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Jay
18th September 2007, 12:39 PM
A few weeks ago I am *sure* I read something about this in Tiesda's "Serenity Tips" page. As I recall, Tiesda said that you could use a softer mast than normally recommended for a given sail and get improved prerformance (I guess because the optimum mast for a given sail is not specified with ultra light winds in mind). Now in re-reading the Tips page I no longer see that. Did I imagine the whole thing? Was it a dream? Or has was it removed on purpose for some reason?

OK, assuming it was there (or is still there and I didn't see it on second read), here are my questions:

1) I want to be sure I understand why this is the case. A softer mast would bend more for a given amount of DH. So you would end up with a flatter sail and more twist at the standard DH setting. I'm not sure why this is better for ultra light winds and the Serenity. I do know that on sailboats they sometimes set more twist in lighter winds when there are waves but I'm not clear on why that helps. I would have thought that less twist (tighter leach) and a fuller sail would provide more power and pointing ability. Is it that sails stall easier in ultra light winds without adequate twist?

2) I have heard that RDM masts such as Sailworks Backbone, in the longest size (460), are actually softer than equivalent SDM masts (becuase it's harder to make as stiff a RDM mast when it gets that long). So unless you're a lightweight sailor, in normal winds, most 7.5 sails tend to rig better on a 460 SDM than a 460 RDM. My question is whether a 460 RDM (ie, Backbone), being softer, would provide better preformance on a Serenity than a 460 SDM mast? Anyone have any experience comparing SDM to RDM in the 7.5 range?

Thanks!

steveC
19th September 2007, 12:22 AM
Hi Jay,

Check out the following:

http://www.star-board.com/2008/pages/products/tune_serenity.htm

I don't know if it's what you were looking for, but I think that you'll find it interesting.

steveC
19th September 2007, 12:45 AM
Hi Jay,

One more thing. For my 8.3 Windwing Hammer, I use a 490cm Gulftech 100% carbon RDM, and surprisingly, it works very normally in the sail and it exhibits very good range overall. Although I have not used an SDM in this particular sail, I would tend to doubt that the overall character of the rigged sail would deviate that greatly, as the stiffness ratings are the same.

However, I should qualify my comments a bit because I only weigh 71kgs. It could be that a significantly heavier sailor might experience a somewhat different outcome.

Jay
19th September 2007, 01:47 PM
Steve - Thanks, yes, that's the document I was referring to. I seem to recall it having a couple of sentences about the benefits of using a softer mast than normally used ("optimal") on a sail used with the Serenity. Either I'm dreaming or Tiesda removed that reference?

It was the guys at sailworks who mentioned to me that a 460 RDM (ie, Backbone) is much softer than a 460 SDM (ie, Joystick or Speedstick). They said since RDM are reduced diameter (by definition) you just can't get the same stiffness as they get over about 430 length even with the thicker walls - it's just physics.

Tiesda - did you change your Serenity Tips document (see initial post)?

Roger - do you have any thoughts on this?

Thanks!

Jean-Marc
19th September 2007, 02:12 PM
Jay,

I don't think Tiesda removed a sentence about soft mast or whatsoever from his Serenity Tuning Tips page. At least, it's the same document as that of August 16 version that I have made a copy of.

I guess you are referring to this sentence : "To optimize lightwind performance, rigging onto a softer mast and creating a deep draft in the sail is recommended." This is found here : http://www.star-board.com/2008/pages/products/v_serenity.php

Sorry, no "conspiracy theories" are creeping or hiding here...

Cheers !

