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Bradfield Osprey Foiler


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#1 Doug Lord

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Posted 16 September 2011 - 11:01 PM

Dr. Sam Bradfield has been a pioneer in foiler design for over 40 years. Today I had the great pleasure to see and photograph the launch of his 18' Osprey:
LOA 18'
Beam 20' (+ foil tips)
Upwind SA 350 sq.ft.
Weight 400lb.
==================
The boat uses the dual, independent wands Bradfield developed that not only control flying altitude but provide most of the righting moment for the boat. The foils are so effective in doing this that the only limit is the structural strength of the boat.
Congratulations to Dr. Bradfield, Tom Haman and to the builder Matt McDonald(Falcon Marine) who did a tremendous job producing flawless tooling-what a gorgeous finish!

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#2 Doug Lord

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Posted 16 September 2011 - 11:04 PM

Very light air today so no foiling.....More pictures:

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#3 Icedtea

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Posted 16 September 2011 - 11:10 PM

Looks alright, will we ever see it foiling?

#4 Doug Lord

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Posted 16 September 2011 - 11:57 PM

Did I say light air? Why yes I did.......Tom Haman flying.....

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#5 joey g

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Posted 17 September 2011 - 12:02 AM

Did they do this in the ICW?

Joe

#6 Doug Lord

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Posted 17 September 2011 - 12:21 AM

Yes, at Pineda-very light air...

#7 joey g

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Posted 17 September 2011 - 12:22 PM

Yes, at Pineda-very light air...


Very nice, you guys should bring it down for some South Florida events.


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#8 joey g

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Posted 17 September 2011 - 12:22 PM

Yes, at Pineda-very light air...


Very nice, you guys should bring it down for so South Florida events.

Joe

#9 trimariner

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Posted 18 September 2011 - 08:36 AM

Doug, at what true wind speed was she flying? Sure looks impressive, i await more details with great interest.

#10 Doug Lord

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Posted 18 September 2011 - 12:44 PM

Doug, at what true wind speed was she flying? Sure looks impressive, i await more details with great interest.

===================
Guessing: 7-8 knots. They were using straight tubular wands rather than the planing wands pioneered by Bradfield long before being used on the Moth.
They were using the rudder plug rather than the carbon version. But they have some neat adjustment details like a sliding plate that allows the angle of incidence of the main foils to be changed around 3.5 degrees-same thing on the rudder. You can see notches in the trailing edge of the daggerboard: they're to allow two different flying heights-same in the rudder. At some point the boat will use a solid wing...
Lots of development ahead.

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#11 Doug Lord

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Posted 19 September 2011 - 04:22 PM

Some interesting comparative stats:
---W/SA=pounds per sq.ft. sa / smaller number =better
---SA/ws= sail area in sq.ft. divided by wetted surface in sq.ft./ foilers flying
---Osprey to get wing rig......

=============

C Class cat

LOA 25'
Beam 14'
SA 300sq.ft
Boat weight 300lb
crew(estimate) 2@ 175lb=350lb.
Sailing weight(estimate) 650lb
W/SA= 2.16
SA/ws(estimate)=8.42/1

=====================
A Class Cat

LOA 18'
Beam 7.9'
Boat weight 150lb.
crew(estimate) 175lb.
Sailing weight(estimate) 325lb
W/SA= 2.17
SA/ws(estimate)= 6.96/1

=====================
Mirabaud

LOA 32.8'
Beam 17.7'
SA (upwind) 344 sq.ft.
---downwind 527.2 sq.ft.
Boat weight 374lb
crew(estimate) 3@ 175=525lb.
Sailing weight (estimate) 899lb.
W/SA= 2.61
SA/ws= 18/1 (on foils)

===============
Moth

LOA 11'(12.75 incl gantry)
Beam 7.2'
SA 86 sq.ft.
Boat weight 66lb.
crew(estimate) 175lb
Sailing weight (estimate) 241lb
W/SA= 2.8
SA/ws=13.65/1 (on foils)

================
Osprey

LOA 18'
Beam 20'(+foil tips)
SA 350 sq.ft.
Boat weight 400lb.
crew(estimate) 175lb(or less!-foils develop virtually unlimited RM)
Sailing weight (estimate) 575lb
W/SA= 1.64
SA/ws= 18/1

#12 TornadoCAN99

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Posted 19 September 2011 - 05:51 PM

looks like a Marstrom Tornado rig with carbon stick & sails.

