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Exceeding the hull speed on older longboards
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konajoe



Joined: 28 Feb 2010
Posts: 502

PostPosted: Wed Aug 12, 2015 1:45 pm    Post subject: Reply with quote

[/quote]
Once the Formula board can pop up onto plane it's a different story and the long board doesn't stand a chance.
[/quote]

bredtoshred would be.
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konajoe



Joined: 28 Feb 2010
Posts: 502

PostPosted: Wed Aug 12, 2015 1:58 pm    Post subject: Reply with quote

Hi Ittiandro!

Here's something else to think about. Get a variety of boards, a 200 lb weight, a rope, and a strain gauge. Let's say that the boards are your 293, that old Equipe, an 80 ltr wave board, a formula board, and the Mistral Prodigy, which has the same general outline as a formula board, but alot more volume.

Pull all of the boards through the water at 5 kts, and read the gauge. The Equipe is going to be the easiest to pull because of it's combination of volume and width. So, it's going to require the least pull from your sail to go through the water at 5 kts. The 80 ltr board will measure the highest, because it will be partially submerged. It will take the most pull from your sail to get it going 5 kts. The Prodigy will be easier to pull through the water than the formula because of it's extra volume.

So the ability of a board to go through the water at 5 kts will be a function of a bunch of things, including volume and width.
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Sailboarder



Joined: 10 Apr 2011
Posts: 656

PostPosted: Wed Aug 12, 2015 2:02 pm    Post subject: Reply with quote

ittiandro wrote:

I have to credit you for explaining in one short paragraph why the hull speed is relevant only to non planing crafts and not to windsurfing boards, because they can plane, often at close the theoretical hull speed.
This is something I understand less, because, if the theoretical hull speed ( according to my “ primitive” formula, of which later) is about 5 knts/hr, I cannot bring myself to believe that one can plane a board at such a low speed unless he or the board has no weight ( or almost!) and sails with a..12 m2 sail or the wind is far above 6 knts. When you say quote Most longboards (excluding perhaps D2 boards and maybe the Superlight) transition seamlessly to planing somewhere near their theoretical "hull speed"unquote , I must ask YOU, for clarity sake, what you mean by longboards and which ones are these wonder boards I am afraid there is a bit of a hype here.

You also say that I use the most primitive formula for hull speed, because it does not take into account the weight of the craft. You are theoretically correct, however the weight factor is relevant only to non-planing crafts because they have by nature an extremely wide range of weights.. Certainly the hull speed of a 15 ft/150 lbs sailboat is quite different from that of a 50 ft yacht or a supertanker, but becomes irrelevant in computing the hull speed of windsurfing boards: their weight and their weight range is relatively small, unless you go to extremely light( and expensive) materials, like carbon. An older longboard of the 80’s /90’s weighed about 15-16 kgs, almost the same of a Kona 1 today . My Bic 293 is about 15 kg as well. So what relevance does it have to inject the weight into the Hull speed equation? We are always around 5 knts, afterall !

Itiandro


The craft weight is not the weight of the hull, but the whole thing, including sailor. This gives more than 5 kts, more than 8. And the number given earlier of 8 kts of board speed to stay on plane make sense too. It takes more wind than 8 kts to be planing on most longboards though.
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isobars



Joined: 12 Dec 1999
Posts: 19216

PostPosted: Wed Aug 12, 2015 2:16 pm    Post subject: Reply with quote

konajoe wrote:
Your trying to learn this stuff.

Or just start a hypothetical academic physics discussion.
After all, if we wanted to know what type of boards are fastest under what conditions, we'd discuss THAT, by brand and model, rather than displacement hull physics.
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ittiandro



Joined: 22 Nov 2009
Posts: 248

PostPosted: Wed Aug 12, 2015 4:47 pm    Post subject: Reply with quote

[quote="cgoudie1"]Greeting ittiandro,

You can derfine longboard however you like, but the standard
windsurfing definition of longboard is a board with a centerboard
(or daggerboard).

I won't insist on hair splitting about definitions, also because it is not known which authority( if there is one) has officially defined longboards the way you think, unless one is to rely on the marketing spin of manufacturers, like Bic, which market the Bic 293 as a longboard just to lure customers who don't know better...I was one of them when I bought my Bic 293 ! Four years after, when I compare my Bic 293 it to a Mistral Equipe, with its far superior performance in sub-planing, I have come to realise that calling a Bic a 293 a longboard is not only a substantial stretch of imagination,but a misnomer.

