A screacher puts alot higher loads on the components like mast and bows. It is basically an oversized jib and needs comparable luff tension to work well. A furling asymmetric spinnaker could be possible though.

Personally I think the bridle+pole is the simpler solution then any pole-less bridle arrangement as seen on for example the Swell Shadow. Also choosing either makes a HUGE difference in the max attainable spi area. It can easily make the difference between a 8.5 sq. mtr spi and a 5.0 sq. mtr spi.

The simplest solution will however be a symmetic spinnaker (no pole or bridles) and that one can easily be a mast top spinnaker as well due to the very low loads associated with it.

Wouter

Trapeze and spi halyard at the mast top would work, especially with a ram vang instead of a traveller.
A topmast asymetric would be big, but a bridle or shorter pole would bring the area back to normal.
The pole takes only longitudinal (compression) loads, while the bridles take the lateral ones. If the pole isn't longer than the bow, the effort in the bridles should be the same with or without pole.

While I'm not designing to include a trapeze, I'm sure one can be fitted nevertheless. No components will fail but I also make no guarantees that the sail shape or sailing behavior will be optimal. I feel that I can about guarentee that with the asymmetric spinnaker.



About 12.5 sq. mtr. I think ; if we maximize it.





You overlook the sheet and tack halyard loads here; the ones that pull the tack the spi sail and therefore any bridles backward. Ergo one can not simply remove the pole (even if it did not go past the bows) and assume the bridles will see the same laods or even stay in the same place.

The Swell Shadow catamaran has a pole less design but needs an additional line coming of the forestay (which are fitted to the bows in this case) to stabilize the spi bridle. See the attached picture. My design doesn't have a fore stay and adding one is more complex then simply adding a spi pole, which in my design is incidently the same as the mainsail boom. Not having a forestay reduces the stresses placed on the bows and allows for lighter and simpler construction of the hulls. It is also one thing less to pay for or worry about.

This pole-less setup will pull the spi bridle well back from the bow, closing off the opening between the spi sail luff and the mainsail luff. The end result is a much reduced overall sail area for the spi; more like at max 5 sq. mtr. And lets not to forget the web of lines on the front of the boat. Neither looks nice or is it easy to rig. The pole setup is better in the achievable area, in the spi-to-mainsail slot and in construction.

Wouter

Understood.
Your are probably going for a poled narrow furling asymetrical hoisted to the mast top. A tall spi requires more time to douse and a narrow spi furls really fast. The narrow spi is less bulky when furled than a wide spi, so it has less windage when the spi is not lowered.

Actually, I'm currently "investicating" teh setup as depicted earlier. That means a non-mast-top asymmetric spinnaker on a shortened pole. I have not decided towards either the furling option or "retrieved" option, but I do know this. A spinnaker of 8.5 sq. mtr. size is easily set and retrieved by hand even without a snuffer system. The sail is so small that only two swings with the arms is enough to pack it into a bundle before you. Windward retrievals by hand are easy that way as well. There is just so little load involved that a teenager can simply overpower it even in strong breezes. With the windward douce the spi sail slides down the mast and mainsail when the halyard is released.

I'm actually thinking about going the old fashion way with this spi meaning no suffer system at all. Cheaper and simpler, while noting this is viable for a spinnaker this small. I know that by experience. And of course, the spi is an option as this moment not intended for any youth class racing. More for recreational sailing like the coastal trips as Gato has done or for mum / dad to have some fun in a light wind day.

The none mast-top aspect of the current situation has a side benefit that I haven't disclosed at this time yet. But let me put it this way. It interacts nicely with another design feature of the mast avoiding the need for any additional hardware while still being able to transmit a good portion of the load to the mast directly (and not via the sail).

This makes the spinnaker as an aftermarket option/upgrade more marketable.

I'm actually designing this craft more and more along the lines of "Bloody simple, but effective". Sort of like using the boom as the spi pole as well.

But other then that, the depicted spi is very similar to the ones used already on spi boats and that means that we can lock in directly into to the experience about what makes a good spi design. Make it work first time around, that sort of thing.

Wouter

Hi Wouter,

I like the direction this is heading, ie. simple and effective. I like the idea of the additional volume to give better load carrying capacity, cos at the end of the day I want something my kids can flog around a race course on, but also like the idea I can jump on, and have some fun. Very much like the self supporting rig with option for kite turning block sewn into the front of the sock.

My only comment (very much personal preference) stick with center boards, and not skegs. I think you hit the nail on the head, it will be more appealling to the teens.

