Rig Tension Question

BCC Forum
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I’m doing my first dockside rig tuning and after studying Brion Toss’ video on the subject I’m left scratching my head as to how to tune the bowsprit and boomkin.

I’m hoping for some rules of thumb, something general that will help me recognize if I’m getting close.

Currently, the boomkin’s two short shrouds are very tight, as in bar tight. This makes sense to me given the short length of the wire and what I imagine would be considerable load in a heavy seaway.The bowsprit bobstay is similarly tensioned. This too makes sense to me, but then again, I’m not sure. The bowsprit shrouds are tensioned to fairly firm, I would say similar to my newly-tuned (Toss, again) mast lowers, but given the loads and the occasional strolls I take on the bowsprit shrouds, I’m wondering if they are firm enough. All these shrouds and such have turnbuckles.

When eyeballed, the bowsprit does not appear to dip or climb and the same can be said for the boomkin.

I don’t have a Loos guage (yet) and am using Toss’ push/pull/listen approach. So far so good. The wood mast is standing straight with a very slight bend to stern at the top (This is okay for a wooden mast, isn’t it?)

Thanks heaps for any pointers or advice.

Warren Fraser

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wfraser Wrote:

I’m doing my first dockside rig tuning and after
studying Brion Toss’ video on the subject I’m left
scratching my head as to how to tune the bowsprit
and boomkin.

I’m hoping for some rules of thumb, something
general that will help me recognize if I’m getting
close.

Here are a few thoughts, based on years of racing dinghys with very bendy masts and adjustable rigs, and just a little experience setting up Itchen’s very unbendy Forespar mast. Surely there are many out there with a lot more experience with BCC rig tune?! First time i did it I checked Toss to see what he had to say and saw nothing to disagree with – a lot of books have been written on the subject and there’s much similarity of approach

Currently, the boomkin’s two short shrouds are
very tight, as in bar tight. This makes sense to
me given the short length of the wire and what I
imagine would be considerable load in a heavy
seaway.The bowsprit bobstay is similarly
tensioned. This too makes sense to me, but then
again, I’m not sure. The bowsprit shrouds are
tensioned to fairly firm, I would say similar to
my newly-tuned (Toss, again) mast lowers, but
given the loads and the occasional strolls I take
on the bowsprit shrouds, I’m wondering if they are
firm enough. All these shrouds and such have
turnbuckles.

When eyeballed, the bowsprit does not appear to
dip or climb and the same can be said for the
boomkin.

That’s what you want to see, no bend in the bowsprit, and the boomkin the same.
Next the mast in column with no bend and with whatever rake seems appropriate. Rake is already more or less fixed unless the step is movable. My feeling based on Itchen’s performance and comments of others is to aim for as little aft rake as one can manage to avoid any more weather helm than probably already exists.

Then I set up the lower and upper shrouds snugly but not too tight and use the main halliard to make sure that the masthead is centered athwartships. Just cleat it at an appropriate length and see if it touches the gunwale equally port & stbd. Then I set up headstay and backstay quite tight, and the staysail stay less so and eyeball the mast to see if it is still “in column” with no bend. Obviously, the lower shrouds versus the staysail stay will interact and have a lot to do with fore and aft bend and sidewise “S curves” which are definitely to be avoided! After all looks good I then crank up the tension on the backstay and headstay until it is “just right”. Impossible to quantify, but one wants to avoid headstay sag in a breeze as much as is reasonable so IMHO this is the critical adjustment and should be quite tight. The do whatever is needed to bring the staysail stay into synch with everything else. Then eyeball the mast column again and make sure no nasty curves have appeared.

Fianlly, go sailing in a 2-reef breeze and see how it looks when going to windward. Mast should still be straight with minimal leeward sag at the masthead and the leeward uppers & lowers should still be snug – not “bar tight” but certainly not flopping around. Then get another BCC to match race with you (Iduna are you there?) and make fussy little adjustments to get those last few seconds per mile improvement in rig tune. Just kidding, I think the BCC has a very unfussy rig and a basic setup works fine and can be left untouched once “in the ballpark”. A Loos tension gauge is nice for tuning racing dinghys but probably overkill for a BCC, but gadgets are fun, so why not, (especially if you can borrow one from a hot one design racer)!
I found the trickiest adjustment to be backstay and headstay versus bobstay so as to get adequate headstay tension without bowsprit bend. The bowsprit whisker stays (shrouds) need to be quite tight – I think it is hard to over do this, as there is a lot of sidewise pressure when hard on the wind, and I like not having them wobble back & forth when used as a foot rest.

