It would be prudent for us to address the three general wind regimes with the open source design for sure. Light (0-7 knots), Medium (7-15 knots) and Heavy (15-25 knots).

It probably only affects the centreboards, rudders and hulls though, because the effectiveness of these items will change with the speed and heel of the boat, but the structures will have to withstand the highest loads anyway.

Are we designing for windward-leeward courses or other? A simple design aspect that will be affected by this decision will be the height of the bow. If shy/tight reaching much, I would want a fairly high and full bow to take the trimming moment from the sails, if doing windward leewards (hotdogs) we can get away with much less reserve volume in the bow. If designing for both, I would want to be on the conservative side of a full bow.

Speaking of bows, I have debated for a long time the effectiveness of wave piercing designs. With kite/spinnaker cats, the bow will rarely bury upwind, and will certainly not be succeptible to nose diving upwind. Downwind, the kite will lift the bows significantly. I think "wave piercers" are more effective at removing weight from the bow of the boat rather than actually piercing waves. Probably looking at a kilo or two on each hull, which is nothing to sneeze about all the way out at the end of the bow. Reducing weight at the extremities of the boat is an effective and proven way to improve boatspeed.

I'll admit that wave piercing may be effective on A-Class cats because they have such little hull depth and no kite to lift the bow downwind. But again, the weight reduction in the bow probably has more effect.

I doubt the reduced bow profile on the 'A's is a wave piercing issue but rather a move to reduce the volume forward to reduce windage and improve pointing. Valid for most cats, particularly if you have a spi pole and snuffer pulling the bows down.

ooh yeah, I forgot about windage...

We have set up a catamaran based wiki at f18.ca which you are very welcome to add content to.

Which site are we supposed to use for this F16 open design?

5 Options are:

1.

2.

3.

4.

5. Use all 4 platform, it is only a matter of copying and pasting the information that is Open Source in the first place


I prefer no 3

I've been trying option 3 but it just doesn't "work" for me. I find working with it too cumbersome.

Wouter

Same

I see the problem with no 3,

How ever you do not offer an alternative,

We can use this forum (catsailor)

Put a general sticky Thread with links to every subject of the project, that way it will be easy to find the information.

Simple!

???

Next question, which should've really been asked much earlier, one-up or two-up (cat or sloop rigged with one or two crew). This will affect the weight significantly.

I've been working away on a two-up design because that's how my boat will be sailed 99% of the time.

Surely the reason it wasn't asked is because it's irrelevant. The F16 class is not about optimising for solo or two-up. The whole point of the class is its flexibility in either mode. We need to look at the min weight rule really as it makes a distinction where there should be none. (Just my personal view)

This is a 14ft model. It could be stretched to fit the F-16 rules. The Center of Buoyancy and Beam @ Water line could be manipulated according to Crew weight and Rig Dimensions and centers. Feedback is welcome.

Ricky

Sail one-up with out jib and at 134 to 140 kg total crew weight two-up, with jib and stiff upper battens in the same main sail. <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" /> Since you asked, I want a boat for both conditions.

That is the original intention, right?

As I mentioned previously, I have no intension of contributing to this design process but because you seem to be stalling out and I’d like to see what you as a group will come up with, I’d like to suggest some refinements to the process you’re following. While its fun to play with hull shapes etc., at this stage it’s a waste of time. I recommended the following process.

1. Compile a list of all the equipment to go on the boat including its weight (if known).
2. Draw a layout (plan view) of the boat showing all the equipment etc. (at this stage you’ll need to discuss and decide on a first guess location of the beams and and settle on a “standard” system for halyards etc.)
3. Draw a preliminary sail plan.
4. Make the assumption that your hull isn’t contributing to lateral resistance and determine size and placement of foils. When doing this locate the foils for the 2up option. If you place the foils for the 1up option you’ll end up with lee helm if sailing 2 up, however, the extra weather helm from having no jib if foils are placed for 2up can be offset with rudder angle.
5. Generate a weight estimate including an LCG (longitudinal Centre of gravity) by combining your equipment list with the data from the drawings. You’ll need to decide here on ideal (2up) crew weight and where you would like the 2 crew to be located going up wind (also check where a single sailer will end up to keep the same overall LCG). For your first pass through the process assume that the hull’s centre of gravity is at midships (this will be refined later).
6. Having done all this, now you can start playing with hull shapes. Things to consider: Location of LCB (longitudinal centre of buoyancy)
Location of LCF (longitudinal centre of flotation) the point the hull pivots around when changing trim.
Prismatic coefficient (how much buoyancy is in the ends below water lines).
Desired transom height (above or below water etc)
How the LCB and trim move as you transition from two hulls to one

7. Design the hull structure.
8. Calculate hull weight.
9. Go back to 1. and replace best guesses with new data.
10. Repeat 1-9 until nothing changes each time you do a loop or you run out of time and have to start building.

