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Forums > Land Yacht Sailing > Construction > I'm building my first dirt boat, I have lots of ?
Author I'm building my first dirt boat, I have lots of ?
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United States
7 Posts
Posted 16/8/2008, 4:12 am        Report
Greetings folks, from the wilds of Northern California USA. I'm new here and very excited to read all the good information I've already seen. I am actualizing my dream to build a land sailer from recycled materials. (very California. The hull is a very aerodynamically slippery river kayak, shortened and reinforced. The front wheel and forks are from a 50 cc pocket bike. There is a very sexy looking 4" disc brake which I fancy because in the hull I can't brake with me feet when returning to camp. Rear wheels are Dunlop "mags" and tires at 3.50 x 8; beach wheels from a Zodiac inflatable. The rear axles are made from laminated downhill racing skis. The tips are removed and the tails cut off to provide two four foot units which are springy yet quite stable and only slightly heavier than optimum. I"ll power the boat with a wind surf rig working against a "hound post", guyed three ways. So, questions. The deeply reclining position and requirement to cantilever the axles creates a space conflict. I'm considering angling the axles FORWARD, the opposite of the arrangement of a Fed 5 or Pac. Magic. The axles would mount under my head rest, and extend forward. Are there any physical (as in physics) demons that immediately come to the minds of the experts? Where does the real benefit come from angling the wheels like on a PM? I have the choice to mimic the physical dimensions of either a Manta twin, or a Pac. Magic. Can anyone share anything about the proper location of the mast and support post? This is the basic configuration of an Ice Flyer except in my case the pilot is in the rear. I hope this gets something started. I'll check back regularly to dialog. Thanks in advance. I'm excited that I have the opportunity for technical advice from the land of OZ! Way cool! Graybeard...(Perry)
QLD
190 Posts
Posted 16/8/2008, 9:43 am        Report
G'day Perry, Welcome to the Aussie world of sandyachts. I'm sure you will find all the info and help you need here within this forum, it's absolutely the best there is. You talked about swept forward axles, scroll down (bottom left corner) and go to page 2. Look for my post (by Kody) on "Building a C/5, a new approach". I/we discuss the pro's and con's of swept forward axles. Using downhill ski's for the rear axles is something different. Very few people in Western Australia (where Landyacht lives) would have access to/ or use, any form of snow ski's and I know nothing about them. Please post some photos as you build to share with us, we would all love to see your work. Ask as many questions you have and you will certainly find the answers here. "Landyacht", (Paul) will help with with the sail location and other yachting info you need, he's a walking encyclopedia on yachts and a great cobber (guy, in US yabber). Hope to see you here often. Kody (Joe)
Posted 16/8/2008, 10:04 am        Report
Welcome Perry, ditto on what Joe said. Also under news/articles Promogirl has loaded the plans for the pacific magic. Even though you're not building one you can still get the measurments from it about where the mast is positioned etc. Looking forward to seeing pics of your project progress!!
WA
5194 Posts
Posted 16/8/2008, 9:04 pm        Report
What do you Weight? In kgs please ,Im metric. A cl 5 is a good choice for the US. I would contemplate building to Class 5PROMO specs( see the FISLY site for those ) as your wheels will fit. I suspect if you use skis for back axles you will need to have them very short otherwise you will build a very wobbly ,slow yacht. Im looking at one right now( yes , in Kalgoorlie) and I wouldnt bother on a 5 sized yacht. other than that do what the others have suggested. if you look at the way we use a pipe mount on the Lake Lefroy mini for the mast and sail youll realize that the wire stays are unessesary and IMHO the Iceflyer sysem will only give you grief and slow you down
United States
7 Posts
Posted 18/8/2008, 4:44 am        Report
Howdy Paul: Thanks for your response. To answer your first question, I tip the scales at 15 stone, or 95.2543977 kilos. (210 lbs.) That will change next time I pee! I'm not too concerned about racing classes. Where I sail, the most boats I've ever seen at one time was about nine. I want to go relatively fast, but light air sailing is even more inportant in that we travel seven hours to the playa, and it is too much of an investment to sit around in moderate wind waiting for it to get up to 12-15 mph. (19.3121-24.1402 kph) Where the PM's and Manta's get started. I'm curious to know how many skis were laminated to form the axle which you thought would not be effective. I have found that to be similar to the flex in the Manta twin axle, three skis are required. Relative to the question about angling the axles forward or rearward and the toe-in/out question: Is there a component of axle flex that contributes to instability in the forward design when bicycling? I can't see how rotating either of these tricycle designs on their long axis would create toe-in/out. My main interest in angling the axles forward is to get my body weight over the contact point of the rear wheels to avoid the constant "crabbing" and regular "twitchiness" that I get with the Manta in the 80 kph range. I'm going to attempt to add a couple of images. The Manta Twinjammer has been modified to change the canvas twin seat to a rotomolded bucket, it is otherwise box stock. I now call it a "Twingle". It was moving in the high 70 kph range in this photo. If you go to Google Earth and navigate to 42 degrees 30' 25.61" N and 118 degrees 31' 48.66 W you will have arrived at our normal campsite. You can then scan around for views of the playa, the hot springs etc. Here is a little slide show made with a free site I found: http://www.photoshow.com/watch/WG5Nc6ii Enough for now. Hey...Good on 'ya for a GREAT competition in Olympic swimming! Perry
QLD
6188 Posts
Posted 18/8/2008, 8:07 am        Report