I'll say that in common parlance, the watershed criterion defining longboards as opposed to shortboards is the type of hull: manufacturers can make their boards as long as they like and put a centerboard on them, but as long as they are flat-bottomed (as ALL the shortboards are) these " longboards" are still shortboards, because their water-dynamics are entirely different from the hydrodynamics of a displacement type of hull. THe presence of a centerboard will never make a flat-bottomed shortboard behave as a V-shaped hull.

Ittiandro
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isobars



Joined: 12 Dec 1999
Posts: 19216

PostPosted: Wed Aug 12, 2015 5:12 pm    Post subject: Reply with quote

If one of us can choose or even change the long-accepted definition of a longboard (a board with a daggerboard), I guess one of us can declare all of today's boards "flatbottomed". However, that simply introduces a new and undefined term to the mix: Define a "flat bottom". i.e., HOW flat ... especially considering that having vee defined a displacement hull just a few posts ago? And are we talking flat laterally, longitudinally, both, or neither?

Naaah. If it's got a daggerboard, it's a longboard, and vice versa. That's worked for millions of WSers on at least 6 continents for 40 years; no one person, not even Baron Bic, has the gravitas to just up and change it now.
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dllee



Joined: 03 Jul 2009
Posts: 4552
Location: East Bay

PostPosted: Wed Aug 12, 2015 5:52 pm    Post subject: Reply with quote

D-2 boards like the Crit and Lechner blows doors on anything in slogging conditions.
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NickB



Joined: 30 Jun 2009
Posts: 510
Location: Alameda, CA

PostPosted: Wed Aug 12, 2015 5:59 pm    Post subject: Reply with quote

since the term "longboard" seems a bit controversial, maybe for this discussion a better differentiator would be "sailboard" vs. "windsurf", i.e. hull design based on sailing boat vs. surf board.
Her's some info from an 1980 sailboard racing book I have:



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whitevan01



Joined: 29 Jun 2007
Posts: 605

PostPosted: Wed Aug 12, 2015 6:59 pm    Post subject: Reply with quote

awesome, Nick.

Ittiandro,

Equipe, Ultramegacat, Phantom - these are really raceboards (www.raceboard.org) -by the way, there is a lot of great info about raceboards, hybrid raceboards, etc. at this site under the "Rules and Regulations" button. Your Bic is listed as an R 300 board, not a longboard raceboard.

Exocet Pacer, NP RSX Olympic board, Prodigy - these were marketed as hybrid boards, and were supposed to combine the light wind and upwind abilities of raceboards with the planing capability of formula boards. I have a Pacer with the 9.5 Pacer sail, it goes upwind with raceboards in light winds but it much slower off the wind in subplaning conditions as it is not long enough. However, it does plane in lighter wind than a raceboard, but doesn't have the speed or early planing of a formula or large slalom board. (the Prodigy is a dog compared to the RSX or Pacer. the Pacer is actually faster than the RSX but NP offered the IOC a full kit of rig and board whereas Exocet only offered the Pacer board, so the IOC (or whomever is responsible for choosing Olympics boards) chose the RSX. the RSX replaced the Mistral IMCO which is based, IIRC, on the Equipe. The idea was to get a windsurf/sailboard in the Olympics which could plane so would be more exciting to watch but which could also be sailed in non-planing conditions, considering that wind conditions are not one of the criteria on which Olympic venue decisions are made).

Your Bic was designed to be a one design board to be used as a trainer board for kids who wanted to go the RSX Olympic windsurfing route.

I can understand your disappointment in the non-planing speed of your Bic, after all, it's only 293 cm long. I had a similar disappointment with the Pacer 300, and although I still have it, I also acquired a Fanatic Megacat which is awesome, esp off the wind, in sub-planing mode. (380 cm long and narrow)

The good thing about your Bic is that you can sail it in all wind strengths, but won't be as good as boards designed for particular wind/wave/swell conditions.

also, don't dismiss my suggestion to read C.A. Marchaj if you really want to know about all the science stuff. I read at least a couple of books that he wrote during my education in physics and fluid mechanics as related to sailing. He, quite literally, wrote the book(s). You'll learn about what others have posted on here as well as prismatic coefficient, Froude number, etc.

flat bottomed boards w/o daggerboards are sometimes called "funboards" as opposed to raceboards. V- or round bottom displacement boards were called Div. 2 boards and have all but disappeared, mostly because they are not "fun", as far as I can tell. (http://www.opendivision2.org/)

If you want to go real fast in non-planing conditions, there is a board from Australia called the Jim French Dart (http://www.seabreeze.com.au/forums/Windsurfing/General/OPEN-CLASS-BOARDS/) that is basically a very narrow laser sailboat, or go find a Starboard Serenity.