JM

Roger
19th September 2007, 07:01 PM
Hi Jay,
I'm not going to get into what Tiesda may have said/may not have said!
As far as using a softer mast, to gain some added light wind performance, yes, you
can try that.
It may work nicely, and then again on some sails or with some masts, it may actually be a neagtive in terms of overall performance.
The sail/rig I've used the most on the Serenity is the Severne Glide 7.5 m2.
The added perfromance with this rig is it's use of exotic (and expensive) materials to reduce the over all weight of the rig, and the significantly deeper profile (pretty much top to bottom in the entire sail) that has been designed into this rig to give it the perfromance characteristics of a larger (8.5-9.0 m2 per the German "Surf: magazine) rig.
Combining the low wind draft depth, and ultra light weight makes this rig somewhat "Serenity specific".
You can try some softer RDM's in your sails. RDM's have the smaller diameter, and this usually results in a slightly deeper profile when rigged in sails designed for SDM masts.
The Sailworks Backbone Masts are good in this respect as the designer made the tip of the upper section slightly stiffer than normal CC RDM's so you get a little added shape in the top of your sails vs other RDMs.
Hope this helps,

Jean-Marc
20th September 2007, 11:28 PM
Jay,

I think the general message about using softer mast with the Serenity has more to do by creating a powerfull sail with a very deep draft than using a softer mast to create more twist in the sail.

The Severne Glide or old raceboard sails from the '80-'90 era are cut with lots of cloth around the luff panel, thus creating a deep profile from top to bottom. However, with modern high wind sails, using a softer mast might be counter-productive because freeride, freerace or racing sails are cut with flatter profile and high tension skin along the luff panel. Swapping a SDM mast for a RDM will generally yield a softer sail with a loosier leech and a flatter profile, something very usefull for high wind.

However, having an excessively loose leech and flatter profile is not the best option to get a powerfull sail in ultra light wind when using a softer mast. I tend to prefer a tighter leech and a deep draft to have lots of power once underpowered in say 1-5 knots of wind with either a NP RX2 10.6 (NP Race Pro 520 flex top SDM mast) or a Severne CR2 11.0 sail (Severne Red Line 530 constant curve SDM mast + 30 cm mast tip extension). The key trim in such low wind is to set for minimal downhaul and outhaul and get a baggy sail, with the sail body touching the boom all the way from the clew up to the front harness line attachment or more.
Such a trim is way too powerfull in say 5-7 knots of wind, i.e., lots of back hand pressure, I have to fight very hard by pushing with the front hand and the baggy sail trim becomes ineffective because it acts as a brake. A normal downhaul and outhaul is then required to get a balanced sail, be able to further accelerate and still keep control of the sail (and board) once well- to over-powered.

This is my experience with fairly large sails I reckon, so I dunno whether the same holds true with medium sized sails around 7.5 m2 for example, so Hugh, John, Roger and other are welcomed to add their views on this subject below. I also remember a post from Rémi on the french forum ± a year ago who was strongly advocating the use of old soft raceboard class sails with the Serenity, so I'll leave to him to add his comments further below.

Cheers !

JM

Jay
21st September 2007, 04:11 AM
Jean-Marc - thanks for your comments. Thanks also for finding that sentence - yes, that's what I remembered. It turns out it just wasn't where I remembered it!

Regarding the softer mast - I guess what confuses me about the recommendation to use a softer mast for the serenity to increase power is that, as you said, I would think a softer mast would actually reduce draft and increase twist. If that's true, why does the product page suggest that?

Roger - thanks for your comments. Have you ever tried rigging a Severne Glide or a Retro 7.5 with a 460 Backbone? I'd be very interested in whether there are any advantages to doing that over rigging them on a Joystick, Speedstick, or Lightstick.

Thanks!

Roger
21st September 2007, 04:46 AM
Hi Jay,
I do not have any cams for the Glide 7.5 that would fit an RDM.
Something we all need to remember here is that when using a softer mast, we can vay the amount of downhaul and outhaul and get significantly different results than are possible on a stiffer mast.
If you back off on the downhaul with the softer mast, you will get a fuller foil both at the top and in the lower sections of the sail.
This is what the Glide 7.5 is all about. Lighter in weight, fuller foil, all the way to the top of the sail, with only minmal twist at lower downhaul tension.
You can increase the downhaul tension and get more twist (lot's of twist actually) but for super light marginal wind conditions, it seems twist is counterproductive. When the windspeed gets up to around 10-12 knots, then a bit more downhaul and twist become desireable.
Also if using the Glide 7.5 on an early planing shortboard (like the Apollo) a bit more downhaul and twist really helps the top speed.
It's all about making your sails and masts work together to acheive different goals.
Hope this helps,

