Technical Tips......

From a previous Class 6 posting.....

Well cisco.... as you already have an existing yacht most of the variables you could change are limited...
it comes down to

1. whats making you NOT GO
and
2. what makes you GO

Dealing with the first one first ....How much force does it take to move your yacht?
Get a fishermans spring scale and pull the yacht on the surface you sail on or similar (with a pilot in it...) and see what it takes to move it in "Kgs" [ you dont need the rig to do this]

Tyre pressure ... increase / decrease "then measure again"
Bearings ....old vs new , oil vs grease, side seals vs no seals "then measure again"
Wheel Balance ....are your wheels balanced? .....have you had an unbalanced wheel on your car at 60kmph?
Tyres ....are they light or heavy that might take a lot of effort to get spinning? ... do you run 4 or 6 ply tyres when a 2 ply tyre is lighter and still do the job?

this will keep your thoughts going for an hour or so ...more later

Brian

A section from a reply from cisco..........

As I understand it , when a landyacht is sailing with the windward wheel well off the ground, it is not sailing efficiently. When the windward wheel is just skimming the ground we are at, or near, optimum efficiency. This being the case, a land yacht effectively sails on it's front wheel and leeward wheel. The question of rear wheel toe in arises. If the rear wheels' toe in are adjusted so that their track lines coincide with the front wheel contact patch, will we get optimum tracking or have we just set it up to be a pitchpoling stunt yacht. No Dutch Rolls for me thanks.
...............................................................................................................


Yes your thinking cap is on.. you are right that the fastest ( in the ideal conditions) is with the windward wheel just off the ground ...BUT this then loads up ALL the forces on the leeward wheel......counteracting any advantage....
You are also right in relationship of wheel tracking and lots of forces being put onto the bearings ..... sometimes bearings with a LOT of play in them some times seem to work better as they self align in the situation you have come up with...
[Please refer to the first part of this posting.....]

Cheers Brian

Excellent thanks Brian. Remains to be seen if the method is still current.

I have to challenge the accuracy of the method though. The calculation of base area will be slightly less than actual due to the bend in the luff.

In calculating the areas of the irregular four sided shapes along the leech, I have used a different method and come up with a substantially different result.

By taking the distance between perpendiculars of the figure as the base and multiplying it by the overall height, gives the area of a rectangle. The areas of the triangles thus created are then added or subtracted as dictated by the orientation of the figure.

It has been 40 years since I have done any serious Maths B, but I think it is correct.

This is possibly another area of Australian Land Yachting that needs to be brought up to date. Looking forward to more. Cheers Cisco.

cisco.. "wildfire" (class 5) the frame & back axle were aluminium scaff tube with all other tubing steel.
The brackets were made from steel tube i think about 52mm??? 3mm wall then cut across with an angle grinder, 2 x 1/2" Square nuts were welded either side of the slot and opened up about 10mm, A 3/8" bolt then is used to clamp the bracket around the scaff tube.
All sorts of flats plates were then welded to the brackets to suit the needs.
The use of clamp brackets enable changes to be made to the chassis and rig without drilling holes.....

problem is when you get to the beach and say"show me where it says that in the Rules" you tend to get dumb stares fom the scrutineers. you have to ask in the official language of that class. Due to translations most of the promos at the WC08 complied with the french and spanish version of the rules but not the english version. It was explained to me at one stage via an interpreter that " the new amendments to the new rules had not yet been translated to english". when I checked the French version on the computer it hadnt been changed either, but the french knew about the changes months before when thier yachts were packed in containers.
If you ever go to sail in their world be ready for this kind of scenario.
I have been emailing all week to a Argentinian sailmaker who is having the same difficulties as us working out which of the bits of the measuring system is wrong and which is right. you need to measure a sail on the ground and religeously follow the instructions to find the errors

Thank You Paul. You have cleared up many doubts. So now, when go to beach always ask man "You Speaka da Engwish?"

Also "Watch sail maker like Hawk."

I will answer your questions one by one...
Yes..scaffold tube is successful as it is a high tensile aluminum. 48.4mm OD with a wall thickness of approx 4.5mm.
The bend angle was to make the seat base level with the ground.
The bend never failed ..many yachts had similar bends all worked ok...
see your local exhaust place to bend the tube ( they will not be keen but tell them its ok with bends good to max 45 deg from straight MAXIUM [not that you need to go that far])
YES the mast fitting was also a clamp and could be adjusted up and down.( had to remove mast from yacht to do it safely.
There was a clamp on the main spine as the mast step this could also be adjusted.
The mast rake could be altered with a combination of the "mast clamp" / "mast step" and the "rear axle clamps"... move out = mast back--- move inwards = mast more upright etc.
Yes the seat was made from cheap 6mm ply covered with glass matt and resin then painted.

