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Volvo Extreme 40 specs?

Posted By: DHO

Volvo Extreme 40 specs? - 06/02/06 01:13 AM

Anyone know these? Is it a "box rule" such as A
class? The pitchpole picture looks like a 30 foot beam.

David Ho
TheMightyHobie18 1067
Posted By: Boomer

Re: Volvo Extreme 40 specs? - 06/02/06 07:32 AM

LOA 40 ft.
BEAM MAX 23 ft.
MAST HIGHT (2 part mast -100 kg) 62 ft.

MAIN area 75 m ²
JIB area 25 m ²
GENAKER area 78 m ²

DISPLACEMENT
(including safety & engine) 1250 kg
TOP SPEED 40 kts.
4 crew + 1 Non Participant

The link :

http://www.volvoextreme40.org/vx40.asp
Posted By: waterbug_wpb

Re: Volvo Extreme 40 specs? - 06/02/06 01:36 PM

Where do they put the "non-participant"?

The scene from "What About Bob" comes to mind....
Posted By: Wouter

Re: Volvo Extreme 40 specs? - 06/02/06 04:11 PM



Quote

TOP SPEED 40 kts.



Hell; why not 50 knots ? Better still 60 !

Ohh darn, no water born sail craft ever went beyond 50 knots, so that will be a little too obvious.

Okay lets settle on 40 knots then. Only 8.6 knots slower then the most technologically advanced multihull ever. Never mind that it could achieve this speed only on a starboard tack, we'll just say we can do 40 knots on either tack using a low tech soft sail rig. The people in the world are simply too dumb to think for themselfs anyway, they will believe anything we say.

Who out there truly understands that this is aerodynamically impossible ?

Wouter
Posted By: howlin

Re: Volvo Extreme 40 specs? - 06/06/06 10:11 AM

Wouter,

Now, I remember you! Weren't you the tall, skinny Dutchman standing at the foot of the Kill Devil Dune, screaming "It'll never fly!"?
Posted By: Rolf_Nilsen

Re: Volvo Extreme 40 specs? - 06/06/06 11:32 AM

Howlin,

got any documentation showing that the VX40's have done 40 knots or above (or even anything closely resembling such speeds)?

The Tornado class (and others) have claimed 30 knots, but there is no documentation. GPS logs from users on this forum show a max speed for beachcats around 25knots. At least they did so the last time we had this discussion.


Media/PR-companies and sailors make outrageous claims about speeds from time to time. Like the VOR70's doing 35 to 40 knots in the southern ocean.. Yes, perhaps free-falling off a wave generating a high local speed on the GPS, but it is not something they are able to (or want to) reproduce, more a measuring problem.
I dont believe much of whatever speed a class claims unless the documentation is there. Knowing who the marketing genius behind the VX40s is, I make a point out of not believing any speed claims before they are documented.


The Wright brothers knew what they were doing. Plenty of prior art and others along the same path. The same goes for the VX40s, plenty of similar crafts who has not gone to 40knots.
Posted By: bvining

Re: Volvo Extreme 40 specs? - 06/06/06 11:51 AM

How do they get these puppies across the pond? Do they sail them? or do they get a ride on a larger vessel?
Posted By: Rolf_Nilsen

Re: Volvo Extreme 40 specs? - 06/06/06 11:55 AM

I think I heard that they was shipped in containers. Mast is two-part, so it should be quick and easy.
Posted By: Anonymous

Re: Volvo Extreme 40 specs? - 06/06/06 01:56 PM

I heard on the video on the site that Holmatro was clocked at 36 kts.
Posted By: howlin

Re: Volvo Extreme 40 specs? - 06/06/06 03:30 PM

Rolf,

Something must have been lost in translation! I was poking fun at Wouter's ascertation that 40knts was impossible...............

I do not doubt the 40knt claim, as I have been on a cat clocked at 30knts plus,according to the on-board GPS.
Posted By: bvining

Re: Volvo Extreme 40 specs? - 06/06/06 04:14 PM

Quote
Who out there truly understands that this is aerodynamically impossible ?


Wouter,
First of all - lighten up
Second the VX40 website says "max" speed 40knots
Third if a soft sail Crossbow II went and AVERAGE of 36knots in 1980 on a 500M course, what makes you so sure a VX40 cant hit 40 for a brief moment or two?

We've had 26 years of technology since Crossbow to add 4knots? I'm thinking this isnt beyond belief. Its a rather extravegant claim, but its not necessarily improssible.

You've never sailed a VX40 - right?
You've never seen one sailing? (in person) Right?
Have you even seen one at the dock?

What makes you an expert on how fast they can go?

Bill
Posted By: Wouter

Re: Volvo Extreme 40 specs? - 06/06/06 04:17 PM


BullSh!T

Show us the track and the GPS log. And they better be showing us a stable and sustained speed track with consistant coordinate points.

Currently I got two tracks showing a F16 did 110 km/h and 400 km/h. Both were GPS measurement glitches like Rolf said. Every now and then a GPS receiver miscalculates a point, sometimes even by several hundred meters (hence the over 400 km/h speed recording ! The boat was actually stationary on the beach at the time)

So don't give us smack talk just give us proof !

