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Re: How important is relative boat weight? [Re: Wouter] #138085
03/31/08 11:30 PM
03/31/08 11:30 PM
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Home is where the harness is.....
Will_R Offline
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Interesting thought here. When the 18HT was used in the Tybee5 a huge complaint about the boat was that it didn't have the momentum to have much punching power. It just sat and bobbed back and forth.... in that cast it was a boat that was too light. The 20' light boats don't seem to have that problem, I suspect it's b/c of the longer waterlines.

-- Have You Seen This? --
Re: How important is relative boat weight? [Re: srm] #138086
04/01/08 01:37 AM
04/01/08 01:37 AM
Joined: May 2005
Posts: 87
Trondheim, Norway
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jimi Offline
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Quote
Air and water are both fluids, so the hull drag goes up with respect to velocity squared as well. That's why planing and hydrofoiling craft are able to get up to these high speeds- they reduce surface area as their speed increases.
sm


You are right of course (take de Morrison's equation on forces on cylindricals for instance, the same is the case there for the "drag-part" of the equation). What I was thinking is that on these wessels, the wetted surface is relatively small compared to the sail area/area causing wind drag. Hence, the wind drag should be the biggest drag factor..?

Re: How important is relative boat weight? [Re: Wouter] #138087
04/01/08 04:40 AM
04/01/08 04:40 AM
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Posts: 242
Brisveagas
Aido Offline
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Racing catamarans may spend most of their time at sustained speed. But any good cat racer knows that its Blasting off the startline and smooth tacks and bouy roundings are where most of the ground is made in a steady breeze. Accelertion to top speed is essential for this.

I know what you do for a living, you've told everyone it seems. I just believe you are grossly over complicating the argument. Im suggesting that you should go back to the basics to get a better understanding of whats going on.

I try not to spend too much time decelerating when racing so i dont need a heavy boat.

Sue

Are you explaining junior grade secondairy education physics to me and then misapplying it ?

You really have no idea of what I do in my professional life do you ?

Quote

Is all about the sum of the forces (F)


of which the drag forces are an very important part as the accelleration is only the result of the net difference between drag forces and drive forces. When both are equal and opposite to eachother the boat stops accellerating and had achieves max sustained speed (=topspeed).

Newtons second law of motion is therefor not a factor with respect to sustained straight line speed (=topspeed) which is what racing catamarans spend by far most of their time doing.

Of course, in reverse, a heavier boat decellerates (slows down) less then a lighter boat in the lulls and when encountering waves. A light boat may win at the start-line but will loose in the lulls by the same token.

You cherry pick concepts and then simply ignore the reverse effects to argue your case. A failing grade skill level even for a junior secondairy level pupil/student.

Wouter [/quote]


Aido
Viper 288
Re: How important is relative boat weight? [Re: Will_R] #138088
04/01/08 05:12 AM
04/01/08 05:12 AM
Joined: Jun 2001
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North-West Europe
Wouter Offline
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It is not so much a factor of being lightweight but more of being insufficiently damped.

It is the same with a car that has worn down dampers in its shock absorbers; it is very difficult to keep that car on the road in corners or uneven roads as well for exactly the same reason.

A long hull will introduce disproportionately more damping then the increase in mass-a-top and sailarea. All these dependencies are highly no-linear and that is why so many people become confused when the only look at the specs of boats and not model the behaviour mathematically.

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
Re: How important is relative boat weight? [Re: Wouter] #138089
04/01/08 07:06 AM
04/01/08 07:06 AM
Joined: Aug 2002
Posts: 545
Brighton, UK
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In the context of beach catamaran's (and high performance dinghies) which is what I beleive this thread is all about, Uffa Fox's comments still hold true, a lighter boat is always better than a heavier one.

Of course that does not mean that you can't design a lighter boat that is slower than a heavier boat, and you will be able to find examples where this does not hold true, but that is only because the lighter boat was not properly optimised.

Gareth

Re: How important is relative boat weight? [Re: jimi] #138090
04/01/08 07:17 AM
04/01/08 07:17 AM
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>>>Hence, the wind drag should be the biggest drag factor..?

I can't comment on the relative proportions of all the drag components, but consider that if you take a high performance rig and stick it on an ice boat it is capable of going 4 or 5 times faster than on a beach catamaran. To me, that's convincing evidence that the hull drag is still the highest contributor to overall drag.

sm

Re: How important is relative boat weight? [Re: srm] #138091
04/01/08 09:57 AM
04/01/08 09:57 AM
Joined: Jun 2001
Posts: 1,021
Australia
macca Offline
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You can have a light boat, even one built without exotics. But it won't be as strong or as stiff as one thats built with high modulus materials.

I mention this here because I have been banned from the F16 Forum and there was an active discussion happening there until the moderators decided that it wasn't in the class' best interests.

no prizes for guessing what this boat is <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

[Linked Image]

Attached Files
140604-IMG_0155.jpg (20 downloads)
Last edited by macca; 04/01/08 09:59 AM.