Jean-Marc
21st September 2007, 04:55 AM
Jay,

A SDM mast in a standard sleeve of a camberless sail will make the batten head go to the side of the mast, thus creating some sort of a draft. Once loaded with wind, the initial shape of the luff curve will create the draft of the sail as intended by the sail designer (usually max deep profile is found at 30-40% behind the mast).
In contrast to a RDM mast in a standard sleeve, the excess sleeve cloth around the mast will make the batten heads go behind the mast, thus creating a much flatter profile on a static state. However, once powered up, this excess sleeve material will be under tension and will create a draft further away from the mast (up to 50% behind the mast) because once loaded with wind in a dynamic state, the excess sleeve material will be added to the initial shape of the luff curve.

With a camber sail, the result is worst in a standard sleeve: a flatter profile will be obtained with a RDM mast simply because there will be much less pressure on the mast by the camber. If you cannot adjust the cam pressure with cam spacers, you're stuck with a flat profile, no matter the static or dynamic state you are in. When using a RDM mast in a RDM camber sail, the result is as intended by the sail designer.

Sailing the Serenity in low wind is like sailing a sail boat in non planing conditions : baggy main sail trim with a tight leech to get lots of power (lots of depression between the lee- and wind-ward side of the sail).

Let's see what Rémi or Tiesda have to say about soft mast/soft sail on the Serenity.

Cheers !

JM

Jean-Marc
21st September 2007, 05:16 AM
If you back off on the downhaul with the softer mast, you will get a fuller foil both at the top and in the lower sections of the sail.


Why is that, Roger ?

I tought the contrary, i.e., a harder mast will deflect less, will tension more the leech and will not tension enough the luff curve (bend curve less than intended, thus making sleeve cloth more fuller because of less skin tension) below and above the boom whereas a softer mast will deflect more, will tension less the leech and will tension more the luff curve (bend curve more than intended, thus making sleeve cloth less fuller because of more skin tension). A bit confused as well...

Cheers !

JM

steveC
21st September 2007, 09:12 AM
With all due respect, the one thing that I have noticed is that static and dynamic loading produce clearly different results, regardless of SDM or RDM usage, at least with Bill Hansen's designs (Windwing, and now Hansen Sails). In fact, I've had to make some major adjustments in my outlook with more current designs (starting with the Bash model designs). What might look very loose leech on the beach changes significantly once on the water. While I'm not suggesting that that can be expected in other sail brands, we do need to keep in mind that things might not always be the same between different sail brands, and especially including the bends and characteristics of recommended masts (or not).

Jay
21st September 2007, 01:16 PM
Roger, thanks. I had forgot the Glide was cambered. So instead have you had the opportunity to compare a Backbone vs Joystick (or Speedstick or Lightstick) on a Retro? I would think that a Backbone 460 might be good with a Retro 7.5 on the Serenity because it is softer than a Joystick 460 and I would expect the smaller diameter of the RDM mast to leave more luff sleave to create a bigger pocket for a deeper draft. Does this thinking make sense?

Jean-Marc, thanks. Very helpful.
Just one clarification - when you said: "In contrast to a RDM mast in a standard sleeve, the excess sleeve cloth around the mast will make the batten heads go behind the mast, thus creating a much flatter profile on a static state. However, once powered up, this excess sleeve material will be under tension and will create a draft further away from the mast (up to 50% behind the mast) because once loaded with wind in a dynamic state, the excess sleeve material will be added to the initial shape of the luff curve." - you lost me a bit here. First to clarify - is this paragraph describing an SDM mast in an SDM luff sleeve or an RDM mast in a SDM luff sleeve? I guess I'm trying to understand your bottom line - are you saying that an RDM mast in a SDM sleeve gives more or less sail fullness (for the same amount of DH)?

Thanks guys - I really appreciate your help in figuring out the these issues!