Forums > Land Yacht Sailing Construction

Class Five Design

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Created by blake52 > 9 months ago, 3 Dec 2010
aus230
WA, 1659 posts
5 May 2011 6:58PM
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Thanks Rhys
I understand it now, Thanks I value your input. We need you here
Cheers
Vic

cisco
QLD, 12310 posts
5 May 2011 9:42PM
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kiwi307 said...

aus230 said...

not sure how this center of effort thing works. Any diagram's on how the measurements are taken and where does the pilots size and weight come into the effect. All quite new to me and I should imagine there would be plenty of others interested.
Cheers
Vic

Hi Vic, in relation to the centre of effort SOLELY, THE POINT IS THAT YOU DON'T MEASURE ANYTHING! What you do is make a scale model of the rig from card, Put a pinhole in each corner, and hang from each in turn. From the same pin hang a plumb line. Draw a pencil line roghly in the middle, then hang from the next corner and repeat. Where the lines cross is the THEORETICAL centre of effort. Previously a method used was to measure the midpoint of each side and run a line to the opposite apex. Again repeated for each side.
The other 2 points of interest for a design on paper are, 1) the centre of gravity with pilot in place, and 2) the centre of lateral resistance. Neither of these have I been able to find anything other than a "suck it and see" method (except huge amounts of complicated maths). Bill Finch showed me his method about 29 years ago and I still use it.
Centre of gravity, balance the whole yacht (with pilot) on a brick and move the yacht back and forwards till you have the CofG noted, it's where it balances.
Centre of Lateral resistance is found by tying a rope on and try to drag the whole yacht sideways (peagravel or wet grass is easiest). With a bit of luck and a fair bit of empirical testing (otherwise known as messing about) you will find this point.
If all 3 points line up, ie Cof E directly above the C of G which co-incides with the CLR, you will have a really sweet yacht with minimal steering input to keep straight. Strangely it also seems to be the fastest ones too!



Rhys,
That is the best description of how to set up a land yacht I have seen yet.

I do hope you will stay with us because I for one highly value your input. Cheers Cisco.

niaychi
97 posts
5 May 2011 9:16PM
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kiwi307 said...

Nikrum said...

So KIWI 307. You seem to be telling us to build the Chassis, less Mast Step, to the Rolling Stage Fit the Seat and a bunch of weight, to the point of EML (Estimated maximum Load) then start Dragging this lot about the Paddock, Sideways, on a rope until through adjustment you find a point of EB (Equidistant Balance) and at this point the mast Step should be placed???? No?
Ron



As you finished by saying NO. If you can tell me how to have a complete yacht without a mast, mast step and sail, please advise, never have seen it done!
The C of G and your previously unheard of EML (at least by me) are not convergent. The Cof G can be easily adjusted, just move your own weight around. Previously you accused me of not being able to read!!!
Who said anything about equidistant balance?
CLR can be adjusted by weight, tyre size, pressures and any other thing you feel like , but don't put words I never used in my mouth.
Bye Bye Seabreeze, cant be bothered any more.

kiwi 307 you gave a very clear explanation on how to set up a landyacht,so stick around we need people like you.
your comments nikrum are bewildering i am not sure what you are about at times.

Nikrum
TAS, 1972 posts
5 May 2011 11:26PM
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kiwi307 said...

Nikrum said...

So KIWI 307. You seem to be telling us to build the Chassis, less Mast Step, to the Rolling Stage Fit the Seat and a bunch of weight, to the point of EML (Estimated maximum Load) then start Dragging this lot about the Paddock, Sideways, on a rope until through adjustment you find a point of EB (Equidistant Balance) and at this point the mast Step should be placed???? No?
Ron



As you finished by saying NO. If you can tell me how to have a complete yacht without a mast, mast step and sail, please advise, never have seen it done!
The C of G and your previously unheard of EML (at least by me) are not convergent. The Cof G can be easily adjusted, just move your own weight around. Previously you accused me of not being able to read!!!
Who said anything about equidistant balance?
CLR can be adjusted by weight, tyre size, pressures and any other thing you feel like , but don't put words I never used in my mouth.
Bye Bye Seabreeze, cant be bothered any more.


KIWI307,
I'll not apologize for something that was not the case. In fact further from the case you couldn't get. Please learn to read and understand punctuation..This mark means QUESTION ?. Inflection can not be shown in the English language.......Not that I know of. You also should understand sense of Humour.. No? in this instance was used with a Rising Inflection, a sense of Humour, and as a Question. (Am I wrong????).