A seven hour trip to go for a sail. That's a very strong committment there Perry but by the looks of your slide show very well worth it. The Manta sail looks very basic and unsophisticated in comparison to many other land yacht sails yet you are getting 70kmh plus out of it. What has been your top speed so far and in what wind speed? Best speed I have had from my blokart is 66kmh in what I think was a 40kmh (20 knots+) breeze. This was with a 4m sail. I believe it would have been faster with a 3m sail but not much more. A friend was using a 3m sail at the same time and I think he was getting 3-5kmh more than I. Cheers Cisco
WA
5194 Posts
Posted 18/8/2008, 6:44 pm        Report
since you weigh in the plus 85kg range I would have the axles at 90degrees and move your body weight forward of the rear axle. Now I realize that your going to laminate the skis i say do it , photograph it an let us know how it goes. .I would build the chassis to the lefroy mini dimensions and wack a 5-5.5m sail on in the light wind dropping to a 4m when the wind gets up. most importantly keep it light. Throw away the brakes and learn to stop without them. Build your mini as a simple torsional frame ,leaving off all those extra bars. the skis are going to take all the shock loads and allow you to carry a bigger rig. cheers paul
United States
7 Posts
Posted 19/8/2008, 3:25 am        Report
Thanks Paul...all advice duly noted. I may disagree with losing the brake as I will be in an enclosed hull, and the whole brake system weighs maybe a kilo. So...on to masts. I have a pile of sail board masts from which to choose. I like one 465 cm carbon fiber unit in particular. I also love the idea of simplicity in installing it in a support tube. I've read that you blokes are using sail board masts in addition to those incredibly heavy vertical ballast made of steel. What is the preferred technique to install a tapered fiberglass or carbon mast in a cylindrical tube attached to the boat? Please tell me about reinforcing the mast at that obvious stress point at the top of the mountng tube. I do have the option of installing a mast section (fiberglass) inside the carbon mast. The top end of the inner section would NOT fit tightly against the inside walls of the outer section, but this seems to serve the purpose of distributing the forces at THAT stress point. Is this equal to slotting the top of the inner mast section as I've read on this site? Just FYI, here are some images of what may be local state of the art in large Manta sized dirt boats with sail board rigs.
United States
7 Posts
Posted 19/8/2008, 3:40 am        Report
Cisco: Those speeds were achieved in in winds of 25-30 mph. Pretty near the safe limit for the five meter sail. Personally I've only been clocked at 50 mph by a pick up truck running along side. The manufacturer claims the Manta twin is capable of 70 mph. Here's the shot from the pick up.
QLD
6188 Posts
Posted 19/8/2008, 1:45 pm        Report
Thanks for the pics Perry. Really like the detail shots. You fellas are pretty good improvisers by the looks of it. I hope you aren't going to tell us that the owner of that yacht packs it up into that aeroplane and flies in and out of his favourite land sailing venues. Please don't tell us that. It will start a designing and building frenzy of ultra light aircraft convertible into land yachts. Cheers Cisco.
Posted 19/8/2008, 2:24 pm        Report
cisco said... Please don't tell us that. It will start a designing and building frenzy of ultra light aircraft convertible into land yachts.
Hmmm, now there's a thought, although surely it would be a glider!
United States
7 Posts
Posted 19/8/2008, 3:35 pm        Report
Cisco...you are closer than you might think to the truth. The Manta land sailers originally were built by an ultralight aircraft company. The pilot just dropped in to visit friends. This playa is a great place for flying. We often see ultralights, we were once visited by a sail plane that had been aloft for eight hours and had run out of thermals. And, on one occasion I was dive bombed several times by a mob flying R/C fighter planes at me as I sailed past! Don't forget my question about mast steps!!
SA
2386 Posts
Posted 19/8/2008, 5:33 pm        Report
WA
5194 Posts
Posted 19/8/2008, 6:41 pm        Report
http://www.seabreeze.com.au/forums/topic.asp?TOPIC_ID=37931 this topic was on the conversion of a glass mast( no carbon ) to mini yacht use. the important bit for you is that we simply put a piece of wood up the lowest section at the base . It is important to have a short mast step if building the lefroy minis as a torsional frame. this allows the mast to bend and take away a focal point for stresses. the mast tube on the minis is only 250mm. On the PROMO cl 5 yachts the mast step is also 250mm and they are carrying 5.5m of sail AND a heavy stiff Alloy mast. . It is important t set up your sheetingso that the boom IS NOT pushing into the mast when loaded up, This was always a problem with the manta type yachts here is some photos of the boom set up and sheeting I use on the minis sail is 4m but could be 5 heres the front of the boom showing the hieght of the mast step.
WA
5194 Posts
Posted 19/8/2008, 7:03 pm        Report
sorry had to cut that post short for family duties. The idea of 1 mast inside another works really well . Its a good way of using the old sun damaged masts as the insert and the offcut can be used as a boom. all my mini booms are broken sailboard masts. i would recommend masts of about 30% carbon . thats the hghest level Ive tested. there have been some higher content masts tested by others but they have snapped.. My favourite mast is a 460 glass mast with a 10% carbon insert. it gives te best bend of all my masts ,but is a full length mast and doesnt pack IN the trailer. Next question please, GURU is on a roll tonight
United States
7 Posts
Posted 21/8/2008, 2:40 am        Report
Hey Landy... What about the issue of the tapering mast in a cylindrical step? Isn't there slop at the top, or does this slight movement just play into the overall sail design as it "looks like" the angle of the mast when board sailing? More later. (You can count on it) Perry
WA
5194 Posts
Posted 21/8/2008, 6:19 pm        Report
the sailboard mast dont start tapering till at least 1m up the mast. I have some Kilwell lower sections that are not even tapered
 
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