Question about spreader/rigging geometry - SailNet Community
 8Likes
Reply
 
LinkBack Thread Tools
post #1 of 31 Old 06-15-2015 Thread Starter
Senior Member
 
__floater__'s Avatar
 
Join Date: Nov 2014
Location: New Scotland
Posts: 109
Thanks: 5
Thanked 1 Time in 1 Post
Rep Power: 5
 
Question Question about spreader/rigging geometry

My 27 foot sloop is a 7/8 (approximately) fractional rig with the swept spreaders normally associated with a fractional rig. The spreaders themselves have a wing-like profile which "plug" into a matching receptacle which is rivited to the mast. The shrouds pass through slots under the outer end caps of the spreaders.

While ascending the mast Saturday to repair a windex that was damaged in branches during launch, I noticed the spreaders are "bending" downward. This came as no surprise to me because I always considered the geometry of sailboat rigs to be flawed at the spreaders.

My question is, why are spreaders configured to be perpendicular to the mast (where they are already securely fastened) and not to the shrouds (where the spreaders can slip down the wire by the forces of the load)?

If the spreader were angled up to become perpendicular to the shroud, the load would be transfered to the mast more effeciently. I just never understood this geometry.

I asked a rigger of 26 years about the situation and he had no answer.

SV Whisper
1981 Aloha 8.2
Hull #50

Last edited by __floater__; 06-15-2015 at 12:39 PM.
__floater__ is offline  
Sponsored Links
Advertisement
 
post #2 of 31 Old 06-15-2015
Master Mariner
 
capta's Avatar
 
Join Date: Jun 2011
Location: somewhere south of civilization
Posts: 6,952
Thanks: 135
Thanked 365 Times in 353 Posts
Rep Power: 8
 
Re: Question about spreader/rigging geometry

On a single spreader rig such as yours, the shroud changes direction at the spreader. Where exactly in this change of direction or angle, would you expect this perpendicular angle?

"Any idiot can make a boat go; it takes a sailor to stop one." Spike Africa aboard the schooner Wanderer in Sausalito, Ca. 1964.
“Believe me, my young friend, there is nothing - absolutely nothing - half so much worth doing as simply messing about in boats.” ― Kenneth Grahame, The Wind in the Willows

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

facebook.com/svskippingstone
capta is online now  
post #3 of 31 Old 06-15-2015
Load Bearing Member
 
CarbonSink62's Avatar
 
Join Date: Sep 2011
Location: Derry, NH
Posts: 644
Thanks: 9
Thanked 15 Times in 13 Posts
Rep Power: 8
 
Dock
Re: Question about spreader/rigging geometry

I would expect that splitting the difference between the 2 angles would create a situation where the spreaders wouldn't want to move down at the outboard side.

Ken

Zen Again

1978 Bristol 29.9 #122

Testing a mother's love since 1962
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
CarbonSink62 is offline  
 
post #4 of 31 Old 06-15-2015
Senior Member
 
Faster's Avatar
 
Join Date: Sep 2005
Location: New Westminster, BC
Posts: 19,488
Thanks: 160
Thanked 587 Times in 558 Posts
Rep Power: 16
     
Re: Question about spreader/rigging geometry

Quote:
Originally Posted by CarbonSink62 View Post
I would expect that splitting the difference between the 2 angles would create a situation where the spreaders wouldn't want to move down at the outboard side.

Ken
That's the trick.. there should be enough give in the spreader root to create a spreader angle that bisects the shroud angle. That way there's no tendency for the spreader tip to slide up or down due to forces from the shroud itself. Not a bad idea to wire/clamp the spreader in position too, as in some cases as the leeward shroud slacks in a breeze and lump they can move about some.
Markwesti likes this.

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)
Faster is offline  
post #5 of 31 Old 06-15-2015
Barquito
 
Barquito's Avatar
 
Join Date: Dec 2007
Location: Madison, WI
Posts: 3,330
Thanks: 1
Thanked 86 Times in 85 Posts
Rep Power: 12
 
Re: Question about spreader/rigging geometry

I think Floater is saying that the two angles are not equal. Same on my boat. The spreaders are perpendicular to the mast, therefore, they bisect the shroud forming a more acute angle on the top than on the bottom. Seems like this would put pressure on the spreader to move down at the shroud.
__floater__ likes this.

Valiant 32
Barquito is offline  
post #6 of 31 Old 06-15-2015 Thread Starter
Senior Member
 
__floater__'s Avatar
 
Join Date: Nov 2014
Location: New Scotland
Posts: 109
Thanks: 5
Thanked 1 Time in 1 Post
Rep Power: 5
 
Re: Question about spreader/rigging geometry

Quote:
Originally Posted by Barquito View Post
I think Floater is saying that the two angles are not equal. Same on my boat. The spreaders are perpendicular to the mast, therefore, they bisect the shroud forming a more acute angle on the top than on the bottom. Seems like this would put pressure on the spreader to move down at the shroud.
Exactly.

If the spreaders were 90 degrees to the shroud, the load would be transfered straight back through the spreader, causing no force either up or down. It would however create a downward force at the base of the spreader where it meets the mast, but this would be of no concern because of the strong mechanical connection made at the spreader/mast.

Maybe I don't understand transfer of loads as well as I think I do, but having a "loose" connection on something that is at an angle is just looking for trouble IMO.

