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Wanna help design the next F14? #34572
06/21/04 09:07 PM
06/21/04 09:07 PM
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Bradenton, FL
Sycho15 Offline OP
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For the past couple weeks I've been talking to some designers about designing an F14 to be built in plywood. I would pay for the initial plans and buy the right to post them to the internet for all. That idea didn't go over to well, as they wanted to keep the rights to themselves and sell the plans individually.

So I'm back to designing the boat "myself". I can't figure out the Hullform program for anything, so I figure I'd go with good old paper and pencil.

I would like to build the hulls via the "cylinder mold" method. I believe this method will be faster and cheaper, and enable builders to tinker and tweak more. I would like to make a small change, however, in that the entire hull (minus deck) be laid up at the same time. "V" cuts made in the bow and stern sections of the bottom would help determine the shape of the boat (this instead of building in port/starboard sides). The "V"s would be "stitch and glued" to pull the sides in and form the rocker of the keel.

I think I can work out the construction details once I'm certain of the basic design. So... on to the basics. Remember this is for the "ideal crew weight" of 150lbs.

Hull height: How tall are they going to be? From the bow to the stern, would probably need about 4 locations of height if we weren't getting to fancy

Max. hull width: I'd like to go with 1', as it still gives a 14:1 fineness ratio and makes bending the plywood easier.

Location of max hull width: where does the hull attain it's maximum width? Where does this end? I'd imagine on a 14' boat it has to get wide pretty quick. But you don't want a foot-wide transom either, so where does it start to get skinny again?

Rocker: how much rocker at the bow, how much at the stern, where does it begin, etc. Measurements from the middle of the hull. I hear rocker is to increase maneuverability in waves, but how much is necessary?

What else do we really need for basic hull design? Can't the location of the beams, daggerboard-case, etc. be determined later? They can certainly be changed by whoever is building the boat.



G-Cat 5.7M #583 (sail # currently 100) in Bradenton, FL Hobie 14T
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Re: Wanna help design the next F14? [Re: Sycho15] #34573
06/22/04 09:56 AM
06/22/04 09:56 AM
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Houston
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All of these things you are talking about are interrelated.

The front beam location, sets the mast locations and restricts the allowable center of force. The center of force is related to the dagger board location. All of these are related to the center of volume of the hull which is related to the max width and depth of the hull.

All of these components are related. The relationship is not always linear either. That means moving one component 2 inches does not mean moving all the others 2 inches in the same direction. Sometime when you scale you luck out and sometimes you don't. Some very good designs, appear to be the result of dumb luck in scaling. They had a so-so 18, 19, or 25 footer and they added 1 or 2 ft to the bow or chopped 1 ft off the sterns and 4 ft off the bow and the new design was a LOT better than the old one

You will see some rules of thumb in design books, like "A has to be 90% of B". These rules assume a starting point, like, The mast is 55% of the waterline length from the stern or the boat is 20-24 ft long. If you don't conform to the basic assumption, things don't always work. .

I ran a lot of computer simulations and found you couldn't just scale a 14 from a good A-cat, which was my plan. However, my design had some assumptions, high top speed, stable and self limiting at the extremes.

Enough negatives, you need something to start with. For a race oriented 14 ft boats, 20-22ft cats scale to 14 better that 16-18 ft. A scaled NACRA 6.0 or Tornado ) would make a pretty good 14. If you scale a Flyer in length and width, it would probably work as a 14. For 14 ft versions of all of these I would put more initial volume near the bow to stabilize them.

Other interesting options are to scale a pin tailed Moth in length or take a 14 ft skiff and compress the underwater portion to about 9-10 inches wide

When I say scaling, I don't mean exactly. Try an keep things simple like 7" 1" instead of the exact scaled value of say 7.05479346. This will make things easier to build.

I would be careful of a 12 wide hull. That is pretty wide. You run into a problem with hobby horsing. That is where you hit a wave and the boat rocks like a hobby horse while stopping or slowing way down.

