There is a guy building a F16 in a way that looks very practical for homebuilding F12 hulls.

Go and look at his pics at :

Nicks F16 building pics

John (flatlander) would this be a method you would be comfortable with ?

If we use some heavy (high density) foam and don't skim on the glass layers the I feel we can have F12 hulls produced by homebuilders that won't be very heavy but still have a very high impact resistance.

The most interesting aspect about this building method is that it allows rounded corners on the keel line. I've learning in Aerodynamics class that that is very important for low drag. In effect you can get away with multichine construction and flat panels as long as the transition from one panel to the other is a large rounded corner. This is the way they made car bodies have low drag. The cars still have relatively flat panels under large angles as the main shapem but the intersection lines are strongly rounded.

I'm think of using this trick to make the F12 hulls relatively low drag without complicating the building of them too much. Pretty much we only need to have rounded edges on the keel line as the aerodynamics of a hull is negligiable in relation to the hydrodynamics. So the rest of the hull can still be a simple flat-paneled-bended-in-one-plane design.

More info on the way of building in this thread on the F16 forum :

Nick comments on the new way of building a cat hull

Wouter

At first glance...yes, most definitely! <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Because this method does circumvent any issue we might have sourcing quality ply.

Also I was think you could cut the panel in foam and then glass only one side and then bend this plate into its right curve and then glass the inside. Of course do this for all panels and then assemble the panels and glass tape the inside and outside chines to make a hull.

No scarving is then to be done and you'll end up with a multichine hull.

I have to check with some more knowlegdeable persons by I hear that 150 kg/m^3 foam will make for very durable laminate hulls. The surface area of the 5-chined F12 was 5 sq.mtr. (incl. bulkheads) so a 5 sq.mtr. by 0.008 mtr 150kg/M^3 foam core will only weight 6 kg per hull. Then we probably have to add at least 200 grams/m^2 glassfibre cloth to the inside and outside. Maybe a double layer to the outside and account for the resin. (again I have to check whether this is sufficient) but even if we add 4 layers of 200 grams/m^2 that will only add some 4 kg in glass and maybe the same amount in resin ? Leaving 3 kg for the local beamlanding and stay reinforcements resulting in 17 kg heavy hulls. I would consider that a very good point to start.


Wouter

Hey now that’s innovative. <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />
Looks like spring is finally here for the F12 project, good one!

The Hobie 14 is moving out of the garage, and I am getting an itch to try something like this. I am thinking something similiar to the F-12 idea, but just for fun and for the days that I do not have time to set the 5.2 up.

Where would you get the foam for something like this?

At a supplier ! <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

I can't be more specific if you don't tell us where you are. Besides foam core construction is new to me as well.





That is exactly the same reason I can't let the F12 project go and slip of into oblivion.

I think it would be a great little sailing boat for those small days, afternoons and evenings. And I still see it as an excellent performance boat for kids too. The specs all work out thus far.

For me personally it would mean. Park the boat on the beach next to my big cat and leave the bottom mast section (collapsable mast) on the boat with the other mast pieces inside the sail bag. Flip the mast down, slide the other two mast pieces into the bottom section and slide the sleeved mainsail over the mast. Then walk up this 8 kg (= 18 lbs) alu mast up and secure it with a single bolt (= unstayed rig). The boom is permanently fixed to the sail and so to it is the integrated mainsheet/downhaul system. Walk to the back of the boat and tie the loose end of the mainsheet to the traveller and hook on the snap-on rudders. Then get ready for sailing.

If done this procedure plenty of times on my landyacht and it does only take 5 min. to rig and unrig. THAT I find very attractive.

I had been looking at getting a laser-1 for these small sail trips but they are difficult boats to sail through the surf we got here and so often you don't get to go out and enjoy the wind and water. As this will be a cat, I won't have these problems anymore and it will be faster as well.

I think I have the basic design worked out.

The issue is that alot of stuff needs to be prototyped as most likely be adjusted. This is a totally new design after all and we can really "steal" a good starting point from another sail boat design.

Are you up for something like that ?


