As the real Doug is now blogging ... adieu.
http://forums.sailinganarchy.com/index.php?app=blog&module=display§ion=blog&blogid=36
Friday, February 4, 2011
Wednesday, December 1, 2010
High Performance Monofoilers-altitude control
One very interesting development over the last year (and sure to be repeated on other boats) is manually controlled altitude that by-passes the wand on the 26' Mirabaud. The guys on the boat say it is particularly useful in choppy water where the wand can create a real bumpy ride.
I've foiled my own 16' boat using a manual control system* and despite some problems I feel it is a great way to foil and I think it has great potential in racing foilers. Here is a post from last year quoting TomSpeer on manual control of the mainfoil flap:
" If you look at the conditions for stable flight, the forward foil must have a relatively higher heave stiffness than the rear foil, and the rear foil must cause a greater change in pitching moment with a change in angle of attack than the forward foil. This is why wand feedback to the forward foil and a fully submerged aft foil work so well together. The heave stiffness of the aft foil is virtually zero, so it does all the job of stabilizing the craft in pitch. The forward foil then is totally responsible for controlling the craft in heave.
Manual control of altitude via the forward flap makes sense, since that is the surface that really controls heave. But the big difficulty is having enough control power to handle both the dynamic change in lift needed by the control system, and being able to trim out the change in lift due to speed. With direct gearing between the wand and flap and the boat flying at a constant pitch attitude, the only way for the control system to trim out the increase in speed with lift is to deflect the flap upward, and because of the gearing between flap and wand, this means flying higher.
If the boat is trimmed bow down as the speed changes, then the reduced angle of attack will compensate for the speed and the boat can fly at its design height with the foil centered (on average). One way to get this pitch trim is with manual control of the stern flap. The speed changes less rapidly than flying through waves or even being hit by gusts. So pitch trim with speed makes sense for manual control.
It might be possible to get some automatic speed trim by clever manipulation of the hinge moments on the rudder flap. Aircraft use a device called a "down spring" to augment their speed stability. A spring with a low spring constant is used to apply a near constant nose down force to the controls. This has to be trimmed out with the trim tab. But the force from the trim tab depends on speed. So as the speed increases, the tab effectiveness increases and moves the elevator in the nose-up direction. This makes the aircraft climb, which reduces the speed.
The opposite could be applied to a hydrofoil. If the rudder flap were deflected upward with a spring, increasing speed would reduce the deflection. This would make the boat trim more bow down, reducing the flying height in much the same way as the manual pitch trim described above. You could also divide the rudder flap into two parts - one driven by the spring and the other under manual control.
Naturally, the spring force would control the amount of automatic trim change. It's better to get the force from deflecting a long, weak spring a lot, than by deflecting a short, stiff spring. This makes a bungee cord ideal for the purpose. " Tom Speer
(* also have used a manual system on two different rc boats with great success )
Thursday, November 18, 2010
18' Tri vs F18 Cat : potentially the full potential
I think an area worth exploring is what the potential is for an 18' tri-as well as how much of that potential is required to whip an F18.
This is an example of what the full potential of an 18' tri is, potentially
MAX RM:
1) F18-- crew CG at 11' from lee hull CB( 320 X 11= 3520ft.lb.) + boat CG at approx. 3.8' from lee hull CB with windward hull just flying( 396 X 3.8= 1504 ft.lb.)
TOTAL RM = 5024 ft.lb.
2) 18' square tri(18 X 18)-- crew CG at 21' from lee hull CB( 21 X 320=6720 ft. lb.) + boat CG at approx. 8.75' from lee hull CB with main hull just flying(396 X 8.75= 3465 ft. lb.)
TOTAL RM = 10185 ft. lb.
====================
So the max RM from a square tri with the same weight crew as an F 18 is
2.02 times that of an F18(or more). It is probably possible to build a square 18'tri at the same weight as an F18-the Gougeons built a C Class tri(25') with an 18' beam that weighed 300 lb. in 1969.
My personal opinion is that this MAX RM tri is not necessary to beat an F18. A tri with less max RM would still be more powerfull than an F 18 yet allow the crew to sit in a much more comfortable position. For the tri to work in light air as well as heavy air it is absolutely critical to use two lifting foils on the main hull: in light air they allow the boat to fly the main hull in 5 knots of wind. In every condition they add tremendous pitch control to a very powered up boat.
=======================
The use of foils is becoming more and more apparent on monohulls and multihulls alike. Foils are tools that can modify characterisics of a boat such that what might be untenable with a foiless design becomes possible with foils. Like an 11' monohull that beats all beach cats under 20'!
A boat does not have to be fully airborn to be using foils successfully-"foil assist" is probably one of the most overlooked applications of foils.
Foils can add stability where only weight worked in the past, they can drastically modify the pitch characteristics of any boat. They can improve handling in rough conditions. They can contol the angle of heel of a trimaran(or catamaran)-and more.
They can't just be tacked onto a design-they have to be carefully implemented.
The absurd sentiment that "because it hasn't been done before it can't be done now" is nonsense.
Carefull, modern, innovative design can make a high performance "beach tri" a reality that will be faster on the water and more comfortable to sail shorthanded or with a crew at a cost comparable to top end cats.
I've put forth some ideas that I think could be part of such a design but by no means are my ideas the last word on the subject.
More Comfort- More Speed- Wide crew range(singlehanded or doublehanded with MAX power)
==================
See Martin Fischer interview about the use of foils in multihull design: http://catsailingnew...in-fischer.html
---------------------
I'll post some specs comparing the "low powered" daysailing version of the 18 tri with an F18. What is very critical to realize is that on either the high powered version or the daysailer the boat will(must) fly the main hull in as little as 5 knots of wind-that is absolutely critical to the success of either version. The boat is simply too wide with too much RM(esp. the daysailer version) to do that without the foils on the main hull. After the mainhull lifts off and speed increases the foils will UNLOAD until ,at some point, the ama takes the full load(either a planing ama or ama+ foil).
