Omer

Why and how does LWL matter anymore?

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We are accustomed to boats being faster with longer LWL for displacement sailing conditions. This is a well understood subject of wave making resistance etc. Therefore rating formulas do take LWL as an iportant parameter. But with todays racing boats so eager to get up on a plane and given the right conditions, it is quite likely that a race can be sailed where boats are planing most of the time if not entirely.

This is theoretically where LWL ceases to be a parameter for calculating potential speed. If this is so, what replaces it as the single most important factor?

In other words for all sizes of boats in planing conditions and assuming they all have the same sail area to displacement ratio why should a boat with longer LWL be faster? Can a boat 30 or 40 ft overtake a 60ft  boat, boat for boat?  How can a planing windsurfer  be as fast as a modern racer? Is a line honour possible for any size of boat in those conditions? How do rating formulas cope with that?

If the wind speed is constant for all the boats, and if  you can only go as fast as a percentage of it, or exceed as a percentage of it, then the smaller boats with lower ratings should have a huge advantage based on size. But that is not my point. If line honours are still with larger boats there should be some other important factors still.

In short, is this also as well an understood subject as ''the bigger boat is faster in displacement mode'' as we are used to? 

I am certainly lost in this argument. 

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With more wind, the smaller boats will tend to plane first because they are lighter. Conversely, they get stuffed upwind. On an offshore there are great gains if the crew can manage heavy airs downwind and the course suits. J80's are a great example.

That said, increase the wind and any boat will plane, had an old Swan 50 on a 900nm race a few years ago doing 18kts in 35kts tws with a huge following sea and the 1.25 kite up, was awesome, overtook the whole fleet (on handicap)  - till the wind died and we went back from 3rd to last again as we drifted backwards on the tide....

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2 hours ago, Omer said:

 

This is theoretically where LWL ceases to be a parameter for calculating potential speed for all boats on all points of sail. If this is so, what replaces it as the single most important factor?

In reality this spells the end of the single number rating system. The wide disparity between boat types and potentialities requires a multiple number rating system accounting for both the point of sail and the amount of wind.

To properly assess and assign those ratings the performance factor, SA/D, will be fairly prominent.

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ask the water, it'll tell you longer will always be relevant and faster to varying degrees no matter the proportions of a design or the conditions.

it's like if you were designing an 18 foot skiff, you'd want max LWL simply because it's a net gain in overall ability of that hull's potential to maintain higher speed numbers from light to heavy air. look at a big wave surf board, they're long to better deal with the high speeds they'll attain on a big, fast wave. 

even full foiling designs like an AC35 benefit from a long foil platform (hull) because they will be that much quicker, if only marginally so, while they're in pre-foiling displacement mode and can get up on the foils that much sooner. 

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You forget that:

1. planing keelboats is a way overhyped concept. Even the M32 rarely planes in real racing, and follows the same waterline rules everyone else does around the course.

2. sea state is completely left out of your analysis.

3. There is no such thing as an upwind planing ballasted monohull. So 75% or more of its time in any circuit is going to be waterline dependent. Even the "planing" skiffs are just over the line on waterline. Try cherub 12 versus Austrailan 18 upwind. Again waves matter here/

So yes, waterline will always matter in real world sailing. As for your questions, every one of them is complicated. Yes downwind in flat water a windsurfer is faster than anything but a kiteboard (or a purpose built 1 tack inverted hydovoil) but put waves into the mix and it changes quickly.

 

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WL is still king followed closely by SA/DSPL ratio, distant third is form/shape righting moment.

everything else is relatively inconsequential...

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Heavy displacement boats do not plane no matter how much breeze there is - if it's flat they just load up pushing more water while sinking down. With waves they surf. Not the same thing. And they only surf reaching/running not upwind. 

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Effective waterline length is always king,  when planing for directional stability, especially as water get rougher.

Frank Bethwaite had a formula: Sail Carrying Power, which you can look up in his book “High Performance Sailing”. Essentially it boils down to righting arm divided by heeling arm expressed as a percentage. He reckoned you needed more than 30% to plane upwind. Your average keelboat is lucky to get to 10% Whereas multihulls can easily achieve 30%, but their hulls are so narrow, they don’t plane.

Canting keels and DSS/moustache typefoils increase the keelboat righting arm pretty dramatically, but still would fall short of 30%.

This from Wikipedia on 18 ft skiffs:

The boat will plane upwind starting at a true windspeed of about 8 knots, depending on sea conditions and off the wind can reach speeds that doubles the true windspeed. This is possible through the very high sail-carrying power to total weight ratio, which is above 30% with the no. 1 rig and approaches 40% with the no. 3 rig (for reference, a 30% ratio is needed to plane upwind and a 10% ratio is needed to plane at all. Most cruising boats have a ratio under 5%)”.

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1 hour ago, Raked Aft\\ said:

WL is still king followed closely by SA/DSPL ratio,

Not, I submit, closely followed.

Length is king not only because of wave drag, but because it brings so many fringe benefits as well.

