Mast stiffness sideways
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Can believe there has been nothing on the technical thread in almost a month. Here goes:
I have been reviewing photos of my boats in competion and noticing I have a lot more sideways bend than do most of my competitiors.
Admittedly I am heavier than most at 100kg.
Anyone care to post their mast deflection numbers and thier weight. I am running used C-Techs from Greg Wilcox and Nick Craig (decent pedigree).
I have always felt that I have never been able to get upwind the way i should and think that sideways stiffness may be part of the problem as it makes it much harder to get a wide range of the sail from top to bottom working together. My number are:
Sideways
3/4 as % 1/2 86%
1/4 53
1/2 74
3/4 64
tip 275
1/4 as % of 1/2 72%
F/A
1/4 65
1/2 86
3/4 58
tip 380
Anyone care care to comment on C-Techs and Aardvarks latest thinking?
Thanks all and Merry Christmas.
Brad Johanson
USA-1010 and CAN-500Hi Brad,
it would be massively useful if you could post a couple of the pics that make you feel that it’s mast stiffness causing your problem. You can use the ‘upload attachment’ tab at the bottom of the ‘post a reply’ screen or if you have any prob email them to me ([email protected]) and I’ll put them on.
DaveHi Brad – I see you have temporarily come out of hibernation. There are 3 C=Tec masts in the Turner family – here are the bend measurements:
Andy’s mast: (2007) C-Tec (not high modulus)
¼ ½ ¾ tip
Fore & aft 75 95 73 484
sideways 60 88 73 301Pete Turner’s mast (251) – C-Tec High modulus (2010)
¼ ½ ¾ tip
Fore & aft 71 94 74 568
sideways 48 75 65 252Will Turner’s mast (252) – C-Tec High modulus (2010)
¼ ½ ¾ tip
Fore & aft 70 90 70 542
sideways 53 75 70 250Andy
Hi Brad
I think sideways numbers are less looked at than f/a and are far more important for your weight. The sideways is what gives you power and lets you de-power as well. It is really important to get a mast you can handle in all conditions.
To give you a bit of an idea of what others are using here are some sideways numbers.
I am around 85-87kg and mine are
40 57 49 224Thomas HM is 90 odd kg on a good day
41 61 53 216Really stiff is Bo Teglars again around 90kg
35 53 44 195
Personally I think this is too stiff but he likes it in the light and moderate.This is not the stiffest sideways as Mark Perrow had one at 185. Alistair Deaves said he almost saw it bending in about 25knts with the 115kg Perrow hiking.
Jorgen Svendsen was around 85kg at the worlds and his mast was
41 61 52 221What you can see is that the bottom number is around 40 in all these masts. This means the mast is stiff out of the deck. As the masts are very small in the top they work hard and fast with the high mod carbon. If you think that 10mm at the tip sideways does not make such a difference just imagine how much more carbon it takes to hold the mast straighter with 10kg on the tip over a length of 6m.
This means that if you have a tip deflection of 250 the mast is realistically a lot softer sideways than one with around 225. If you are 100kg then you should really have a mast with a sideways bend of around
38 54 45 210.Hope this helps
GregIs there more than one way of measuring bend? I have what I thought was a pretty stiff ceilidh mast and the bend numbers are completely different.
H
Here is the photo I was reviewing. It is sometimes usefull to be in back of the pack to get a good shot to compare your setting too. It is in Antwerpen at the Belgian Nationals 2011.
Oooh, not so easy to analyse, but roughly sketching in ‘straight masts’ doesn’t look like your mast is wildly bendy: the two GER boats (left in this composite, right in the original) look like they are getting more low bend, but then you’re heeling a bit more, so maybe you’re in a bit of a gust as this pic went off.
Dave
(Bob: I guess that’s a Belgian 10 kilo weight hanging on the crane – different again! )@bob193 wrote:
it all depends on how much a 10kg weight hung off the tip of the mast weighs in ireland hugh
Or even 12kg as recommended in the Ceilidh guide. http://carbonmasts.com/index.php?option=com_content&view=article&id=63:howtodinghybend&catid=43&Itemid=69 That’s what I have and that’s presumably one reason the numbers are different.
Or perhaps we could look at how UK sails in australia do it, which is completely different. There, apparently, you put a line from the end of the boom to the top of the mast and pull on 24kg tension, then measure the numbers.
Hugh, Most of the fleet are using the 10kg test. For comparison purposes I’d keep to that. It’s probably worth testing the measurements. I wouldn’t get phsyced out. The measurements that Greg has stated are really interesting and reflect the last couple of years thinking. Masts are generally getting stiffer. So old stiff could be new soft! I didn’t realise Bo’s mast was that stiff, and now wish I hadn’t started above him at the last race of the Worlds!
From my limited learning curve I think there is a definate compromise to be made. For example the sideways bend becomes the fore and aft on a run. So whilst you don’t want too much sideways bend upwind so you can maintain height, you want the mast moving forward on the run.
All interesting stuff. I’m sure things will move on again this year one way or another.
Tony.There’s a page on the Danish site with a bunch of mast comparisons. They’re from 2005 though, so pretty old. Interesting from a historical viewpoint, perhaps.
http://okjolle.dk/nyheder/2005/mastemaal.htm
It’s in Danish too….and google translate does a dreadful job on Danish..sadly.
H
Blimey Hugh, seven year old mast bend numbers in Danish!
Interesting
?? I really think there’s cause for concern here! Funny, because ‘ought to get out more’ didn’t used to be phrase one associated much with the citizens of the Republic!
Dave@davecooper wrote:
Blimey Hugh, seven year old mast bend numbers in Danish!
Interesting
?? I really think there’s cause for concern here! Funny, because ‘ought to get out more’ didn’t used to be phrase one associated much with the citizens of the Republic!
DaveInteresting from a historical perspective, I think I said.
As understanding of sail dynamics improves we see sailmakers – particularly in open classes – changing leach shapes and profiles, head shapes, mast bend behaviour, etc. Since the OK limits sail outline, mast bend is more important. Since many of the improvements in open classes are essentially found by accident, without a clear understanding of why some new trick is faster, I’m guessing the same is true of OK Dinghy mast bend profiles. Seeing the evolution of mast bend over the years might give insight into how and/or why the latest bend profiles work better.
H
Was just browsing through Marchaj……which I hadn’t even opened for years.
Interesting to read the section on Finn masts. Stiffer was the trend then, reverting from a temporary fashion for soft masts. But that was only the 1970s and things have probably changed twice in the interim.
The biggest eye opener was his recipe for going fast on a run. Not enough to have the main set so that “unstable is fast”. Actual rolling is the recipe for fast. Scary rolling.
H
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