Wanna help design the next F14?

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.

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.

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.

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

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

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

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

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).

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

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

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

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.

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? )

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

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

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 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.

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?

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

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

Wouter

It's not a bad thumb of rule that on a cat you keep the spinnaker just a few sq ft smaller than your working sail area
Remember that unlike cars "more horse power" does not always make a boat go faster. You still have to be able to control all the power (and through a wide range of conditions as well)
Darryl

What are you doing up at this time of night WOUTER (in Holland) did you get my email?? and the attachment??.
I'm sure that Berny will answer, but I think he is running over 140 sq ft of main sail on the 430. It is a little large for my liking but it all seems to work fairly well on his cat.
Darryl

I just spoke to Greg Goodall who is here in NL and after that I dug out my boat that was underneath 300 mm of sand. We had a big storm going over our coastline for the last 2.5 days and I feared my boat got damaged. The hulls are okay but I fear the trampoline has been stretched to its extreme. There was 200 mm of sand on it and as it had rained as well it was waterlogged. Dry sand is given as 1600 kg /m^3. I calculate that some 1.91*1.81* 0,20 * 1600 = 1087 kg !!! was lying on my trampoline. I took it off very carefully. The Trampoline is hard now as all the elasticity has gone and it almost behaves like a hard plate shaped to a 3D shape. I hope it either resumes it manufactured shape over the next couple of days as platics sometimes do or else that I can get it within acceptable parameters again by pulling on some tension strings. Else I'll have a problem for the coming event I'm organising.

Will read your mail now !

Wouter

My previous quote gives a clue
Bern

Oh, I should also have said the boat's presently uni-rigged

Where are you up to with this Brian? I note discussion has stalled. Did you get the help you needed?
Bern

Here's the profile drawing of the "Freestyle 14". It's taken three drafts to get to this point. If you have difficulty seeing the measuring lines, here's some points of reference:
The transom is 1' tall, the tallest section of the hull is 2'6" tall. Along the bottom is 14' with the curve of the bow accounting for the extra 3".
Freestyle 14 profile view

No cross-sections just yet. I need to get some side-walk chalk and a long timber batten to help me figure out some things. Such are my tools

Hello,
you originally asked about rocker. It's a very important curve. Yours looks allitle flat forward and maybe too curved in the last 18"...or did you invent a most superior rocker?
It would be cool if there were a data base of the various rocker curves of existing cats. A data base of the rest of their features like mast height, hull volume would be good too. Guessing that the Texel guys must has some of this data to create their #s.
it's just that a visual curve is good as a spark to the imagination. Maybe if we posted pictures of the side of our hulls we could vectorize the profiles and get the rocker curves.

Because we use alot of it, i would shape the hulls from styro to test different hulls.
the whole project is for those with free time and money to play with.
have fun with it.

I would certainly appreciate some help with the rocker design. Some measurements off a board boat would be helpful. Here's how they would be useful:

Length of waterline of boat measured.
On a flat surface: set the boat so the bow and stern of equal height above the surface and measure that height, as well as what part of the hull is in contact with the ground.

For example: A Prindle 19 has about 18'9" of waterline. If the bow and stern were each 2" off the ground, the section of the hull touching the ground would be 8' from the stern.
(The above example was total random guesstimation, but information in that format would be helpful to me.)

Or... if you can use some sort of board or chalk-line... make a line from the bottom of the bow to the bottom of the stern, and measure the deepest part of the hull and it's location relative to the stern.

Hey,
The best thing to do if you really want to design a boat is look at what makes other boats so good. Is the Flyer really that much better than Goodall and Boyer's mach4 or is it just that all the quick guys Like Ashby and Bags sail flyers. One of the most successfull cats of the last two decades in australian quick cats would have to be the taipan 4.9. Still considered by some as the bees knees. It's greatest point was matching aesthetics with speed and balance, and for the time it came out it was miles ahead of the pack. If you look closely at a taipan you will notice that the butt end resembles very much a mosquito, which boyer was still building at the time of inception. and the front looks a mighty lot like an early A class. The reason they didn't just scale down an A class is that there isn't enough bouyancy for two people with the A hull.

You must remember to take into account things like change in bouyancy when looking at other designs for inspiration. If you down scale a Flyer hull, which seems like a good idea, keap in mind this amount of bouyancy was made to hold up one bloke and 76kg of boat. Not a whole heap in my book, seeing as I build 3500kg bluewater cruising cats. If you down scale something like a Flyer or another A you will lose bouyancy, and the hulls will dig in more unless you're a midget or a pygmy, no offence to m's and p's.