I also was ASKING is my break down of your Post correct?
Instead of you chucking a Hissy Fit and Slinking Off a more correct solution to my question would have been to Clarify further your explanation Thesis further.

I am not a ****ing Moron. I asked these questions because I don't quite have a handle on the situation.. Furthermore I was not suggesting a Mast-less Land Yacht!! Had you read and understood Punctuation correctly you would have noted that a Mast Step was added lastly.. After the CE (Center of Effort) was established.

Yes you have managed to do what no one else has to this point. ENRAGED me.

Ron

nebbian
WA, 6277 posts
5 May 2011 9:50PM
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kiwi307 said...


It is, wait for it... cut out a profile and hang from each corner with a plumb line across it! The windtunnel actually modify this some by moving forward from this point a small %age (not as much as 5%) depending on the draft of the sail.


This will give you a rough idea, but it's a long way from being exact.

The way we do it on a windsurfer is to take the sail outside in some wind, sit the mast on the ground, and hold the boom with one hand. If you're holding it too far towards the front of the sail it will weathercock around, if you're too far back it will twist around and nosedive into the ground. When you can hold it steady with one hand then the centre of effort is where your arm is pointing.

Note that the centre of effort moves backwards in a gust, moves forwards if you increase the clew tension (outhaul), moves down if you increase the downhaul, and moves up if you release the downhaul. None of these effects are taken care of with the paper cutout method.

I would be pretty sure that your actual centre of effort will be a bit forwards and a fair bit lower than the paper cutout method would indicate, due to the belly and twist of a well set-up sail.

cisco
QLD, 12310 posts
6 May 2011 12:07AM
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^^^^ That sounds about right nebs.

Off topic:- Could you please check your PMs or go to the sailing forum and read the "Cruising Forum" thread. Cheers Cisco.

Test pilot 1
WA, 1430 posts
6 May 2011 1:08AM
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Nikrum said...

kiwi307 said...

Nikrum said...

So KIWI 307. You seem to be telling us to build the Chassis, less Mast Step, to the Rolling Stage Fit the Seat and a bunch of weight, to the point of EML (Estimated maximum Load) then start Dragging this lot about the Paddock, Sideways, on a rope until through adjustment you find a point of EB (Equidistant Balance) and at this point the mast Step should be placed???? No?
Ron



As you finished by saying NO. If you can tell me how to have a complete yacht without a mast, mast step and sail, please advise, never have seen it done!
The C of G and your previously unheard of EML (at least by me) are not convergent. The Cof G can be easily adjusted, just move your own weight around. Previously you accused me of not being able to read!!!
Who said anything about equidistant balance?
CLR can be adjusted by weight, tyre size, pressures and any other thing you feel like , but don't put words I never used in my mouth.
Bye Bye Seabreeze, cant be bothered any more.


KIWI307,
I'll not apologize for something that was not the case. In fact further from the case you couldn't get. Please learn to read and understand punctuation..This mark means QUESTION ?. Inflection can not be shown in the English language.......Not that I know of. You also should understand sense of Humour.. No? in this instance was used with a Rising Inflection, a sense of Humour, and as a Question. (Am I wrong????).


I also was ASKING is my break down of your Post correct?
Instead of you chucking a Hissy Fit and Slinking Off a more correct solution to my question would have been to Clarify further your explanation Thesis further.

I am not a ****ing Moron. I asked these questions because I don't quite have a handle on the situation.. Furthermore I was not suggesting a Mast-less Land Yacht!! Had you read and understood Punctuation correctly you would have noted that a Mast Step was added lastly.. After the CE (Center of Effort) was established.

Yes you have managed to do what no one else has to this point. ENRAGED me.

Ron


Kiwi307----1
Nikrum-----0

sabydent
360 posts
6 May 2011 4:35AM
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I have to agree with Nikrum. He was asking a question and Kiwi 307 got his nose bent out of shape.

