Will,
I had a great WE…here some pics I made this year:
http://public.fotki.com/wismerhell/seawind/page2.html
31-34 are the latest. I tried to adjust the twist…I dont think that the boat is faster, however it does response much better!!
Again, thanks a lot for your time and patience…
A very happy Seawind owner…
Wis
_/ if it isn’t broken, don’t fix it! _
Will, Thanks for the simple tutorial on adjusting the rigging like a guitar. Worked great for me an my Marblehead maiden voyage! [:D] Actually I tighten the rigging till the wrinkles were gone then twanged the strings. [:D]
Rcher,
The rig looks really nice.
I looked at the picture in the other thread with the boat on the boatstand and it looked like you might have had a bit too much cunningham. The “bubble” along the luff is due to over-tensioning in that direction. It looks like you sorted that out by the time it hit the water (or perhaps the sails were just luffing and it fooled me?).
Who’s sails are you using? Did they give you a tuning guide with the sails? I’ve worked with Both Rod Carr and Bob Sterne and they both send tuning guides along with the sails…
Will Gorgen
What is the typical range of tensions on an IOM rig? (Lester states up to 15 kg in shrouds in extreme cases, but how rare is that?). I just made my tensiometer and calibrated from 0.5 to 5.5 kg in 0.5 kg steps - will that cover it?
Thanks!
J
They’re Rod Carr’s sails and yes, he did supply a tuning guide. But I’m afraid that I lost the guide somewhere. The picture on the stand was before I started tweeking. There are still a few tweeks that I need to do but it sailed well enough that I’m happy as a dog with two tails! [:D]
J, (Do you work for Men in Black?)
I would think that 5.5 kg would be adequate. 15 kg seems very high. The IOM spars are fairly flexible, so you need to have some fairly high loads to keep things straight. But I would guess that 4-5kg is about as high as any of the shroud tensions. I’m using a 9.7mm IOM spar section (which is a bit thin for the IOM class) with a 1.22m tall rig (a bit shorter than the IOM) and the 3.5 kg force I tensions my lowers to seems pretty high to me.
I might add a few more steps in the lower tension band. It is nice to be able to distinguish between 0.35 and 0.40 kg for the backstay tension. If your tensiometer is as nonlinear as mine and your first mark is at 0.5kg, then you will have difficulty resolving any tuning settings lower than that. If you used a rubberband on you tensiometer, you should have wider spaces between the lower tension marks than between the higher tension marks. So it should be pretty easy to add some marks below 0.5kg.
A thought on the 15kg that Lester mentioned: The rig tensions on the water will be higher than they are when you tension them on shore because of the sail loading. Was Lester talking about the loads that the rig sees when sailing?
Rcher,
Call up Rod and ask him to mail you a new guide. If I know Rod, he will be more than happy to drop that in the mail to you. It is extremely helpful to refer to every so often. It is easy to get into rut where you start playing with only a couple of tuning parameters and you let some of the other ones drift a bit out of range. It is nice to be able to scan quickly through the tuning guide to remind yourself of some of those others that you have been overlooking on your past few sailing outings. I have even gone through and highlighted each of the section headings so that a quick scan of the highlights and I can do a mental checklist to make sure that I have not forgotten something. I have it stapled into my notebook where I keep my notes on tuning settings…
Will Gorgen
<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by wgorgen
Was Lester talking about the loads that the rig sees when sailing?<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>
Hi Will
No, static. The 15 kg is certainly extreme, and relates to using the shrouds to manage mast bend via the spreaders. I’d not expect to see anything larger than around 8 kg “normally” in an IOM shroud. Knowing the exact shroud tension isn’t much of an issue if you are only concerned with the traditional use of shrouds, that is, to just keep the mast upright. For an IOM, a tensiometer ideally needs to (only) be able to measure backstay tensions, and topping lift tensions. AFAICS, other tensions aren’t too relevant in “normal” practice.
Lester Gilbert
http://www.iomclass.org/
http://www.onemetre.net/
I agree to a certain extent, Lester,
I use my tensiometer to mainly tune my backstay (like you say) on a normal basis. After I have set my backstay tension, I check my mast bend. If it seems out of whack, then I double check my lower sidestay tenstions (my lowers are mounted aft on the chainplate so that I can use them as checkstays to control the mast bend). I also use my tensiometer to check my toppinglift tension and if that seems light for the correct backstay tension, I will double check my upper sidestay tensions.
