Main Inverting

Peter Ruggiero · September 26, 2010, 10:33:09 AM

Has anyone experiences issues where the top of the main was inverting on them?

We were racing last Friday and had an issue where the top of the main was inverting on port tack but not on starboard. Since it was happening only on one tack and the jib cars were the same position I am thinking it may be a rigging issue. Uppers were set at 37 on the gauge, lowers were well slacked. True wind was ~17 knts.

Brian Bennet here, http://www.youtube.com/watch?v=_zJ0TH9UL9k says that too little lower shroud tension could cause overbend and cause the main to invert. I thought this may be the problem but when I watched some videos with Paul Young, he seemed to not care about the lowers at all.

Perhaps if the main sheet bridle was offset to one side then the main would be out on one tack more than the other which would cause it to get more backwind from the jib?

It seemed to be inverting just at the top two battens and not the rest of the main.

Any Suggestions?

Thanks,
Pete

Jay Harrell · September 27, 2010, 08:36:58 AM

What kind of sail is it, and how old is it? Were you seeing inversion with the main sheet full "on", or only when you eased out some?

I've seen the top of my main invert when dumping the main in big puffs, but never when sheeted in hard. And I don't think the lowers are going to cause the top two battens to invert - the bend they control is much lower down.

And as you've noticed, Brian and Paul have very different views on the lower shrouds. Thing is, they are probably both right. And it depends on your sail cut.

Peter Ruggiero · September 27, 2010, 09:40:58 AM

Jay,

They are Hyde sails (2008), we were at the stage of vang sheeting so the main was off centerline, but that was true for both tacks.

A little off topic, with your main bridle setup are you able to sheet the main on centerline?

Yes they seem to have very different views on that. I see Brian's point about the over bending may cause the main to invert but it doesn't seem Paul has any issues since he sometimes sails without the lowers.

Justin Scott · September 27, 2010, 03:05:36 PM

As usual, as the class gets more experience with the carbon mast views have met somewhere in the middle. Brian wrote a very good tuning guide late in 2009 where he advocates looser lowers.

I was at CORK in August and Brian suggested loosening my lowers (I had tightened them when launching the boat, because the keel was suspended from my main halyard and I often put 4 turns on the lowers to keep the mast in column. Forgot to take them off). I loosened them and the boat sprang to life in the gusty conditions and I started going forward very nicely. But I dont go as loose as Paul Young. Paul likes his mast to be very dynamic like the aussie 5-0-5 sailors. With

I'm am not sure what you are noticing that the main is inverting. The 2008 Hyde sails are cut very deep and it is very difficult to invert the main. I suffered inversion on an experimental sail from Quantum once. The sail goes flat as a board, no power and the leech falls off. Its distinctly weird and slow. Ive never managed to invert the early Hydes.

If you are seeing the Hyde main bubble and stall at the front, this can be caused by jib backwinding the main or too much depth. I used 2007/8 Hydes in the 2008 NAs very effectively. I used a fair bit of of prebend but the key was to use the mainsheet on hard to get a tight leech.

Do not oversheet the jib in any sail combination. Viper is slow if you pinch.

Since then, Hyde have slightly reduced the depth of their mainsail.

I strongly recommend to all Viper owners that you make the shift to split end main sheeting. (Mark McNamara from Dinghy Locker can get you set up, so can Juan Mauri from Mauri Pro Sailing + you're supporting Viper owners). The split end mainsheeting does away with having to alter the length of your bridle for different wind conditions and trying to precisley center the bridle. You can split end to the center or aft. It is much easier and faster.

Peter Ruggiero · September 27, 2010, 03:13:06 PM

Justin,

Thanks for the good info.

I know what you mean when you say the main bubble stall at the front, this seems to be common during high wind beats where the main may not be centerlined on the boat.

This was definitely not like that, the main was inverting and like I had mentioned early, it seemed to be only on one tack. I think we are going to check the rig make sure it is symmetrical and try and get it close to the tuning guide #'s. If it happens again maybe I can sight up the mast to see if it is doing anything weird.