I tried to build scale models of 14's in tortured ply. With 10 inch wide hulls, I kept breaking the plywood

Don't take my opinion as gospel. I can say with hind sight, I looked in great detail at a very narrow range of designs. There are a lot of other possibilities.

Re: Wanna help design the next F14? [Re: carlbohannon] #34574
06/22/04 07:04 PM
06/22/04 07:04 PM
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Bradenton, FL
Sycho15 Offline OP
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Carl- thank you for the excellent post! That will be most helpful. I will try to look to the larger boats for inspiration in hull design.

Regarding the hull width and building method- cylinder molding is bending two pieces of plywood over each other (over a mold that resembles the cross-section of the hull), and vacuum-bagging them. This process enables the builder to use thin "doorskin" pieces of plywood which bend very easily and are very fair. After the vacuum-bagging you essentially end up with one large curved piece of plywood which is cut and bent to shape the hull.

I'll run whatever design I come up with through this forum before actaully starting to build anything.


G-Cat 5.7M #583 (sail # currently 100) in Bradenton, FL Hobie 14T
Re: Designing the next F14 [Re: Sycho15] #34575
06/23/04 07:10 PM
06/23/04 07:10 PM
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Hi Brian, You should rethink this idea. Even an expertly designed F-14 would not appeal to all interested people because any design is best suited to certain conditions of use. What appeals to one person may be just the opposite of what someone else is looking for and there are design trade-offs in every aspect - from rig considerations to the hull design. If you are truly interested in making as universal a design as possible, then your first task would be to identify your target market and find out what they want. I remember from my marketing classes that too many failed businesses did things the way you are starting - make a product and then find the buyers. Better for success if you identify the buyers and the product they want and then supply it better, cheaper, faster, or whatever than anyone else. Frankly, I cannot imagine anyone scrambling to buy (or even use for free) the design of someone with no knowledge or experience in boat design. That is not meant to be mean to you, just realistic. Your initial idea was much better to pay for a design and build that. At least you will end up with something that satisfies YOUR DESIRES and you will not waste your boatbuilding efforts and expenses. You would learn much and get to exercise your obvious interest in design just by working with a pro to give input on the design of your dreams. I hope this makes sense to you and that you do not feel attacked because that is not how I mean it. I admire your enthusiasm and I would like you to succeed. Your chances of that would be much better if you work with a pro. There will still be plenty for you to do in building, rigging, and competing with the new boat.

Good luck, Mike

Last edited by Mike Fahle; 06/23/04 07:13 PM.
Re: Wanna help design the next F14? [Re: Sycho15] #34576
06/23/04 08:04 PM
06/23/04 08:04 PM
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South Australia
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Forget all the "guru's"! just remember "If you build it, they will come". If you design and build a cat that really performs, is asthetically pleasing, and has a good competative life, it WILL sell. The only determining factor after it is on the market is the way in which it is promoted and exposed to the public -- and that is the most difficult part of any commercial success, the PR work! It could be the worst product available but if it is promoted the right way, it can be a commercial success. If the promotion is bad or non existent, even if it is the best thing since "sliced bread" it will languish in obscurity.
Darryl

Re: Wanna help design the next F14? [Re: Darryl_Barrett] #34577
06/24/04 03:07 AM
06/24/04 03:07 AM
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Sydney Australia
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And don't be tempted to use monohull design principals, they often don't apply to cats.
I've already done what you are trying to do with my '430' but in glass, not plywood so it may not be possible to achieve the same result. I don't have plans for a wood version.
You might like to take a look at a small video someone shot at a regatta I did a couple of w/ends ago. Takes a while to load though
http://boatvids.netfirms.com/
Bern

Attached Files
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Re: Designing the next F14 [Re: Mike Fahle] #34578
06/24/04 08:29 AM
06/24/04 08:29 AM
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Ft. Pierce, Fl. USA
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Hi Mike

"Frankly, I cannot imagine anyone scrambling to buy (or even use for free) the design of someone with no knowledge or experience in boat design. That is not meant to be mean to you, just realistic."