#13 Doug Lord

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Posted 19 September 2011 - 06:04 PM

looks like a Marstrom Tornado rig with carbon stick & sails.

=======
The main is off a 20 footer Falcon decided against producing; the jib is off an F16. Will have a wing when complete...

#14 TheFlash

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Posted 19 September 2011 - 06:54 PM

what's the objective of the platform?

OD Racing prototype?

Family foiler? Mass production?

Just a fun way to spend time for a tinkerer?

#15 blunted

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Posted 19 September 2011 - 08:29 PM


looks like a Marstrom Tornado rig with carbon stick & sails.

=======
The main is off a 20 footer Falcon decided against producing; the jib is off an F16. Will have a wing when complete...

wing? do tell...

#16 GybeSetŪ

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Posted 19 September 2011 - 08:42 PM

{quote name='Mitch' timestamp='1316458487' post='3406826']
what's the objective of the platform?

OD Racing prototype?

Family foiler? Mass production?

Just a fun way to spend time for a tinkerer?
[/quote]
can't be the Peoples Foiler

too exxy

I like it but seems like a flipper

#17 Chris O

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Posted 20 September 2011 - 12:59 AM

Yes, folks... it's time for that favorite SA game show; "Guess the Retail Price of the Dr. Sam Foiler"

For comparison sake, take a look at another production tri of similar size, the M23 and apply all your best, nuanced algorithms to estimate the final retail price of an all-carbon, 20' LOA trimaran foiler in the current market place. Of course, have it built in China, the M23 is built there, after all. So, the parallel should yield some interesting comparisons between a boat that has gotten great reviews with a global footprint and according to the inside dope from a single source, the Osprey, which has a speculative potential as a production machine.

Let the free-wheeling begin.

#18 Doug Lord

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Posted 20 September 2011 - 01:22 AM

Turns out that this boat, at 400lb., is mostly glass with carbon beams and carbon main foils.

#19 TheFlash

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Posted 20 September 2011 - 02:44 AM

It's all fine and good. Not the first multi-foiler - won't be the last.

What's the objective? Giving a tinkerer something fun to do is a fine objective.

#20 Steve Clark

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Posted 23 September 2011 - 02:44 PM

Sam asked me to design a wing for this project.
Matt got too busy to get it built in time for this year.
There was also a bit of a gag response to the cost.
They decided to test it first with the soft rig.
As I understand it, the intent is for a high end One Design racer.
SHC

#21 Frank N

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Posted 27 September 2011 - 03:25 AM

It is always nice to see new one off foilers of any design and perhaps even talk of production?!
Congrats to those responsible for making it happen!

Another point of comparison is below.



Note the Rave (same fundamental design as Osprey) is missing from the above comparisons. Someone should crank those numbers for comparison.

=========================
Trifoiler

LOA 25'
Beam 19'
SA 215sq.ft
Boat weight 320lb
crew(estimate) 1@ 175lb Windward foil develops 14,000+ lbs righting moment).
Sailing weight(estimate) 475lb

wetted surface flying ~10 sq feet ( 18 inch foil depth).
W/SA= 1.48
SA/ws(estimate)=21.5/1

=========================

Note that at wind speeds above 18 kts, TF sails faster with the sails reefed to 150 square feet. Osprey will likely discover the same. Driving issue is foil drag cost to counter excessive righting moment.

Impressed with the 7-8kts needed for Osprey to lift off. TF needs ~10 kts.(full sail).

Curious to see the Polars for Osprey. TF polar is here: http://www.trifoiler...s#Polar_Diagram
Parts of this diagram are considered conservative.

Osprey SA/ws(estimate)=18/1 seems low.
With SA of 350 sq ft, 18:1 works out to 19.4 sq feet of wetted foil or 8.7 sq feet of foil area. That seems like a lot. Perhaps this is the cost of using a mono rig. i.e. the additional righting moment required. Also the potential explanation for the excellent (low) lift off speed. Ultimate cost of the large foil area will be top end speed.

These ratios are interesting to look at but don't tell the whole story. The efficiency (Lift/drag curves) of the air and hydrofoils is pivotal to max speed performance as is the impact on righting moment of unirig vs dual rig. Also the energy cost (effective drag) of the foil flying height regulating system plays a pivotal role in ultimate speed.

