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Tyson of the NW
08-09-2009, 01:07 PM
In my desert fantasy game my party has acquired a sand skiff, and I have a basic idea for how it functions, sails, cargo, shape and all that. However I cannot figure out how to steer it. The ship is a trimaran with a large central hull and to smaller stabilizing hulls. The keels are reinforced with an exotic metal (unobtainium) and resistant to the wear that would normally be associated with sledding across sand It has one large mast slightly aft of center with an old Polynesian take on the spinnaker sail. Brainstorming I came up a few possible steering mechanisms.

The most obvious is a rudder. However this vehicle travels on sand, and a rudder would just slow the ship not turn, being unable to overcome the effects of 3 long runners running parallel forward.
The second is to sails to adjust heading. But the ship is designed to sail perpendicular (reaching) to the wind. So I would need more sails off center of the primary to try and twist the ship around the center mast. Or have just two sails off center and furl and unfurl the sails to turn.
I could adjust the positions of the hulls. Either shifting the outer hulls from forming a square (tips and tails are directly across from each other) to a parallelogram (one hull further forward than the other hull, and both outer hulls pulled in a bit closer. But I am not sure that will change the direction of the ship, or just shift the furrows closer. Or I could angle the side hulls off of parallel to the center hull. But that would put shearing pressure on the lateral struts.
As a skier I can turn while keeping my skis parallel to each other by angling the skis and shifting my weight. In this I lift the long edge of the ski on the outside of the turn and dig in with the edge on the inside of the turn. This would be pretty easy to achieve on a trimaran, to turn this way I also have to shift my weight wen skiing, and I don't think the ship would be able to shift it's weight sufficiently.


Any thoughts on this? Anything I missed? Anything would be helpful. Thank you.

NeonKnight
08-09-2009, 02:43 PM
Easiest method is the same method by which I have seen actual snow sleds made to steer and that is to apply 'level' which can be lowered to create drag on the side in which direction on wishes to turn, much like how a tank or other treaded vehicle turns.

The other method by which to accomplish this is, is by multiple runners. Two stationary runners in the back, and a single or double runner in the front that can then be turned/angled to accomplish a turn.

The trick for me is to not think of sand as a thick viscous water, but instead to think of it as snow.

icosahedron
08-09-2009, 02:58 PM
Hi Tyson,

Sorry, but at the risk of upsetting your well-laid plans, you could try thinking outside the box altogether.

The rudder, as you pointed out, is designed for water and doesn't work well in sand. Unfortunately, the same can be said for the trimaran shape.

A keel is 'not a good idea' for desert travel - as you have found, it simply digs in and creates excessive friction and steering problems. A flat-bottomed vessel, unstable at sea, is much better suited to sand as it reduces the 'ground pressure' and may even allow a rudder to work.

Of course, a totally flat structure may find its corners digging into dunes, so a saucer bottom would be an obvious modification. A pair of outriggers that prevent the craft tipping, but are not normally in contact with the ground may retain a semblance of the trimaran shape, but that's as close as I can get.

Neon Knight is right; think snow - thick viscous snow. ;)

Hope that helps. :)

Talroth
08-09-2009, 05:07 PM
Use skis in the front rather than a rudder at the back. Just keep in mind that you're not going to be able to make nearly as sharp of turns with something like this as you can with a sailing boat.


The other option is more sails and use them. Trim one side and you should turn into the light side as the heavy sailed side pushes it around.

Tyson of the NW
08-10-2009, 05:06 PM
Neon Knight:
I completely spaced on the possibility of using levels to produce drag. That would be an excellent solution. I may use it in conjunction with another method, or possibly the primary means of turning. Definitely gives me something to think about.

Also the sand as snow analog is probably the best to try. thanks.

icosahedron:
When I was first approaching this project I thought of a flat base, however most of the travel will happen perpendicular to the wind. If I were having the ships travel as old Mediterranean Triremes would, with square sails limited to going the same direction as the wind then it would work. However I stuck on the keel as runner idea because it would prevent the ship from sliding sideways with the wind. Thank you for the suggestion though.

Thank you all for your input.

NeonKnight
08-10-2009, 05:29 PM
Yeah, actually, it should have read as LEVERS not LEVEL, but the concept is the same. something gets applied to create drag on the turning side.

NeonKnight
08-10-2009, 06:08 PM
Watching the history channel, here is another way to go about it.

A sail Car, by Dutch Inventor Simon Stevin from the 1500's:

http://en.wikipedia.org/wiki/Land_sailing

Basically, it was a large wagon with a couple of masts with sails attached. Looking at the picture, it held around 10 mean or so.

Tyson of the NW
08-11-2009, 04:07 PM
Ooh! That is great. Thanks for the link.

Midgardsormr
08-11-2009, 05:58 PM
Heh. There's a story from my hometown about the "Wind Wagon." As the story goes, a fellow in Overland Park, KS came up with this notion to make sail-powered Conestoga wagons for crossing the Great Plains. He made a big deal about his first prototype and invited all the town's luminaries to take a ride in it.

The ride started out well--the wind wagon made it out of town, but then the steering mechanism jammed, and the wagon began turning in a huge circle. The mayor and company held on for a while, hoping the inventor could get the wagon under control, but they finally all jumped off.

Humiliated, the creator of the wind wagon set sail and vanished into the west.

Local legend in Wichita holds that "Windwagon Smith" passed through but was never seen again. There's some question about the truth of that particular claim, since the wagon-builder in Overland Park was named Brown. Nevertheless, Admiral "Windwagon" Smith is a prominent folk figure in Wichita's annual city-wide festival.

Anyway, there's your folk legend for the day.