Wouter
Posted By: Wouter

Re: Volvo Extreme 40 specs? - 06/06/06 04:20 PM



Was that the same video were the sped up the footage to make it look like these boat were going really fast (as happened with the Rio de Janero in port VX40 races !)

Wouter
Posted By: bvining

Re: Volvo Extreme 40 specs? - 06/06/06 05:58 PM

Why should they show you proof? Who made you king?

The only other thing you've proven is that you have a crappy GPS unit.
Posted By: MauganN20

Re: Volvo Extreme 40 specs? - 06/06/06 06:55 PM

Quote

The only other thing you've proven is that you have a crappy GPS unit.


And that he has a potty-mouth :P
Posted By: Wouter

Re: Volvo Extreme 40 specs? - 06/06/06 07:23 PM



Still waiting for that proof guys.

Wouter
Posted By: mbounds

Re: Volvo Extreme 40 specs? - 06/06/06 07:34 PM

Quote
So don't give us smack talk just give us proof !


You obviously don't understand the difference between marketing hyperbole and "truth". They have nothing to do with each other.

("35.51 knots? Cool! We can round it up to 40 and use it in advertising!")
Posted By: bvining

Re: Volvo Extreme 40 specs? - 06/06/06 09:39 PM

Quote
So don't give us smack talk just give us proof !


You're the one smack talking.
Posted By: Anonymous

Re: Volvo Extreme 40 specs? - 06/06/06 10:04 PM

Here you go girlie: It was the full version last day Portsmouth race one.
Posted By: Berny

Re: Volvo Extreme 40 specs? - 06/06/06 10:18 PM

Struth! I think you all need to lighten up.

"potty-mouth"??? "smack talk"??? What the...., are you going to give him a good smack and sit him on the potty. How about washing his mouth out with soapy water?
Wouter, you're a naughty, naughty boy. Now go sit on the potty till you can play properly.
Sheeeesh! (oops! Now I'm in trouble)
Posted By: Clayton

Re: Volvo Extreme 40 specs? - 06/06/06 10:52 PM

I've got the popcorn, looks like it will be a good cat fight!!! oops, did I say that?

I think somebody needs a little prozac! Heck maybe we all do... <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Clayton
Posted By: C2 Mike

Re: Volvo Extreme 40 specs? - 06/06/06 10:57 PM

Quote

BullSh!T

Show us the track and the GPS log. And they better be showing us a stable and sustained speed track with consistant coordinate points.

Currently I got two tracks showing a F16 did 110 km/h and 400 km/h. Both were GPS measurement glitches like Rolf said. Every now and then a GPS receiver miscalculates a point, sometimes even by several hundred meters (hence the over 400 km/h speed recording ! The boat was actually stationary on the beach at the time)

So don't give us smack talk just give us proof !

Wouter


You are the one saying it's impossible. IMHO the onus of proof is on you. I'd personally be suprised if they often do such a speed but definatly wouldn't say it's impossible.

Tiger Mike
Posted By: Jake

Re: Volvo Extreme 40 specs? - 06/07/06 12:30 AM

I can tell you that I went faster than I have every been on a cat before in the Tybee...I think it was day 5 to Fernandina. Frank and I were double trapped and wrestling to reach deep (no spinnaker) in a pretty good patch of breeze, Frank is watching the GPS and calling out speeds 23 mph!...22mph! 23.5 mph!...24 mph!...and then a gust hit and about jerked the boat out from under us. Frank dropped the GPS to work with the sheet and I eased the traveler thinking we were doomed. My eyes stayed glued on the bows (I remember wanting to close my eyes but I couldn't look away) but to my amazement they stayed dry. I don't know how fast we actually went, but the GPS recorded a max speed of 29.9mph (26 knots) - and I might actually believe it. I don't think it's that unreasonable to expect one of those beasts to be able to touch 40 knots - unlikely ... maybe ... but all this is simply conjecture.
Posted By: Wouter

Re: Volvo Extreme 40 specs? - 06/07/06 10:38 AM



It is obvious to see. Going from 26 knots to 40 knots sees a 250 % increase in drag. This is why the record breaking boats are foiling or full planing hulls (as crossbow was).

All that drag gas to be overcome by a 250 % bigger thrust while at these angle of attackt leads to 400 % higher capsize moments. These VX40 boat were pitchpoling in 15 knots already. The are lifting a hull in as little as 6 to 7 knots, What do you think 20 to 30 knot winds will do ?

And this thrust has to be produced by soft sails which pretty much max out at an angle of attach of 25 degrees. Below 15 degrees the shape collapes unless you start using landyach setups which have done away with squaretops as you simple can't control them at these small angle of attacks. The VX40 feature very large squaretops.

The energy has to come from somewhere ; if you do the math you come out at required windspeed of at least 20 knots (and that is a very conservative minimum). Crossbow, yellow pages, Minard and even long shot (planing and foiling craft with way less drag) needed winds of AT LEAST 30 knots to break the 40 knots threshold. Why should VX40 do it in anything less ? Even the Maxi cats sustained their records in 30 knots winds or more. Any guesses as to what the seastate is at 30 knots ? Again, crossbow, longshot, yellow pages and the rest of them all made their runs on special locations with extremely flat water conditions.