At first glance, one of the hardest things about designing a good hull for the F16 is the massive difference in displacement that the hulls see in different sailing modes.

i.e. one up with both hulls in the water you need to optimise for 90kg, 105kg boat + 75kg crew =180kg/2= 90kg

Two up flying a hull you need to optimise for 300kg, 110kg boat + 190kg crew = 300kg

The optimised hulls for these two conditions are very different.

However a good compromise hull works surprisingly well when sailed at either 90kg or 300kg.

Here are two graphs that show the drag of three hulls when sailed at 90 kg and 300 kg.

Hull1 is optimised for 90kg, Hull3 for 300kg and Hull2 is my compromise hull.
300kg

90kg


The same graphs but zoomed in on what I consider to be the most important speed range 8-12 knots.

300kg

90kg


As you can see the compromise hull performs well across the displacement range required by the F16 class. I have more data I just need somewhere to put it.

Gareth

What these plots say to me is that it is very attractive to design a 300 kg hull (although I think 190 kg for the crew is a bit high). Because it appears that sailing a 300 kg hull light (180 kg) hardly increases the drag at all. Especially since the hull related drag at max makes up only 20 % of the total drag of a beach catamaran. So even if the 300 kg hull sailed light has 10 % more hull drag then it would only amount to 2% increase in drag over the whole drag of the boat. This is negligiable. Clearly sailing a light hull heavy is much more worse.

Thanks alot for the graphs Grob !




I'm willing to help you guys out in the way of beams etc, but as written earlier I'm not pulling this car and I'm not accepting any cumbersome publication methods.

I do think we got a great project going here, but some of you really do have to get that site up and running and one that is easily backupped and updated.

Why not just make a site with PDF files and have a download corner where the original Word documents are. A person can then download the word file, make the changes and submit the new Word file to be checked and converted to PDF. Simple, easily accessible and spam proof. I'm sure Paul Warren will make space on the formula16.org website. Now we only need someone to check and maintain this segment of the project. I'm already doing the picture and video gallery so count me out of this one. I'll be only a contributor nothing more.

Wouter

I have conducted a preliminary weight estimate based on a mosquito arrangement. This is where a displacement of 260-270kg has come from.(If you are pushing 180kg total soaking wet crew weight or above, you should probably consider an F18 or bigger!) I would share the weight estimate but it is too hard atm. If someone could do a weight estimate for a Blade or Taipan F16, that would be good. Don't forget that we have a rigged minimum weight to meet already, so that simplifies the weight estimate process drastically, it is the structure that can get fine tuned to bring the weight down below this, then add a bit of lead.

I agree with leaving the hull shape to later, it is really influenced by everything else, including crew weight. With a range of displacements from 180kg 1-up to 270kg 2-up, it makes it very difficult to design for all conditions. Just look at the extreme end of 1-up mode, Gary on Altered. It would not perform with 160kg of crew weight onboard, but is very good in a 1-up configuration.

As far as prismatic coefficients go, we would need data for other successful beach cat designs to have an idea of this. I don't believe that data exists in the public domain. If people have this data it could be very beneficial.

I'm looking into a new method of sharing and contributing to this Open Source F16. Bear with me, my skillz at web administration are newberish at best.

Hey these guys have been able to get the Wikipedia software to run their wiki !

http://wiki.sailcut.com/Main_Page

Wouter

I have no objection to (trying to) install MediaWiki as part of the F16 website, but I do not want to be responsible for dealing with any spam. I've found this to be a big problem with wikis in the past, and even installing those irritating "type in the word that's displayed in this image" things doesn't fully solve the problem.

That said, the F16 website's Google PageRank is pretty miserable at the moment, so we'll be very unattractive to spammers for the time being. On that subject, if you have your own webpage, please help to improve Google's opinion of us by linking to http://www.formula16.org

Paul