While your statements are logical, the world we live in doesn't always work logically. Case in point...Hobie Cat 16 was designed and built by a surfer using trial and error methods…yet it was/is the best selling cat of all times. Not the best cat by any means, but by far the best seller…Many superior designs struggle to sell enough boats to keep the doors open because their “timing was off” or they lacked the vision or resources to market their product effectively.

I have to agree with Darryl's comments. It is sad to admit that just about any piece of crap (boat or any other product) can be successful, if backed with right marketing machine. Look at some of the talent less entertainers that have huge followings and make millions of dollars a year because of the ingenious promotional people behind them.

So if people used their common sense instead of their emotions to make a purchase, you would be 100% correct…it’s just that the real world doesn’t work that way.

The other thing to consider is, the back yard builder is much more willing to take a risk on experimental design with his hobbie money than a lot of professional designer/builders are with a paying client and their own reputations. It may or may not apply to catamarans, but in a lot of water sports (surfing, windsurfing, kayaking, kite boarding...to name a few)the backyard builder is often responsible for the “design break thru”, and the “professional” picks up the idea…tweaks it and puts it into production. Both have their place, and their value….Don't discount the importance of either...

Bob

Last edited by Seeker; 06/24/04 10:31 AM.
Re: Wanna help design the next F14? [Re: Sycho15] #34579
06/24/04 10:19 AM
06/24/04 10:19 AM
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Houston
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Also keep in mind that if it does not work out, the hulls are the easiest part to build (if you can reuse everything else).

Re: Wanna help design the next F14? [Re: carlbohannon] #34580
06/24/04 11:12 AM
06/24/04 11:12 AM
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Hi Carlbohannon

What do you think of this idea? Take a plan view and profile drawing of a cat you like (I experimented with the A2) import it to Adobe then compress the drawing in length only. What happens is the boat “fattens up”. So while you are scaling the length down you might be able to manipulate the volume to stay the same.…Just adjust it where you have the length you want and print it to a known scale. Draw your stations over this print and make up your offset table. It is not a finished product, and it is not on CAD but might be a good place to start…The basic volume distribution should balance out near the same point, and if you had a plan view of the hull you could shorten it up, fatten it up, but keep the general water flow paths… The sail plan would have to be entirely different as the rig would be much to high aspect.It would not be a direct copy, but a good reference point from which to explore. Don't infringe on the designers copyright! They are quite wide in scope...

I know that most, if not all boat designers would say you can not change the lenght of a design more than 10% +- without problems...but didn't I read somewhere that the Tornado was born as a scaled down 25 footer???




Bob

Re: Wanna help design the next F14? [Re: Seeker] #34581
06/24/04 07:34 PM
06/24/04 07:34 PM
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The Tornado WAS "scaled down" BUT when they say scaled down they don't mean that it was simply scaled down proportionally, but that it was scaled down incorporated the differences necessary to make the balance and bouancy work at the smaller size ie the length reduced by 20% but the bouancy only by about 5%. Similarly with the depth of the hulls and the entry at the bows and "rocker". When journalists, for their convenience say "scaled down" they just see that the two "look" similar with one being slightly smaller. It would be more accurate to say that the Tornadoe was "BASED" on a previous design of a 25' cat.
Darryl

