New single hander from San Francisco

Use this forum to discuss the latest changes in the class
andersp
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Post by andersp » Sun Dec 18, 2005 6:48 am

I agree with Johan that it would be worth looking at slightly bigger sails if everything else is about to change anyways. I also agree with jimc when he says that the "key thing is to make a boat more interesting to sail". I think we all agree that the main issue with the IC is staying awake while going downwind in light and medium winds. Keeping the sail area and reducing the drag by making the hull narrower might be enough to fix the downwind problem, but won't it create a boat which is impossibly difficult to tack in 20 kts + chop? Tacking is one aspect of IC sailing that intimidates most newcomers and I don't think the narrower hulls are going to alleviate that problem. I think it is hard enough to tack as it is, and this is a real pity because it is so much fun to sail the IC when the breeze is on. To me it is important that the new rule creates boats that can handle a good breeze. And it would be a pity if you needed two different hulls to stay competitive both in light and heavy air.

Anders
Anders Petersson
IC SWE-105

Steve Clark
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Post by Steve Clark » Sun Dec 18, 2005 5:36 pm

Lets look at some numbers shall we?
I think there are two coefficients that are particularly indicative of performance.
They are the displacement length ratio and the sail area displacement ratio.
To my thinking they define how easy it is to drive a boat past hull speed and how much oomph you have to do the driving.
I will use three examples;
You can probably guess what they are.
Excuse the feet and inches, they are how I learned this stuff.
IC old Displacement 375, 17'wl, 114 ft^2 ( 10.6 m^2)
IC new Displacement 300, 17'wl, 114ft^2 ( 10.6 m^2)
A Cat Displacement 355, 18'wl, 150 ft^2 ( 13.94 m^2)
A Cat can be sailed "wild" in moderate air without hoisting additional sail, so the closer we get to their numbers the better.
Displacement length:
IC old 33.98
IC new 27.20
A Cat 27.17
Pretty good, implies we should have a ramp through hull speed similar to the A Cat and significantly better than the already excellent IC.
Sail area displacement:
IC old 35.14
IC new 40.7
A Cat 47.87
The proposed new rules boat is 40% of the way to the A Cat, and significantly "hotter" than the existing boat.
Increased of sail area in 1/2m^2 increments yield the following;
11 m^2 = 42.13
11.5 m^2= 43.91
12 m ^2 = 46.0
Some observations:
Bob Lewis built a 12m^2 rig for Mr Kite for some long distance type races around Vancouver. With the class legal rig, he would always beat the 505s to the outer(windward mark) but lose most of them on the run home. With the larger rig he could hold them off.
Mr. Kite with 12m^2 of sail has a SA/D of 39.82, slightly less hot than the new boat.
Most lighter helms ( Colin in particular) have resisted adding sail because they felt the couldn't hold it down. The A Cat has 47% more righting moment than the IC, and given how they behave in Force 5, you wouldn't want to add that much sail.
My goal in all of this is to add the tactical/strategic interest of tacking down wind to IC sailing.
It seems that 10.6m^2 can achieve this at some critical velocity. It may be desirable to increase the sail area, but it isn't necessarily obvious at this point. I guess we will have to put some stuff on the water and figure it out by testing.
I have finished the prototype design and Henry is cutting out the jigs tomorrow. I will clean up the drawings for Christian to post and will keep you advised as to how we progress.
SHC
Beatings will continue until morale improves

Johan Backsin
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Post by Johan Backsin » Sun Dec 18, 2005 6:32 pm

Interesting numbers, and hard to make any firm conclusions. I agree with Steve, nothing beats real tests. Fortunately we have people in the class who is prepared to invest time and money to do it. Hats off.

I want to stress what I think we agree being the overall goal.

The current IC is a fantastic boat to sail upwind, especially in stronger winds. Downwind its mediocre. The goal is to transform the downwind from currently running with the wind to sail at angles, sail apparent wind, with the helm on the seat. The AC solved this but at the expense of added complexity. The goal is to achieve the same thing without adding complexity to the existing IC.

Do we all agree that above is the main goal?

