Designing to Steve Clark's proposed new rules

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Phil Stevenson
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Post by Phil Stevenson » Thu Jun 01, 2006 10:35 pm

For those IC sailors who were fearfull the new narrow boats would be too Moth like, this photo of a moth hull inside the DC hull should put that opinion in perspective.Image
(I hope this link works out)
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/

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

Post by Phil Stevenson » Thu Jun 01, 2006 10:36 pm

Sorry link failed. The photos are on:
http://au.pg.photos.yahoo.com/ph/philst ... pg&.src=ph
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/

Karl Wittnebel
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Post by Karl Wittnebel » Fri Jun 02, 2006 3:31 am

Hi Phil -

The arced foredecks on current ICs never were very efficient at shedding water. In that sense, a higher, skinnier foredeck is probably much better. But you also have to tack the thing, and if there is too much freeboard up there it tends to get blown off the wind a bit. So a powerful rudder would seem like a good idea.

I will follow your seat building with interest. I always wondered how those ally skate seats were put together and how much they weighed. There are some photos of Andy Paterson's carbon/foam seat on http://www.intcanoe.us if you haven't seen them - he put it together with one-sided carbon/foam panels then bagged the second layer of carbon over the outside when assembled. Neat trick I thought. 7kg - similar to what moulded seats in our fleet weigh.

I think you could easily get an article about your boat published in Wooden Boat magazine or Messing About In Boats - both popular up here. An article about the Swift Solo in Wooden Boat was largely responsible for the take-off in its popularity among home builders - that and a good set of plans and support.

Rgds,
Karl
Karl Wittnebel
NC USA 193 (Lust Puppet)

Phil Stevenson
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Post by Phil Stevenson » Fri Jun 02, 2006 9:08 am

Karl,
Today I cut down the freeboard at the stern by 50mm so I could get the required dish in the aft deck without it draining forward.

I anticipate the cat rig will make tacking more like a moth than a sloop rigged IC so I already have a more moth sized rudder, maybe twice IC size.

Andy has told me there is a lot more in his seat that what appears in the photos.

I am copying a lot of what our local skate sailors are using because I see them every saturday and can see what works, while I only see a couple of ICs occasionally.

The skate plank is two 50mm x 1.6 wt tubes bent to the right curve, separated by some foam and coated in glass cloth. Simple and cheap, they seem to be light but I have not weighed one. Theirs are 3m for the crew and and 2.5m for the skipper, mine will be about 2.4 to reach the lee gunwale.

They do not use a carriage but run the plank under a 25x3mm alloy tube along each gunwale. There is rippled rubber on top of the gunwale to prevent it sliding aft and a small stop on the top at the leeward end to prevent it sliding to leeward. It works for them but if it fails for me, I will make a carriage to run on the two 25mm tubes which will be installed parallel.

More photos on my Yahoo reference.
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/

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

Post by Phil Stevenson » Sat Jun 10, 2006 4:55 am

Some progress this week after some backward steps.

Last weekend I fitted bulkheads and then checked the 750 x 100mm rule chine width. It failed so I had to remove the bulkheads and make some adjustments to the hull. Now back on target and legal shape.

More photos on my Yahoo site soon.
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/

Roland Whitehead
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Location: United Kingdom

Post by Roland Whitehead » Sun Jun 11, 2006 3:23 pm

How I see the development canoe
(or why I am building one)

The IC is the best single-handed dinghy that I have ever sailed. I may not have been that fast in the older boats that I had when I was last sailing ICs but I did get enormous fun out of it. Those that know me, also know that I really enjoy sailing a boat that I have designed or been involved in the design process - from large race yachts down to the impossibly small (for me - I wasn't a 12 year old!) ply "PDQ" skiff.

I have reached a point in time where my family are fed up with my complaints of no action afloat and want to spend some time on the beach watching me enjoy myself. So I have been casting around for something to do. I cruised to the IC site thinking that this might be the way forward and was most excited to see the concept of the development canoe. Here was something that could give me the best of all worlds.

The big problem with IC sailing in the UK has been the emergence of the IC. Yes, I know its fun popping a big kite and blasting down-hill (you should try handing on to an 80 sq m kite, sat 8 m away from the windward hull on a ladder on a 6.5 m Worrell cat if you want to really try asymmetric sailing!) but sail area is not the answer to everything. Besides, its a "10 sq m International Canoe", not a "10 sq m plus-a-whole-lot-extra-for-going-down-hill International Canoe".

10 sq m of sail is a recognized sail size. In the early '80's I was involved in a project to try to beat Doug Pattison's Force 8 10 sq m trifoiler's speed record at 28 knots before the sailboards rather blitzed the whole idea. 10 sq m was an IYRU recognized class - one rule: 10 sq m of sail. If you could get 28 knots sat on a canoe then you'd be really happy!

I'm not suggesting that anyone will get 28 knots from a canoe of any sort - 17 or 18 knots is going to be pretty much the fasted you will get - but the purity of the concept is what appeals. Driving down the hull weight so as to maximise the effect of the crew weight, slimming the hull limited by the point where the beast can actually be sailed and adding the most efficient rig will help. The DC should be faster than an IC on all points of sailing - my estimations suggest anything between 4 and 8%. Upwind and on a reach it should be capable of mauling an AC; downwind will be more of a question of angles and skill as the A class cats with spinnakers in Germany haven't shown themselves to be remarkably faster than those without.

I am rather concerned about the stability issues. Already we have seen two different approaches: the IC derived route from Steve Clark keeping the max beam running as far aft as possible and the Moth derived pin-tail route from Andy Patterson and Phil Stevenson. Its not the stability when moving that is of concern - as we know, IC's don't usually fall over when sailing in a steady state - its during manoeuvers that stability becomes important. Its not much use going fast in straight lines if you fall over at every corner. Unlike a Moth where the helm can simply jump from side to side on those nice wide bouncy mattresses of wings, the IC sailor has to manoeuver around the back of the boom and slide the seat across before moving their own weight out to the other size. As such, the static GZ* of the hull comes into play and keeping volume wide is the best way of maximising the GZ at low angles of heel.

I'm also concerned about dynamic lift from the bow. Steve and Andy have gone very narrow forward but whilst Andy and Phil have kept bow height to prevent the nose dive, Steve has gone for diminishing bow volume as the nose is immersed in the hope that he will go through the waves rather than over them. Both are, I think, banging the corners on the design. Andy and Phil are hoping that a T rudder will keep them out of trouble and I think that Steve will be going down that route too. Andy's extremely flat bottom will help the boat move fast in a flat steady state but once again he will be requiring that T foil to compensate for lack of rocker. A bit more rocker will accentuate the helm's fore and aft positioning and will make the boat a little more of an all-rounder.

So which approach am I taking? I'm sticking to the 10 sq m bit - no kite - and thus chosing the DC route. I'm following the IC derived route of keeping max beam as far aft as I can (that 45 degree rule will be being tested so I'd better be checking that the wife's square in her furniture workshop where construction will be taking place is actually square!). I'll also be able to run the seat carriage a long way back. I have a hard chine running from amidships to keep that static stability high. I'm having moderate flair in the bow low down plus tumblehome (which I don't think I've seen on a racing monohull since the last time that we wapped "Smiffy" in the half-ton cup trials in 1984 - half a life ago). I'll have an ordinary IC rudder (no suface piercing so less wetted surface to counter ther greater area of the wide stern) and an ordinary daggerboard. I'm sharing rigs with Andy so you can wait for his to emerge first, suffice to say that there won't be a jib and will look like a Moth sail on steroids. My rig will be set further back than Andy's (ie more waterplane area forward so more moment to help counter the nose down forces from the sail) but far enough forward so as to give me a moderate dance floor during tacks and gybes. I won't have Andy's little struts for the shrouds as I think that the width of the hull at the chainplates will suffice.

