As previously mentioned the stability of Tuanella 3 was profoundly out of kilter and she road so high on the water as a finger tip could push her to one side or another - this despite a massive lead keel and sacks of aggregate against its sole.
.
This picture shows the water mark some 7 or so inches from the bottom.
She is really just sitting almost on knife edge.
The hull was of 2mm marine aluminium and this was patently too light. Although the cabin is of wood, perspex and aluminium section it was distant enough from the water line to aid toppling the craft.
Having decided at this stage to preserve the engine arrangement I set out to counter the stability with two outriggers. There were to be two but just making one for the moment is all I can manage. I have tried to arrange it so that it will fold up against the port side to aid transport and so, hopefully, all I shall have to do it lower it in the water and let the hinge and strut arrangement hold the pontoon in place. It is close to T3's hull but of a weight and buoyancy that should steady her.
Nothing of the gunwale fittings are attached here to T3 but the general idea of how she will lie is shown.
The general heftiness of the fabricated hinges and slides can be seen in the following.
Just a couple things of note about the fittings above: the double offset hinge rotates both on the hull and the pontoon. This is only at the stern end. Forward the hinge there rotates only on the hull.The attachment of both hinges is well above the envisage new water line. Not knowing quite where the pontoon will find its level the flexibility offered by the hinges will hopefully accommodate this. I expect the maximum displacement or draft of the pontoon to be about two inches in calm water.
There is a worry that when the craft is launched the weight of the pontoon will not be enough to offset the possibility of a tumble to starboard if there is rough water and wind from port side. I guess wearing a life jacket will be important.
Tuesday, September 22, 2015
Thursday, August 27, 2015
How Owls and The Tear Drop Design Are Connected.
On the bbc the other night a nature program on how owls fly without their flapping making a noise and alerting their prey.
The presenter highlighted the special features of their wing and compared them to a pigeon and a hawk. In the case of the owl it showed how feather 'tufting' absorbed sound and emphasised the fact that unlike the others it was a slow flying bird.
I think the pigeon was ill - placed in that group as it is not a hunting bird but more a seed herbivore. It needs speed however to escape predation and so perhaps its inclusion was permissible.
The differences in body shape were noted but the elephant in the room was that they did not stress how important that was in addition to the wing features.
What was so fabulous to see was the owl in flight, slowish, steady, infrequent flapping and mostly in descent and levelling off. What stood out was the shape of the owl in flight. Every feather adorning its marvellous face and neck standing vertical to present the blunt and non-streamlined presence that its face is and then this tapering very quickly to its sharp tail to present a true tear-drop form.
I contend that it is this as much or more than the wing form that enables it to course through the air silently and without ruffling the air it is in. This is easy to comprehend just visually. The broad wing spread of the owl announces it is designed for slow flight.
The presenter highlighted the special features of their wing and compared them to a pigeon and a hawk. In the case of the owl it showed how feather 'tufting' absorbed sound and emphasised the fact that unlike the others it was a slow flying bird.
I think the pigeon was ill - placed in that group as it is not a hunting bird but more a seed herbivore. It needs speed however to escape predation and so perhaps its inclusion was permissible.
The differences in body shape were noted but the elephant in the room was that they did not stress how important that was in addition to the wing features.
What was so fabulous to see was the owl in flight, slowish, steady, infrequent flapping and mostly in descent and levelling off. What stood out was the shape of the owl in flight. Every feather adorning its marvellous face and neck standing vertical to present the blunt and non-streamlined presence that its face is and then this tapering very quickly to its sharp tail to present a true tear-drop form.
I contend that it is this as much or more than the wing form that enables it to course through the air silently and without ruffling the air it is in. This is easy to comprehend just visually. The broad wing spread of the owl announces it is designed for slow flight.
Friday, August 14, 2015
Help required defining the geometry of Tuanella 3 - ? complex integrated conincal?
Tuanella 3 was made from a single sheet of aluminium. The remit was to have a hull like structure blunt (rounded) at one end and sharp at the other - subserving those fundamentals I hope to elucidate about the generality of most natural forms that find their way through a gas or fluid.
