Spreaders - to pivot or not to pivot?

Moderator: GreenLake

Spreaders - to pivot or not to pivot?

Postby Alan » Thu Jun 09, 2011 2:20 pm

I sprang for a set of the aerodynamic spreader bars that Dwyer mast offers, partly because they appear to very strong, and partly because - I admit it - they look yachty.

They come without pin holes. The old brackets, and the new one-piece bracket I bought with them, have two pin holes per side. The old spreader bars have just one pin hole, so they're free to pivot around the pin's axis, allowing adjustment of the fore-and-aft position of the bars' outer ends.

My question to the experts: Would you use just one pin per side to allow adjustability, or would you use two pins per side for the extra strength?
Alan
 
Posts: 696
Joined: Wed Jun 17, 2009 4:39 pm

Postby GreenLake » Thu Jun 09, 2011 6:57 pm

I'm not an expert, but you might find this thread interesting.

http://www.boatdesign.net/forums/sailboats/pivoting-spreaders-17519.html
~ green ~ lake ~ ~
GreenLake
 
Posts: 5195
Joined: Mon Jun 18, 2007 3:54 am

Postby K.C. Walker » Thu Jun 09, 2011 7:31 pm

Because you're asking, I would say no to fixed spreader angle. It seems to me that if you fix the spreader angle you need to know why you want it in that position and be right. With free swinging spreaders they are self adjusting.

Also, top racing sailors in our class such as Phill Root and Mike Gillum use free swinging spreaders very effectively. Why complicate it?
KC Walker, DS 1 #7002
K.C. Walker
 
Posts: 1335
Joined: Sun Jul 06, 2008 10:50 pm
Location: North Stonington, Connecticut

Postby GreenLake » Thu Jun 09, 2011 9:23 pm

There are two angles. The fore and aft and the vertical angle.

Assuming that he fixtures are designed to hold your spreaders at the correct fore and aft angle, a two-hole design would better support vertical loads that come from a small misalignment of the spreaders.

The way the fittings on my boat are designed they are very sensitive to vertical loads, while at the same time making it difficult to position the spreaders correctly to minimize those loads (they are factory original, but O'Day apparently substituted the Javelin version on a few of the boats they built).

What you want is to bisect the angle of the shroud, and that means having the spreaders ever so slightly point upward. Only then will there be 0 vertical loads. My fittings don't really allow that much vertical movement, and the previous set of spreaders broke from excess vertical loads at the pin.

A two hole design should provide more definite support, so as long as the horizontal angle is correct, it might provide some advantage. If the horizontal angle is not correct, or if it changes with sailing loads, then a fixed support would also have to hold horizontal loads - and those can be considerable.

That's all the thoughts I have on this subject.
~ green ~ lake ~ ~
GreenLake
 
Posts: 5195
Joined: Mon Jun 18, 2007 3:54 am

Postby Alan » Thu Jun 09, 2011 9:55 pm

GreenLake, K.C.:

Thanks to you both. I've been puzzling over for this for some time now. I'm mulling over your advice, and I'll probably be back tomorrow with more questions.
Alan
 
Posts: 696
Joined: Wed Jun 17, 2009 4:39 pm

Postby K.C. Walker » Thu Jun 09, 2011 10:20 pm

I was assuming a Style A bracket or a Style B bracket. http://www.dwyermast.com/items.asp?cat1 ... Airfoil%29 These brackets predetermine vertical alignment. The bracket itself should provide as much vertical strength as you are going to get. I wouldn't think adding another pin would make any difference. The hinge pin for the spreader goes in the outboard hole but the spreaders go all the way to the mast in the bracket.

With limited swing spreaders, as opposed to fixed, when you put on more vang and sheet tension the spreaders swing back, relative to the mast. This helps to bend the mast forward more evenly to flatten out the sail for close hauled work in heavy air.

If you knew what you wanted for pre-bend or you wanted to experiment with rig tune you could get some of the Selden adjustable spreaders http://www.seldenmast.co.uk/fittings/co ... gory_ID=29 .
KC Walker, DS 1 #7002
K.C. Walker
 
Posts: 1335
Joined: Sun Jul 06, 2008 10:50 pm
Location: North Stonington, Connecticut

Postby Alan » Thu Jun 09, 2011 10:34 pm

Style B, for no reason other than that it looked like the load transfer of a one-piece would give it more strength than two separate pieces.

For what it's worth, the aerodynamic spreaders are a very nice fit into either the Style B bracket (which I bought) or the Style A brackets (which are on the mast now). And as noted, neither one allows adjustment of the vertical angle.
Alan
 
Posts: 696
Joined: Wed Jun 17, 2009 4:39 pm

Postby Mike Gillum » Fri Jun 10, 2011 12:10 pm

Dave Keran won several DS NAC's with #316 that had free swinging spreaders on a really old original tapered Proctor Mast.
Dave's spreaders consisted of inexpensive aluminum tubing that were through-bolted to short pieces of inexpensive aluminum Angle that were riveted to the mast.
About as primitive as it gets but still very competitve and inexpensive is my reference for materials readily available at the local Hardware Store instead of APS!
The tapered 1/8" aluminum Flat Bar spreaders on 2772's Ballenger Mast came fixed and they've stayed that way.
I can wrap my head around the idea of allowing the spreaders to swing allowing them to align at all times between the hounds and chainplates but I'm not sure if it makes any real difference when the results are posted.
Mike Gillum
 
Posts: 163
Joined: Wed Jul 26, 2006 7:28 pm
Location: Loomis, California

Postby Alan » Sun Jul 24, 2011 10:11 pm

A little slow on the uptake here, but I just wanted to thank people for the detailed, well thought out responses.

So, I'm going to do some well thinking out over the winter. Thanks again. :)
Alan
 
Posts: 696
Joined: Wed Jun 17, 2009 4:39 pm

Postby ctenidae » Mon Jul 25, 2011 10:36 am

Mike Gillum wrote:Dave Keran won several DS NAC's with #316 that had free swinging spreaders on a really old original tapered Proctor Mast.
Dave's spreaders consisted of inexpensive aluminum tubing that were through-bolted to short pieces of inexpensive aluminum Angle that were riveted to the mast.
About as primitive as it gets but still very competitve and inexpensive is my reference for materials readily available at the local Hardware Store instead of APS!


That's the setup I have on 1114. Only instead of through-bolted, they're held in place with cotter pins. Works so far...
Formerly 28 cents
DS1 1114

Now, sadly, powered boating...
ctenidae
 
Posts: 243
Joined: Mon Oct 05, 2009 8:25 am
Location: Norwalk, CT


Return to Rigging

Who is online

Users browsing this forum: No registered users and 1 guest

cron