5 years the 505 increased the size of the spinnaker lengthening the luff by 1 meter. It made it pay to wire-run (sailing apparent wind) at 8-9 knots wind (fun) rather than before at 12-13 knots. The 505 class loves it. We likely will see a similar result. Dependent on sail area the new IC will transform from paying to run with the wind to apparent wind at a certain wind strength, but it need to be at a much lower wind speed than lets say 15 knots

Again, nothing will beat real tests.

BTW, the 505 class uses below guiding principles whenever the review a rule change. They are pretty sound:
- Does it make the boat easier and more fun to sail
- Does it make the boat go faster
- How much does it cost to implement
- Will it make existing boats obsolete

Given that this rule change scores very low on the last two, it needs to score very high on the first two.

If the new IC’s downwind performance and way of sailing it (on the seat and at angles) will be achieved it think many will support it. If not, it will not get my vote.

Johan

andersp
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Post by andersp » Sun Dec 18, 2005 7:19 pm

Steve,

Your ratios are interesting, but they seem to indicate that we can get the boat we want by just making the current IC lighter. Why is it necessary to make it so narrow? Is it to reduce wetted surface for light air performance? What is the relevant ratio for manouverablity? Perhaps something like (sail force) times (sail center of effort above waterline) divided by (hull beam)? Reducing the beam to 3/4 of what we have today would increase the "tippiness" ratio by 4/3, i.e. 33 percent. This concerns me.

Anders
Anders Petersson
IC SWE-105

Steve Clark
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Post by Steve Clark » Sun Dec 18, 2005 9:53 pm

Anders,
The beam is not mandated. 750mm is the minimum. 1070mm is the maximum. The minimum in the pre Nethercott rule was 30". The numbers are within 12mm or so. Slurps and Lust Puppet have a waterline max beam of 876mm even though the were at the minimum rise of floor beam under the old rule.
So this really isn't something that hasn't been done before. It's not like we are going to 300mm.
Otherwise, I am pretty focused on wave encounters and trying to assure that the canoe is not slowed as it passes a wave. I think this is critical to generating and maintaining apparent wind. When sailing angles, it's all about maintaining speed and a not wallowing in the wave troughs.
Once again, it's something we have to test to find the better answers.
SHC
Beatings will continue until morale improves

jimc
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Post by jimc » Mon Dec 19, 2005 3:44 pm

I'd question those 505 parameters pretty hard actually.

Will it make the boat faster is, I suggest, utterly irrelevant. It won't make the boats slower because existing boats are still legal. That's all you need to know about that.

How about

Will it make the boats more enjoyable to own and sail?
What will the effect be on the purchase price of new boats?
Will it cause a net loss or gain of numbers in the class?

The last is pretty imponderable of course, but the important one. On the other hand with the number of new ICs being built at the moment the bar ain't very high.

Phillip Evans
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Post by Phillip Evans » Wed Dec 21, 2005 1:29 pm

Steve, could you equitably include the helms weight in the equations somehow to determine an individuals sail area and put everyone on a level playing field. You never know the punters might even have a look at us.

Phill
Phillip Evans

Steve Clark
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Post by Steve Clark » Wed Dec 21, 2005 8:16 pm

I suppose it would be possible.
You would chose a sail area displacement ratio,
Something like "42" because it is a good number and close to where we are going to be anyway.
You back calculate the SA/D ratio and that gives you the area available.
This takes advantage of the fact that we don't have production sails and potentially improves the racing for a broader range of people.
On the down side, it means that every ones kit is pretty exclusively theirs and you couldn't swap stuff around.
If you weighed in at a regatta lighter than your declared displacement, because , I don't know you have a hang over, you could add lead to get back to where you are supposed to be.
I think we would have to play around with that to see how it worked out.
SHC
Beatings will continue until morale improves

Johan Backsin
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Post by Johan Backsin » Wed Dec 21, 2005 9:41 pm

The more I look at Steve’s numbers, the more I’m convinced only real tests are meaningful. As an example, an AC has much better Sail Area Displacement number than an A-Cat downwind by a mile, but I doubt its quicker. You could go on and still come to the same conclusion, only real test on the water will provide any answers.

