main backwinding - masthead rig

[capnsensible]

Loadsa good advice. However, I am totally with Twister Ken here, how much of it is valid for 160% genoa???

Dont see that sort of sail much these days, yet on my 1977 Moody, it is normal! I reckon a bit of backwinding of the main is acceptable.

During a stint ashore in the early 80's, I was lucky to be invited to crew a half tonner for a couple of Cowes weeks. It was a fantastic experience and I was taught a bit about sail trim, with that big overlap. Would have been even better if we had won something!

To drift a tad, the yacht had one of those petrol engines that when put astern, stopped and then restarted in reverse, no gearbox. As this was always accompanied, either way, by a very noisy backfire, it made entry into Portsmouth, with the Warships nearby, rather interesting. A sure way to get a Mod Plod escort.

 

[ShaunG]

Neil Y - Thanks for that picture, it is almost an exact replica of the how my main looks.

Maybe....just Maybe....i might be a little better at sail trim than i thought.....i can live in hope.

Thank you for all of your advice, i will be playing with all of it next week, although i am now not quite so concerned about the bubble, i quite like the name speed bubble i can tell SWMBO that it makes us go fast and means i have got the sail trim right for once

 

[KREW2]

Just been looking at this old thread because I wanted to search about back winding.
Today we had a race to Lulworth Cove and back.
On the return journey the wind freshened to 20/24 apparent, and the sea got up, so a reef in the main and 3/4 of a 135% genoa out. There was a bit of tide against but, I was struggling to get bloody 5 knots SOG, a problem that has been with me all season. The boat is a Westerly Storm the mainsail is new this season, with my old tired main I would still have expected to get about 7 knots. I don't think it's the cut of the sail, maybe I had too much genny out, or maybe I needed to "open the slot" by bringing the genoa cars back. In the 2 hours it took us to sail back I got fed up, retired and motor-sailed back to Portland. What the hell is wrong
I was hoping to go on the Scuttlebutt cruise to Cherboug but with this type of performance I will give it a miss

 

[Lakesailor]

How about getting a pack of wool tell tales and sticking them 1/3rd and 2/3rds way back on the main at different levels?
Get out in a steady breeze with a few crew and try moving things about until you get them all flying.

 

[KREW2]

How about getting a pack of wool tell tales and sticking them 1/3rd and 2/3rds way back on the main at different levels?
Get out in a steady breeze with a few crew and try moving things about until you get them all flying.

Yesterdays race was a family day, unfortunately both my wife and son were poorly, my daughter, while willing and handy cannot sail, but doesn't get seasick. There was little enthusiasm for fine tuning, even so, sailing single handed I have had better speeds.
I am racing again tonight, with usual crew, the wind looks as if it is going to be fresh, 25 kn gusts. As you mentioned, I will use it to experiment with different sail configurations, and car positions. I may even put the old main on out of desperation.

 

[jamesjermain]

Don't bust a gut trying to achieve the impossible. In the higher wind strengths you are talking about the main will back wind to an extent and its a good thing too. It's reducing its drive and tendency to give weather helm. A 160 genoa will be doing almost all the work so loosing a bit from the main wont make much difference. Sail to the genoa telltales and point as high as the genoa allows, ignoring the main. This is the way we all used to sail forty years ago.

 

[KREW2]

Don't bust a gut trying to achieve the impossible. In the higher wind strengths you are talking about the main will back wind to an extent and its a good thing too. It's reducing its drive and tendency to give weather helm. A 160 genoa will be doing almost all the work so loosing a bit from the main wont make much difference. Sail to the genoa telltales and point as high as the genoa allows, ignoring the main. This is the way we all used to sail forty years ago.

I must be doing something different to what I used to, maybe 2 reefs, in the rather large main and more genoa out could be the answer, The boat is capable of reaching 7 knts upwind. All I know for sure I am not getting the speed I used to in strong winds. It's frustrating not to be able to keep up with 22 footers.

