[Omatako]

Med:
You have a lot of catching up to do. A lot.
Bend has almost nothing to do with it. Bend is more important on a masthead rig where you use bend to increase headstay tension and flatten the main. With a frac rig you get headstay tension with runners or swept spreaders. And, if you sweep your spreaders 20 or more degrees you are not going to be bending the mast much.

This of the rig as one big foil. The jib is just the leading edge.
With a big main and a small headsail you no longer have to change headsails for optimal performance, theoretically anyway. There are heavy weight jibs and light weights jibs but the LP will remain about the same.

The photo you posted is misleading. Only one boat is flying a masthead foresail and this sail is a code zero. It is not their working headsail. It is a reaching sail. The other boats in the pic clearly show frac rigs. Look closely.

Tomorrow I race FRANCIS. Big, tall frac rig and I will make it sing.

In the end we know that one, articulated wing sail is the best sail for speed. The frac rig comes close to replicating the "one foil" approach than does the masthead rig

Bob, whilst I unreservedly bow to your superior knowledge, it would be great for me to share some of it. Nothing in the post above leads me to an understanding of why/how a frac rig trumps a masthead rig.

 

[Omatako]

Med:
That guy has never sailed a modern frac rig. As I said in my post, with spreaders often swept to 30 degrees there is no mast bending to the degree it was some in old masthead IOR rigs.. You can bend the small top proportion if you want to but below the hounds the mast will be dead straight. I know becuase I design and sail these boats. I don't hypothesize or speculate. You can tune in a little pre-bend if you like. But once sailing there is little you can do with bending the mast. That doesn't always stop us from trying.

Ditto my response above. Please give me something I can believe in.

 

[Omatako]

So let's look at physics and ignore all the bilge myths.

What is different about the interaction of the sails (main and fore) when you have a fractional rig? Well, there's a vortex coming off the end of every wing and that turbulence creates drag. With a masthead rig, and the main and foresail both having their top ends in the same place, wouldn't those two vortexes reinforce and create extra drag, and a loss of lift on the top of the main?

Aha. Maybe, maybe not, but has anyone ever bought time in a wind tunnel and actually examined that? I don't know, I've never heard mention of it but I'm not into heavy reading of aerodynamic testing.

Now take the same two sails, and stagger them so the two tip vortexes do NOT intermingle and reinforce each other. What do you have? A fractional rig!

Maybe it could be that simple. Simple physics, which no one has bothered to document or examine in detail because "everyone knows" the fractional rig with less sail area magically is faster. Magically. Hmmm, maybe that way the vortex coming off the tip on the foresail actually increases the flow below the tip of the main, actually boosting the performance of the main as well?!

And finally someone comes up with a possible explanation. Thanks HS.

But I still have a problem believing that the mingled vortices at the top end of the main will create sufficient drag to over come the additional sail area of 140%, low footed, masthead genoa.

Strangely, I actually believe that a frac rig is better because I cannot forget marvelling at the giant AC trimaran back in Valencia going to windward and dropping the headsail altogether and going faster. Or the relatively tiny jibs on the AC foiling cats.

But still I haven't heard any compelling evidence to suggest this is true of a non-wing rig.

Maybe someone who designs and builds boats will take a frac rig and sail it for a month then change it to a masthead rig and sail it for a month and provide some real comparative data to prove the point. Then we would have something to believe in.

I will follow this thread with interest even though I have no intention of ditching my masthead rig.

 

[Stumble]

Then why is the mast head rig J29 faster then the frac rig 29, same with the Thomas 35 or even the J35 vs the J36? Hard to figure sometimes.

Simple, the J-29 MH has more sail area than the fractional downwind by about 10% thanks to a much bigger spinnaker flown from the top instead of at the fractional point. Based on standard PHRF rules if the FH switched to a MH kite it would be penalized 6 seconds making it 3 seconds faster than the MH.

While discussing why is beyond my knowledge base looking at boats that are limited in sail area but not sail plan I think are instructive. Those classes with just a sail area maximum have pretty much all switched over to high aspect cat rigs, those with main sail are maximums have high aspect mains and overlapping jibs, those with max main and max jib area use high aspect mains and high aspect non overlapping jibs.

