Running backstays on a condo cat

[Tornadosailing]

So is this a great idea or a terrible idea?

Flying a big symmetric spinnaker on my boat makes me a little concerned considering a video I saw with a new FP cat flying the spin and had significant headstay sag. I just purchased a used symmetric spin (52' luff, 29' foot) Makes me concerned about what happens if I get a sudden gust. Could I be in danger of losing the rig? So it got me thinking about running backstays. Dyneema is cheap, and I could get a pair of chainplates made for pretty cheap, and the blocks to make it happen would be reasonable. Plus, if I could pull some of the sag out of the headstay on a beat, could I improve my (pathetic) pointing by a few degrees?

My thought was that I could stow them by securing at the mid ship chainplate along side the existing shrouds, then deploy them to a new set of chainplates bolted on near the aft bulkhead. I bet I could get the whole thing done for about a grand.

Thoughts?

[LoudMusic]

Are there any records of rig failure during spinnaker sailing?

You could theoretically make them multipurpose - boom lift and backstay. Should be an easy swap between the two roles.

But I think it's likely all overkill.

[mark_morwood]

I wondered about the same thing, particularly as we almost always had the main down when sailing deep, so I would just crank on the main sheet with the topping lift to provide at least the appearance of extra support.

[LeeV]

We installed runners on our Corsair 36 trimaran, even though they were not considered necessary, nor offered by Corsair. Lots of load on our huge Code 0.

Easily done by a yard and relatively inexpensive. Dyneema was covered for UV, U bolts through bolted on mast, and the runners simply came down to pad eyes installed on the aft end of the amas (outer hulls). See photo.

[MikeFergie]

Yup put on a 10mm dyneema topping lift on my Leopard. I tightened this when flying my asymmetrical spinnaker which is 115m2. I have flown her doing 10 knots SOG with the wind at 150 degrees and apparent wind at 18 knots. I certainly have no probs without a back stay

[DerekKelsall]

As designer I have always drawn cat sail plans with runners. The typical three stay rig support in profile will have about 18 degree angle to the mast. The aft support from the fixed shrouds is about 8-9 degrees. This requires pretension and puts a hich compression load on the mast. Runners open up the angle to about 20 degrees and no pretension needed. A discussion with a spar maker - the owners ask for no runners. I am now going for a week end sail - with runners. Happy boating, Derek.

[Bean Counter]

Originally Posted by Tornadosailing

So is this a great idea or a terrible idea?

Flying a big symmetric spinnaker on my boat makes me a little concerned considering a video I saw with a new FP cat flying the spin and had significant headstay sag. I just purchased a used symmetric spin (52' luff, 29' foot) Makes me concerned about what happens if I get a sudden gust. Could I be in danger of losing the rig? So it got me thinking about running backstays. Dyneema is cheap, and I could get a pair of chainplates made for pretty cheap, and the blocks to make it happen would be reasonable. Plus, if I could pull some of the sag out of the headstay on a beat, could I improve my (pathetic) pointing by a few degrees?

My thought was that I could stow them by securing at the mid ship chainplate along side the existing shrouds, then deploy them to a new set of chainplates bolted on near the aft bulkhead. I bet I could get the whole thing done for about a grand.

Thoughts?

What is the maximum spinnaker size recommended by the manufacturer?
For our Lagoon 450 with an I of 58.2ft (17.9m) the Symmetric spinnaker option from the factory is 2044 sq ft (190m2).


May be your rig needs a tune too, it should have a noticeable amount of pre-bend in it.

[admiralslater]

Our Outremer 45 is fitted with runners from the factory and I use them mostly for piece of mind. We had a sport cat a PDQ 27 (similar to Stileto)with runners ,we ran them so tight that somtimes the weather stay was slack

[Falbala60]

Originally Posted by DerekKelsall

As designer I have always drawn cat sail plans with runners. The typical three stay rig support in profile will have about 18 degree angle to the mast. The aft support from the fixed shrouds is about 8-9 degrees. This requires pretension and puts a hich compression load on the mast. Runners open up the angle to about 20 degrees and no pretension needed. A discussion with a spar maker - the owners ask for no runners. I am now going for a week end sail - with runners. Happy boating, Derek.

