Spreader length question

Moderator: GreenLake

Spreader length question

Postby Baysailer » Thu May 06, 2010 4:09 pm

OK not a daysailer question but one I'll post it here anyway.

My Rhodes has a replacement mast, it meets class standards but is slightly out of tolerance in cross section (larger) so I assume it's stiffer. It's also straight where R19 class does allow tapered masts. The spreaders are much shorter than what I've seen on other Rhodes, about 13-14" where the rule book states 24".

My question is how does altering the spreaders to length affect the mast or sailing characteristics? Or put another way if I use longer spreaders what does that do for me or to me?

Note: This is how I got it and have been sailing it for years and don't know any different. Basically asking before I put it in the water.

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Postby GreenLake » Thu May 06, 2010 9:29 pm

My five minute reply. To help answer your question, think of two extreme cases, and figure out what they do.

If the spreader length is so short that the spreaders don't spread the shrouds (shrouds would angled in, in an otherwise straight line):

a) the shrouds act only at their top attachment point.
b) the leverage to counteract sideways loads at the top is minimal.

If the spreader length is so long that the shrouds are vertical in their lower part:

a) the leverage at the top is much better
b) the spreaders now provide sideways load of their own.

With swept-back spreaders, as on the DS, you get this in two dimensions. In the fore-aft direction, the action of the spreaders adds. So the longer your spreaders are, the more bend you should get in your mast, because of the combined action of forestay, shrouds and spreaders.

Anyway, that's my quick guess, of what might change.
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Postby K.C. Walker » Thu May 06, 2010 9:30 pm

If 24 inches is the maximum set by the rulebook you would most likely want to be within an inch or 2 of that. 10 inches or more is a country mile, broadside of the barn, huge difference. It's generally recommended to set your mast up with the maximum length spreaders and work them shorter by half inches at a time to tune the rig.

Long spreaders tend to bow the mast forward and to windward when you are close hauled. The heavier the wind the more the effect and this is to a point desirable. It tends to flatten the sail a bit, moving the draft forward, and opens the slot. Having short spreaders allows the mast to sag to leeward which tends to close the slot and lets the sail bag out and the draft moves aft.

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Spreader length update

Postby Baysailer » Tue May 11, 2010 5:12 pm

Just an update, I contacted Dwyer Mast and they designed their Rhodes 19 Package with 16" spreaders (which is the length I have). Appearantly they took into account their mast extrusions were stiffer than stock to begin with so the shorter stays gets similar characteristics to the original setup. Since I think they know more than me I'll leave them as is.

One difference for the R19 compared to other setups (like the DS) is the spreaders are fixed and not swept back. You get no mast bend from the spreaders. Backsatay works that into play and the forestay is looser than on a DS to allow the bend when you apply backstay.

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