Don't jump in the deep end with this, talk to lots of people about this. People who know what they're talking about. If you can get a hold of guys who have built prototypes before talk to them about what went wrong and then don't add that to your design. prototypes take time. The first AHPC F18 capricorn took about 12 months to make it to the water.

One thing you might like to know. A guy buy the name of Russell Denholm who has won every class in the Taipan classes, 5.7, 4.9sloop, 4.9cat, the only other to do so was Glenn Ashby. Russell has built an A class catamaran that from a birds eye view looks like a foil. the widest part of the hull being just forward of the front beam. It was much quicker than any of the top A boys on their Flyers bot the thing couldn't turn. This problem will be solved with the next prototype to be finished soon. You may also have to do this yourself. Maybe 2 or 3. Remember also, you dagger boards should sit equal with the draft of your mainsail. Meaning the deepest part of the main. Papertigers have altered their center of effort over time using foil rake, to mave the COE back as masts became rakier and rakier.

You will need to keap everything in mind. Keap looking at other boats of all sizes for ideas though. You may have to name it after the huge number of boats you stole ideas from.

Beddoe(wookie)

Here is the latest-and-greatest attempt at the profile view of the Freestyle 14 catamaran. I've been to a few regattas lately and sailed on a couple spinnaker boats and have been taking notes on their hull designs. [note: this picture is not exactly level]



Comments and critiques would be greatly appreciated!

The 2'6" deep hull is way too deep. THe Tornado is only about 24" deep, and you are only going to be hauling 1 person and a 150 lb boat. At one time, I had 800 lbs of crew on my 360lb T and was out in big wind, and had a problem smacking beams on 3' waves then, but you should not with 350 lbs total. You need to be careful with the volume up front. I did not do that on an A that I built (it had the max width nearly straight from the front to the 9 ft mark), and the hulls were real prone to go nose down so had to cut the bottoms off and spread them a bit. Then the next bottom was too fat up front... both great (if expensive) learning experiences. So that is 2 mistakes I will not have to make next time You will likely also want a bit of rocker on the front of the hull so that it will turn easier, like in the first 2 ft. I honestly beleive that the extreme rocker that you have on the back of your hull will cause you to go slow, by making the hulls drag along too much water. Go take a long look at a T which is a superbly designed boat, even though old. Plus take a look at the Flyer if you can find one. The back half of the hulls are a nearly flat line: meaning all the rocker curve is near the middle of the boat. My personal opinion is that the straight rocker on the back sections are required for good speed, and my next A-cat will have that trait.

If it were me building this hull, with only 14 ft to work with, I would make a high aspect ratio mainsail, using the 26 foot Carbon fibre mast as quoted. I would make the sail a square top main with about a 5.5 ft chord that would continue for a good distance up the mast and then taper to 2 ft square top. I would put a circular traveler on it, and put the rear beam about 1'8" from the rear of the hulls, so that you can have atleast a 1'4" arm on the tillers. If you use a 6 inch chord wingmast with the pivot about 2 inches from the front of the mast, the center of your main beam would be about 5'7" from the center of the rear beam if you put the traveler on top of your rear beam. Personally I would make the hulls about 13 or 14 inches wide at the top in a tapered shape similar to the T at the middle and then taper to about 10 inches wide at the transom. I am also now a big fan of the tapered top on the front of a hull that Bill Roberts pioneered, leaving the thickest part of the hull in the middle. The Taipan 4.9 does this a bit on the very front of its hull, too, and that is a great little boat.

Maybe if I remember this thread while at home, I will draft up something that I would consider way better than what you designed and post it. It only takes about an hour now after having done so many versions of the A-Cat.

I think the 14 needs to be re-thought and radical (especialy if it is someone else's time and money?)
I would try deep hulls so the boat is less prone to hobby horsing (short shallow hulls will be a disaster in this regard, even though there may be strong arguments to support planing hulls)
This could be countered with a mast well aft and large rudders, no centerboards. While twitchy and not easy to "get rolling" the boat would tack and drive really well. A cable type traveller "track" for the mainsheet from rudder gudgeon to rudder gudgeon? I believe that in the real world of chop-whenever-it-blows any, the extra wetted surface of narrow deep hulls would pay off in fore-aft stability (not "shaking the wind out the sails")
Mast aft also reduces pitch poling off the wind. While the moment produced is unchanged (center of effort is still acting at same height) the mast weight and inertia are further aft which effects the countering moment and response time.
Maybe a longitudinal center beam from fore to aft crossbeams with multiple mast ball mounting holes and multiple shroud plate mountings at the hull fabrication stage would be reasonably cheap to do, and you could learn a lot fast. Maybe you could do without a hooter pole, a savings in itself? if the mast was way back.

