix) you wonder why it is so fat. Even though it might nbe min beam at the WL.
In drafting the rules, I didn't start with a fresh sheet of paper and didn't include all options, buty chose to stay fairly close to the limits of the 1934 rules and onlr vary where current best practices indicated they were way out of date. This means basicly reducing the all up weight to a modern level and revising the beam measurement to reflect the lessons learned by other classes.
Beatings will continue until morale improves

Mal Smith
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Post by Mal Smith » Mon Nov 14, 2005 1:35 am

I have put up another design at http://www.internationalcanoe.yachting. ... ts/13267/0 which I called “Crazy Diamond”. If you have a look at it, you will see that what I have done is to move the beam measurement station as far aft as is allowed. For a hullform such as this one which has a flat run aft, the effect of moving the measurement station aft is that the measurement points are raised relative to what they would be if the measurement station was at midships. The result is that the waterline can be significantly narrower, and at the centre of bouyancy (where it matters most for stability), the waterline is narrower still. The boat also has a very fine wave piercing bow.

I produced this hull as an attempt to see what extremes the rule could be taken too. One question raised is, is this an acceptable hullform, aesthetically, and in degree of difficulty to sail? Another question I have is, whereas the plan shape of this hull is basically two straight lines from bow and stern meeting at a radiused point at the measurement station, how small could the radius be and still measure in as a “fair continuous curve”.

Mal Smith.

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Post by Andy P » Mon Nov 14, 2005 1:46 pm

re the 'Crazy Diamond' -

I have seen many wacky extreme moth designs ( including some of my own ) , and it appears that the 'nice' hull shapes that are more evenly curved and balanced are faster and have less handling vices. The extreme designs sometimes show better speed, but in very limited circumstances, and tend to be pigs to sail!

So I don't think the rule needs changing - you could make the diamond design if you want.... but I wouldn't advise it!

The rule was drawn up so that the nasty bumps at the measurement point would be avoided, with the beam narrow enough, and the position so far aft that no-one would actually want to bump the hull. ( because bumps are slow, unless you are fighting a too restrictive rule )

The latest rule proposal says only 'continuous curve '

My design also has the beam measurement at about the furthest aft possible, but is much more even curve.

My latest design has the deck moulded on the hull mould, with the aft section split and flipped to give the concave section behind the seat. The foredeck back to the seat would be symmetrical to the underside. This means no deck mould needed, and also the hull/deck joint can be engineered simply, light and strong.

Andy P - K 176

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Post by Emo » Thu Nov 17, 2005 5:58 am

Has it struck anyone yet that the minimum beam is too narrow for the conventional rig to work? Also, should a stayless rig be adopted, the torsional loadings on the hull would twist it apart evetually (even if the hulls are nomex/pre-preg carbon).

There is a good reason why the early skates were narrower than the modern ones: while the old 'coffin' boats would get to the top mark quicker, they'd start sinking shortly after rounding as the rig literally twisted the hulls apart, which led to the wider, stronger hulls overtaking the swamped narrow boats and winning. When a wider hull was adopted, they went quicker off the wind and more importantly held together in one piece for more than one leg.

So, why again are you folk considering going from a well proven, aesthetically pleasing, incredibly fast hull that can be sailed by more than olympic-level athletes (basically anyone who has 10 years sailing experience should be able to sail a current IC and maybe even an AC) to something that will simply be a longer cousin of a skiff moth, that will basically make the existing hulls obsolete overnight? I think that move sounds like a practical example of the Chubaca theory: "It does not make any sense!".

Although skates and canoes aren't directly related, it may be possbile to use some of the hard-learnt lessons from other classes (which in the skates case turns out to be quite a few, as the class in around 50 years old!).

Still, I have done a quick Maxsurf design of a potential hull; it would probably carry a stayless carbon aerofoil section mast (the base/step would be round, but the rest of the mast would be faired into an aerofoil section) and either a forestay supporting the self-tacking jib or an inclined secondary stayless mast with a pocket luff jib, similar to an access 303 or liberty. Hull length on maximum, beam 820mm, BWL 800mm. When the renders and done I'll send 'em off to the aus webmaster with some comments etc.

(don't have an IC, but wouldn't mind getting one!!)
Is the glass 1/2 full or 1/2 empty? I don't care as long as I'm drunk!

Mike Rowe
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Post by Mike Rowe » Thu Nov 17, 2005 7:35 am

I don't believe anybody has yet done any valid calculations on rig loading on the narrower hull shape. These need to take into account dynamic loading through waves, and make allowances for shroud stretch, hull twist and mast compression and twist. The possibility that the whole lot will buckle and collapse in use is real, especially with less exotic hull construction materials that some propose.

I'd recommend that somebody tests the integrity of the rig on a narrower hull by:

1. Detaching the shrouds from the hull on an existing IC.

2. Fitting a solid bar between the shroud points.

3. Re-attaching the shrouds to a take-off point on the bar at an appropriate distance from the hull centreline.

The test is not completely valid because one might expect more twist from a narrower hull, especially if ply stitch and glue, but it will go some way towards proving the rig is viable.


PS It is issues like this which reinforce the belief in the UK that we need to do some trials before moving into the unknown by changing the rules.

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Post by GBR242 » Thu Nov 17, 2005 10:28 am

Strange that...

In my part of the UK, we believe that a 'development' class means designing a boat that gets the best possible performance out of a given set of rules.

That is the fun of it!

If for any reason at all, the proposed new rules allow a boat that is slower or less effective at winning races than what is currently available......then the old designs will continue to win.

If this is so, then there is no problem with obsolesence of old they will still be winning!

Strangely enough, as others have mentioned....I think it will take a year or so for the new designs to catch up and learn how to make the most of the new (sorry original pre-1970s) rule. This can only lead to a more exciting racing experience during the change over period when lightweight nethercots (and skinny nethercots) remain competative.

The idea of the game is to design and build a boat that is fast enough to win, easy enough to sail and reliable enough to continue racing.

If you think that boat is a nethercot.....then race one!

If you want to experiment to try and find out how to produce a skinny boat that is 'fast', 'sailable' and 'reliable'.....then design and build one.

In the end it seems to me to come down to a simple decision...

Do we want the IC to be a Development Class or do we want it to become a 'one-design' like the AC?

From where I come from in the UK....we want the opportunity to be part of the proud history of the IC as a development class.

ed Bremner

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