| View previous topic :: View next topic |
| Author |
Message |
coachg
Joined: 10 Sep 2000
Posts: 3550
|
|
| Back to top |
|
 |
DelCarpenter
Joined: 06 Nov 2008
Posts: 499
Location: Cedar Falls, IA
|
 Posted: Thu Aug 13, 2015 2:25 am Post subject: |
 |
|
Imagine a sailing ship with a bow wider than 12 ft. That ship creates a bow wave that is larger than the height of waves in most sea states. Every longboard windsurfer I've ever been on creates a bow wave that is tiny compared to the height of waves in most sea states. How could the windsurfers bow wave be as limiting as that of a sailing ship with a 12ft wide bow? My experiences as a longboard windsurfer prove to me that the general formula for hull speed limits doesn't apply to some hull proportions and some hull sizes.
So I went to the Wikipedia "hull speed" article and learned some things. Here are three quotes:
"From a technical perspective, at hull speed the bow and stern waves interfere constructively, creating relatively large waves, and thus a relatively large value of wave drag. Though the term "hull speed" seems to suggest that it is some sort of "speed limit" for a boat, in fact drag for a displacement hull increases smoothly and at an increasing rate with speed as hull speed is approached and exceeded, often with no noticeable inflection at hull speed."
"The concept of hull speed is not used in modern naval architecture, where considerations of speed-length ratio or Froude number are considered more helpful."
"Light, narrow boats with hulls not designed for planing can easily exceed hull speed without planing; indeed, once above hull speed, the unfavorable amplification of wave height due to constructive interference diminishes as speed increases. For example, world-class racing kayaks can exceed hull speed by more than 100%,[1] even though they do not plane. Semi-displacement hulls are usually intermediate between these two extremes."
Responding to a post from NickB: the term "sailboard" arose from the need to not infringe on the "Windsurfer" patent to describe the various boards that were trying to compete with the "Windsurfer" company. "Sailboard" then and now refers to all boards used in all aspects of the sport we call windsurfing. |
|
| Back to top |
|
|
GURGLETROUSERS
Joined: 30 Dec 2009
Posts: 2643
|
| Posted: Thu Aug 13, 2015 3:28 am Post subject: |
|
|
Illiandro. Liked your quote 'It is like a symphony without a conductor, in the end a dismal cacophony.' Some contributors though, are trying to be helpful, and not just 'clever'.
Second Mr Carpenters post. Sea kayakers are well aware that long narrow sea kayaks have a natural and economically maintained cruising speed. (Mine is 4 m.p.h.) Once at that speed, the craft just 'locks in'. It can be exceeded (5 or 6 m.p.h.) for periods, but only at a disproportionate expenditure of energy.
I find something a little alike with longboards in light wind sub planing conditions, though NOT exactly so. If the board settles to its 'natural' sub planing glide speed, the size of sail, as Illiandro's friend claimed, doesn't really make a lot of difference. A bigger sail will give a slightly greater push (as upping kayak paddling power) but with only a little extra pace.
For that reason, some of us prefer to use a smaller sail (7.0 metre my favourite) in predominantly non planing breezes, which will still plane anyway in gusts. |
|
| Back to top |
|
|
boardsurfr
Joined: 23 Aug 2001
Posts: 1266
|
| Posted: Thu Aug 13, 2015 9:56 am Post subject: |
|
|
| ittiandro wrote: | | .. but what I meant by “ longboard” should have been clear in my context, since I mentioned the Mistral ( Equipe) and similar boards having a V-shaped displacement-type of hull . Frankly, I don’t even recall that there have ever been flat-bottomed longboards in the 80’s and 90’s. My “non-standard” definition of longboards couldn’t but refer to the ones having the classic V-shaped displacement-type of hull. |
You'll be hard pressed to find someone who agrees with you that the Mistral Equipe has a "V-shaped hull". As others have pointed out, there were indeed boards that have a pure displacement hull - the D2 boards. The Equipe is not in this category. The later version of the Equipe where rather similar in shape to classical longboards like the Fanatic Ultra/Mega Cat and the F2 Lightning. In fact, the Equipes from the 90s actually had a wider and flatter shape than the Cats, and planed up a bit earlier.
Your problem seems to arise from believing that the Techno 293 is a longboard, comparable to Mistral Equipe. It's not. It is more than 2 feet shorter, even 3 feet shorter than the longer race boards. It's also primarily oriented towards planing. Yes, it does shlog better than a shorter board, especially if you know how to rail with the daggerboard. But it is slower than longer boards.
| ittiandro wrote: | | 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. |
You are contradicting yourself here - at other places you write that you are only interested in the non-planing aspects.