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If you play around with various VPP formulas, eg: Base Speed, you can see that if you increase effective LWL or sail area or decrease Displ by, say, 10 %, the speed increase for length is almost double sail area and double displacement.... Plus less pitching etc.

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LWL (& displacement) can be interesting in handicap races.  

Lioness is 40’, displaces 20,000# and rates 174 with fixed prop. We get 6 sec a mile from J-24 in NORCAL.  

Light air (< 5kts)  & downwind with chute vs our genoa they kill us.

Given 10+ kts TWs we heel over, LWL goes from 29->36’ and we simply roll them below planing speeds, as well as drive thru chop that stops them. 

It’s all fun. 

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10 hours ago, Parma said:

In reality this spells the end of the single number rating system.

Is that so? Planing dinghies race with single number systems.

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7 hours ago, dogwatch said:

Is that so? Planing dinghies race with single number systems.

when they are all planing dinghies that works fine. But US portsmouth isn't single number -- it has wind speed ranges.

MHS came along because even in the 70s, Professor Milgram came to the conclusion that single number would never work. (He wasn't the only one to make that obvious observations but he did something about it...)

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21 hours ago, Omer said:

I am certainly lost in this argument

Yes. Yes you are.

So am I though, so there’s that...

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8 hours ago, dogwatch said:

Is that so? Planing dinghies race with single number systems.

I meant in mixed fleets.

Take Lioness example above; multiple ratings for different points of sail & wind strengths would flatten out  that expectancy curve, and that's just a typical example. Once you move to the more extreme boats, like Island Packet 45s or McConaghey 31/38 the difference in performance for different points of sail & wind strengths only distorts further, leading some boats to show up for some races and other boats for other events.

Same amount of fun on the fun days without the frustration of the frustrating times.

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Here's the thing: there will never be a perfect handicap. If you want and need some sort of absolute measurement of your abilities, you simply must sail one design. But if you are able to be satisfied and happy that on some days you will not be on the podium, then handicap racing is fun. The absolute is less interesting than the relative performance. You will learn a lot about sailing yacht dynamics and performance. You may know you won't do well in some windstrength but you can still measure how well relatively you do against your competitors. "Hey, last time we sailed in 20, we were down 6% on racer X but today we were down 3%."

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6 hours ago, Parma said:

leading some boats to show up for some races and other boats for other events

If you don't race because it's not your ideal conditions, that's tragic. Good sportsmanship is you run what you brung, and congratulate the winners. Some events such as the RBBS here probably wouldn't accept our entry, though we meet all published requirements, as we are "too slow" which I get reduces the number of races you can run in a day. We used to go to the NE PHRF championships out of Marblehead back in the day, and the first year we were not DFL was celebratory.

6 hours ago, comcrudesgru8 said:

water lining someone on a glorious reach is all that really matters......the rest trivial persiflage.....

Our Holy Lady of Prismatic Coefficient, hallowed be her name... 

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On 6/10/2018 at 12:10 PM, 3to1 said:

 look at a big wave surf board, they're long to better deal with the high speeds they'll attain on a big, fast wave. 

 

Big wave boards are smaller than small wave boards. Big waves are further apart and therefor travel faster. Add the drop from 20 feet, versus the drop from 6 feet, and the big wave rider is going much faster. The larger boards turn too fast and help cause wipe outs. So the big wave board is smaller, has a smaller skeg, and is more tapered in towards the rear. All to slow down the quickness of the turn. A negative side affect is they paddle slower, which in turn makes getting up to speed to catch the wave more difficult. 

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2 hours ago, Unkle Crusty said:

Big wave boards are smaller than small wave boards. Big waves are further apart and therefor travel faster. Add the drop from 20 feet, versus the drop from 6 feet, and the big wave rider is going much faster. The larger boards turn too fast and help cause wipe outs. So the big wave board is smaller, has a smaller skeg, and is more tapered in towards the rear. All to slow down the quickness of the turn. A negative side affect is they paddle slower, which in turn makes getting up to speed to catch the wave more difficult. 

How many drugs did you take.

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31 minutes ago, doghouse said:

How many drugs did you take.

Just enough for the circumstances. How many big waves have you surfed?

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2 minutes ago, Unkle Crusty said:

Just enough for the circumstances. How many big waves have you surfed?

A lot. 

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12 minutes ago, doghouse said:

A lot. 

Well by crikey I checked the latest thoughts on the subject. Depending who we quote, we are both correct. Seems some surfers are using longer boards to get a faster paddling speed that I referred to, and some are using shorter boards for several reasons. I will assume the smaller skeg and tapered back end is fairly standard. I do not think there would be a lot of difference in speed once on a large wave, as it is mostly a free fall. Cross wave travelling speeds could vary a bit, from more wetted surface, and surfers weight.

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1 hour ago, Unkle Crusty said:

Well by crikey I checked the latest thoughts on the subject. Depending who we quote, we are both correct. Seems some surfers are using longer boards to get a faster paddling speed that I referred to, and some are using shorter boards for several reasons. I will assume the smaller skeg and tapered back end is fairly standard. I do not think there would be a lot of difference in speed once on a large wave, as it is mostly a free fall. Cross wave travelling speeds could vary a bit, from more wetted surface, and surfers weight.