Kiwi 307- 0
Nikrum -1

Hiko
1229 posts
6 May 2011 7:17AM
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At the top of the page under help there is a forum crash course that talks about misunderstandings etc
The written word can often be misinterpreted as it lacks the
facial expressions gestures and so on that are also part of communication
Any one who uses skype will know this
I believe that that is all this is
We have had it before and moved on We can do it again

desertyank
1260 posts
6 May 2011 7:51AM
Thumbs Up

kiwi307 said...

aus230 said...

not sure how this center of effort thing works. Any diagram's on how the measurements are taken and where does the pilots size and weight come into the effect. All quite new to me and I should imagine there would be plenty of others interested.
Cheers
Vic

Hi Vic, in relation to the centre of effort SOLELY, THE POINT IS THAT YOU DON'T MEASURE ANYTHING! What you do is make a scale model of the rig from card, Put a pinhole in each corner, and hang from each in turn. From the same pin hang a plumb line. Draw a pencil line roghly in the middle, then hang from the next corner and repeat. Where the lines cross is the THEORETICAL centre of effort. Previously a method used was to measure the midpoint of each side and run a line to the opposite apex. Again repeated for each side.
The other 2 points of interest for a design on paper are, 1) the centre of gravity with pilot in place, and 2) the centre of lateral resistance. Neither of these have I been able to find anything other than a "suck it and see" method (except huge amounts of complicated maths). Bill Finch showed me his method about 29 years ago and I still use it.
Centre of gravity, balance the whole yacht (with pilot) on a brick and move the yacht back and forwards till you have the CofG noted, it's where it balances.
Centre of Lateral resistance is found by tying a rope on and try to drag the whole yacht sideways (peagravel or wet grass is easiest). With a bit of luck and a fair bit of empirical testing (otherwise known as messing about) you will find this point.
If all 3 points line up, ie Cof E directly above the C of G which co-incides with the CLR, you will have a really sweet yacht with minimal steering input to keep straight. Strangely it also seems to be the fastest ones too!




Hey Rhys,

I liked your explanation of the 'centers' of all coming together. Makes sense. Now the tough question; how the feck do you make them all line up? The c/g of the rig, and the center of effort from the sail I can see could be matched by moving the mast/sail in the mast step, and/or pilot back and forth.

What's the method for adjusting the center of lateral force? Moving the pilot starts the whole process over, right? Seems like a lot of going around in circles may be in my future to make the big red beast sail at it's sweetest

Oh, if you have any video of you in a rig being dragged sideways, please post it!!!

Nikrum
TAS, 1972 posts
6 May 2011 10:39AM
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It seems to me that people from across the Globe have a better understanding of Aussie Vernacular, colloquialisms, Slang etc. than our favored neighboring Sparing partners do. Aus' and NZ being so remote from the rest of the Anglicized Global population, until recent years, should have a greater affinity for each other than for a simple misguided assumption to cause a War of words as this.
Anyway, "WTF" I'm over it. We can't all agree with each other all of the time. It is part of the human condition and what adds a little Spice to Life.
Thanks Sabydent, obviously you enjoy my Banter.. All it takes is a Thick Hide and an Evil Snese of Humor..
Ron
PS; It is nice to understand what is being discussed, even if you are unlikely to use it.

Gizmo
SA, 2865 posts
6 May 2011 10:26AM
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The balance of CE, CG, CR is a VERY variable thing and constantly changes during sailing.

CE, [Center of Effort] the paper model is an interesting way of creating a theoretical point but it doesn't take into account the 3 dimensional shape of a sail, the real life CE point can be moved forward or back by down haul pressure, batten tension, sail out haul and sail sheeting angle as nebbian mentioned. Most wings and that's what a sail is, the maximum lift point is approx 1/3 from the leading edge... so the longer the leading edge the more lift, ever wonder why gliders have long thin wings compared to powered planes? and souring birds have longer wings (Eagles, Albatross and even Seagulls)
Mast rake also effects CE, it will go up and down with sail trim where as a straight up mast the CE would tend to be more consistent like a stayed mast water yacht.

CG, [Centre of Gravity] depends on the yacht construction I have found it on smaller yachts to be about in line with the front on the rear wheels BUT this will vary with the size, weight and proportion of the pilot.

CR, [Centre of Resistance] will depend on tyre size, inflation pressure, tread pattern of all 3 tyres. New tyres v worn out tyres and also the surface will effect CR.

The other often forgotten thing is the surface you sail on, asphalt and salt have very little side slip, sand will vary from beach to beach wet or dry, mud and wet grass are a different ball game again.

There are SO MANY variables when it comes to CE,CG,CR

More info on wings....
en.wikipedia.org/wiki/Aspect_ratio(wing)
en.wikipedia.org/wiki/Bird_flight

niaychi
97 posts
6 May 2011 9:26AM
Thumbs Up

Nikrum said...