Are either of you familiar with the Formula 14 class specs? We've got 14'3" of waterline to play with, and 300 sq.ft. of sail. Running without the reacher isn't even being considered, especially after the H14Ms showing at Spring Fever 2004.

In the picture, the mast is shown with no rake because it was easier to draw it that way; it will be raked back a bit. The mainsail area is ~140sq.ft. The reacher will likely be the same.

The hull rocker more closely resembles the AHCP Capricorn and a few other F18s I've looked at. I only have 14'3" to work with, so I can't have the long clean straight lines they get. I have that steep rocker in the back so I can really leverage myself off the stern of the boat to keep the bows up without too much bouyancy fighting against me.

I haven't done cross-sections yet, but the hulls will have a high Cp, with the volume down very low. The bows will curve back together at the top, with pretty much no flat deck ahead of the mast beam. The reason for the tall bows is to allow me to create this curved section without compromising the shape, and to give me the extra "stuff it" ability in heavy air while carrying the reacher. It shouldn't add much weight at all, and the extra windage should be minimized by the curved shape.

On the off-chance you didn't notice, clicking on the picture takes you to a much larger version.

Concerning the rake aft of the knuckle:
The water only knows its relative speed to the hull. Therefore if the rake here is steeper than other boats of comparable speed, who have it figured out, it will be draggy (want to detach, but can't) Bernouli says the decrease in velocity must cause an increase in pressure, so the water slows to fill the hole, and its surface climbs to correspond with the increase in pressure. Now if the boat is past its hull speed, the former bow wave or trough may be back here, and so what happens then?
Personally, I theorise that rocker has no place in a short fast boat, and turning ability has to be achieved by other means. (ref previous poster) This leads to a canoe stern below waterline at keel-line elevation(bottom of boat) and a wedge shape in plan at deck elevation ( no reverse taper to stern, but taperd all the way to the bow from stern). If you can accept dxf or dwg files, I will send you an iso of one I worked out. Basicly a minimum drag at keeline, transitioning to min waveform at waterline. (Built a 1:10 model of hull form and then got side tracked)

Hi guys,

Sorry to jump in on your topic, just came across it and had a few thoughts.

Perhaps you should be looking at other high performance short boats like the Moth. As you're dealing with a very short hull length and a conceivably very high power to weight ratio, perhaps there is potential to have quite a flat bottom (in terms of rocker) that is only very narrow in width (ie 150mm) that has a flat bottomed planing area?

Two Moths strapped together with a nice big powerful rig on them is a very interesting prospect indeed. Pity they're only 11ft long.

[img]http://www.catsailor.com/gallery/display.php?album=lastup&cat=10032&pos=3[/img]

how's this http://www.catsailor.com.gallery/

Yep, ok. feeling pretty dumb about now will do some more research before posting next time so I know what I'm talking about.

Looks like a great little boat Darryl, rake the mast a little, and whack a kite on the front and lock the feet in some footstraps down the back and off we go!

Sorry if I'm igniting the spinnaker debate again but 14ft is probably the right size for single handed with kite - get a bit intimidated by my Taipan with kite solo (with my crew its not too bad).

Have fun guys! I'll pop in from time to time and see how things are going.

Andy.

If you notice on one of the photos there is a little black cylindrical fitting of delrin in the middle of the front beam in front of the mast base! thats the supporting base for the carbon spinnaker pole (which is standard -thats why it is an F14!!). There wasn't any wind whatsoever on Saturday the 27th of November (when the shots were taken) so not only did we not sail but it seemed a little premature to rig up the spinnaker?

Very nice boat Darryl! Have you tested it much yet?

To the person comparing a Tornado to the F14, especially regarding the bow height, please remember that you have two men almost 20' from the bow of that boat which gives you a whole lot more leverage than a single person only 14' away. Especially considering the F14 is aimed at lighter crews. The heavier guys would likely be on an I17. We'd like to see the F14 class be able to cater to women and children as well as the rest of us, and are designing accordingly. I'm doing everything I can think of to keep this little boat of mine from ever wanting to pitchpole.

Shouldn't the Capricorn be slower than other boats in it's class, as it also has a lot of rocker in the stern while many other boats in it's class don't. Instead, it's kicking butt and taking names. However... I'm working on a drawing that will reduce the aft rocker to 6" instead of 12" by having the deck drop by 6" after the rear beam... I'll be posting a new drawing tomorrow (Wednesday)

Mr. Barrett,
tell us about those rudderheads, if you please.