An excellent measure that wraps all of this together is the ratio of boat speed to True wind speed. For TF, this is ~ 2:1. I would be curious to see these numbers for Osprey.

====================================================
Longshot 2, the last of the TF based record boats has wing sails, ~50 lbs less weight. Holds the A-class speed record with membrane sails (not wing sails) .
====================================================
More TF info here:
http://www.trifoiler...title=Main_Page

Frank%simrex.com replace % with @.

#22 Doug Lord

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Posted 27 September 2011 - 12:52 PM

Frank, all the other comparisons above were done with the same basic crew weight @175lb.(Mirabaud 3 X 175). So if the HT was done that way the W/SA =2.3 (495/215= 2.3) Are you sure on wetted surface? Another advantage to the HT is the greater effective aspect ratio of the foils vs T-foils-still looking into that.
For what it's worth, Bradfields foils retract and also have two flying positions.
Thanks for your post!

#23 Doug Lord

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Posted 18 December 2011 - 11:18 PM

Short video:




#24 trenace

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Posted 18 December 2011 - 11:38 PM

Note that at wind speeds above 18 kts, TF sails faster with the sails reefed to 150 square feet. Osprey will likely discover the same. Driving issue is foil drag cost to counter excessive righting moment.

In light air conditions the ability to generate (when there's more breeze) downforce from the windward foil will allow a larger rig and so could aid speed when in the light conditions.

However as you say, once breeze is enough to require downforce from the windward foil, the added sail area and the downforce seem counterproductive. While sail carrying power does increase as righting moment increases this way, there's twice as much (roughly) drag as usual for the added power.

(Twice, because the leeward foil's lift must also beyond sailing displacement by the same amount.)

Hard to see how added sail area requiring twice the drag per amount of sail force can yield more speed. Certainly the lift/drag ratio worsens as well.

I was having trouble seeing, in another thread, where speed limitation from lack of righting moment in the first place (center of gravity vs center of lift) could possibly be overcome by adding downforce: it continues to seem unlikely. I do see where the resulting ability to carry more sail means this can give more performance in light air while still being able to handle heavier air -- until losing downforce from whatever cause (cavitation, waves, a dynamic excursion, a control failure), then over you go quite rapidly.

#25 Doug Lord

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Posted 18 December 2011 - 11:51 PM

Gee Trenace, I thought Greg Ketterman explained that to you? You can't just second guess stuff like this: the L/D of the foil system is calculated and will function as the designer wants it to-especially in the case of Greg Ketterman and Dr. Bradfield. This is a well proven concept done by guys that hold hydrofoil speed records-have a little faith-or study a bit more. Reefing would be likely in conditions where the designer has determined that structural limits could be exceeded.
I'll give Greg another chance:

HYDROFOIL SAILBOATS IN GENERAL
"Hydrofoil boats can be categorized into two categories; 1) Incidence controlled hydrofoils* and 2) surface piercing hydrofoils. The difference lies in the way the boat maintains the proper altitude above the water surface. A surface piercing hydrofoil boat maintains proper height by varying the amount of foil submerged. The boat raises up as the speed increases and reduces the amount of foil submerged and therefore the lift. The boat finds equilibrium at the proper altitude. An incidence controlled hydrofoil sailboat has a mechanism that controls the angle of attack of the foil to maintain the proper altitude. It is generally believed that surface piercing is simpler, but incidence control is more efficient. In reality, it is the method that works with fewer problems that is simpler.
From the beginning it was felt that incidence control was better suited for a sailboat even though most of the existing hydrofoil sailboats were of the surface piercing type. There are many advantages of the incidence controlled foils; however, the most important is what I call the DLA (dynamic leveling affect). This is the increase in righting moment or stability due to the ability of the windward foil to pull down. The DLA has little affect on the low wind performance, but it essentially makes the top speed of the boat limited to the strength of the boat. Conventional boats with a finite amount of righting moment can only extract so much power from the wind, but with the DLA, the righting moment is virtually unlimited.
Intuitively many people think that the added drag of the windward foil plus the increased induced drag of the leeward foil would offset the gain in righting moment, but calculations show and practice proves otherwise. The dynamic leveling affect not only produces a dramatic increase in top speed, but is also responsible for all the other key features that this stability provides.
The other major advantage of the incidence controlled foils is they are less affected by the waves and other surface affects. Drag and losses associated with the surface are the major reason incidence controlled foils are more efficient.
All hydrofoil sailboats have problems with ventilation; however, surface piercing foils have larger problems, because the foils are piercing the surface at a smaller dihedral angle which makes it easier to ventilate."