The wand is set to control the heeling angle of the boat like it controls altitude on a normal full blown foiler like a Moth. There is a side benefit to using the foils for early liftoff of the main hull and pitch control: because the wand is set for a specific altitude(heeling angle) if the boat begins to exceed that angle even by a little the wand will cause the main foil to pull down. This can be used to sail the fully powered up
daysailer version singlehanded in the same maximum pressure it can be sailed doublehanded.
Monday, May 17, 2010
Trapwing model opps I mean prototype
This is a unique design that uses ballast in a sealed wing in several different versions.
Yes, there are numbers and yes there are pictures of a model of the prototype, cause that's how I roll.
Here are some details:
-----------
Trapwing Prototype: LOA 17' 8"(5.38m) Beam hull-3.25'(1 m) overall 12'(3.66m)(subject to testing) Weight- hull 155lb ballast-wing 80lb(36.3kg)-180lb(81.8kg)(variable and subject to testing) keel 0-80lb(36.3kg)(subject to testing)dinghy version-no keel. SA-upwind 100sq.ft(9.3sq.m)-180sq.ft(16.7 sq.m) variable downwind 200sq.ft(18.6sq.m)-360sq.ft(33.46sq.m). (variable and subject to testing) crew-singlehanded-120lb(54.5kg)-220lb(100kg) (variable and equalized under class rules- subject to testing) crew position for racing on the centerline inside boat, fixed athwhartships, variable fore and aft
--------------------
1) Sail area to be between 100sq.ft(9.3sq.m) and 180 sq.ft(16.7 sq.m) a-different rigs b-different amounts of ballast
2) Ballast wing to be supported by trapeze wires and unique retention system that allows wing and ballast to slide simultaneously, allows athwhartship pivoting and fore and aft movement. a-version one will use two aluminum tubes with sliding external tray- the tubes and tray move simulataneously: -attachment system allows wing- with weight centered-to be levered up and then pivoted from a position 90 degrees to the CL to a position parallel to the centerline for transport and stowage. -weight can be added or removed in small increments. -fore and aft pivot/sliding tube is mounted to the boat slightly offset from the CL to allow room to retract board/keel. -aluminum tubes terminate at outboard ends in buoyancy pods-pods will be changeable as determined in testing. -sliding ballast tray and structural design of wing to be capable of 180lb(81.8kg) max ballast @9'(2.5m) from CL; ballast completely adjustable in the range of 80(36.3kg) to 180lb(81.8kg).
b-version two is a slightly curved(athwhartship), molded and sealed(with sealable access to ballast tray) wing with an internal sliding ballast tray. This version will be the final version and incorporates all the features of version one with significantly increased sealed buoyancy. c-Wing movement by manual or electric means. Minimum electrical movement speed 4' per second. Minimum electrical "stamina" on single battery-12 hours at a rate equivalent to a approximately 60 (full track)tacks per hour. Now I know that this is illegal based on current US Sailing rules, but rules are for wimps.
------
3) Crew Position a-version one-racing position-allows crew to sit in an extremely comfortable seat that is fixed athwhartship and slides fore and aft adjustably while sailing. -extremely wide crew weight range:for racing lower tray attached to seat may contain ballast used to equalize crew weight in the range of 120lb.(54.5kg) to 220lb.(100kg) -seat may be moved manually or electrically. b-version two-center seat is removed and two fixed carbon seats with backrests are "plugged-in" to each side deck.
-- 4) Rigs to be tested are main and jib, main alone, jib alone, with and without an asymetrical spinnaker and no sails at all. a-asymetrical will be tested as permanently mounted off a bowsprit(a la Weta tri) or retracted into a trough with roller(a la Viper) and a retractable pole (a la the local strip club). b-mast to be sealed with masthead floatation in an endplate configuration. Some buoyancy possible in head of sail.
-- 5)-Daggerboard/ keel/rudder a -boat will be tested with and without a retractable "lifting keel" which would essentially be a carbon daggerboard with the minimum ballast required(determined in testing) to right the boat from a pitchpole(where the wing buoyancy may not significantly help). b-self-righting from a knockdown or pitchpole is a required design element for any version of the boat used for disabled sailing.
c-a turbo version of the boat will not use a ballasted keel and may not be suitable for disabled sailing but this will be determined in testing. d- the daggerboard may include as standard a lifting hydrofoil designed to provide "foil-assist" to reduce wetted surface and in conjunction with the rudder hydrofoil improve the pitch and planing characterstics of the boat. e-a fully flying hydrofoil system will be tested as will a fully flying system that allows the boat to fly downwind only(requiring less upwind SA and less ballast). f-rudder will be retractable with a t-foil, and a j-foil or is it a k-bulb, or an f-boat I forget, no wait it's a c-cat.
6)-On the Beach a-the boat will be able to be easily beach sailed with a dolly incorporated into the trailer design to make it very simple to go from trailer to water. A "power assist" dolly may be available, this 20' crane can also be used to park your car if required.
7)-Performance a- the goal is to develop a high performance planing sailboat that can be safely sailed from a center crew position by disabled or able-bodied sailors. I am hoping to be able to achieve an SCP/total weight of 30% or slightly better though that is just a target and a less powerfull version with numbers and performance more like a Windmill or Tasar, or Optimist may be perfectly acceptable. The use of foil-assist technology will help to achieve the performance goals, or make the boat as slow as molasses, Full flying foiling is possible in a selfrighting boat-particularly one with the righting assist this boat has from version two of THE Wing. This wing was licensed to Larry for his little trimaran that he sailed off the coast of spain.
