Some thoughts on what's going through my head at present (while I wait for answers to the questions I sent the GC) for interested parties:

As most of you know there has been a discussion on the main forum about "Better cat design" and one of the main points that most seem to agree on is the need for more volume (as seen on the Infusion in F18 and Aussie Blade in F16), however, the A cats have been going in the opposite direction for quite a while. I believe this divergance is for two reasons.

The addition of a spinnaker and its added horsepower has seen modern designs focussing on making it easier to harness this power rather than efficiency. So we've maybe given up 1 or 2% top end speed in order to make it possible to sail the boat flat out 95% of the time rather than 85% of the time.

The other main difference is the displacement length ratio of the hulls. Using Dimensionless values these are:

F18 : 1.96 (crew weight 150kg)
F16 : 1.90 (2 up crew weight 130kg)
F16 : 1.47 (1 up crew weight 80kg)
A Cat : 0.94 (crew weight 80kg)

Of interest here is the F16 two up and F18 have very similar values, which is resulting in these boats converging on a similar "Max volume" philosophy.

The A Cat is much lower (50%) and as a result can achieve different targets and performance, which is why a lot of A cat concepts and shapes can't be translated straight into F16 and 18.

As mentioned before, my boat is being designed as a one up boat only which gives it a disp/length ratio smack bang in the middle. So the first thought becomes "ok will A cat shapes now work?" and then how much volume do I want and where. Needless to say the computer is getting sick of running models.

Any sail area to weight ratios for comparison? Upwind and downwind.

Upwind

F18 : 0.44
F16(2) : 0.49
F16 (1) : 0.47
A cat : 0.48

Downwind:

F18 : 0.88
F16 (2) : 0.95
F16 (1) : 1.02
A cat : 0.48

These calcs are Sail area (sq.m) / (Displace (kg) ^2/3)

mmm, interesting...

From those ratios upwind F16 is pretty close to an A but downwind it is somewhere between A and F18.

It is going to be an interesting compromise. The solo F16 is going to be pretty much smack bang in the middle of an F18 and A. Maybe end up with a small profile similar to an A to reduce windage upwind but higher volume hulls than an A to drive it hard downwind with kite. A fatter taipan?

What was the conclusion reached with Altered?

Do you think that is realistic? TBH I don't that many crews that combine out to anything like that.

Are you talking an adult and a child? hell I know guys sailing that could almost make that weight on their own!

In the maricat class rules if a skipper can make min crew weight on his/her own they are allowed to use the jib and compete as sloop. do the f-16 rules allow for this?

Dazz,

I used 130 because I see the majority of heavier crews going F18. 130 is a typical crew weight for a competitive H16 team which is who I see as the target audience for the two up f16.

Simular target weight for 4.9 crews also.

More boyancy in the bows would always be welcolm. Plenty of clearance also between rear beam and water.

In the two up F16 configuration I think you should be able to get more weight back further than in one up mode. do you think this will have a big effect on the design of the hull?

No min crew weight on the F16.

Single handed you sail with main and Spi ONLY.

There is a sort of minimumum crew weight - the class rules require the crew to be able to right the boat unaided in all normal sailing conditions. It is permitted to use righting devices. This means that a paricularly light crew say, <60Kg, will need to carry a righting bag or pole. I'm 65Kg and I can just about nright the boat in no wind which is the worst scenario.
The organisers of an F16 event can require any crew over which there is doubt to demonstrate that they can comply with this class rule.

Hi all,

"Altered" performed with less than A class bouyancy, better than it could have been expected. Of course it did best upwind but still performed OK downwind to a point. I would look for more freeboard primarily, as excessive forward bouyancy on the water line may make it hard to drive upwind. My guesstimate from experience on "Altered" It was the beams hitting the water that stopped it as often as not.

Opps, me bad. I should have mentioned that...

That will make an exciting protest someday

I doubt it.

Please go and right your boat.

Boat gets righted (or not), end of discussion.

From I have gethered it is not so much bow volume that is sought but rather a high freeboard and a good clearance of beams above the waterline/wavetops.

Especially a tall freeboard seems to work more then expected.

On the downwind the desire to keep the bows out is still present but there are other ways in achieving this, for example T-foil rudders. So in my opinion you can still fully optimize the F16 hulls for low drag if you accept fitting the boat with T-foil rudders.

The usefulness of transferring A-cat characteristics to F16's and F18's has long been put in doubt. The designs are simply too different for such a thing to be of much value. I also believe that the very high length to width or weight ratio of the A's offset the results achieved in that class. Basically their hulls are too long for what they really need to withstand the rig forces. F18's and F16's are at the other end of teh spectrum, never enough hull length when going full power downwind under spinnaker. Where the F16 has the added drawback of being very quick in its movements (nervous feel) giving the crew less time or margin in which to respond.

Wouter

But then if you fit T foils as they are currently being fitted (ie no control mechanisms) you are adding drag to all but the optimum case. I see T foils as an example of giving up some theoretical performance in order to achieve better averages. Adding bow volume is the same.

True. Sounds like Scarecrow and Roarke is working along the same theories.

From my little one-up experience on a Vectorworks Blade (normally sailed 2-up) I can tell the following:

Upwind: up to 5 knots -> A's point a lot higher and have more lift and speed.
FX One and others point lower and are slower
Up to 10 knots -> good A sailors point higher, average sailors (as I am) point the same. The same for speed and lift. When the wind picks up more I start to get overpowered (guess that me not trimming correctly).

Downwind: Faster in every wind condition. In flat seas and 10 knots I leave the boards down and sit about a feet in front of the rear beam just to make the boat go. So for one up I don't think you would want any more volume.

That's it for my experience. I don't really understand the number discussion :-)

I could have done with a little more hull volume up front at Forster

From a lot of practical on the water experience/testing, there is NO apparent or measurable efficiency or extra drag penalty when using “T” foils as opposed to normal rudders. The very noticeable effects are that there is a DRAMATIC reduction of pitch under all conditions and points of sail with a very measurable increase in overall performance combined with a near complete reduction in the propensity of pitch pole under spinnaker. I am not saying that it makes pitch pole impossible But since installing “T” foil rudders some three seasons ago neither of two cats sailing with them has ever pitch poled, even in quite extreme conditions, whereas before the fitting of them, both cats pitch poled quite regularly when pushed hard downwind – even when they were pushed much less than they have been since fitting the “T”’s.