It be fantastic if a fair weight/sail area equalization system could be created, but it will be very difficult to agree on it (the ratio). The only “no questions asked” would be seat length / Weight (lead) system, but the problem is that would slow everybody down.

Jim, the new DC will be faster, no doubt. 34Kg lighter, 25% narrower beam, ~25% lesser wetted area, and more modern hull design. If adopted, all current IC will obsolete as far as racing is concerned.

To reiterate my previous point …. If the new IC will change the way we sail downwind, going wild instead of running more or less square with the wind, it might just be the ticket the IC need.

We will find out on the water.

Cheers, Johan

Paul Scott
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Post by Paul Scott » Thu Dec 22, 2005 3:21 am

Steve-

Enjoyed the numbers- but for light wind and downwind, how about sail area/wetted surface? What I'm seeing in my own efforts hover around 3.3-3.9, given about 27 - 33 square feet wetted surface if you want an easily planing hull (I think). (The Nethercutt hull, by my guestimate is around the high 20's(28?))

A round hull (like Div II sailboards) might be more, er, fun?

I'm seeing friction and wave numbers of about equal values for boxy hulls, with very little wave hump (at a .558 prismatic). That what you're seeing? Anybody have any thoughts about prismatics at low SLR's for this type of machine?


Paul
"Exuberance is better than good taste" -Flaubert

Karl Wittnebel
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Post by Karl Wittnebel » Thu Dec 22, 2005 10:44 pm

I'm sure Bill Beaver does. Will have to get him to chime in. Certainly his AD hulls are very round, and I know he thought about prismatics when designing it. He also has rather immediate access to a tow tank...
Karl Wittnebel
NC USA 193 (Lust Puppet)

Paul Scott
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Post by Paul Scott » Fri Dec 23, 2005 6:15 am

OK- crunched some round hulls. If you go prismatic 4.79 with V/Circular/V cross sections, I got the wetted surface down around 23 sq feet, which gives a Wetted Surface/SA of 4.6. Really round sections all over gets you 23 sq feet @ prismatic 5.5, which gives a WS/SA of about the same- 4.6. The cool thing about the 4.9 prismatic is friction = 7 & wave never gets above 4! Negative hump! Wheras the 5.5 prismatic has a big wave hump. Unless i'm taxing my Vacanti wave resistance calcs too much. Probably. But when does the hull begin to lift? And where?

The Lower Prismatic Hulls really look good, too.

Paul
"Exuberance is better than good taste" -Flaubert

Paul Scott
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Post by Paul Scott » Fri Dec 23, 2005 6:24 am

Actually the 5.5 prismatic hull comes in at 23.5, which gives 4.5.
"Exuberance is better than good taste" -Flaubert

Phil Stevenson
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Post by Phil Stevenson » Fri Dec 23, 2005 8:04 am

The lowest wetted surfase is a hemishere but a boat that shape would not sail. I believe that energy wasted in wave making and the energy needed to pass surface waves has become much more appreciated in small boat design.

Catamarans found out in the 1960s that sharp bows are faster than blunt ones. Moths found out in the 1990s. They just get through wave upwind and downwind so much more easilly.

Moth and cat sailors know the world has moved a long way past just wetted surface. The IC has the opportunity to join in, please do not waste it.
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
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Post by Paul Scott » Fri Dec 23, 2005 6:31 pm

I was hacking shapes at the proposed minimum beam & max length that look like IC's. Low SLR regimes fascinate me, if the shapes also work at planing speeds. And! You can get a very sharp bow at lower prismatics. Does anyone have any idea if the higher SA/WS ratio would have much of an advantage in low SLR conditions? It seems to have been messed with around the late 1800's, but I haven't been able to find race results with enough wind strength/ type of course info to make any conclusions.

Question is, how much round in cross section on a IC can a human sail without needing a support boat? Div II boards showed the way in this type of low Wetted Surface high performance sailing, I think, but just staying on some of them could prove troublesome, esp. downwind, and Some of Them depended on moving weight foward in light airs to get the stern out of the water to lower Wetted Surface. But how practical is that on an IC without moving the seat for and aft? Or standing up? Or having a really wide seat? And is that width controlled by the proposed rules?

Paul
"Exuberance is better than good taste" -Flaubert

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