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Re: How to proceed. [Re: ] #123431
12/07/07 05:44 AM
12/07/07 05:44 AM
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I think the only guys needed to weight in are Phill and Luiz at this stage. If they all agree (and why would they object) then I think we can move to accept this change.

So Phill, Luiz ?

And can we also have a raising of hands by everybody else.

The proposal is of course to increase F12 hull length to 3.80 mtr from the current 3.75 mtr. That is a 2 inches increase for our US friends.

Voting ends on sunday.


Quote

RG have any of your guys started building yet?


We here in EU won't start on this before Jan 2008 we are first going to celebrate X-mas and new year overhere. So we got time to fix some other specs as well if that is required. Resizing is not an issue for me as I got my model implementing in excel sheets with scaling factor. I only have to punch in a new numbers to get the new panel offsets.

Wouter

Last edited by Wouter; 12/07/07 05:48 AM.

Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
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Re: How to proceed. [Re: ] #123432
12/07/07 06:39 AM
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RG have any of your guys started building yet? If not I vote to change. Is anyone against, if we're changing I want to update all my drawings on Monday.


I have delivered one set of plans, but they haven't started yet, so I can still change stuff easily....so I vote to change

Re: How to proceed. [Re: RetiredGeek] #123433
12/07/07 09:20 AM
12/07/07 09:20 AM
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I believe the length of Phill's design is clearly his vote. Are you sure it is exactly 3,80? if it is more, I'd go for it to make sure his design is class compliant.
But keep it under 3,88.
3,9 or 3,89 would look like the goal was 4,0 and we decided to give a discount... <img src="http://www.catsailor.com/forums/images/graemlins/laugh.gif" alt="" />


Luiz
Re: How to proceed. [Re: Luiz] #123434
12/07/07 12:54 PM
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Okay, Phill what is the length of your hulls measured between the verticals excluding the rudders and rudder pintles and with the boat leveled to its waterline ?

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
Re: How to proceed. [Re: Wouter] #123435
12/09/07 09:22 PM
12/09/07 09:22 PM

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Given the rapid acceptance of stretching the “rule” to get Phill’s boat into the box do we want to each publish a couple of extra dimensions in order to create a box that fits each of the current designs (shouldn’t be far off Wouter’s original numbers). I figure this will keep the majority happy (although it won’t be one design) by making sure the boats all have similar performance potential. Obviously numbers will be maximums and there is nothing stopping people choosing to go lower (ie Phill’s beam and sail area).

My numbers are:

Length: 3.8m
Beam: 2.0m
Sail area: 7.0sq.m (including mast)
Luff (P): 5.27 m
Mast (above top of beam): 5.8 m

From a previous post Wouter’s dimensions are:

Length: 3.75m (will probably change)
Beam: 2.0m
Sail area: 7.0sq.m (including sleave)
Luff (P): 5.3 m
Mast (above top of beam): 6.0 m

Are there any other dimensions which people believe should be limited?

Note we’ve also been talking about a minimum weight (60kg), however, I believe we should wait and see what the first few boats come out at before fixing this.

Re: How to proceed. [Re: ] #123436
12/09/07 09:39 PM
12/09/07 09:39 PM
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Or how about this combination...

Length: 3.80m
Beam: 2.0m
Sail area: 7.0sq.m (and maybe a 4.5 version for the beginners and/or smaller kids?) <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />
Luff (P): 5.3 m
Mast (above top of beam): 6.0 m


"House prices have risen by nearly 25 percent over the past two years. Although speculative activity has increased in some areas, at a national level these price increases largely reflect strong economic fundamentals." – Ben Bernanke – 2005
Re: How to proceed. [Re: Buccaneer] #123437
12/09/07 11:16 PM
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If we have a sail area and mast length restriction, why do we need a luff restriction ? .... you can't stretch it it longer than the mast or lower than the boom.

Cheers
RG

Last edited by RetiredGeek; 12/09/07 11:17 PM.
Re: How to proceed. [Re: RetiredGeek] #123438
12/09/07 11:24 PM
12/09/07 11:24 PM

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I agree, however, I know Wouter was keen on the luff number and I'm indifferent as to whether its there or not.

