A-Frame Mast

[ericdalene]

Hello - Am new to this forum, but am excited to ask a question :

Is there anyone familiar with A-frame mast configuration for a sailboat, combined with a roller furling genoa and a roller furling main ?

I would be very thankful for information and experiences with such a design -

1. Practical nature

2. Handling peculiarities

3. Ability to head into the wind

4. Advantages / Disadvantages

Thank you

 

[chabrenas]

The A-frame design I remember just had a single sail - the genoa. How would you set the main? Straight up and down inside the A frame? I don't think you'd gain anything by using it - just the genoa is equivalent to a lateen (dhow) rig without the problems of tacking it. Good to windward and close reaching, but some kind of boom would help fownwind.

I presume you plan to fit it to a multihull of some sort?

 

[RHP]

The A frame has been discussed in some detail on other threads, do a search and you'll come up with something.

 

[ericdalene]

A-Frame

Thank you so much for your helpful responses. I will search the site more.

The application in this case would be a monohull. I believe to that downwind would not be as favorable.

 

[Norman Brown]

I am also interested in the A-frame mast. If you have found any good articles I would be interested as this seems ideal for my 42.5 ft yacht now being built.
Regards. Norman Brown

 

[alan white]

The only problems, I assume, would be extra cost, weight, and windage. Otherwise, roller reefing and furling would be the way to go. Definitely could have a main and jib. No mast in the cabin.
Two masts would still need to stay in column, both being a bit longer than a single mast. Otherwise the masts diameters would be quite large (remember windage?).
Twice the weight aloft, complicated staying to keep masts light (or large diameter masts). Only masthead type rigs would make sense.
We don't see them out there for all the above reasons, or at least I've never seen one.

 

[PAR]

There was an attempt at a bi-mast rig in the early 90's. One of the major sponsors was Harken if I remember correctly. The main was on a roller furler as was the headsails. The leading edge of the main was aerodynamically clean, but the windage of the additional mast offsetted the efficiency increases. This boat was a test bed for a number of interesting innovations. I think it was called "Paragon"

 

[Eric Sponberg]

There was an attempt at a bi-mast rig in the early 90's. One of the major sponsors was Harken if I remember correctly. The main was on a roller furler as was the headsails. The leading edge of the main was aerodynamically clean, but the windage of the additional mast offsetted the efficiency increases. This boat was a test bed for a number of interesting innovations. I think it was called "Paragon"

Actually, it is Amoco Procyon, and it has been discussed before on this forum:

http://www.boatdesign.net/forums/sailboats/procyon-project-bold-experiment-10771.html

In my opinion, the extra weight and cost of an A-frame rig are not attractive enough for the different aerodynamics (not necessarily better on all points) that one gets. One mast is cheaper and lighter than two masts.

It was a test bed for a number of different ideas, including canting keels. Some of the ideas have become more prevalent in yacht design, but the bipod rig is not one of them.

I had occasion to go aboard Amoco Procyon, I'd say about 10 years ago. It's interior design--all stainless steel--was stark to say the least. I heard one noted yacht designer say "If this is the future of yacht design, we've just gone backwards about 20 years." But the Harken brothers are to be commended to at least trying and putting their money where their mouth is.

Eric

 

[alan white]

I can see how Harken's Polygon would have been a good test bed for a whole boatload of equipment that would become necessary had the design caught on.
You can have a main with a jib type luff by putting a single mast in the eyes of the boat canted back, with headsail on a sprit. 3/4 rig though, not masthead because of tensioning issues (gunter style "wing" spar extends above the masthead).

 

[alan white]

I meant Procreation.

 

[tom28571]

I saw Procyon somewhere, possibly at the Annapolis boat show but I think it was more than 10 years ago. I think they had to add a strut between the masts to reduce the span. The masts were in great compression from both sails and backstay.

 

[multicapt]

The A Frame Mast

The A frame can be made very cheaply and will remain standing longer than a conventional mast due to the absence of shrouds/stays ,the cons however far out weigh the pros .
As mentioned weight could be an issue aerodynamics another .
On a big baffy stable multihull before the wind hell why not? you could climb the mast with ease and enjoy the scenery but don't expect to race round the cans on a monohull.
I have actually made an A frame mast and attached a main and genoa with predictable results as mentioned above ...... of course it works BADLY.

 

[pool]

SMG / A-frame masts

SMG cats use the A-frame mast, and appear to be quite fast in local regattas http://www.sail-the-difference.com/fileadmin/users/9/news/2009-05-05-Kornati_cup_results.pdf
Further, their hull design has no keels or daggerboards, quoted as "asymetric".

Anotherone just crossed the Atlantic successfully from Capetown to Brazil http://do-re-mi-2010.blogspot.com/

Anyone had a closer look at, or have experience with these designs?

 

[ancient kayaker]

The A-frame mast does have to be heavy if properly designed to take full advantage of the different ways forces are reacted to the hull. However it imposes different stresses on the hull than a conventional mast so they have to be designed as a system, especially if performance is an objective.

 

[Angélique]

Hi, here a A-frame mast with a lateen rig with a boom at the bottom which front swivels. The lateen is hanging in the A-frame in with what seems to be a reefing claw.

The original forum is not always on line and some pics are gone. So here what I once saved from the Google webcache with the original links...

Cheers,
Angel

Website + pics

Calidris is 21ft overall and was launched in 2000. The hull is based on Iain Oughtred’s Caledonia Yawl, the rest is mine - the twin drop keels, the rudder, the cabin, deck layout, and the lateen rig, etc. The lapstrake construction is marineply on oak, almost everything is held together with epoxy resin!