A 10 foot high pacific wave may have a 14 to 18 second period.

A 10 footer on the Atlantic is likely 10 or 12 seconds unless you got lucky and picked up a hurricane swell.

The speed difference is about Sqrt(18)/(sqrt (10) so  you have to paddle 34% faster on the west coast...

I'm not a surfer but I like bodysurfing and windsurfing. First time in Waikiki it was weird. The waves were small, but there was so much time between them and you had to swim soooo fast!

 

Just checking right now with summer conditions and the west coast dominant wave period is 9-12 seconds while here in the northeast it is 7-8 seconds.

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On 6/10/2018 at 2:02 PM, Raked Aft\\ said:

WL is still king followed closely by SA/DSPL ratio, distant third is form/shape righting moment.

everything else is relatively inconsequential...

It's all about physics

Until you start foinling

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5 hours ago, Unkle Crusty said:

Big wave boards are smaller than small wave boards. Big waves are further apart and therefor travel faster. Add the drop from 20 feet, versus the drop from 6 feet, and the big wave rider is going much faster. The larger boards turn too fast and help cause wipe outs. So the big wave board is smaller, has a smaller skeg, and is more tapered in towards the rear. All to slow down the quickness of the turn. A negative side affect is they paddle slower, which in turn makes getting up to speed to catch the wave more difficult. 

 

3 hours ago, doghouse said:

How many drugs did you take.

He must have taken all of them

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27 minutes ago, Gutterblack said:

 

 

He must have taken all of them

Do you have anything of substance to offer? I guess for some folks it is just easier to make disparaging remarks. Like boats, the shape and size of surfboards has changed. If I or others, used a certain size and type of board at the Makaha contest, and another size and type at Sunset, then what I am reporting is factual for that era. Nobody got towed back when.

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Crusty, 

if you're getting towed the board is usually shorter, w foot straps similar to a skurfer

as for the boardshape...the back end might be straighter(think snowboard or skiiing gs vs slalom). The higher speed tail will be straighter to hold the turn and not get rodeo'ed.

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9 hours ago, Unkle Crusty said:

Big wave boards are smaller than small wave boards. 

huh, well I'll be dipped in shit..

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I'm loving the thread drift. I'm glad there's no handicap to contend with when surfing apart from the surfer! 

Board size? Tow boards are pretty tiny, guns have plenty of length and volume to paddle comparable waves. 9'+ mal is great fun down to 1' waves, but a 5' 8" fish can also be fun in small waves.... aaaaand how many fins?

I love the diversity of design of both forms of watercraft, and accelerating down a wave on boat, board, ski, body (what'd I forget?) makes life a whole lot better!

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I actually still have an 8 foot gun. Why, I have no idea, as I doubt I will ever use it again.

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one of the things I learned with my first 'planing' boat is that yes, it's true the small sporty will get up on plane sooner than a bigger boat, which may not plane at all. but in the case of my elliott, where hull speed was somewhere around 6.4 knots, planing and surfing just meant anything above 7 or 8 knots, which  is still the same speed as the bigger non-planing boats in the class. If I'm doing 9 - 10 knots downwind, clearly 3 or 4 knots faster than hull speed, but still only 1 knot faster than, say a Frers 33 that's plowing its way toward the leeward mark. Then I have to go uphill again as a 25' boat. "Planing" is not a magic elixir. Until you've got nuking conditions of course. Then maybe it matters more. LWL is still relevant.

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17 hours ago, LionessRacing said:

If you don't race because it's not your ideal conditions, that's tragic.

Nobody said anything about ideal conditions, but a reasonable, or even a "chance" is the calculus.......just look at all the boats that stay home because they know it would be a waste of time.

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For fun the other day I was looking at polars for the Pogo 30, 36 and 12.50 versus my 1987 ~10T First 405. From memory, hull speeds weren't exceeded until reaching in 20kt TWS - the 36 was quite close to my 405 (similar LWL) in other conditions. 

It was a good reminder that as sexy as they are, the modern planing designs don’t really seem to confer much of an advantage in lighter wind areas like here in San Diego unless you have a crazy turbo rig. My conclusion was that if I want to go a lot faster I’d need a lightweight multi. Or a kiteboard :)

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15 hours ago, Meat Wad said:

It's all about physics

Until you start foinling

Foinling... that sounds like something Harvey Weinstein mighta done..

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3 hours ago, Parma said:

Nobody said anything about ideal conditions, but a reasonable, or even a "chance" is the calculus.......just look at all the boats that stay home because they know it would be a waste of time.

If someone will only race because there's  a chance of winning, that's tragic. I race for fun, and we win our share. Winning is generally more fun than losing, sailing well is always more fun than sailing poorly. If we sail well and get killed on handicap, we don't whinge and fuss, we enjoy our day on the water, and know that sometime in the future the weather & handicap will align and somebody else will be the "loser", but in the mean time we have enjoyed the process as well as the result.

  

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