Forums > Land Yacht Sailing Construction

Axle

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Created by clayhubler Two weeks ago, 3 Jul 2019
clayhubler
5 posts
3 Jul 2019 2:03AM
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Working on the design of my first land yacht build. I have purchased perter lynn kite buggy wheels and tires that come with the 20mm bearings. I'm using 1-1/2 inch alum pipe for the axle, and I want to weld a piece of round stock with internal threads tapped for the 20mm bolt which will secure the wheel. I'm wondering if the bolt has too much slop in the outer diameter and if I would be better to machine a shaft onto the roundstock and cut external threads for a nut which would then secure the wheel. The internal threads with a bolt would be a lot easier.
Any opinions on this subject?
Thanks,
Clay,
Washington state, USA

kennatt
48 posts
3 Jul 2019 1:45PM
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hi clay and welcome to forum where you will find more advice than anywhere else. I see that you intend to use aly , if this is because you are worried about weight ,don't. weight of a land yacht is not the main consideration, strength is.If you look at the seagull land yacht site most of their yachts are anywhere from 30k to 40k some a lot more,blowkarts are about 29k I can't remember seeing a aluminum framed land yacht but there probably are some,,most are built from stainless or galvanized steel,I think the main problem being that the stresses,on the joints of aluminium could be a problem in hard use, especially at the mast base to main frame which takes at lot of force. Also if very light land yachts are very hard to control in strong wind ,you need to have enough weight on the wheel to prevent side slip on the rear and wheel skip on the front when turning. if very light they will constantly be onto two wheels and very tippy. Some even add weight with sand bags when racing. I have peter lynn buggie wheel and they are fine ,except if they are tubeless,fit tubes or you will be always blowing them up. Windsurfer masts are fine,as long as you add internal support on the base,if you find two use the top of one into the base of the other as a strengthener ,again plenty of advice on here re that. Dimension wise, the ones in the know seam to advocate 2m long by 1.5m wide as a base to work from for a mini. The best advice by all on here is ,make it strong , and keep it simple. As an aside I have converted my two self builds into ski axles,best thing I ever did, clatters over rough rippled beaches without shaking my eyeballs,out of my head,other similar shaped body parts as well .
god luck ken.

Bynorthsea
99 posts
3 Jul 2019 2:44PM
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20mm bolts are fine, make sure you have a spacer fitted between the bearings and clamp up tight. 1.5 dia axles seems small. If you are considering different ideas for wheel fixing think about a steel collar clamped around the outside of the tube with a 20mm stud connector nut welded on, you can set up the geometry easily with this set up.

clayhubler
5 posts
3 Jul 2019 11:53PM
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Thanks for the input. I think I will stick with the internal threads then and just use the 20mm bolt. That will save some material. The main reason for using aluminum is because the yacht is going to be a two seater and I wanted it lighter for moving around and handling. Also, I'm using it stricly on the beach, so I wanted the corrosion resistance, and aluminum is cheaper than stainless steel. My axles are going to be 1.5" x .125" wall thickness. If this isn't strong enough then I will upsize them or modify the yacht in some manner.
I haven't picked up a mast yet, but from what I read the rdm windsurfing masts are 1.5" or 38mm inside diameter, which should slide over the 1.5" od tube I plan to use for the mast base. Any input on how far the mast should slide over the tubing? I'm going to talk to the guy at the windsurfing shop where I plan to buy the mast about this, but I haven't yet.
I have seen most of your posts about ski axles, and I may try that in the future. For now I'm just trying to build as simple as possible, because I want to get out there before the summer is over.

kennatt
48 posts
4 Jul 2019 2:38PM
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you may get a shock when you see the price of a rdm mast,they are around 500 pound in U K some more than that for 100% carbon.