I don’t have a Loos guage (yet) and am using Toss’
push/pull/listen approach. So far so good. The
wood mast is standing straight with a very slight
bend to stern at the top (This is okay for a
wooden mast, isn’t it?)

I’m the wrong peron to comment on this – it has been over forty years since I had anything to do with a wooden mast, all my practical experience is with aluminum masts. I’d be VERY careful about too much bend, or any “s-curve” at all. There are just opinions, I have no special expertise and would be interested in the experiences of other BCC owners. Anyone ever lose their rig in a blow?

Thanks heaps for any pointers or advice.

Warren Fraser

Warren Fraser
s/v Voyager of Yokohama

Edited 1 times. Last edit at 03/31/08 06:09AM by
wfraser.

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Warren:

 Send me your direct address (mine=whitewings@charter.net) and I will send you my Loos gauge settings.  They basically match the tension recommendations in Toss for any given wire size and seem to work well.  No leward stay sag beating to weather and the sprit stays centered in the gammon iron.

 After some years of experimenting, I have figured out the correct length for the bob stay and boomkin stays that will keep both structures un-bent when I have proper tension on the head stay and back stay.  Given the gauge of those wires, once you get the length correct, they are not going to stretch so I leave them alone.  I always eyeball the sprit and boomkin when I rig each Spring just to be sure but have not changed them in the last 3-4 years.

 I set my mast fore and aft with the stays at about 3/4 final tension.  I then start from the bottom up.  Lowers, mids, caps....to 1/2 tension, 3/4 tension, then full tension. (I do the head and back stays to full once I've got everything else to 3/4)  I know many books tell you to start from the top down but it has never made much sense to me as you are putting the spar in compression and will chase s-bends until the cows come home.  I leave the staysail stay until last.  You have to fiddle a bit with it and the lowers, particularly, as a change in one will change the tension of the other.

 I grew up as a dingy sailor with finely calibrated fingers for rig tension and used the same technique on my BCC at first. I bought the less expensive Loos gauge several years ago (at the urging of Bil Hansen who is a terrific BCC tech resource) and was surprised to find out how much tighter my stays needed to be than my "calibrated" fingers thought.  As the important thing is rig tension symmetry, the cheaper of the Loos gauges is just fine for a BCC. Might not be exactly the desired foot/lb but we're not racing are we?  OK...some of us are not racing.

 One caution on using the halyard to measure the spar position athwartships, my memory is that the Sam Morse hulls are slightly assymetrical (maybe 1 1/2") which will trick you when using halyard measurements to center the spar. My incremental tightening technique from the bottom up seems to give me a pretty plumb spar.  An eyeball check from across the marina confirms that.

                                   Tom.......BCC118
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Scott, thanks for the information. Tom, thanks for the offer for the guage settings-- I sent you an email earlier today. I’ll be on the boat this weekend tweaking the rigging to tighten things up. Thus far I’ve managed to avoid putting any esses into the mast and think I straightened out a mast top bend to port by easing the starboard upper a tad and tightening the port one. She now stands in column. The question remains whether the rigging as a whole is tight enough.

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Having gotten several requests for my rig tension, Loos settings…I’m putting it on the forum. The first chart in the attachment is from Bil Hansen, I believe they are load data for our wire sizes from Toss’s book. His Loos settings were the one’s I started with and I have ended up using very similar settings now.

 The second chart lists my Loos setting from last season.  I waffle back and forth on the whisker stays...used 37 last summer which seemed to work fine. Being able to hide more easily in the Great Lakes, I rarely see more than 30-35 Kts but, if the sprit is going to shift, that should be enough of a test.

 I also cheat a bit on the headstay as, with a furler, the Loos gauge won't work.  I know what it feels like when the back stay turnbuckle is tightened properly so I guesstimate the same setting on the headstay.  I do them incrementally just like all the other stays.

 I use the cheaper Loos model 90, aluminum guage....good idea not to use it after a big night out as hand tremors will throw off your readings.

 Feel free to contact me if you have any other questions.......Tom
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Having gotten several requests for my rig tension, Loos settings…I’m putting it on the forum. Bil Hansen’s Loos settings were the one’s I started with and I have ended up using very similar settings now.

 The chart below lists my Loos setting from last season.  I waffle back and forth on the whisker stays...used 37 last summer which seemed to work fine. Being able to hide more easily in the Great Lakes, I rarely see more than 30-35 Kts but, if the sprit is going to shift, that should be enough of a test.

 I also cheat a bit on the headstay as, with a furler, the Loos gauge won't work.  I know what it feels like when the back stay turnbuckle is tightened properly so I guesstimate the same setting on the headstay.  I do them incrementally just like all the other stays.  Also, I eyeball the furler for sag and the sprit for straight.