And we must not forget that by far most of these record breakers were all using asymmetrical rigs and boards. I think longshot is the exception. This means that they were fully tweaked to run very fast on one tack ONLY. We all know that the VX40 is fully symmetrical. This is a serious hinderance to high speeds.

Being lightweight or not is not really an issue in these record speed attemps. Optimizing lift to drag ratios is. That is why these record attemps either use solid sails are very rigid windsurfer rigs.

It quickly becomes a problem of aerodynamics. And that is only when you have solved the hydrodynamics part first. 40 knots on a displacement hull is not a receipy for succes. The amount of drag goes through the roof. So you'll need planing hulls, bruce foils or full foiling. But even foils get into cavitation problems above 45 knots.

Enineering wise going from 26 knots to 40 knots is a major undertaking where you optimizing everything to achieve that single goal of high speed. Accepting pay off in all other areas. Areas like pointing, low wind speed, symmetry. All areas where the VX40 DID NOT skim on.

Therefor the idea of a VX40 doing 40 knots as max speed is just nonsense. I will be impressed if they do 30 knots. Using some carbon or kevlar doesn't change any of the engineering problems that took several teams (like crossbow etc) decades to solve. It is not about materials it is about hulls and rig design.

If you don't believe me then that is alright, go to college and do maritime engineering yourself for about 4 years, then spend about a decade to develop your own models and validate them with experimental data and then see whether you still believe these boats do 40 knots, just like that.

Wouter
Posted By: grob

Re: Volvo Extreme 40 specs? - 06/07/06 12:52 PM

Your post doesn't give any reason why 40 knots on a VX40 is impossible. Improbable maybe, you appear to be trying to confuse people with bad science.

Quote
"Going from 26 knots to 40 knots sees a 250 % increase in drag",

When the big multihulls go fast they do so in high winds with reefed sails, the centre of effort in the sail drops enabling you to handle more power.
Quote
These VX40 boat were pitchpoling in 15 knots already. The are lifting a hull in as little as 6 to 7 knots


we have all pitchpolled at low speeds it doesn't mean the boat can't handle higher windspeeds. Are you trying to perpetuate the myth that catamarans are unsafe in high winds?

Quote
"Any guesses as to what the seastate is at 30 knots


Speed records are set in flat water conditions why should the VX40 be subject to different rules.

Are you saying that square top sails are no good at high windspeeds, thats not correct, look at the windsurfer sails that break the speed records in very high windpeeds.

I am not saying its going top be easy but I don't see that max speeds of 40knots are impossible.

In previous threads you were arguing that windsurfers were slower than cats, whats it goin to be.

Quote
go to college and do maritime engineering yourself for about 4 years, then spend about a decade to develop your own models and validate them with experimental data and then see whether you still believe these boats do 40 knots, just like that.


Are you saying that you can only argue with you if you have this level of expertise, you certainly do not. I would imagine that these boats have been through some analysis of the type you describe and it is not inconceivable that this is where the 40 knot number comes from. The designers are quite reputable I guess they would want to stop any wildly inacuurate statements made about their boats as it would damage their own reputation.

Gareth
www.fourhulls.com
Posted By: MauganN20

Re: Volvo Extreme 40 specs? - 06/07/06 12:52 PM

blah blah blah...

I see a bunch of jargon up there and "geek speak" however one thing I know is...

the naval architects that designed the VX40's are better than you are Wouter. Which is why they are designing 40' racing cats and you're sitting there naked in front of your computer.
Posted By: davidtilley

Re: Volvo Extreme 40 specs? - 06/07/06 01:22 PM

I think Wouter made a pretty fair argument. I think the windspeeds required by record breaking planing windsurfers make their mechanics pretty irrelevant.
I dont think it would be too hard to figure the drag on the displacement hulls at 40 kt and figure that that much force a reasonable distance up the mast would have turned it over (one way or the other - )
I also know that anyone who sticks their neck out with a logical argument inviting discussion should be encouraged. That is why I come to this forum.
Basicly, if your post knocks someone else and contributes nothing, don't continue, it just makes more scrolling for all of us. Thanks for scrolling.
Posted By: MauganN20

Re: Volvo Extreme 40 specs? - 06/07/06 01:32 PM

well could the brainiacs in the group figure out how much more oomph it takes to push it from 36knots to 40?
Posted By: steveh

Re: Volvo Extreme 40 specs? - 06/07/06 02:32 PM

Quote
well could the brainiacs in the group figure out how much more oomph it takes to push it from 36knots to 40?


If you don't know this, then you shouldn't be knocking Wouter's "geek-speak."

Drag goes with velocity squared, so...

(40/36)^2 = 1.234 or 23% more drag. Therefore 23% more thrust and at least 23% more stress throughout the rigging.