A thin sheet can be formed into a conical structure by bringing the ends of one side towards each other and the angle formed can be changed by overlapping those ends.
If the apex of the cone is closed and the overlap sealed then a container is generated. The standard laboratory funnel filter is made by indenting a disc of filter paper from a point on its circumference towards its centre and allowing the indent to overlap and lie flat on the cone so generated.
.............................................................
If an oblong sheet is cut anywhere along its length from its margins towards its centre anywhere a cone can be made. Choosing to do this in three places one can create a container which will float if the cut edges are sealed.
Unlike boats made from single sheets of metal where the sheet is sectioned and joined edge to edge
and generated angle at those joins the use of multiple cones results only flat and curved surfaces which in terms of boats makes for an aesthetic appearance.
Selectively cutting can produce many shapes with a range of cross-sectional profiles that approach
those seen in many boats with the sole of those shape varying from a rounded v to a flattish section that might be seen to offer a degree of bilge to the form.
A thin sheet can be formed into a conical structure by bringing the ends of one side towards each other and the angle formed can be changed by overlapping those ends.
If the apex of the cone is closed and the overlap sealed then a container is generated. The standard laboratory funnel filter is made by indenting a disc of filter paper from a point on its circumference towards its centre and allowing the indent to overlap and lie flat on the cone so generated.
.............................................................
If an oblong sheet is cut anywhere along its length from its margins towards its centre anywhere a cone can be made. Choosing to do this in three places one can create a container which will float if the cut edges are sealed.
Unlike boats made from single sheets of metal where the sheet is sectioned and joined edge to edge
and generated angle at those joins the use of multiple cones results only flat and curved surfaces which in terms of boats makes for an aesthetic appearance.
Selectively cutting can produce many shapes with a range of cross-sectional profiles that approach
those seen in many boats with the sole of those shape varying from a rounded v to a flattish section that might be seen to offer a degree of bilge to the form.
The general overall cross section is V and this offers a bilge that will plunge significantly before offering buoyancy. However if the hull is rotated laterally in the static situation that I propose for the catamaran then this plunge effect is diminished markedly and replaced with increased buoyancy and a tendency to plane. In the dynamic situation of a single hull driven by wind heeling will also rapidly reproduce this situation . Heeling will, of course reduce the directional stability the V section might offer but can't at least be countered somewhat if there are a pair of angled rudders. which is particularly good for the catamaran concept.
.....................................................................Tuesday, August 11, 2015
Some observations on the need for strength in hulls of catamarans.
I understand that one of the principle reasons the costs of catamarans is high related to the obvious ie there are two hulls. In the nature of any hull has to be the inherent strength by way of its shape to hold it shape and secondly retain attachments or resist separation of attachments like the keel, rudder, mast, engine, bulkheads. Not only do catamaran have over mono-hulls the spread of the load but especially when it comes to keels they mostly do without them stability being the mutual out-rigging of the other. If the underwater surface offers some directional form this too is a bonus .
I contend the reversed tear-drop form made in the single sheet manner I have described does this well as a mono hull but for the hulls of catamarans there can be another notable bonus. If the hull topsides are rotated inwards so as to make the outer sides nigh on vertical the increase in the free-board offered remarkable and with this rotation outwards of the bottom of the hull so too and significant increase in the boats stability. Of course the free-board of the inner sides is correspondingly reduced. This gunwales of these side now form the margins of the connecting pan like floor that will join them.
The deck is made from the 'roofing' that connects the outer gunwales.
The space that has been generated from doing this is quite staggering and all still without any intrusion of structures above the deck - pure central living space.
Geometrically the cross-section along its length is an isosceles trapezium (trapezoid in USA). Therein are inherent triangular derivatives that offer great strength here especially from the distance in height from the floor to the ceiling (deck).
In terms of offering a site for suspending a keel, fixed or lifting, placing the engine, chain lockers and workspace it is perfect aft wise and forward great for a mutual below deck dining and galley with immediate access to the hull containing the cabins, showers and heads. or otherwise it is perfect.
An above deck cabin and wheel house is easy to install between bulkhead and thus without structurally affecting the hull.
