Do what you must guys.

Personally I don't any kid carry 45 kg by himself either, let alone take it off the roof rack by himself. That is just not the way these things work. But more importantly I don't see many commercial builders go for a 45 kg boat and garantee/warrantee it too. Technically they can but commercially they won't.

I know that cat classes in Aus and NZ have typically build featherweight boats, but sadly none ever broke through internationally. Surely their light weights should have made these classes extremely hot.

I learned to rig and sail on a 750 kg sailboat when I was 12 and the fun wasn't any less for it.

The most popular dinghies for kids and teenagers (up to 16 years of age) are the optimist, splash and laser radial at respectively ready to sail weights of 45kg, 70kg and 80kg. I have never seen the kids handle these boats all by themselves.

We had this discussion many times before and the class will fail on this discussion over and over again. At some point you have got to make a decision. Go for a small 30 kg homebuilder class with main focus in NZ and Aus, or go for a fully international class and make concessions to allow for full growth and allow commercial builders to keep their pants in one piece.

I think I'm sounding like a broken record by now so I'll stop.

Wouter

A kid can drag their own weight no problem my 8yo at 45kg can drag 45kg. There is always going to be adult assistance when water and kids is involved but at 45kg a mum can help and be involved in the club or sail themselves. Hobie already has production 12 footers that fit within the F12 box rule, that are heavy and presumably their margins are tight to sell them. So I'm going to do what the original plan was thats build a light, modern looking, uncomplicated, easy to rig cat that suits the kids and myself. At 45kg or 50kg Arafura cadets can compete in F12 races and if that gets more kids sailing then its right.

Billby, the 50kg weight for the PT is platform only. The all up boat would be approx 65kg (I was corrected on this in a earlier thread).

Wouter, I can't help but think you are playing word games. The only person who has mentioned a 30kg boat is you. we're all talking around 45-55kg depending on what THE ACTUAL BOATS COME OUT AT.

Since I know you like numbers here are some.

3mm Gaboon DS12 kit 12kg (includes hull skins, bulkheads and longitudinal ring frame)

4mm Gaboon DS12 kit 15kg.

Note. this kit has been designed for easy almost "measurement free" construction and at least 2 kg could be cut out of it if you were looking to save weight.

Weight of glass/ resin / bog in DS 12 approx 4-5kg (much of this could be eliminated but has been included to make the boat more robust)

Carbon mast like Gatos 6kg rigged (his number not mine)

Aluminium mast rigged 6-7kg rigged (depending on selected section)

Weight of beams 4kg

etc etc.

Even the 4mm boat shouldn't come out at much over 50kg.

Rather than theorising build a boat and see where you come out. If you need a hand send me your geometry and I'll generate some cutfiles for you.

Gentlemen,

This group defined the F12 as a global multihull class for kids; that we want to bring kids to multihull sailing, that rationality and common sense shall prevail and that low cost, simplicity, safety and ease of assembly/disassembly are good goals, among other things. As a consequence, some measurements have been agreed on. Now we are focusing on minimum weight.

This is how I summarize the facts:

• A rotomolded F12 would be less expensive for mass production.
• A rotomolded F12 using today’s technology would weight around 70 kg.
• The rotomolded F12 would be more convenient to clubs, resorts and some individuals.
• The weight (and other) constraints associated to rotomolding will change over time.

…on the other hand,

• The ply or glass/foam home built F12s are today’s reality.
• The first home built boat weighted 52 kg. Its hull and foils were built with conservative methods/materials and the mast with carbon. From this boat alone it would seem that 50 kg is a reasonable number.
• Light boats are easier to transport and handle. They also perform well.
• Transport is a greater issue for home builders than for resorts and clubs.

Also:

• Rotomolding or other mass production technique will be possible after the class starts to grow steadily. It could take a year, ten years or forever.
• Scarecrow would like to have fixed rules as soon as possible.
• Wouter wants to keep this forum as the decision center.