Yeah, it's only 4 knots.
Posted By: steveh

Re: Volvo Extreme 40 specs? - 06/07/06 02:41 PM

BTW, I doubt that it's nav archs that design the speed boats. I'm guessing that more engineers are involved, specifically aeronautical. The nav arch curriculum simply doesn't get into the specialized aerodynamics and hydrodynamics involved in speed sailing. Not that it can't be learned.
Posted By: MauganN20

Re: Volvo Extreme 40 specs? - 06/07/06 02:55 PM

Quote
If you don't know this, then you shouldn't be knocking Wouter's "geek-speak."


Fortunately for me, I don't have to rely on Wouter speaking geek for me to knock on him.

He provides plenty of ammunition without it.
Posted By: Wouter

Re: Volvo Extreme 40 specs? - 06/07/06 10:57 PM


Quote

well could the brainiacs in the group figure out how much more oomph it takes to push it from 36knots to 40?



For an efficient displacement hull 30 % more drive (thrust) is needed. With the higher speed this means that 52 % higher energy input (=more horsepower) is needed. For a sailcraft this also means major improvements in the rig efficiency as the rig needs to harvest 52 % more energy from the same conditions BEFORE it can be translated into higher speed. A significant portion of the initial energy harvesting goes into kinetic energy of the craft; ergo into accellerating the craft to a high speed. This is why Macquarie Innovation needs a long track where it can pick up speed before it enters the measurement track of 500 meters.

You don't just hit 40 knots in a gust guys; you take a long time getting there.

I know some of you think :"Well it is only a short hop from 36 knots to 40 knots, how hard can it be ?"

Well, just find 50 % extra efficiency somewhere and your in.

That is not too much to ask, right ?

Wouter
Posted By: Wouter

Re: Volvo Extreme 40 specs? - 06/07/06 10:59 PM



Quote

Drag goes with velocity squared, so...



That is a conservative approach.

For displacement hulls a power factor of 2.5 is more appropriete.

Wouter
Posted By: Wouter

Re: Volvo Extreme 40 specs? - 06/07/06 11:17 PM


They were doing 36 knots in 15 knots wind ?

Yeah, Right !


BULLSH!T

Wouter
Posted By: jollyrodgers

Re: Volvo Extreme 40 specs? - 06/08/06 02:12 AM

top speed 40 knots just sounds like bad marketing to me. in sales it's best to be a vague as possible. limiting the abilities of the boat with the words top speed doesn't make much sense.
they said in the brasil article that the boats were at peak performance in something like 15 knots of wind, so the boats obviously are not really made for sailing comfortably in the kind of winds that you would need to go 40 knots. if you weren't on a speed course you would need to be in some radical open ocean stuff surfing down a giant wave to go 40. somehow i doubt they race those things like that. i have my doubts that they would ever hit 40 even at maalaea where we have pretty flat offshore conditions with sick high winds all summer long.

question- why isn't there a speed division of cat sailing? if i made a speed sailing cat it would have deep v hulls similar to a gcat or sizzler.-that statement should start a controversy, but i really think that's a fast shape.
Posted By: steveh

Re: Volvo Extreme 40 specs? - 06/08/06 04:10 AM

Quote
For an efficient displacement hull 30 % more drive (thrust) is needed. With the higher speed this means that 52 % higher energy input (=more horsepower) is needed. For a sailcraft this also means major improvements in the rig efficiency as the rig needs to harvest 52 % more energy from the same conditions BEFORE it can be translated into higher speed. A significant portion of the initial energy harvesting goes into kinetic energy of the craft; ergo into accellerating the craft to a high speed. This is why Macquarie Innovation needs a long track where it can pick up speed before it enters the measurement track of 500 meters.

Wouter


That mix of units is giving me a headache. <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />
power <> energy <> unitless efficiency
and
kinetic energy <> acceleration


Quote


Quote

Drag goes with velocity squared, so...



That is a conservative approach.

For displacement hulls a power factor of 2.5 is more appropriete.

Wouter


Except that at 30+ knots, a 40ft boat is well beyond displacement mode. I know, I know, a long, slender sailing cat hull "planes" differently than a short, wide power hull, but no way can it be considered displacement.
Posted By: Berny

Re: Volvo Extreme 40 specs? - 06/08/06 08:10 AM

I also doubt that general displacement principles strictly transfer directly to catamaran hull forms. I believe this has been a limiting factor in the development of catamarans over the years. Generally, classic displacement hull profiles are too radical IMHO, dictating too much rocker, and bow and transom lift resulting in the classic hobby horsing seen in early cats designed using these principles.
Not being an marine architect I can't back my suppositions with technical explanations, only experience and Logos.
Posted By: Wouter

Re: Volvo Extreme 40 specs? - 06/08/06 12:24 PM



So you are saying that a Navy Frigat doing 35 knots with its twin 10.000 HP gas turbine engines at full throttle (expending just over 1 liter fuel per second) is in planing mode ?

Speed itself doesn't determine wether you plane or not. The hulls shape has to be designed to go up on a plane otherwise you pretty much stay in displacement mode.

Remember the very old assie 18 skiffs ? Before the introduction of the planing hulls ? Same sailarea and still they couldn't get up to a plane.