What this indicates to me is that for the same sail area upwind the ideal seems to be a massive main. If you have to divide it up then add the smallest jib possible, finally if you have extra sail area you tack it on to a bigger jib.

 

[capecodda]

I'm an engineer, but I skipped the fluids course, but now regret that.

As a cruiser, I like the fractional rig for practical reasons. Usually, the mast is further forward, allowing the boat to balance reasonably even with the jib rolled up. Small jib is easy to tack, a bigger fully battened main is easy to handle, you can hold a full jib into an increasing wind while reefing the main only (partially rolled jibs usually don't hold their shape well), the boat will sail to windward on main alone when short tacking allowing someone to easily work the foredeck to get the anchor ready or grab a mooring, and a furling code zero (a super easy to deploy light wind sail for cruisers) can be launched easily in front of the rolled up jib.

I read a little about Bernoulli and Reynolds numbers, but cannot remember any of it

 

[bobperry]

Stumble makes a very good point. The basic modern frac rig is a much bigger rig than the masthead rig of 20 years ago. A typical SA/D today could be 21.00 while a typical SA/D of 20 years back could be 16.5.

Tako:
I'll give you something to believe in SA (and I don't mean Sail area). Yesterday we raced FRANCIS with it's tall frac rig and got a First to finish and a First in Corrected Time win. We did this with a crew of four on a 63'er. Believe in that.

 

[RichH]

I'm an engineer, but I skipped the fluids course, but now regret that.

As a cruiser, I like the fractional rig for practical reasons. Usually, the mast is further forward, allowing the boat to balance reasonably even with the jib rolled up. Small jib is easy to tack, a bigger fully battened main is easy to handle, you can hold a full jib into an increasing wind while reefing the main only (partially rolled jibs usually don't hold their shape well), the boat will sail to windward on main alone when short tacking allowing someone to easily work the foredeck to get the anchor ready or grab a mooring, and a furling code zero (a super easy to deploy light wind sail for cruisers) can be launched easily in front of the rolled up jib.

I read a little about Bernoulli and Reynolds numbers, but cannot remember any of it

There is no need to review Bernoulli, Reynolds or even Prandtl, etc. All you have to do is keenly observe that most frac rigs (compared on an equal/similar basis) overwhelm masthead rigs when going to weather; and on the 'down side' the very same frac rigs will invariably use a spinnaker to beat the pants off a masthead (using a large LP genoa) 'going down'.

Such kind of strongly suggests that a masthead rig is only a compromise ... using the BIG jib/genoa instead of a 'proper' downwind sail and at the expense of 'pointing ability' for going uphill, to boot. It also suggests that the 'aerodynamics' of sailing more or increasingly 'optimize' with the fractional rig.
No 'iterated numbers' or 'theories' required, the 'ratings' databanks, the compilation of racing result over many many years seem to confirm this; all the while, the 'modern' (post ~1903) theories of aerodynamics help to explain 'why' that is.

All this stated, I still dont want an overly-tall rigid wing-sail on my crab-crusher 'Perryboat', thank you. But yet, I still fly a staysail 'under' a yankee topsail, as the speedo results show an increase of forward speed & VMG when pointing with this 'combo' .... and even that the staysail doesnt visibly seem to be 'drawing' - thanks to modern theories of aerodynamics.

;-)

 

[Liquorice]

Capt Vimes,
In support of RichH - you need to read the full article!

 

[Spider0804]

I would wonder why if the merits of fractional rigging are so beneficial to speed, why the fastest sailboat in the world uses a masthead overlapping jib.

One has got to think they have done more science models in a windtunnel than most other people.

http://hydroptere.com/news/508/146/...San_Francisco3-Copyright-Chrisophe_Launay.jpg

I think fractional shows benefits in racing classes but if we are talking about cruising I do not really think it matters too much where sail area is not restricted.

 

[capt vimes]

first of all - the fastest sail"boat" is this one:

top speed over 500 m: 65.45 kts...
and secondly - i do not see hydroptere to be mast headed:

edit:
it is not even mast headed in your image... look closely again: the hounds are probably 9/10 of the mast - the tapered wingmast gives the look as being mast headed...

