First of all let me apoligize for bad grammar and spelling!
The main use for the design is a fast boat for evening-sailing singlehanded/ weekends and once a year a one week trip for two/ occasionally weekends for four. It must be dismounteble for roadtransport (mainly for storage during winter).

I really like John Harris proa Madness, and i have used that as a refference for many parts of this design.
Gardagast is a 10m long and just over 5m wide pacific proa with a sailing disp at 900-100kg, Boatweight around 500kg. Constructed of strip wood and epoxy/glass (maybe epoxy/carbon if it doesnt add to much to total sail away budget))

If you look at the first image attachment, it show the main differences between Gardagast and Madness.

First. I like wavepiercing bows for less hobbyhorsing anf longer waterline for a given weight/airdrag. The material in the bows are redistributed shown in red.

Second. I want the most interior volume in the middle where it is useful for living and get more of the weight to the center of the boat, shown in blue.

Third. I want highly effective hight AR foils that allways are in use, dont want to build and carry the weight of 2 boards with only two of them active at the time. The front rudder swing 180 degrees during shunt. Both boards in circular trunks.

Forth. I dont want to buy and store sails that can not be used at the same time. And want to do shunts from the cockpit without running from side to side with a jib. The solution is a single mainsail on a sliding wingmast (like Gaias dream without the engine).

Fifth. The second attached image show in a yellow a longer pod that allow two double berths with a area for cooking and socialization.

Gardagast is a bit less wide than Madness to reduce weight, windage, initial RM and docking fees.
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Numbers for those who like that!
Aka
Length: 10m
Width waterline: 0.6m (1:16,5)
Total surfacearea: 37sqm

Ama
Length: 6.6m
Width waterline: 0.4m (1:16,5)
Sailing disp: 200kg
Full disp: 1000kg
Total surfacearea: 9sqm
Waterballast: around 400kg?

Total boat
Width centerlines: 3,8m
WA: 10,5m2 (incl boards)
Sailarea: 35m2 (incl wingmast)
Internal headroom: 1,6m
Height above water: 12,5m
Depth boards up: 0,26m
Depth boards down: 1.76m
Mastmovement: 2,6m
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One problem I see is that it will be tricky to get a good hatch in to the boat with the sliding mast arrangement…
And i guess it will be hard to get the center of effort of the sail far enough centered/forward to not get to much weatherhelm with both boards fully down.

I would really appreciate your thoughts of the design and I gladly take advise and ideas to solve some of the remaining and probably some not yet known problems!

I hope to start a boatbuild withing a few years, but at the moment it is in the dreaming and making drawings and models stage.

Kind wishes
/Garg

Some more pictures.

Hi Gargen,

Welcome! Nothing to apologise for. The proficiency that you and others here who have English as a second language amaze me. Besides, it’s about ideas and not language.

Your renderings show a very elegant shape, indeed. Great profile. The movable mast is an intriguing idea. I wonder how Inigo is finding his movable mast’s performance? It would seem that the mast requires a track for the step that is higher at the ends than the mid point. Your cabin roof is shaped the other way, of course. Where do you plan to step the mast?

http://www.youtube.com/watch?v=iS270ousYwg&feature=player_embedded#!

Thank you James.

Well the position of the moveable mast is one of the big things to solve.
I think it is wise to have it as far to weather as possible while the loads still can get into the mainhull in a simple way, and i would like the cockpit to be to weather of the mast to make it easier to trim and for the feeling of safety.
The attached image below show how i think it could be done, but the entrancehatch for the mainhull will be very far up, allmost like a hole you jump into. And the hatch must not be blocked by the mast or the boom.
I’m not really satisfied with the solution, other ideas will greatly be appreciated!

/Garg

Sexy design!
Should go like sh1t of s shovel!!
(Like busses, wait for ages, 3 come along, who’s going to post the third!!!)

In reality getting the sliding mast means a tripod arrangment out to the ama - sort of spoils the looks? 

The sliding track wil need to be a substancial piece of kit, wing mast and rudders equally highly engineered.  Is this just dreaming or have you won the lottery?

Mark

Thanks Mark!

If you have not seen it yet(bet you hace) take a look at “die fledemaus”
There’s your third (or rightfully first) in my opnion. A awesome fictional design by Michael!
/Garg

I dont gamble, so unfortunaly winning a lottery seams not likely. (not that rich either)

If the mast stands on a little trollie and rotates in one single point up in the mast, then the trollie has to take the whole load of the mast + compression loads
at the endpoints of the sliding(or roling) track. Midway there is still mast weight and some compression, but less of it.
Why would a tripod be needed? (or do you by tripod mean wire/syntetic stays? That is what i have planned for)
Another placement of the of the sliding track could be on the roofe, as close to the cockpit as possible, and have the hatch under the track. It would be a little cramped to get in and out of the cabin, but at least the mast cannot lock the way.
Btw. I dont think the track need to rise so much at the ends, i guess around 15cm (easy to calc, but i’ll do that another day)

And yes, the rudders are rather high AR, but a naca 12% profile still make them 3.6cm thick. But i guess they unfortunaly have to be made of carbon.
Mast would be made of wood and glassfibre (read somewhere that due to big stretch difference in carbon and wood, that they are not suited to be ued together.
I dont want/can afford more carbon than what is needed, but i think rudders and if possible mastreinforcement is well spent money due to the stiffness needed in those parts. A cat or tri would also gain from carbon in the crossbeams, but i dont think stiffness is that important in proa crossbeams. Does it sound logic or am i totaly off?

Thanks for your thoughts, ideas and critics this far. I really appreciate it!
/Garg

The tripod arrangement to which Mark referred is implemented on Gaia’s Dream; you’ll see the rigid mast supporting the main mast or yard in the image I attached. It’s quite like a canting mast on a polynesian proa. Gaia’s dream needs it for support since the mast track is positioned on the main hull itself; I see yours is positioned more to windward so maybe you don’t need a support mast. Or you could use the same solution so that you can place the hatch wherever you want to.

Ah, can´t belive i have missed that Gaias dream got that!

My main reason to have the mast to ww from centerline is to reduce weatherhelm when both boards are fully down when going to weather. The weatherhelm problem is allso the main reason why i need the mast to slide (to shift CE forward toward), increased sail area is a welcomed bonus of that.

I painted some on a front view, yellow is the slide track and purple the cabin hatch.
Very clear that the cabin over track version is not an option. The mast and boom will block the hatch, and you have to step over the control ropes for the slide track to get inside. not a safe option!

The track on hatch on the other hand could work from a entrance perspective, but then the stays for the mast get very low angles (and back on problem with weatherhelm)

Maybe i’ll have to rethink the sliding una rig and go for a more conventional rig…
Ideas will be appreciated!

/Garg

Hi Gargen!

That is a very nice looking proa you are drawing.
I like the wavepiercing bows, just remeber to have some floatation/freeboard near the ends or the bow could bury down into a wave a pitchpool the proa. With wavepiercing bows it is very important to have a very low center of gravity, and that means (among other things) low weight mast, rigging and sails.

The sliding track wil need to be a substancial piece of kit,

I don’t think thats very hard or expensive to build.
A thick steel tube bent to the right radius should make an excellent track.

I think you should make your akas (crossbeams) thinner and more flexible. That is one of the very nice things with a proa. They don’t have to take any bending or twisting forces. They only have to hold the ama out to the side. Ofcourse they have to be strong enough to take shock-loads, but nothing close to the loads on a trimaran or catamaran.

Cheers
Johannes

Thank you Johannes for pushing me to post, was a while since last time.

I started to build a one meter model of Gardagast over a month ago, but I’ve had very little time to work on it, but i’ll show where the build are right now.
I build it the same wat i will/would build the real boat, but using strips of balsa instead of swedish fir. unfortunaly the balsa strips are 1cm wide, 3mm would have been better to better follow the form of the mould, and they would allso twist less. Therefor i split them in two with a rather bad accury, but it works. The balsa will (hopefully) soon be covered with a rediculousy thin/light glassfiber wave (25g/sqm if i remember correct).

The computer model has changed a little compared to the balsa model (wich is exactly the same as the pictures earlier in this thread). The computer model are now 10cm lower (taken between waterline and leepod) and also the leepod have been made less wide with 10cm in the center part. The ama have allso had a minor facelift.

The biggest change (still evolving though) is that the una-rig is replaced with two unarigs, a schooner! (with no jib).
This make it less prone to get cought in irons, move the CE closer to the centerline, and everything else that is good with schooners on proas, covered on other threads on this forum. BUT one thing is extra beneficial to this design, and that is that two mast need two tracks, and between those tracks i fit my cabin hatch!
Allso, two masts weigh more than one, but the weight on one specefic point of the track will be much less.

I’m allso considering to make the tracksangeled compared to the boat centerline, so that the forward mast will be leaned a little to create vertical lift, and the back mast will create som vertical negative lift, just by a small amount to compensate for bow down attitude (wich I think is likely).
Thinking of one stay from each bow to the nearest mast, one stay between the mast, and one stay from each mast to the ama. all stays attached at the top of the masts, that way the masts can be canted as much as possible and thereby pushing the CE forward, and it will allso be possible to feather the forward sail in case of an cought aback situation, emediatly makeing the boat luff to the windeye.

I’ll gladly here ally thoughts you have about this.
Kind regards
/Garg

Hi Garg…...

Your hull design is too good to have an inefficient schooner rig with two complicated sliding mast feet…....

Attached is a couple of rig options which keeps the CE pretty central, pretty much as suggested by Othmar, but without 2 masts. The mainsail boom is pivoted about a third of the way back and the pivot is located on the lee side of the vaka to give room for the front third of the boom to tack/shunt without crossing the cockpit.

I am seriously considering the second option which adds a roller furling windward staysail clubbed/boomed as well.
This gives more than enough sail area without having to change jibs at each end of the boat when you want to change tack. The staysail has a very low heeling arm and if the boat heels, the staysail inherently has the canted to leeward Pizzey effect…..

Regards,

Rob

Yes, you are right, i would most of all have one solid, high ar wing for least possible drag upwind. But that got some big limitations. Next step in the low upwind drag-route would be one unstayed unarig with a fairly larg wingmast, but that screw up the CE wich i need a third board + raising/ lowering rudders each shunt. There caught in iron problem is allso large.

Your/Othmar sugested rig looks nice, but i think all that stays will be rather dragy, and how will you keep “forestay” tention? When yousheet in/down the boom the firestay will sack, .ot good for upwind work.
And if you center the CE of the sail around it’s own rotationpoint, then would it not be hard to quickly feather the sail in a big puff?

But maybe you are right, the schooner is not effective enough. I’ll rethink the possibility of a unstayed una rig. Thank you Rob (:
Another thing that have been through my head is to put the two schooner masts so close to each other that the sails overlap and therby a t like a jib+mainsail (but without havi.g to hoist and lower the jib each shunt)

More thoughts and comments are apreciated!
Best wishes
/Garg

Johannes, i would for sure like to make the cross beams smaller/thinner, but they may not brake in a caught aback situation. That means the crossarms need to be able to handle around 1000kg static weight (the weight of the boat and allso the fully submerged disp of the ama) so that the aka lifts from the water before they brake.
Or do others think differently about this?

/Garg

Let me say first that I like really like your design. I like your original sliding una rig and would try and find ways to make it work. I am sure you can find a way around the hatch problem.

Garg,

Firstly, I agree with Timothy….. For your ideals, your original una rig has to be the way to go….do 2 hatches or something else to solve the problem….

With regard to simple clean “no wires” rigs, in the end invariably they are less efficient, heavier and more expensive than “wired” rigs , otherwise the designers of almost every race boat (mono or multihull) today have got their wires crossed!!! Two masts instead of one is even worse.

With regard to Proactive 2’s possible “Othmar” rig, it is the counterbalance which gives you the extra sail area and reduced sheet loads for the same air draught. Luff/ forestay tension in the mainsail would be primarily controlled by an adjustable boom strut / vang in compression.  Luff forestay tension in the windward staysail would be primarily controlled by an adjustable waterstay.  You could also do it with topping lifts to the end of the booms, but that would be 2 extra wires…..  Also, any increase in leach tension is doubled on the luff, so the strut / waterstay maintains the minimum, the rest is done through sail setting.

Being caught aback is no worse than a mainsail alone and much better than a conventional jib which can’t be instantly released. It might be that the pivot fixing location on the booms will have to be adjustable to find the right balance, so to speak, if there proves to be a problem.

Rob