Forums > Land Yacht Sailing General

width to length ratios

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Created by kennatt A week ago, 12 Nov 2017
kennatt
14 posts
12 Nov 2017 5:24PM
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looking at the various builds ,between classes there is obvious large variance in the length /widths .I understand that the mast step position in relation to the centre of effort and lateral resistance needs to be calculated. or experimented with .But what benefit is a longer wheel base. For instance if I extended the length of a mini(forget about conforming to a class,) would that allow vastly larger sails,and how much would the mast step position need to be changed.As an example I looked at two potties side by side the other day one being the extended model it looked to me that the mast step positions were not much different in relation to the front wheel. Is there a recognized ratio between mast step and length as a starting point in a build. Just curious ,been thinking about extending/altering my mini(Windbob)

Chook2
WA, 1178 posts
13 Nov 2017 8:14AM
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Hope someone with some maths helps you. Mine has been trial and error to balance the yacht over time.

I have slowly worked the mast forward on different chassis to take the bigger sails and go on the handling when sailing.
My current mini is 120mm narrower than long to meet the 5.6 rule. But I do know Greg's is wider than long, when we sail on the softer surfaces locally.
My mast base is 280mm to the centre from the rear edge of the front tyre and I can use up to 9m2 sails. I move the mast back 120mm again from this, to go down to my 5.7 storm cambered sail for up to 40 knots of wind. (All cambered windsurfer sails with -2 degrees of forward mast rake). I weigh 110kg and my belly button sits over the top of my rear axle when sailing.

Look forward to a more detailed response from other builders/designers.

Test pilot 1
WA, 1420 posts
13 Nov 2017 8:59AM
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A table with all variances would be great, but trying to collate would a headache, of which i have too many already

lachlan3556
VIC, 1039 posts
13 Nov 2017 12:40PM
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Bring on the 4D plotting software...

....actually, more like 40D

Oh so many variables!

Lucky its fun testing though

Gizmo
SA, 2818 posts
13 Nov 2017 6:56PM
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This thread may be of interest.....

www.seabreeze.com.au/forums/Land-Yacht-Sailing/General/axle-width

kennatt
14 posts
13 Nov 2017 5:37PM
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thanks for reply chook,I take it you are running with an adjustable mast base as in other threads. My mini has m base set to chassis with adjustable front from chassis to wheel,so although I can move front wheel in or out .The mast base stays same in relation to rear axle.Could I bother you for the length from mast base to rear axle,for your 5.7 or near enough,I intend trying to use a 6 metre twin cam ,although I have windsurf sails from 4m to9.5 with masts to suite , and standard yacht sails 3m and 4m, I'm trying to compete(just fun racing not classes) with a few who run 5.5 land yacht sail,and find 4m just not powerful enough in the 15knt winds we generally get. Not bothered about going bigger than the 6m. thanks in advance.

Chook2
WA, 1178 posts
13 Nov 2017 10:36PM
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Hi yes I'm still running replaceable mast stalks of different angles to suit my needs. You can change them over in about 2 minutes.

My newest yacht is 1120mm from the rear mast base (for my 5.7 sail) to the center of the rear axle.

Since December 2014 I have built 2 more LLM 5.6 minis as they wear out/fatigue at the T junction.
Its metal fatigue that gets them in the end. This is good as it gives me an excuse to alter/build a new design.

Last weekend I replaced the 32x3mm doublers on each side of my current ride, (pic below) extending them right to the outside edge with 32x5mm Flat bar to stop them bending again. Should have done it originally but the hole is for a button stopper clip and there is a jam nut on the front bottom edge pushing up at 45 degrees on the corner of the axle to keep it firmly in place. See the gaps between the clamped on bits before the repair) They cop a flogging and do lots of hours along with my kite buggy as well. (I just completed 10,000kms last weekend for this current year, on "wind powered wheels" for the second year in a row.)
These bends were from a crash on Lake Lefroy at high speed. Danced from wheel to wheel in a double pirouette bending all 3 axles.

This pic is my December 2014 build when new (Cant find my current #26 mini build pics on my new computer) and the only real changes to my new one is to the rear T junction being beefed up even more, with gussets to spread the load at the pipe to square intersection. Length and front ends are all done in my jigs, so the last 3 have now remained the same mast base and chassis dimensions. It has 25mm less than the 5.6mtr rope rule.


Good luck with your mods and hope this helps.
Chook

Hiko
1155 posts
Wednesday , 15 Nov 2017 4:07PM
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International Mini 5.6 rules have evolved into two classes now
Sport and Spirit The spirit class is more restrictive to keep the original
low cost concept. One of the rules for this class is the mast step position. The mast must be no closer than 200mm from the back of the front tyre One of my minis falls foul of this rule so it is classed as a Sport
The other has the mast in the same position as Chooks latest one
which is 1120 mm from centre of rear axle to rear of mast and is 280 mm from rear of front tyre so it comes in as a Spirit or Sport
They both comply in all other respects
All of this only applies to those who want to seriously race of course

kennatt
14 posts
Wednesday , 15 Nov 2017 6:34PM
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thanks for info,will be doing a bit of cutting and welding soon,can use blowkart in the meantime.
Always curious regarding class rules,what advantage ,if any,is there, with the mast being closer to the front wheel on one chassis and not on a competitors when racing within the classes.
,The organizers must think,or know there is to set these rules. Can understand the overall size rules ,and sail and mast types.but why restrict the forwards limit of base bearing in mind you could move it backwards as far as you want, or is there a rear limit as well. All good fun , I remember when I used to be involved in windsurf racing ,where our club had a 7.5m upper sail limit ,I was 14 stone and most of the rest of the club were about 11 to 12stone ,guess who used to be last,in lightish airs,different when it was windy

