Alternate F12 Design

Just to let you know that you are not the only one working a new design, I have taken a different tack as I am trying to build as cheaply as possible. hence the windsurfing rig. It will have stays attached around the boom attachment point, maybe with a sub-mast as is my current boat.

Having started teaching youths to sail I agree with you about daggerboards as manoeuvrability is very important, although I may go with leeboards.

I am also considering going with just a single central rudder.

I know of at least one other person working on a F12 design so this is not dead yet.

Gareth

You guys may add me to the listing as I'm still working on it. Thanks to Gareth (Grob) I have a nice 3D drawing of it as well, although a few modifications need to be made before the pics will be publicized on this forum.

I too use a non rotating mast, but it is also unstayed. Interestingly my rig is somewhat a cross between the rig by Gareth and Chris.

I too intend to make it available to homebuilders.

Maybe it is wise for the interested parties (designers) to get into contact and finalize the F12 specs between us.

As Gareth is certain right, the F12 is not dead yet.

Wouter

Now that's an F12! <img src=

alt=

/> In my opinion by far the best design so far. How much do you figure it'll cost to build?

Buccaneer,

I haven't tried to price up the design (and probably won't at this stage). As I mentioned in the first post this was literally a morning's work. I logged onto catsailor at about 9am and read through the F12 forum for the first time. At present I'm doing a lot of powerboat work, which I don't find very stimulating, so I decided to have a quick play with F12 concepts. I'd settled on the above design at lunch time, had a meeting with a client and then logged back on to post the drawings in the afternoon.

My reason for doing it aside from my own enjoyment was to bring the design process back towards what I believed to be a more universally acceptable solution. Without wanting to attack the people working on them I don't believe non-stayed rigs or modified windsurfer rigs offer the best solution. By definition a non-stayed rig will end up heavier and windsurfer rigs aren't designed for the righting moment available to this vessel. As a result it will be necessary to use a very stiff Carbon Tube to get it to work which will result in this style of rig being more expensive than a traditional aluminium mast.

I also wanted to demonstrate the much improved hull shapes available by adding one more chine to the hull shape. As Phill mentioned in another thread, there is only a couple of days work required to produce a set of plans and cut files for a boat like this. While I'm happy to spend the time doing this I don't currently have the time to be building a boat (otherwise I'd be building an F16) but as I mentioned above if people genuinely want the drawings I'm happy to produce them and there is no reason for the boat not to

work

although it won't be a fully optimised design.

I did do a full weight and cost analysis and I'm hovering around 2500 Euro's for homebuild boat were you buy the rudders and stocks of a commericial company.

In the way of weight analysis, my 6.400 mtr long unstayed mast comes out at 10 kg or less and this is 1.5 kg per mtr. I don't think this to be too heavy especially if you recognize that most weight is concentrated low on the mast where the mast is widest. The unstayed rig is tapered you see, where the mast at the bottom is 60 mm wide with 5 mm wall and at the top is 40 mm wide with a 2 mm wall. The centre of mass is at 2.5 mtr (or less) instead of at 6.4/2 = 3.2 mtr as would be the case with a untapered conventional mast section.

This data is dependable as I have measured and sailed with 3 different kind of unstayed masts on my landyachts and these masts take a good amount of abuse. The landyachts have 5.5 to 6.5 sq. mtr of sailarea and easily lift a 50 kg cart with a 90 kg skipper of the ground. That is in the wind we sail our landyachts in.

This is one reason why my F12 will have a unstayed rig. The other is that the rig you can have with an unstayed mast is so easy and so quick to rig and unrig. Pretty much it is a sleeved mainsail that you shoove over the mast before stepping the mast. Fully rigging my landyacht from the trailer takes a few minutes at the absolute maximum. Derigging is done under 2 min. I really would like to have that feature for my F12 design as well.

Having said all that, I think it to be very healthy to explore different routes, so please continue developping the stayed F12 !

Afterwards we'll compare all designs and settle on the most promising.

Wouter

Chris
Could you post a view from above (plan view)?
Thanks,
Bob

Wouter,

with all due respect, I'd recommend checking your mast calcs. The F12 will have significantly more righting moment than your land yacht and it is righting moment not sail area that defines mast requirements. I did some quick calcs on your proposed mast and you appear to be lacking section modulus (shear area is ok however). You might want to look at increasing the diameter and reducing the wall thickness.

