I was running over a landsailer design in my head on the way to work. I was trying to figure out the best configuration to keep the yacht on 3 wheels. Wanting some thoughts on the direction of force that the mast exerts on the chassis.
Hi Squish Man,
I would suggest you apply Einsteins Special Theory of Relativity E = mc2 squared.
Ron
I've found the mast is constantly trying to tip you over 
A Heroic stuggle between Good (speed) and Evil (having your landyacht act as a sunshade).
Squishman,
The most sensible explanation I can think of incorporates Lachies theory, Yes the wind is constantly trying to drop you on your side therefore you counter it and motivate forward. The stiffer the mast the and the higher the wind, the more likely you are to tip over. Which in itself relies on your astuteness in reflex control.
I find with the Windsurfer 100% CF Mast it is stiff enough to be able to get good speed but soft enough to absorb any heavy Gusts, this in turn is then transferred back to the wheels in a more friendly manor. A stiff mast will give you good speed but your reactions will have to be pretty much spot on and with Dust Devils/Willy Willies you don't have much of a show. TP1 demonstrated it and he is an Old Fart with a lot off experience. In short you have to make a decision as too where you want to go.
Think about it and use your "What a Dog knows, how to re procreate with"
Stay Upright
Ron
Yeah, nevermind me. I think I asked the question without really thinking it through.
Sorry Squish, you caught me on a funny day. 
No I don't have an intelligent answer to your question 
Just do a google search on "How a sail works"... most people think the wind "pushes" on the sail but its actually the back of the sail that does the work, the yacht is sucked along in the low pressure that the sail creates.
One could say we fly the wing on it's side. The principle is exactly the same. Half a Hang Glider on wheels.
Ron
Since geometry is the topic, is there a rule of thumb about the relationship between axle width and wheelbase? How does a 'long but relatively narrow' yacht differ in handling, stability and other ways from a 'short but wide' one?
This might help a little...
Many years ago there was an idea of a ratio of about 1.5:1 - 1.75:1 was the most workable in smaller yachts.
A short wide stubby yacht has good initial stability but at speed it gets unstable where as a longer yacht has poor initial stability but good at speed.
The Class5 and Class5 promo have maximum width and length measurements and most people tent to work with those. The Mini class has a 5.6m rope rule that does allow for the flexibility of length / width ratio change. Often the answer is see what yachts are out there and change the L/W ratio a bit and see how they then compare rather than go radical. (but keep it within the rule)
My personal opinion would be if you wanted a slow full power yacht with a full draft sail to be used on grass of soft beaches go slightly wider and if you had hard surfaces to sail on go a slightly longer chassis and use a flat sail.... I hope that makes sense.
That makes perfect sense, thanks very much.
I have seen that diagram a couple of times in my travels through the forum and one thing has always puzzled me. Why is the arrow from the cg drawn perpendicular to the roll axis? Would it not be more useful to represent the force from the centre of effort of the sail to the roll axis (which I imagine is always acting in much the same direction relative to the centreline of the yacht for any of these configurations, if they are all sheeted in hard)?
The roll axis would only come into play when the windward wheel lifts up, prior to that moment its the CR "centre of resistance" would be the critical thing.
OK! So how would all this be affected by different wind directions ? Let us say directly along the Roll axis or opposite??
Ron
Assuming that the true wind is coming from the Starboard quarter at 40deg. Where would the Apparent wind be working from? Directly opposite?? Or does this question lie in the sail shape??
Ron
This is the best explanation of "Apparent wind" and land sailing that I have found.
www.greenbird.co.uk/about-the-greenbird/how-it-works