Re: Wanna help design the next F14? [Re: Darryl_Barrett] #34582
06/24/04 07:55 PM
06/24/04 07:55 PM
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If you want some where to start in designing a set of hulls (and that is the first and most important thing that you have to do - the rest, ie rigging mast boards etc follow a more "standard" criteria -) then go around and take all the appropriate measurements of existing 12, 14, 15, and even 16 foot cats that you can find, scale them out on paper with conventional elevation, plan and end elevation drawings, then look at what you want to do with a design around those dimensions. If you have that base data to start with you shouldn't go to wrong with your design and you will gain enormous insight as to how/why different hulls"work/don't work". You have to have some sort of accumulated knowledge to even think of starting to design anything, you either get that through traditional study or experience. It is very, very, rare that a person can just go out and "create" anything based simply on their intuitive brilliance and or genious. You HAVE to put in some of the hard yards before you will get any thing like satisfactory results, but don't get discouraged, even if it doesn't work at first, often the solutions are only found by making the mistakes first, and remember the person who never made a mistake, never made anything!!
Since you first posting some months ago, concerning "free plans on the internet" I have searched extensively and I'm afraid that there is no joy there, I haven't found any suitable site that offer "free" plans, they are all there for sale, and from their descriptions, 99% of them I wouldn't even use for toilet paper.
Darryl

Re: Designing the next F14 [Re: Mike Fahle] #34583
06/24/04 08:47 PM
06/24/04 08:47 PM
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Sycho15 Offline OP
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Thank you for all the posts, especially regarding methods to collect existing design information.

I'm also discussing this on The Multihull Forums, which has a lot of people who've built small and large boats and are very knowlegeable about different construction methods and materials.
I've been informed that my idea about using CM won't quite work out, and that the stressform method (folding ply around bulkheads) would be easier/quicker.

I have plans for the Quattro14 by Richard Woods, which I'm using as a general "how to build a boat" guide. It's got too much of a Deep-V shape to the hulls, too much rocker, no dagger-boards, and an exterior deck-flange. Looks like a fun boat to sail and likely competitive with most of the current F14 fleet, but by no means a modern performance-driven design.

It's too out-of-date to even base a modern design on, and that is my purpose in this venture: to give the public a design as modern as possible so they will have a starting-point for building their own boat. I'm not trying to sell anything, and (after testing, if the boat proves to be worth building!) will post the design free to the internet.
I'm also trying to figure out how to design sails so that I can post the patterns for making the sails out of Dacron. I'm trying to keep in the "spirit" of the F14 class for good, cheap fun

My biggest concern at the moment is how to transfer a 3D design to a 2D surface. Basically, what shape will I be cutting out of the plywood that will fold up into the boat I design. Towards this end, I'm going to take some large rolls of paper, Tyvek or what-not, and lay them out on some upturned hulls and trace the pattern. I want to check out some TheMightyHobie18 hulls, P18-2 hulls, and Hobie Wave hulls, and study the difference in the patterns. Obviously, I'll be shooting for somewhere in-between.

Also, I'm concerned with how much radius I can bend into the 4mm plywood. This will ultimately dictate wether or not I end up with a nice round bilge or a rounded-v shape.


G-Cat 5.7M #583 (sail # currently 100) in Bradenton, FL Hobie 14T
Re: Designing the next F14 [Re: Sycho15] #34584
06/25/04 12:02 AM
06/25/04 12:02 AM
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Sycho15 Offline OP
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So... I sat down to draw a to-scale (1"=1') side-view of what I want the boat to look like, basic dimensions, beam-placement, board placement, etc.. It was quite the learning expirience!

I drew the hulls first, then referred to my Quattro 14 plans for beam placement (has the leading-edge of the mast beam at the 7' mark), then drew in the dagger-board and sloped the stern end of the keel up to the transom (might have made the transom too short, will deal with that later). It looked pretty nice, until I drew in the mast and boom To get a 140sq.ft. mainsail I had to go with a 23' luff and 8' boom with a roachy square-top (this was by playing in Sailform). The boom would overhang the transoms by over a foot, and the dagger-board (and thus CLR) would be well forward of the CoE. (I drew the mast in with a very slight rake to it)

I realized that, as a boardless/skeg boat, the Quattro 14 would benefit for it's mast placement by keeping the CoE closer to the rudders, which must make up a good portion of its lateral resistance. However, going with a boarded design requires some changes.