The internal rotation of the hulls means the forward 'flatness' of the sole become some v shaped offering more directional stability.
In the diagram I have treated each pair of hull identically by adding the two deck options and the two floor options . In each pair I have shown the inner side of the hull cut down to bring the floor down .
Even if this is not done in the lower pair the shaded area represents the gain over the upper pair and this is a feather off one and half times the cross section of one hull and this is without the curvature of the deck added in. Indeed a great increase in space and hopefully the movement of buoyancy outermost.
I contend the reversed tear-drop form made in the single sheet manner I have described does this well as a mono hull but for the hulls of catamarans there can be another notable bonus. If the hull topsides are rotated inwards so as to make the outer sides nigh on vertical the increase in the free-board offered remarkable and with this rotation outwards of the bottom of the hull so too and significant increase in the boats stability. Of course the free-board of the inner sides is correspondingly reduced. This gunwales of these side now form the margins of the connecting pan like floor that will join them.
The deck is made from the 'roofing' that connects the outer gunwales.
The space that has been generated from doing this is quite staggering and all still without any intrusion of structures above the deck - pure central living space.
Geometrically the cross-section along its length is an isosceles trapezium (trapezoid in USA). Therein are inherent triangular derivatives that offer great strength here especially from the distance in height from the floor to the ceiling (deck).
In terms of offering a site for suspending a keel, fixed or lifting, placing the engine, chain lockers and workspace it is perfect aft wise and forward great for a mutual below deck dining and galley with immediate access to the hull containing the cabins, showers and heads. or otherwise it is perfect.
An above deck cabin and wheel house is easy to install between bulkhead and thus without structurally affecting the hull.
The internal rotation of the hulls means the forward 'flatness' of the sole become some v shaped offering more directional stability.
In the diagram I have treated each pair of hull identically by adding the two deck options and the two floor options . In each pair I have shown the inner side of the hull cut down to bring the floor down .
Even if this is not done in the lower pair the shaded area represents the gain over the upper pair and this is a feather off one and half times the cross section of one hull and this is without the curvature of the deck added in. Indeed a great increase in space and hopefully the movement of buoyancy outermost.
Wednesday, April 1, 2015
A reiteration of aims
The idea that in nature, for the preservation of energy and to aid and avoid predation in any fluid, liquid or gas, the presence of a rounded front and pointed tail, is fundamental.
The sheer instability obvious in the mono-hull I built rather puts a single hull out of the picture in the matter of building a fast and cheaply built cruising sailing boat. But that fault, its lightness, may indeed be it's salvation when used as one of a pair in the building of a catamaran.
The success of catamarans on skids and thus low wetted surface areas was shown in the last America's Cup. Their instability however was also sadly demonstrated with the loss of life and it must have struck many as obvious that in heavy weather of any sort purchase on the sea and thus stability was going to be pretty precarious.
Here the use of two hulls, made similarly as the one before, from a single sheet of metal, means they can be absolutely identical and such reinforcements as needed on the sole of the hull or any other part can be identical and utterly flush as there is no 'belly or 3rd dimension' to it. Those reinforcements should leave no gap and riveting them in place with perhaps a thin lay of silicone filler should offer a very sound strengthening.
Here the use of two hulls, made similarly as the one before, from a single sheet of metal, means they can be absolutely identical and such reinforcements as needed on the sole of the hull or any other part can be identical and utterly flush as there is no 'belly or 3rd dimension' to it. Those reinforcements should leave no gap and riveting them in place with perhaps a thin lay of silicone filler should offer a very sound strengthening.
Wednesday, March 4, 2015
An Update On What I Am Doing Now.
The failure to appropriately ballast T3 left me with two options. One was to re-ballast: this would mean the opening to the engine well inside the boat would be so close to the waterline that the chance of swamping the boat from inside would be great - dangerous from heeling and rocking except perhaps on a mill pond; removing the engine well and the outboard engine arrangement and replacing it with a hefty inboard well forward where there is maximum buoyancy, and offering up a long shaft along the sole with a standard propeller housing aft would solve this. Thence I could re-ballast to my heart's content.
