Reefing a headsail??? - 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 > Skills and Seamanship > Learning to Sail
 Not a Member? 


Like Tree13Likes
Reply
 
LinkBack Thread Tools
  #21  
Old 01-09-2013
oysterman23's Avatar
S/V Wyndwitch - Morgan 24
 
Join Date: Jul 2011
Location: South Shore LI. NY
Posts: 309
Thanks: 95
Thanked 7 Times in 6 Posts
Rep Power: 4
oysterman23 is on a distinguished road
Re: Reefing a headsail???

Quote:
Originally Posted by RichH View Post

The use of a (slab) reefable jib, etc. is a VERY good way ensure good sail SHAPE, especially needed for going 'upwind' in gnarly conditions. This is a strategic advantage over a roller furled jib that typically can only be 'roller reefed' to approx 30% sail area reduction before the shape -- goes all to hell and you get extreme bagginess in the important luff section and thus lose important 'pointing ability'.

I prefer the jib, etc. reef points to run along at an 'up angle' towards the clew for two reasons:
1. if carefully 'angled' you dont have to reset (much) the fore/aft position of the jib fairlead car.
3. the resultant higher (new) clew position will be 'far above the deck' for less trapping of 'green water'. Another way to state this is the my reef points are arranged so that I effectively change a relatively low clew 'normal' shape into a 'yankee' shape with 'high' clew when deep reefed.

Well said...I noticed this on my previous boat which really needed a jib reef when it got over 25 and would become very tame and able to beat upwind quite closely afterwards....Reasons I am thinking of removing my furling on the new boat. grrrr decisions decisions!
Reply With Quote Quick reply to this message Share with Facebook
  #22  
Old 01-09-2013
ASA and PSIA Instructor
 
Join Date: Apr 2000
Posts: 3,471
Thanks: 6
Thanked 18 Times in 18 Posts
Rep Power: 15
sailingfool will become famous soon enough
Re: Reefing a headsail???

Quote:
Originally Posted by deltaten View Post
....WHile that's all good, the foot *is* what he sent me, dimension-wise; a measured 16'-3". Doing the math; it looks like I am the new owner of a 150% Genoa!! .
If you actually measured the length of the foot, that is not what you measure to determine the size of the jib, you need to measure the LP or luff perpendicular, the length perpendicular from the luff to the clew...so the sail should turn out to be a good deal less than a 150%.
jackdale likes this.
__________________
Certified...in several regards...
Reply With Quote Quick reply to this message Share with Facebook
  #23  
Old 01-09-2013
deltaten's Avatar
Senior Member
 
Join Date: Oct 2012
Location: Lancaster Co. PA/ North East, MD
Posts: 707
Thanks: 7
Thanked 15 Times in 15 Posts
Rep Power: 3
deltaten is on a distinguished road
Send a message via Yahoo to deltaten
Re: Reefing a headsail???

sailingfool;
I'd appreciate a link to that info... on how ya calculate the percent overage.

Thanks,
Paul
Reply With Quote Quick reply to this message Share with Facebook
  #24  
Old 01-10-2013
jackdale's Avatar
Senior Member
 
Join Date: Dec 2008
Location: Calgary, AB, Canada
Posts: 8,945
Thanks: 27
Thanked 53 Times in 50 Posts
Rep Power: 6
jackdale will become famous soon enough
Re: Reefing a headsail???

As an aside. When you furl a a genoa, the C of E goes higher and forward - exaxctly the wrong direction.

I used to use a boat with a slab reefing jib. It was great. I remember beating in 35 knots (with few waves, no fetch). No problem. Double reefed main.
oysterman23 likes this.
__________________
__________________
ISPA Yachtmaster Offshore Instructor Evaluator
Sail Canada Advanced Cruising Instructor
IYT Yachtmaster Coastal Instructor
ASA 201, 203, 204, 205, 206, 214
As I sail, I praise God, and care not. (Luke Foxe)
Reply With Quote Quick reply to this message Share with Facebook
  #25  
Old 01-10-2013
RichH's Avatar
Senior Member
 
Join Date: Jul 2000
Location: Pennsylvania
Posts: 2,887
Thanks: 9
Thanked 78 Times in 71 Posts
Rep Power: 15
RichH will become famous soon enough
Re: Reefing a headsail???

Here ya go on determining the LP (length perpendicular) ... see the second dwg. on the page.
Sail Measurement Assistance
Reply With Quote Quick reply to this message Share with Facebook
  #26  
Old 01-10-2013
deltaten's Avatar
Senior Member
 
Join Date: Oct 2012
Location: Lancaster Co. PA/ North East, MD
Posts: 707
Thanks: 7
Thanked 15 Times in 15 Posts
Rep Power: 3
deltaten is on a distinguished road
Send a message via Yahoo to deltaten
Re: Reefing a headsail???