For the lowers I keep reading stuff like "I can touch the uppers 3' above the turnbuckles". Is this usually just by taking the slack out of the lowers you able to have them touch the uppers this high up or does one have to pull hard on the lowers to achieve this?

Thanks again,
Pete

Tac Boston · September 28, 2010, 09:25:07 AM

I bet you did not have enough vang on. Vang is your friend, I know that when it is really windy, on Jackpot, both Brad and Eric put together to get enough vang.

that is what it sounds like to me. you actually did not have enough mast bend to suck the luff curve out of the main.
Tac

Peter Ruggiero · September 28, 2010, 09:28:32 AM

Tac,

Could be right, but we did pull what I felt was a lot of vang on although we didn't have two people trying at the same time. Do you find that you need two people pulling with the main luffing to get it right? Although I don't know how that would explain it happening on one tack and not he other. We are going to take it out on Friday and Saturday so I will report back.

For 18-20 TWS do you guys find that you have more than 37 on the gauge for the uppers?

Out boat speed was pretty good (I think and comparing with Norths "polars") as we were holding 6.0-6.2 knts pretty consistantly.

Drew Harper · September 28, 2010, 12:15:00 PM

Quote from: Peter Ruggiero on September 28, 2010, 09:28:32 AM
Tac,

Could be right, but we did pull what I felt was a lot of vang on although we didn't have two people trying at the same time. Do you find that you need two people pulling with the main luffing to get it right? Although I don't know how that would explain it happening on one tack and not he other. We are going to take it out on Friday and Saturday so I will report back.

For 18-20 TWS do you guys find that you have more than 37 on the gauge for the uppers?

Out boat speed was pretty good (I think and comparing with Norths "polars") as we were holding 6.0-6.2 knts pretty consistantly.

The Gen II Hydes had lots of luff curve and were damn near impossible to invert. The Gen III's are considerably flatter and can invert with more than the normal 4.5" of prebend.

Garett and I will be making a 'bend' gauge that will give you a real measurement of mast bend. This is all working towards an updated tuning guide. I think each of the sailmakers should put one out there and it'd be great to incorporate some polars as part of their guide.

Here's North Sails Viper Tuning Guide...for review.

Peter Ruggiero · September 28, 2010, 12:21:04 PM

Drew,

Thanks for the info, what is the easiest way to found out what gen of hyde sails we may have. The boat is #76 if that helps. I could see if the port upper shroud was tighter than the starboard one then maybe it was trying to flatten out the sail too much.

The 4.5" prebend is measured at the spreaders correct? I was thinking it may be useful to put a mark on the spreaders that is 4.5" back from the mast (not 4.5" along the spreader) this way you could use the main halyard and see where you are relative to the marks on the spreaders.

Drew Harper · September 28, 2010, 04:18:57 PM

If they are original, then they're Gen 1. Just shy of 7 inches of luff curve.

Prebend is just so damn subjective...that's why we're making the gauge. It'll become a real number/look.

Yes, measure at the spreaders. Do remember that blocking at the partners changes where the bend happens though.

Peter Ruggiero · September 28, 2010, 04:22:19 PM

Man 7" of luff curve, that would help to explain the feeling of being over powered in those conditions.

Drew Harper · September 28, 2010, 04:34:12 PM

I sailed Gen II main a LOT in SF Bay. 7 1/4" luff. 50+ days in over 25. I just wind on turns and it's all good.

Pretty common for me to carry 6" of prebend to counter the occasional 30 knot puff and the 4' square chop we get here on ebb days.

Peter Ruggiero · September 28, 2010, 04:46:21 PM

Sounds like the mast can take some serious pre bend, when you were running that high of pre bend how loose did you have the lowers?

Robert Bernard · September 29, 2010, 08:22:25 AM

Pete, I am thinking we may have had the uppers to tight and uneven, coupled with the jib cars too far forward.

Peter Ruggiero · September 29, 2010, 11:02:52 AM

Yeah I think something in the rigging (probably the uppers) were uneven, even though I did check them with the gauge.

I am curious as to what sails the Bennet tuning guide was made for if even the different generations of Hyde sails vary that much.

If they are Gen I sails with a lot of luff curve then it may of been an issue of having the main too full.