Re: How to proceed. [Re: ] #123439
12/10/07 01:47 AM
12/10/07 01:47 AM
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Wouter, why exactly do we need a max luff dimension ? to me that seems like just having a rule for the sake of having one and I can't think of a good reason for having it unless you want to rule out boomless rigs?

Cheers
RG

Re: How to proceed. [Re: ] #123440
12/10/07 05:39 AM
12/10/07 05:39 AM
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Scarecrow,
Beam is 1800mm
Sail area is 5.7sq m.
Agree as mentioned on weight.

Regards,
Phill

Last edited by phill; 12/10/07 05:42 AM.

I know that the voices in my head aint real,
but they have some pretty good ideas.
There is no such thing as a quick fix and I've never had free lunch!

Re: How to proceed. [Re: phill] #123441
12/10/07 06:34 AM
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Just finished the weight study for mine with the foam/glass panels and I'm looking at around 53-54 kg.

Cheers
RG

Re: How to proceed. [Re: RetiredGeek] #123442
12/10/07 08:53 AM
12/10/07 08:53 AM
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Quote


Just finished the weight study for mine with the foam/glass panels and I'm looking at around 53-54 kg.



How much weight is saved or added building with the rotomolded honeycomb?


Luiz
Re: How to proceed. [Re: RetiredGeek] #123443
12/10/07 09:13 AM
12/10/07 09:13 AM
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Quote


...why exactly do we need a max luff dimension?



Maybe the intention is to leave reasonable headroom under the sail.

If the luff length is not limited, the highest aspect ratio (best performance) is achieved using the entire mast length for the luff. This reduces the headroom necessary for kids to move on the tramp, making the boat uncomfortable, less fun and potentially unsafe.


Luiz
Re: How to proceed. [Re: Luiz] #123444
12/10/07 05:29 PM
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[/quote]

How much weight is saved or added building with the rotomolded honeycomb? [/quote]

Luiz,
right now I'm guessing till I get a sample panel made <will have it sometime next week> but I'd guess that if the numbers I've been told are correct, then it will only add somewhere between 3-4 kg to the boat. The weight is not the real issue, its the time to manufacture them that will see the real gains plus the drop in price.

Cheers
RG

Re: How to proceed. [Re: Luiz] #123445
12/10/07 05:36 PM
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[/quote]

Maybe the intention is to leave reasonable headroom under the sail.

If the luff length is not limited, the highest aspect ratio (best performance) is achieved using the entire mast length for the luff. This reduces the headroom necessary for kids to move on the tramp, making the boat uncomfortable, less fun and potentially unsafe. [/quote]

Luiz,
yes there may be a performance gain, so Im all for that but I seriously doubt its unsafe....the opposite in fact because there is no boom to whack them on the head.

Attached pic is of the boomless rig on one of the LR2's which gave a ton of room to to get thru safely.
Cheers
RG

[Linked Image]

Attached Files
127369-boomless.jpg (343 downloads)
Re: How to proceed. [Re: RetiredGeek] #123446
12/10/07 06:09 PM
12/10/07 06:09 PM
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Now thats hot! do those dinky little rudders and centreboards work? Wheres the holes for the centreboards? regards


Jeff Southall
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Re: How to proceed. [Re: Luiz] #123447
12/10/07 07:13 PM
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Okay, can we now official fix the maximum length of the hulls as defined ... to 3.80 mtr ?

Luiz, you are the official leader so you are the one to strike down the hammer and make it official.

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
Re: How to proceed. [Re: RetiredGeek] #123448
12/10/07 07:33 PM
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Quote

Wouter, why exactly do we need a max luff dimension ? to me that seems like just having a rule for the sake of having one and I can't think of a good reason for having it unless you want to rule out boomless rigs?



Setting the max luff length has nothing to do with ruling out boomless rigs. I actually don't even see how those two are linked in any meaning full way. Please explain to me how you think that they are, maybe I'm overlooking something here ?

The true reason for the max luff length is equality in performance, equality in perception, equality to Laser standard rig, good view to the leeward side of the boat, ease of tacking and with respect to my design it is a critical measurement to stiffen up the unstayed mast without increasing mast and boat weight.

Without a luff max limit I strongly expect a run for the lowest Boom/Foot height possible (see A-cats) to gain maximal (perceived) advantage. I think this to be undesireable from several aspects while fixing a max luff length doesn't really have any significant drawbacks.

