Hi, all.
I'm about to cut and weld the rear axles on my homebuild.
I notice that some yachts have the rear wheels splayed out at their base, whereas others don't.
Is this about tipping resistance, and if so, is there a limit to the angle?
Thanks.
Hi Fibertooth
What your describing is called camber. Its more about angles of force than tipping resistance.
Think about where the center of effort (CE) is on your sail and how that effort translates through the frame to the wheels you should see that a square or upright wheel has a sideways force on it and the resistance to that force is translated into forward motion so you want to angle your wheel to best resist that force.
The optimum camber will vary depending on type and diameter of wheels, yacht design, surface or ground type, position of CE.
Usually you will see camber between 5 and 12 degrees. Can you ask other sailors in your area what camber they prefer for your local conditions.
Just as a point of interest, I sail on Lake Lefroy which is very hard salt.
Originally I added 26" upright rear wheels to my kite buggy unfortunately in that configuration it was almost unusable, as the rear wheels loaded up the whole craft would chatter and skip sideways towards the kite. Adding 8 degrees of camber fixed everything, was like sailing a totaly different craft. Now as the side load increases the loaded wheel bites harder and the power is transferred to forward motion.
Many thanks for replies. And great explanations.
I'm gonna go with around 7 or 8 degrees, as that also is my gut feeling.
Unfortunately, even tho I spend a lot of time at beaches here in Southern Tasmania, I haven't actually seen a land yacht sailing locally for over two decades.
So, winging this.
She'll have overall length of 4.2m, beam at axle of 2.2m, suspension on rear wheels and side by side seats for depending which tack I'm on. 
Suggest you read a bit deeper on some of the other construction threads.
There has been a lot written about why rear suspension is almost always a bad idea and about why a seat large enough to move about on will cost you more in air drag than you will gain.
Fibretooth, your yacht dimensions seem a bit odd... Over the years the best width to length ratio has sort of been worked out about 1:1.5 to about 1:75.
The axle width of 2.2m seems VERY wide for a yacht of that size, often in smallish yachts you need to lean over and rotate the wheel just to get moving, the Class5 yachts have a maximum width (to outside of the wheels + axles of 2m) and at times that is a stretch to reach the wheels, so another 100+mm to each side would give problems.
You mention a dual seat and swapping sides when tacking......Sailing a twin seat yacht one up is a real pain in the 'rear end' (been there done that on a 2 seat Manta style yacht) How would your seat belt work? And please don't say you won't use a seat belt, a flip at 60kmh is not nice.
Rear suspension isn't much use and actually takes away the force needed that is generated by the sail to load up the suspension first before the yacht will move.
Have a look at the LLMini plans that are tried and tested and makes an ideal entry yacht into the sport of land sailing.
www.seabreeze.com.au/forums/Land-Yacht-Sailing/Construction/Build-a-Landyacht-Lake-Lefroy-Mini-Yacht/
Gosh. Aah, thanks for input. However it's just possible that the type of sailing intentions of some are somewhat different from yours or even the majority. It wasn't asked of me. Sorry for the bluntness, but I've seen many times on this forum a seeming personal offense if a patron doesn't automatically go for the blokart.
Fibre I dint think anyone is telling you to go for a bloKart. I like class 5's and Gizmo suggested you look at a mini.
The point is we want to see more people entering and enjoying this sport and knowing roughly what works and what doesn't we don't like to stand by and watch someone make mistakes which will make them lees likely to stay in the sport.
This forum is hear to share experience and ideas and help each other build better, faster, more enjoyable toys.
Cheers John.
The thing is, I've long wanted to make this yacht. A yacht capable of what I have in mind.
I also enjoy, and am capable, of starting things from scratch, including design.
Of course this forum can be well utilized, with the vast knowledge and experience, and indeed generosity of others. That is why I posted the original question. Which was quite specific. And originally answered as such.
I've long believed the best advice is that which is asked for. And I received good advice in answer to my question.
