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Old Mar 01, 2011, 05:49 AM
Don't lie to my dog.
Gregg28's Avatar
United States, DE, Wilmington
Joined Jun 2005
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Thanks Mike.

Quote:
Originally Posted by iomthinkin View Post
Ted, why do you need to prebend your mast? I`m assuming you are building your new boat!! If your sails are not yet made I`d suggest that you advise your sail maker that you intend to run a straight/ non prebent mast, IE that he (sail maker) incorporates a luff curve into the build. This down the line makes things a little more simple...."my theory".

I`d be interested in knowing more on the mast weight & its ability of memory (or lack thereof)

Mike, this is also directed at you, as you already have the section.

As I understand it, the pre-bend is forward, not back. It allows for more tension on the backstay and therefor the forstay without putting a lot of curvature in the main luff and flattening it out. Ideally, the prebend would give you a tight forestay and a straight mast.
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Old Mar 01, 2011, 07:40 AM
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Singapore
Joined Nov 2004
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Gregg,
The mast , after pre-bend, should adapt the luff curve of the sail and is not usually straight when you tension the backstay. Having a straight mast would usually induce a lot of "shape" in the sail which may not be suitable in most conditions as the wind may detach from the leeward side of the main. This is especially so at the top of the sail.

http://www.rcgroups.com/forums/attac...mentid=3017967
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Old Mar 01, 2011, 07:49 AM
Don't lie to my dog.
Gregg28's Avatar
United States, DE, Wilmington
Joined Jun 2005
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Quote:
Originally Posted by scully View Post
Gregg,
The mast , after pre-bend, should adapt the luff curve of the sail and is not usually straight when you tension the backstay. Having a straight mast would usually induce a lot of "shape" in the sail which may not be suitable in most conditions as the wind may detach from the leeward side of the main. This is especially so at the top of the sail.

http://www.rcgroups.com/forums/attac...mentid=3017967
Well, yes on a"normally" cut sail. If the sail luff is cut for a straight mast, then its shape would be best on a straight mast. My reference to "putting a lot of curvature" was referring to overbend.
However, I have not seen an adequate explanation of prebend lately and it is different than the normal use of "prebend, particullarly in full size boats. Since masts are not infinitely stiff and IOMs are fractionally rigged, in order to get the forestay tension you want you must tension the backstay. The forstay attachment acts as a fulcrum so the top of the mast bends to maintain the tension. The prebend is a way to increase the forestay tension and decrease the bend by "preloading" the mast.

The prebend is forward bend to give additional force to the forestay.
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Last edited by Gregg28; Mar 01, 2011 at 03:58 PM. Reason: Left out the key idea that "prebend" is referring to forward bend.
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Old Mar 01, 2011, 02:58 PM
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Australia (Sydney)
Joined Apr 2010
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AH HA, a can of worms, eh!!

I agree with Greg, quote" I have not seen an adequate explanation of pre bend "unquote. Provided the sail luff has been cut appropriately.

Fore stay tension is set by an opposing force, that being the force applied by back stay tension. (& to some degree shroud tension if mounted aft of the mast)

Sail shape is adjusted by many means, shrouds, fore stay, back stay, vang, outhaul, etc etc.

To those of you who subscribe to mast pre bend (forward bend) I would like to ask , how many of you when ordering your sails, what instruction did you give to your sail maker? IE: What radius did you instruct him to build into your luff?
I`ll suggest that most do not know, or simply order blind assuming the sail maker knows all and has mind reading abilities!!

Food for thought? or more discussion?
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Old Mar 01, 2011, 03:25 PM
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This is one subject that go on forever. Some people like it some don't, I do.

Before I start my reasoning I want to make sure we all are talking the same language, pre-bend (to me) is forward bend when there is no load on the mast.

I only use enough pre-bend to give me the forestay tension, and therefore jib boom load at the the leech end. I want enough prebend so that I get the jib boom load I want without over-bending the mast with the back stay. Which could cause the top of the sail to invert and be very flat.

I am not a big believer in sails made for pre-bend or not. If I end up with with the mast with slight rearward bend or not really doesn't matter to me as long as I get the shape I am looking for in the top of the sail. So if the sail likes a straight mast I may want more pre-bend so that when the mast in straight I have the proper forestay load.

I usually don't tell my sailmaker anything, I ask him what I should use for pre-bend (or not). He is the one with all the experience.

If you want to discuss load on the leech end of the jib boom that can be an equally long discussion. All I will say for now is that I don't want my jib leech opening by itself because there isn't enough load on it. Remember the forestay and jib topping lift for a triangle and load on one effects the other.



Ted
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Old Mar 01, 2011, 04:03 PM
Don't lie to my dog.
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We have a very bendy (rearward) mast on our J105. Arguments have been made that a lot of bend in the mast gives better aerodynamic shape (reduced tip vortex) provided the sail is cut for it. If there is a difference it is relatively small compared to the thumbs on the box, but the little things do add up.
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Old Mar 01, 2011, 06:02 PM
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USA-Michigan
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Lots of full size boats use a lot of bend in their mast. Part of the reason they go it is to to have a fuller sail once you start sheeting out, same for IOM's. Think about that for a bit.

If the sail is kind of flat for upwind with a lot of rear bend as you let the main out it is now on a perfectly straight mast and gets really full. That is because the main has a lot of luff curve to match the bent mast. I used to sail Lightnings and we bent the heck out of them with blocking at the deck and carefully adjusting the side stays. Those boats had so much rig tension and forward push at the deck (like our ram) the mast would stand with no forestay or backstay. The class eventually had to put a rule in place to limit the amount of sidestay tension. People were destroying their hulls with all the vertical load, pushed the darn mast out the bottom.