However I had several rdms,as a result of years of windsurfing,So my experience................., I used a 4.30 100% carbon and made up a separate base ie ... length 2 foot, top section 8 inch to fit inside mast ,bottom section slightly wider than outside dia. of mast so that the mast butted up to the bottom section. then using another section of old sdm mast as extra external support , fitted it to the outside of the rdm ,the same 8 inch length as the internal pin. I copied this design from a custom build one that a friend has for SDM masts produced by X sail and Yorker land Yachts.
To fit the mast to yacht mast tube .....,fit made up base to rdm mast and find a length of tube to drop into yacht mast base tube so that the bottom of the mast is level with the top of the mast tube. At first I thought that this would never be strong enough with only about 8 inches inside the mast,but that's about all there was in the commercially built ones. You could of course make the base bottom section long enough to do away with the extra length of tube. Used extensively with 3.3m and 4,7m sail and no problem However ........................ Tried a different set up ie long internal stiffener inside another 4.30 100% rdm about 4 foot up the mast, and dropped this straight into the mast base tube,thinking that with the stiffener inside and the long mast base on outside it would be strong enough, 30 seconds after using for first time, sheered off at exactly where the internal stiffener ended.Just to test this again ,using the trimmed broken mast and the same internal support fitted the same way,set off again same breakage at exactly same point.
Still can't see how only 8'' of support holds when 4 foot inside and outside breaks, but that's about all there X sail ones have. I do think it,s essential to have the short outside support to prevent the mast splitting at the bottom but the X sail and Yorker users just drop the sdm mast straight on so who knows.
You could of course make it up so that the made up base and mast drop into the mast base tube so that the top of the internal pin is level with the top of the mast base tube,doing away with the extra short external support ,it seems as though theses points must line up.
Would never have tried this system without seeing the X sail one ,wouldn't have thought it strong enough but it seems to be, actually have tried it on a 4.60 with tip extension mast with a 7.5m windsurf sail and that held up as well.
not got a digital camera so no photo so ,hope description is enough.Others may have different experience but this works for me.

Just measured my windsurfing mast base pin for rdm masts just over 1.1/4'' but basically 1.1/4 OD so your 1.5 base pin would not fit inside mast,

Bynorthsea
99 posts
4 Jul 2019 3:16PM
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Mast step needs to strong. 1.5 ally will not survive. A standard diameter mast will mount on a piece of ally scaffold tube, I would suggest you need about 750mm inside. Going back to the concept an all ally chassis sounds good but in practice very difficult to build and it might not rust but it will fracture. Accept you will have to wash off a painted steel chassis after use or get it galvanised. Poke around the site see whats been done with round or rectangular steel.

kennatt
48 posts
4 Jul 2019 3:33PM
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just seen that you intend copy of manta windjammer ,which is very similar to blowkart,with support from top of mast tube to axles built with ally tube, so advice re strength and mast fit given, probably doesn't apply, the dimensions are the same , however the friend with the mast base mod for rdm mast uses it on a x sail, similar design as manta which just fits into the top of his mast tube as described previously .Take it you are confident in welding ally,I tried and could never get a satisfactory join,take my hat off to you if you are. good luck and keep your build coming . the more the better.

sn
WA, 2561 posts
4 Jul 2019 6:54PM
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regular steel tube chassis' as per the lake Lefroy mini's last ages on the salt flats - cruising around on [or in] super concentrated brine.

keep it simple - build in steel, give it a decent paint job.
rinse off with a garden pressure sprayer when you get to the carpark to remove the bulk of the salt residue - then hose it off again when you get home, followed by a squirt of lanolin grease [or whatever you prefer] over any bearings, axles, exposed metal surfaces etc.

kennatt
48 posts
5 Jul 2019 1:57PM
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I think he's building a two seater,so concerned re weight.the manta twinjammer is quoted as about49k,don't know what it would be in steel

Bynorthsea
99 posts
6 Jul 2019 1:00AM
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The weight is in the pilot and passenger, dont worry about it, get a bigger sail

clayhubler
5 posts
7 Jul 2019 11:34AM
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What difference does the angle of the front wheel make? I see on the mantas, it is mostly upright, but on blokarts and others I've seen on this forum the headtube is almost horizontal.