I would like to offer the following:

• If everything could be planned and calculated from the start and written in concrete, it would be done already. It didn’t happen in the past and it is unlikely to happen now. Instead of chasing the elusive ‘greater truth’, I guess we should focus on how to make the class grow now.
• If I’d build today, I wouldn’t care about the minimum weight, only about the (perceived) optimum balance between economy, safety and light weight.
• It is useless to tell homebuilders that the minimum weight is X. If they want lighter boats, they will build them their way and add ballast only if and when the class grows enough to organize a race with boats of different weights in their area.
• Inexpensive rotomolded boats would be great, but how long will it take until we can have them built? What will be the achievable weight at that time? I believe we don’t know the answers.
• We are not an industry designing a new product; we are nurturing a class that will evolve. It is following an evolutionary path, so things will change over time.
• We can not predict the future. As a consequence, we don’t know what the ‘final’ minimum weight will be, when an intelligent adjustment will be required or who will be in charge at that time.
• Boat weights can be predicted with reasonable accuracy and the entire discussion can be based on one boat and calculations, but why do we have to do it right now? I’d rather have a few boats of each type sailing before taking the decision about the first minimum weight. The figure seems to be unnecessary until F12s of different designs race against each other. I suggest we postpone the discussion until that time. This would give more freedom to designers and builders and will improve our chances to achieve a better decision.
• If for any reason we must decide now, it would be best if the four designers agree on a safe number for boats built with the lowest and cheapest technology/materials they are willing to recommend for home building. Today I guess it would be between 40 and 60 kg.

I'm on vocation sailing with the family, with limited access to the net. It may take a while until I read answers.

All the best,
Luiz

Luiz,

Excellent post. The reason I'm advocating "committing" to a set of rules is because of the feedback I'm getting from many of the people who have requested copies of the DS12 plans. Few people want to build a boat that may become a white elephant. Its also worth noting that I'm only advocating a temporary minimum weight until the class has enough critical mass and data points to make an informed decision.

Billby how far of are the Vudus? A second data point would be very usefull at this time. Do you have a finished hull you can weigh?

I'm not theorising, remember I was the first one to produce a fully detailed listing of components and weights.

http://www.xs4all.nl/~whijink/F12/

http://www.xs4all.nl/~whijink/F12/F12_weight_and_cost_push_setup.xls

I found that things do tend to add up. Granted, I did include some margins here and there because amateurs and builders of series will typically not be extremely focussed on working very cleanly (light) but rather tend to be lazy or pressed for time (labour costs)

And my arguement revolves completely around the expected need to attract commercial builders to the F12 class and concept in order to succeed in our goal for the F12 to become THE youth/teenage trainer for larger cats and a viable alternative to youth/teenager dinghies.


Still, I would be happy to go for a very low ready to sail weight if it can be proven that such a setup is economically viable in a commercial sense. Gato's build DS's is indeed a good example of a robust boat (glassed over 4 mm ply), but building in ply is not really commercially viable at this time, mostly because high quality ply is getting more and more rare. Bending straight foam/glass panels or rotomolding are alot more viable economically in the long run. But foam/glass plates need relatively high density foam to avoid easy denting.

What I'm trying to do here it is underscore the long term effects the choice for a minimal ready to sail weight can have. We need to look at several different building methods and strike a good balance between all of these.


But indeed, if you all decide to go for a low number then I will submit myself to that. For my own frame I need all the weight savings in the boat I can get !

Wouter

Two reactions.

I'm with Scarecrow here on setting an initial minimum weight and re-evaluating it at a later time.

Also I feel it is very important to reach an agreement on the class rules soon, even if some values may be subject to change at a later time. At least the general setup, structure and a pretty accurate "feel" for the values should be set. Currently we still have the change to do it the easy way. Once several 10's of boats, plans have been build c.q. sold the discussion will only get alot harder. For this reason I'm personally very willing to compromise on any values.

I strongly prefer to start relatively high and adjust it downwards later, this is alot easier to enforce at a later time as a heavier boat will always be compliant under any new rules. This is pure an organisational benefit.


With respect to rotomoulding. I think the technology is readily available at this time. I had a look over the state of things in the Kayak sector and the shaping c.q. detailing that can be had with rotomoulding these days is quite impressive. Currently in kayaks, builders make one design and produce the same product both in glass laminates and rotomoulded PE. There is no design difference in shape left.

For us it could be as easy as going to a rotomoulded kayak producer with any of the existing F12 designs and buy into their expertise and tooling. The hard part at this time is to find a party willing to invest in this and that requires economic viability.

Wouter

That is a very welcome offer.

I do really like what you have done with the DS12. A very nice building plan and the hard chined hull looks every bit as modern as a compound curve hull shape.