We are limited by how creative we can in part because of the rules that requires one set of sidestays.
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Old Mar 02, 2011, 03:43 PM
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Ace project in the Netherlands

Please see http://picasaweb.google.com/10564894...WACEStart2010#
Last two pictures are actually video clips of the maiden trip.
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Last edited by Fasterboats; May 26, 2011 at 02:43 PM. Reason: Ace NED099 participating at the 2011 Worlds.
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Old Mar 04, 2011, 06:52 AM
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Joined Dec 2010
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Can anyone tell me how critical the leading edge angle of a IOM keel is. Mine is about 5 degrees off verticle and I need to know if this is right before I bond my bulb.
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Old Mar 04, 2011, 08:37 AM
I love being the underdog!!!
Romano Ramirez's Avatar
Bermuda
Joined Jan 2011
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IOM Bermuda Fleet march 3 2011

IOM Bermuda Fleet March 3 2011 (4 min 15 sec)
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Old Mar 04, 2011, 08:39 AM
I love being the underdog!!!
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Bermuda
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IOM Bermuda Fleet March 3 2011 #2

IOM Sailing Bermuda Fleet March 3 2011 (4 min 11 sec)
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Old Mar 04, 2011, 09:11 AM
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USA-Michigan
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Quote:
Originally Posted by themightysmiff View Post
Can anyone tell me how critical the leading edge angle of a IOM keel is. Mine is about 5 degrees off verticle and I need to know if this is right before I bond my bulb.
Are you talking side to side or front to back?
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Last edited by Ted Flack; Mar 04, 2011 at 09:21 AM. Reason: Question
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Old Mar 04, 2011, 10:19 AM
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Quote:
Originally Posted by Romano Ramirez View Post
I think we could do without the bad language from the competitors, most unsportsman like and pure bad manners:-

It could be sited as a case for disciplinary action under the following rule in the ISAF Racing Rules of Sailing:-
http://www.sailing.org/tools/documents/RRS2009-2012-[5950].pdf

Action by a National Authority or Initial Action by the ISAF
(a) When a national authority or the ISAF receives a report alleg- ing a gross breach of a rule, good manners or sportsmanship, a
report alleging conduct that has brought the sport into disrepute,
or a report required by rule 69.1(c) or 69.1(e), it may
conduct an investigation and, when appropriate, shall conduct a
hearing. It may then take any disciplinary action within its
jurisdiction it considers appropriate against the competitor or
boat, or other person involved, including suspending eligibility,
permanently or for a specified period of time, to compete in
any event held within its jurisdiction, and suspending ISAF eligibility
under ISAF Regulation 19.

Brian
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Old Mar 04, 2011, 04:35 PM
I love being the underdog!!!
Romano Ramirez's Avatar
Bermuda
Joined Jan 2011
123 Posts
Purpose

Quote:
Originally Posted by Brian Wa View Post
I think we could do without the bad language from the competitors, most unsportsman like and pure bad manners:-

It could be sited as a case for disciplinary action under the following rule in the ISAF Racing Rules of Sailing:-
http://www.sailing.org/tools/documents/RRS2009-2012-[5950].pdf

Action by a National Authority or Initial Action by the ISAF
(a) When a national authority or the ISAF receives a report alleg- ing a gross breach of a rule, good manners or sportsmanship, a
report alleging conduct that has brought the sport into disrepute,
or a report required by rule 69.1(c) or 69.1(e), it may
conduct an investigation and, when appropriate, shall conduct a
hearing. It may then take any disciplinary action within its
jurisdiction it considers appropriate against the competitor or
boat, or other person involved, including suspending eligibility,
permanently or for a specified period of time, to compete in
any event held within its jurisdiction, and suspending ISAF eligibility
under ISAF Regulation 19.

Brian
Thank you for your comment. The purpose of me joining this forum is to share our fleets experiences good or bad. And to gain imput from unbiased comments such as yours,so that our fleet can mature. The language is a big problem as we have spectators, its unsportsmanlike, I don't personally use it at all. The rule is very helpful.
I started sailing with these guys since October and we have yet to sit down and have a sincere meeting about our rules, conduct,whos in charge to establish our club to international standards. I record races out of frustration because of the arguing.. The camera doesn't lie. I debate whether to upload these. BUT if it can trigger a response that I can put on the table when the time comes, then it is in my opinion of good reason. If anybody is offended then I will nolonger post them. I have raced nitro model boats for years and if they can complete over 180 races in 2 days with many different classes without nonsense, then I'm sure a 10 race regatta can do likewise. I thank you ALL so much for your comments. I am sorry if I sound like our guys are a bunch of kuckleheads, but overall I simply think we need a good dose of structure to keep things in order. I'm the new guy.... Just trying to enjoy the competition and aim to compete internationally in the future.
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Old Mar 04, 2011, 11:43 PM
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Dick L.'s Avatar
Minnesota, USA
Joined Aug 2002
2,017 Posts
Good luck with your effort. Some will stay, some will leave - but if you don't set the rules that the majority want to play by, it will just continue and get worse. Whether it's language, touching (hitting ??) marks or other boats, illegal equipment or sail area, knowledge or lack thereof of sailing/racing rules, hardcore club or fun club, there are so many things that need to be considered. Local race rules may be fun, but for anyone wanting to sail nationals or internationals - it will be frustrating. Some will get upset that the rules are too tuff - others will simply leave after having a boat hit theirs (with or without explanation) racing rules clinics are too boring, and on and on. Just pointing out what you and others will see/hear going forward.

My advice - play by the rules, and don't make local rules out of convenience. The good sailors will stay to learn and feel they are racing fairly - the others, well, perhaps best if they do leave.

Good luck.
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