 

[Spider0804]

I just figured that thin bit at the top was an antenna or something, looks too small to be a mast.

I know they have many configurations and run a lower height fractional for ocean going though.

 

[capt vimes]

well - in your image they were flying the jib and the main with the first reef...
in mine the main still with one reef and the smaller staysail, the jib furled away...

 

[Spider0804]

I am 95% sure that tiny bit on top is not part of the mast, but an antenna.

http://img.dailymail.co.uk/i/pix/2008/04_03/HydroptereLIV_468x225.jpg
http://4.bp.blogspot.com/_83C0d9qWNoU/TKTOwT6UZdI/AAAAAAAAYlg/INdqDNaPZJs/s1600/test.jpg
http://www.boatdesign.net/forums/at...70-15mph-peak-hydroptere-maxi-libryd-copy.jpg

Yea I am fairly certain it is masthead rigged.

In my picture the top of the jib goes all the way to the start of that spike.

Can not find any good pictures of just the top of the mast...

Anyway if it is fractional the stay is too high up to have the reason be mast bending and the jib goes higher than the mainsail or even with it depending how they run.

Is that not effectively the same as a masthead where the jib and main are the same height?

I was trying to make the point that if there was a benefit to doing it differently they would be doing it differently.

 

[Stumble]

That isn't a jib, it's a code sail. And on your diagram above it is still running a fractional genniker.

I would point out that hydroptere is so weird in its design and configuration I don't know e many iterations of sails it has. It is very possible that they have tried masthead rigs, fractional rigs, cat rigs, ect... The boat is a working test platform and doesn't really have a final configuration. You could probably find all sorts of weird combinations that have little to do with what the program thinks is fast.

I think mastheads are fine, but they are a compromise. Beating upwind a fractional is always going to point higher and be faster. Reaching a asymetric is always going to be faster, downwind a spinnaker is always faster. The upside to a masthead jib however is that it does them all well on one sail. If you will never consider a furling genniker then a masthead is likely faster all round. But not on any one point of sail, it's more of an 'on average' rig.

 

[Omatako]

I think mastheads are fine, but they are a compromise. Beating upwind a fractional is always going to point higher and be faster.

Yes you may be (and probably are) right but why? And please don't do like other posts and show me a picture of a boat that won a race and say "This is why". Geez

Reaching a asymetric is always going to be faster, downwind a spinnaker is always faster. The upside to a masthead jib however is that it does them all well on one sail. If you will never consider a furling genniker then a masthead is likely faster all round. But not on any one point of sail, it's more of an 'on average' rig.

What reason is there to assume that a masthead rig will not use a code sail, gennaker or spinnaker off the wind? If a frac rig furls the headsail and a masthead furls the headsail and both fly similar downwind sails why would the frac be faster off the wind? Maybe a taller rig, maybe a bigger main, I'm not saying it isn't faster, all I'm trying to do is understand why.

 

[bobperry]

Oma;
Boy, you are a snide little guy.

Time you educated yourself. All the info is out there. Lots has been presented here. We can't "make you" understand. It's not our lot to educate you. That's your job. You seem determined to stay in the dark when the light switch is right at hand.

Reach for the switch. Most of us did, years ago.

 

[Stumble]

Oma,

Are you asking for mandates or realities? Fractional boats have a different rig system and sail profile than a masthead, it isn't just moving the forestay lower on the mast. There are a lot of things that change like main size, lead angles, J leingth, mast bend issues, aspect ratios. These things then change again as other things are decide like backstay vs running backs, shroud angles, ect. All of these things change and interact with each other thus it is very difficult to discuss one in isolation.

Fractional rigs have the mast further forward, which allows for a larger main, along with a the smaller jib means that the sail area stays pretty close to the same. However it also results in a shorter J so you get a smaller spinnaker particularly on a symmetric which is limited typically by the J leingth. On the other hand an asymetric is less driven by the J length since the sprint pole makes up a significant portion of the foot leingth.

A good example of how this works is the dimensions on the J-29 since there is both a MH and a FH boat designed to perform the same.

The MH rig is 3.8' taller, .5' longer J, 1' shorter boom, ect...

