Rigg A Bad design??

Discuss the IOM class rules and interpretations

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sven.gester
Posts: 2
Joined: 12 Jan 2010, 22:20
Sail number: SWE 104
Club: GRSS
Design: Duzt

Rigg A Bad design??

Post by sven.gester » 08 Oct 2010, 17:45

It took years before I understood how you have to prebend the A rig mast to to prevent the jib boom lift in the gusts of uncontrolled luff as a result and whit entangled lift as result. How can we defend that booms is forbidden to be pre-bended when the mast may bend as much as you want? Is it reasonable?
It is easy to see the sailors that doesn't understand the need of prebending the mast. They use a loop to avoid the lift gets stuck in the spreaders. That loop is not necessary if you have enough forestay tension. Or if you use a flat Bantock wire that dosn't get stucked in the spreader. But the uncontroled luffs will still be there.

Is it time to move to a new type of A rig? Where forestay is attached higher up and the mast is not allowed to be prebent when unloaded. Why not allow a carbon fiber tubes in such a rig. They are cheap today and can't be prebended. Sailmakers are then forced to design sails that works without tricking the mast.
Or, make lower shroud legal, as an option. With lower shrouds, you can easily control mast curve and increase forestay tension. Yes I know, the shroud also makes the boat more expensive. But if shrouds is an option, you can choose yourself.

Now I have bought an expensive prebended mast and hope that it stays prebended.
But how do I know that matrialet in this mast meets the class rule's specification for allowable alloys?

Patrick Parisienne
Posts: 10
Joined: 01 Sep 2010, 09:04
Sail number: AUS 38
Club: Albert Park Model Yacht Club
Design: Obsession

Re: Rigg A Bad design??

Post by Patrick Parisienne » 10 Oct 2010, 11:15

I don't think there is any problem with the masts at present. Aluminium masts are very cheap, and prebend is something easily done at home. As well as sailing, I believe rig construction and setting is also part of the sport. For your information, most people also prebend the B & C rig. As for legality of various alloys, all suitable grades are legal as far as i know. Finally, the prebend should remain in the mast permanently. You can easily adjust your prebend by hand.

Regards,
Pat

sven.gester
Posts: 2
Joined: 12 Jan 2010, 22:20
Sail number: SWE 104
Club: GRSS
Design: Duzt

Re: Rigg A Bad design??

Post by sven.gester » 10 Oct 2010, 17:45

The only reason that class rule allows prebending of mast is that the design is very poor. And if we didn't allow it the boat shoul sail very bad i upper A vind register. If you think this is no problem, then you forget how we handle new sailors in IOM class. Who is telling them to prebend? Where on the web do you find a good instruction, decribing how much prebend and how prebend curve shoud look like to fit sail when mast is in tension? The sailmaker do not provide you with that information as far I know.
We risk losing new sailors before they understood the importance of prebend.
Either we sit still and watch while the class is shrinking, or we take care of the problem.
Meny sailors that lern how to prebend doun't tell there competitors in the local club. They will awake some day standing alone on the saling area. And be very sad over there bad investment in a expensive toy and no friends.

If you want a fast boat in both light air and strong rigg A wind. You probably need two A rigs (or more). One with heavy prebend for upper wind and one with less prebend for light. I now, you are not allowed to have more then one rigg off each during a regatta. But you can chose one off many before regatta starts. Her in Sweden wind conditions changes pritty slow. So having several rigs should work fine here.

Allowing lower shrouds (as option, of course) to controle mast curve is, in my opinion, the best and cheapest way so minimize the problem. The cost for this is about 12 euro. And if you think its to complicated, doun't use them. Continue to prebend mast.

Lester
Posts: 611
Joined: 14 Oct 2004, 22:29
Location: GBR 105
Contact:

Re: Rigg A Bad design??

Post by Lester » 11 Oct 2010, 10:14

Hi Sven

I have some sympathy with you finding out how your fellow sailors keep their little secrets to themselves. That's why I started my Web site (smile). I mention mast pre-bend here:

http://onemetre.net/Build/Makemast/Makemast.htm

I think the IOM rig is an excellent design, and not the bad one you say it is. Of course, our mileages differ... Technically known as a fractional rig, it is a challenge and requires subtlety, skill, and thoughtful experience to tune well. In this age of dumbing-down, I find it very welcome!
Lester Gilbert
http://www.onemetre.net/

Patrick Parisienne
Posts: 10
Joined: 01 Sep 2010, 09:04
Sail number: AUS 38
Club: Albert Park Model Yacht Club
Design: Obsession

Re: Rigg A Bad design??

Post by Patrick Parisienne » 12 Oct 2010, 00:54

Hi Sven,

I also find it sad that people don't share their information. :( We believe that if EVERYONE is fast, then we all become better racers. :D I have also found that the best sailors are always the most helpful with advice. That's why I always as them the questions I have (Craig Smith, Paul Jones & Brad Gibson).

As well as Lester's fantastic site, you should visit Craig Smith's site. Just type TS-2 Homepage into Google, and you should see it as a link at the bottom of the page. This is a very detailed rig building guide, and gives clear advice on prebending masts. I have found the need for more prebend than what this guide suggests, with about 20mm for 10.8mm masts, and 25mm for 11.1mm Groovy masts. My advice is always to start with a small amount, and increase it if needed afterwards if requied....

I have found that if you ask most sailmakers, they will advise you on the amount of prebend required.

As for lower shrouds, the rules do allow for checkstays down low. However, I think the mast ram/strut, that nearly every IOM has, is very effective. I find adjusting this very quick and simple, and makes changing rigs in a short time easier.

We have also found (in Australia) there is no need for 2 different A rigs. With adjustment of sidestay tension, backstay, and mast ram, we can soften the rig enough to be good in light weather, even with prebended masts.

Feel free to ask for advice on this forum. I think you wil find many people willing to help you.

Regards,

Pat

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