Have fun!!!!
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ittiandro



Joined: 22 Nov 2009
Posts: 248

PostPosted: Wed Aug 12, 2015 11:38 pm    Post subject: Reply with quote

konajoe wrote:
Hi Ittiandro!

I'll take a crack at some of your questions. I think your getting hung up on making planing and subplaning a sudden transition. If you looked at a 30ft sailboat, it's waterline would be the same from zero up to it's maximum speed. Not so with that Equipe or your 293 or any board. Your waterline will change with speed. So, think of subplaning, slow planing, medium planing, full planing. Does that help?

Things get really nutty if you get hung up on that waterline formula. Think about it. You get a small puff, and the attitude changes to a little more nose up. Oops, your water line just got shorter, so the max speed just went down.

You're trying to learn this stuff, and you trusted someone who gave you some bad info. Happens to all of us, no matter what we're trying to learn.


Thank you for your comments
There is so much background noise surrounding this thread that it is difficult to see how many of the statements made by members ( true or false) are relevant to the issue and to my original question. It is like a symphony without a conductor, in the end a dismal cacophony..
Let me walk you back to my initial post opening the thread. I had asked a well-known windsurfer and windsurfing expert why an old Mistral ( which I still insist on calling a true longboard ) was performing so much better in subplaning mode than my flat-bottomed Bic 293, (which I still call a shortboard, in spite of the desperate quibbling of those who muddle the issue by asking me to… define how flat a flat-bottomed hull should be to be called ..flat. Sounds like the vacuous “ laudes fumi et pulveris“, i.e the “ Praises of smoke and dust” in which the Byzantine intellectuals engaged and spent a considerable amount of their in other aspects so remarkable intellectual energies..
The”expert’s” reply was :
Quote With longboards, sail size doesn't matter nearly as much. In non-planing mode a board has a "hull speed" based on its length. It doesn't take much power to get near to the hull speed, but it takes a lot of power to go faster than the hull speed. So you can cruise at a reasonable speed with a small sail like a 6.5, and a bigger sail like an 8.5 will only make you a little bit faster, unless it's windy enough to plane Unquote

He brought in the concept of hull speed and, based on the general formula H.S.=1.34 X LWL, I read him as implying 1) that the board could plane with as little as 5 knts /hr and 2) that it is very difficult to exceed the hull speed. This puzzled me because I never seen anybody planing in 5 knts and, on the other hand, because in the transition between sub-planing and planing, people substantially exceed the 5 knts hull speed, especially with large sails and a relatively small weight...
When you say that in my attempt to learn, I relied on somebody who gave me the wrong info, do you refer to statement I quoted above? If so, well, it was none other than James Douglass and, honestly, I’d rather think that it was me to have misunderstood him in raising the question. In fact somebody pointed out that when I defined the hull speed of a 12 ft longboard as approx 5 knts/hr, I didn’t take into account the weight factor. This is the turning point of the whole discussion: in fact by taking the weight into account, the hull speed would increase to approx 8 knts, which is more in line with the speed people can plane in light winds, especially with larger sails and a relatively small weight. Unfortunately only one or two people saw where my problem ( the weight factor) was and corrected me. The vast majority lashed out with less relevant or even irrelevant points, however true they may have been.. Furthermore, he person who qualified my statements as “ bloody nonsense” was not the one who saw and told me where I was wrong..

As to your remarks on the waterline changing with speed, I agree with them but I don’t see how they should clarify my original question and explain the better subplaning performance of the Mistral or similar long boards as compared to the my Bic 293 and similar shortboards..Neither do I understand how the max speed would go down with a decreased waterline..As I see it, the waterline decreases as the board approaches the planing point by rising to the surface of the water. The board should increase its speed, not decrease it, because there is less water resistance in planing..

Ittiandro
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