Adjustable Mast Extension

I just realized I put a copyright claim on that sketch I posted. That was unintentional. The idea is public domain and the sketch is anybodies. I'm hoping Decrep will get around to giving the project his best attention.

The next thing it needs is a convenient "on the water" downhaul adjuster.

Hey Grinch, what happened to your enthusiasm. I hope I didn't deflate it for you. I tend to be a cynical cold bath sometimes. I should pull my head in.

I'm still here!!
And fully pumped with the idea.

I'm thinking about making a working version too.

You could use a standard diameter extension for the outer sleeve and a carbon skinny for the inner.
Simple wheels could work between the two sleeves although they would have to be fairly strong to take the lateral force.
I think that the system should be 'one-pull' I.e. the sail eylet is pulled to the bottom of the mast by the system and THEN the system starts auto adjusting itself for length.

Not sure I can get my head round the rigging of the pulleys, What does the ratio work out to? Cos you will need atleast 4:1 I reckon.

Also, the system has to work for skinnies too. This is a REAL headache since we are talking a VERY skinner inner sleeve with this setup. But that bridge can be crossed later. I think just concentrating on a standard mast system first is a way to go.

Gaz

You mean using hydaulics? Or screw?

I like the idea of the hydaulics but i think it would be far to heavy.
Keeping it simple is the only solution I think. And pulleys are freely available, light and require little if no maintenance.

2 downhaul systems - que?

Sorry DL I disagree, I have a few sails that need 0 extension on the mast. Therefore it takes maximum downhaul to get the sail to the extension. The extension system can not be used at all on these sails!!!! Unless I chop several cm off the mast.

Except going down in mast size means going down in stiffness. And for some of my sails I'm already on my smallest mast.

This type of mast extension is best suited to race sails as they benefit most of the gap-closing theory **. This implies that the extension is going to need a longer version, to be able to extend by nearly 50cm for the big sail sizes.

** although all sails benefit from lower center of mass.

On the 10.7 RS5 I can use a single loop through the eyelet (+ using a screw driver) to get it about 30cm from the base. On the under-6m KA Koncepts I can get them to between 15-20cm. This help?

Guys.

I, not very eloquently, referred to this problem in the design 'draft'.

This is one of the major features that 'the grinch' needs. You must be able to pull the sail down to the mast foot and then extend the mast in 'one pull'. One system!! Not two.

This could be done by a pin that first locks the extension in place, to allow the sail eye to be pulled down too the base. This 'first phase' needs to be geared! A pin could then be released to allow the mechanism to slide and extend as required. As per DL's design.

If the mast is exactly long enough and the extension doesnt need to extending then you dont need a maste extension!! Just use a bog standard pulley onto mast foot with a cleat.

So, we have three hurdles.

1. A 'one system' design. I.e, getting the foot to to the base first and then extending.
2. Friction between the outer and inner sleeve. (wheels?)
3. Skinny masts. The inner sleeve will be VERY Skinny!

Finally the biggest problem

What colour should it be ?

I think Green

If you don't need any extension use one of those stub extensions instead. Its going to be lighter. Most wave sails have a head strap anyway so the mast can be moved up the luff a bit.

I have a feeling it may be asking too much to have it work on a skinny. Skinny extensions barely make it as it is. Better to use a drop shape skinny with a Big Bird extension. The North ratchet extension is only available in standard diameter afaik and its a big success. If it can be made to work with a skinny that's wonderful however if it can't its not the end of the project.

quote:

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Originally posted by NotWal

The North ratchet extension is only available in standard diameter afaik and its a big success.

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The only place I have seen one was on the NS website:

http://www.north-windsurf.com/rig-components/needle-carbon-extensions.en

Good point with the skinnys...

BTW, I had a std diameter one 2 seasons ago. Did not float my boat. Extender mast extension is a great idea!

Did anyone end up building a prototype?

Here's a thought from well outside the square.. (okay, I'll confess, I don't even know what this 'square' that everyone talks about is supposed to look like from the inside!)

Why does an 'extension' have to fit INSIDE the mast at all?

As they say in that song 'flip it and reverse it'..

Take your "Cure for Cancer":
Turn it on it's head so that the thinner tube represents the mast, and the fatter tube is the extension. So.. instead of pushing the extension DOWN.. you push the mast UP..

Now shift the pulleys around so that the rope runs in the gap between the extension tube and the mast. You could put as many pulleys around the circumference of the tube as you liked to get an appropriate ratio.

That would work with skinnies too. The downside would be that it'd mess a little with the luff tube on the sail at the bottom. Probably only 10mm or so though..

Maybe?

quote:

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Originally posted by frant

Now is your extension going to be cheaper , stronger, lighter, more reliable and easier to rig?

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Compared to buying a seperate mast, extension, and boom for each sail?

An adjustable extension would definitely be cheaper! (assuming that you're buying decent kit..)

Your sail sizes look like they'd need massively different size (and stifness) masts, so in your case, an adjustable extension wouldn't help.

In my case, I have 4.7, 5.0 and 5.7m sails all of which rig on a 430/21 with differing lengths of extension. I could buy two more 430/21's, two more extensions, and two more booms (and a bigger car to fit it all in) OR.. I can adjust my extension, and boom length.

It's admittedly easier than making a fancy extension to just buy a marker pen, rig up each sail, and mark the settings on the extension/boom. BUT.. that wasn't Grinches goal.

I'm afraid I cast my mind back, sit here in the present and look to the future and I'm still poor.

Sure Grinch - as you suggested, it's nothing flash, but with a bit of imagination you can hopefully see what I had in mind.

www.seabreeze.com.au/gallery/gallery.asp?imageid=5563

The bottom greenbit gets pulled upwards when the 'downhaul' line is pulled. The mast is sitting on the bottom greenbit, and passes through the middle of the upper greenbit (We need to come up with some better jargon!). The ropes run in the gap between the outer wall of the Mk2 Grinchostender and the mast.

Obviously, the pulleys need to be thin (the drawing is nowhere near to scale - a 3mm wall, and maybe 5mm sleeve/pulley insert?), and the greater number of them that you have, the longer your piece of 'downhaul'. The good news is that there's going to be a nice cavity inside there once you push the mast up, so you can stick all the extra up a hole somewhere.