Look forward to seeing your design progress. I'll be moving country soon, but will be going to a place where beaches and sailing are both plentyful, so look forward to potentially putting something like this on the water.

Cheers.

Thanks Ross,

Thanks for your support.




I understand this line of reasoning very well. It is actually not a big issue to do both (leaving the choice to the owner), the only worry there is that it may fraction the organisation or class formed around this boat. Mostly, because a good skeg hull is really not that similar to a good hull shape when fitted with daggers.

All the other bits will be the same however.

Anyway keep an eye on this forum and you'll be kept updated.

If anybody else wants to weight in on the skeg vs daggerboard choice then please do so now.

Wouter

All other F12s have boards, so...

- A boat to win races against them requires boards. In this case go all the way and use bruce foils and rudder foils like the new Hydroptere. Note that their foils are not dagger style, they are external and the board pivots up and down.

- A boat to be the simplest option should not have the added complexity of daggerboards.

- A boat to be both faster and simpler will require a new approach/solution. I wonder if Hydroptere's external pivoting foils are simpler to use than a simple daggerboard in the F12 scale? They could be. Also, they could be made to work also in the vertical position, rendering the central daggerboard unnecessary.

Yes, but all the other F12's have fully stayed rigs that can't be broken down in smaller sections either. And of course smaller hull volumes.

I'm not sure whether my F12 with compare closely to the others even when fitted with daggerboards.

So this is not a convincing reason in my personal opinion.




Yeah, this consideration is weighting very heavily in my judgement as well.


Actually, on the reach and downwind legs the skegs often proof to be the better option when compared to daggerboards. The disadvantage is too be found on the upwind leg but only when there is sufficient boat speed. In light winds, you'll be surprised how well skegs perform, even upwind.

So is the hit on the upwind legs in winds over say 8 knots worth the additional complexity and expenses ?

I personally dare not give a straight answer to that question, but for the F12 design I'm leaning towards the skegs.

It is just so much simpler (probably lighter), cheaper and the difference is very small or the region where you'll notice any performance hit the most, in light airs.

I also think that skegs really make the design attractive to resorts, novices and owners looking to do day trips along a rugged shore line. They sure as hell make sailing in the surf alot easier and practical.

Wouter

Hi Wouter,

As I have said previously, I very much like the direction your design is taking, with exception of the skegs. Maybe you would consider an option of either.

Cheers

Well, this is basically the last outstanding issue.

All others are at best further refinement after having gained experience with a prototype.

The big issue is of course that an optimal skeg hull is significantly different from a daggerboard hull design. Now it is very much possible to take the skeg hull design, remove the skeg and install a daggerboard well. THAT is not the issue, it is just that that particular hull is not expected to show a significant performance increase. Such a things would require a whole reshaping of the hull. It is the same the other way around although the performance loss when fitting a modern round keel hull shape with a skeg is a pretty bad choice performance wise. You'll need to fit a very large skeg then as the hulls don't do much in the side ways resistance on these boat. This is evidenced by how much sideways these sail when no boards are set.

So "switching over" does not hold much promise; it is better to make a decision to go one way and fully optimized that. This will also be less confusing to the intended customer base. So marketing wise one really doesn't want to come out with two versions.


Ross, may I pester you with one more question ?

What is it that you personally expect from fitting daggerboards ? Or what it is that you specifically do not like about the skegs.

I ask this as I want to fully understand the situation. It is not intended in anyway as an argument. I just what to be further entlightend before a decision is made either way.

Many thanks in advance.

Wouter

Hi Wouter,

Happy to answer your question. It is actually for one of the reasons you favour the skeg - I do not want to build a surf/resort beach cat. I want to build a sexy looking (contemporty design), reasonably well performing 12 foot cat. Not suggesting for a moment that a skegged cat does not perform well, but for me it is really more about what the boat represents. Do kids want to jump on a boat that has skegs, or do they want to jump on a boat, and keep sailing it season on season, that is similar in concept and style to their parents A, F18, F16, etc.

Once again only my humble opinion, and maybe I'm contradicting myself by being concerned by this when the rig is completely different, however for me, the rig seems to be a logical step forward, while fitting skegs feels like to step towards a surf cat.

I have one other question for you. On this forum there has been a bit of talk about possibly fitting a jib to some of the designs to promote two up kids sailing. I assume the inherent flex in an unstayed mast would mean that it would be difficult to maintain jib luff tension, making a jib pointless in this situation. Is this how you see it?

Cheers.