I wrote down a short list of solutions:
1) move board aft (but it would have to be very near the aft beam to balance the main)
2) move the mast forward (looks like it would have to be moved ~1'6" forwards
3) move the mast forwards 1' and the board aft 6"

I'm leaning more towards #2. I know most of the new high-performance boats have the mast right about center or aft of it, but they also have much higher-aspect mainsails that keep more of the drive close to the mast.

I posted this to "test my logic" with you all, as I'm going on eyeball-assumptions from my drawings for right now. I'll be making a few more drawings tomorrow and see how things turn out.

(Berny, I'm currently kicking myself for thinking a 24' mast would be tall enough. I think I'd prefer a taller mast and shorter foot to get the 140-150sq.ft. mainsail! Anyone care to re-write the F14 rules to allow taller masts? )


G-Cat 5.7M #583 (sail # currently 100) in Bradenton, FL Hobie 14T
Re: Designing the next F14 [Re: Sycho15] #34585
06/25/04 12:25 AM
06/25/04 12:25 AM
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If you were to use a 25'6" mast section and a slightly shorter boom and dont try for "140 sq ft" of sail area (remember that half the diameter of the mast bounded by the luff length of the sail is counted as sail area, and it is) you should end up with an actual sail area (minus the mast area) of about 130 to 135 sq ft. That is more than enough on a 14' cat with that aspec ration for the main sail, any more on the main and the boat becomes very "condition specific" losing out on conditions other than its "ideal", the "actual sail area" of an "A" class main sail is only a few sq ft more!! And only use about 6" of aft mast rake at the head of the mast, if the boat is balanced that should be all that is required (forget about Hobie 14 and similar, they have a sail plan that is basically unbalanced and use extreme aft rake to try to correct other inefficiencies in their design). When you have the sail plan worked out and scaled onto the plan, then position the C/B position to suit the C of E of the sail, not visa versa. It is not critical how far back the C/B's are positioned aft (with in reason) the only real effect is that the further aft the boards are the higher the boat will sail to windward - Take a look at where the mast and C/B's are on the last few "C" class cats - their rigs and C/Boards are as far back as it is possible to put them and they seem to perform fairly well!!
Darryl

Re: Designing the next F14 [Re: Darryl_Barrett] #34586
06/25/04 12:43 AM
06/25/04 12:43 AM
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Our rules for an F14 (as a completely new class/design but by incorporation of existing 14'cats by encouraging their inclusion by useing a "grandfathering" rule) allows any length of mast you like, but you will find that you soon reach the maximum practical mast height some where about 26' after that the rig becomes imbalanced, in fact I personally feel that around 25'6' is as high as you want to go and still have an all round balance to the boat, others may differ but thats why there is no restriction on the mast height so that experiment and innovation can occur while still remaining within the "box rule" of the total sail area that can be used. As far as mast step position is concerned, the best balance is at or behind the centre of the hulls,fore and aft, if you place it forward of centre then only place it as small an amount as you have to as the further forward it is the more pressure is put on the bows while sailing and the more prone the boat is to pitch pole.
Darryl

Re: Designing the next F14 [Re: Sycho15] #34587
06/25/04 05:46 AM
06/25/04 05:46 AM
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I'll make one comment :

140-150sq.ft. mainsail! is to much for a 14 foot catamaran. Forget about that area. Even if you do managed to get it in the mainsail the boat will not be well behaved as the short hull are far less resistant to pitching. I know 140-150 sq.ft. sounds cool to have but I trully think this to be an illusion I would try 110-120 sq.ft first as an absolute max. My calcs suggest 7 mtr mast = 22.95, 10.17 sq. mtr. sail = 109.35 sq.ft. of mainsail and a foot of about 1.93 mtr = 6.34 ft. If we round everything of then lets say 7 mtr mast, 110 sq.ft main with 6.5 ft foot. This box is a scaled down F18 mainsail with a modern squaretop and with the boom at 0.350= 1'2" above the tramp near the mast = low. This rig is scaled to the seriously reduced dive resistance of the F14. In flat water and with this rig it will behave much like a F18. In waves the short hulls will be at an disadvantage more as the waves can not be scaled to suit the F14; that is something to just accept. To approach the F18 performance the platform + crew weight needs to approach 153 kg = 337 lbs. Thus assuming the F14 is sailed with 75 kg's skipper = 165 lbs you'll need to build the platform to 78 kg = 172 lbs.