Up to this time I have mostly concentrated on other aspects of the F12 design then hulls. And I do lack the experience with software to calculate the cutfiles. I can learn of course but I don't have to time to invest in that right now. So yes indeed, any help in this department will be warmly welcomed. Besides, I have to get down with several new software packages relating to my research assignment already, at one point enough is enough !

Also I want to proof the unstayed rig concept first before doing hull optimizing. I may even just use one of the currently available hull plans if I managed to gether the investment for a prototype.

Personally, I like the DS-12 best but I want it to be capable enough for a 90 kg body frame and have a tall bow section. The conditions over here are quite choppy and a low bow simply does not work as well as a taller one; that experience I gethered from the F16's. There doesn't have to be volume high up in the bow as long as the deck stays above the surface. When the deck submerges then something changes significantly enough for the dive to suddenly aggrevate. Fine decks help but not enough. Also I would like a sufficiently strong stern to take T-foil rudders and a high enough freeboard to have the beams clear the small chop. Apart from those items pretty much any hullshape will do.

Wouter

Wouter,

give a plan, profile and midship section in ACAD or similar and I'll make time to do the rest.

There hasn't been much talk of the tried and tested dinghy construction method of single skin fibreglass. This to me seems like a very viable alternative for mass production purposes, particularly compared with ply or cored composite construction. Home builders could also produce a single skin hull easier than a cored hull. Chined, semi-chined and compound curvature hulls can all be produced with single skin composite construction.

Admittedly it doesn't have the weight saving benefits of a cored composite, but this is only a small boat so significant weight savings are going to be hard to find with material changes alone.

Scarecrow, what is your basic hull surface area? (I haven't started a design yet.)

3.7 sq.m per hull. Yes single skin is definately an option just a little more work from a tooling point of view.

if you go through the old threads there is one with both my and RG's hydrostatics.

Thanks mate. A preliminary weight estimate looks promising from that info.

I'll probably incorporate a wet layup single skin into any design I do. I've got some ideas to put forward for construction as well...just to make life easier. After the mould is constructed, the aim is for a hull popped out in a day, or atleast the hull halves. Just need to sort out the beam mounts now.

Why not glass in a plate and tap the fwd ones and then just use a shed load of glass aft.

Scarecrow, do you have the drawings of the roung bilged hull ready? In that case I could have a go at a round bilged hull in foam/glass (stripplanking), and make mould of that one to be able to make production if needed.

Gato,

If you want to do one let me know I'll need a couple of days to tidy up the model. Its very preliminary.

If we do one we should call it the "hug and kisses, cherry blossom 12"

Edit...

Actually what we should do is I'll work with Ncik (if he's interested) to develop his design and you could build it. That way we'll get more ideas and designers into the class.

Guys,

It seems the voting for our basic set of class rule values is going very well.

Basically, we have no votes against the following values :

max length = 3.80 mtr
max width = 2.00 mtr
max sail area = 7.00 mtr.
min ready to sail weight = 60 kg plus a review of this value at a later time and after gaining more practical experience.

I think we must thank Scarecrow for giving the class rules discussion another try at exactly the right time. Well done mate. It looks likes this time we are going to reach a consensus.

This setup is already a pretty good box rule. Anybody want to add another limit to the rules. I'm thinking about introducing a max mast height to close the box off in the vertical sense. This will make all F12 very close in general appearence and general performance. Also avoid extremely high aspect sails that are difficult to trim, not something we want in a trainer class for impatient youths and teenagers.

Scarecrow, maybe you can make a last ballot on mast length. I proper 6 mtr because that is a nice round number (+ comparable to the Laser dinghy) and appears to sit right in comparison with the other specs.

Wouter

My boats, Gatos, RG's wont be F12's then Im not going to add a bag of concrete so that my kids can race.

A preliminary look at the Optimist rules indicates that they weigh about 45kg ready to sail. 35kg min hull weight (with bouyancy bags), approx 10kg rig???

The F12 is a bigger boat with a similar structural integrity requirement and bigger rig so it should be expected to weigh a bit more. A 50-60kg rigged weight with a corresponding platform weight of about 40-45kg does not seem an unreasonable minimum weight range at this early stage of the class.

Does this match up with Gato's experience?

Optimist Rules

Ncik,

working backwards...

Gato's finished boat 52 kg so the platform weight would be apprx 40kg. From memory his hulls are approx 15kg each

Scarecrow, knock something down with Nick and I give it a try.
To have a fair chanse to have it in the water when we still have the green "winter" I need something to start with beg. August.