Indeed, the is the exact same worry I have as well. Skegs can be made to work well technically, no real issues there, but aestetically or from a marketing point of view they have the close association to "training wheels".

Thanks for your answer.






Well, as long as there is leech tension, there will also be forestay tension. An unstayed mast will be less "stable" with respect to this but it probably can be made to work well enough on a boat of this size (sails of this size).

However, despite the fact that I'm a believer in the sloop rig for boats like the Nacra 500, F16's and F18's I'm not a supporter of sloop rigs on the F12's. I think these have unacceptable disadvantages for the F12's such as :

-1- They load up the bows requiring heavier construction
-2- Require bridles that need local reinforcements in the bow
-3- Require at least a forestay and a hound fitting on the mast.
-4- Dumping the mainsheet on the unstayed rig will see the forestay go slack and have the jib pump (possibly violantly)
-5- Add significantly more cost to the boat then sail area.
-6- Jibs flap about in strong winds making them harder to rig and scaring novice sailors.
-7- A spinnaker will do more for overall performance and similar costs

So I think rigging a jib on an unstayed mast can be made to work reasonably (although not really well) I think this so-so characteristic combined with the above points make F12 jibs unattractive. It is also just not the natural thing to do with an unstayed rig either. Additionally, adding a jib typically increases heeling and pitching force by some 15% while adding 25% is overal area and drive (roughly speaking). For the F12's I think adding 15% area to the mainsail is a better choice especially when the craft is also fitted with an asymmetric spi. It will feel as the same craft in the way of pitching and heeling and only lack 10% drive upwind while more then just compensating for that loss by increased downwind performance.

I also think the the spi to be more in line with the F16's and F18, and I think it will be more enjoyed by the owners c.q. their kids. More in line with the hot dinghies like the 29er as well. I do believe that far more 2-up 12 year old crews will sail the F12 then 1-up 12 year olds. I envision the crew working the mainsail upwind and the spinnaker on the downwind with the skipper steering and trimming. I see no particular advantage in adding a jib to that mix. And IF a trapeze is added for these 2-up crews then adding more heeling moment (as required then) is best done by adding mainsail area / mast length.

I trust this answers your question.

Wouter

Thank Wouter.

Clear for me. Look forward to following your design as it progresses, and with additional volume, would be my pick to build so far.

Cheers

Just a note in support of Wouter's design direction. I like the "Keep It Simple, Stupid" approach combined with the target audience adaptability (think Laser). The boat with its sleeved mainsail is something of a paradigm shift, which may be harder for us "Insiders" to accept than it would ever be for the potential audience that is "out there". Skegs could be marketed as a major safety / durability / ease of use benefit(esp. to outsiders, that is new entrants to cat sailing), not as training wheels (insider thinking). I see this concept as having the potential to do what the windsurfer did in the early '80s.
I sure wish I had the time and money to invest in this... I'll at least be keeping a close eye on these developments.
Dennis

Wouter... Can you give us an indication of what the theoretical top speed ( or time around the race course) difference would be between a 1.9 m X 3.8 m cat VS a 2.14 X 4.3 meter cat?

Assuming the weight is the same (or within a few percent) and the rig style is the same with a proportionately larger sale for the 4.3m cat...and also would be nice to know with the exact same size rig.

There are a lot of variables that could color this scenario that I don’t want to muddy the water with. You have been suggesting an adult F-12, which makes perfect sense to me as well….others here are saying they would want to go up to a 14’ hull length for an adult “spur of the moment” cat. In general term, what kind of performance increase (percentage) would be gained by adding .5 meters in length?

I know there is a world of difference between Darrel’s A&O F-14 and the F-12 that has been under discussion for adult after work sailing …that’s given…what I am asking for….apples to apples how much is .5 meters going to help? I have a Styrofoam hull/plug shaped out right now at 4.3 m and just looking at it full size it doesn’t look like shorting it .5 meters would make much difference at all. What is your take on it from an engineering stand point? As numbers seldom, if ever lie.

Thanks for the info.

If you want a god example of the foam construction method John & Ian Lindahl have used on his last 3 boats click here

In an update on other stuff, not sure that the original round bilge design is going to make it to production anymore....as with most of the planet, the builder has money issues.
That said, I have been working (very very sporadically) on another F12 design, no builder or customer in mind, more or less for my own pleasure. This is not being offered, nor will it be available to anyone anytime soon....the attached pics are just eye candy.
Cheers
RG

A few more pics, this time wave modelling...this is at about 9 knots with a little leeway

This lot are pressures and wave heights.