Designing to Steve Clark's proposed new rules

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

Post by Steve Clark » Sun Oct 29, 2006 4:33 pm

What we DO know from years of canoe design is that the curve of areas needs to be very balanced.
A fat ass needs a fat bow and vice versa.
Lou Whitman was and Bill Beaver is very certain on that point.
SHC
Beatings will continue until morale improves

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

Post by Mal Smith » Mon Oct 30, 2006 1:35 am

The IC hull is fairly unique among performance dinghies due to its high length to beam ratio. It is more a semi displacement hull than a planing hull, which is probably why it has proven best to maintain a balanced curve of areas, and other characteristics which make the hull more efficient in the below planing speed range. The suggestion is that the compromises needed to produce a high speed planing hull just don’t pay off over the full range of sailing conditions. This would explain the alleged upper end speed limit for the IC of around 18 knots.

However, with the DC we have changed the parameters, mainly by reducing the overall weight. The old rules of thumb may no longer apply. Having said that, I personally am still inclined to concentrate on minimising wetted surface and developing a balanced displacement hull.

Mal.
AUS019

Paul Scott
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Location: USA

Post by Paul Scott » Mon Oct 30, 2006 5:45 pm

Hi all-

The discussion above is why I've been obsessing on old school big wave boards (also known as guns- like you need a big one to kill an elephant)- paddle out = low SLR, surf back in = high SLR, with a (welcome) hesitation at the top of the wave. Also my experience with long windsurfers- 15'-16'. As long as you're getting lift to plane, and the stern doesn't slow you down... It really boils down to the middle SLR range in my mind, and that gets back to the hump, and when you get your dynamic lift. I think the new Serenity sailboard is a good example of this to think on, as it is modelled towards low to mediumish SLR's, and is long -16'+

If you model guns (sic) as a class, pretty low Cp. Also, my 40' cruising sled, which is aimed at low wind smokin' has a pretty low Cp (I think I'm bound by my contract with my architect not to say what) but it does plane, without any huge lag where the hump should be.

I also have been aiming at low Cp because of the effect mentioned above (and one I've mentioned before) that the fore and aft motion of the seat is more effective for trim, and, on a correctly modeled hullform, can be adapted for changing conditions. Let me illustrate: 1) Low SLR's: move forward, get lower Cp (and lower WS); 2) Middle SLR's: in the middle, a mid Cp (and longer WL); 3) High SLR's, move back, higher Cp (and lower WS).

The problem with the legal single chine canoe, as I see it, is that, and as I've modelled it, going forward lowers WS, bu not Cp so much (Which might be ok, but would limit acceleration a bit.). Moving back (to position #3) does raise Cp, and lower wetted surface, which is good.

[:p]Mild Rant follows. Please do not take seriously.[:p]

I'm dissapointed about the new outrigger rule, and seat length limitation. Also freeboard.8) End rant.

On the subject of Freeboard, it seems everyone has gone to more freeboard anyway- is this to obtain more modulus?

Paul
"Exuberance is better than good taste" -Flaubert

Paul Scott
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Location: USA

Post by Paul Scott » Mon Oct 30, 2006 5:55 pm

Or to get the seat higher?

Paul8)
"Exuberance is better than good taste" -Flaubert

Phil Stevenson
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Location: Australia

Post by Phil Stevenson » Mon Oct 30, 2006 9:24 pm

I think Andy and I have higher freeboard that you might have expected becasue we both have sailed moths, where low freeboard means lots of stuff dragging in the water. The narrow DC boats were also expected to sink slightly deeper than the wide boats.

I can not feel any hump as my boat accellerates onto a plane. I think its a function of being narrow. A sharper bow makes less bow wave so there is less hump for the boat to climb over. Even Frank Bethwaite acknowledged that the Nethercott behaved like this. (and 50 years before he supposedly invented the term.)
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
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Joined: Fri Aug 01, 2003 2:26 pm

Post by Steve Clark » Tue Oct 31, 2006 1:48 am

The IC rule always had a depth of hull measurement. In the grand days it was calculated as a function of beam and length. So was weight. I chose to simplify and have single values.
As the beam measurement is shifted aft, this carries an increase in freeboard aft as well, so the new designs seem higher sided back aft.
It has also been a trend over the last 20 years to move the seat further off the sheer. In my old boats the bottom of the seat was about 25mm above the gunwales. On more recent boats this has been closer to 75-80mm. Some have even been higher than that.
So it will seem that the hulls have a bit more sheer, but the seat's clearance above the water is pretty close to the same. The advantage is that the hull is stiffer in torsion. The disadvantage is more skin area. But you could trade that back by moving Bmax forward....
SHC
Beatings will continue until morale improves

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

Post by Andy P » Tue Oct 31, 2006 8:29 pm

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Paul Scott</i>
<br />[:p]Mild Rant follows. Please do not take seriously.[:p]

I'm dissapointed about the new outrigger rule,
Paul



<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

The outrigger rule is unchanged.