Wouter
Posted By: Tony_F18

Re: Volvo Extreme 40 specs? - 06/08/06 12:41 PM

Who honestly gives a toss whether they can do 40kts or not?

I'm gonna check'em out in rotterdam this weekend and head for Texel next week, hope to see as many of you there.
Posted By: _flatlander_

Re: Volvo Extreme 40 specs? - 06/08/06 01:40 PM

Quote
question- why isn't there a speed division of cat sailing? if i made a speed sailing cat it would have deep v hulls similar to a gcat or sizzler.-that statement should start a controversy, but i really think that's a fast shape.


Yea, why not? Hope that SF Bay competition is successful. www.sanfransiscospeed.com
Posted By: steveh

Re: Volvo Extreme 40 specs? - 06/08/06 03:24 PM

Quote


So you are saying that a Navy Frigat doing 35 knots with its twin 10.000 HP gas turbine engines at full throttle (expending just over 1 liter fuel per second) is in planing mode ?

Speed itself doesn't determine wether you plane or not. The hulls shape has to be designed to go up on a plane otherwise you pretty much stay in displacement mode.

Remember the very old assie 18 skiffs ? Before the introduction of the planing hulls ? Same sailarea and still they couldn't get up to a plane.

Wouter


Hull speed of a 450 ft LOA FFG-7 class frigate is going to be about 27 kn. Published max speed for the FFG is 29 kn, so not planing.

However, a 40 ft cat (hull speed 8.5 kn) at 30+ kn is not acting as a displacement hull and if it's not planing, then it must be in the "fourth mode."
Posted By: Wouter

Re: Volvo Extreme 40 specs? - 06/08/06 03:29 PM


I still derives by far most of it's "gravitational suspension" due to archimedes law therefor it is still in its displacement mode.

Bethwaite invented some extra modes, but that is a different topic.

Wouter
Posted By: Jalani

Re: Volvo Extreme 40 specs? - 06/08/06 03:42 PM

Quote
then it must be in the "fourth mode."




Please, please don't go anywhere near mentioning HWSNBN!! <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />
Posted By: grob

Re: Volvo Extreme 40 specs? - 06/08/06 03:58 PM

It is very hard to say at what point a boat is planing, you will always generate some lift regardless of speed.

Interestingly if you plug a beach cat into the simple planing eqn given in http://www.hydrocompinc.com/knowledge/whitepapers/HC113-MinPlaningSpeed.pdf

You get a planing speed of about 30knots, and a VX40 gets on the plane at 40knots!

Is this the fourth mode <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Gareth
Posted By: steveh

Re: Volvo Extreme 40 specs? - 06/08/06 06:29 PM

Quote

I still derives by far most of it's "gravitational suspension" due to archimedes law therefor it is still in its displacement mode.

Wouter


Hmmmm, can you prove that, or am I required to disprove it? Also, define "most." Also, I have yet to see a consensus as to when a boat is planing. Or stating it another way, I have yet to see a consensus on what defines a planing boat. However, if you look at the immersed lines of the leeward hull of the attached F16, you see some straight, flat runs. So you have speed well in excess of hull speed, some percentage (most? significant?) of boat weight and sail force counteracted by dynamic lift, flow separating cleanly from the transom and a portion of the hull of proper (if compromised) planing geometry. If not planing, then in that power-sucking semi-planing regime. But not displacement.

[Linked Image]
Posted By: Wouter

Re: Volvo Extreme 40 specs? - 06/08/06 07:36 PM



Hull speed formulae are boogus when looking at beach catamarans. The hullspeed formula that is so often thrown about is really a misintepretation of the Froude law which actually only links wave length to wave speed.

For some boats the Froude law coincided with the maximum speed they can attained given a limited drive due to some factor. Of course all sailboats are limited in drive their sails can produce because of stability considerations.

Now Froude's law applied to beach cats as well it just that the commonly encoutered misintepretation of it is not rightfully applied to these designs. Hence the parados that catamarans can sail faster then "their maximum hull speed".

I can tell everybody out there that debunking the "max hull speed formula" is like fighting the multi-headed hydra. For some reason this "error" is immortal and ever since its rise to fame it has dominated discussions where. I'm done with it. If you don't understand the true meaning of Froude's law and the true nature of the "max hull speed" formula that is derived of it, then there is simply no use in continueing the discussion. It is like arguing that the earth is round with a midevil christian fundamentalist who thinks it is actually a flat pancake because he can see with his own eyes that it is flat. Sorry about this, but that is just the way things are.


Quote

If not planing, then in that power-sucking semi-planing regime. But not displacement.



Read Bethwaite very carefully again and then see where his "modes" are just names he gives to a limited series of specific displacement craft. He doesn't include catamarans for example and later on in the book he actually writes that cats are "different" and don't seem to have the forced displacement mode (or whatever he calls it). So his model is only applicable to a specific type of sail craft and it falls down when looking at more different craft.