Hiko
1155 posts
Thursday , 16 Nov 2017 12:16AM
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This mast position thing is a bit of a mystery to me also
As I don't very often sail with other yachts it is very hard to judge if any changes are improvements or not
After seeing the mast positions right forward on race winners in Europe I thought I would try that too and it SEEMED
to be an improvement but only when I went to a full sized wheel on the front (sailing on beaches)
The fact that the rule makers have introduced a restriction on mast position in the new Spirit class seems to suggest that there is some advantage in moving the mast forward

Chook2
WA, 1178 posts
Thursday , 16 Nov 2017 8:12AM
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I built a "Hiko" mast over the steering head (Thanks for your input into the design) but I found it had too much weight over the front wheel on our softer surfaces. Worked really well on rock hard salt at Lake Lefroy. The steering was absolutely "point and shoot" direct, which was fantastic, but suffered from front wheel drag from the increased down pressure when the yacht was fully fired up.

I study my wheel tracks to see what the balance of the yacht is like. One slight rooster tail on the rear and 2 other tyre marks is what I aim for on a broad reach. This is on the softer gypsum surfaced lake we use.

Hiko
1155 posts
Thursday , 16 Nov 2017 9:20AM
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Like you Chook I found the front wheel dragged with the mast right forward but by laying the mast right back in my oval mast step and fitting a fallshaw 400 x8
wheel to the front I really like the way it sails now on the beach

I have repositioned my second mini ,s. mast from standard to the same as your
1120 mm from back axle measurement and hope to try that out in the not too distant future I am thinking that it might be a little more versatile with the smaller size sails than mini number one Not that I use much less than 5.5 myself as I am not a lightweight but might be better for others to sail.

kennatt
14 posts
Thursday , 16 Nov 2017 4:45PM
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very interesting,Just had a though It would be relatively easy to make an adjustable base for a blowkart. The top is held permanently but the bottom of the tube could be rigged so that it slid forwards and back(Could be made to work on the fly) there's 3 inches of space to the front and unrestricted to the rear. It would have the effect of moving the centre of effort back and down with it right forwards and the reverse right back.It would give weather helm right forwards increasing the upwind pointing,And lee helm right back for downwind.
We were constantly sliding the mast back and forwards when windsurf racing with longboards and they had a simple foot pedal to facilitate this. . another thing to keep me awake at night
.Is there any restriction,just out of curiosity ,regarding the blowkart rules,regarding this,can't be the first to think of it. Probably a totally stupid idea,not the first one in my 72 years.

kennatt
14 posts
Thursday , 16 Nov 2017 10:53PM
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would need to rig up uj on steering arm since the angle would alter through the base,or alter to foot steering so may be a stupid idea,still thinking about it

Hiko
1155 posts
Saturday , 18 Nov 2017 2:32AM
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I don't consider foot steering a stupid idea

Chook2
WA, 1178 posts
Saturday , 18 Nov 2017 6:47AM
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Bryan "fastest blokart on earth" pilot, has foot steering on one of his karts and it works well in my opinion, as you have both hands to sheet with.

It was originally built for an Esperance, West Australian pilot called Shane, that only had one arm.

I also have a hand steering setup for a LLMini. I made it up for a mate that had a leg in plaster while he was here on holidays and he stuck to the really smooth areas to sail on. It got him out of the house!!!

Hiko
1155 posts
Saturday , 18 Nov 2017 6:47AM
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Here is my two minis the one in the rear has had the mast moved right forward
With the mast raked right back and a windsurf 6m sail coupled with a full 400x8 wheel it is great on the beach
The one in the front has mast moved forward to 1120 mm from back axle and has yet to be sailed
Both have Ski rear axles which I have found great



Chook2
WA, 1178 posts
Saturday , 18 Nov 2017 6:59AM
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Great photo Hiko!!!!

So my chassis is 120mm longer than yours, due to my twin mast mountings.
I'm 280mm from the rear of the tyre to the centre of the front mast mount and then another 120mm back to the centre of the rear mounting for the smaller sails. Then 1120 to centre of rear axle.

Hiko
1155 posts
Saturday , 18 Nov 2017 8:13AM
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Hi Chook and all
It gets a bit confusing due to the different mast steps
My mast step is a squashed 75 mm tube so it is 90mm front to back
From the rear of the front tyre to the centre of the mast step is 275mm and from there to the centre of the rear axle is 1160mm making a total
of 1435mm Yours seems to be 280+ 120+1120 = 1520 making it 85mm longer I think.
The rear one in the photo comes out at 1460 mm
I hope to try it out in the not too distant future. I want to get both ready for the school holidays so the grandies can have some fun.
I dont have to worry about the foot pedal positions any more as they are all taller than me now.. even the girls and I am not short!

kennatt
14 posts
Saturday , 18 Nov 2017 3:55PM
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like the look of your blue seated mini hiko also looks to put your weight right over the rear axle. Would think that takes the weight off the front wheel which has to prevent a bit of drag .....increase speed.
I'm logging all these measurements and keep looking at my sand bob,which I got mainly for my grandchildren ,with me using the blokart.
I can see the grinder,cutting discs,new tubing and welder coming out soon



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"width to length ratios" started by kennatt