I am new to catamaran, my Lucia is now on a cargo to Florida. When looking at catamaran rigging, all brands FP, Lagoon, etc., I am surprized that the shrouds are with a so small angle backward from the mast.

What is the reason for not moving them more back to give a better support to the mast ? A brilliant answer is required.

[thinwater]

The important question is "what is the direction of the apparent wind?" [actually the halyard angle is what matters, but the difference is generally small]



On faster multies, I doubt it is ever more than 20 degrees behind the beam. Even on heavy cats, perhaps 30 degrees aft. We don't run deep in terms of AW, like monos. 15-25 degrees would alighn the load very well with the shroud. You could make it larger.



So where is the runner load coming from? If you are curious about the direction of the load, look at the halyard angle and then decide.



Additionally, sheeting the main tighten the forestay sailing to windward and gives some side stability, depending on prebend and rotation, with the chute up, but it is probably at 90 degrees to the chute load.

[catsketcher]

It would be pretty dangerous to have the sidestays on a 3 stay rig at an angle of 15 degrees. The normal angle is about 30 degrees aft.

If you want to live dangerously then you can sail like old IOR fractional boats that used to need runners on or they would lose their masts over the front. Or you will need a rig that can safely handle loads from all directions, including one a square run.

It is vital that the boat is safe on all angles of sail, including a square run. Sometimes you will want to square run under full sail in a squall. All of the full load of the rig will be directed forward.

An angle of 30 degrees aft will have half its hypotenuse vector acting aft - make a triangle and do the trig to see. So if the sidestay has enough strength to take the full hull flying load (or whatever max load is) then two sidestays each at 30 degrees will have the same load taking ability.

You really don't want the stays at 15 -20 degrees. This is narrowing the staying base on a square. It will put increased load on the stays and the mast through compression. If you read a book on boat design like Skenes it goes through the issues with staying base. In this instance the staying base has to be thought of fore and aft as well. As cats are so stable the wider staying base is really helpful - sideways and fore and aft.

I often square run with my cat. Often I have only a kite up, or will have the main and a poled out genoa/reacher up as well, so the rig needs to be bulletproof on a square.

That being said - you could use runners to help with the load from screechers etc. The loads from these get really high and if you want to take them close to the wind then the halyard tension needs to be opposed by something. You can use the mainsheet tension which is what many dinghies do. There are some issues with blowing the sheet when going fast. Skiffs can lose mast tips when they ease the vang with the big kite up, even with caps.

cheers

Phil

[Bean Counter]

Interesting article regarding B&R rigs used in most Hunter mono hulls.
https://www.boats.com/reviews/boats/the-bampr-rig/

[Training Wheels]

I get the advantage of the B&R rig of being able to have a large, big roach, full batten main, but it seems that most boats with this rig instead have in-mast furling mains. So, what’s the point?

[Jim Cate]

Originally Posted by Training Wheels

I get the advantage of the B&R rig of being able to have a large, big roach, full batten main, but it seems that most boats with this rig instead have in-mast furling mains. So, what’s the point?

Interesting observation... I'm curious, too!

The big roach main is a worthwhile addition if good sailing performance is of interest, but all too many folks are not really sailors and don't much care about such details!

Jim

[catsketcher]

Here is an article on rig design by Chris Mitchell who is a gun designer of mono racing rigs. This, measuring other cats and talks with rig makers is where I got the 30 degree sweepback angle from.

https://www.aes.net.nz/info.html

I didn't realise that Derek drew rigs with 20 degree sweepback. Derek has been drawing fab multis for longer than I have been alive. I learn something new.

cheers

Phil