And that Stealth F16 is definatly still in displacement mode. It may have a component of dynamic lift somewhere. Either from the angled foils or from some pressure build-up under the hull, but 80 % of its weight is still carried by archimedes law. Therefor it is a displacement craft. I'm sorry

Wouter
Posted By: davidtilley

Re: Volvo Extreme 40 specs? - 06/08/06 07:36 PM

I think it is a little simpler than that. Long slender hulls when exceeding hull speed have no benefit from cleaving the water surface, other than reducing surface friction, because the deck is in the air, which has less viscous drag than water. At these speeds, to be totally immersed starts to look good. Wave form drag is bad news. Every wave is literally energy running away from the boat. The "fourth mode" would be submarine mode. Large ships have recognised this with a practical compromise - the bulbous bow.
Posted By: scooby_simon

Re: Volvo Extreme 40 specs? - 06/08/06 07:52 PM

Who really cares

The Marketing boys have got people talking about the boats and so they are happy.



I just want a go on a Vx40
Posted By: Rolf_Nilsen

Re: Volvo Extreme 40 specs? - 06/08/06 09:07 PM

I also want a go on one, Simon. <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

I find this part of the discussion quite interesting. We just need some hard figures from the crews now to establish what kind of top speeds they have reached so far. Perhaps somebody has the opportunity to ask one of the crew?

Now, to derail the discussion. It's quite a huge and steep stern wave from that Stealth in the photo. Lower part of mainsail is very deep, large twist (and boom is characteristically out of column). Are they on some kind of reach?
Posted By: grob

Re: Volvo Extreme 40 specs? - 06/08/06 09:11 PM

Quote
Hull speed formulae are boogus when looking at beach catamarans.


I don't think anyone is talking about hull speed here, we have progressed to talking about planing speeds. I am certain from towing tests that I have perfromed that long slender hulls with elliptical profiles do plane. I had a video to prove it. But I wiped it, actually that sounds a bit like the alien autopsy story so forget I said it. <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />

You only have to look at planing moths to realise that long slender hulls can plane (just depends upon how long and how slender).
Posted By: scooby_simon

Re: Volvo Extreme 40 specs? - 06/08/06 10:46 PM

Quote
I find this part of the discussion quite interesting. We just need some hard figures from the crews now to establish what kind of top speeds they have reached so far. Perhaps somebody has the opportunity to ask one of the crew?


I'm hoping to catch up with Will Howden in the next few weeks - he's been on Motorola a fair bit.

I'll see what he has to say !
Posted By: macca

Re: Volvo Extreme 40 specs? - 06/09/06 12:44 AM

I think you need to remember that these are peak speeds they are claiming, not averaged over a 500m course as the record attempts are. The VO70's are hitting very close to 40kts and the theoreticaly should be no where near those speeds...
Posted By: davidtilley

Re: Volvo Extreme 40 specs? - 06/09/06 01:12 AM

Yes, water skis are long and slender (and badly designed for purely planing) but they defnitely plane. The problem is that hulls with rocker or a knuckle resist planing and literally suck themselves into a hole in the water. Some cruiser cats claim the stern upcurve as providing negative lift to resist forward pitching off the wind.!!!
Posted By: Keith

Re: Volvo Extreme 40 specs? - 06/09/06 01:21 AM

From reading about this a long time there is one problem when people throw about the usual hull speed formula - finess ratio. The formula in its common usage has a ratio that is kind of universally used to describe a wide but common variety of displacement shapes. Unless you apply a different ratio to it you don't get anything meaningful for catamarans. This was in a Sailing World article a long time ago (I probably still have it somewhere) that addressed this very question. Using different finess ratios that more closely reflected the shape of the hulls the hull speed numbers became more reasonable, at least when they stay in displacement mode. When you put up a big headsail and get the newer designs honking on the flat section of the hulls things are a little different. But just because a cat may go faster than the traditional hull speed equation says it should does not necessarily mean it is planing, although it may ultimately do that as well.
Posted By: jollyrodgers

Re: Volvo Extreme 40 specs? - 06/09/06 01:58 AM

waterskis do have some curvature to the tail rocker which is where the ski contacts the water whilst planning.
the fastest speed boards are flat in the tail, but wave boards have curved tailrocker.
also Bethwaite's book is incorrect on the statement that he makes about windsurfboards. he sure didn't see them as being possible holders of the speed record. the book is otherwise quite informative.
topspeed 40knots is an attention getter so the statement does work from that angle. something a little more creative would have been nice IMHO. they are preaching to the choir in our case anyway. obviously we all want to take one of those bad boys out for a ride.
Posted By: Jalani

Re: Volvo Extreme 40 specs? - 06/09/06 07:50 AM

Hi Rolf,

That pic was taken early 2005 as I recall, during a club race. We are beam reaching (just too shy for the kite) to our West Mark, in about 12-15mph of wind. It was just after this that I replaced the carbon boom with a stiffer ali one. We've got almost 180Kgs out on the wire!

That huge stern wave is more than likely caused by a bit of weed around the rudder - a permanent problem when our courses take us down into that corner of our sailing area!

In terms of displacement/planing arguments I'd hesitate to suggest that that pic proves anything!
Posted By: Rolf_Nilsen

Re: Volvo Extreme 40 specs? - 06/09/06 08:04 AM

Thanks John, everything explained..

