new stuff in the a-class

juniordave nz

Member
355
1
Auckland
Cheers samc99us.

I was really on interested in the interaction between the wing and rudder in the simulations, so not too fussed about the upper boundary. The results are relative to each other and may not resemble real world conditions that well. I usually find it helpful to look at simulations of things like this, you often pick up on flow characteristics that you otherwise might not have considered. And because its free for me to carry out thousands of dollars worth of simulations, I'm quite happy to run things for my interest.

the rudder is painted now and as soon as my rig arrives I will test it without the wing to get rudder angle right for the boat and will then mount the wing.

I'm really pleased with how they are coming out and the fit the cases very well, I do however have to modify the push rod, as it needs to be a bit shorter for my rudders, but I will make sure I have enough screw adjustment to fit the old rudders as well.

It seems I will have to set the rudder with the front edge pretty much vertical judging by how the old rudders were set up, this is a bit of a pain as it's not how I designed them, but pretty dam close. Sailing shall tell.

 

david r

Anarchist
595
55
pond
JDNZ,

Was your answer of winglet 90 degrees to the rudder figured out with the boat heeled over to normal sailing trim?

thanks

 

juniordave nz

Member
355
1
Auckland
My main interest was the interaction between the wing and the rudder. So in that regard, not so much.

My design is to always have two wings in the water, so if I was to have an angle greater than 90 degrees, then I would not gain any extra lift overall.

Another consideration was if the boat does go to foiling next season, possible but not overly likely, then it will be more horizontal. As when flying max power/min drag is when the boat is flat.

I did simulate about 20 different flows over the rudder, so can get force vectors in any direction for those flows, so I could use the results to look at the vertical lift when the boat is healed.

I will post all the lift and drag values for all simulations once I get round to lining them up with the flow.

At the moment though I am concentration on getting my boat on the water and getting another rudder out of the molds.

 

juniordave nz

Member
355
1
Auckland
Went for my first sail yesterday. Boat feels great. Need to sort my systems out a bit, mainsheet was crap.

Boat was balanced on boat tacks up and down wind, with new rudder on 1 side and old on other.

Current rake puts the front edge of the rudder pretty much vertical, in my design I have it at about 4degrees, so its a little bit off, I didn't try it as designed, probably should have, but had a bit on sailing the boat.

Heres some pictures for comparison:

Next ones will hopefully come out of the mold white, just trying that now one one of my smaller molds.

P1050990.jpg

P1050991.jpg

P1050992.jpg

 

BingC

New member
Has anyone looked at the data from the F16 stealth with T-foil blades? I'm wondering why they haven't been more prevalent in the A's before now and why more folks aren't using them in the F16 class? Are the tuning issues Simon discussed a hindrance to the average sailor who ends up getting worse performance with foils than without? Or are earlier designs not as refined as the new t-foils on the DNA and others?
I have had a Stealth for 7 yrs, and don't do a massive amount of racing to be able to comment against other boats, i have the boat to sail with my kids as crew (6,7,9 yrs old when we got it),

though now they are using it without me, and as far as i can tell it the winglets on the rudders just save our arse when pushing downwind in breeze.

I sailed Tornados and Hurricaines and F18s before, all too big to have the boys as crew, so chose the Stealth as a good looking, proper cat, but for the smaller crew.

 

juniordave nz

Member
355
1
Auckland
That is a solid carbon section glued up inside both the foil and wing. I wasn't totally happy with it though, so have also put 800gsm of uni over each side of the joint that I will lightly fair in. Not my ideal solution, but it will have to do for now.

 

juniordave nz

Member
355
1
Auckland
Finally got out sailing with them today. Worked really well until one of the rudders blew up going down wind. Have a bit of a repair job to do before the worlds.

P1060151.jpg

 

Xlot

Super Anarchist
8,697
1,139
Rome
Perhaps more of interest .. pictures at

http://www.catsailingnews.com/

of Mischa's windsurf-style boom and deck seal, very logical. Not so, a huge daggerboard cassette to get around the "inserted from the top" stipulation. Should entail major structural reinforcements to hulls, not good

 

juniordave nz

Member
355
1
Auckland
How the hell do you tack the boat with that?

Rudder broke just below cassette where bending loads are greatest. Split the rudder in half down the join and crumpled the carbon below the cassette. Whole thing is still intact, just broken. Was lucky to get the boat back to land without breaking much else as my rudders don't tilt much above the water line so I was dragging the wing the whole way in.

The one the broke was hollow, the other is completely full with foam and I don't think would break like that. Also I had the wing creating a bit too much lift, I needed to rake the rudder back a touch.

They made trapeezing downwind so much easier though. It was fairly choppy, 10 gusting maybe 15 and the boat felt great. So I don't want to have to go back to using my other rudders if I can avoid it.

 

bacho

Member
Perhaps more of interest .. pictures at

http://www.catsailingnews.com/

of Mischa's windsurf-style boom and deck seal, very logical. Not so, a huge daggerboard cassette to get around the "inserted from the top" stipulation. Should entail major structural reinforcements to hulls, not good
I've been thinking that a cassette like that was the way to go for some time now. I don't think the structure problems would be too hard to address.

 

SimonN

Super Anarchist
10,533
755
Sydney ex London
Agreed, it shouldn't be too hard to resolve the structural integrity problems. It just needs 2 lateral bulkheads and 2 longitudinal ones with a little thought to ensure they don't cause a hard spot in the hulls.

 

Foghorn77

Super Anarchist
1,133
21
Agreed, it shouldn't be too hard to resolve the structural integrity problems. It just needs 2 lateral bulkheads and 2 longitudinal ones with a little thought to ensure they don't cause a hard spot in the hulls.
and still come in at weight.

 

SimonN

Super Anarchist
10,533
755
Sydney ex London
Weight is the key issue I have been going on about for a while. I find it hard to see this solution weighing less than 3kgs more than a conventional case. As most builders seem to be struggling to make minimum weight at the moment, that suggests builders need to use more exotic construction to reduce weight in order to then add 3kgs with these cases. That means a significantly more expensive boat because of 2 factors.First, more exotics (hi-mod carbon, definitely honeycomb prepreg etc) plus the case and associated bulkheads will take significant time to make, above and beyond a conventional case. And the one thing we don't need is more expensive A's!

 




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