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.

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

^^^^ 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.

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

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!!!

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

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 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...

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.

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

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?

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.

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?

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.

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.