The other option, which I am now taking, is to deprive the boat of the hefty lead filled aluminium ballasting keel and take the view that she will sit on the water, precariously of course, on her sole.
She will sit like those pond insects - water skaters - barely infringing on the water's surface tension.
Of course she will be impossibly unstable like that and tip immediately.
That is where the outrigger I am building comes in. That, by virtue of its weight and disposition will keep her upright and hopefully, because of its minute draft, and bow form, offer little resistance.
Such a plan means I can keep the present engine well arrangement.
I am doing this before the re-ballasting mentioned above simply to investigate the potential of the option. I am not hopeful of a resplendent outcome but it is a 'suck it and see' situation.
The cumbersomeness of transporting what I'm building pressures me to build in some sort of folding
mechanism for the outrigger to lie against the hull during transit. Such an arrangement required some modelling and I show below some of it, however crude, by way of determining the hinge arrangement. This latter has to accommodate the lines of the hull, the folding of the outrigger to the hull, and fixation to the hull when it has been lowered.
Such hinging I'm sure one can appreciate has to be rather outsize. I show a mock up in mdf and wood to get a perspective and the clearances right. I propose to make it in aluminium plate, and the welding of aluminium tubing to it to accommodate stainless steel rod to form the hinge. I have tried to demonstrate on the model the need for the hinge mechanisms to have a universal flexibility to allow for the curving lines of the hull.
This shows the general lie of the pontoon, fore and aft, and is pretty close to where I expect it to sit against the hull when both are in the water. It looks very long in the above but is only 8 ft and is gently tapered, the width across the nose being shorter than that across her stern. This is to keep her outer side parallel to the T3's lubber line and the inner side pretty much the same with respect to the hull side.
The other option, which I am now taking, is to deprive the boat of the hefty lead filled aluminium ballasting keel and take the view that she will sit on the water, precariously of course, on her sole.
She will sit like those pond insects - water skaters - barely infringing on the water's surface tension.
Of course she will be impossibly unstable like that and tip immediately.
That is where the outrigger I am building comes in. That, by virtue of its weight and disposition will keep her upright and hopefully, because of its minute draft, and bow form, offer little resistance.
Such a plan means I can keep the present engine well arrangement.
I am doing this before the re-ballasting mentioned above simply to investigate the potential of the option. I am not hopeful of a resplendent outcome but it is a 'suck it and see' situation.
The cumbersomeness of transporting what I'm building pressures me to build in some sort of folding
mechanism for the outrigger to lie against the hull during transit. Such an arrangement required some modelling and I show below some of it, however crude, by way of determining the hinge arrangement. This latter has to accommodate the lines of the hull, the folding of the outrigger to the hull, and fixation to the hull when it has been lowered.
Such hinging I'm sure one can appreciate has to be rather outsize. I show a mock up in mdf and wood to get a perspective and the clearances right. I propose to make it in aluminium plate, and the welding of aluminium tubing to it to accommodate stainless steel rod to form the hinge. I have tried to demonstrate on the model the need for the hinge mechanisms to have a universal flexibility to allow for the curving lines of the hull.
This attachment near the water line needs some flex-ability there as the pontoon outrigger has to find a 'best fit' position in relation ot the hull when it is lowered into the water. Stabilisation will come from a fore and aft spare which will come from the gunwale to the far side of the pontoon. These too I hope to make adjustable, again to fine tune a 'best fit' when she is in the water. I hope the triangulation provides a stiff enough purchase!
The shown siting of the hinge below is too central but was just to show the hinge above in place.
It also shows, as does the picture below at the aft end, the added bolstering of the pontoon deck where it will receive the hinges and gunwale struts.
In both a central pillar connects the deck to the bottom and thus hopefully spreading the stresses between it and the hull.
This shows the general lie of the pontoon, fore and aft, and is pretty close to where I expect it to sit against the hull when both are in the water. It looks very long in the above but is only 8 ft and is gently tapered, the width across the nose being shorter than that across her stern. This is to keep her outer side parallel to the T3's lubber line and the inner side pretty much the same with respect to the hull side.