------
* On the Trifoiler the entire foil was moved to control RM, lift and negative lift hence the term "incidence controlled foils". On the Rave the incidence was generally fixed at +2.5 degrees for the main foils though some owners found a way to decrease the incidence on the windward foil. Lift and negative lift on a Rave foiler is generated by the wand (designed by Dr. Sam Bradfield), a surface sensor(dragging in the water) and attached directly via linkage to a flap on each main foil. The wands are independent just like the trifoiler "incidence controlled" foil sensors.

http://www.hobiecat....ihulls 1990.htm

#26 trenace

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Posted 19 December 2011 - 01:06 AM

Gee Trenace, I thought Greg Ketterman explained that to you? You can't just second guess stuff like this: the L/D of the foil system is calculated and will function as the designer wants it to-especially in the case of Greg Ketterman and Dr. Bradfield. This is a well proven concept done by guys that hold hydrofoil speed records-have a little faith-or study a bit more. Reefing would be likely in conditions where the designer has determined that structural limits could be exceeded.
I'll give Greg another chance:

HYDROFOIL SAILBOATS IN GENERAL
"Hydrofoil boats can be categorized into two categories; 1) Incidence controlled hydrofoils* and 2) surface piercing hydrofoils. The difference lies in the way the boat maintains the proper altitude above the water surface. A surface piercing hydrofoil boat maintains proper height by varying the amount of foil submerged. The boat raises up as the speed increases and reduces the amount of foil submerged and therefore the lift. The boat finds equilibrium at the proper altitude. An incidence controlled hydrofoil sailboat has a mechanism that controls the angle of attack of the foil to maintain the proper altitude. It is generally believed that surface piercing is simpler, but incidence control is more efficient. In reality, it is the method that works with fewer problems that is simpler.
From the beginning it was felt that incidence control was better suited for a sailboat even though most of the existing hydrofoil sailboats were of the surface piercing type. There are many advantages of the incidence controlled foils; however, the most important is what I call the DLA (dynamic leveling affect). This is the increase in righting moment or stability due to the ability of the windward foil to pull down. The DLA has little affect on the low wind performance, but it essentially makes the top speed of the boat limited to the strength of the boat. Conventional boats with a finite amount of righting moment can only extract so much power from the wind, but with the DLA, the righting moment is virtually unlimited.
Intuitively many people think that the added drag of the windward foil plus the increased induced drag of the leeward foil would offset the gain in righting moment, but calculations show and practice proves otherwise. The dynamic leveling affect not only produces a dramatic increase in top speed, but is also responsible for all the other key features that this stability provides.
The other major advantage of the incidence controlled foils is they are less affected by the waves and other surface affects. Drag and losses associated with the surface are the major reason incidence controlled foils are more efficient.
All hydrofoil sailboats have problems with ventilation; however, surface piercing foils have larger problems, because the foils are piercing the surface at a smaller dihedral angle which makes it easier to ventilate."

------
* On the Trifoiler the entire foil was moved to control RM, lift and negative lift hence the term "incidence controlled foils". On the Rave the incidence was generally fixed at +2.5 degrees for the main foils though some owners found a way to decrease the incidence on the windward foil. Lift and negative lift on a Rave foiler is generated by the wand (designed by Dr. Sam Bradfield), a surface sensor(dragging in the water) and attached directly via linkage to a flap on each main foil. The wands are independent just like the trifoiler "incidence controlled" foil sensors.

http://www.hobiecat....ulls%201990.htm


Okay, instead of looking at it as added sail area adding a need for, for example, 100 lb added downforce at the windward foil and this also requiring another 100 lb upforce at the leeward foil to keep the boat up, which would be double, I should have figured it as needing 50 lb downforce at the windward foil and 50 lb compensating upforce at the leeward foil, giving same ratio of righting moment to drag. Thanks.

However, it would help if you saw that you present these things as assertions and as "so and so said that," but lacking the why and how, rather than providing direct and clear explanation. "Calculations prove otherwise," without providing the calculations. "The L/D of the foil system is calculated and will function as the designer wants it to," etc. People should not accept on authority but on actual explanation and facts.

And better on actual boats sailing -- I mean with people -- which this builder does do, though this boat has not had the opportunity yet to prove any speed advantage, but you do not.