This is all within realistically achievable specs. So if you want the short and effective route to a very decent F14. get the measurements of an F18 you like and scale everything by a factor of (F14 Length/F18 length) = 4.27/5.52 = 0.7735 or maybe 4.30/ 5.52 = 0.7790 as I don't know what the maxim F15 length is. I think a factor of 0.78 would work well and be accurate enough.

This is something I would do with one exception. I would decrease the height of the hulls much less than the ratio suggest as you'll need to clearence to stay clear of the waves. However the underwater body can be directly copied using this factor, beam locations and board locations as well.

One more comment : Be very careful of scaling down an A-cat as the ratios of this boat are completely different than most other catamarans certainly when compared to a F14.

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
Re: Designing the next F14 [Re: Wouter] #34588
06/25/04 06:53 PM
06/25/04 06:53 PM
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Sydney Australia
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Quote


I'll make one comment :

140-150sq.ft. mainsail! is to much for a 14 foot catamaran..............

Wouter


Wouter ask Phil how a well designed 14 with 145sqft goes in 20k+

Bern
P.S. Brian, here in Oz we are not restricting the mast height in our F14 draft regs.

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Last edited by Berny; 06/25/04 06:56 PM.
Re: Designing the next F14 [Re: Berny] #34589
06/25/04 08:20 PM
06/25/04 08:20 PM
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I re-drew the design today, and I have to say it looks much better balanced.

I moved the mast-beam forward 6" so the mast is sitting directly mid-ship. I moved the dagger-board aft 6". I drew the mast verticle (5 degrees of rake shouldn't change things too much and I didn't have a protractor handy), resized the mast to 25' and shortened the boom to 7'. The mainsail has a luff of 24', a foot of 6'10", and 139.99sq.ft. of sail area (aspect ratio went from 3:1 to 3.5:1, for comparison: my G-Cat is about 4:1 and a H14 is about 2.75:1). I drew the mainsail with two reefing points in it, so that makes any argument about needing a shorter mast and smaller sail a moot point.

The drawing has a 10' spinnaker pole, which is pure guesstimation (it looked good on paper) of how long it should be. The r/f reacher just needs to be under 160sq.ft., so whatever its dimensions work out to be is what will dictate pole length. I can get uber-cheap windsurfer masts at a local shop, so that's what the spinnaker pole (and maybe a righting pole so lighter crew can right the boat) will be made from.

I'm just waiting on my next paycheck (~ 7/1) to get some plywood and do some bending tests to determine what the bilge-shape can be. What do you suggest as the best plywood for this?


G-Cat 5.7M #583 (sail # currently 100) in Bradenton, FL Hobie 14T
Re: Designing the next F14 [Re: Sycho15] #34590
06/25/04 09:36 PM
06/25/04 09:36 PM
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Posts: 1,012
South Australia
Make the spinnaker pole come to exactly 1 metre in from of the front of the hulls. Will give plenty of spinnaker and keep it controlable throughout a large range of conditions and the boat will pretty well balance. Don't go for "the largest spinnaker that you can fit on the boat" as you would find that you will have area but you won't be able to set it in all but a few specific conditions, and it is better to have a smaller spinnaker that sets in light airs than a giant that won't fill. In heavy airs the smaller and more controlable the kite the better you perform.
Darryl

Re: Designing the next F14 [Re: Berny] #34591
06/25/04 09:40 PM
06/25/04 09:40 PM
Joined: Jun 2001
Posts: 9,582
North-West Europe
Wouter Offline
Carpal Tunnel
Wouter  Offline
Carpal Tunnel

Joined: Jun 2001
Posts: 9,582
North-West Europe


Okay I'll bite ; how much sail area is on your 430 ?

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
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