 I use the cheaper Loos model 90, aluminum guage....good idea not to use it after a big night out as hand tremors will throw off your readings.

 Feel free to contact me if you have any other questions.......Tom

Stay and Shroud tension: Loos gauge figures
Harrer-May ?07
Whisker ? Port 37-39
Whisker ? Stbd 37-39
Staysail 42
Cap ? Port 41
Cap ? Starboard 41
Intermediate - Port 39
Intermediate - Stbd 39
Lower Fwd - Port 37
Lower Fwd - Stbd 37
Lower Aft - Port 37
Lower Aft - Stbd 37
Back & Fore Stays 47

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As it is soon time to “tune” again this thread caught my eye and prompted me to review my yearly numbers. Whether from laziness or isolation I seem to have drifted to the “undertuned” side of things. Further I had forgotten that this is worse for the boat than maybe a little tight. I had kept the main things in mind: fwd lowers slightly tighter than the aft, and the stasl shroud can really put the bend in the mast, and forestay has to be tight to prevent leeward falloff and maintain pointing ability.
I believe my standing rigging is slightly different from the standard BCC as far as I can tell from reviewing the pictures. I have (2) “mids” or intermediates. One goes to the middle tang along with the “upper” or cap. The other goes to the aft tang with the aft lower shroud. Further I have running backs that only get used when needed. Other than that the set up seems to be the same. My standing rigging is 5/16", the bobstay is 1/2" and the boomkin is 3/8". I will have to check on the whisker stays, can’t remember.
So in summary I am going to increase my tensions this year. I use a Loos PT-3 guage and go by the numbers. However, if I look at the recommended % of breaking strength I would still come out with much lower numbers than those listed in the prior post. I wonder if the difference is in the two different guages used or some other reason? Any thoughts on this would be appreciated.

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 I cannot speak to the difference in Loos guages but, my Model 90 has a table that gives tension as a function of wire size and Loos number.  If memory serves, my settings give tension numbers very close to what the Brian Toss..Rigger's Apprentice book recommends.  Bil Hansen has a nice chart that calculates all that and, again memory here, pretty much confirms Toss' numbers with the Loos settings he and I use.

                           Tom
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OK and thanks for the reply. My Loos also has a table that gives a “scale number” from 7-50, then (4) different cable diamters and for each scale number under the different diameters there is a “lbs. tension” number and “% breaking strength” number corresponding to the scale number. I guess my question was: for a reading of “37” for your lowers what lbs tension or % breaking strength does that 37 represent? Seems to me that either one of those values would allow comparison of apples to apples, hopefully. Again thanks for the information.
Stephen

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Stephen:

 My gauge is on the boat and it will be at least Friday before I am back there.  I will make some notes then if you can wait...........Tom
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Tom,
Sounds fine and thanks for your interest.
Stephen

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Stay Diameter
(inches) Length (pin to pin)(feet and inches) Breaking Strength (lbs) Tension(lbs) (theory) Loos Gauge figure
Headstay 9/32 40? 2.75? 8700
Bobstay 3/8 8? 0.5? 14800
Whisker stays 1/4 14? 0.5? 6900
Staysail stay 9/32 26? 6? 8700
Cap shrouds 1/4 37? 9? 6900 1035-1400 39-40
Intermediate shrouds 1/4 26? 7.5? 6900 1035 39-40
Lower forward shrouds 1/4 15? 4? 6900 690 36-37
Lower aft shrouds 1/4 15? 8.5? 6900 690 36-37
Backstay 9/32 8700 1740 48
Boomkin stay 5/16 3? 10? 10600

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Stephen:

Attached (I think) is a set of shroud tension calculations that Bil Hansen did.  He's the one that got me using a Loos gauge in the first place.  We use the same gauge so our settings are very similar.  If you need more data from my gauge, let me know.  If you don't have Toss'. .. The complete Rigger's Apprentice" it's a worthwhile investment.

                     Hope this helps............T

SHROUD TENSION CALCS.jpg
SHROUD TENSION CALCS.jpg1275×1245 96.1 KB

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Tom,
The mystery is cleared up regarding the numbers. On my Loos PT-3 as an example: for 1/4" wire 1035-1400 lbs tension corresponds to a “scale number” of 10-15. Further, 690 lbs tension on 1/4" wire is scale number 7. So it is due to using different guages. I still have to tune up my rigging abit however, as I was a running somewhat slack so the thread was real helpful to me. I certainly do have Toss’ book(s), video(s), and couldn’t live without the rigging tape although I gather it is just a 3M product he repackages and sells. Hope to find a source here in Canada as shipping it (in the small quantities I wanted) from Port Townsend was prohibitive this year. Again thanks, Stephen