Alan - I am not too sure where the camber calculations will get you as I have no idea what % camber I am running. The process has been pure trial and error and experimentation. I was surprised to see the graph for calculating the camber and I havn’t had a chance to relate what I did to the formula given with the graph. ( been too busy sailing - my bad!) I wish I knew it existed when I first started out building sails!
My technique is now to use the same thickness wedge 1.5mm for the seams that have camber. Some do and some don’t - I cant credit where I read it but it makes sense.
So,
1st seam above the boom has camber added(both spacers) max @ 40% from luff
2nd has 1 spacer @ the luff. max @ 50%
3rd no camber
4th both spacers and 45% max
5th both and 45%
6th both and 45%
The idea is that the max draft moves back as you go up 1/2 way and then moves forward for the top 1/2… this is then balanced by the luff curve bringing the max draft fwd again…
The luff curve is calculated by rigging the mast with no main, pull on as much backstay tension a you dare and use a straight edge resting on the gooseneck and touching the head of the rig to measure the deflection of the mast. I do this in a couple of places to make sure the curve is correct and note the height of max bend. This curve is the transferred to the sail. I have had luff curves as much as 15mm on softer rigs, but somewhere around 10mm was good for this new mast.
Claudio,
Thanks for the analysis and I have adjusted the jib boom. It was only 10mm out from 25%. I put it as you suggested and it is harder to butterfly than before.
You are right about the counter balance, there isn’t one fitted. the plan is to see how it goes! I really do not like the idea of adding weight in those areas… so I am going to see if I can invent a lightweight solution.
Not really going to get much further for a couple of weeks as I am off to Stockholm on Monday, Plenty of thinking time though!
I make sails for different model sailboat classes here in the US and I do the same thing as you mentioned. I start with my max draft in the main sail at about 40-45% at the bottom seam and as the seams go up I move the draft back to about 55%. Normal sails that I am making are standard cut (not fat head) sails…I have been recently making more fat head sails and I think your ideas are correct in moving the draft back forward once you get above the diagonal batten or battens…
Alan,did you laminate your mast section? i.e. Make it your self?
One other question to any who may have the information but is their any plans for BMW Oracle ACC 120 class? After I build my AC100, I am going to be moving on to a AC120…and would like to support my nationality…
Thanks and again your boat looks great Alan!
Brian
Check into this site http://iacc120cup.altervista.org/Main0E.html look under IACC 120 projects and all the plans are there including that black & white boat you were talking about
Uh hmm Brian … me laminate a mast !? wow not at that level of boat building but thanks anyway … Jim is the Brains here, this his is boat SWE 96 not mine …I’m the gooding looking one
Hey wanna see a build log on you black & white thingie … Ok ?
Yes the mast is one that I made. Hi Modulus carbon with a sailtrack. The section is 20 x 6.5mm leading edge and 5.5mm trailing. I wanted the stiffest mast possible fore and aft.
That allows a longer mast head crane/ higher forestay tension for a given mast rake.
Alan - thanks for the compliment and I shouldn’t be so hard on yourself mate!!
I looked on that site before and didn’t find anything on BMW Oracle ACC. Might have to develop my own lines from pictures on the web, like what Renato did…
Thanks for the info! And I will post my build progress once I start.
There has been a bit of playing today so I will break up the items by subject…
As Claudio pointed out the jib is a bit reluctant to flick onto the opposite side to the main going downwind.
This is my first attempt at a jib centering device to help promote the butterfly.
Just a piece of lightweight shockcord.
So far it works okay, but I need to compare it to a real counterweight to give a fair judgment.
I had been keeping a keen eye on the forecast as I knew that there was going to be some wind heading our way for this afternoon.
The sailing started out pretty serene and laid back - started with 2 knts, then a nice 5 -7 knts.
Then the water turned dark as the weather changed… and I now have a new speed record for SWE 96 of 8 knts (15 kph) Smashing the last record set by the prototype by 1 knt.
Here is the results from the GPS logger. I know its for a short burst, but the way the graph shoots up shows the acceleration.
I said this paint was slippery and there is a reason its used by all the top sailing teams
I had to finish the sailing early as I have to fly to Sweden tomorrow.
I have been building travel boxes last week and I wanted to try them out. It was a perfect opportunity to pull the yacht apart and see how they worked out.
Pictures say it better so here are some more -
Compliments on a beautifull and well performing boat. It’s like a rocket going down wind, amazing!