I am asking for interpretations of this rule, but the old ( 25 years? ) rule has not been altered for the appendix iv DC/IC.

Paul Scott
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Location: USA

Post by Paul Scott » Tue Oct 31, 2006 9:35 pm

Oh! :oops: Old rule. heh heh

Anyway, if any of you guys are interested, some web addresses about the Serenity, if you don't know about it already;

http://star-board.com/viewpage.php?page_id=37

http://www.boardseekermag.com/equipment ... renity.htm

http://www.windsurfingmag.com/article.jsp?ID=44221

Concepts Converge-

Paul8)
"Exuberance is better than good taste" -Flaubert

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

Post by Paul Scott » Tue Oct 31, 2006 9:40 pm

"Exuberance is better than good taste" -Flaubert

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

Post by Paul Scott » Fri Nov 10, 2006 3:29 am

So outriggers are defined as......?

Paul8)
"Exuberance is better than good taste" -Flaubert

Chris Maas
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Joined: Tue Oct 10, 2006 10:45 pm
Location: USA

Post by Chris Maas » Tue Dec 05, 2006 8:52 pm

Here, I hope, are some pictures of my DC hull mold. I'm still a paper and pencil man so I can't post the lines.
The sections are U-shaped forward flattening aft but still fairly round. Waterlines are fine and straight forward and wide aft. There is a fair bit of rocker. At 140kg the bow knuckle and stern are immersed 25mm. There is very little spring to the rocker and buttocks in the aft 2m. The max depth of keel is at 2750mm from the stern. I've pulled the chine up to about 25mm above the static waterline.
The Beam Measurement Station is at 1500mm from the stern.
The seat carriage track is incorporated as a gunwhale that runs from the chainplates to 750mm from the stern. Limited by the tiller rather than my desire not to get back further on those lively SF Bay reaches.
Not shown in the pictures is the topsides flair that brings the deck beam out to 880mm.
The rudder is mounted in a cassette through a slot in the stern rather than through the deck. The rudder trailing edge is at the stern. I suspect I'll need a t-foil rudder for downwind survival in a breeze but I'll try it without first.
The rig is the conventional sloop with a self tacking jib. I like the idea of the Una rig but am not sure that, since we're so limited on mast height, you can get enough upwind drive just by adding roach to the sail plan. Downwind those things should be fast though. If the Una sail turns out to be fast that would be really cool.
Paul, the Cp is .54 and the wetted surface is about 27sq.ft with my svelt 200lbs aboard.
It should be pretty slippery in light and moderate wind and maybe a bit challenging at the corners in a breeze. Bow down and heeled in less than 6kts this thing should be a rocket upwind. For the rest of the time, well I'm sure I've become a lot more agile in the 20years since I last sailed ICs and will be able to compensate for any twitchyness in the design.

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

Post by Andy P » Tue Dec 05, 2006 9:15 pm

Nice!

(If a bit chopped V transom 'normal' hull instead of double-ender canoe hull.) - but maybe that's good.

But looks very nice and smooth.

Good to see a few more boats being built!

Phil Stevenson
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Location: Australia

Post by Phil Stevenson » Wed Dec 06, 2006 7:34 am

Yes, the front half looks a bit like mine and Andy's but the back is much more skiff like.

Chris it is great that you have let everyone know another DC is underway. I understand you are in the NW of US. Its a big shame that so far these great boats are all so spread out around the world. My count now is 3 complete and three under construction, and maybe another 4 in planning.
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 » Wed Dec 06, 2006 5:16 pm

Chris-

Looks good! Funny, .53-.54 Cp & 26-28 sq f WS is where i've been gravitating lately. Is the WS computed with blades?

Zoom sail experience involved in your rig? Although your reasoning for a sloop rig does make a ot of sense.

We met down at the beach at Golden Gardens a few months ago when you were demo-ing the Zoom. Are you living in the San Juans now?

What is the name of your brother's CF business? He told me but I forgot.

Paul8)
"Exuberance is better than good taste" -Flaubert

Chris Maas
Posts: 110
Joined: Tue Oct 10, 2006 10:45 pm
Location: USA

Post by Chris Maas » Wed Dec 06, 2006 5:40 pm

Paul,

The WS is without blades.

Hoot not Zoom. Geeze! The Design intent of the Hoot is so different from the IC that I really can't transfer much of what we've learned from the Hoot rig. There are a lot of similarities in the hull shapes.

Yep. I'm in the San Juans. I'll bring the IC down to Seattle when it's done.

Alex is acmecarbon.com. I'll be leaning on him heavily for carbon bits and pieces. He's made some nice square tube for my seat carriage track.

Maybe I'll call the new boat Zoom.

Chris

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