Brian

Yep the hand steering (tiller type action) was a bit hard to get used to for some people....But anyone used to water sailing it would come naturally...
I found it GREAT on push starts .. you could run like hell and then jump in AND still control the yacht...
The other thing is you could slide right down into the seat to maintain a low profile to reduce wind drag....Didnt need to have your knees up slightly to steer.
But mind you i never built another hand steer landyacht!!!

Hi All ... i found this question on a US forum about landsailing it might answer some questions for some...
groups.yahoo.com/neo/groups/landsailors/conversations/topics/53
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Whew!

Ok we have nice breezes today. 21.74 mph with gust to 29.57. I think I might need more weight on the front end. When the gusts hit it moves the front end several inches. And why didn't anyone express the importance of seat belts? My landsailer turns faster than I can hang on.


Kelly

Re: Whew!


Your front end sliding is likely because the sail center of effort
(CE) is slightly in front of the boat center of gravity. What you want
is the opposite where the sail is pushing slightly (but not much)
behind the boats center of gravity. When the big gust hits, you want
the back end to slide out as this is controllable and safer. Im pretty
sure the front sliding problem will be a fair amount worse when you
get the boat on a dry lake bed (or ice) so its worth dealing with.

Where your boats CG is gets a little complicated when sailing as the
mast downward force can shift the CG from where it is with no wind on
the boat but in "general", you may want to move the sail center of
effort back or move the boats center of gravity up. Adding the weight
to the front will move the CG up which is good(and make the boat turn
even quicker) but now your carrying around extra weight. The front
weight will also help in general making the boat safer to sail in your
"typical" winds in western Kansas. You can move the sail CE back by
either moving the mast track back or raking the sail back more. Moving
the mast track back generally will result in the boat handling higher
winds better but if the boat is small, it might also turn the mast
into a "nut cruncher" if it comes to a stop suddenly, something whose
importance might depend on if your done having children yet. DN ice
boats had this problem many many years ago and I believed they for the
most part solved the problem by raking the sail back further. Almost
every design which has been around for a while has the safer "weather
helm" balancing so you might take a look at dimensions of existing
designs but keep in mind that the upper wind limit that the boats can
be controlled in varries by a huge amount for different designs.

Im thinking about driving out to your mile square chuck of concrete
next weekend. Have you sailed it yet?

There is also a small get together of dirt boats in Southern New
Mexico near the end of April (near Deming).

Wally Hall
Denver
(note, I of course take zero liabiliy for the advice on boat balancing
above, anything you try is - as you know- completely at your own risk
and can be dangerous. Beware also, you may have too much fun
experimenting).

I know the caster angle of the front wheel of land yachts have changed over the years..... But this might be an interesting read

en.wikipedia.org/wiki/Caster_angle

I set my pivot angle to intersect the ground just ahead, maybe 20-30mm, of the wheels contact point. That way the yacht always wants to track straight when no pressure is applied to the pedals. I may have coppied this from the Iceflyer plans but I've also seen it on gokart steering (you have to lift the front of both machines up to turn).

Of course too much ahead and like you said, concrete steering

Here is something else i found that might be of interest if your into sails....
I know its about Water Yachts .. but have a read
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What is different about sails for planning dinghies, catamarans, and trimarans?

HIGH SPEED SAILS...

A better understanding of high-speed sails can aid in the design of other sails.

Everyone who owns a catamaran or a trimaran knows that there are important difference between his sails and those of a neighbor with a displacement sailboat. But what are they? How do high-speed sails differ from "normal" ones?

It is the design of the sails that distinguishes them. These design differences are very important, but they are differences of degree rather than kind. Indeed, the discussion below should be useful even for those who never intend to build catamaran or trimaran sails, since it will point the way for those who need a bit more speed from the sails that they are using. By discussing the extreme, it should be possible to elucidate the middle ground.

There are three places to look for differences: in the two-dimensional shape of the sails, in the design of their draft or fullness, and in the manner in which they are rigged. We will take up each one in turn.