#27 Doug Lord

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Posted 19 December 2011 - 01:31 AM


Gee Trenace, I thought Greg Ketterman explained that to you? You can't just second guess stuff like this: the L/D of the foil system is calculated and will function as the designer wants it to-especially in the case of Greg Ketterman and Dr. Bradfield. This is a well proven concept done by guys that hold hydrofoil speed records-have a little faith-or study a bit more. Reefing would be likely in conditions where the designer has determined that structural limits could be exceeded.
I'll give Greg another chance:

HYDROFOIL SAILBOATS IN GENERAL
"Hydrofoil boats can be categorized into two categories; 1) Incidence controlled hydrofoils* and 2) surface piercing hydrofoils. The difference lies in the way the boat maintains the proper altitude above the water surface. A surface piercing hydrofoil boat maintains proper height by varying the amount of foil submerged. The boat raises up as the speed increases and reduces the amount of foil submerged and therefore the lift. The boat finds equilibrium at the proper altitude. An incidence controlled hydrofoil sailboat has a mechanism that controls the angle of attack of the foil to maintain the proper altitude. It is generally believed that surface piercing is simpler, but incidence control is more efficient. In reality, it is the method that works with fewer problems that is simpler.
From the beginning it was felt that incidence control was better suited for a sailboat even though most of the existing hydrofoil sailboats were of the surface piercing type. There are many advantages of the incidence controlled foils; however, the most important is what I call the DLA (dynamic leveling affect). This is the increase in righting moment or stability due to the ability of the windward foil to pull down. The DLA has little affect on the low wind performance, but it essentially makes the top speed of the boat limited to the strength of the boat. Conventional boats with a finite amount of righting moment can only extract so much power from the wind, but with the DLA, the righting moment is virtually unlimited.
Intuitively many people think that the added drag of the windward foil plus the increased induced drag of the leeward foil would offset the gain in righting moment, but calculations show and practice proves otherwise. The dynamic leveling affect not only produces a dramatic increase in top speed, but is also responsible for all the other key features that this stability provides.
The other major advantage of the incidence controlled foils is they are less affected by the waves and other surface affects. Drag and losses associated with the surface are the major reason incidence controlled foils are more efficient.
All hydrofoil sailboats have problems with ventilation; however, surface piercing foils have larger problems, because the foils are piercing the surface at a smaller dihedral angle which makes it easier to ventilate."

------
* On the Trifoiler the entire foil was moved to control RM, lift and negative lift hence the term "incidence controlled foils". On the Rave the incidence was generally fixed at +2.5 degrees for the main foils though some owners found a way to decrease the incidence on the windward foil. Lift and negative lift on a Rave foiler is generated by the wand (designed by Dr. Sam Bradfield), a surface sensor(dragging in the water) and attached directly via linkage to a flap on each main foil. The wands are independent just like the trifoiler "incidence controlled" foil sensors.

http://www.hobiecat....ulls%201990.htm


Okay, instead of looking at it as added sail area adding a need for, for example, 100 lb added downforce at the windward foil and this also requiring another 100 lb upforce at the leeward foil to keep the boat up, which would be double, I should have figured it as needing 50 lb downforce at the windward foil and 50 lb compensating upforce at the leeward foil, giving same ratio of righting moment to drag. Thanks.

However, it would help if you saw that you present these things as assertions and as "so and so said that," but lacking the why and how, rather than providing direct and clear explanation. "Calculations prove otherwise," without providing the calculations. "The L/D of the foil system is calculated and will function as the designer wants it to," etc. People should not accept on authority but on actual explanation and facts.

And better on actual boats sailing -- I mean with people -- which this builder does do, though this boat has not had the opportunity yet to prove any speed advantage, but you do not.

============================
Trenace, if I had designed either boat I would have provided the calculations! I am unable to do much more than quote the designers of these two boats(Osprey and Trifoiler) since there is much detail I don't know. I have sailed Bradfields Rave(not the Osprey) and designed the first production RC foiler the F3(which I have published a lot of detail for). Details on my new SRT and MPX 12 are in threads on boatdesign in great detail.
I think it is fair to ask people to accept "on authority" comments relating to the Trifoiler from Greg Ketterman.
I think I presented a fair amount of detail regarding the Rave.....If you have any questions about the Rave, F3, SRT or MPX-12 I'll be glad to answer in detail.