 

[BobPrell]

Just been looking at this old thread because I wanted to search about back winding.
I was hoping to go on the Scuttlebutt cruise to Cherboug but with this type of performance I will give it a miss

I hope all this advice has been some help, though I notice you have not actually said you have back-winding. A number of answers have pointed out that it may be normal. I will add that when I watched the America's Cup back in 1983 I noticed that the boats sailed all the time with very obvious bubbles at the luff of the main. When I read John Bertrand's book a few years later he said that was the standard procedure to trim sails - adjust the genoa so it was right, and adjust the main so it balanced the rig for a slight weather-helm. If that meant a bubble in the main then so be it. This agrees with most of the posts from the year '10 and now.

If I may add something you may consider off-topic - it is to lighten up and sail a bit looser, when you are off to Cherbourg. It's a cruise Man!

Your family may well enjoy sailing with you a lot more if you are not chasing Vmax all the time.

 

[Sybarite]

Don't bust a gut trying to achieve the impossible. In the higher wind strengths you are talking about the main will back wind to an extent and its a good thing too. It's reducing its drive and tendency to give weather helm. A 160 genoa will be doing almost all the work so loosing a bit from the main wont make much difference. Sail to the genoa telltales and point as high as the genoa allows, ignoring the main. This is the way we all used to sail forty years ago.

Does hauling the mainsheet traveller to weather adversely affect the performance? I know that on mine it kills the flutter. I don't notice any fall-off but then I am strictly cruising rather than racing.

 

[KREW2]

Thanks for the replies.
Well firstly yes it was backwinding, quite frankly it can wind where it wants, I don't care I just want to be able to go to upwind at a speed suitable for the boat
With regards to Cherbourg, if the wind goes round to the NW I don't fancy beating at 5 knots for 16/18 hours.
Hauling the traveller up to wind makes us heel more not really noticeable speed loss though. I could get her up to 6knots but I had to come off to 65/70 degrees to the wind.

 

[[23929]]

I would say a limied amount of backwinded main (in the lower sections) is normal for a well set up boat trimmed for sailing upwind. A bit of searching to find a suitable picture came up with the wb-sails ltd who have an excellent site with graphic and picture explanations of sail trim.

Ah, nice graphic showing why the luff of the main will back-wind and ruin the performance.

The cut of the jib is wrong. The camber should remain the same or decrease slightly as it is measured from bottom to top. In the graphic, the mid point camber (16%) is greater than the bottom (13%) and the top (15%) is greater than the bottom (13%).

This jib should have been cut with the mid and top cambers at 12% and 11% respectively and the mainsail back-winding will disappear when the jib is sheeted correctly.

The mistake in the graphic is that the jib is shown with a straight luff which is impossible to achieve. It will always have a sag. The sag is greatest in the middle of the luff an causes a very large increase in the camber of the upper jib sections because the sag is applied to a shorter cord. This increase in camber towards the top of the jib is what is meant by the leach "hooking".

The sail maker MUST cut a corresponding hollow in the jib luff to accommodate the inevitable luff sag and this hollow must be enough to ensure the jib camber is equal or slightly reducing towards the head of the jib.

When sailing, with the your desired jib luff tension, just photo you jib from the deck upwards, print the photo and draw on it the camber, depth and cord lines. You can then pretty much work out how much jib luff hollow is required to correct the camber at all points. Then ask a sail maker to re-cut the jib.

Old jibs often stretch into weird shapes and can be given a new lease of life by re-cutting the luff hollow. And many brand new jibs are made incorrectly and will also need re-cutting.

Anyway, here is the graphic again with my somewhat exaggerated edits showing the what really happens when sailing. Big jib luff sag with corresponding horrible jib camber leading to horrible main sail luff back-winding

Edit: It is not only overlapping jibs but also blade jibs with no overlap that will cause back-winding of the main if they are cut with an increasing camber.

 

[KREW2]

It has been said that in order to cut down on the main backwinding, have the genoa car further back so as to open the slot on the leach of the sail. By my reckoning this would produce the opposite effect as to what you want to eliminate.
Anyway it's blowing nicely and stopped raining so just of to try a few things out.
I will report back.