It seems to me that people from across the Globe have a better understanding of Aussie Vernacular, colloquialisms, Slang etc. than our favored neighboring Sparing partners do. Aus' and NZ being so remote from the rest of the Anglicized Global population, until recent years, should have a greater affinity for each other than for a simple misguided assumption to cause a War of words as this.
Anyway, "WTF" I'm over it. We can't all agree with each other all of the time. It is part of the human condition and what adds a little Spice to Life.
Thanks Sabydent, obviously you enjoy my Banter.. All it takes is a Thick Hide and an Evil Snese of Humor..
Ron
PS; It is nice to understand what is being discussed, even if you are unlikely to use it.
must be a tasmanian thing

nebbian
WA, 6277 posts
6 May 2011 9:32AM
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Gizmo said...

CR, [Centre of Resistance] will depend on tyre size, inflation pressure, tread pattern of all 3 tyres. New tyres v worn out tyres and also the surface will effect CR.



Won't CR always line up with the CG, providing all three tyres have the same coefficient of friction? I guess you're saying that tyre size, inflation pressure etc affects coefficient of friction, which would then affect CR in turn if the front and back were wildly different.

Hmmm maybe toe-in and camber might have something to do with it as well?

My head hurts

Gizmo
SA, 2865 posts
6 May 2011 11:12AM
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nebbian said...

Won't CR always line up with the CG, providing all three tyres have the same coefficient of friction?

Hmmm maybe toe-in and camber might have something to do with it as well?



No CR and CG won't ALWAYS align, for example take a Blokart or a yacht that uses a different size or style (pushbike) as a front wheel, or when you haul the sail on pressure will transfer to the down wind rear wheel changing the balance.
Water yachts are a lot more predictable with center boards and rudders.

nebbian
WA, 6277 posts
6 May 2011 10:36AM
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Gizmo said...



No CR and CG won't ALWAYS align, ...or when you haul the sail on pressure will transfer to the down wind rear wheel changing the balance.



But isn't hauling on the sail changing the CE, not the CR? Of course this will change the balance as one would expect, because then the CE has moved relative to the CR. I would have thought that CG and CR would usually be in the same spot (looking from the side).

The reason I say this is because the equations for friction are completely proportional to the weight on the tyre. More weight = more resistance to sideways load. So if all your weight is over the rear wheels then your CR will be at that spot too. If all your weight is over the front wheel then your CR will be at the front. Therefore your CR will always be very close to the CG, unless your tyres have wildly different coefficients of friction.

Also note that static friction is different to sliding friction...

Gizmo
SA, 2865 posts
6 May 2011 2:37PM
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CG and CR would be very closely related and do move slightly forward when a yacht goes up on 2 wheels as the rotational axis line is front wheel to back wheel and not the centre line of the yacht.
The main problems occur when CE and CR/CG get way out of whack, to far back and the rear wheels break away side ways, to far forward and its hard to steer. And as I have said before it will very much depend on the surface your sailing on. IE. if you sail on grass or a slightly muddy surface you may want the rig further forward [move CE forward] to minimise the back end breaking away. On salt you may want CE back further with the extra grip from the salt.
Yachts evolve differently depending on the location they sail, many years ago the Perth yachts had lower aspect ratio rigs and much wider seats due to the prevailing wind conditions at their club than the Lefroy yachts.
Just as sailboards are different for flat water to surf and strong winds to light.

Clemco
430 posts
6 May 2011 1:47PM
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Just to complicate this subject further.... The way the Y frame yachts heel over is different than the T frame yachts. The Y frame does tend to heel over parallel to the center line of the frame, as it also leans back as it heels over.

Gizmo
SA, 2865 posts
6 May 2011 4:32PM
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It's FAR from an exact science... compared to F1 race cars for example.
And maybe thats half the fun of land sailing.

nebbian
WA, 6277 posts
6 May 2011 5:14PM
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Interesting...

So if you felt the back starting to break away you could scoot your body weight back a bit which would then make the CR move back as well?

Cool

bazl
WA, 700 posts
6 May 2011 7:17PM
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This is doing my head in. I think I will just go sailing.

landyacht
WA, 5921 posts
7 May 2011 6:30PM
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Nikrum said...

So KIWI 307. You seem to be telling us to build the Chassis, less Mast Step, to the Rolling Stage Fit the Seat and a bunch of weight, to the point of EML (Estimated maximum Load) then start Dragging this lot about the Paddock, Sideways, on a rope until through adjustment you find a point of EB (Equidistant Balance) and at this point the mast Step should be placed???? No?
Ron

No Ron, you build the yacht as per your plans and get in it , fully rigged to get your centre of gravity and your lateral resistance point. Probably not a good idea to invent a new term or 2(EML,EB) , it might get confusing .
The CE of the sail, already decided from the cardboard cut out affects where you mount the mast step. this is where suck it and see building falls down , you need to start drawing plans and the like BEFORE you start cutting.
adding a No and lots of question marks does add an odd sense to the whole previous statement, which further confuses the reader. Is it possibly a slightly archaic verbal thing that doesnt translate well to the internet?


Nikrum
TAS, 1972 posts
7 May 2011 11:12PM
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Your are probably right Paul, people do get confused when I start asking questions or the methods of doing so.

It is just that Under the new Sail and the conditions I have used it, it seems to me there is more torque on the Rear Wheels than with the Pryde Re-Cut. I will have to reconfirm that though but there is a total difference in how that new sail works compared to the others. So it would seem to me that this really is conjecture unless a Rolling Chassis and Sail are a Bespoke thing or constructed similar to Desertyanks Red Thing, (Long Mast Step)

That incident seemed to me like that bloke didn't like being questioned. Ain't none of us make things clear to all people, That is the way things are and we should never get our noses out of joint over being questioned or misunderstood. If that is going to be the reaction or behavior then give up trying to teach. Damn! Just imagine if Tassiefubar got that way. His students wouldn't have any respect for him and there would be no Landyachts in that school, let alone any other of their projects.

Ron

PS; You yourself have said to go ahead and ask questions even if they seem silly. There are only questions none are silly, that is a quantity that is relevant to some parties, not all

Gizmo
SA, 2865 posts
7 May 2011 10:49PM
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Ron, can you take a picture of the 2 sails you are refering to, one over lapping the other so we can compare the mast curves. And we will see if we can work out why they are so different in performance.

nebbian
WA, 6277 posts
7 May 2011 11:27PM
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Hey Nikrum:

I agree with Gizmo, it would be very instructive if you could take a photo of the yacht rigged up the sail that worked, and again with the sail that didn't work, so we can compare the centre of effort of both sails and see if we can figure out an easy way to tune for the second sail. You may already have these photos...

If we can figure out the centre of effort of both sails, when rigged up, then it would be really cool to verify that the calculations line up with actual real world results

nebbian
WA, 6277 posts
7 May 2011 11:34PM
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Here are the pictures I found:





Judging by this they don't look that different in the CE department...

Can you remember how much belly the new sail had? Also do you think it could have something to do with the different pulley arrangement?

Nikrum
TAS, 1972 posts
8 May 2011 9:29AM
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Good Morning Nebian,
As near as I can make out , the mast curves are pretty much the same. I am thinking that the effect comes in most likely with the amount of sail along the trailing edge that is near or behind the Rear Axles even though the Sail Foot is shorter. With the Pryde Cut the majority of the trailing edge is low down and I think in slower moving Air whereas the converse is true of the Gastra Re-Cut. Both Sails shape nicely under preasure even though I've not had a constant strong wind to trial the Gasttra. Up shot; My feeling is the Sail Shape is throwing the Center of Effort further towards the Rear of OR. I know that sounds all wrong but that is my feeling at the moment. Further info when I can run more trials. Another thing is it seems to point Higher into the Wind on the Strip, Tarmac Surface.
Ron

I just had a little Play In Corel Photo Paint. Pic's you asked for.




nebbian
WA, 6277 posts
8 May 2011 10:08AM
Thumbs Up

Thanks for that Nikrum

Does the pic with the gaastra show the front pulley as hauled in as it can go? Because it looks like it needs at least another 5 cm of downhaul... This would definitely affect handling. You may be able to make a 5 cm mast tip extension which would do the same thing.

Nikrum
TAS, 1972 posts
8 May 2011 12:20PM
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Nebian,
I already have an extension in there but can adjust it without too much trouble..
What effect do you think that will have??
Ron

nebbian
WA, 6277 posts
8 May 2011 10:29AM
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More downhaul will stop the centre of effort wandering around like a lost sheep, which is, I imagine, what you could feel when you took it for a spin.

The sail is designed to set in a particular way, and if it's set up in a different way then it won't work nearly as well.



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"Class Five Design" started by blake52