A more detailed analysis follows now :

-1- Performance

Sails that share the same overall area and luff length will have largely an equal potential for producing sail drive forced on them. Only variables left will be amount of draft, position of draft and overall shape. Our proposed sail area with that luff length will already force a squaretop design as sailshape to such an extend that the variable of sail shape is not a significant discriminator anymore. That leaves draft and position of draft. I would like to get this open in order to have crew suit the sails to their body make-up and sailing style. I think this has been proven to work well other cat classes; in fact this seems to further equalized performance when only one sail per event is allowed to be used. But maybe more importantly the sails will now look very much the same from design to design, with only very small differences that are difficult to spot. I feel this will install alot more confidence in equality of performance in persons who are otherwise not educated technically = youths and most parents.

Basically, the less obvious the differences between rigs are the less cause for parent or crew related "concerns for inequality". And rigs are very important in this respect, even more so then hullshapes.

Drawbacks of a fixed MAX luff length ? The only one I can name are loose some very small amount of performance relative to say a luff the length of the mast. But this is not really a disadvantage as long as everybody is limited to a single luff length (=equality). I just prefer to fix this limit to a measurement smaller then the full mast length and I think the above benefits are sufficiently prefering 5.30 mtr as this will allow sail with aspect ratio of 4 which is already high.
F18/F16 have 4.25 ; hobie 14/hobie wave = 3.2 and 3.5


-2- Equality in perception

This is already partly covered in the paragraph above. Differences in rigs and sails are very easily spotted. Alot more so then any other difference between boats like hulls. Sail that are fixed both in area and luff length will look alot less different, even when fitted to masts of different lengths or when their drafts are significantly different. I also think that to take out this easily spotted difference is good for younger sailors as I expect them to feel more equal to eachother.


-3- Equality to Laser standard rig

I'm intending to have the F12 be very similar to the Laser dinghy in important specs like the waterline length (which is equal now with our max 3.8 mtr hull length limit). Same with respect to masts (5.9 mtr in laser although class allows 6.16 mtr) and sail area (=equal already) and luff length (laser = 5.260 mtr.) The difference in laser mast specs in mostly likely due to some people including the part that is in the pod and below decks. Our 6.00 mtr mast length above "deck" = beam would be highly similar.

Basically I just rounded off the number to these or what I had determined to be very attractive specs. Again, sail aspect ratio of 4 with a 7.00 sq. mtr. rig requires a 5.29 mtr luff length that I rounded off to 5.300 mtr.

I'm after laser equality in these specs for marketing purposes. F12 will definately beat the laser, especially the youth versions of the laser, and by keeping the specs pretty equal we avoid this performance difference being explained away by mono fanatics by refering to some "significant" differs like a "taller sail". I want the F12 to proof the cat design strong points in relation to a mono and partly increase acceptance of all catamarans in the larger fraternaty of sailing.

Again the benefits of fixing the luff length to another limit (like mast mast length) too small to outweight these benefits.


-4- Good view to the leeward side of the boat

I do indeed think this to be a safety issue. I also want to avoid sails with windows in them. The laminate that these windows are made off is sensitive to abuse and rips easily. It is also another thing to do to a sail by a sailmaker and will add cost. I think it is better to be able to look under the boom/foot-of-sail. Mostly I'm unimpressed by the view through these windows anyway, especially in rough weather when lots of water droplets deteriorate the view.

Having a minimal boom/foot height that is sufficiently high (at least shorter then the mast length)is an easy and cheap solution. I know from measurements that 0.5 mtr is pretty much a minimum and the 0.7 mtr boom/foot clearance given by the laser-equality and sail-aspect=4 criteria would therefor be sufficient too.

I also think that having this clearance near the mast is important as boats travelling upwind at equal speeds and equal relative positions (= collision) are to be spotted in this area. Boats that are to be seen further back along the boom will pass behind and boats seen in front of the mast will pass in front.

I don't think this aspect of the design should be discarded without a careful analysis.


-5- Ease of tacking

Low booms are a pain in the neck on a catamaran especially when their hulls are boardless. In order to come close to tacking the F12 much like a laser the F12 crew needs to roll tack. And you'll need to be very quick but smooth in crossing the trampoline as bobbing the boat around slows a lightweight boat down very quickly and being to slow capsizes you. I fear that on the short F12 there is not alot of room to have the boom/foot angle upwards quickly enough.