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Re: How important is relative boat weight? [Re: macca] #138092
04/01/08 10:02 AM
04/01/08 10:02 AM
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Australia
macca Offline
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Another pic of a lightweight boat... [Linked Image]

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Last edited by macca; 04/01/08 10:03 AM.

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Re: How important is relative boat weight? [Re: macca] #138093
04/01/08 10:08 AM
04/01/08 10:08 AM
Joined: Jun 2001
Posts: 9,582
North-West Europe
Wouter Offline
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Macca,

Quote

I mention this here because I have been banned from the F16 Forum ...


You have not been banned ! (yet !)

It is only that your posts concerning F16 class rules and F16 boat weight are being locked down or deleted as you refuse to adhere to official F16 class procedures regarding rule changes and common respect for factual discussions. Many times over you have been both invited to submit official proposals for processing and warned of the next steps in the disciplinary path when continuing to grandstand.

Stop playing the victom !

Wouter

Last edited by Wouter; 04/01/08 10:15 AM.
Re: How important is relative boat weight? [Re: grob] #138094
04/01/08 10:14 AM
04/01/08 10:14 AM
Joined: Aug 2002
Posts: 545
Brighton, UK
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Quote
In the context of beach catamaran's (and high performance dinghies) which is what I beleive this thread is all about, Uffa Fox's comments still hold true, a lighter boat is always better than a heavier one.

Gareth


Macca makes a good point, when I said a light boat is better than a heavy one, I meant in terms of performance only, if you can't finish the race then you have gone too light <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

I should have said a lighter boat is always quicker than a heavier one all other things being equal, but not necassarily better.

Gareth

Re: How important is relative boat weight? [Re: macca] #138095
04/01/08 10:14 AM
04/01/08 10:14 AM
Joined: Nov 2002
Posts: 5,558
Key Largo, FL & Put-in-Bay, OH...
Mary Offline OP
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That kind of cracking does not just happen on lightweight boats. That same kind of vertical hull crack, aft of the front beam, happened to us on a Hobie 18. I, as crew, was out on the trapeze, and it was maybe a couple of minutes after the start of the race when all of a sudden the hull just started to split open right in front of my forward foot. Very unusual location for a crack like that.

We managed to get the boat to the beach on the same starboard tack, keeping the starboard hull as far out of the water as possible. (Still got full of water, though.)

Re: How important is relative boat weight? [Re: Mary] #138096
04/01/08 10:20 AM
04/01/08 10:20 AM
Joined: Feb 2004
Posts: 3,528
Looking for a Job, I got credi...
scooby_simon Offline
Hull Flying, Snow Sliding....
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Quote
That kind of cracking does not just happen on lightweight boats. That same kind of vertical hull crack, aft of the front beam, happened to us on a Hobie 18. I, as crew, was out on the trapeze, and it was maybe a couple of minutes after the start of the race when all of a sudden the hull just started to split open right in front of my forward foot. Very unusual location for a crack like that.

We managed to get the boat to the beach on the same starboard tack, keeping the starboard hull as far out of the water as possible. (Still got full of water, though.)


Mary,

Did you ever find out what caused the failure?


F16 - GBR 553 - SOLD

I also talk sport here
Re: How important is relative boat weight? [Re: Mary] #138097
04/01/08 10:23 AM
04/01/08 10:23 AM
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Wouter Offline
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Such a crack will happen on any catamaran irrespectibally whether it is a 180 kg F18, 75 kg A-cat or a 18 ton Groupama 3 when an internal element like a bulkhead or subdeck comes undone or cracks due to production errors and no longer supports the hull skin.

As a result such damage has happened to pretty much any design out there in the world today and will continue to happen in the future. Boat builders are still not applying aeronautical or space-age quality control systems; as such these incidental mishaps are recurring.

More importantly is whether the company building/selling the boat takes responsibility and handles the warrantee in a proper way. That has always happened thus far.

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
Re: How important is relative boat weight? [Re: Mary] #138098
04/01/08 11:09 AM
04/01/08 11:09 AM
Joined: Jun 2001
Posts: 3,291
Long Beach, California
John Williams Offline
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Mary's right - I have seen a very similar-looking issue on other "heavy" boats. Showed up on my old Mystere 4.3, which could never be confused with a high-tech lightweight boat. Not nearly a fatal issue, either - it was a straightforward repair and was completely invisible when complete. I sailed the boat for another two or three seasons without recurrence.

In the right hands, boat repair is not a death knell for racing boats - I think too many boats are "totaled out" after collisions and failures. Effective repair doesn't necessarily mean significant weight added.