The owner who had my boat before me had stainless steel saddle clamps on the shrouds beneath (actually touching) the spreaders. I didn't like the ideal of pinching the shrouds and I'd never seen it done before so I removed them. Maybe I'll have to put them back!
Markwesti likes this.

SV Whisper
1981 Aloha 8.2
Hull #50

Last edited by __floater__; 06-15-2015 at 01:53 PM.
__floater__ is offline  
post #7 of 31 Old 06-15-2015 Thread Starter
Senior Member
 
__floater__'s Avatar
 
Join Date: Nov 2014
Location: New Scotland
Posts: 109
Thanks: 5
Thanked 1 Time in 1 Post
Rep Power: 5
 
Re: Question about spreader/rigging geometry

Quote:
Originally Posted by Faster View Post
That's the trick.. there should be enough give in the spreader root to create a spreader angle that bisects the shroud angle. That way there's no tendency for the spreader tip to slide up or down due to forces from the shroud itself. Not a bad idea to wire/clamp the spreader in position too, as in some cases as the leeward shroud slacks in a breeze and lump they can move about some.
As I said in the post above, I don't like to clamp a shroud. Maybe it doesn't hurt but it seems wrong to me.

What I am considering though is "assistant uppers" that would fasten a few inches below where the uppers terminate at the mast and a couple inches in from the end of the spreader, which would hold the spreaders up.

SV Whisper
1981 Aloha 8.2
Hull #50
__floater__ is offline  
post #8 of 31 Old 06-15-2015
Senior Member
 
Faster's Avatar
 
Join Date: Sep 2005
Location: New Westminster, BC
Posts: 19,488
Thanks: 160
Thanked 587 Times in 558 Posts
Rep Power: 16
     
Re: Question about spreader/rigging geometry

Quote:
Originally Posted by __floater__ View Post
As I said in the post above, I don't like to clamp a shroud. Maybe it doesn't hurt but it seems wrong to me.
Our spreaders have a clamp bracket built into the ends..

Quote:
Originally Posted by __floater__ View Post
What I am considering though is "assistant uppers" that would fasten a few inches below where the uppers terminate at the mast and a couple inches in from the end of the spreader, which would hold the spreaders up.
C&C did this on their late 70's/early 80s 34.

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)
Faster is offline  
post #9 of 31 Old 06-15-2015
Senior Member
 
overbored's Avatar
 
Join Date: Oct 2010
Location: Dana Point, Ca
Posts: 2,581
Thanks: 2
Thanked 185 Times in 182 Posts
Rep Power: 9
 
Re: Question about spreader/rigging geometry

Quote:
Originally Posted by __floater__ View Post
My 27 foot sloop is a 7/8 (approximately) fractional rig with the swept spreaders normally associated with a fractional rig. The spreaders themselves have a wing-like profile which "plug" into a matching receptacle which is rivited to the mast. The shrouds pass through slots under the outer end caps of the spreaders.

While ascending the mast Saturday to repair a windex that was damaged in branches during launch, I noticed the spreaders are "bending" downward. This came as no surprise to me because I always considered the geometry of sailboat rigs to be flawed at the spreaders.

My question is, why are spreaders configured to be perpendicular to the mast (where they are already securely fastened) and not to the shrouds (where the spreaders can slip down the wire by the forces of the load)?

If the spreader were angled up to become perpendicular to the shroud, the load would be transfered to the mast more effeciently. I just never understood this geometry.

I asked a rigger of 26 years about the situation and he had no answer.
first there is no normal for a fractional rig. there any number of ways it has been done. most new modern rigs have the spreader angled up at about the intersect angle of the shrouds. some are perpendicular to the mast. the ones I have seen that angle down are because the fittings are bending down over time and were most likely perpendicular when new. the newer masts have a carry thru solid spar that the spreader slides over and is thru bolted.
if they are angled down I would take a closer look at the attachments as the may be bent or they have been installed upside down. I have seen this on a sparcraft mast where the owner did not know and installed the carry thur and the spreaders upside down. we set him straight at the yard as they were rigging the boat

"FULL TILT II" 2011 BENETEAU FIRST 30
"GOLD RUSH" PRINDLE 16
overbored is online now  
post #10 of 31 Old 06-15-2015
Senior Member
 
Markwesti's Avatar
 
Join Date: Dec 2012
Location: Seal Beach Ca. ( Long Beach )
Posts: 1,308
Thanks: 117
Thanked 63 Times in 63 Posts
Rep Power: 7
 
Re: Question about spreader/rigging geometry

This is a interesting thread . On our boat the spreaders float a little at mast where they connect and angle up a couple of degrees . One time , along time ago one spreader sagged a bit I just shoved it back up and it never did it again . We also have the extra shrouds that start about 2" from the tip of the spreaders and attach about 3' above the spreaders . I asked the guy that used to run the Westsail factory what they were for , he said "they are there support for when you are standing on a spreader trying to see over the horizon" .
Markwesti is online now  
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:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
Extra spreader question Swordhors Gear & Maintenance 3 12-19-2012 01:54 PM
Spreader question Stevyboy Gear & Maintenance 7 02-09-2011 09:25 PM
Variable Geometry Wing Sails VGWS1 Introduce Yourself 8 01-25-2011 06:40 PM
Mast Standing Rigging Spreader Replacement. sce56 Gear & Maintenance 2 05-08-2009 11:12 PM
yet another spreader question Gorlog Gear & Maintenance 3 04-27-2007 10:51 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome