GARDAGAST???
Greetings from Tasmania…..
I have enjoyed following the forums for quite a while now….. There are a number of design philosophies and features on Gardagast which are similar to designs I have been working on for a long time.
Attached are some early 3D wireframe images of an 8.5 metre proa I hope to build later this year…....Basically it has been designed for me to sail singlehanded, but can accomodate up to 3 below, albeit cramped.
Basic Stats:
LOA: 8.5 metres
Loaded Displacement: 837 kg
Displ/Length Ratio: 28.22
Basic Sail Area: 30 m2
Static Righting Moment: 1503 kgm
Total righting moment including Dynamic RM: 3195 kgm
Minimum Sail Area/Displ Ratio: 34.56.
Sail Carrying Power: 35 to 70%, depending on sail and foil combination. (You need 30% plus to plane upwind consistently)
Construction: GRP sheathed 2x6mm cold moulded Pawlonia veneers. Additional 12mm on midsection bottoms. Additional Kevlar sheathing below upper chines.
Mast will probably be an ACT 185x65mm carbon fibre wing mast with double diamonds.
Auxilliary power will be either a Torqueedo electric outboard or a retracting counter rotating bow thruster set amidships.PV panels located on the outboard end of the aka and along the leeward edge of the cabintop. Batteries located in the ama.
It has been designed to be built in two hinged halves folded over to fit on a car towed trailer.
The centreboard foil is ogive asymetric and will be pivoted outboard to lift the float clear of the water ASAP, reducing drag, or pivoted inboard, to contribute significantly to righting moment and ultimate stability. I don’t
aim to use water ballast , just the boat’s speed and the apparent wind created to provide additional dynamic righting moment.
The bridgedeck aka is an inverted aerofoil, which contributes to rather than reduces righting moment whilst minimising drag, and will house a cockpit, storage and water tanks as well.
Windage on the main hull, particularly the bow topside is minimised and should also improve jib efficiency and encourage spray to fly off to leeward and not in your face…
Hello Rob!
Very nice looking boat you’ve got there!
We have clearly been thinking around the same lines and solutions, great minds think alike! (but dumb minds do too) (:
Do you plan for drumrudders or the kinds Brown/Harris use? I would really want drumrudders for the endplate effect and to be able to steer with boards halfway up. But the boards need to be so narrow/high ar to fit in to trunks that need to fit within the slim proa hull. (i think i need more total board area on Gardagast)
I have just like you planned the crossbeam to minimize airdrag and incoporate cockpit and storage, but mostly for light stuff like fenders and ropes( want to keep the heavy stuff far down in the mainhull as counterweight when the boat float on the pod)
One additional benefit with the solid wing beam is the possibility for a fold up srayhood!
Think i’ll settle there for now.
Really glad you posted your design! (maybe you need a name on it?)
/Garg
Static Righting Moment: 1503 kgm
Total righting moment including Dynamic RM: 3195 kgm
[....]
The centreboard foil is ogive asymetric and will be pivoted outboard to lift the float clear of the water ASAP, reducing drag, or pivoted inboard, to contribute significantly to righting moment and ultimate stability. I don’t
aim to use water ballast , just the boat’s speed and the apparent wind created to provide additional dynamic righting moment.
Could you tell us more about how you calculate the dynamic righting moment?
The foil seems to be straight. That should make it inherently unstable when angled in to pull down. If the foil comes out of the water a bit when sailing over a wave, the centre of pressure moves down, reducing the lever arm, so you loose stability. That has also been Paul Ashford’s experience with the tacking Bruce foiler he sailed about 40 years ago. It worked on both tacks on lakes, it was fine in a seaway with the foil to lee, but the foil tended to come unstuck when it was upwind in a seaway.
One way to counter that is to make the boat so wide that the Bruce foil overcompensates for the heeling moment and pulls the ama into the water. That would give you reserve stability, but would conflict with your aim to get the ama out of the water for reduced drag.
The other options are curved and hinged foils. An example of a curved fixed foil is the one on Sailrocket. That could give you what you want, though only over a limited range of heeling angles. Fritz Roth used that idea on his vector foil proa, and reports that his 8 metre long test boat worked very well. You can find youtube videos of model versions. Then on the Yahoo group, we had long discussions about what factors are relevant to scaling up his design. He then adopted the hinged foils proposed by Hagedoorn and by Costes. You can see a description of his current design at http://www.proadesign.com, and a description of the building of his latest boat at http://blog.proadesign.com/. The hinge design is ingenious. A model test in surf is at http://www.youtube.com/watch?v=1pK4olWjm2k. The movement of the hinged foil can be seen more clearly here: http://www.youtube.com/watch?v=8pjdoy4H3RQ
Tom Speer has analysed foil sections for proas. The ogive section is mediocre. He proposes a few alternatives, but note that the data are based on fluid dynamics software, not empirical measurements. See http://www.basiliscus.com/ProaSections/ProaIndex.html
Regards
Robert Biegler
Gargen,
Many thanks for your comments…...Lets call my design ” PROACTIVE 2”.
Rudders:
I belong to the 2 active lifting rudders outside of the main hull school. For space saving, for shallow water steering, for greater control in tight spaces and for ultimate safety: I would rather lose an entire rudder assembly than risk compromising the main hull below waterline. I can carry a spare rudder blade or two easily, but spare through hull rudder assemblies are not so practical to carry and are very heavy if engineered to be bulletproof anyhow…..You pay your money and take your choice!!
With regard to your design, I am not so sure that you need such big/deep rudders in a through hull design with both rudders active…Sailing with them half up could be interesting as well….My limited experience and observation on monohulls with two rudders is that if they are as big in area together as only one active rudder, then you are about right.
Canopy:
The canopy and the cockpit aren’t shown, but the cockpit has been designed so that 2 people can sit on the floor and be covered by a canopy. Spray and apparent wind blast and chill have to be big comfort and safety factors if you want to go long distances.
Regards,
Rob
Robert,
Many thanks for your comments…..
For the record, the foil righting moment, right or wrong, was a “fag packet” calculation using a foil of no specific section at 45 degrees using a lift cooefficient of 1.00. Notwithstanding your valid comments, I can already see from the Tom Speer info that this was optimistic…..Hydrofoils at speed in waves are sensitive and hypercritical. So whilst the idea of using them is very appealing, if I can’t find a broad range practical solution, the overall design isn’t dependent on them. The ama will plane without lifting foils.
I am grateful for the many links, some I was aware of. Another of Fritz Roth’s ideas, the jib attached to the weather shroud interests me as well. Do you know if he has ever set the jib on the other tack so to speak whilst going upwind??? If it works, then the drive generated becomes a significant righting moment and should improve VMG??
With regard to greatly increased righting moment, maybe a large (trolling) paravane is the answer?? Have you ever tried pulling one in at speed??
Regards,
Rob
Welcome Rob, from a fellow Tasmanian! I would love to see this proa built! Good luck with it.
Great looking design. What design tool, do you mind posting the file?
Quite sophisticated shapes. Will add to the build time. My thoughts are if experimental keep it simple.
12mm of timber + glass = a bit heavy. Look at Jzerro’s scantlings.
Rudders outboard. As on Harryproa. Looks pretty ugly and createa spray. Unless you plan on sailing in shallow water often, see / read what Sven has to say about his Newick style.
Looks like a high performance craft, no lee pod, is this wise?
Foil in ama, is this tilted out, does it lift or pull down? Lifting may actually work in reducing the drag of the ama, kind of counter intuitive?
Cheers
Mark
I have to second Marks question about the leepod. A small shelf to lee would not have to poke out far from the hull to stop the boat from going over.
I hink the weight increase easely will be justified when you can drive the boat to 98% instead of 80% (made up numbers).
You’ve got many valid reasons to mount the boards outside the aka, but i think spacesaving is not one of them because you “need” watertight bulkheads anddont want any weight at the bows anyway. On the other hand, a single bunk for sure weight less than a rudder…
Have you been thinking about where to put the hatch to the cabin? (something i’m struggling with Gardagast at the moment)
Maybe try 10°-20° angled to weather rudders to lift the aka some? (:
/Garg
Another of Fritz Roth’s ideas, the jib attached to the weather shroud interests me as well. Do you know if he has ever set the jib on the other tack so to speak whilst going upwind???
I am not sure what you mean. As far as I know, Fritz Roth used the windward staysail on both tacks. Only the jib at the stern was furled and the one at the new bow unfurled after a shunt. When Fritz was on the yahoo group, we never discussed the windward staysail, because it was not controversial, and I realised only last year what a good idea it could be. I have discussed that sail here in a thread on two new proa rigs at http://proafile.com/forums/viewthread/94/
With regard to greatly increased righting moment, maybe a large (trolling) paravane is the answer?? Have you ever tried pulling one in at speed??
My experiments have been limited to two sailing canoes, at modest speeds. I described both experiments, one a tacking sailing canoe, one a shunting proa, in AYRS Catalyst (http://www.ayrs.org/catalyst.htm). The online index lists the first article as being in Catalyst 3, but I can’t find it in the pdf copy. Perhaps it is where the pdf has a blank page. You might still like that issue for its article on a Bolger-designed proa. That proa’s rig is discussed a bit more in Catalyst 8.
The proa paravane I described in an article in Catalyst 23. Catalyst 22 also has a little proa content in some calculations on a self-righting proa.
My experiments with paravanes were restricted to pretty low speeds (because of the boats to which they were attached) and small waves (because neither Loch Lomond nor Trondheimsfjorden had much waves when I messed about with paravanes). I then went to hinged foils because I could never work out a good way of retrieving the unused paravane on a tacking boat, and the proa version suffers from extra drag from the attitude control foils. It could certainly be made cleaner than my improvised design in 2000, but I’m not sure that the increased righting moment would compensate for the extra drag. A hinged foil doesn’t need the attitude control foils, and I figured it would be faster.
For a high speed paravane, search youtube for “Swedish speed sailing challenge”. That is still flat water, though, and the people involved never published their paravane design in any place that I have seen.
Seaglider (http://seaglider.fr/Seaglider/Welcome.html) sells one for use with kites. Quite pricy, though.
Dave Culp pointed out that, in steady state conditions, ballast is always faster than a hold-down foil. You get the same increased displacement of your lee hull, but the foil creates extra drag when it generates that force. The foil might still win out in conditions that vary too much for you to adjust the water ballast precisely. However, my tests with model monohulls did not show greater speed for the boat with hinged foils. I attribute that to having two extra things breaking the surface and making waves, and to greater wetted surface. A proa would have only one foil, and it might gain by stable hull flying.
Regards
Robert Biegler
To answer some of the various questions posed as best as I can:
Scantlings:
I am looking to use pawlonia timber (http://www.portphillip.com.au/marine.html) which is two thirds the weight of gaboon/okoume plywood.Pawlonia is also more insulative, rot resistant, fire resistant and about as soft. So my scantlings weight will be the equivalent of 7-8mm of gaboon/oukoume plywood, Jzerro has closely spaced permanent stringers. I will have far fewer, in part due to the more curved shape. So I anticipate that in the end overall unit structural weight will be slightly lighter and stiffer than Jzerro.
Pods:
I have an 8.5 metre by 660mm wide pod in the form of heavily flared leeward topsides.The upper leeward chine will dig in at around 30 degrees, moving the CB outward by around a metre. At 90 degrees, the leeward chine (ie most of the vaka) will be be around 150mm above water. The cabin arrangement also adds significantly to this at 90 degrees and beyond. There should be less tendency to develop lee helm than a conventional pod digging in. It was also a way of taking volume out of the bow (which wind and waves see) and hiding it to leeward, so that it can still provide reserve buoyancy in extreme circumstances. It should be easier to build than a conventional pod and gives you more usable room below overall. I have also thought of fixing an inflated (or automatically inflating) rubber tube down the leeward side as a bolt on if found to be necessary and turn the proa into a RIB!!
Rudders:
I will be doing a lot of shallow water sailing, but in any case, the critical thing with rudders is the distance between bearings. With Rob Denney’s proas, the vaka has very low freeboard at the rudders and as a consequence the bottom bearing is very close to the water and does make a mess.
On Proactive 2 with much greater freeboard, the bottom rudder bearing is some 400mm above the water, so I expect far less wave contact.
Access Hatches:
I have two hatches, one near each end of the cabin. Underway, I will use the “aft” one to minimise water ingress below. I have always thought that a central access was perverse in the sense that you waste a large chunk of the greatest volume in a proa just getting below. You want cross ventilation anyhow.
Windward staysails:
I have often wondered what would happen if a staysail was hoisted up the weather shroud and then set on the opposite tack to the jib and main. In other words, if a proa is sailing on starboard tack, with the main and jib set accordingly, but you set the windward staysail on port tack. I would love to know what it would do for RM and VMG? Off the wind, it is a no brainer…....I will be using a full luff windward staysail for that if nothing else.
Regards,
Rob
Windward staysails:
I have often wondered what would happen if a staysail was hoisted up the weather shroud and then set on the opposite tack to the jib and main. In other words, if a proa is sailing on starboard tack, with the main and jib set accordingly, but you set the windward staysail on port tack.
If I correctly interpret your description, the resultant sail force would point up and aft. You would lift the ama and pull it back, giving you more weather helm.
I would love to know what it would do for RM and VMG?
Reduce both, I think. What you propose seems useful to turn the boat when shunting, but I don’t see any benefit while sailing in a straight line.
Regards
Robert Biegler
“If I correctly interpret your description, the resultant sail force would point up and aft. You would lift the ama and pull it back, giving you more weather helm.”
If the sails on the rest of the proa sailing hard on the wind on starboard tack were set for 25- 30 degrees apparent to the longitudinal centreline, the port tack windward staysail would be set for 60-65 degrees apparent to transverse centreline. I would guess that the resultant force would be up, as you say, but straight out to windward, not aft thereby improving VMG? If the CE of the staysail projected down prependicular to the luff was higher than CLR, that force should also result in a righting moment not a heeling moment?
If the sails on the rest of the proa sailing hard on the wind on starboard tack were set for 25- 30 degrees apparent to the longitudinal centreline, the port tack windward staysail would be set for 60-65 degrees apparent to transverse centreline. I would guess that the resultant force would be up, as you say, but straight out to windward, not aft thereby improving VMG?
Sorry, but in the mental image I get from your description I still don’t see how this would be possible. Perhaps you could draw it? Right now, what I get is this: the windward staysail is like the windward sail of a biplane rig. If I look at biplane rig catamarans, like Team Philips or a Trifoiler, you seem to describe sheeting the windward sail to towards the centreline so that the wind hits the side facing the leeward sail. Then the windward sail would pull aft and turn the boat to weather. But I am not sure why you shift reference frame to a transverse centreline, and how that angle is different from the apparently complementary angle to the longitudinal centreline. Could you just draw a bird’s eye viw of what you have in mind?
If the CE of the staysail projected down prependicular to the luff was higher than CLR, that force should also result in a righting moment not a heeling moment?
You would get a righting moment once the resultant force from the windward staysail crosses under the centre of buoyancy lower (not higher) than the CLR. Of course, the centre of buoyancy moves leeward as the ama comes out of the water, so this should be dynamically stable under some conditions. The staysail acts in the air like Bruce foil acts in the water, at least on the wind. You progressively lose that effect as you turn downwind.
You get the potential for having a balanced sail plan on a proa, you don’t need to raise and lower sails, and you get reduced heeling or even some righting moment as well. Seems like it might be a reasonable trade for some loss of efficiency upwind due to the inclination of the sail.
Regards
Robert Biegler
With all sails set on the same tack, a biplane as you put it, the staysail thrust is slightly forward and down, but above the CB / CLR so it would be a heeling force, which is good in light conditions where you want to take weight off the ama to reduce drag and increase speed. At some point, when you have enough heeling force, you “tack” only the staysail, so it is as per the staysail diagram attached. This hopefully means that the staysail thrust is now pulling the proa more or less directly out to windward hopefully improving VMG, and the heeling force should become a righting force, because it is working in pretty much the opposite direction????
The staysail would probably need to have a boom of some sort to have sufficient control of shape and angle of attack.
With all sails set on the same tack, a biplane as you put it, the staysail thrust is slightly forward and down, but above the CB / CLR so it would be a heeling force, which is good in light conditions where you want to take weight off the ama to reduce drag and increase speed.
Thanks. That sorts out one problem I had. I was thinking of a wider boat with a more inclined stay. If you reef a bit, then the downforce provides righting moment, not heeling moment. But you are right about your setup with a more steeply angled staysail and with full sail set. I just misunderstood what you meant because I was too focused on my own thinking about this subject.
At some point, when you have enough heeling force, you “tack” only the staysail, so it is as per the staysail diagram attached. This hopefully means that the staysail thrust is now pulling the proa more or less directly out to windward hopefully improving VMG, and the heeling force should become a righting force, because it is working in pretty much the opposite direction????
It would provide a righting moment, but you would get a greater effect if you did that with the more upright mainsail. It has a greater lever arm. Even better if you had a wing at the mast top that you controlled separately from the sail.
Nevertheless, all this stabilisation comes with increased drag. The force vector you drew for the windward staysail is impossible according to present understanding of physics. For the mainsail and jib, you have resultant forces that point aft of a line perpendicular to undisturbed air flow. You have lift and drag. You have drawn your staysail’s resultant force as pointing forward of that perpendicular. It has negative drag. If there were a wing profile with that feature, I could put it on a bunch of rotor blades, and set the rotor moving in still air. The negative drag would keep accelerating the rotor. I could take energy out of the rotor and out of the airstream that the rotor produces, without any energy being put into the rotor or airstream. A wing profile with negative drag gives you a perpetuum mobile. It would break the law of conservation of energy. Conservation of energy is both theoretically fundamental and empirically well supported, so I wouldn’t bet against it.
If you draw in a force vector with the same lift to drag ratio as your jib and mainsail, then tacking the windward staysail will slow you down and give you weather helm.
Regards
Robert Biegler
Many thanks Robert, nothing more to say…..other than the (spare) conventional jib proposed would fit as a staysail, so there is no harm in trying it if I ever get the proa on the water.
Regards,
Rob.