What do yo do on the Stealth when you catch weed on the rudders? Park the boat to clean them?
Posted By: scooby_simon

Re: Volvo Extreme 40 specs? - 06/09/06 08:17 AM

Quote
Thanks John, everything explained..

What do yo do on the Stealth when you catch weed on the rudders? Park the boat to clean them?


Try and sail faster !

Acttually a good question Rolf.. Not so easy to just flip the rudders up !
Posted By: Jalani

Re: Volvo Extreme 40 specs? - 06/09/06 08:23 AM

I don't know about everyone else, but I take the opportunity mid-tack to lean over the stern and pull the weed off. Takes maybe 3-4 seconds, then another 5-6 seconds to get out of irons if it all works out! <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />
Posted By: Wouter

Re: Volvo Extreme 40 specs? - 06/10/06 08:36 AM


Using correction factors like that is nothing more then fitting the errornous formulae to reflect the data. And there that formula become extremely limited in its use. Afterall you must already now the REAL max speed to even calculate the correcttion factor needed. Additionally you screw up the relationship and you magnify the error.

Max. hull speed is nothing more then Froude's law with a different (and often errornous) intepretation.

Froude's law says that a wave with a wave length of X has a speed of Y ;

Wave speed = 1.54 * (wave length)^2

For alot of (displacement) sail boats this coincides with their maximum speed their hulls can travel through the water as their hull get trapped between two wave tops with insufficient drive to overcome the rapid rise in hull drag.

A good number of other sailcraft design DO HAVE enough drive to overcome this rise or have reduced the magnitude of the increase in drag to such an extend that it no longer plays an important role. The standard example of that is the catamaran hull shape.

It is of no use to use a corrector factor and just IMAGINE that the wave system is actually travelling faster then it is in real life just so to assume that that this corrected wave system encloses the cat hull at much higher speeds than it does in REALITY. We can just as well think up a story then little goblins start pushing against the bow of the hull at 20 knots; it has the same amoun to reality value = none.

That is the eternal myth of the max hull speed formula. And it is indeed immortal as in 12 months time we'll have this discussion AGAIN. In the mean time you can read this law 10's of times on so called professional boating magazines because the bulk of those journalists don't know squad about science as well AND because this formula is pretty accurate for heavy yachts.

And this is the way the "max hull speed" formula survives.

Wouter
Posted By: Keith

Re: Volvo Extreme 40 specs? - 06/12/06 05:21 AM

A few notes.

1 - The article did not take observed boat speeds and work backwards to make a correction fit. An approach was taken by which a different number was used in place of the standard 1.34, one method being to use hull length to beam ratio if I remember right. They then applied the approach to various different cats of the time to see how close it worked and reported the findings. In most cases it was fairly close.

2 - Don't know, but I don't believe the article was penned by a journalist. Of course, just because a journalist were to write something does not make it wrong. People with wonderful credentials can be just as wrong.

3 - The modification of the constant is in recognition that not all displacement boats get trapped by the wave system. Planing hulls climb over the bow wave, lighter displacement hulls with a narrow form cut through them. In this case the attempt is not to imagine that the wave system magically moves faster, by goblins or other means, but simply to characterize a hull type that doesn't get trapped. Is it an appropriate extension of the original formula then? Maybe not, but does that make it wrong? It probably tries to move towards a simplistic estimation of how the hull plows through the water regardless of the wave system using beam to length and displacement.

Anyway, out the cats I've sailed, all have greatly exceeded the traditional hull speed (using the traditional without the goblins method of calculation), and the only one that I would characterize as planing to any degree has been the I-20.

Of course, then there's the Farrier tris where the main hull has planing sections and the floats do not...
Posted By: Wouter

Re: Volvo Extreme 40 specs? - 06/12/06 08:17 AM



Quote

1 - The article did not take observed boat speeds and work backwards to make a correction fit. ...



So how was this correction factor derived ?


To me it still sounds like adjusting the gravitational constant to have the formula for falling speed reflect the true speed of a bag of feathers better.

Wouter
Posted By: Keith

Re: Volvo Extreme 40 specs? - 06/12/06 01:52 PM

Quote


Quote

1 - The article did not take observed boat speeds and work backwards to make a correction fit. ...



So how was this correction factor derived ?


To me it still sounds like adjusting the gravitational constant to have the formula for falling speed reflect the true speed of a bag of feathers better.

Wouter


Once again, by looking at the hull shape and characterizing beam to length ratios, displacement, perhaps prizmatic coefficient... I don't have the exact formula used in this case, but I do remember that they did not work backwords. But I have seen other approaches that use the displacement of the hull, and again, this is because it is known (as you have also stated) that narrow hull forms and those of lighter displacement can break out of the wave system without planing. ULDB monos are another case in point (although they may also plane). So again, they're not trying to make the wave system faster. They're trying to characterize the speeds of the boats.

And checking your numbers back against real data can help refine your approach as long you don't get into the "for a Hobie-18 use this factor, for a Taipan 4.9 use this other factor" trap. If you find from emperical testing that the calculations are more correct for light displacement boats of a certain LWL range if a certain factor is used, then that's ok.