If someone's interest was piqued at my intention, then ask, rather than assume. Advice from that base point can well be appreciated.
Re suspension, after much thought the night before, I'd decided to let it go, even tho I'd spent much time designing the system.
What I want is a yacht capable of rough terrain, not a speedster. Also the necessity to carry quite a load. And windward ability.
I'll also use it on my local beach, altho it's designed more primarily for the former.
It is being constructed mostly out of bits and pieces I already have from a hang glider and old boats.
It is designed to have a foresail, and the dual seat thing is because I anticipate being on the one beat for extended periods.
I certainly don't want to burn bridges on this forum as I HAVE received great advice, but seriously, I have seen many times here disdain metered out on the real do-it-yourselfers for not fitting into the convenient boxes.
The fact is that the designs that many here adore were won by living outside those boxes.
Fibretooth- I have only built one land yacht so others may be able to comment further but I choose stock for the rear axle which has enough spring to smooth out the ride for rough surfaces.
I also built for the rough/beach use and my setup works well in these venues.
The stock I used is 1/8"x1.25"x3" oval aluminum set plate wise.
The setup I used is also a suspension of sorts as I mounted the axle specifically to allow spring through as much of the stock length as possible with a simple arrangement of central rubber mount at frame and travel stops on free outboard ends- wrks a treat..
Thanks trbnt.
It's a great idea. I'm making stub axles tho, for ground clearance. Was going to use the tried and true suspension that ultralight trikes use...namely bungee cord wrapped around a rod emanating from the swing arm, but decided against. Figuring good wheels/tyres and a comfy seat, complete with seatbelts will suffice.
One thing- the leeward wheel loads plenty when up on two wheels- my axle I used has spring but is still fairly stiff..
Stub axles- yep LOL but I am assuming you mean stub axles from frame...
I have a one piece axle which is secured to frame cross member in center via a welded post which rides in Delrin bushing.
A block of rubber cushions things and allows spring over over arc from leeward wheel to stop active on windward side.
All this does really in my case is to allow the axle to spring just as if you mount the wheels the jump up and down on axle free from cart.
Works- nice ride and stiff enough to keep from acting as a energy sink to kill power.
My frame is very rigid where the axle mounts so this is all a expedient to not have too stiff of a ride.
Beautiful work! Yep, from what was going to be the swing arm. I'll have around 350mm ground clearance at the rear. Will post photos a) when they're finished, and b) when I figure out how to post them!
The most beach capable yacht I have ever seen is one using old aircraft tyres and built from a simple 'T' frame from Aluminium scaffold tube.
The yacht could actually sail in the VERY soft areas of a beach and also over sand dunes.
www.seabreeze.com.au/forums/Land-Yacht-Sailing/Events-Competitions/Beach-Blast/
That was a wonderful read- thanks for posting.
Are you one of the members of that trip??
Author?
Yes, Gizmo...awesome article. And that part of the country is awesome too...glad to have been reminded. And inspired.
I get good ground clearance for soft sand and rough ground using quad bike wheels made to fit standard 20mm axles. They also handle soft salt/mud quite well with bigger surface area they dont sink so much. the fact that they arent driven means they dont bite in and are great when going over dunes hills and bushes. For the front wheel I use a normal wheel/tyre with a second tyre minus the bead section over main tyre, this increases protection from thorns and sharp rocks and as its a slower run wheel wobble dosnt matter so much. 
For beach sailing I have always worked on at least 100- 150mm of clearance under EVERYTHING...... That way clumps of seaweed don't seem to be a problem.
do keep in mind that all these wiz bang materials and suspension came along because competition landyachts had a rule forbiding the humble wooden axle. if you arent rule constrained then a simple piece of 20mm x190mm x2000m tassie oak,ash or similar would be the cheaper ,simpler more obvious answer. for us old builders with 100+ yachts under our belts , the golden rule of ally axles is only weld when not using as an ally axle
