This is the thing i find the most interesting in the sport of landsailing. It's far from an exact science.
With race cars over time things are perfected and refined, as with land sailing things are also getting more advanced, but its a case of trial and error and with every error is a little more to learn.
The internet and forums are a wonderful place to exchange ideas, learn, and try your own thoughts (how people did it years ago is beyond me).

In other words i have no exact answer to why it works or doesn't on landyachts.
but im eager to learn

Have you tried "thorn proof "tubes?
In South Australia we have a weed called a "3 corner jack" some people call them a "bindi eye" and they are bad news on bike tyres.
On the yacht "Richshaw" with 20 inch bike wheels i replaced the normal tubes to thorn proof it stoped the punctures but it slowed the yachts acceleration a huge amount.
The added weight in the tyre/tube made a very big difference, i noticed a similar effect between 8 ply, 4 ply and 2 ply tyres on wheel barrow wheels on class 5 yachts.
I do some casual work for a tyre importer and have noticed that many of the high performance / race tyres are VERY light compared to standard road tyres of the same size. Maybe for the very same reason ..Acceleration !!!!

I thought is might be something like that,
BUT i did find the heavier tyres/tubes worked better in good or gusty winds and a big course. (perhaps they were working like "fly wheels")
The lighter tyres/tubes worked better with a small course and or light winds.

Don't get the cr (centre of resistance) mixed up with a factor that hasn't been discussed which is cg (center of gravity).
The cr of a land yacht will never be behind the back wheels but on the other hand if cg is behind the back wheels the front will come up like a seesaw.

Mind you please keep in mind these variables as well...

CF Centre of Focus this may swap between the wife and the esky filled with ice cold beer.
CPr Centre of Pride again this may change from the kids on board to the boat itself.
CA Centre of Attention this will often change between the wife, kids, boat, and the beer.
CPa Centre of Passion this will vary between water and landsailing (and the wife)
CR Centre of Resistance this can often refer to what stops the yacht going side ways or the wife stopping you spending more money on sailing stuff.
CE Centre of Effort this the amount of effort to go sailing, get the beer or the wife and often associated with CPa

Thanks for the import guys,I am back at work in Kambalda at the moment so I have not been able to do much work on the yacht (800km away)but will be home again in two weeks and I will sail it again with the changes made and will post the effects. I may be that it is not suited to the surface at Safety Bay and I may have to revert to a yacht with smaller wheels for that surface but I dont want to give up yet as I see it as part of the experience
Cheers
AUS230

Note:
I did not bring the yacht to Kambalda for testing on Lefroy as the lake is currently flooded.

Hiko said...
if a yacht is moving forward at say 60kms/hr the axles will be doing the same but the top of the tyre will be doing double that and the bottom will be stationary or it will be skidding on the ground

If the sand yacht is traveling at 60kph, the axle is also moving at 60kph. The bottom of the wheel is stationary, it's not moving, and the top of the tyre directly above the axle is moving forward at 120kph.
Have a look at a crawler dozer or an army tank as it rolls over the ground. The top of the tracks are moving forward at high speed but the bottom of the track is not moving at all. The bottom track only moves after the rear drive wheel has passed and the track is picked up. Your tyre does exactly the same thing, be it on a car or a sand tacht. The length of the "footprint" is what creates lots of friction and resistance to easy moving. This is why a steel wheel (railway wheels) roll so easily, there is a minute contact point between the wheel and the rail making almost no resistance.

Kody

It looked fast when I saw it on the trailer last Sunday

I just noticed that under the FISLY rules a class 5 no longer has to have an aliminum mast it can be constructed out of any metal. Promos still require that it is constructed out of aliminum. Question ? what type of metal would they be refering to(just out of interest, I like my aly mast)

Cheers
AUS230

MAST
M1. The mast must be made of round section metal tube, the outer diameter of which must not exceed 60 MM. At rest, the mast must be straight.
M2. The mast may be made from a maximum of four different diameter tubes, each tube must have a constant outer diameter and wall thickness over its full length. At each change of diameter, 3 CM are free to allow for chamfering or for protection of the mast pocket.
M3. The mast must be rigidly supported by an arrangement of metal tubes, all not higher than 1.20 M above ground level.
M4. The position of the mast must not be modifiable with the yacht in motion.
M5. The length of the mast shall be such that the distance from the top of the mast to its foot plus the distance from the mast foot to the ground shall not exceed 5.50 M.

ALSA class 5 specs
C. MAST

1.MATERIALS, The mast shall be made of one piece of round section tube (or a maximum of 4 different tubes, each having constant outer diameter and wall thickness), with the outer diameter not exceeding 60 mm.

The mast may have any kind of fixed internal stiffeners.

2. LENGTH, The total length of the mast, plus the distance from the mast foot to the ground, shall not exceed 5.15 metres.

3. When not in use the mast must be straight.
EDIT in the pacrim 2006 and FISLY 2007 they say "metal " tube not ally, the ALSA specs say"round section " tube............ no mention of metal.
I shall dig out the hardcopy and check this,



I believe you could use steel inside he mast as long as it was only as a stiffener!!!!!

Wrap a high percentage carbon fibre mast with aluminium foil.

Easy [}:)]

Do you think those three windsurfer masts I got at the dump for $6.66 each will be good enough if I fill them with a mix of coal dust and epoxy resin?

Class 5 FISLY rules NEVER said alloy tube! I know cos I was one of the 4 person committee who wrote them.
Reason was that at the time we were trying to be inclusive of any yacht which was out there, and a number had masts which included steel sections. The reason for the 4 outer diameters was that John Glen had recently had great success with a yacht built for Mark White and couple of others (me included) which had 17 outer diameters. The tip was about the size of your little finger. To have replicated these, for the average guy was very expensive. The rule relating to 30mm tapering etc is to give an "engineeringly sound" change, ie eliminate, within reason the stress riser.
Most of the rules, are/were actually to keep a lid on the cost. Also the rules were formulated to have as little interpretation as possible, ie it was clear what was meant. They must be OK as they have changed very little in over 20 years!

Gizmo said...

Quite often what is decided at meetings are not actually what ends up on paper
Where is "The rule relating to 30mm tapering"?..
Here is what is said on the FISLY site for promo 5 specs.
http://www.fisly.org/index.php?id=2
It clearly says "Aluminium"



The original or International Class5 specs don't mention aluminium but does say maxium of 4 sections, with a constant diameter.....

Yes you are right about PROMO, I was talking about class 5.
30mm tapering, the rules I just read say "At each change of diameter, 3 CM are free to allow for chamfering or for protection of the mast pocket."


I was going to build a promo, but the rules are so ambiguous that I can see potential protests galore, eg
Sail battens must be of polyester resin.
Now for absolute certainty I have yet to find a polyester batten, all the commercial ones I can find are Vinylester, and advertised as such.
The rule did say, and I am NOT quoting, that the chassis shall be made from 60mm tube, later says that at any change of size..... My mind says SHALL is compulsory, so there can not be a change of size?
Mast shall be of given tube sizes, unavailable in any reasonable quality in the southern hemisphere according to my aluminium stockists.
I thought the Promo was supposed to be an affordable yacht, why make it compulsory to ship bits from Europe to have a "legal" yacht.

Damn the detailitis of the rules I say. Turn up at a race meet with two yachts. One that conforms to the outdated rules and one that has the latest technical innovations.

After the formal racing have informal racing to have a preview of the direction the sport NEEDS to go.

INNOVATION is the predicted growth industry of the future.