 

[[23929]]

It has been said that in order to cut down on the main backwinding, have the genoa car further back so as to open the slot on the leach of the sail.

This will work but you will progressively loose drive from the upper parts of the jib which you need in light to medium winds, hence, losing performance. In increasingly strong winds, moving the cars aft will simply rag off the upper jib leach and sometimes you need to do this to reduce heeling but maintain drive in the lower part of the jib .

What I tried to explain in my post with the graphic was the optimum jib set up for max drive when conditions are not over-powering. And this is the starting point. Get this right and all other jib trimming in lighter or higher winds is straight forward.

Incorrectly cut jibs are very common and made worse by slack forestay tension.

With regard to the Americas Cup yachts showing back-winding of the mainsail ; these have special problems due to their relative, very narrow beam ( and jib sheeting angle). Also, the massive forestay length on their huge rigs was a nightmare to maintain tensioned to an acceptable level without destroying the boats. Average cruising yachts are relatively much wider and shouldn't suffer mainsail back-winding.

 

[KREW2]

Sailing in light airs does not seem so much of a problem, it's when true wind starts to exceed 15knots that pointing and speed become an issue.
Anyway I was going out tonight to try a few things, I thought
The pontoons leading out to our ferry were being jostled about by a good southerly breeze, as I stepped down into the ferry I lost my footing fell cracked my head and ended up in the minor injuries unit with mild concussion.
I'll try again tomorrow.

 

[Dipper]

Sailing in light airs does not seem so much of a problem, it's when true wind starts to exceed 15knots that pointing and speed become an issue.
Anyway I was going out tonight to try a few things, I thought
The pontoons leading out to our ferry were being jostled about by a good southerly breeze, as I stepped down into the ferry I lost my footing fell cracked my head and ended up in the minor injuries unit with mild concussion.
I'll try again tomorrow.

That's bad luck. I hope you feel OK.

 

[Dipper]

I will add that when I watched the America's Cup back in 1983 I noticed that the boats sailed all the time with very obvious bubbles at the luff of the main.

Some years ago (I can't remember when) they televised Lymington Cup match racing and had on board cameras. I was quite surprised to see those boats backwinding the main near the luff when close hauled.

My boat does it but after seeing that I stopped worrying. It didn't stop me winning races.

 

[spearhead]

3 thoughts

The backstay tensioner is vital when the wind gets up - it straightens the forestay (and if you're cruising helps the luff foil to rotate as you reef) and puts a bit of curve into the mast to flatten the main at the same time. Just don't overdo it (the lifelines may start to go slack) and remember to ease it correspondingly when you turn downwind and/or in the marina.

Secondly, at this time of year check under the hull for slime growth - that could easily account for the 2 knots you have lost!

Finally, it pays enormous dividends if you can find a friend with a similar boat to practise with. Take it in turns to sail 2 tacks to windward in formation, one boat playing with the strings while the other just concentrates on helming, then vice versa.

 

[wotayottie]

Robertj

"the first 20% should back wind "

Ummm, a backwinded main indicates the flow is not linear, and is therefore not generating power.

If the backwinding cannot be adjusted out by the existing control systems, then the sail is badly cut.

Or you are oversheeting the genoa and closing the slot.

 

[KREW2]

Or you are oversheeting the genoa and closing the slot.

The slot that's it.
Yesterday Dipper of this parish, and I went out for a three hour test run.
In 15knts of true wind, one reef in the main, about 3/4 of the genoa out, and the genoa cars pulled back things were much better, achieving 6 kts sog close hauled.
Letting out a bit more genoa gradually was giving better results 6.6/8knts after experimenting with car positions over a few short beats.
We decided to do one more run across Portland Harbour with 2 reefs in the main, most of the genoa out and cars moved forward, this was good, but gave a little too much weather helm. So we pulled the cars back, it's that slot thing again, let the main traveller down to leeward, picked up to 6.9 and briefly hit 7knts.
I believe there is still room for improvement, so I am going to continue playing.

 

[Champagne Murphy]

A quick question, please forgive me if its already been answered earlier; does this problem persist with a fully battened main?