#28 dacarls

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Posted 19 December 2011 - 05:33 AM

"Intuitively many people think that the added drag of the windward foil plus the increased induced drag of the leeward foil would offset the gain in righting moment, but calculations show and practice proves otherwise."

So why was this not done with OffYerRocker? As far as I could see in the tech analysis, no attempt was made to change incidence of the weather foil, and the Dremel cutting wheel quickly came into play.


#29 Doug Lord

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Posted 19 December 2011 - 01:13 PM

"Intuitively many people think that the added drag of the windward foil plus the increased induced drag of the leeward foil would offset the gain in righting moment, but calculations show and practice proves otherwise."

So why was this not done with OffYerRocker? As far as I could see in the tech analysis, no attempt was made to change incidence of the weather foil, and the Dremel cutting wheel quickly came into play.

--------------
DC, one of the keys to the viability of dual independent wands is beam: cl to cl on Osprey(18'LOA) is 20', on Rocker it would have been less than
14' by the foil tips- and Rocker had 4 surface piercing vertical foils(2 daggerboards and 2 rudders)-all combined must have made a difference.
Rocker had dual independent wands as well which means this was done-automatically! In otherwords, as the boat heeled the windward wand automatically decreased the flap angle, while the leeward wand automatically increased the (down) flap angle.

#30 nautichic

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Posted 19 December 2011 - 01:20 PM

"Intuitively many people think that the added drag of the windward foil plus the increased induced drag of the leeward foil would offset the gain in righting moment, but calculations show and practice proves otherwise."

So why was this not done with OffYerRocker? As far as I could see in the tech analysis, no attempt was made to change incidence of the weather foil, and the Dremel cutting wheel quickly came into play.


For the one hundredth time, every possible combo was tried, do you think we would go to all the trouble to build that boat and not try every combo? What are we fuckin stupid? (Mostly not, occassionaly yes) The incidence of the weather foil was not changed as we didn't really need too, it was a flapped foil with plenty of range to play through, both positive and negative.

Foils up, foils down, wands on, wands off, bikinis inside out, right side out, we did it all. The boat wasn't wide enough to play that game and still had too much junk in the water even with half the foils retracted.

#31 tikipete

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Posted 19 December 2011 - 01:52 PM

:rolleyes: Are those yours?

#32 sailorbob

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Posted 19 December 2011 - 01:54 PM

Short video:




Can anyone tell me the name and artist of the background music on this video?

#33 blunted

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Posted 19 December 2011 - 03:02 PM

:rolleyes: Are those yours?


No they are my wife's, I forgot she was logged in and not me.

B

#34 tikipete

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Posted 19 December 2011 - 03:28 PM

Lucky man.

#35 SC65

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Posted 20 December 2011 - 12:29 AM


:rolleyes: Are those yours?


No they are my wife's, I forgot she was logged in and not me.

B


Do you think "off the rocker" would have been more successful if it would have used only one central board and rudder and would have been sailed more like a moth, canted to windward?
I believe Rohan tried canting to windward when helming your boat but he also later stated his believe that the foils used were not the most developed shapes compared to those nowadays seen on a moth and one of the reasons for the amount of drag encountered.

I used to race A cats when the boards were still straight and spend a year in a Mach2 moth. Impressed by the increase in boats speed once the moth starts foiling but not impressed by the rig itself nor the design wise limited short distance between front and rudder foil at the moth, I believe that mounting a Mach2 foil package under an A central in front of the frontbeam might actually work and [while restricted by nowadays class rules] would be more efficient than those curved foils which can only contribute partly lift. What are your thoughts on the idea of a central foil with a flap versus using curved foils?

thx

#36 P Flados

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Posted 20 December 2011 - 02:30 AM

The Steve Killing paper I read on the foiled C-Class did not make complete sense and left me wondering (no matter how many times I read it).

On the Tri-foiler series of boats (and Rave I believe), boat speed increase with wind speed well after the windward foil is pulling down. This continues until the foil cavitates (or so goes the general assumption) or a structural limit is reached. I read Greg Ketterman's paper on his results (have not been able to find a link lately) and everything made sense. Yes the overall results were rough given the simplifying assumptions and their lack of understanding of stuff that is still somewhat mysterious (foil limits etc.). Given the slightly crude numerical approach, I think that there was probably a lot of good choices made using "it just seemed right" that led to much their success.

The Off Yer Rocker effort did not duplicate this finding at all. From a basic physics standpoint, I have never been able to reconcile the results.

