Something about the fractional rig that I just don't get... - Page 3 - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > General Interest > General Discussion (sailing related)
 Not a Member? 


Like Tree19Likes
Reply
 
LinkBack Thread Tools
  #21  
Old 04-26-2014
Omatako's Avatar
Senior Member
 
Join Date: Sep 2003
Location: Auckland New Zealand
Posts: 2,376
Thanks: 0
Thanked 25 Times in 22 Posts
Rep Power: 11
Omatako will become famous soon enough
Re: Something about the fractional rig that I just don't get...

Quote:
Originally Posted by bobperry View Post
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.
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

__________________

"Two possibilities exist: Either we are alone in the Universe or we are not. Both are equally terrifying."

Arthur C. Clarke
Reply With Quote Share with Facebook
  #22  
Old 04-26-2014
Omatako's Avatar
Senior Member
 
Join Date: Sep 2003
Location: Auckland New Zealand
Posts: 2,376
Thanks: 0
Thanked 25 Times in 22 Posts
Rep Power: 11
Omatako will become famous soon enough
Re: Something about the fractional rig that I just don't get...

Quote:
Originally Posted by bobperry View Post
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.
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

__________________

"Two possibilities exist: Either we are alone in the Universe or we are not. Both are equally terrifying."

Arthur C. Clarke

Last edited by Omatako; 04-26-2014 at 04:11 PM.
Reply With Quote Share with Facebook
  #23  
Old 04-26-2014
Omatako's Avatar
Senior Member
 
Join Date: Sep 2003
Location: Auckland New Zealand
Posts: 2,376
Thanks: 0
Thanked 25 Times in 22 Posts
Rep Power: 11
Omatako will become famous soon enough
Re: Something about the fractional rig that I just don't get...

Quote:
Originally Posted by hellosailor View Post
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.
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

__________________

"Two possibilities exist: Either we are alone in the Universe or we are not. Both are equally terrifying."

Arthur C. Clarke

Last edited by Omatako; 04-26-2014 at 04:08 PM.
Reply With Quote Share with Facebook
  #24  
Old 04-26-2014
Senior Member
 
Join Date: Feb 2012
Location: New Orleans Louisiana
Posts: 1,760
Thanks: 6
Thanked 38 Times in 36 Posts
Rep Power: 3
Stumble is on a distinguished road
Re: Something about the fractional rig that I just don't get...

Quote:
Originally Posted by Shockwave View Post
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.
__________________
Greg Rubin
Attorney
Reply With Quote Share with Facebook
  #25  
Old 04-27-2014
Senior Member
 
Join Date: Oct 2009
Location: Cape Cod
Posts: 515
Thanks: 4
Thanked 18 Times in 18 Posts
Rep Power: 5
capecodda is on a distinguished road
Re: Something about the fractional rig that I just don't get...

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
Reply With Quote Share with Facebook
  #26  
Old 04-27-2014
grumpy old man
 
Join Date: Apr 2011
Posts: 3,542
Thanks: 1
Thanked 72 Times in 68 Posts
Rep Power: 4
bobperry will become famous soon enough
Re: Something about the fractional rig that I just don't get...

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.
__________________
Please visit my blog. It's fun to read.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Bob's Blog ....


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Share with Facebook
  #27  
Old 04-27-2014
RichH's Avatar
Senior Member
 
Join Date: Jul 2000
Location: Pennsylvania
Posts: 2,742
Thanks: 9
Thanked 63 Times in 56 Posts
Rep Power: 15
RichH will become famous soon enough
Re: Something about the fractional rig that I just don't get...

Quote:
Originally Posted by capecodda View Post
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.

;-)

Last edited by RichH; 04-27-2014 at 01:25 PM.
Reply With Quote Share with Facebook
  #28  
Old 04-27-2014
Liquorice's Avatar
Senior Member
 
Join Date: Nov 2007
Location: Alberta, Canada
Posts: 163
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 7
Liquorice is on a distinguished road
Re: Something about the fractional rig that I just don't get...

Capt Vimes,
In support of RichH - you need to read the full article!
__________________
sam :-)
Just because you're paranoid ...doesn't mean they're not after you!
Reply With Quote Share with Facebook
  #29  
Old 04-27-2014
Member
 
Join Date: Oct 2011
Posts: 53
Thanks: 2
Thanked 0 Times in 0 Posts
Rep Power: 3
Spider0804 is on a distinguished road
Re: Something about the fractional rig that I just don't get...

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/H...phe_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.

Last edited by Spider0804; 04-27-2014 at 10:06 PM.
Reply With Quote Share with Facebook
  #30  
Old 04-28-2014
capt vimes's Avatar
Senior Member
 
Join Date: Dec 2013
Posts: 590
Thanks: 7
Thanked 16 Times in 16 Posts
Rep Power: 1
capt vimes is on a distinguished road
Re: Something about the fractional rig that I just don't get...

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...

Last edited by capt vimes; 04-28-2014 at 05:15 AM.
Reply With Quote Share with Facebook
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
7/8 Fractional Rig micheck Gear & Maintenance 3 03-19-2011 02:26 PM
Fractional Rig overbored General Discussion (sailing related) 1 10-08-2010 01:56 PM
Fractional Rig vs. Mast Head Rig c130king Sailboat Design and Construction 66 03-09-2008 11:38 AM
Fractional vs. Masthead Rig max-on Boat Review and Purchase Forum 7 06-14-2004 01:37 PM
Fractional to Full Rig? rhbroehl General Discussion (sailing related) 2 02-12-2003 03:32 PM


All times are GMT -4. The time now is 11:08 PM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012