A Frame Masts

brian eiland · Feb 5, 2016

Gus7119 said: ↑

Ok so heres a question for anyone with an sort of engineering background. I was on a building site earlier today where to my amazement i saw an 11m A fame that was spread at the bottom 4.5 meters with 5 spares inbetween it it was a aluminium build and was being used for a rig lifting bricks. Hard to explain and I didnt have my phone so no pics. But if anyone has seen the the A frame scaffolding you can hire from places like kennards hire and such it was like a larger version of those but the arms met at the very top. Now these guys reckon that they can lift 4 tonnes of bricks with the full weight of the bricks load being suspended by this frame. Yet the frame was so lite that one person could lift it.
I asked if it had to be leveled off and secured prior to use or if they had a table for spans and weights but like the good Aussies they were they said nope just did it by eye and hadnt broken it even when thet got lazy at the end of the day and over loaded it. I then asked why I hadn't seen it used anywhere before or anything like it. The answer again in typical Aussie response was 'mate do you know how bloody hard it is to shift those Fing things? So I went to a mates place and after a few cases of beer we thought bugger if we weld this thing together it'll be like, easy'.

Anyway my question is with my head thinking now if their getting four tonnes vertically and off vertical with this frame and its at the centerline of my hulls and I throw a main and jib on it Id have a ready built mast. Now I know without doing snapping tests compression test stress tests on the material itself its a little hard. But give 4 tonnes and more gets exerted on this thing and has done from what I was told for 2 or more years with no weld breaking no bending and no cracking would sails exert more pressure on it then its intented use. It was rectangular tubes Id say aluminium?
And after seeing this I am off to Kennards to hire one of their fres to use on my 14ft cat. So I dont have to gerry rig anything as I know itll hold the sails fine and you can get them in the perfect spread distance at the base so I'll b able to do the test with a normal rig and A frame on the same boats head to head. Although I dont expect the Aframe ro win in this test I hope its not to far off the mark. I may even try it with two sails up front and a main but mow not having to build the a frame I can sfart on rigging.
I know to some this will be a rambling mess to other a WTF moment but I hope someone understands it and after trying to make sense of it ccan help.
Cheers
Click to expand...

Gus, short simplistic answer. I believe you are looking at the A-frame mast idea much as some others have in the past,...that's it just a good stable spread leg configuration that will accept compression loads readily. And your brick loading guys can make great use of that feature.

But a sailing rig has to support quite different loads, and a very significant side loading that not so easily accommodated by the A-frame configuration. For example consider the very significant side loading by the head of the mainsail at at the top of the mast, and trying to pull the boat over on its side. Or the masthead genoa also trying to pull the top of the mast both forward and over to the side. The A-frame configuartion does not bode so well here.

Think of a std mast rig were the windward shroud is in big tension, and the leeward one is slack. How is the A-frame going to cope here? Are there some situations where the windward leg of the A-frame going to have to provide tension force vs just compression force?

If you look thru that extensive subject thread on Procyon you will also discover a couple of problems they experienced,...1) some significant problems tying the two heads together, 2) with the bases set out to the extreme beams of the vessel, there were several occasions where the vessel heeled over at the dock and experienced damage from the tall pilings it was docked next to.

The A-frame is interesting, but not a cure-all.

brian eiland · Feb 5, 2016

brian eiland said: ↑

Does it appear as though he has experimented with several different flap sizes? Is this a larger flap in this photo?
https://chriswhitedesigns.smugmug.com/ATLANTIC-CATAMARANS/Atlantic-47/Atlantic-47/i-BTDDfL4
Click to expand...

Looks like a larger flap size was utilized in the prototype cat as well
https://chriswhitedesigns.smugmug.com/Other/Prototype/i-spKxqLj

Spiv · Feb 6, 2016

Gus7119 said: ↑

Please grav lots of photos and keep us updated. Let him know hes got some very intrested people egar for some knowledge.
So he built the masts himself out of glass with carbon reinforcement. Any chance you could get some more sneaky details of age old rig and how he found and choice designer.

Cheers
Gus
Click to expand...

Gus, I have taken lots of photos, will shrink and upload them soon...
The designer of the A frame is Dereck Kelsall, the same designer of the cat.

UpOnStands
Spiv, the weeks are going to be too slow. Inquiring minds want to hear your experience, how well does it sail.
Click to expand...

Yea, agree, time passes too quickly, especially when one is over 60......
The cat hasn't been sailed for a while and needs hull cleaning first. I offered the owner to help him, but I live 250k from him....
He is keen to take me for a sail and get some cat sailing comments from me.
We are in touch and as soon as he is ready I will go and take notes, I will try and make a Polar diagram and post it to this thread.

waikikin · Feb 6, 2016

brian eiland said: ↑

Gus, short simplistic answer. I believe you are looking at the A-frame mast idea much as some others have in the past,...that's it just a good stable spread leg configuration that will accept compression loads readily. And your brick loading guys can make great use of that feature.

But a sailing rig has to support quite different loads, and a very significant side loading that not so easily accommodated by the A-frame configuration. For example consider the very significant side loading by the head of the mainsail at at the top of the mast, and trying to pull the boat over on its side. Or the masthead genoa also trying to pull the top of the mast both forward and over to the side. The A-frame configuartion does not bode so well here.
Surely this is shared to the backstays as usual?
Think of a std mast rig were the windward shroud is in big tension, and the leeward one is slack. How is the A-frame going to cope here? Are there some situations where the windward leg of the A-frame going to have to provide tension force vs just compression force?
The greater section(over wire) of the windward leg surely would take tension if of metal or alighned fiber construction, also the staying base(thinking included angle to tension/compression members in that case possibly lowering compression) is possibly doubled by the A frame over a central mast with wire stays... here I'm thinking of the typical three stay rig common to cats- also lays the innefficiencies of greater weight and windage already identified to discussion
If you look thru that extensive subject thread on Procyon you will also discover a couple of problems they experienced,...1) some significant problems tying the two heads together, 2) with the bases set out to the extreme beams of the vessel, there were several occasions where the vessel heeled over at the dock and experienced damage from the tall pilings it was docked next to.
The issue of rigging interaction to wharf and other vessels vessels rafting up exists regardless of the configuration, maybe much less so to the cat/multihull?
The A-frame is interesting, but not a cure-all.
Click to expand...

Hi Brian, some conjecture from myself in green to your post... not because I know but because I'd like to.
Regards from Jeff

hump101 · Feb 8, 2016

Not sure if this has been seen before, but a still from the latest Sailing La Vagabonde video (episode 29) at 3.20. Boat is in Bonaire, I think.

Gus7119 · Feb 9, 2016

Spaceship

hump101 said: ↑

Not sure if this has been seen before, but a still from the latest Sailing La Vagabonde video (episode 29) at 3.20. Boat is in Bonaire, I think.
Click to expand...

"Its a space ship!" Yep I saw that last night on its release also. Strange looking boat.

Steveso · Feb 18, 2016

Headsail sag can be controlled by adjusting the backstay tension, but How to control luff sag in the sail which is between the masts?

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A Frame Masts

brian eiland Senior Member

brian eiland Senior Member

Spiv Ancient Mariner

waikikin Senior Member

hump101 Senior Member

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Gus7119 Senior Member

Steveso Junior Member

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