The end result is the MH gives up 50 sq foot of mainsail, and gains 50 sq foot of jib sail area. But gains 150sq foot of downwind sail area because of the taller spinnaker. On the other hand if you were to put a MH kite on the FH the total sail area would be much higher downwind.

It gets complicated because there are so many variables, which is why it is instructive to look at what the fastest boats are doing. Simply because they have the time and money to spend playing with the permutations. If you really want to learn why, you need to spend some time reading books on rig design and engineering. Because it is a complicated subject (and way past my expertise).

 

[capt vimes]

another point might also be - but i could be wrong - that with new materials for the sails the main improved in performance a lot...
i see so many boats nowadays with fully battened mains from whatever-stuff-that-be and thus hugely increased performance when you compare it to the old white cloth hanging lousily from the mast...
the main is also easier and better to trim and thus there was a shift from small main, huge jib to huge main, small jib...

oh - and higher aspect ratio sails, i.e. smaller foresails with less J on a taller mast, just perform even better to windward...

 

[Osprey 26]

My guess is most of our wind measuring instruments, wind tunnel experiments show only one kind of wind. If there is only that kind of wind there would be nothing left behind so to speak.
Sir Isaac was probably right in explaining how things work.
Yes some sails do catch better then the other some of that extra unmeasured wind.
Faster then wind speed is result of this phenomenon on ice boats and such.
Probably to simple to be any good.

 

[Shockwave]

Your numbers are a little off if the leech is 12% and the SMW is 1.8 on a J29. The mh downwind sail area is 667, the frac downwind sail area is 644. So a delta of 23 sq ft. Is this 23 sq ft enough to overcome the taller rig the frac j enjoys?

Upwind with blades the frac has an additional 3 sq ft, upwind with overlap the advantage goes to the mh rig (sorry, didn't bother to figure that delta) but again the frac has a taller rig and should be able to sail in more breeze and enjoy more shear.

But at the end of the day the mh is rated 6 seconds faster and is simply a better all around boat. My personal belief is the lower ce of the mh rig is a bigger advantage then initially thought. The mh boat stands up better.

Where is the frac an advantage? It's an easier boat to sail provided the extrusion/layup is strong enough to allow mh sails (codes through kites) and the spreaders are swept so runners and checks aren't required to keep the rig in the boat. Where is it a disadvantage? When more power is needed in the light stuff upwind a small j and I just doesn't give enough oomph with overlap. Hence the strong development of the mh codes and sprits. You can't simply add I because the geometry of the sail is structurally unfeasible, the aspect ratio doesn't work. So modern boats add j (sprit) and I (mast head sheave boxes) and essentially become a mh boat with a very big rig.

What's best? MH or frac? Looking at the J 29 the MH is best, looking at other boats, I don't know, there aren't many boats built as both MH and frac.

Oma,

Are you asking for mandates or realities? Fractional boats have a different rig system and sail profile than a masthead, it isn't just moving the forestay lower on the mast. There are a lot of things that change like main size, lead angles, J leingth, mast bend issues, aspect ratios. These things then change again as other things are decide like backstay vs running backs, shroud angles, ect. All of these things change and interact with each other thus it is very difficult to discuss one in isolation.

Fractional rigs have the mast further forward, which allows for a larger main, along with a the smaller jib means that the sail area stays pretty close to the same. However it also results in a shorter J so you get a smaller spinnaker particularly on a symmetric which is limited typically by the J leingth. On the other hand an asymetric is less driven by the J length since the sprint pole makes up a significant portion of the foot leingth.

A good example of how this works is the dimensions on the J-29 since there is both a MH and a FH boat designed to perform the same.

The MH rig is 3.8' taller, .5' longer J, 1' shorter boom, ect...

The end result is the MH gives up 50 sq foot of mainsail, and gains 50 sq foot of jib sail area. But gains 150sq foot of downwind sail area because of the taller spinnaker. On the other hand if you were to put a MH kite on the FH the total sail area would be much higher downwind.

It gets complicated because there are so many variables, which is why it is instructive to look at what the fastest boats are doing. Simply because they have the time and money to spend playing with the permutations. If you really want to learn why, you need to spend some time reading books on rig design and engineering. Because it is a complicated subject (and way past my expertise).