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Old 24-06-2011, 19:55   #16
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Two Production Aft Mast Rigs

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Maren: I've satisfied my need to save the world from dead-ends, and will gladly apologize to everyone when someone builds a successful Eiland design.
Have you seen or heard of these motorsailing powercats being built over in Thailand...2 finished now for Hong Kong owners
HK40' - Power Sailing Catamaran. (HK40' - Power Sailing Catamaran.)
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Old 24-06-2011, 20:03   #17
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Rigging Force Review for Aft-Mast

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Originally Posted by sandy daugherty View Post
Finite element analysis is overkill, freshman Engineering Dynamics will at least resolve the loads. You can build a boat to support three times the load at the mast base and 8 times the load at the back-stays, and still have too much sag in the fore and jack-stays to furl the sails,...
I went back to that freshman vector analysis form of review and posted it over on this other subject thread....but no response ??
The Ketch-Rigged Cat

Did it really end up with those HUGE loads you spoke of?

Oops, I see that the columns of figures in that posting got skewed out of line. Here is an easier view of those columns of figures:
Aftmast rigs??? - Page 23 - Boat Design Forums
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Old 24-06-2011, 20:20   #18
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the other tread

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Originally Posted by Maren View Post
...I do think the other thread is worth reading as there were several good exchanges, and the links were good.
I just discovered this thread myself....and felt compelled to answer a few of the postings with some new news.
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Old 24-06-2011, 20:34   #19
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Re: aft mast ketch rig

[QUOTE=SkiprJohn]Why is it called a ketch rig? I thought ketch rigs were two-masted with the aft mast being the shortest. Am I wrong?

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Oh, sorry. I guess I do know what a ketch rig is. Had one for many years. Great for cruising but kind of unhandy for day sailing.
Kind regards,
JohnL
Quoted right out of my website
Sail Propulsion - Revisiting a Mast-Aft Sailing Rig
"So what did I come up with? Lets call it a marriage between a cutter and a ketch without the mainsail.

...Adding a mizzen sail to one of the backstays turned the boat into a ketch without the addition of another mast and its associated rigging. This increased my total available sail area on this single-masted rig. A ketch rig divides the sail area up into more manageable size sails, and it produces a rig with a lower center of effort (less overturning moment) than a sloop of the same sail area."

And technically even though I don't have a second mast, the mizzen sail is attached to a member that is ahead of the rudder post.

I'll bet you might find this 'ketch rig' easy to use in a 'day-sailing' situation:
The Ketch-Rigged Cat
"You know I can still imagine sailing a big 65-foot catamaran with this rig right off the mooring, and back to the mooring, without the engine, by myself, with so little effort that I might take it out having only a few spare hours to kill or a daysail."

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Old 26-06-2011, 18:54   #20
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Re: aft mast ketch rig

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The convenience of this rig is that reefing can be done from the cockpit. big wind = reef the genoa anyway.

Downwind, dont worry about the main, stick that big genoa out.

The mast is better supported because it is in a position that allows a substantial load spread, rather than perched on top of an unsupported part of the main roof.
My 43' catamaran which has just been launched has the mast at the forward end of the cockpit - it is not 'unsupported' but has a support that is part of the rear salon bulkhead going down to one of the box beams. The designer gave me a choice (probably not a good thing with a complete novice) of where I wanted the mast - sort of in the center of the salon or at the aft salon bulkhead. Having followed a similar discussion some years ago, some of the arguments of powering the boat using only headsails, seemed to make some sense. I therefore opted for the further aft location since I didn't want the mast support in the salon and didn't see a downside to bigger headsails. My designer/builder often builds sailing catamarans with no mainsail and they seem to work OK. The rig has now been changed somewhat (possibly because of my commenting on the lack of a mainsail several times) to now include the possibility of a small footloose mainsail.

We all think outside the box on occasion - my oddball design feature was to make it safer to go forward to the mast and stays by moving the side walkways to the center (with the hull cabins being larger and carried out to the edge of the hulls). I thought that this would save space as one would only need one walkway instead of two (although one could still walk on the cabin top), and it would be sheltered in heavy weather (and easily shaded in good). It doesn't seem to me that it would add windage as the central salon would have been at the same height. I don't know why this is not done, but I assume that there must be a good reason since no one does it. Still, there was a time not long ago when the concept of getting stability out of having two hulls instead of a keel was also considered a novel design solution - and there are those who clearly don't approve of the concept even today.
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Old 27-06-2011, 12:21   #21
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Re: aft mast ketch rig

Bruce,
I for one would love to see some photos. Did you end up building the center walkway saloon?
Mike
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Old 28-06-2011, 05:24   #22
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Re: aft mast ketch rig

No, my builder constructs his designs and I didn't want to open discussions on such a large modification - expense, and after all, what do i know anyway? Its just a regular condomaran I want to live on - likely for just coastal cruising and living on the hook here in the central Philippines where there are almost no marinas. This thread has a couple of pictures : Catamaran in the Philippines and i will be gooing down to see it later this week so perhaps some more pictures - I am not sure if it is rigged yet - it is typhoon season here.
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Old 10-06-2014, 21:07   #23
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New Lagoon 52 moves its mast aft

Interesting new twist, Lagoon 52 design moves mast aft to carry larger headsails and smaller mainsail.