When is this happening? Well from now on. I haven't cut any wood (it'll be ply with carbon wrap) and I don't have much time (hence the aim of the design is to build as quick as possible. I'll be building over the summer and hope to be afloat in the autumn. Where? Hopefully Hayling - I'll be looking for someone to get me past the club's massive waiting list. Then it should be noted that I have some unfinished business at McCrae from 1987...


Roland

* For those wondering what the hell GZ is, its all about the hull's righting moment at different angles of heel. The higher the GZ is at any angle, the more the hull wants to return to upright. At some angle of heel the GZ hits zero and over you go... <http://www.sailbuyersguide.com/articles ... ZCurve.cfm>


Image

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(Note that some distortion is shown in these images thanks to the panel design tools that I've been using and that some of the chines and the stem profile will be rather softened in build...)<b></b>

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

Post by Phil Stevenson » Mon Jun 12, 2006 7:02 am

Nice to see #4 DC starting construction.

Talking of mast and seat positions, I would be interested to compare notes.
My mast is 1.5m from the bow and will be quite well raked. The seat can go from 2.7 to 3.8m from bow, although it can slew further aft if I retain the Skate type rail system in place of carriage.

Not intending to use a T foil rudder at this stage but we will see ahat is needed.

More photos added today to http://au.pg.photos.yahoo.com/ph/philst ... r=/64b6scd
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/

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

Post by Andy P » Tue Jun 13, 2006 8:43 pm

my dimensions from bow
to mast about 1500mm
to mid of board about 2500mm ( with tip of mast about here too )
to mid of seat ( fixed position ) about 3500mm

Dunno about GZ, but i do know that it is zero at any angle on a moth, zero at about 5 degrees on a cherub, so I would guess similar ( ie not very stable at all ) on my IC/DC.

Interesting that the 2 boats built by moth sailors are simlilar pintails, and the other 2 by people who know more about ICs are more like 'proper' boats but with a Vee transom.

sfrosh
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Post by sfrosh » Thu Jun 15, 2006 9:06 am

Hi Phil, I enjoyed looking at the construction in progress, photos on Yahoo. With the mast stub rigidly attached into the hull, and bearing in mind that this is a new design, is there any way to change the balance of the helm, or are you fairly confident of the relative positions of CE and CLR being fairly close.
Sam :)

Phil Stevenson
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Post by Phil Stevenson » Thu Jun 15, 2006 12:19 pm

Sam,
I am hoping it is right, because it will be a major rebuild to change later. Relative locations are based on Christians table of sloop rig'ged nethercotts and a stack of moth dimensions all adjusted by various fudge factors. There is also the benefit of the rudder being a long way aft to moderate any helm dicrepancy.

You can not tack a moth in any reasonable breaze until you learn to dip the new windward wing. They steer on heal at low speed rather than by rudder. Even when going the helm does not go neutral until they are healing to windward. I suspect the cat rigged narrow canoe will be similar.

I should get the decks on in the next few days.
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/

jimc
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Post by jimc » Thu Jun 15, 2006 4:32 pm

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by sfrosh</i>
is there any way to change the balance of the helm, or are you fairly confident of the relative positions of CE and CLR being fairly close.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

On previous boats I've had them set up so some of the side load is on the rudder. I've found that this means the boat is an awful lot less sensitive to rake etc for balance than it used to be - the difference between 80/20 db and rudder and 70/30 isn't that critical for performance. It does mandate a larger rudder and a smaller daggerboard of course.

How are most Canoes set up? Can you sail them with the rudder removed or is in essential to to have it in there to keep the boat tracking. That's the easy way of telling whether the rudder is contributing side force. On the one hand I'd expect the balanced rudders to be good for that, on the other hand they're quite small.