So on occasion, I do have to verify the more highly loaded sidestays.
My Fairwind is, of course, a plastic boat. I have added a re-enforcing bulkhead under the deck and mast step that traverses the boat between the chainplates. This allows me to load up my sidestays quite a bit. But even so, 8 to 10 lbs is about as high as I want to go. I am a bit worried about the compressive loading in the mast. With my deck stepped mast, I am worried about buckling the mast.
8kg is more than double this tension. That seems really high to me but perhaps with the stronger composite hull of an IOM, the keel stepped mast base with partners and the larger mast diameter, those sorts of loads are tolerable. Or perhaps I am just not brave enough to test the structural limits of my boat and rig…
Will Gorgen
<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by wgorgen
8kg is more than double this tension. That seems really high to me but perhaps with the stronger composite hull of an IOM, the keel stepped mast base with partners and the larger mast diameter, those sorts of loads are tolerable.<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>
Hi Will
A well-built IOM should take 8 kg. A poorly built one will not, and as you say 8 lb would be more like it. I asked SAILSetc to build my current Italiko to take 15 kg – the interior strengthening is impressive… Yes, you’d need to be running a 12.7 mm (1/2") mast to do this, and considerable “V” in your spreaders to take much of the tension away into the chainplates rather than just forcing it all into the mast step, otherwise the mast will simply squiggle out of column (“squiggle” – technical term meaning to take up the shape of soggy spaghetti…).
Lester Gilbert
http://www.iomclass.org/
http://www.onemetre.net/
I once sailed on a 60 footer with a 4 spreader mast. The boat had just been delivered to a new owner and I was invited by a freind of mine to help with some boat tuning. when I layed on the deck and looked up the mast while we were sailing, I was apalled at how squiggled that mast was. It took me and one of the other crew members the better part of 3 days to de-squiggle it. That squiggle was due to poorly adjusted intermediate shrouds rather than excessive compressive load, but the resulting mast shape is jsut about the same.
When you sqiggle a mast with excessive compressive loading, you are just begging for that mast to come out of column and buckle. I’ve seen that happen on a couple of experimental rigs and it is not pretty…
Will Gorgen
At a previous North Americans for our cats up at Traverse City Michigan, I had a unique opportunity to see a mast begin “pumping” from wind speed and sail load.
First a bit of detail:
Cat mast is a single diamond with spreader for the lower 2/3 of mast.
It has a short forestay “pigtail” which then has two forward stays attached from pigtail to each bow
It has a single set of side shrouds (one each side) to each hull.
The stays and shrouds also connect to same tang area as the diamonds.
Since cat rigs are designed to rotate - they cannot use a backstay for mast control/bend.
The diamonds are left loose (relatively) and as the mast rotates to apparent wind, the mast bends sideways. More bend equals flatter sail for higher winds. The trick is knowing how loose of diamond wires and how far to allow mast to bend.
The top 1/3 of mast (LOA = 31 feet) is unstayed and allowed to bend off in gusts, depowering the top part of the mainsail.
That’s the basics of the standing rigging set up.
On several upwind beats, in pretty strong winds with gusts, the mast rotated as it should, and flattened the sail. Unfortunately, when the gusts started hitting above 20 mph, the top of the mast did it’s thing, and fell off to leeward to dump power. On several occassions during the upwind leg, the mast seemed to get into harmonics with the gusts and as I was sailing, I could actually see the mast “pumping” back and forth from side to side. Easing off the sheet and footing a bit ended the shaking until I sheeted in and headed back up and it would start once again. Only experienced this on one day and two different windward legs - but was enough to cause me to adjust diamonds a bit tighter. After that no further problems.
So as you indicate, Will - very disconcerting to have the mast “go squiggly” and start shaking about. Was an even bigger problem since boat is a singlehander and there is no crew to send forward to lever the diamonds tighter.
Just an experience I recalled based on your experience. Wonder if we have same problem on our little boats but never see it cause we are too far away. It was one of those things that make you say “YIKES!”
This is getting perhaps a bit off topic, but here is what comes to mind when I think of squiggly masts that make you say “Yikes!”
Will Gorgen
<center><font size=“3”>YeeeHaaaa ! </font id=“size3”></center>
<center>Ya gotta do it to appreciate it… ice boating, not bending masts [:D]</center>
[:-graduate] And for the “What it’s worth” deprtment -
USA 4691 = John Dennis, current (2004) North American Champion
USA 4061 = Paul Goodwin chasing