Tuesday, January 6, 2015
Some Observations On Her Run On The Pond.
The hulls are steel and heavy and the rig probably barely proportional for her size. Despite this, and in the absence of any self steering and rig adjustment for her aspect to the breeze, she got along at a fair old pace. I trust that this is a reflection of her hull shape. The almost complete absence of heel means there's virtually no spill as one would get with a mono-hull so in a real life situation the rigging must take an immense hammering when there are gusts - of course if the hull is compliant and the set of the sails is good then the hull speed should shift considerably - such compliance safeguarding the rig to a degree.
Of course one can have hefty rig or just be vigilant in easing it in gusts and blows.
What I did notice was that when the breeze was stronger and more aft that her nose dug in somewhat. naturally more on the lee hull, and this despite having most of her buoyancy forward and with her rounded nose.
How much more would this have been the case had the bow been fine and the bulk of the buoyancy aft!
One of the prime motives for proposing the generality of the reverse hull idea is that it might be a safer one when running before the weather and sea.
On the pond one of monohulls, well laden with lead ballast, showed particularly good steerage, going almost faultlessly straight when pushed from the shore. When pushed out with the sharp end as the bow there was no directional stability at all. I can suggest reasons for this though I don't know how valid they are.
As the bow ploughs into the water, at that front, there is likely to be a quite a mixed population of eddies and waves etc present at the time and then those generated by the forward movement of the hull, both in the water, at the interface and in the air above these. One would think that a sharp bow would generate less forward disturbance if any at all. But like the keen edge of an axe descending on a block of wood slipping rapidly into what would be the mean of the grain(s) in the wood, the sharp bow with much of it above as well as under the water now finds quickly the mean of the water currents, edies, and any wind above, and the hull mass like the hefty back of the axe head allows those influences on the bow to determine her direction.
In the case of a rounded bow its bluntness is aggravating the water it is entering already, compressing and generally lining up at right angles to itself that population of variant forces and making them one
or less numerous. Cut into them it must the bow now is pushing through this somewhat prepared and now more homogeneous milieu. It parts and such banked up energy as occurs from this parting forms a pressure head, equalish on both sided of the lubber line and as the greatest width of bow curvature passes this it dissipates its energy in squeezing the hull aft of this greatest curvature (width) forward.
I might have said it before but I heard somewhere that perfect hull would leave no wake.
Of course one can have hefty rig or just be vigilant in easing it in gusts and blows.
What I did notice was that when the breeze was stronger and more aft that her nose dug in somewhat. naturally more on the lee hull, and this despite having most of her buoyancy forward and with her rounded nose.
How much more would this have been the case had the bow been fine and the bulk of the buoyancy aft!
One of the prime motives for proposing the generality of the reverse hull idea is that it might be a safer one when running before the weather and sea.
On the pond one of monohulls, well laden with lead ballast, showed particularly good steerage, going almost faultlessly straight when pushed from the shore. When pushed out with the sharp end as the bow there was no directional stability at all. I can suggest reasons for this though I don't know how valid they are.
As the bow ploughs into the water, at that front, there is likely to be a quite a mixed population of eddies and waves etc present at the time and then those generated by the forward movement of the hull, both in the water, at the interface and in the air above these. One would think that a sharp bow would generate less forward disturbance if any at all. But like the keen edge of an axe descending on a block of wood slipping rapidly into what would be the mean of the grain(s) in the wood, the sharp bow with much of it above as well as under the water now finds quickly the mean of the water currents, edies, and any wind above, and the hull mass like the hefty back of the axe head allows those influences on the bow to determine her direction.
In the case of a rounded bow its bluntness is aggravating the water it is entering already, compressing and generally lining up at right angles to itself that population of variant forces and making them one
or less numerous. Cut into them it must the bow now is pushing through this somewhat prepared and now more homogeneous milieu. It parts and such banked up energy as occurs from this parting forms a pressure head, equalish on both sided of the lubber line and as the greatest width of bow curvature passes this it dissipates its energy in squeezing the hull aft of this greatest curvature (width) forward.
I might have said it before but I heard somewhere that perfect hull would leave no wake.
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