The formula you used predicts that the hull speed will be the same for boats of equal weight, regardless of weight. But is is well known that a lighter boat will be faster than a heavier boat of the same length. This also means that a 200 lb windsurf "boat" will have a significantly faster hull speed than a sail boat of the same size that weighs substantially more. In simplified terms, more weight equals more displacement, which creates larger bow and stern waves, which will limit the hull speed more than smaller waves.
The simple formula you used was developed for typical sail boats. Ignoring weight works reasonably well for typical (i.e. non-racing) sail boats, the differences are minimal. But for much lighter crafts like windsurfers, the differences are big. Using 200 lb for total boat weight, the hull speed for a 12 foot longboard increases from 4.6 to 8.4 knots. For your BIC 293, you get a hull speed of 6 knots (actually, 5.5 is probably a better number, since you waterline length will be less than the total boat length).
So, if you read the article "A Better Way To Estimate Hull Speed", and plug in the numbers, you may discover that it is not "always around 5 knts". A decent longboard will go about 50% faster than your BIC 293 in non-planing conditions (unless you both are railing up, which is a way of planing). The hull shape of the longboard will determine how much power (sail size) you need to get to that speed. Besides the factors that others have mentioned, the widths is rather important there. Typical old longboards are somewhere around 60-65 cm wide. The Kona One is 70 cm wide, which is one reason why it will be slower, assuming the same sail size. The BIC Techno 293 is 79 cm wide: in first approximation, you'll need 30% more sail to reach the same speed. Reality may be worse, since most longboards (excluding the Kona) have a more displacement-oriented front shape.
| ittiandro wrote: | | Finally, with all due respect, if any debate implies a difference of opinion, arguments don’t become more convincing by being bombastic... |
You call it "all due respect" when you call people "bombastic", or "surmise" that a simple formula for hull speed is "too academic"?
This was not a debate. You asked a question about hull speed. You did not state clearly what you were apparently most concerned about - your BIC 293. Instead, you mentioned a "12 foot longboard".
I tried to answer your questions. I have you screen shots of GPS tracks from a 12 foot longboard that clearly shows that there is no "hull speed limit". I also gave you a link to an article that describes a better way of estimating hull speeds, which gives much more meaningful results in this context. I also crunched the numbers using this formula, and pointed out that they confirm what we can see in GPS tracks from shortboards.
But apparently, it is not worth your time to learn about the better ways of estimating hull speed - you already know that "We are always around 5 knts". Someone spend some time to research this and run the numbers, but you disregard that completely. That is neither debate nor respect, that is arrogance.
At the same time, you are displaying an amazing level of ignorance:
| ittiandro wrote: | | Frankly, I don’t even recall that there have ever been flat-bottomed longboards in the 80’s and 90’s. |
I happen to have two longboards from the 80s and 90s in my garage. I have participated in several longboard races, and I am actually organizing races where we see lots of longboards - most from the 80s and 90s, some even older, some newer. The vast majority of these longboards (including the 2 in my garage) have as "flat" a bottom behind the mast track as any of my shortboards or slalom boards. Of course, the actual shapes are never really "flat" - there are Vs, concaves, triple concaves going into Vs, and more. But the boards are definitely made for planing, as well as for efficient light wind sailing.
If everyone here disagrees with your "definition" of longboards, perhaps it should tell you something? Insisting that your "definition" is correct is, simply speaking, troll-like behavior. Seeing how you ignore or diss all responses that do not agree with your views, your original post indeed seems to be more trolling than asking a question. |
|
| Back to top |
|
|
konajoe
Joined: 28 Feb 2010
Posts: 517
|
| Posted: Thu Aug 13, 2015 10:33 am Post subject: |
|
|
More stuff:
Those formulas are based on waterline, not hull length. Don't get confused. I watched my longboard as I was sailing last night. It's waterline length changes constantly. As it speeds up, the length of the waterline gets shorter. Kayaks don't do that. Big sail boats don't do that.
Ittiandro, read my comments about making measurements with a strain gauge. Unfortunately, if you got the 293 to do light wind cruising, you got the wrong board. The good news is that longboards can commonly be found for about $100.