How do you know ?

Besides righting moment is not all of the picture, it is only a minor part. Most of the bending stresses are the result of the mainsheet used. On my landyacht this is a 7:1 tackle and that really cranks on the loads. My F12 will only have a 3:1 tackle.

I did all the math, at length. I know what I'm talking about.

Wouter

Thanks for posting the picture Chris...I am a little surprised at the narrow width of the bows... with the volume of the bows being the deciding factor on how hard a cat can be pushed, what determines the height of the rig, etc...Wouldn't it be beneficial to increase the width of the individual hull slightly (to increase hull volume) in the forward area instead of it being such a wedge shape? Looking at the profile and plan shapes together it seems you have a very balanced volume flow from bow to stern...I take it you feel this is of greater benefit than having increasing buoyancy as you move towards the bow. Could you explain your reasoning?

Best Regards,
Bob

Wouter, if you're happy, I'm happy.

Seeker, one of the things I've observed, is that the last thing novice sailors (and kids) learn is where to place their weight longitudinally. With this in mind and realising that the need to come to the back beam when they tack will probably keep them towards the back of the boat, I tried to keep the LCB (longitudinal centre of bouyancy) as far aft as possible (hence the fat butt). Experiance also shows that if you can keep the LCF (long. centre of floatation) as close to the LCB as possible you will use less energy (speed) when pitching (the same reason we keep weight out of the ends of boats). Given the short length of the boat this resulted in the straightish (there is curve there)run aft. You should also note that the important bouyancy in the bow is related to how far it is fwd of the LCF, so by moving the LCF aft we can remove some volume fwd (does that make sense). I hope this helps.

Chris

Chris (and others),

Up till now I'm happy with the data.

To support my earlier statements and my

How do you know ?

; I here provide you with some data. But indeed I feel both paths should be followed, stayed c.q. unstayed and see what works best.

Largest unstayed mast sailed in abundance (Standart Landyacht : http://www.char-a-voile.com/franc2/seagull.html) and measured by me was fitted to a 2.60 mtr wide landyacht of 75 kg car weight with a 90 kg skipper in it (me), carrying a 6.0 sq. mtr sail. The mast weights 8.15 kg overall and is 5.51 mtr long. It also uses a 8:1 tackle system (more then my own class 5 yacht).

Interestingly enough this landyacht righting moment is almost exactly the same as my 60 kg F12 with 1.85 mtr width with a 60 kg crew hiking of the side (not trapezing).

The 3:1 tackle system of my F12 at the end of the boom (2 mtr) results in less bending moment then the 7:1 tackle system at 1 mtr along the boom of the standart landyacht. Not much less but still less.

Interestingly enough both designs are quite close in there load pattern.

But also my current unstayed F12 mast design is 6.4 mtr long weights 9.5 kg and has a centre of mass of 2.400 mtr and it is (stepwise) tapered. The latter means that it is made up of plain prismatic tubing of decreasing diameters (3 or 4 sections). This makes it easy to homebuild and too collaps it into smaller section for transport.

Interestingly enough a plain conventional prismatic mast section must be no more then 7.125 kg in order to arrive at the same righting moment when horizntal. That is 1.12 kg/mtr and that is quite light for an alu mast. Note that the F16 alu masts are 1.65 kg/mtr. Actually 1.10 kg/mtr is only achieved on carbon F16 mast, but is used diamond wires as well as the F12 mast will not.

So this unstayed alu mast concept is not at all without attractive promises, especially when noting that real life version of this design has been in use for many years already and have proven to be reliable.

This is one reason why I'm continueing with this path. And indeed I have done math along that way.

So my mainpoint here is that we should not discard the unstayed mast to easily. The landyacht people have really progressed this idea into a dependable and high performance design.

Wouter

Chris how hard would it be to have kick up centreboards instead of slot in. The boards appeal to me and I know they don't have to be in at first but 7yr olds and boards
regards

Jeff sorry for the delayed reply. This week has been crazy. No reason you couldn't do these, they are a little more complicated to build. Basically they would be a scaled down Tornado board.

That would make them a scaled down Stingray board then <img src=

alt=

/> Would there be any advantage in having removable skegs like a windsurfer centreboard that plug in the centreboard case from underneath and are designed to be dragged on the beach for the least experienced sailors
regards