Thanks Rich;

I'm having some trouble digesting the text stating; " The LP defines the sail size in terms of percentage increase beyond the J measurement as in the following examples." with the chart immediately below. It shows, under the "LP" column, a direct correlation to unit "J" past the "I" line.
It appears that roller furlers need the "LP" figure to relate the amount of sail exposed, as that's the direction of reduction; but regular (geometric term) foresail calcs rely on straight "J" numbers.
Am I missing something??
Doesn't the "IJ" fore-triangle calc describe a geometric area potentially filled by a headsail at 100% (not necessarily the actual measurements)? As I was led to believe, the increase in percentage was a function of the amount of the (base/"J") jib triangle passing the mast (height/"I") of the theoretical/geometric right triangle??

Last edited by deltaten; 01-10-2013 at 08:47 AM.
Reply With Quote Quick reply to this message Share with Facebook
  #27  
Old 01-10-2013
ASA and PSIA Instructor
 
Join Date: Apr 2000
Posts: 3,471
Thanks: 6
Thanked 18 Times in 18 Posts
Rep Power: 15
sailingfool will become famous soon enough
Re: Reefing a headsail???

Hmmm. Just lose the concept that the genoa size relates to the foretriangle area - it does not. It relates solely to the LP relationship to the J. If you do the geometry, a 100% genoa will have an area equal to the (square root of (I squared plus P squared)/I) times the foretriangle area. So if the measurements of a W27 are:

I J P E
34.75ft 11.00ft 29.00ft) 10.75ft

then the area of a 100% jib will be 1.05 times the foretriangle area of 1/2*IP or 529 sq. ft.

I think.
__________________
Certified...in several regards...
Reply With Quote Quick reply to this message Share with Facebook
  #28  
Old 01-10-2013
Faster's Avatar
Just another Moderator
 
Join Date: Sep 2005
Location: New Westminster, BC
Posts: 15,003
Thanks: 81
Thanked 223 Times in 215 Posts
Rep Power: 10
Faster has a spectacular aura about Faster has a spectacular aura about Faster has a spectacular aura about
Re: Reefing a headsail???

I think SF has it... if your boat has a J measurement of 12 feet, say, and if you drew a line through the clew at 90 degrees to the luff (ie LP) and it measured 18 feet, that's a '150%' genoa
__________________
Ron

1984 Fast/Nicholson 345 "FastForward"

".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
Reply With Quote Quick reply to this message Share with Facebook
  #29  
Old 01-10-2013
AdamLein's Avatar
Senior Member
 
Join Date: Nov 2007
Location: Coquitlam, BC
Posts: 1,866
Thanks: 1
Thanked 0 Times in 0 Posts
Rep Power: 7
AdamLein will become famous soon enough
Re: Reefing a headsail???

Quote:
Originally Posted by sailingfool View Post
Hmmm. Just lose the concept that the genoa size relates to the foretriangle area - it does not. It relates solely to the LP relationship to the J. If you do the geometry, a 100% genoa will have an area equal to the (square root of (I squared plus P squared)/I) times the foretriangle area. So if the measurements of a W27 are:

I J P E
34.75ft 11.00ft 29.00ft) 10.75ft

then the area of a 100% jib will be 1.05 times the foretriangle area of 1/2*IP or 529 sq. ft.

I think.
529 ft² sounds big for a 100% jib on a 27-foot boat. Isn't P just for the mainsail?

I would think jib area is LP * Luff / 2. If Luff = forestay length, then for that boat it's

100% * 11.00 ft * sqrt((34.75 ft)² + (11 ft)²) / 2 = 200.5 ft².
__________________
s/v Essorant
1972 Catalina 27
Reply With Quote Quick reply to this message Share with Facebook
  #30  
Old 01-10-2013
ASA and PSIA Instructor
 
Join Date: Apr 2000
Posts: 3,471
Thanks: 6
Thanked 18 Times in 18 Posts
Rep Power: 15
sailingfool will become famous soon enough
Re: Reefing a headsail???

Quote:
Originally Posted by AdamLein View Post
529 ft² sounds big for a 100% jib on a 27-foot boat. Isn't P just for the mainsail?

I would think jib area is LP * Luff / 2. If Luff = forestay length, then for that boat it's

100% * 11.00 ft * sqrt((34.75 ft)² + (11 ft)²) / 2 = 200.5 ft².
So much for the back of the envelop. You are right, the correct the formula for adjusting the foretriangle area is stated as "(square root of (I squared plus J squared)/I) times the foretriangle area".

I used the correct formula in calculating the 1.05 adjustment for a 100% jib. If you calculate the foretriangle area of I*J/2 to
191, adjust by the 1.05 and you get the 200.5 that you calculated directly...
__________________
Certified...in several regards...
Reply With Quote Quick reply to this message Share with Facebook
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




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
"Reefing Point" for Roller Furled Headsail? rhumbunctious Gear & Maintenance 1 05-13-2012 06:44 AM
Reefing without reefing points Rup Seamanship & Navigation 29 12-03-2009 04:19 PM
converting a furling headsail to a hanked on headsail mrkeith Gear & Maintenance 6 02-15-2007 02:36 PM
Headsail Reefing Basics Brian Hancock Seamanship Articles 0 08-05-2004 08:00 PM
Headsail Reefing Basics Brian Hancock Gear and Maintenance Articles 0 08-05-2004 08:00 PM


All times are GMT -4. The time now is 01:57 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

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.