BTW :

The specs thus far are :

Weight ready to sail : 60 kg (132 lbs)
Length : 3.70 mtr (12 feet 2 inches)
width : 1.85 mtr (6 feet 1 inch)
mast height : 6.000 mtr (19 feet 8 inches)
mainsail luff length : 5.500 mtr (18 feet)
mainsail area : 7.00 sq. mtr. (75.3 sq. ft.)
boom length 2.000 mtr (6 feet 6 inches)

No dagger- or centre boards, no skegs.
unstayed rig with a sleeved mainsail.
no trapeze, just hiking (for now, could later be added I think)
Almost no sailing hardware. Baout 4 to 5 simple blocks and a few eyestraps/shackles.

Performance estimate : 30 % slower then an F18, 10 % faster then a hobie wave, about the same speed as a Hobie 14. 20 % faster then a laser 1 dinghy.

projected building cost : under 4000 US, less if you build your own sail and rudder setup.



Wouter

See if there is a dedicated fiberglass supply company in your area...they ususally sell divinycell...I would use 6mm H80 plain for core material...it comes in 4'X 8' Sheets...I get mine from Merritt Marine Supply in Pompano Florida...You might try http://boatbuildercentral.com/products. Try to get it local if you can or the shipping will eat you alive...The funny thing is the same outfits that usually sell divinycell also sell high grade marine plywood.

Regards,
Bob

Well, first of all I am in Oklahoma, smack dab in the middle of the US.

I have a laser and have only had it out once and was not impressed at all. It felt like I was crawling after sailing my 5.2 so I am looking for something more exciting.

Secondly now that i have been crawling around boards that I normally do not I am becoming very interest in the F-16 class. I need a boat I can single hand and still carry another person without suffering. The F-16 class seems to fit that need and I like the idea of homebuilding. I will have all summer off from school and could really devote alot of time to something like this so now I have to decide to try and get into F-16 sailing or try something smaller first.

Wouter

I would be very interested in knowing what you have come up with in regards to the following questions... as related to each individual hull:
The volume (one hull)?
Overall width at its widest point (one hull)?
Overall depth at the deepest point (one hull)?
The center of flotation?
Cross beam location (measured from the bow)?

Look forward to hearing your findings... thank you for sharing.

Regards,
Bob

Bob,




I have a few different hulls designs on the background, varying in complixity. Right now I'm mainly looking to get a very simple board- and skegless hull that is easy and quick to build. In effect no compounded curves.

The Arrow and Arafura Cadet designs seem to achieve very good performance and decents looks for a hull shape that is board and skeg less. See pictures. So I'll give you the preliminary specs on those hulls. For more pics follow the link :

Phill Branders Arrow and Arafura Cadet page

Arrow (14 ft)


Arafura cadet (12 ft)




So I'm looking to make a first simple hull design along those lines. An additional reason is that if this boat can plane downwind it will only do so with a flat keel line as these cat designs have.




285 liters per hull.



Width deck at widest point = 0.200 mtr



Currently I'm at 0.450 mtr.





See picture below.

Upper line is when lifting luff hull clear of water. The lower line is the waterline in no wind.







Haven't decided yet. In looking in the range 2.000 - 2.200 mm from the stem (54% - 60 % from the stem)


Note that all these specs may change when the hull design progresses and I know more about the pressure points in the sails etc. But this is a good starting point.


Wouter

Thanks Wouter

Observation given for your consideration...I like the possibility of a hard chine in your design...anyone who researches planning craft of any type will find that the harder the chine the quicker to plane...It is very easy to see the effects when building surfboards and sailboards...especially sailboards...you can take the exact same plane shape, same rocker line, the same volume, same rig and get radically different abilities to plane by just how hard the chines are (rails in Sailboard and surfboard lingo) You might have to back off the rocker too if you want to full exploit this planning feature...that is the second most critical factor in getting these small planning vehicles up and going. It will all come down to how much sub-planning performance you want to sacrifice to get superior planning performance when conditions permit.

Hard Chine’s and minimal rocker might make it plane faster but will most likely hurt its maneuverability...so the dilemma of getting the best of both worlds to avoid a "one trick pony"...

Thanks again for sharing...

