Jib leech twist – BayRaider

[Alf Lande]

When going to windward I get the impression that the aft jib leech is too tight – hence the airflow over the lower part of the main sail is restricted causing turbulence over the mainsail.

I removed the sheeting from the jib club-boom, and attached the sheets directly to sail clew. This gave the jib more twist, and the drive from the jib improved significantly.

So my conclusion so far is that by sheeting the jib directly to the sail clew a more effective sailtrim is obtained when going to windward.

The down side is that the jib self-sheeting as well as the advantage of excellent jib control going downwind is jeopardised.

The cause of the stretched aft leech is that the tension from the forestay is counterbalanced by the jib aft leech tension.

Suggested improvement:
I am considering “fixing” the club-boom to the foredeck a bit forward of the mast foot. A peace of teak will be attached to the foredeck, and the clubroom to be tied down by ropes to this teak clamp.
When going to windward I will sheet the jib directly (fixing the club-boom sit in mid-ship position). When going downwind I intend to release the club-boom (un-tie the ropes), and pull tight the foot tension line which is attaching the boom and the jib clew. (The clubboom foot tension line should always be attached to the jib clew).

The loss of the self-tacking does not worry me much as the sheeting is so easily done on the BayRaider, and most often adjustments will have to be done after tacking anyway due to change in wind, boat heading etc.

I am interested in other sailer’s experiences wrt jib twist and possible solutions.
Any ideas, suggestions and comments are welcome.

Alf Lande
Stavanger
Norway

[Edwin Davies 2]

I have been thinking about this aspect of the self tacking jib setup. Not having a boat to experiment on. BR 17 on order. I noticed in a photograph of the BR in strong winds the jib seems to have too much twist. I hesitate to say it but on model racing yachts our self tacking boom is connected to the jib head fitting by a thin cord. This enables the luff tension to be set with no regard to leech tension as the twist in the sail is controlled by this leech line. I have no idea as to the practicality of this on a full size rig. I will be experimenting when I get a boat. It would be an ideal use for dyneema.

It may mean moving the attachment point of the jib boom to deck further aft to give more leverage.

[Craic]

When going to windward I get the impression that the aft jib leech is too tight – hence the airflow over the lower part of the main sail is restricted causing turbulence over the mainsail. ...

Alf,
cannot say I noticed myself. Interesting. If it is so as you say, and if one wanted to retain the self-tacking, one could change the balance of the clubboom. One could fit a strip of hardwood reaching out a bit further over the bow and bring the swivel point of the clubboom forward. Which would reduce the lever force on the aft leech from the luff tension. You could use the winch eye on the bow to absorb the tension on the overhanging wooden bit. Sort of a little bowsprit with a waterstay.
OR, you could shorten the foot of the jib.

Good luck with experimenting, sounds fun.

[Guy Rossey]

[quote Edwin Davies 2 link
" I noticed in a photograph of the BR in strong winds the jib seems to have too much twist. I hesitate to say it but on model racing yachts our self tacking boom is connected to the jib head fitting by a thin cord. This enables the luff tension to be set with no regard to leech tension as the twist in the sail is controlled by this leech line."

I also considered a few options to allow the jib to breathe in light air until I was given the advice (by Wolfgang Friedl) to simply install an additional hall-yard to lift the jib club-boom. Installed and tried yesterday in F2-3 wind. It works well, no problem when tacking. Maybe the leech is still too much windward, but the jib has definitely a nicer shape in light air.


 

[Graham W]

Sounds like yet another use for the spinnaker halyard.

[Peter Cockerton]

[quote Edwin Davies 2 link
" I noticed in a photograph of the BR in strong winds the jib seems to have too much twist. I hesitate to say it but on model racing yachts our self tacking boom is connected to the jib head fitting by a thin cord. This enables the luff tension to be set with no regard to leech tension as the twist in the sail is controlled by this leech line."

I also considered a few options to allow the jib to breathe in light air until I was given the advice (by Wolfgang Friedl) to simply install an additional hall-yard to lift the jib club-boom. Installed and tried yesterday in F2-3 wind. It works well, no problem when tacking. Maybe the leech is still too much windward, but the jib has definitely a nicer shape in light air.

Guy

I can't get a nice shape in my jib either under the conditions you describe, whilst out on Rutland the other day in very light winds it was was very difficult to get the jib to fill with it's flat shape. I eventually changed the sheeting arrangement to control the sail with sheets on the clew and managed to get some drive from the jib.