kennatt
48 posts
7 Jul 2019 1:44PM
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Simply.... A line through the tube must point at the contact point of the tyre to ground or very slightly in front,to give the wheel trail for self centering, If you look at the manta ,or any land yacht you will see that they all do the same. where you see the difference is that to get the axles ,front and rear at the same height ,which you need to do. the angle of the tubes/head set, needs to be different .Hence the curved and upwards swept arms etc.If you look at the Potty they have done it by an upwards crank in the main spine,but the tube still points at the tyre contact patch,the blowkart is a straight through spine so the tube needs to be near to flat .Most on here advocate 35% +/-, but that only works on a flat straight through spine. If you start to build and raise or lower the main spine in relation to the axles ,you need to compensate for that by altering that tube angle. Also the relation to the tube angle and the contact point alters depending on where the front axle is. ie if say you set the angle at 35% but then move the wheel towards the tube with a shorter arm, that contact point moves forwards as well,so you are now pointing in front of the patch .away from the tube with a longer arm and its now too far back.
all good fun,but all you need to do is make sure that that line hits the patch Good luck

clayhubler
5 posts
10 Jul 2019 11:41AM
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Thanks
And what effect does mast rake have on performance? I'm making a 6m2 sail.
I just got my mast, it is a %60 carbon 460cm rdm, hope it will work. The inner diameter is indeed 1.25 inches as kennatt said. Guess I will just have to insert a 1.25" tube or shaft inside the 1.5" tube steel mast base. The bottom of the mast inserts about 8" or so into the top, so I was thinking thats probably all the more insert it needs at the bottom into the mast base? I will see what I can do about a ring or something at the bottom of the mast to keep it from splitting.
Thanks for all the input.

kennatt
48 posts
10 Jul 2019 3:30PM
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Don't know what mast you have but...... one of the main advantages of rdm masts (probably the only one) was that they could make the wall thickness larger than sdm and keep the weight down, They are about twice to three times thicker. I was employed for a long time in the windsurfing industry and on the introduction of RDM found a massive reduction in warrantee returns on RDM as compared to SDM.There are other advantages re reflex and finer entry,not really applicable to L yachting.

I have measured all of my RDMs, all 100% carbon, and apart from the 400 ,the others 4.30 and 4.60 are outside diameter 1 and9/8ths of an inch so 8th of an inch over your 1.5. So if you are saying that your 60% mast will fit inside your proposed 1.5 inch mast tube ,making it smaller than 1.5, with an internal at 1.4, Then it must be pretty thin walled.If so, and it does drop into the mast base tube you will be unable to re-enforce the base of the mast and you will have a serious weak spot at the point on the top of the base tube where it interfaces with the mast. Don't know how long it will hold out.

If you are intent on using the proposed tubing,you would be better off rigging this way............buy a windsurfing universal joint and mast base with pin and extension, fit the base directly to the spine of your yacht just behind your mast tube,Assuming that you are copying the manta,where there are two supports from rear axle to the top of the mast tube,this would then allow you to simply fit mast as it is to the windsurfing mast base and rig up an attachment to the top of the tube to hold the mast ,a clamp of some sort, higher up the mast, This area is re-enforced ,its the area where the windsurfing boom fits ,its usually very robust for about two foot ,You will see and be able to feel it on your mast. This gets rid of the weak spot.
if mast now too short for your sail rig up an extension for the top,you can buy them but easy to make up.

All assuming manta type build.

Mast rake is all about matching centre of effort of sail to line up with the centre of lateral resistance of the yacht, If done properly the yacht is in balance and will stay straight in line, if effort is in front of resistance yacht will tend to run down wind,if behind will want to turn into the wind. don't fret about it if you stick to manta dimensions as suggested ,then it will already have been calculated by Manta designers.
The only time you will need to do anything about it is if you get smaller and larger sails than your propose 6m. If your mast tube is bolted to the spine(Take it that's what the manta has like the blowkart) then in the future you could easily make the spars from the axles adjustable so you would be able to alter the mast rake to suit.
good luck

kennatt
48 posts
11 Jul 2019 1:53PM
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meant 5/ 8ths not 9/8ths but still 1/8 th over the 1.5inch



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"Axle" started by clayhubler