Best Regards,
Bob

Wouter...
You wrote "The specs thus far are :

Weight ready to sail : 60 kg (132 lbs)
Length : 3.70 mtr (12 feet 2 inches)
width : 1.85 mtr (6 feet 1 inch)
mast height : 6.000 mtr (19 feet 8 inches)
mainsail luff length : 5.500 mtr (18 feet)
mainsail area : 7.00 sq. mtr. (75.3 sq. ft.)
boom length 2.000 mtr (6 feet 6 inches)"

What is the designed crew weight for this particular boat?
Please excuse me if you have already answered this in a earlier post...the F12 topic has gone through so many incarnations that its hard to keep track of what went with what...

Thanks,
Bob

The current design allows a 1.5 mtr tall person weighting 40 kg to right the boat unaided in no wind and flat water.

This should allow ON AVERAGE boys AND girls of 12 years and older to sail and right this boat singlehandedly. They will be fast on it, about as fast as a Hobie 14.

But also very important is the fact that all women above 16 and all men above 14 will be able to sail this design as even as the 5% bottom portion of the demographic in both categories will be at least 40 kgs and 1.5 mtr tall.

The boat will still sail well with 60 kg crews and I'm trying to make it as good as possible for crews all the way up to 90 kg's. After that the boat will become a bad sailor as the beams will come too close to the watersurface and its hull drag will be rather high.

I'm designing it to be overloaded to crews weighting 150 kg's so that a parent can take a child with him (her) and still dependent on the boat to hold up and get somewhere.

Pretty much the optimal range will be 40 kg - 65 kg. This pretty much means boys and girls from 12-18 years of age and small adults.

But I at 85 kg would love to sail one myself. Afterall the hull can be redesigned to suit that weight better, but that will only be a one-off design. The standard design will be as above.

Wouter

Wouter
You wrote "But I at 85 kg would love to sail one myself. After all the hull can be redesigned to suit that weight better, but that will only be a one-off design. The standard design will be as above."

I am more interested in your thoughts of a cat that can quickly be out on the water after work, with a crew weight of a typical adult male. I think it’s great for the youth to have a F-12 cat for all the obvious reasons but my interest in a different direction...tell me more about your modifications for heavier crew weight…Inquiring minds want to know…

Best Regards,
Bob

Let me rephrase that.

The standard version of the F12 will be for the weights given above. However for myself and others who are adult like and overweight I design a more volumious hull. This will will still be 12 feet long and everything will be the same except the volume of the hulls. The hulls will even have the same shape, but be just a little wider overall to have sufficient clearance between the beams and the water surface.

The rig should be powerful enough, afterall the laser-1 dinghy has 7.00 sq. mtr sail area too ! With a ready to sail weight of 80 kg's, which makes 160 kg with the 80 kg that an optimal skipper needs to be in the laser class. F12 will still come out at 60+80 = 140 kg with such a skipper but using the same sized mainsail with a MUCH better profile (= high aspect squaretop).

Just don't race a 50 kg kid for the car keys when you're over 80 kg yourself, that is all. Not of interest for recreational afternoon/evening sailing some adults are planning with this thing. Me included !

Wouter

Wouter,

Can you point out the disadvantages of a more bouyant hull design, when sailed at the optimum 12 to 18 year old weight.

Will the boat become a "bucking horse"?

Will a more bouyant design for crew heavier than optimum raise the boat weight above the intended minimum?

I don't understand how a more bouyant hull can detract from performance.

Or do I need to simplify this more and look at it from a ratio standpoint. Is this like sailing an F16 with an 180kg crew and extra bouyancy is a must?

I was also excited by the quick setup and speed comparable to a H16. I am sorry to see it has turned into this.

Matt

Not to beat a dead horse, again and again, but I thought 16 and up should be the target market. Maybe the youth boat could be open source one design. F12 could be for 16+.

There is no reason why this baby couldn't be great fun for 16+ skippers.

The concept is not complex and it is very easily scaled up. There is no reason why a 12 foot hull can not be made to suit your sailing weight. If required then it will be a piece of cake to entlarge the sail area and or lengthen the mast. The basic design is very open to that, especially since the mast is unstayed !

Just grap longer tubes while making the mast and use more cloth for the sail. The beams and mast section will easily withstand the forces, the basic concept is that forgiving in the way of loads and stresses.

Personally I think a high aspect 7.0 sq. mtr. sail on 6 mtr mast is plenty. The boat weights only 60 kg ready-to-sail and that is halve the weight of a Hobie wave.

Wouter