And yes, because it takes something that worked for a specific case based on a certain principle and tries to make it reflect something else you can argue the merits of it. I think when you're out of the wave trap and still displacement that displacement, prizmatic coefficient, and water line length will act to determine a ballpark theoretical speed for the hull. So this actually may be useful even though it no longer holds to the principle it started with. Do I have all the numbers? Nope. But I also know that just because a Hobie 16 can do more than the speed indicated by the traditional hull speed formula does not mean it is on plane. And this may just be a good way to get a ballpark estimate, although it doesn't work in the traditional wave theory sense.

Note that I say ballpark - because any of these basic formulas take no real life things into account. It's strictly the hull in the water. Nothing about how efficient the rig is, upwind or downwind, how ungodly huge the wind resistance of the cabin structure is, how far the boat is heeled, or how many cheeseburgers the crew has snarfed in the last 12 hours.

Go back to the days of old when racing design formulas would restrict waterline length at rest. Large over hangs front and rear dramatically increased the waterline length when the boat was heeled.

If it's ballpark does it matter? To some people. At least they can have a better explanation as why cat hulls are not constrained by the usual thinking on displacement hulls. If I had a dime for every time somebody told me my cat was fast because it planed... Another explanation - multihulls are fast because you multiply the waterline length by the numbers of hulls, and thus the equation almost works again. I have to remind them that the boat should then slow dramatically when you fly a hull...

Anyway, good discussion, and yes we'll be debating this again soon. With respect to the original question of whether the V40 can do 40 knots. I suspect somebody came up with a theoretical max for the hull form of around 40 mph, and somebody turned that into knots because it sounded good that a V40 could do 40, and nautical types like to talk knots, donchano. The fact that the boats will never actually achieve that in real life doesn't matter unless they put the boats into speed trials...
Posted By: Jake

Re: Volvo Extreme 40 specs? - 06/12/06 02:46 PM

While we're talking about Volvo 40's <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />....

note the BOLD text below!

Quote
June 9, 2006, Rotterdam, The Netherlands – The Nieuwe Maas in Rotterdam provided some tricky conditions for the first day of the Volvo Extreme 40 grand prix racing series.

Team Motorola-CHR helmed by British Tornado sailor Leigh McMillan successfully mastered the light winds and tricky tides to finish the first day of the final grand prix series in first place overall. A second place in the first race was swiftly followed up with two race wins to give the British team of McMillan, Conrad Humphreys, Will Howden and Hamish Oliphant an early regatta lead. Team Motorola-CHR leads by four points to their nearest rival Team Tommy Hilfiger.

Skipper of Motorola-CHR, Conrad Humphreys was very pleased with his team’s performance, “It was a good day for us but it was hard to be consistent in the conditions. Plus it’s nice to find some form after Portsmouth. I think the extra work on the foils has definitely made a difference. We have spent quite a bit of time on them. The other important thing is to keep your cool when you are out there in not a lot of breeze because even if you are last you never know what can happen to the others.”


Team Tommy Hilfiger, the current overall series leaders also had a exciting day, skipper Randy Smyth commented, “It was a great work out today!”. Crew member Jonathan Farrar spoke of the challenging conditions compared to the heavy weather they had in Portsmouth. “It was pretty fickle breeze out there so it was hard to showcase the boats but I think we did a good job of it. We are really looking forward to sailing tomorrow outside in the sea off the Hoek van Holland. We should have lots more breeze and a great spectator fleet.”


Newcomer to the fleet Nigel Pitt, helming Volvo Ocean Race, is currently third today after scoring a 4-2-5 scoreline, followed by Basilica in fourth. James Grant skipper of the all British boat was obviously disappointed by their result today after winning the Portsmouth series. “We took the wrong side so we had to tack twice and lost out to Tommy Hilfiger with the lack of breeze. But really it was only three races and we have 15 left so it’s all to play for. In Portsmouth we got full points on the first day and today we only managed 50% so if you average that out it’s not too bad. It was real game of snakes and ladders out there.”

Mitch Booth and his team on Holmatro came in fifth place despite getting the same points as Basilica. On count back Basilica beat Booth in the last race after having level peggings till that point. “It was a hard day for a sailor who wants to go racing today. Unfortunately the little wind made sailing very tricky out there. We saw a few good little rides at times which would have been good for the spectators and TV but for the sailors it was a tough day.”
Tomorrow the fleet will head out of the Maas to Hoek van Holland on the North Sea where they will race on the Volvo Open 70 in-port race course and greet the arriving Volvo Open 70’s.

The Volvo Extreme 40s will be towed out of the Maas and will race a number of short races before making a ‘dash for cash’ up the Maas where a 1000 Euro prize purse will be up for grabs.
Posted By: Wouter

Re: Volvo Extreme 40 specs? - 06/12/06 03:59 PM



Okay lets put this discussion to bed.

One last note. Your last post did remind me alot of what the Texel and ISAF measurement handicap systems are actually doing. It is surprising accurate, even though you won''t find a physics basis to the coefficients and formulae.

Is this actually called heuristics ?

Wouter
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