Hi,

I'm now part of the familly. I have bought a Plume Kart (www.plumekart.com/). And I have to transpose my catamaran and windsurf knowledge to land yachts ;-)

I've been told that when reaching the high wind range of the sail, I had to tighten at the tack (OK, flattens the bottom) and increase the mast rake.

I know the importance of the CoE / CLR on ship steering balance, but for high wind ? Increasing the rake will lower a bit the CoE, but not much. The CoE will move back more and give weather helm: does not looks so interesting.

How do mast rake helps when in high wind range?

JMF

Since you have windsurfing experience,As you will know downhauling a w.rig causes the sail to flatten,but more importantly it cause the sail to fall away from the top downwards ,This then allows to upper part of the sail twist off to the downwind side therefore reducing the power of the sail.The more downhaul the more power dumped ,Most modern w.sails can be downhauled to the point where you can just about drop the power from ,say a 6.5 down to 5.7ish

Not so effective on conventional L.yacht sail,but still has an effect,I think the plume has a rear sheeting point,with sheet leading from rear of boom to the front and down to chassis,so as you sheet in hard ,the sail is pulled down at the leach/tack ie downhauled,at the same time ,because you are also pulling the rear of the boom down,it bends the mast as well. If you have a downhaul system on the plume,when you set it and then sheet in hard you will see the downhaul slacken as extra downhaul is applied .Its why a lot of land yachts don't bother with a fixed downhaul or kicking strap,just more complication.
Because of this the centre of effort,dosen't move back as much as you may think,it does move but not enough to cause a great deal of weather helm because you are also automatically downhauling at the same time, It locks the C of E pretty much where it was designed to be. The control of power being to outhaul the sail so flattening the foil . Don't forget that there's a lot more lateral resistance from the tyres and surface on a land yacht in comparison to a small fin /daggerboard on a water based craft.

The biggest factor in controlling lee and weather helm is the position of the mast base,a commercially built yacht (The plume) will have this at the optimum position from various trial and error by the designer. Home builders tend to build with an adjustable mast base to allow for slight design issues .Don't think you will have any problems unless you try to use sails way out of the range of the original design.

A lot of L yachters are now experimenting with W.surf rigs with some benefit. If you have some, worth trying a few, been a lot of discussion re this
Good luck

Thanks for the explanation. All makes sense. The point that I may not have stressed enough is that this small land yacht has an adjustable mast rake. There about 8 degrees trim for the mast to chassis angle (with a screw at the mast base). This looks like a big difference with the sail rigged.

The Plume manufacturer advice to put more rake (mast more backward) when more wind. This I still do not understand why.

From your message, I understand that the land yacht will be less sensitive to weather helm if I put more rake. Sail force will be a bit lower (good) and a bit more back (do not know if this is good/neutral/back).

JMF

On the website, the manufacturer says that the adjustable rake allows to adjust the "power" of the kart. That's the concept that bothers me :-)

Its mainly to cover different sail sizes,to balance C of E over Cof resistance. Smaller, more rake to rear,larger tip it forwards,Its basically trial and error, for the rider to sort out. Bearing in mind that the weight of the sailor has an significant influence of where the balance point is, It would be impossible for the designers to set it at a point where it suited all weights,so put a sail on ,take it out and move the mast until you feel happy with it .Then mark it for each sail you use.
I built one of my minis (No 2 I believe it was, or 3) with a similar system but to be honest with sails in the 4m to 5m range didn't see much difference in where the rake was set.Probably does between a 3.3.and 7.5 but the predominant wind we get on my local beach puts the main sail size at 5m +/- so didn't bother doing it with any of the others I built.
There are other aspects as to the effect of rake,a rig tipped forwards develops more lift in light winds but less top speed once fully powered in stronger,again its a suck it and see.
The best way to find perfect angle of rake with each sail is to take it out and once fully powered up take your feet off the steering and see where it heads ,Obviously stays straight is the optimum, There not many yachts commercial or home built that will not at some stage (,ie if you put a 6m on and the windspeed increases by 30%+) become unstable .So power control is 90% about selecting the sail size to suit the expected wind .Most of my yachts have very slight weather helm, only a slight drift ,but believe this is safer than it diving off down wind. Could be a throwback from my dinghy sailing days when that was always recommended.
One tip,when you eventually get up and running, from your cat'/dinghy sailing days,when suddenly overpowered the safe way was to head up to kill the power which you probably know. . With the land yacht ..When sudden gust overpowers it......... and lifts the windard wheel ,if you now head up it will instantly capsize, if you let go the sheet it will drop back but if you want to keep the power on turn downwind and it will stay upright and accelerate and drop back onto three. Eventually you will be able to control this to the point where you can get it onto two and keep it balanced for several metres .
The main skill is with the sailor ,get out as often as you can(With other experienced sailors if possible) try to beat them up and down. practice makes perfect.,
Good luck

Super clear. Thanks a lot. And willing to practice now

JMF

keep us updated when you eventually get out/

As of context, I'm starting land yachting with a sailing mate (he convinced me). He bought 2 Blokarts. I now have my Plume Kart. A friend is doing a DIY mini. We normally sail A-Cat catamarans here g.page/CNBerrois?share

This is south of France: no large sand beaches, no desert, no flat free space near the location. Especially as I'm a lazzy driver reluctant to drive more than 30 minutes to practive

The initial intention was to practice on parking lots, but it proves more difficult than expected: Shops are more and more open on Sunday (before it was much more exceptionnal). They now often devide them with kerbs, trees, obstacles... and put solar panels on top. Too bad, this greatly reduces nearby places.

There are some small aeroclubs around, with large flat space, but it does not looks so easy to acces that space and share with planes.

But it is still discovery time, and we hope to find better places.

And if accepting to drive (much more) more, we can practice there:
goo.gl/maps/ZM4vF4DdrLAoAR1WA
goo.gl/maps/ABoRn5iHBsvpK4J79
goo.gl/maps/uwJP6EzuM9YAexQ6A

JMF

Hi, I had few opportunities to sail, but at least las week-end, I went to a beach bigger than the parking lot of soccer playgrounds I normally practice on. The wind was OK, around 12-15 knts. Unfortunatly the sand on the best part was too soft for my technical level (static start or rolling wheels with the hands). So we had to stay where cars are used to drive, as it was harder.

I called the Plume kart manufacturer. He explained me that the rake was influencing the sail draft. More vertical = more draft = more power dans vice-versa.

I think it comes from more rake = more chord = less draft as percentage of the chord.