I've read this thread and it's esoteric theory, anecdotal evidence, suppositions, etc. Simply proof to me that too much time is spent on worrying about reasons for a poor showing. There was a glimmer of light when people started ranking time on the boat above other issues, but then the wheels came off again. Full-circle, we're back to F16 sniping? *yawn*


John Williams

- The harder you practice, the luckier you get -
Gary Player, pro golfer

After watching Lionel Messi play, I realize I need to sail harder.
Re: How important is relative boat weight? [Re: Will_R] #138099
04/01/08 01:11 PM
04/01/08 01:11 PM
Joined: Sep 2007
Posts: 571
Hamburg
Smiths_Cat Offline
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Here, I have a simple way to look at this and exclude the discussions about physics, fluid dynamics etc.

Look at the US Sailing Portsmouth numbers and compare these three boats; M20, CFR20 and I20. They have different rigs (uni vs. sloop) but carry similar sail areas both upwind and down wind (I know the M20 is 1' wider but it's still a good reference point). I probably should have pulled the Texel numbers and compared the I20 to the Eagle 20 Carbon but.... I did this....

Key
Boat - weight, SA up x SA Down, Portsmouth numbers

M20 - ~255lbs, 24m^2 x 25m^2, 58.0 61.0 59.0 57.5 55.0
CFR - ~265lbs, 24m^2 x 25m^2, 58.0 61.5 58.2 58.1 57.3
I20 - ~390lbs, 24.25m^2 x 24m^2, 59.3 62.0 60.2 58.5 57.5

Notice that in light/med conditions the light boats are rated faster. As wind speed goes up the gap closes for the I20 and the CFR but not the M20 (the beam starts paying off).

I think the conclusion should be obvious. Lighter is faster. (don't rake me over the coals a/b the sloop vs. uni, I know I know....)

One more anecdotal account. I have sailed with some upper upper level sailors. If weight didn't matter, I don't think they would be so anal about using small light lines and keeping the garbage off the boat.


Thanks for the numbers, that brings some light in the discussion. I don't worry about cat/sloop. Also the quality of Portsmouth numbers may be debated, but for our discussion it is fine.
In light winds, where we all agree that lighter is faster, 125lb heavier is just a 2.2% penalty. So 12.5lb weight increase is 0.2% penalty. That is just nothing, at least for me.
Maybe you talk with your upper skill sailor friends about this 125lb = 2.2% slower relation. Could get another anecdote.
What is the beam and mast height of a CFR20?

Cheers,

Klaus

Re: How important is relative boat weight? [Re: Aido] #138100
04/01/08 01:39 PM
04/01/08 01:39 PM
Joined: Sep 2007
Posts: 571
Hamburg
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Sue,

Quote
Racing catamarans may spend most of their time at sustained speed... Accelertion to top speed is essential for this.

It must be very calm with no waves, that you can maintain a constant boat speed (and ones again, I agree, that in light wind the lighter boat is faster). I have attached a speed vs time gps track. Medium off-shore winds, waves 0.5m, Dart 18, data points are spaced every 15s. You can see the tacks as deep low speed points. But between these points there is not really a constant speed. Well, maybe I am a bad sailor... <img src="http://www.catsailor.com/forums/images/graemlins/frown.gif" alt="" /> then again I spend better my time in sailing the reducing the weight.

Quote
You cherry pick concepts and then simply ignore the reverse effects to argue your case.
No, I don't, I think about about acceleration and de-acceleration, about light and strong wind, about steady movement and dynamic movement, so please don't blame me.

Cheers,

Klaus

Attached Files
140654-boatspeed.jpg (39 downloads)
Re: How important is relative boat weight? [Re: Smiths_Cat] #138101
04/01/08 02:51 PM
04/01/08 02:51 PM
Joined: Jun 2001
Posts: 730
Home is where the harness is.....
Will_R Offline
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Home is where the harness is.....
The CFR currently has a beam of 8.5' and the same mast/main sail as the M20.

Re: How important is relative boat weight? [Re: Wouter] #138102
04/01/08 11:36 PM
04/01/08 11:36 PM
Joined: Jun 2001
Posts: 1,021
Australia
macca Offline
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Quote

Such a crack will happen on any catamaran irrespectibally whether it is a 180 kg F18, 75 kg A-cat
Wouter


I have yet to see a F18 with such a failure. but to build a boat down to a very light weight and not use exotics will increase the chances of such a failure. Hence the Photos I posted of a F16 with catastrophic hull failure.


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Re: How important is relative boat weight? [Re: macca] #138103
04/02/08 12:09 AM
04/02/08 12:09 AM
Joined: Nov 2002
Posts: 5,558
Key Largo, FL & Put-in-Bay, OH...
Mary Offline OP
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Macca, you did not say what brand of boat that was, and where, when, and how it happened.

Re: How important is relative boat weight? [Re: Mary] #138104
04/02/08 01:33 AM
04/02/08 01:33 AM
Joined: Jun 2001
Posts: 1,021
Australia
macca Offline
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I could give the details but then I would be accused of picking on a particular class...

They know who they are and they also know my position on their boat weights and current class rules.


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