I want the F12 to be a really well behaved boat, after all it will be compared to modern dinghies which have a few significant strong points here, boom clearance on the laser and Open Bic is one of these. I don't think a very low boom is any benefit that isn't outweighted heavily by its drawbacks.

So for this reason a mas luff length shorter then the max mast length is to be prefered. I know from many measurements and test sailing on a score of boats that 0.50 mtr is very much the minimum.


-6- It is a critical measurement for my own design.

I shall make no secret off it. The push rod setup needs a max luff length shorter then max mast length for ease of raising the mast, stiffening up the mast sufficiently, lowering the stresses on the parts and hulls AND safety !

Safety because I'm counting on my design being able to completely weathervane the rig. When a kid gets surprised by a squal he just unthreads the mainsheet and the rig will completely weathervane itself. If he needs to sail downwind to safety in a blow he can over rotate the rig so the boom is angled forward by 45 degrees and loose all capsize moment (!) and most of the pitchpole moment. For upwind and reaching legs he can of course let out the sail with the same results. As such a kid can always sail to safety on any course with a very calm and easily controlled boat.

On the beach the rig can also weathervane which makes boats tipping over a thing of the past as well as dumb mistakes like slam gybing the boat on the beach by turning it the wrong way.

For the weathervane property the boom/foot needs to be above the push rods. And I'd like to have the push rods as high as I possibly can without compromising looks and performance too much. 5.3 mtr luff length on a 6 mtr mast does the trick for me.

Stiffness of the unstayed rig. The difference in the top of the mast flexing off between my push rod design and Phill pod design, when using the same mast, is 40%.

In effect, the difference is between the top flexing off 0.85 mtr or 1.20 mtr; a difference of 0.35 mtr. and this is alot. (Phill, remember my "feel the need to tell ..." moment ? That was this (and some more I may tell later).

With a max luff length of 5.3 mtr on a 6.0 mtr mast I can have a homebuild mast from basic alu tubing that weights less then 9.00 kg and has sufficient stiffness to not look to bendy and not pump to much. Without it we can probably kiss the unstayed mast principle good-bye.

Seen that way NOT having a max luff length rule (or minimum boom/foot clearance rule) is the same as effectively ruling out unstayed rigs. These already have a performance disadvantage to stayed rigs, with no such limit the disadvantage is getting worse.

Having an unstayed rig is also a critical element in my design; the whole concept of simplicity is designed around it. From the free hanging boom (no fittings) and cheap mast production to the ease of car roof transport and shed storage.


Wouter

Last edited by Wouter; 12/10/07 08:21 PM.

Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
Re: How to proceed. [Re: RetiredGeek] #123449
12/10/07 07:42 PM
12/10/07 07:42 PM
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Quote
yes there may be a performance gain, so Im all for that but I seriously doubt its unsafe....the opposite in fact because there is no boom to whack them on the head.


Agreed. Headroom will not be a problem if the sail is well designed. Also, I forgot that the Supercat 17 is using this configuration for decades...

Someone recently suggested something along this line for a boat using the push rod mast support system, like the Hobie Bravo.

The idea was to double velcro the lower part of the sail around the mast support tube below the bars (gooseneck) so that the entire mast length could be used for the luff. It seems to makes sense after all... <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />

(couldn't resist... sorry! <img src="http://www.catsailor.com/forums/images/graemlins/tongue.gif" alt="" /> )


Luiz
Re: How to proceed. [Re: Luiz] #123450
12/10/07 08:45 PM
12/10/07 08:45 PM
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Sorry, none of this make much technical sense. Later more on this.

But also the reasons for having a max luff limit are the same for both boomed and boomless sails.

Booms only "smack over" on slow mono's as the boom only comes over very gently when a cat at normal boat speed is gybed. Remember which direction the apparent wind is coming from on a cat.


Quote

The idea was to double velcro the lower part of the sail around the mast support tube below the bars (gooseneck) so that the entire mast length could be used for the luff. It seems to makes sense after all...



That still doesn't allow the rig to weathervane or even to achieve large boom angles as the rods will hook the sail then at 45 degree angle. This max angle could make the boat hard to control on courses between beam reaches and broad reaches in a blow.