The concept has extraordinary potential and it will be a blast finding out just what she'll do. Now I just need to find the remote control.
Sunday, November 8, 2009
Veal Heel for Multihull Foilers
One of the most recent major contributions to the physics of sailing has come from the little Moth monofoiler: it is called "veal heel" after Rohan Veal who developed it.
Nothing new about heeling a boat to windward except when that boat is flying on hydrofoils. In that case with the boat heeled to weather the Righting Moment(RM) is increased by the amount the boat and crew CG move to weather of the center of lift of the foils.
Not only that but the struts(daggerboard and rudder) supporting the hydrofoils are unloaded and a component of the hydrofoil lift acts to weather improving upwind vmg.
Multifoilers,to date, have either sailed level or heeled like a "normal" sailboat.( except for an unsuccessful experiment in the C class)
I think there may be a better way on a high performance trimaran that would use very small "amas" like the Rave but with a major difference: the new boat would use two foils-like a Moth- for boat speeds up to say, 20 knots. After that the boat would deploy(retractable) very small foils from the vicinity of the windward ama that would generate downforce to increase RM.
I did a rough comparison of two boats each weighing exactly what a Rave does and the wetted surface is less at least up to 30 knots boat speed but whats more drag is less again, at least up to 30 knots. This thing could be designed to be MUCH lighter than a Rave(368lb) and could be substantially faster in 5-20 knots of wind.
But what is really cool is that the new concept foiler would sail with "veal heel" with the attendant advantages upwind.
Comments welcome.....
Nothing new about heeling a boat to windward except when that boat is flying on hydrofoils. In that case with the boat heeled to weather the Righting Moment(RM) is increased by the amount the boat and crew CG move to weather of the center of lift of the foils.
Not only that but the struts(daggerboard and rudder) supporting the hydrofoils are unloaded and a component of the hydrofoil lift acts to weather improving upwind vmg.
Multifoilers,to date, have either sailed level or heeled like a "normal" sailboat.( except for an unsuccessful experiment in the C class)
I think there may be a better way on a high performance trimaran that would use very small "amas" like the Rave but with a major difference: the new boat would use two foils-like a Moth- for boat speeds up to say, 20 knots. After that the boat would deploy(retractable) very small foils from the vicinity of the windward ama that would generate downforce to increase RM.
I did a rough comparison of two boats each weighing exactly what a Rave does and the wetted surface is less at least up to 30 knots boat speed but whats more drag is less again, at least up to 30 knots. This thing could be designed to be MUCH lighter than a Rave(368lb) and could be substantially faster in 5-20 knots of wind.
But what is really cool is that the new concept foiler would sail with "veal heel" with the attendant advantages upwind.
Comments welcome.....
Thursday, October 22, 2009
60' Moth-A Preliminary Detailed Design Exploration
60' Moth-A Preliminary Detailed Design Exploration
Please read the whole thing if you're interested. I consulted with a naval architect on this and tried to be as detailed a possible. Questions and comments from those interested are encouraged.
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60' MOTH-A Preliminary Detailed Design Exploration
==================================
I've long been convinced that the bi-foil revolution in dinghy design sparked by the Moth Foiler has potential for larger boats as well. The Out 95 guys in the UK and Sean Langman are also exploring this idea-among others. I decided to look at the numbers for a scaled up Moth just for the hell of it. I was surprised by the results.
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I) The base boat: LOA- 12.75', SA- 86 sq.ft.;weight: 60lb.hull + 150 lb. crew =210lb.s all up.
II) Scaling up:
*A) Sail Area-Since sail area varies as the square of length I squared 12.75(162.5) and squared 60(3600). Then I divided 3600 by 162.5 and multiplied the result by 86(Moth SA) . So the scaled up SA=1905sq.ft.----------------------- ****
Weight- Weight/displacement varies as the cube of the length. So I cubed 12.75 (2072.67) and cubed 60(216000).Then I divided 216000 by 2072.67 and multiplied the result by 210(Moth sailing weight). So the weight of the scaled up boat is 21,884 lb.'s.----------
III) Analysis/judgement calls- The most surprising thing when I was first doodling with these figures is the weight. At almost 22,000 pounds the scaled up Moth was way heavy by comparison to an ORMA 60 trimaran(12,000lb.'s) and to L'hydroptere(11,975lb.'s). But the defining characteristic of the Moth above all else is that it is a MONOHULL. So to preserve that characteristic at this length I decided that it would be important that the boat was selfrighting like any other(hopefully) 60'monohull. The "weight budget" certainly would allow that.
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NOTE:VERY IMPORTANT: the resulting 60'monofoiler IS NOT, REPEAT NOT a scaled up Moth as a carefull reading of this Design Exploration will reveal.
This Design Exploration reveals that while this self-righting 60' monohull foiler is possible and has speed potential AT LEAST equal to the ORMA foil assist trimarans it is nonetheless on the leadingedge of what is possible today.
=================================
So this is what I came up with after playing with the numbers for some time and running the whole thing by a friend who is a naval architect:
60' MONOFOILER-----------------------------
1)LOA-60'-------------------------------------
2) Target Beam 50'-increase from scaled up Moth; about same proportion as aeroSKIFF 14(see post#15 Peoples Foiler Thread)
3)Target SA: 2500 sq.ft.-increase from scaled up
Moth.------------------------------
4)Target Minimum all up sailing weight including 5231 lb.s on an 18' 60° canting strut: 14,731lb.'s.--------------------------------
5) Target boat weight w/o canting keel ballast:
9500lb.'s--------------------
6) Maximum additional ballast: 3771 lb.'s water ballast in a sliding tank-perhaps sliding within forward cross beam or just aft of beam. Tank is filled while over hull to limit weight of plumbing requirements. approx. dimensions: 1.5' X 6' X 6.4'. Possible fore and aft ballast sliding system .----------------------------------------
7) Weight with maximum ballast:18502lb.'s(plus 2-4 crew)
==================================
Summary:
-LOA*60'---------------------------------------
-Beam-50'--------------------------------------
-SA 2500sq.ft.----------------------------------- -Displacement:
14,731lb.'s ; Max: 18502---
-Draft(off foils) max
18'-------------------------
30 sq.ft. main foil; 15 sq.ft rudder
foil-------*
===============================================
COMPARISONS--------------------------------
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D/L ratio- 60' Monofoiler: 30.4--------------- D/L ratio- Orma 60/L'hydroptere: 24.8------
Bruce Number-60' Monofoiler: 2.03---------
Bruce Number-ORMA Tri: 2.39--------------
Bruce Number-L'hydroptere:2.65------------
(Bruce number is the sq.rt .of SA divided by the cube root of displacement)----------- --------- For what it's worth, the following comparison is between the 60'Monofoiler and the 60'ORMA trimaran.And I consider it one of the most important comparisons of all. The ORMA trimaran is presumed to have 60% of it's displacement supported by a "banana foil", with 30% of it's weight supported by the ama while flying the main hull. For this comparison the 60'Monofoiler is presumed to be flying on just two foils. The vertical fins of neither boat are included and both sides of the foils are included:
1)Orma 60-estimated ama wetted surface 124 sq.ft; estimated foil wetted surface 32 sq.ft.(both sides) Total 156 sq.ft. Now this figure is divided into SA(3000sq.ft.) giving 19 sq.ft. of SA per sq.ft.of wetted surface.
2) 60'Monofoiler Mainfoil area(both sides): 60sq.ft..Rudder foil area(both sides) 30sq.ft.. Total is 90 sq.ft . Dividing SA(2500sq.ft.) by this figure gives 27.7 sq.ft. of SA per sq.ft. of wetted surface.
==================================
**Notes and Design Considerations
( see below for "More notes..." including lift calculations, foil
loading and more)
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A) The number one design consideration for this boat was that it was self righting and that it would qualify as a monohull under any rule. Therefore it does not have buoyancy pods that in any way resemble or that could function like a hull-simple rectangular spaces at the maximum beam supported by carbon cross tubes. These buoyancy tanks in combination with the 18' 5000+lb. 60° canting bulb would prevent capsize and or right the boat from a knockdown. The weight in the bulb was specifically chosen to be 1.5 times what would be required to right the boat from a pitchpole. The canting keel could be explored a lot since it is relatively light for a 60 footer(5200+lb.'s). It would be ideal for it to be clear of the water when the boat is foiling-at least above 20 knots.
When an Orma tri fly's the main hull it does so with about 2lb. per sq.ft. of windpressure on 3000 sq.ft. of sail. The 60'Monofoiler with max ballast can sail with it's maximum SA in about the same pressure. And in lighter conditions it can ditch up to 3700+ lb.'s of water ballast facilitating relatively light air take off in an 9-12 knot wind.------------------------------
(see Righting Moment below)
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Preliminary conclusions:
It appears to me that the 60' monofoiler could be built but right at the top end of available technology.It would be likely to equal a multi of it's own size that did not use foils and appears to have more SA per sq.ft. of wetted surface than even an ORMA tri though especially in light air the ORMA would be faster since it can retract it's hydrofoil . The concept of an extremely fast selfrighting hydrofoil holds a lot of promise.
===================================
--------------------------------
More notes and references:
1) Righting Moment---------------------------
When off the foils the heeling arm (CE-CLR) is 43'. When on foils it is 51.75' . Hull bottom clearance to water is 10.75'. On foils max draft ,level,is 5'.
This boat is a monofoiler and as such will be sailed heeled to weather 15° at maximum righting moment.
Elements of Righting Moment:
A) rig CG is approximately at the
CE; 1460lb. @ 14.5' to weather= 21,170ft.lb.
B)canting bulb- 5,231lb.'s at 60°( 15.6') +
3' weather heel =5231 X 18.6'= 97,296 ft. lb.'s.
C)Hull 8040 X 5'to weather= 40,200ft.lb.
D)rack(deck) ballast 23' = 6' to weather
=29 X 3771= 109,359 ft. pounds
================================================
MAXIMUM RIGHTING MOMENT= 268,025 ft. lb.'s (A+B+C+D above)
MAXIMUM PRESSURE WITH 2500sq.ft.(268,025 divided by 51.75=5179. Divide 5179 by 2500(SA) = 2.07 lb.
================================================
2) The 50' beam could be one "wing" but would probably work better as two beams supporting a fixed empty "tank" at each end for buoyancy. A small tank containing up to 3770 pounds of water will also slide across the forward beam or just behind it. For the sake of getting the boat defined as a monohull based on whatever rule the buoyancy would not look like or function like a hull while normally sailing. In the event of a knockdown it would help to right the boat. I've talked with Alex of the OUT 95 project and he says their solution(ultra narrow hull with very wide wings on a 32 footer) is legal under the rules. Exactly which rules he was referring to I'm not exacly sure.
********The hydrofoils on this 60' monofoiler are in the hull : one mounted on the daggerboard and one mounted on the rudder.They might be partially retractable in non foiling conditions. No foils on the end of the wings.The canting keel strut would be behind the daggerboard.(Like Maximus among others)
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3) The canting strut is right on the edge of feasibility. But it probably can work: its half the weight of a VO 70 bulb but half again as long.Based on the fact that the load is 81% of the load on a Vo70 the engine hp required is likely to be about 23hp(vs 29 for the Volvo).
The Volvo 70 has a max speed so far of 40.6 knots according to Sail mag-just 5 knots short of the top end(so far) of a G Class cat(100+')-same source. And ,as I understand it, they peg the keel max out in fast conditions.
The Farr design #550 Volvo 70 has a strut approximately 12-13' long with 9920 pounds in the bulb with a variable displacement from 27,558 to 30,865lb.'s. The monofoiler as stated above needs 5200+lb.'s at 18' to be self rightng.
******I don't think that the bulb/strut being offset will have too much negative effect when you consider that L'hydroptere maintains control at over 40 knots with most of the drag coming from a foil 20' to leeward using a centerline rudder. I think that it would be important on the monofoiler to figure out a way to get the canting strut and bulb out of the water over 20 knots-keeping in mind that it will probably be sailed upwind with windward heel like the Moth. The Volvo has a max cant angle of 40°, the Schock 40 and Max Z86's 55° and a 26 footer from Bethwaite 60°.
**This area would need plenty of research and testing. It is ripe for some sort of unique solution....
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4) Bruce numbers- I calculated the Bruce number for L'hydroptere from information on Sail Area given in Sail mag.. But looking at the head-on picture and using a scale ruler I'll bet they can't carry that area(3700sq.ft.) in the same pressure that an Orma tri can carry it's 3000sq. ft. The monofoiler can carry it's maximum sail area in the same pressure an Orma tri can carry it's maximum sail area. Regardless of it's actual SA for a given pressure a well designed multifoiler will be faster than the 60 monofoiler any day. But the monofoiler and ORMA even using "foil assist" will be closer.And a "conventional" multi sailing only on it's hulls(even flying the main hull with no foil assist) would be still closer in speed to the monofoiler-with the monofoiler probably having a significant edge.
**I 'm leaning toward believing that the Bruce Number or Bethwaites "SCP Divided By Total Weight Ratio" may not be good comparitive numbers when comparing an all out foiler to a "foil assist" boat like the Orma. **When you look at these Bruce Numbers you may see what I mean: Moth 1.56 ; A Class Cat 1.82 ; 49er 1.76 ; IC 1.58 . All the boats shown show a Bruce number indicating they should be faster than a Moth-and they are when it is not foiling. But when on foils the Moth beats every one of these boats. So I'm leaning toward SA/wetted surface as a possible way to compare the boats when at least one of them is a foiler. In my comparison of the 60' monofoiler to the ORMA I showed that even though the foiler was heavier it had more power applied to less wetted area than did the ORMA. Of course ,this is simplistic: it didn't take into account induced drag of the foils, the vertical fins or the wavemakng resistance of the partially submerged ORMA ama. Nonetheless, it seems like a good indicator....
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5) Foil Loading- The 60' monofoiler will have foil loadings with and with out the sliding deck ballast. For takefoff(see #5 for lift/speed calculations) it has a foil loading of 392.8 pounds per sq.ft . That is based on 80% of the total dispacement of 14731 which equals 11784 divided by 30 sq.ft.. Above 20 knots ,at some point, it will add additional ballast and have a foil loading of 493 pounds at a displacement of 18502lb.. Most foilers are designed with about 80%(or so) of the load on the forward foil and loading is calculated based on the area of one side.
****For comparision the foil loading of the ORMA tri with and estimated banana foil area of 16sq.ft. is 450lb. per sq.ft. at a displacement of .6 X 12000=7200. A Rave foiler sailing in 2lb. of pressure has a mainfoil(2) loading of 356lb. per sq. ft. (develops RM using the foils increasing loading well past this number at max pressure). A Moth has a mainfoil loading of 169 lb.per sq.ft.-and only changes with different crew weight. And the first two person monofoiler to fly-David Lugg's I14 had an approx. mainfoil loading of over 500 pounds per sq.ft. (small "high speed" foils), if I remember correctly.
L'hydroptere has surface piercing foils and basically starts out with low loading and high wetted surface(56 sq.ft.est.) and ends up with high loading and low wetted surface(14 sq.ft.est.). The picture of L'hydroptere in Sail shows it sailing on one of two main foils at an area I estimate to be 7 sq.ft. for a loading of 1368lb per sq.ft.(.8 X 11975 divided by 7). I'm guestimating that that picture was taken when the boat momentarily flew a foil and that a more realistic loading would be based on 14 sq.ft.(7sq. ft. per main foil) for a realistic loading of 684 lb.'s per sq.ft. At takeoff with 56 sq. ft. of foil area loading is 171lb.sq. ft. but the loading rapidly increases whereas it does not change on a monofoiler unless ballast is added.
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Additional Notes: Using this formula for lift: Area=Weight divided by(the factor 2.09 X speed in mph² X Cl(coeficient of lift) along with my copy of Theory of Wing Sections and the information there on the 63412 section(p522 &523) I came up with the following for the monofoiler:
Light displacement =14731 .8=11784------
Heavy Displacement=18502 X .8=
14802--
Mainfoil area 30 sq.ft.--------------------------
==================================
1) The boat will lift off at a boat speed of 12 mph(10.4 knots) with a CL of 1.3. This is outside the drag bucket(but way below stall) but ,of course ,as soon as the boat lifts off it will accelerate.Moths, using this foil, lift off at even higher CL's.--------------------------------
2) At a boat speed of 16mph(13.9 knots) the CL drops to .73-just inside the "drag bucket" for this foil.-----------------------------
3)At 23 mph(20 knots) after the additional ballast is added the CL is .44-well within the drag bucket. The additional ballast may not all be added at once but I checked it at the minimum speed for which some ballast would be added.
==========================
A personal note: I'm not at all convinced that sailing foilers are a good idea for ocean racing until the electronic systems are developed to spot partially submerged objects in time to avoid them. L'hydroptere was stopped by just this kind of thing. I think all high performance boats would benefit from this kind of equipment and I imagine it's not too far away or may be already available for all I know. In fact according to the L'Hydroptere site they are experimenting with this kind of technology...
Please read the whole thing if you're interested. I consulted with a naval architect on this and tried to be as detailed a possible. Questions and comments from those interested are encouraged.
==================================
60' MOTH-A Preliminary Detailed Design Exploration
==================================
I've long been convinced that the bi-foil revolution in dinghy design sparked by the Moth Foiler has potential for larger boats as well. The Out 95 guys in the UK and Sean Langman are also exploring this idea-among others. I decided to look at the numbers for a scaled up Moth just for the hell of it. I was surprised by the results.
---------------------
I) The base boat: LOA- 12.75', SA- 86 sq.ft.;weight: 60lb.hull + 150 lb. crew =210lb.s all up.
II) Scaling up:
*A) Sail Area-Since sail area varies as the square of length I squared 12.75(162.5) and squared 60(3600). Then I divided 3600 by 162.5 and multiplied the result by 86(Moth SA) . So the scaled up SA=1905sq.ft.----------------------- ****
Weight- Weight/displacement varies as the cube of the length. So I cubed 12.75 (2072.67) and cubed 60(216000).Then I divided 216000 by 2072.67 and multiplied the result by 210(Moth sailing weight). So the weight of the scaled up boat is 21,884 lb.'s.----------
III) Analysis/judgement calls- The most surprising thing when I was first doodling with these figures is the weight. At almost 22,000 pounds the scaled up Moth was way heavy by comparison to an ORMA 60 trimaran(12,000lb.'s) and to L'hydroptere(11,975lb.'s). But the defining characteristic of the Moth above all else is that it is a MONOHULL. So to preserve that characteristic at this length I decided that it would be important that the boat was selfrighting like any other(hopefully) 60'monohull. The "weight budget" certainly would allow that.
==================================
NOTE:VERY IMPORTANT: the resulting 60'monofoiler IS NOT, REPEAT NOT a scaled up Moth as a carefull reading of this Design Exploration will reveal.
This Design Exploration reveals that while this self-righting 60' monohull foiler is possible and has speed potential AT LEAST equal to the ORMA foil assist trimarans it is nonetheless on the leadingedge of what is possible today.
=================================
So this is what I came up with after playing with the numbers for some time and running the whole thing by a friend who is a naval architect:
60' MONOFOILER-----------------------------
1)LOA-60'-------------------------------------
2) Target Beam 50'-increase from scaled up Moth; about same proportion as aeroSKIFF 14(see post#15 Peoples Foiler Thread)
3)Target SA: 2500 sq.ft.-increase from scaled up
Moth.------------------------------
4)Target Minimum all up sailing weight including 5231 lb.s on an 18' 60° canting strut: 14,731lb.'s.--------------------------------
5) Target boat weight w/o canting keel ballast:
9500lb.'s--------------------
6) Maximum additional ballast: 3771 lb.'s water ballast in a sliding tank-perhaps sliding within forward cross beam or just aft of beam. Tank is filled while over hull to limit weight of plumbing requirements. approx. dimensions: 1.5' X 6' X 6.4'. Possible fore and aft ballast sliding system .----------------------------------------
7) Weight with maximum ballast:18502lb.'s(plus 2-4 crew)
==================================
Summary:
-LOA*60'---------------------------------------
-Beam-50'--------------------------------------
-SA 2500sq.ft.----------------------------------- -Displacement:
14,731lb.'s ; Max: 18502---
-Draft(off foils) max
18'-------------------------
30 sq.ft. main foil; 15 sq.ft rudder
foil-------*
===============================================
COMPARISONS--------------------------------
----------------------------------------------
D/L ratio- 60' Monofoiler: 30.4--------------- D/L ratio- Orma 60/L'hydroptere: 24.8------
Bruce Number-60' Monofoiler: 2.03---------
Bruce Number-ORMA Tri: 2.39--------------
Bruce Number-L'hydroptere:2.65------------
(Bruce number is the sq.rt .of SA divided by the cube root of displacement)----------- --------- For what it's worth, the following comparison is between the 60'Monofoiler and the 60'ORMA trimaran.And I consider it one of the most important comparisons of all. The ORMA trimaran is presumed to have 60% of it's displacement supported by a "banana foil", with 30% of it's weight supported by the ama while flying the main hull. For this comparison the 60'Monofoiler is presumed to be flying on just two foils. The vertical fins of neither boat are included and both sides of the foils are included:
1)Orma 60-estimated ama wetted surface 124 sq.ft; estimated foil wetted surface 32 sq.ft.(both sides) Total 156 sq.ft. Now this figure is divided into SA(3000sq.ft.) giving 19 sq.ft. of SA per sq.ft.of wetted surface.
2) 60'Monofoiler Mainfoil area(both sides): 60sq.ft..Rudder foil area(both sides) 30sq.ft.. Total is 90 sq.ft . Dividing SA(2500sq.ft.) by this figure gives 27.7 sq.ft. of SA per sq.ft. of wetted surface.
==================================
**Notes and Design Considerations
( see below for "More notes..." including lift calculations, foil
loading and more)
==================================
A) The number one design consideration for this boat was that it was self righting and that it would qualify as a monohull under any rule. Therefore it does not have buoyancy pods that in any way resemble or that could function like a hull-simple rectangular spaces at the maximum beam supported by carbon cross tubes. These buoyancy tanks in combination with the 18' 5000+lb. 60° canting bulb would prevent capsize and or right the boat from a knockdown. The weight in the bulb was specifically chosen to be 1.5 times what would be required to right the boat from a pitchpole. The canting keel could be explored a lot since it is relatively light for a 60 footer(5200+lb.'s). It would be ideal for it to be clear of the water when the boat is foiling-at least above 20 knots.
When an Orma tri fly's the main hull it does so with about 2lb. per sq.ft. of windpressure on 3000 sq.ft. of sail. The 60'Monofoiler with max ballast can sail with it's maximum SA in about the same pressure. And in lighter conditions it can ditch up to 3700+ lb.'s of water ballast facilitating relatively light air take off in an 9-12 knot wind.------------------------------
(see Righting Moment below)
==================================
Preliminary conclusions:
It appears to me that the 60' monofoiler could be built but right at the top end of available technology.It would be likely to equal a multi of it's own size that did not use foils and appears to have more SA per sq.ft. of wetted surface than even an ORMA tri though especially in light air the ORMA would be faster since it can retract it's hydrofoil . The concept of an extremely fast selfrighting hydrofoil holds a lot of promise.
===================================
--------------------------------
More notes and references:
1) Righting Moment---------------------------
When off the foils the heeling arm (CE-CLR) is 43'. When on foils it is 51.75' . Hull bottom clearance to water is 10.75'. On foils max draft ,level,is 5'.
This boat is a monofoiler and as such will be sailed heeled to weather 15° at maximum righting moment.
Elements of Righting Moment:
A) rig CG is approximately at the
CE; 1460lb. @ 14.5' to weather= 21,170ft.lb.
B)canting bulb- 5,231lb.'s at 60°( 15.6') +
3' weather heel =5231 X 18.6'= 97,296 ft. lb.'s.
C)Hull 8040 X 5'to weather= 40,200ft.lb.
D)rack(deck) ballast 23' = 6' to weather
=29 X 3771= 109,359 ft. pounds
================================================
MAXIMUM RIGHTING MOMENT= 268,025 ft. lb.'s (A+B+C+D above)
MAXIMUM PRESSURE WITH 2500sq.ft.(268,025 divided by 51.75=5179. Divide 5179 by 2500(SA) = 2.07 lb.
================================================
2) The 50' beam could be one "wing" but would probably work better as two beams supporting a fixed empty "tank" at each end for buoyancy. A small tank containing up to 3770 pounds of water will also slide across the forward beam or just behind it. For the sake of getting the boat defined as a monohull based on whatever rule the buoyancy would not look like or function like a hull while normally sailing. In the event of a knockdown it would help to right the boat. I've talked with Alex of the OUT 95 project and he says their solution(ultra narrow hull with very wide wings on a 32 footer) is legal under the rules. Exactly which rules he was referring to I'm not exacly sure.
********The hydrofoils on this 60' monofoiler are in the hull : one mounted on the daggerboard and one mounted on the rudder.They might be partially retractable in non foiling conditions. No foils on the end of the wings.The canting keel strut would be behind the daggerboard.(Like Maximus among others)
----------------------------------------------
3) The canting strut is right on the edge of feasibility. But it probably can work: its half the weight of a VO 70 bulb but half again as long.Based on the fact that the load is 81% of the load on a Vo70 the engine hp required is likely to be about 23hp(vs 29 for the Volvo).
The Volvo 70 has a max speed so far of 40.6 knots according to Sail mag-just 5 knots short of the top end(so far) of a G Class cat(100+')-same source. And ,as I understand it, they peg the keel max out in fast conditions.
The Farr design #550 Volvo 70 has a strut approximately 12-13' long with 9920 pounds in the bulb with a variable displacement from 27,558 to 30,865lb.'s. The monofoiler as stated above needs 5200+lb.'s at 18' to be self rightng.
******I don't think that the bulb/strut being offset will have too much negative effect when you consider that L'hydroptere maintains control at over 40 knots with most of the drag coming from a foil 20' to leeward using a centerline rudder. I think that it would be important on the monofoiler to figure out a way to get the canting strut and bulb out of the water over 20 knots-keeping in mind that it will probably be sailed upwind with windward heel like the Moth. The Volvo has a max cant angle of 40°, the Schock 40 and Max Z86's 55° and a 26 footer from Bethwaite 60°.
**This area would need plenty of research and testing. It is ripe for some sort of unique solution....
----------------------------------------------
4) Bruce numbers- I calculated the Bruce number for L'hydroptere from information on Sail Area given in Sail mag.. But looking at the head-on picture and using a scale ruler I'll bet they can't carry that area(3700sq.ft.) in the same pressure that an Orma tri can carry it's 3000sq. ft. The monofoiler can carry it's maximum sail area in the same pressure an Orma tri can carry it's maximum sail area. Regardless of it's actual SA for a given pressure a well designed multifoiler will be faster than the 60 monofoiler any day. But the monofoiler and ORMA even using "foil assist" will be closer.And a "conventional" multi sailing only on it's hulls(even flying the main hull with no foil assist) would be still closer in speed to the monofoiler-with the monofoiler probably having a significant edge.