Lagoon 52 | Sail Magazine
Quote:
Although you might not immediately notice the differences between this boat and its predecessors, they are dramatic. For example, moving the mast back to the 43 percent point to get a larger foretriangle required moving the center of buoyancy of the hulls aft as well. That, in turn, meant reshaping the hulls and making the bows sharper, not to mention adjusting the overall center of lateral resistance to keep the boat balanced with the big jib and small mainsail.

Moving the mast aft also required some kind of new support, as the main bulkhead at the forward end of the saloon is no longer usable as a base. That meant creating an entirely new support structure: which Lagoon has done in the form of a big, stiff, reinforced grid concealed within the cabin and hull, and a strong compression post in the middle of the boat

Putting the helm up on a flybridge created yet more structural challenges due to the strains of the running rigging and the weight of people up there. Finally, the short boom (another result of the aft position of the mast) calls for a taller rig to replace the lost sail area.

Amazingly, all of it works on the Lagoon 52: the tall rig is efficient; the mainsail is easy to trim, raise and furl (although the standard electric halyard winch is still essential); the roller-furled headsails behave nicely; and the boat really goes. VPLP Design got it right.
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Old 11-06-2014, 08:54   #24
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Re: New Lagoon moves its mast aft

For the purpose of historical accuracy, the piece in Sail magazine seems to credit the Lagoon designers with the idea of moving the mast back & the design changes needed to support it, viz. "VPLP Design got it right."

However, actually some folks from Lagoon saw the Stanton FreeFlow 52 with the aft mast placement and support engineering being built & rigged in China (long before the Lagoon 52) & got (apparently) very excited as they examined it judging by the intensity of the chattering in French, so I am told.

The FreeFlow builders joked at the time that it wouldn't be long before we would see an aft masted Lagoon, for which they would claim credit.
And.... voila!

Just saying. Nathan Stanton should get kudos for making this work in the FreeFlow designs. It has some great advantages for short-handed bluewater cruising. See FreeFlow Catamarans

If you look at the FreeFlow 52 interior rendering, the mast support pole is placed even further back than it seems to be in the Lagoon 52, so opens up the useable space in the saloon even better IMHO.
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Old 11-06-2014, 17:46   #25
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Re: New Lagoon moves its mast aft

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Originally Posted by BigBeakie View Post
For the purpose of historical accuracy, the piece in Sail magazine seems to credit the Lagoon designers with the idea of moving the mast back & the design changes needed to support it, viz. "VPLP Design got it right."

However, actually some folks from Lagoon saw the Stanton FreeFlow 52 with the aft mast placement and support engineering being built & rigged in China (long before the Lagoon 52) & got (apparently) very excited as they examined it judging by the intensity of the chattering in French, so I am told.

The FreeFlow builders joked at the time that it wouldn't be long before we would see an aft masted Lagoon, for which they would claim credit.
And.... voila!

Just saying. Nathan Stanton should get kudos for making this work in the FreeFlow designs. It has some great advantages for short-handed bluewater cruising. See FreeFlow Catamarans

If you look at the FreeFlow 52 interior rendering, the mast support pole is placed even further back than it seems to be in the Lagoon 52, so opens up the useable space in the saloon even better IMHO.
Correct. Essentially the rig is centrally located.
kudos to Nathan.
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Old 11-06-2014, 18:06   #26
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Re: Aft Mast Ketch Rig

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Ok, I concede. I didn't realize there were two masts.
Kind regards,
JohnL
I'll choose to stand with you! How could they call it a ketch? It's as if those that invented the Segway had decided to call it a bicycle!
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Old 11-06-2014, 22:22   #27
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Re: Aft Mast Ketch Rig

Nathan Stanton?

How about the Prout brothers?
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Old 11-06-2014, 22:46   #28
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Re: Aft Mast Ketch Rig

StuM,

I didn't mean to imply that Nathan Stanton was absolutely the first designer to come up with a mast moved aft. I recall Lock Crowther did a boat a long time ago with an aft mast and bigger headsails.

I was just commenting on the implication in the Sail article that Lagoon did.

And for all I know, maybe the Lagoon 52 was on the drawing board and they had everything already figured out when the Lagoon fellows saw Nathan's boat at the Chinese yard. But I doubt it
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Old 11-06-2014, 23:08   #29
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Re: Aft Mast Ketch Rig

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Nathan Stanton?

How about the Prout brothers?
StwM,

The FF and Lagoon are more centrally located masts than the aft mast of the Prouts.

I can recall Nathan saying that many of the ocean racer concepts had centered the mains thus larger foresails. Its more the adaption of center mounted mast in a cruiser. I note Dascat has an southern ocean 46 with similar mid mounted mast in design but haven't built it yet. Expect we will see more.

http://www.dazcat.co.uk/Dazcat_SO47.html

Not that pitchpoling is a big issues thesedays but it would certainly help in souther ocean cruising in a cat.
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Old 12-06-2014, 07:35   #30
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Re: Aft Mast Ketch Rig

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I'll choose to stand with you! How could they call it a ketch?....
I don't think they are calling it a ketch.

I believe I originated that word description when I referred to my mast-aft design in an alternate manner as a 'single-masted ketch', due to my adding a 'mizzen' sail onto my 'cutter type' headsail rig.

I was originally inspired by the combination of ownership of a wooden ketch, and the Prout rig, and another old sailor.
Sail Propulsion - Revisiting a Mast-Aft Sailing Rig

Before I became computer literate (somewhat...ha..ha), I had several published references in 1974, 1975
RunningTideYachts, Ltd. - Archives
RunningTideYachts, Ltd. - Archives
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