High Aspect Ratio

High-speed sails benefit from a very high aspect ratio. In part this is because high aspect ratio is most effective when going to windward and high speeds tend to move the apparent wind forward to the point where almost every point of sail is a beat. When wind is flowing over a sail from front to back, air circulates over the top and under the bottom of the sail. This circulating air both reduces the efficiency of the foil and creates induced drag. If sail area is distributed over a high and narrow foil, the relative importance of this bypass flow will be greatly reduced. Thus, any given area is more efficient when it is distributed over a long leading edge, so long as air flows over the foil rather than "around" it.

A high aspect ratio benefits a high-speed sailboat in another important respect: the potential speed generated by the foil will be higher. The velocity of the air moving over the foil will be greater along its leading edge. At this point the friction drag of the sail has not slowed the flow of air or rendered it turbulent. As a result, thrust can be generated into a higher range.

Note that I am not suggesting that total force will be higher; the force generated by a foil of given size is a constant, assuming all other variables are constant, but the same force can be generated by a small volume of air at high speed as by a large volume of air at a slower speed. High aspect ratio sails characteristically work with smaller volumes of air but at a higher speed than sails with low aspect ratios. *

High aspect ratio is not enough to make a sail efficient on a high-speed boat. The three-dimensional shape of the foil must also be appropriate. Obviously the sail must be relatively flat. Flat sails generate less power than full ones but can be used effectively at lower angles of incidence to the wind and operate effectively at higher speeds than fuller sails.

The appropriate depth for any given sail is not easily determined apart from experience. The weight of the boat, the size of its rig, the shape of the hull(s), the water and wind conditions on a given day, even the helming technique of the skipper--all of these play an important role In determining the proper fullness for the sails. As a general rule, however, it can be assumed that light, fast boats will be best served by sails of from 1:14 to 1:17 draft ratio, that is, for every inch of depth in the sails, they will be from 14 to 17 inches in chord.

There is a second aspect of three-dimensional shape. The depth of the sails must be in the proper place. High-speed sails always benefit from draft farther forward than "normal." This forward draft can be conceived as working with air that is moving at speeds close to those in the free stream. Chances are that air will also still be moving smoothly in a boundary layer flow. Aft draft may result in the sail affecting more gross volume of air, but it is accomplished only by slowing and disturbing the air flow to such a point that potential speed to be derived from the sail is much reduced. Unfortunately, just as in all mechanical devices, an increase in power requires a decrease in potential speed. So, the faster the boat, the farther forward draft should be moved.

The entry curve for high-speed sails should also be very rounded. A rounded entry curve or leading edge tends to reduce stalling tendencies. This does not directly lead to increased speed potential, it is nevertheless necessary with high-speed boats since they are generally very light. As a result, they are hard to maintain on a constant course. In addition their rapid acceleration or deceleration leads to rapid change in the apparent wind directions. All of this requires a sharply rounded leading edge in their sails.

Cat Rig and Battens

Finally, consider the rig appropriate for these high-speed boats. You will have noticed that most high performance catamarans have a cat rig. This follows from our discussion of aspect ratios. The sloop rig tends to spread sail area out, in effect, decreasing aspect ratio. That sloop rig will make possible more power, but it will cut down the potential speed of the boat. If the boat is so easily driven that this power is not required in order to get it moving, it is best to place all sail area in a single, tall sail.

One more thing: high-speed sails should have full-length battens. These battens are tied into the sail with enough compressive force to bend them into the desired shape. As a result, the sail becomes so rigid that the sail must be "popped" from one side to the other when the boat is tacked. This rigidity holds the sail in shape in spite of rapid acceleration and deceleration and in spite of the abrupt apparent wind shifts, which accompany those changes in speed.

The rigidity imparted by the battens also lets the sail operate at higher angles of incidence than would otherwise be possible (see Marchaj's Sailing Theory and Practice, page 70). Once again, this can be very useful on a boat that moves the apparent wind well forward just because its own speed is so high. The power developed by such a sail will be relatively low, but its potential speed will be very high.

There are, in conclusion, no secrets in the building of high-speed sails. They are simply the result of extending the same lessons we have learned with "normal" sail design.

*This discussion is somewhat simplified. If you are interested in more detail, see C. A. Marchaj, Sailing Theory and Practice (N.Y.: Dodd, Mead & Co., 1964), pages 84-88.

Thats correct... it is the front of the mast AND sail combination ...
They make reference to a rounded edge is better than a sharp edge... the mast does achieve the rounding of that edge.......

I will add this link to show how sails work

http://www.lksc.org/myhtml/howsailswork.pdf

If anyone is wanting a FREE Cad software program to do Technical drawings with go to.....

www.cadstd.com/

And download the FREE version

A simple program looks good and works well....