**I 'm leaning toward believing that the Bruce Number or Bethwaites "SCP Divided By Total Weight Ratio" may not be good comparitive numbers when comparing an all out foiler to a "foil assist" boat like the Orma. **When you look at these Bruce Numbers you may see what I mean: Moth 1.56 ; A Class Cat 1.82 ; 49er 1.76 ; IC 1.58 . All the boats shown show a Bruce number indicating they should be faster than a Moth-and they are when it is not foiling. But when on foils the Moth beats every one of these boats. So I'm leaning toward SA/wetted surface as a possible way to compare the boats when at least one of them is a foiler. In my comparison of the 60' monofoiler to the ORMA I showed that even though the foiler was heavier it had more power applied to less wetted area than did the ORMA. Of course ,this is simplistic: it didn't take into account induced drag of the foils, the vertical fins or the wavemakng resistance of the partially submerged ORMA ama. Nonetheless, it seems like a good indicator....
----------------------------------------------
5) Foil Loading- The 60' monofoiler will have foil loadings with and with out the sliding deck ballast. For takefoff(see #5 for lift/speed calculations) it has a foil loading of 392.8 pounds per sq.ft . That is based on 80% of the total dispacement of 14731 which equals 11784 divided by 30 sq.ft.. Above 20 knots ,at some point, it will add additional ballast and have a foil loading of 493 pounds at a displacement of 18502lb.. Most foilers are designed with about 80%(or so) of the load on the forward foil and loading is calculated based on the area of one side.
****For comparision the foil loading of the ORMA tri with and estimated banana foil area of 16sq.ft. is 450lb. per sq.ft. at a displacement of .6 X 12000=7200. A Rave foiler sailing in 2lb. of pressure has a mainfoil(2) loading of 356lb. per sq. ft. (develops RM using the foils increasing loading well past this number at max pressure). A Moth has a mainfoil loading of 169 lb.per sq.ft.-and only changes with different crew weight. And the first two person monofoiler to fly-David Lugg's I14 had an approx. mainfoil loading of over 500 pounds per sq.ft. (small "high speed" foils), if I remember correctly.
L'hydroptere has surface piercing foils and basically starts out with low loading and high wetted surface(56 sq.ft.est.) and ends up with high loading and low wetted surface(14 sq.ft.est.). The picture of L'hydroptere in Sail shows it sailing on one of two main foils at an area I estimate to be 7 sq.ft. for a loading of 1368lb per sq.ft.(.8 X 11975 divided by 7). I'm guestimating that that picture was taken when the boat momentarily flew a foil and that a more realistic loading would be based on 14 sq.ft.(7sq. ft. per main foil) for a realistic loading of 684 lb.'s per sq.ft. At takeoff with 56 sq. ft. of foil area loading is 171lb.sq. ft. but the loading rapidly increases whereas it does not change on a monofoiler unless ballast is added.
----------------------------------------------
----------------------------------------------
Additional Notes: Using this formula for lift: Area=Weight divided by(the factor 2.09 X speed in mph² X Cl(coeficient of lift) along with my copy of Theory of Wing Sections and the information there on the 63412 section(p522 &523) I came up with the following for the monofoiler:
Light displacement =14731 .8=11784------
Heavy Displacement=18502 X .8=
14802--
Mainfoil area 30 sq.ft.--------------------------
==================================
1) The boat will lift off at a boat speed of 12 mph(10.4 knots) with a CL of 1.3. This is outside the drag bucket(but way below stall) but ,of course ,as soon as the boat lifts off it will accelerate.Moths, using this foil, lift off at even higher CL's.--------------------------------
2) At a boat speed of 16mph(13.9 knots) the CL drops to .73-just inside the "drag bucket" for this foil.-----------------------------
3)At 23 mph(20 knots) after the additional ballast is added the CL is .44-well within the drag bucket. The additional ballast may not all be added at once but I checked it at the minimum speed for which some ballast would be added.
==========================
A personal note: I'm not at all convinced that sailing foilers are a good idea for ocean racing until the electronic systems are developed to spot partially submerged objects in time to avoid them. L'hydroptere was stopped by just this kind of thing. I think all high performance boats would benefit from this kind of equipment and I imagine it's not too far away or may be already available for all I know. In fact according to the L'Hydroptere site they are experimenting with this kind of technology...
Tuesday, October 20, 2009
three boats in one
I've started my second monohull foiler platform that will actually be three boats in one. The idea is to have a basic platform with interchangeable parts that will allow a 22' foiler, a 22' trimaran with planing amas and a 22' Trapwing experimental movable ballast boat.
All these variations use foils to one degree or another and the plan is to get the hardware built and be able to spend huge amounts of time sailing instead of building.
I should have a whole lot of fun and learn a lot over the next five years while I explore these ideas.
Thanks to my experience with Dr. Bradfield I've sailed a Rave a lot and coupled with the limited foiling on my own 16 footer I can tell you that foiling is one of the most thrilling things you can do on the water! Try it on any boat you can.
And keep in mind these are early days in the bi-foiler revolution-don't buy into the "its too hard" bull or that crap about having to walk a foiler out to deep water. The newer boats will be much more user friendly and yes,it is a revolution!
All these variations use foils to one degree or another and the plan is to get the hardware built and be able to spend huge amounts of time sailing instead of building.
I should have a whole lot of fun and learn a lot over the next five years while I explore these ideas.
Thanks to my experience with Dr. Bradfield I've sailed a Rave a lot and coupled with the limited foiling on my own 16 footer I can tell you that foiling is one of the most thrilling things you can do on the water! Try it on any boat you can.
And keep in mind these are early days in the bi-foiler revolution-don't buy into the "its too hard" bull or that crap about having to walk a foiler out to deep water. The newer boats will be much more user friendly and yes,it is a revolution!
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