A lot of "little" changes in Draft #5.

1)The section of maximum width was moved from being centered under the mast to being entirely ahead of the mast. The reason being to give a better foil shape to the entire hull, and to gain more leverage against the rig.

2)The daggerboard has been moved forwards 6". This puts it around 1/3 aft of the mainsail luff.

3)The mast rake has been drawn in. I set it so the sidestays go almost vertically from the chainplates to the mast hound (which is set 2/3 up the mast)

4)The deck drops 6" after the rear beam. This allows the rudders to be mounted lower and allows the aft rocker to be lessened to 6" from the previous 12".

5) The fore rocker is still only 3", but it now ends 5' from the bows instead of 6'



I might move the fore rocker back to the 6' mark, I'm not sure I like it as much in this draft as in the previous one.

I drew the boat on an oversized grid to help you all get a feel for the dimensions, and actually managed to get a pretty level picture of it this time.

Darryl's rudder design looks amazingly similar to the G-Cat system. If my original G-Cat rudder housings hadn't been destroyed, I would still be running them and loving every second of it. It's a great, simple, and very effective design.

I have designed and used many different styles of rudder stocks, rudder head shapes, and rudder lock downs, over the years, and these are as simple as I could make in our work shop using nylon turned down and shaped for most of the components with a threaded both ends, stainless steel rod as the "pull up/ push down". It was simple, works faultlessly, is strong, and most of all it is easily and quickly manufactured in house on a good cost basis.

As far as the actual "rudder head" is concerned, they are shaped with a small protruding "crane" facing aft to give the correct leverage and arc to the rudder swing in the stocks.

as previously asked in the other thread, what do you expect your F14 to be sold for darryl?

Hi Darryl,
Please could you post a pic or 2 of your boat directly on the forum, if I follow your link to the catsailor albums I get hung up for half an hour, and then see a white screen, which is not much to go by.

Cheers
Steve

well,
i must have meant rudder stock when i wrote rudder head. if they were on a hobie they would be castings. what is the black material that is on the sides? If you sold them or the plans for the stocks, how much would they be?
i dream of building a mini version of that giant cat with the seaplane hulls and 2 masts. Although the hulls of the mini may not be the seaplane type hulls, the rigs and beams i like.
cheers

I have tried repeatenly to post pictures direct onto the forum steve, but I have given it up as a "black art" that I can't seem to crack the code of.
The rudder stocks, as almost ever other part of the cat, are 100% carbon fibre (except where we have used Kevlar as well) We make the stocks from moulds that I have made in the work shop. We would sell any part of the cat as individual items to any one who was interested in them, but it is still a little premature for us to have worked out the price structure for individual items, our main concern at present is to fully test the cat as a whole over the next few months so that we are confident in it's performance as well as the structural integrity of ALL the componentry before any of it is "put onto the marketplace" besides things like rudder stocks for one cat are not necessarily suitable (due to the differences in transoms) for all other cats

Not to sound like a whiney bastard, but could you start a seperate thread regarding the rudder system you've developed? It'll bring more attention to your rudder system and not side-track this thread which is supposed to focus on hull design (though it does seem to have stagnated a bit). I should be putting another draft of the Freestyle 14 up this week. Just more work on the rocker, hoping to get a general "thumbs up" on it so I can get on to developing the cross sections.

Sorry about that but if you read back through the immediate posts, you will see that all that I have done is to respond to direct questions. Still it is your thread and I apologise for conjesting it with other matters, mind you what has been said should be of some interest and advantage to you while working on your own design, like they say "a designer can never have too much imformation"

Darryl, I actually want to hear all about your rudder system- just not in this thread. People who are looking for rudder information will likely skip this thread and the information will be lost to them. For my rudder systems, I've got two sets of Dotan Sampson 25s and two sets of Hobie 14s. Likely I'll make the mounts set for the Hobie 14 system and adjust the Dotans to fit. Then I can run whatever system will hold up better. The Dotans won't hold up at all on my G-Cat 5.7M, but I think the F14 is just the boat for them.

well sir,
i gotta say the rudder system is part of designing a cat, and the title doesn't say only the hull design. didn't mean to side track your thread.
i seek to post a side view of a c class hull which has a fast looking rocker. admittedly cogito has a curvier rocker and was faster around the course. cogito's hulls came out of the paitent lady molds which have got to be over 10 years old. so i recomend that you closely follow existing design.

the attachment seems to have worked. all i did was hit the browse button and navigate to my desktop where the picture resided. the catsailor server seems to host the picture for us once uploaded from our computers.

Mmm, is that a wooden rudder I can see at the stern??