The current Sailrocket results with a foil based speed limit even while using a supercavitating foil (or so goes the general assumption) also makes no sense.

Both of these experiences are real and should not be discounted. What they really say is that we do not really understand what limiting aspect of physics tripped us up in our expectations.

The conclusion of the Steve Killing paper included "We encourage other teams to learn from our experiments and go forward to find the solution that will push hydrofoiling catamarans to the next level of performance."

If we really understood things better we would find that many experiments were considered "failed" when they only missed "success" by some single small error in understanding. This is normal and does nothing to diminish the value of their efforts. It only means that someone needs to get up the courage to try again, go in with a questioning attitude and find the darn little nugget of understanding that was missed previously. We all know how many times Thomas Edison failed before he produce a working bulb.

I fully expect that repeated efforts at a foiling C Class could find a breakthrough such that the boat would excel in the upper range of the class winds speeds. I am not sure how competitive it would be in light air.

#37 blunted

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Posted 20 December 2011 - 01:20 PM

I feel like we keep going in circles on this.

Tri-foilers and C-class are apples and oranges. a tri-foiler is about as wide as it is long, a C-cat is half that beam. Once you start looking at the centers of force on foils the beam shrinks more. The rig on a C-cat is way taller, so pitch and heeling moments are quite high compared to a tri-foiler.

Once you look at those two factors you start seeing diminishing returns, big time. If you study Kettermans project, beam adds very healthy performance returns, which is simply illegal in C-cat's narrow box. I suspect if you did a C-cat even 2' wider, in a foiler, you might start to see some progress past more archemedian boats. But alas, we have rules for a reason.

As for one central foil set... Well you need a lot of windward heel to start to get in the range where the added mass of the wing to weather makes sense, and you need a really deep foil to pull it off as well which offers up some structural challenges in and of itself. Yep, I have looked at this extensively this summer. Just balancing off heeling and righting moments, and the penalty you pay in additional heeling moment for flying the boat high enough to clear waves and heel to weather. you could cut beam to make it easier to heel but then you are pissing away your most valuable resource, righting moment. Which is also an issue in having a center foil, you are giving up a ton of leverage to achieve the simplicity of a single foil scheme.

#38 Kenny Dumas

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Posted 20 December 2011 - 07:03 PM

Blunted, on max beaam: "But alas, we have rules for a reason."

But rules are meant to be broken as well, or changed. It would be so cool to see foils combined with the C-class wings. If all it takes is a rule change, would you just remove the max beam rule or pick a new max beam? Any discussion amongst the competitors on this?

#39 Doug Lord

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Posted 20 December 2011 - 09:31 PM

Blunted, on max beaam: "But alas, we have rules for a reason."

But rules are meant to be broken as well, or changed. It would be so cool to see foils combined with the C-class wings. If all it takes is a rule change, would you just remove the max beam rule or pick a new max beam? Any discussion amongst the competitors on this?

----------------------------
C Class catamaran compared to C Class monofoiler, in detail : http://www.boatdesig...csrr-31154.html

#40 Fat Point Jack

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Posted 20 December 2011 - 09:45 PM

Do ya think Dr. Bradfield could bring the foiler to the Kelly Park Regatta in early June?

Matt Mac Donald is generally there.

It would be interesting to see how it performs doing WL's.

#41 Doug Lord

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Posted 20 December 2011 - 10:04 PM

Do ya think Dr. Bradfield could bring the foiler to the Kelly Park Regatta in early June?

Matt Mac Donald is generally there.

It would be interesting to see how it performs doing WL's.

-------
I have no idea what ther plans are-I'll mention it next time I see them. I'd like to see that too!

#42 P Flados

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Posted 21 December 2011 - 01:43 AM

Tri-foilers and C-class are apples and oranges. a tri-foiler is about as wide as it is long, a C-cat is half that beam. Once you start looking at the centers of force on foils the beam shrinks more. The rig on a C-cat is way taller, so pitch and heeling moments are quite high compared to a tri-foiler.


The above actually states an aspect of the Off Yer Rocker that I had either not read or had not fully understood, thanks for the insight.

The C Class is set up for a specific wind speed range and this has led to features that are drastically different than what the Kettermans and Dr. Bradfield had in their early efforts.

