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Old 24-08-2013, 21:42   #1
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Wharram's don't have spreaders?

Why is it that wharrams don't have spreaders and ...most... Of the other boats I see do have spreaders? I know there is a more technical answer than mine.

My answer was that they are sailing and the mast is still up. Someone has gotta be able to do better than that.
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Old 25-08-2013, 01:13   #2
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re: Wharram's don't have spreaders?

They dont need them there stays go to the outside of the hulls which is a wide enough angle.
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Old 25-08-2013, 02:17   #3
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Re: Wharram's don't have spreaders?

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Originally Posted by boatsail View Post
Why is it that wharrams don't have spreaders and ...most... Of the other boats I see do have spreaders? I know there is a more technical answer than mine.

My answer was that they are sailing and the mast is still up. Someone has gotta be able to do better than that.
Look at older sailing workboats. They often don't have spreaders either. What they do have is thick, strong (and heavy) masts. Often the masts are relatively short as well.

The rig on the Wharrams is relatively short as well, and is inspired by the rig on Dutch sailing barges.
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Old 25-08-2013, 09:35   #4
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Re: Wharram's don't have spreaders?

When you have plenty of beam and/or enough mast stiffness, you do not spreaders.

Plenty of masts with no spreaders.

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Old 25-08-2013, 13:07   #5
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Re: Wharram's don't have spreaders?

The optimum angle for the shroud to mast connection is around 12 degrees. Any more acute angle, the compression load skyrockets. Larger angle, the compression load drops off. On a mono hull you are limited to how far outboard you can put the chainplates and still get that 12 degree or more angle at the masthead. To keep that angle at the masthead and the resultant compression load on the mast at a reasonable level, masts are built with spreaders. On a multihull, you aren't limited by the width as severely. Designers can get that magic 12 degree angle or even larger by mounting the chain plates out on the hulls without spreaders.

Strangely, the most complicated rigs I've seen have been on multihulls. To keep from having shrouds angling out to the hulls and the mast in column, they've gone to spreaders and wire that are anchored to the base of the mast with only a spreaderless cap shroud to the masthead to hold it up.
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Old 25-08-2013, 13:16   #6
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Re: Wharram's don't have spreaders?

Short answer: with enough mast stiffness I guess you dont need them. But beam width has nothing to do with it. A mast is a column, columns in compression only fail when they dont stay straight. Spreaders keep the mast straight athwartships. You either need spreaders to keep the column straight or a stout mast cross-section/short mast.
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Old 25-08-2013, 13:42   #7
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Re: Wharram's don't have spreaders?

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The optimum angle for the shroud to mast connection is around 12 degrees. Any more acute angle, the compression load skyrockets. Larger angle, the compression load drops off. On a mono hull you are limited to how far outboard you can put the chainplates and still get that 12 degree or more angle at the masthead. To keep that angle at the masthead and the resultant compression load on the mast at a reasonable level, masts are built with spreaders. On a multihull, you aren't limited by the width as severely. Designers can get that magic 12 degree angle or even larger by mounting the chain plates out on the hulls without spreaders.

Strangely, the most complicated rigs I've seen have been on multihulls. To keep from having shrouds angling out to the hulls and the mast in column, they've gone to spreaders and wire that are anchored to the base of the mast with only a spreaderless cap shroud to the masthead to hold it up.
What he said. Been on racing boats with hydraulic rams located in the mast step to provide enough tension in the shrouds to stop the mast from falling over where narrow spreaders allowed for tight sheeting angles of overlapping headsails.

Also, a rig without spreaders allows for a sleeve luff like on a Laser. I believe Wharram refers to this as a "poor man's wingsail" in that it provides many of the benefits of a rotating mast/wingsail ie. reduced turbulance off the mast. The round mast section can be made from readily accessible tubing or even a tree instead of a more costly extrusion with a bolt rope.

Funny thing about today's square top mainsails, they look a lot like Wharram rigs that have been around for twenty years, maybe he's not such a kook after all.
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Old 25-08-2013, 18:29   #8
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Many cats, not just Wharrams, do not have spreaders on the side stays because it is not necessary. The purpose of spreaders is to create an adequate angle so that the side stays will take the load...with a wide beam you do not need them.

Many cats do have "diamond stays" which provide addition mast support. This is a system of spreaders and wires which all attach to the mast ... none to the deck. This creates a stronger mast system w out adding significant weight (as increased extrusion thickness would do) There is no signifcant difference in the cross section of a mid sized monohull mast versus a mid sized cat.
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Old 25-08-2013, 18:42   #9
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Re: Wharram's don't have spreaders?

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The optimum angle for the shroud to mast connection is around 12 degrees.(...)
Yes. And it is an optimum minimum.

(Wider bases further limit loads BUT they may be undesirable for non-structural reasons).

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Old 26-08-2013, 08:23   #10
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Re: Wharram's don't have spreaders?

Tiki Wingsail Rig | James Wharram Designs
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Old 26-08-2013, 08:31   #11
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Re: Wharram's don't have spreaders?

Awesome answers.

How does one take on and off the wingsail without removal of the mast?
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Old 26-08-2013, 08:38   #12
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Re: Wharram's don't have spreaders?

The original Wharrams have a wingsail design like Gord linked to. The entire leading edge is a sleeve that wraps all the way around the mast. Spreaders would get in the way. Also most of the larger Wharrams are ketch rigged which means smaller masts so less strength required. And finally many have been built with solid timber masts which are super strong but heavier.
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Old 26-08-2013, 08:42   #13
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Re: Wharram's don't have spreaders?

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Awesome answers.

How does one take on and off the wingsail without removal of the mast?
I think it is often a zipper with Velcro flap.
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