The half yard solution i will try with the spinnaker halyard but it will need lengthening and shortening will it not depending on the point of sail as the boom arcs or it will lift the leech.

Is the idea of a rail attached to the foredeck for the boom to arc across a practical one, this would seperate the luff and leach tension association and subsequent sail shape issues raised. How to make it both practical and not ugly though i guess will be a problem. Just a thought.

Peter

[Guy Rossey]

Hi Peter,
whereas on a previous boom I had observed  some lateral bending in heavier winds, with its design and with the actual (thicker) boom I didn't observe any vertical arc nor leech being lifted. Also, the setup is used in light winds primarily. I tried it twice so far. The halyard goes through a triple block at the top of the mast. I will continue testing the setup having your comments in mind.
Good luck!
Guy

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Catchando Bay (BR 48)

[Peter Cockerton]

Guy

In light winds at Rutland the other day i did try using the spi halyard to support the end of the club boom which then allowed the jib leech to be freed. The sail then provided more power this way. Unfortunately though when beating to windward the arrangement had to be reversed to flatten the sail sufficiently to point as high as it did before. The vertical arc i was referring to was not due to club boom bending it was due the length of the spi halyard being shorter as the club boom moved away from the mid position following the sail and as such lifting the club boom. However i did not find this a problem in practice when i tried it the other day.

I will use the spi halyard in this way again when the conditions are right as the pull from the filled jib increases the boat speed i found by a upto a knot.

Peter

_________________
Catchando Bay (BR 48)
[/quote]

[Graham W]

I have now tried lifting the end of the jib boom with the spinnaker halyard and can report that, like the others, I was able to achieve much better control of the shape of the jib.  The only downside that I noticed was that when tacking in very light winds, the jib was a bit reluctant to move over fully.  Otherwise, another excellent (and cheap!) innovation. Well done Edwin Davies 2 for the original suggestion.

[Guy Rossey]

Peter,
Sorry for replying only today! I thought, as you, that the hallyard would not allow the clubboom to move easily but this didn't prove right, probably because of the length of the hallyard.

Edwin,
On which kind of model boats do you have this setup? Would you possibly have a picture ?

__________________
Catchando Bay (BR48)

[Edwin Davies 2]

I have put a short video on youtube showing the setup. We have a light line about 33% up the leach to restrict the line, without this it can catch on the spreaders when ballooning in a gust.

http://www.youtube.com/watch?v=LV4Wp23h7VU&feature=plcp

Ed

[Anthony Huggett]

I've been following this with interest since I noticed the same twist problem when test sailing Matt's BR17 in a very light breeze (nearly 2 years ago now).

It seems that this fix will also solve the loss of rig tension issue when the genoa is furled, keeping the club boom off the deck.

The only question in my mind is whether it is more convenient to have the leech relief line adjusted with a cleat on the club boom or use an extra sheave and cleat on the mast. Not having finished my build I'm in no position to test it out.

Also, a line from the masthead will cause the boom to lift as the sheet is eased, and may prevent the club boom from easing (due to gravity). Sheeting from nearer the top swivel on the forestay might help. It would have to be above the swivel to keep the boom up when the sail is furled. But does it then get caught in the swivel?

Opinions please?

[Jonathan Stuart]

I have tried this on my BRe, not because of leech twist but to stop the jib boom falling wherever it happens to be when the jib is furled. On a BR that probably isn't an issue, but on a BRe it can mean that the jib boom drops to, say, the side decks unless the crew is careful and it isn't ideal for my crew to have to control the jib boom when, say, we are dropping sails to anchor. If the jib boom does drop to the side deck then that causes a big drop in forestay tension and you sit at anchor with a mast pivoting in its tabernacle.

I used 6mm line and tied it to the D shackle where the jib halyard attaches to the jib. The other end goes through a clamcleat with roller (CL236 - Roller Fairlead Mk1 Racing Junior) at the aft end of the jib boom, which was conventiently left from the old furling setup when I switched to the new furling setup (http://www.swallowyachtsassociation.org/?page_id=319). The line is kept close and parallel to the jib leech, which I think will mean it doesn't affect the geometry of the jib boom's swing, which could affect jib performance.

So far it has worked faultlessly. The jib boom remained raised and forestay tension constant when the jib was furled, and in use the jib moves as before. As a bonus, the tail of the line can be used to hold the jib boom to one side when the jib is furled, keeping the jib boom clear of the forward cabin hatch, etc.