The very tall rig and beam limit really does shift all of the equations a lot. If the beam limit were re-worded to be waterline only, a J Foil extending outboard of the hulls would increase the effective foil spacing drastically. But the rules are the rules, and changes should only be considered when there is a real reason to.

On the other hand, general improvements in understanding how to optimize foil use can shift the equations around in different directions.

If the current Osprey can be tweaked and this results in a high performance t-foil cat, lesson learned from his efforts may be usable for other cat efforts.

#43 Doug Lord

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Posted 21 December 2011 - 01:56 AM


Tri-foilers and C-class are apples and oranges. a tri-foiler is about as wide as it is long, a C-cat is half that beam. Once you start looking at the centers of force on foils the beam shrinks more. The rig on a C-cat is way taller, so pitch and heeling moments are quite high compared to a tri-foiler.


The above actually states an aspect of the Off Yer Rocker that I had either not read or had not fully understood, thanks for the insight.

The C Class is set up for a specific wind speed range and this has led to features that are drastically different than what the Kettermans and Dr. Bradfield had in their early efforts.

The very tall rig and beam limit really does shift all of the equations a lot. If the beam limit were re-worded to be waterline only, a J Foil extending outboard of the hulls would increase the effective foil spacing drastically. But the rules are the rules, and changes should only be considered when there is a real reason to.

On the other hand, general improvements in understanding how to optimize foil use can shift the equations around in different directions.

If the current Osprey can be tweaked and this results in a high performance t-foil cat, lesson learned from his efforts may be usable for other cat efforts.

============
PF- this won't work- Ketterman tried it on the Trifoiler. Simply put the aspect ratio of the foil is negatively affected by leeway resulting in high and low pressure on the same side of the lee foil. Go here and read post 54 and Kettermans paper on the subject: http://www.boatdesig...ce-36401-4.html This is also the reason why Ketterman believes a "J" foil(pointed inboard) is superior to a t-foil for main lifting foils.....

#44 P Flados

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Posted 21 December 2011 - 03:16 AM

PF- this won't work- Ketterman tried it on the Trifoiler. Simply put the aspect ratio of the foil is negatively affected by leeway resulting in high and low pressure on the same side of the lee foil. Go here and read post 54 and Kettermans paper on the subject: http://www.boatdesig...ce-36401-4.html This is also the reason why Ketterman believes a "J" foil(pointed inboard) is superior to a t-foil for main lifting foils.....


Argh foiled again.

Actually I knew this, but it had slipped my mind.

I like the physics of the inward pointed foil.

It would be interesting to take an Osprey or similar platform and do some sided by side testing again.

#45 dacarls

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Posted 21 December 2011 - 04:39 AM

Blunted has actually answered my question on the utility of changing the incidence on the weather foil of OffYerRocker to reduce its lift: "The incidence of the weather foil was not changed as we didn't really need too, it was a flapped foil with plenty of range to play through, both positive and negative".

Ah So..They didn't change it: Thank you very much. Since I never saw or sailed Rocker, I am totally qualified to say that this might have worked. 8^)

As PF said. I didn't understand all of S. Killing's paper either, but when he said they had to sheet out the wing because of excessive lift of the weather T-foil.....
No wonder its polars were slower. Just sayin'.

I would have answered yesterday but I was still gobsmacked by Nauti....

#46 Doug Lord

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Posted 27 January 2012 - 02:04 AM

Very good video of Osprey two up in lightish wind. Matt McDonald sailing:



#47 Doug Lord

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Posted 27 January 2012 - 08:15 PM

Correction: Mike McGarry(sp?) sailing......

#48 Dawg Gonit

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Posted 01 February 2012 - 04:42 AM

So how come we can't have a small version where you sit in the center hull.

Something to replace the 2.4mR in the Paralympics???

#49 Doug Lord

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Posted 01 February 2012 - 02:01 PM

So how come we can't have a small version where you sit in the center hull.

Something to replace the 2.4mR in the Paralympics???

--------------------
Not one single reason except cost of development. Bradfiel started with the Rave where you sit in the center hull but it was slow in under 10-12 knots. A sit-in foiler could be built as small as 12' but it would have to be 100% carbon and would be fairly expensive. Bradfields Osprey is 60 grand.....12 footer between 15 and $18,000 w/o dealer pricing included.

#50 trenace

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Posted 01 February 2012 - 05:47 PM

Wow... three hulls not one, dual wands and foils, and yet comparable price to a Moth.

Fantastic!

And I do mean, fantastic.




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