Karl Wittnebel
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Post by Karl Wittnebel » Fri Jun 16, 2006 8:16 pm

In current IC rig configuration the rudder is highly loaded going upwind. I have sheared two of them off for structural reasons and the boat is unsailable - rounds up immediately and capsizes. So it is generating a fair amount of lift back there. Some people seem to think this is a better idea than others; distances from DB to back of mast vary quite a bit.
Karl Wittnebel
NC USA 193 (Lust Puppet)

Roland Whitehead
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Post by Roland Whitehead » Mon Jun 19, 2006 11:49 am

If IC rudders are being loaded to balance the boat, how come they haven't increased in aspect ratio? If they increase in aspect ratio to cover the load more efficiently then they will decrease in chord which then increases both the Reynold's no and the Froude No of the foil to the point where things become interesting (ie at high speed, low angles, you need a different section and chord distribution to low speed manoevering). In addition the shaft will need beefing up and therefore the weight could go up. IMHO I would suggest that the way to lower drag is to try to balance the boat so that there is as little load on the rudder as possible (OK some load is a good idea because we all hate sailing with leehelm) and to put the load on the daggerboard. It does surprise me that people rarely build in flexibility in foil position as this is a fairly basic way to gain performance. Instead everyone relies upon rig rake variation which itself can cause issues with performance.... I guess that this is why race boat design is still an art and not a science - even in the America's Cup arena foils are often moving back and forth because it genuinely is very difficult to get that optimum balance. I'm building in some fore-and-aft movement...!

Steve Clark
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Post by Steve Clark » Mon Jun 19, 2006 5:32 pm

Well, when Oliver broke the shaft in RedShifts rudder, he sailed 4 miles upwind in force 4-5 with the rudder blade stuffed in the slot and sort of held in place with a bungee. Not that this wasn't semi tough and there were more than a few uncalled for tacks and swims.
My current rudder has a root chord of 150 mm and a tip chord of 50 mm and is 850mm deep. Or at least it was, during Sunday it mysteriously became a shallower blade.
The biggest hindrance to making the blades narrow is fitting a shaft that is big enough and not letting the section get too fat. We can go round and round.
But the point is that many ICs are very well balanced and can be sailed hands off for a long time and that the rudders can be and have often been quite high aspect ratio foils. As always the trade offs are personal preference and sometimes driven by how things turn out. For example my rudder is now shallower. I will fair in the new tip instead of building a new blade, I don't expect a big performance change....
SHC
Beatings will continue until morale improves

jimc
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Post by jimc » Mon Jun 19, 2006 5:35 pm

The logic behind the loaded rudder theory as its been explained to me is that if you have to drag a foil through the water with the wetted surface it may as well do something, so you can run with a smaller daggerboard. So presumably you'd end up with less wetted surface, but greater induced drag (two tips) and so on. Is that logical? It was certainly noticeable that Cherub daggerboards got much smaller through the 1975-2000 timescale.

Whats interesting though is that my experience is that the limiting factor for daggerboard area is low speed coming out of tacks, especially in lighter airs, rather than what is required in a normal sailing situation. Now does the fact that you can unstall a rudder readily help or hinder? Also in this regime a high aspect ratio low drag foil is presumably at its least effective. How should this affect choices. You folk have possibly never experienced it - certainly I've never managed to get my IC to do it, but coming out of tacks with the daggerboard stalled is a really effective race losing manouver!

Presumably the optimum rudder position is exactly on the centreline so its taking up the same angle of attack as the cb: if it were unloaded it would be fractionally to leeward, and clearly if its to windward of the centreline the rudder is acting at a greater angle of attack than the DB, which I suppose could in a small way be a good thing if the rudder is a fatter section for steering efficiency and the db is a low drag laminar flow section... Or am I talking rubbish? Presumably also the rudder tends to run in the downwash of the daggerboard which must affect things too mustn't it?

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