Realy looking forward to finish my SWE 96, but with the current pace, it will be finished in about 1-2 years :-). Meanwhile I will admire yours and others boats.
Looking good Jim … little more tuning & practice and that will be one sick package … well done! how’s Stef’s boat coming along, did he get it finished ?
@ Anders, hey man gotta get it finished over winter so we can get a central European regatta started early next year
He’s back!.. After a very snowy and cold Stockholm…
Alan, as for Stephane’s boat - he has moved along with it, but has some ground to cover still.
As the base is closing - I will be moving all my tools to my apartment (an easy 1000 kg!!) so I am sure he will be a frequent visitor in the new year!
Whilst away I had a good time to reflect on the yacht and realised that I had get my act together to get a bit more ‘scientific’ with my tune up.
Until now I have just been testing the boat and getting to know her.
The next stage (in the campaign) is the acquisition of raw data and analysis of performance.
For the science-y part that means GADGETS! Now I love gadgets and my world is full of them… but there was one thing missing.
Now I don’t know how much performance gain or loss I going to attain from this gadget, but after reflecting on the various “variables” that you can play with, I concluded that I needed a tension gauge for tuning the rig.
I have some ideas using rig tension that I would like to experiment with and, so to achieve realistic results you need to associate - rig tension/rig deflection/sail shape/speed.
So - my rig tension gauge.
This is in its infancy - I made this from odds and ends in less than 20 mins…
I have yet to calibrate it correctly, ( 20 mins remember!) so at the moment the scale is only in MM. I was able to then check the rig and found all but 1 D2 to be equal tension to its partner.
I have another reason for this gauge - Because I am 100% composite rigged, a small adjustment has a huge change on the rig tension. It is therefore even more important to know where I am and where I need to go.
My experimental mast structure has been tested to 30kg of compression without a problem (‘max’ on the scales…) and I would like to know what the loads are in real terms.
I am interested to see what loads these baby’s are subjected too… It always helps - when you build the next one of course!
Here is a picture of a tension gauge type that is popular in the EC12 class. It works well and is easy to read.
I could not find a link to the original document. It is part of the instructions on building an EC12. So I have uploaded the content as a Word document. The credit for this belongs to the EC12 organization.
For the Word document, be sure to scroll down for pages 2 and 3.
Does this mean my finger twang to feel for same shroud tension, is not worth squat or what ?
I guess my question is … how significant is micro-measurement/adjustment tension on a IACC 120 rig ? and are we talking all rig, backstay/forestay and or just shrounds.
Understand big AC boats with sensors all over the boat to ensure they control tension & don’t break the boat …
My aim is to be able to use the tension gauge to set up the yacht every time, not by feel but by hard numbers.
When I get some more time I also want to do some research with tension settings to see if I can get the mast tip to bend over to leeward, open the leech at the head of the main to de-power in the big gusts automatically like the windsurf rigs do.
The best result of this is that I would be able to carry the same suit of sails for a much broader wind range.
So using a combination of GPS+mini camera+rig gauge+anemometer I hope to see the effects, note down what numbers work for future reference.
Then I can have a table with a few base settings that I trust.
So do I Alan, I am getting fed up with sailing solo!.. Praying for some wind as I hope to meet up with the Valencian sailing club today and line up against their boats with 96…
Hey Jim, a couple of questions if you do not mind?
In the sailmaking post, you inserted one shim on the luff side, with max at 55% for some of the middle seams. I read this as 1 shim on the luff side, with the bendy-piece attachment point at 55% of the seam. Now it seams to me that this will have the effect of moving the max draft forward, not back? If you are only insering the shim on the luff side, the maximum draft point moves forward? Maybe I am misinterpreting? (I just finished seaming my second set of sails, so far, they look better than the first but I am really looking to learn more)
Secondly, and don’t answer this if you dont’s want to… I am very curios about construction techniques, and a rank amature at composites, but I am realy enjoying the learning process. Now the question… How did you do the sailtrack in the mast? I built a “dual tube wrapped in cloth” version and really like the look, but not the weight… Yours looks like cloth laid over a mold but I don’t see the sailtrack?
Know that feeling only too well … There is the Southern IACC 120 Cup, Round Robin #4 coming up in Rome weekend of January 23rd, I have pencilled it in my calendar, if I’m here (not work travelling) as the first appearance of Jaguar GBR 75 (blast from the past) … any chance of possibly making it there for you ?
Otherwise we could always try and organise a IACC 120 event in Valencia … that would be cool, we could all use the original team bases :lol::lol:
