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:

Mirabaud-manual control lever.jpg


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


1) F18-- crew CG at 11' from lee hull CB( 320 X 11= + boat CG at approx. 3.8' from lee hull CB with windward hull just flying( 396 X 3.8= 1504
TOTAL RM = 5024

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:


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.