Author Topic: Rig Tension  (Read 188 times)

Gubby_uk

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Rig Tension
« on: May 10, 2021, 08:20:50 AM »
Hi all,
I've finally been able to go to the club and start putting Kairos back together. I've put all the rigging up in the air to try and see what's what. I'm not used to gaff rigs as I've only ever sailed Bermudan types, so please excuse any daft questions.
How tight should the forestay and shrouds be please? I'm guessing not like a bowstring but how mine are quite loose. Before I start winding up the bottle screws is there a rough guide please? Also, any pictures as to how the rig should be set up would be appreciated. Topping lift, reefing etc.
Thank you

VROUW KIRSTEN

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Re: Rig Tension
« Reply #1 on: May 20, 2021, 04:03:33 PM »
Hello Gubby,

I don't know of any specific instructions or measurements for the pretensioning of the forestay or shrouds of my Winklebrig.
If you take into account that the mast is on deck and that excessive pre-tensioning acts on the deck structure via the mast, it quickly becomes clear that high pre-tensioning is not sensible. In addition, it depends on the sail position which shroud supports the mast, the windward side is then tensioned accordingly and the leeward side is relieved. For this reason, too, excessive tensioning of the mast via the shrouds is not necessary.
Several factors play a role in the forestay: Do you tension the forestay via a tack or via a tensioner? What form of furling jib do you use? These factors influence the possible as well as the necessary pre-tensioning. I set the forestay over a block, so I don't get the high pretension that would be possible with careless handling of a tensioner, for example.
In the end, I worked my way towards the "right" pretension. And the gaff rigging is much more forgiving than a Bermuda rig.

Kind regards

Gerold
Life is happy, life is sweet, on a gaff rigged boat of 16 feet!

robin

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Re: Rig Tension
« Reply #2 on: May 22, 2021, 04:38:35 AM »
Hi Gubby-seems we are going through a similar head scratching over the rig.My boat,no 106,is a high peak gaff(not gunter,as some describe)but raises the same questions.Vrouw is right in that it is only the forestay that requires some tension as the gaff mainsail rig itself due to its weight and when filled with wind creates its own tensions,hopefully in the right places.What I am doing is adding an extra pair of shrouds plus an inner forestay using dyneema-belt and braces for the same sailing area as yourself.This in itself raises the question of a mast support which I am working on by adding a forward bulkhead,with a door,so that 'Cockle' will have a chain locker.This will put some weight lower down in the bows to help with stability and waves.One or two other owners(Martin Cartwright)have also added extra ballast under the cabin floor which I intend to do myself but am a bit eager to get afloat and go sailing,perhaps to Ashlett creek which I used to visit regularly(very welcoming sailing club there-money in the honesty box) and since the pub changed hands a nice lunch to be had.Best regards,Robin.
« Last Edit: May 22, 2021, 04:41:54 AM by robin »

JOD

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Re: Rig Tension
« Reply #3 on: June 06, 2021, 09:43:09 PM »
The beauty of the WB is that it is of the size of a dinghy with a low stressed traditional rig. It is best to keep it simple. The trad lacing for the shroud attachment is more forgiving (safer) than bottle screws.
Tighten each shroud as equally and tightly as you can by hand then tack, progressively taking in the slack on the lee side. Repeat on the other tack.
A single block on the forestay provides sufficient tension.
The WB is not a Merlin Rocket or RS400. Don't spend ages on rig tension and don't overstress it.
« Last Edit: June 06, 2021, 09:49:57 PM by JOD »

John Burton

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Re: Rig Tension
« Reply #4 on: June 07, 2021, 10:22:27 AM »
Hi Robin, I have been fortunate enough to have had very useful advice from David Bone and have added second shrouds, inner forestay and mast support like yourself. David gave me ballast in the form of lead encased in plywood that sits on the cabin sole which certainly helps, but the biggest advance came with the drop plates. Your WB will probably have plywood boards with steel ends and mine actually had positive buoyancy. Following Davidís example, I routed out parts of the boards and inserted lead, melted down from scrap bits. I then encased the whole lot with glassfibre cloth and resin. The extra weight low down has made the boat appreciably less tender and is well worth doing. I believe the drop plates on earlier boats were of heavier construction, not made of plywood.

VROUW KIRSTEN

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Re: Rig Tension
« Reply #5 on: June 07, 2021, 11:51:12 AM »
Hello,

I thought the design with double shrouds and forestay made sense for my WB too, but after consulting with a local boat builder I decided against this conversion. I trust the original design and make sure that the relevant materials are in good condition. Measures such as these or trim changes due to additional weight should always be evaluated in the context of the physics of the whole boat and the planned sailing activities. And I have great respect for the individual experiences and appreciate them very much!

The centreboards on my WB were also made of wood with steel, I have replaced them with centreboards made entirely of aluminium (seaworthy).  They should not be too heavy, as the anchoring in the hull must not be mechanically overloaded. And two small M6 screws per axle are definitely not very resilient.

Gerold

Life is happy, life is sweet, on a gaff rigged boat of 16 feet!

John Burton

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Re: Rig Tension
« Reply #6 on: June 07, 2021, 01:54:00 PM »
Good points Gerold. My plates are now about 17kg which I think is roughly the same as the earlier GRP encapsulated steel plates. Another point is the angle they are allowed to drop down, when I first bought the WB the stopper knot in the drop plate rope allowed them to drop down a full 90 degrees, putting too much stress on the mountings. I did consider copying your design for aluminium plates until I investigated the cost of aluminium plate!

VROUW KIRSTEN

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Re: Rig Tension
« Reply #7 on: June 08, 2021, 04:58:12 PM »
Hey John,

I can add the technical drawing of the plate if it is interesting. In my Company I have the Option for water jet cutting, in a second step we optimised the profile of the panel slightly on our milling machine to get a little more streamlining.
I will stop here because centreboards do not fit "Rigging"  8)

Gerold
« Last Edit: June 08, 2021, 06:17:24 PM by VROUW KIRSTEN »
Life is happy, life is sweet, on a gaff rigged boat of 16 feet!

John Burton

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Re: Rig Tension
« Reply #8 on: June 08, 2021, 07:43:04 PM »
Hi Gerold, a very impressive result, you must be very pleased. I remember seeing your technical drawings in another post. You should go into production!

robin

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Re: Rig Tension
« Reply #9 on: Today at 06:08:03 AM »
Hi Gerold-your new aluminium bilge plates look fantastic and I would be very interested to hear how they perform under sail.The reason I have added an inner forestay plus 2nd pair of shrouds is that all of my sailing is on the sea in fairly open water and mainly on my own, so do not like the idea of the mast coming down on my head! As to rig design-do like the look of 'Titsou' sailing at Rochelle with battened mainsail and two foresails.Happy sailing,regards,Robin.