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 Post subject: Woo Hoo! Operation bodge
PostPosted: Fri May 20, 2011 1:11 pm 
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Joined: Fri Jul 24, 2009 3:08 pm
Posts: 77
:D All you retired folk have a lot to answer for! Inspiring me!

Got me an alloy pole for mainmast (Free)
Fibreglass rod for a twisty top (Free)
One barely used windsurf sail for high winds. (£10 Poor bloke I bought it from was giving up windsurfing after 20 years and seemed a bit down. He'd lost his agility)
Misc cordage.

The Hobie sail is actually quite big, I will remove the top where the Yellow batten is resting and move the end cap down. Initially it will not be furling.

Image

Pictures of final result coming soon. Should look something like this...maybe..maybe not. Any design advice, feel free to contribute
http://youtu.be/2bWCULJRmwQ


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PostPosted: Fri May 20, 2011 1:41 pm 
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Joined: Wed Jan 27, 2010 12:38 pm
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Location: Roswell, GA - USA
Windsurfing sails are designed for a flexible mast and a decent amount of downhaul (pulling on the bottom of the sail with the top fixed at the top of the mast) which will give the sail the proper shape. You might want to use a std windsurfing mast (maybe buy used).

Good luck.


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PostPosted: Fri May 20, 2011 5:18 pm 
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I have a little theatre technique for just this stretching purpose. I'm not as daft as I look :? :D


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PostPosted: Fri May 20, 2011 7:36 pm 
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Joined: Sat Nov 12, 2005 10:46 pm
Posts: 2361
Location: Escondido
Pretty lofty goal, but then you sail designers are amazing. Here's the creation of a 16 year old prodigy, the material salvaged from an old tarpaulin -- even done on a tighter budget! His friends seem to be as impressed as I was! :wink:
Image


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PostPosted: Sat May 21, 2011 12:37 pm 
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Joined: Sun Aug 12, 2007 5:17 pm
Posts: 484
Location: Auckland NZ
I am an ex windsurfer too.

My smallest sails (for high winds) were 3.5sqm and they got a lot of use around the world. Typically the small windsurfing sails are for higher wind and they are cut very flat to cope with the acute sheeting angles associated with higher speeds and with the foil shape held in place by many and/or stiff battens. On paper these characteristics do not lend themselves well to the very light winds and low speeds of typical Hobie kayak sailing but who knows...

I believe you have an Oasis? I have an Outfitter and my mate has an Oasis. The standard Hobie sail can be used on both these boats but it does not make for particularly exciting sailing (if I can put it that way). On my Adventure I frequently increase the sail area by flying a jib as well as the Hobie main (very light winds only). Doing this almost doubles the sail area and, while I have not deployed this sail on my Outfitter I am sure it would transform the sailing performance of the boat (my mate sometimes sails his Oasis as a schooner using 2 Hobie sails instead of the usual 1 and it works well too).

It all depends, of course on the amount of wind, the amount of ballast on board and the amount of risk you are willing to take, but 2-up and in typical sailing conditions having more canvas on either of these boats will make them sail a lot better.

So, personally, I would hang-fire before applying the scissors to my sail until I had been able to do an on the water test ! For this choose a good day... a beefy crew... don't tell them what you are trying until you are out at sea... wear wetsuits... do not do your testing in winter !


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PostPosted: Sat May 21, 2011 4:53 pm 
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Joined: Fri Jul 24, 2009 3:08 pm
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Roger! will do. I'm not after performance, I just canny afford the official sail.
With a thinner mast I actually gain a bit of curve from the spare material at the mast sleeve and will experiment with/out battens.



stobbo wrote:
So, personally, I would hang-fire before applying the scissors to my sail until I had been able to do an on the water test ! For this choose a good day... a beefy crew... don't tell them what you are trying until you are out at sea... wear wetsuits... do not do your testing in winter !


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PostPosted: Sat May 21, 2011 9:33 pm 
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Joined: Sun Aug 12, 2007 5:17 pm
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Location: Auckland NZ
Aye well that's a good thing cos "performance" is a relative term with these wee boats.

However the performance you get out of the stock standard sail on a fully laden double is not going to set your heart racing unless you try going out in stronger winds and in these conditions the mast tends to bend considerably as the inertia of the boat resists the press of wind in the sail which means the sail loses its shape and... you guessed it... its performance.

To avoid the mast bend the sail needs to be more lightly loaded (i.e. lighter winds) but on the double there's then not really enough oomph in the sails to push the boat along at all quickly.

I reckon there are three possible solutions for your double (it is not simply a case of running up more canvas: if this is all you do, the load on the mast will increase and the performance of the sail(s) will probably decrease as a consequence, due to mast bend):
1) stay the mast - if you can find a way of preventing the mast bending the sail will retain its proper shape in the higher winds needed to drive the boat along well - the way to do this is via stays (on yachts these are the wires that hold the mast up) - I use very light spectra line. it is easy enough to do and removes mast bend and transforms sailing performance.
2) add another mast - using 2 sails on separate masts will ~halve the load on each mast - this is why the schooner rig seems to work so well. If you think about it, it is logical that if the standard rig works well on a single then 2 should perform pretty much the same way on a double without much modification... and from what I have seen and heard they do, probably because the loads on the schooner's rigs are about the same on a fully loaded double as they would be for a single mast on a single.
3) use a stronger mast with a larger sail (for similar sailing performance on a double as that of a single) or a stronger mast with a similarly-sized sail (expecting to sail the double in stronger winds than would be realistic on a single). Either way the mast needs to be stronger to support the additional pressure of the wind in the sail. Your windsurfer rig may fit the bill here but be careful because a larger and heavier rig will put more stress on the mast-base arrangement...

A couple of other observations: don't dismiss the blue plastic tarpaulin sail idea - it has been demonstrated to work very well on some long ocean passages by yachts and is as cheap as chips - could work out as the cheapest entry into Hobie kayak sailing and any old stick for a mast should suffice. Don't forget you can only run up a certain amount of canvas in any given wind strength - a scrap of canvas will do in high winds - set on a short stick mast to keep the centre of effort low down this would be just as practicable in stronger winds as the fancy schmancy Hobie sail is in lighter winds. Staying the mast is pretty straight forward and inexpensive; stays should reduce loads on the mastbase (of a heavier rig) and would create a foretriangle to allow you to run up a jib... You need 3 stays: 2 backstays, one on either side of the boat, and one forestay - my backstays are "running" backstays (in other words the one on the windward side is tightened to support the mast while the one on the leeward side is slackened to allow the sail to fill; on changing tack the taut one is slackened and the slack one is tightened). As i have said before staying the mast has transformed my Hobie kayak sailing because it improves sail shape so much.

Hope these thoughts help.


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