In addition this flap makes no aerodynamic sense. Many believe that it does, but it really doesn't.


- first technical reason

All area used up by the flap needs to come out of the total sail area. So low above the watersurface the windspeed is only a fraction of the windspeed higher up the mast. As such the same area is MUCH more effective when used higher up in the sail.


- second technical reason

Because of the relatively low windspeed so low to the watersurface and the fact that the flow here is largely disturbed or even blocked by the hull makes any lift gains here negligiable and any drag looses when not having the flap to small too matter. The loose flap and felcro are more work for the sailmaker (more labour costs) and more stuff to get broken without any measureable benefits in performance or simplicity of design. I've used a similar setup on the 49-er I sailed for a while and I would have gladly removed that whole flap. It was the first part of the sail to crack up and once the velcro is gone it undoes itself and flutters in the wind. By the way, Nothing is as draggy as a fluttering piece of cloth, even if only the leech flutters then that increases airfoil drag by 20-40 % No amount of sail drive of the same piece of cloth can every correct for that.


- third technical reason

For an airfoil to work in unstable flow (as we see all the time while sailing) it needs to have a sufficiently large cord. Wind is basically an unstable airflow that is made more unstable by waves, chop and macro turbulance induced by the wind rubbing against the ground/watersurface or passing buildings, trees, hills, dunes, other sailboats and whatever else was in its way.

Very short cord foils stall very easily and have trouble reattaching the airflow. The flap is basically a very short cord foil unless it reaches back very far along the boom. This can of course not be had for other reasons.

A short cord foil also stalls at significantly lower angle of attacks then a longer cord airfoil. Of course you'll set the boom angle for the lower portion of the sail (= long cord) and the flap (short cord) is set accordingly as well. By any analysis it will be suboptimal. If you are lucky (!) its lift will cancel out its drag and the drag of the mast (but still lower the effective sail drive area of the sail that is above the boom, probably losing some performance)


- forth technical reason

Alot of people think that the flap will smooth out the flow around the mast and thus lower the drag of that part of the mast.

Even if it does that (and it most probably don't) then the drag of that part of the mast must be sufficiently large to matter, which it most definately is not. A 50 mm diameter round tube of 0.750 mtr length (my exposed mast below the mainsail sleeve) produces at max 0.50 kg of drag when sailed at 15 knots on a 45 degree upwind course in 20 knot of winds. It is probably significantly less as the wind so close to the watersurface is travelling significantly slower then the windspeed readings that are officially taken at 10 meters altitude. Additionally you can never remove the total amount of drag of this portion of the mast, even with the flap a portion will remain. So the total drag amount is less then 2% of the total already.

But this assumes that the flap actually smooths out the flow over the mast here. If a round mast with a sleeved flap is used then this won't happen to any significantl extent. Even if the flow was laminair before it reaches the mast (unlikely) then it will become turbulent and detach from the mast+flap BEFORE the side of the mast is reached. When teh flap is properly aligned then the flow will reattach some distance behind the mast. If the flap is too small then flow will not reattach at all and the flow pattern around the mast will be the same as with the flap (foil) completely stalled. In that situation there will be hardly any lift created and the drag of the mast+flap setup will not be less then just the mast alone. In fact, it will mostly likely be more because as a due to the angle of attack (20-25 degrees) a larger portion of the flow will be disturbed.

In effect it is better to have a very small area operate at a bad drag coefficient then a large area operating at a mediocre drag coefficient. A flap is alot larger in area then just the round tube of the mast.


It is interesting to note that flapped mainsails are not found in EU. Any design that had them like the older Nacra's and supercats had these flaps removed because the measurement based rating systems like Texel and SCHRS counted this area with the same weight as area higher up along the mast. It was found that it was better to remove the flap and make the sail above the boom a little larger.

Other area's using yardstick systems still see these flaps as here these systems don't not look at the total amount of sail area just at the performance that is achieved.


For these reasons I see no technical reasons to have flap below the boom to try to maximize luff length. It is either a full sail going down closer to the mainbeam or just cut off the foot along some horinzontal. The jury is still out on the "angled upward booms", but I'm personally skeptical of them as well.

Wouter

Last edited by Wouter; 12/10/07 09:08 PM.

Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
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