Give me a big sail. The idea of a bigger sail not being faster in light winds got started by the guy who owned the biggest sail in a light wind race, and still lost. It wasn't his lack of skill. |
|
| Back to top |
|
|
isobars
Joined: 12 Dec 1999
Posts: 20935
|
| Posted: Thu Aug 13, 2015 11:22 am Post subject: |
|
|
| coachg wrote: | Is it just me or does anyone else feel like this?  |
I suspect many of my posts trigger that response.
If it's just in bystanders, remember: reading them is optional.
If in the OP whose question I'm answering, no sympathy here; if ya don't want to read a thorough answer, don't ask the question. 
Mike \m/ |
|
| Back to top |
|
|
GURGLETROUSERS
Joined: 30 Dec 2009
Posts: 2643
|
| Posted: Fri Aug 14, 2015 4:00 am Post subject: |
|
|
Off topic (which seems to have come to a stop) but with Father Time breathing down my neck, and my marbles coming a little loose, It's time to lash out on a new super performance longboard.
There are two clear candidates; the Kona Carbone, or the Batwing Phantom, both of which are horribly expensive! The Carbone is a 'leg up' performance wise over the standard Kona but is still basically the same board, while the Batwing Phantom, from what I gather from the racing circuit, is now a clear leap ahead of the old classic longboards, especially in the lighter to mid range wind strengths. (My primary interest.) The racing results now seem to reflect that.
What ISN'T clear is the durability v, fragility of these two boards, over a number of years normal usage. (Realistically 10 years, which is as far ahead as I'll likely be able to remember to put my pants on before leaving the house.)
I'm leaning towards the Phantom purely for its exciting, highly strung, lighter to moderate wind ability, while keeping my standard Kona for the more serious (sometime rock bashing) journeys. Is anybody able to spread any light on the probable durability (as, say, with old longboards) of these two boards, bearing in mind just how expensive either of them is? |
|
| Back to top |
|
|
Sailboarder
Joined: 10 Apr 2011
Posts: 656
|
| Posted: Fri Aug 14, 2015 8:06 am Post subject: |
|
|
| GURGLETROUSERS wrote: | h out on a new super performance longboard.
There are two clear candidates; the Kona Carbone, or the Batwing Phantom, both of which are horribly expensive! The Carbone is a 'leg up' performance wise over the standard Kona but is still basically the same board, while the Batwing Phantom, from what I gather from the racing circuit, is now a clear leap ahead of the old classic longboards, especially in the lighter to mid range wind strengths. (My primary interest.) The racing results now seem to reflect that.
What ISN'T clear is the durability v, fragility of these two boards, over a number of years normal usage. (Realistically 10 years, which is as far ahead as I'll likely be able to remember to put my pants on before leaving the house.)
|
If I had the money, I'd go for both!!! Quite different boards.
I haven't seen both of them, so I can't comment from experience. I guess the CarbOne would last me more for two reasons. First, the shape is simpler, with less plugs and no wings, meaning repairs will be much easier. Second, the CarbOne is smaller, and I'm quite used to manipulate it, so I'm convinced I would ding it less than the Phantom.
If I had the money now, I'd get a Phantom while my K1 is still running. If something ever happens to the K1, I think I'll replace it with a CarbOne. |
|
| Back to top |
|
|
Sailboarder
Joined: 10 Apr 2011
Posts: 656
|
| Posted: Fri Aug 14, 2015 8:22 am Post subject: |
|
|
Del,
Sailboard is also the name of a German company that use to make nice boards, my cousin and I still have ours!
Gurgle,
Thanks for pointing out the kayaks, I had a nice read about them yesterday. From what I read, I think the enhanced hull speed calculation gives the easy cruising speed they get, and they are more or less similar for comparable sizes. If you provide more power to exceed the cruising speed, the wetted area, through simple friction, seems to be the limiting factor. Sea racing kayaks can be less than 45 cm wide for that reason.
Boardsurfer,
Thanks for taking the time to write down your answers. I found them helpfull, I hope ittiandro did too. |
|
| Back to top |
|
|
whitevan01
Joined: 29 Jun 2007
Posts: 607
|
| Posted: Fri Aug 14, 2015 9:55 am Post subject: |
|
|
| even though my 2 previous posts in this topic seem to have been ignored (now I know what isobars feels like), this discussion did inspire me to take my Megacat out for a sail yesterday, I planed for over 3 hours in 10 mph or so wind. great day!! so thank you to all for that. |
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You can attach files in this forum
You can download files in this forum
|
|
|
Search
Profile
Log in to check your private messages
Register