Iain Oughtred - Caledonia Yawl - forum

Cabin for a CY

by: kenjamin
Location: Tallahassee

on Tue Jun 17, 2008 5:02 am

The owner of the CY with a cabin, Derek Burnett, and I have been exchanging information and pictures on our experimental sailing rigs and design departures from Iain Oughtred's standard plan for the Caledonia Yawl. It's interesting that Derek has even tried a bermudian rig for his boat last season.

I thought you all might find it interesting to hear in Derek's own words about his boat so I will share with you all three e-mails. The last one gives permission to share this information:

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e-mail 1:
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Hello Ken,

Xena looks real fun! Great set of photos too! Will take closer look.

We carry oars on Calidris, but have never had to use them seriously.
I wouldn't like to have to row her for any distance especially in anything except slight winds and current - but then I'm not that fit these days.
You need to know that Calidris is a stretched version of the lovely CY design.
She has twin drop keels and a 10hp engine, so with all this and other paraphenalia she weighs in at anything up to 750kg or 3/4ton!!
The cabin design minimises windage problems but must add windage compared to the open boat.
The underwater profile grips the water well so once underway she holds her line.
The rowing position is a little far aft to be ideal.
Can be rowed in conventional manner by one person or two sitting sde by side - or by one sitting and facing facing forward.
If I got serious about rowing her I would add another rowing position.
Two fit crew could probably make rowing a feasible means of propulsion.
I have designed a sweep based on the yuloh concept which theoretically could push her along easily - but like many things have yet to get round to making it!!
Sampans ( similar size) have been using a single sweep for centuries!

Feel free to use images from website. Let me know if you want more information.

I unfortunately have limited range of really good photos - this may change later this year as 'Watercraft' Magazine want to do an article on Calidris.

Where are you based?

I'm in the UK - theWirral.
Tend to trail Calidris to other areas.

Best regards,
Derek Burnett

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e-mail 2:
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The basic design brief I gave myself for Calidris was based on the following considerations/limitations.

1. The space I had to build in. I built as big as I could in the space I had.
2. Trailability - this put another constraint on size, also on weight for towing
3. Handling - easy to sail, launch and recover single-handed
4. Suitable for exploring estuaries, inshore waters, large lakes and Lochs
5. Have reasonable stability and bouyancy
6. Basic shelter for at least two people.
7. She had to look good!

I bought the plans from Iain and decided that I could stretch the dimensions and design a cabin without compromising the lovely lines of the hull he created.

Calidris is 20' 10" from stem to stem ( 21'8" including the rudder). 18' LWL with 6'6" beam.
Sail Area is Lateen 144 sq ft. Mizzen 31sq ft.
I have managed to create more space inside by replacing the use of a centreplate with twin dropkeels that are totally outside the hull. All this has allowed me to build a very dry and snug cabin that allows for two berths and some stowage so camping aboard is, by many standards, almost luxurious!!

In answer to your question apart from the hull lines the whole process of design and construction was done by myself. The only job I outsourced was the fabrication of the drop keels.
Everything else including the sails has been my handiwork!
It took the best part of four years.
I built outdoors so was very limited by season and weather!
I also had a full time job lecturing which tended to get in the way!
I also wanted a platform for experimentation with the my rig concept and other ideas.
As you know the lateen is a very old rig design that's still in use today.
It can be a very efficient and powerful driving force but has two main drawbacks - it's difficult to reef, most lateen rigs use a brailing system which holds the sail to the mast, leaving a lot of windage high up. It is also a pain to go about.
The yard has to dipped and taken the other side of the mast so the boat is weathered rather than tacked.
My design is an attempt to overcome both these problems. The sail is reefed by rolling it onto the yard whilst the A frame allows the sail to tack . The system is very easy to use - a mainsheet and reefing line both of which are led to the cockpit, along with two lines to adjust the tack-boom which is attached to the base of the yard.
On the run the tack-boom is outboard , closehauled it is centred or just upwind of centre.
As with all things new it needed a little development. All the spars are made from recycled and reinforced windsurfing masts!
The first yard I made was too flexible - I solved this by using carbon fibre. Great fun curing the stuff at high temperature!! The A frame needed some adjustments at the top. She sails well with the rig.
The mizzen adds balance and just large enough to add a little drive to the rig.
Good damping effect when choppy and under power or just loafing!
Just for comparison I rigged Calidris with a bermudian main and jib last season.
It does allow for more sail configurations and when reefed brings the centre of effort lower than with the lateen but it has an awful lot more rope to get tangled and doesn't look quite as well as the lateen.
There is no one perfect system both rigs have there +++ and --- but the lateen rig and boat pretty well fulfil the design brief I set myself.
There are things to improve and other ideas to try out - all part of the fun - I must be mad!! Much easier to go and buy something off the shelf!!

I hope to try out a boom for the lateen this year.
Though the speed at which the year is passing I might be lucky to get her on the water at all!

What's the sail area of your rig?
I'm intrigued as to the construction detail of the mast.
It must be great having got support for your idea.
I hope that the patent rights sort out well in your favour.
Are you thinking of marketing and producing the rig yourself or selling the idea on?

Have attached a couple more images of Calidris.
Hope the above is of interest to you and goes some way to answering your questions, feel free to ask more or give comment!

Have fun!

Best regards,
Derek

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e-mail 3:
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Hi again,

If anything the lateen points better than the bermudian.

Feel free as regards forum.

Sorry it's so short a reply - have yet to read your email in detail.

Save sailing
Derek