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Author Topic: Mainsheet position?  (Read 2059 times)

rmaddock

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Mainsheet position?
« on: March 04, 2012, 05:51:01 PM »

Hello Mayhemmers!

Thoughts have turned to the sheeting in the Nobby. Particularly to the mainsheet.



This is the stern of the real boat. The mainsheet goes from the traveler on the rear counter out to the end of the boom. I am planning on using some Hitec sail winches that are already in my possession. However, they do not have enough travel in them by a very long stretch...probably a factor of 100%!

The best I can probably do would be to take the sheet from the traveler forwards to a block held over the middle of the cockpit and then to the middle of the boom.  I'm working on the assumption that going straight from the traveler to the middle of the boom would give me very little torque when sheeted right in.

I'm not sure that I want to spend money on bigger winches or start fiddling about with micro swithces etc etc.

Any thoughts?
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boatmadman

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Re: Mainsheet position?
« Reply #1 on: March 04, 2012, 06:13:55 PM »

Something to think about...

its a bit like a lever and a lump of weight - the longer the lever, the easier it is to lift, but, the longer the lever, the more you have to move it for the same movement of the weight.

Any help? Prob not - I'll get me coat!
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rmaddock

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Re: Mainsheet position?
« Reply #2 on: March 04, 2012, 06:17:16 PM »

Any help? Prob not - I'll get me coat!

 {-) {-) {-)
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dreadnought72

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Re: Mainsheet position?
« Reply #3 on: March 04, 2012, 06:41:03 PM »

Why not keep the original's sheeting arrangement and just increase the diameter of the winch drum to suit?

What you lose in terms of torque with a bigger diameter drum, you gain from using the full length of the yard.

Andy
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rmaddock

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Re: Mainsheet position?
« Reply #4 on: March 04, 2012, 06:49:35 PM »

Hmm. Yes. I hadn't thought of that. I realised that you loose torque with a bigger drum but I hadn't put that together with the increased leverage.
That'd be a happier solution. I wonder how big the disc would need to be?....Let me think......

A quick measurement says that 1,000mm of sheeting would be needed for scale appearance. The winches will do up to 480mm.

So, that's 250mm per revolution....a diameter therefore of (call it) 80mm!  (250 / pi?)

Can such things be bought commercially? I think I've seen them made from CDs and the like on here before now.
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pugwash

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Re: Mainsheet position?
« Reply #5 on: March 04, 2012, 06:50:25 PM »

So far you have kept pretty much to the original where possible.  Seems a shame to start now by altering the running rigging,  Even if you
move main sheet to the centre of the boom you are still going to need a lot of rope going onto some type of drum be it a geared electric motor
or a sail servo so why not leave the main sheet lower block at the stern, either on a traveller or on a certreline position. Fitting a traveller would give
you further problems feeding  the line onto the servo drum but should be possible if you fit a pulley block between the lower block and the servo drum.
I don't see how you can do it justice without a sail winch type servo.

Geoff
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rmaddock

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Re: Mainsheet position?
« Reply #6 on: March 04, 2012, 07:06:31 PM »

Hi Geoff,

Still planning on a winch...always have.  I agree with you about sticking to the scale....it's what I'm aiming for.  The original plan was to have the winch below the foredeck...the only space big enough for all three of them......and a closed loop within that space. The main sheet would come from there and be shepherded down the length of the hull, below the floors, to emerge at the stern in a scale like position......possibly from within one of the stanchions so that a false knot around the same would make it look like it's a real sheet tied-off.  Is everybody following me so far?  The sheet would then go to a block on the traveller which I'd probably have fixed in the middle for simplicity.  From there, to the boom. 

That's where it goes wrong as I don't have enough travel available in the standard sheeting to get the boom more than about half way out.  My thought was to have a second block. This would be slung between the sides of the cockpit on "ropes" in a scale-like way. The main-sheet would go through this and up to the middle of the boom......thus giving enough boom movement. Phew! To quote the annoying meerkats; "Simples!?"

However, the larger drum and original sheeting arrangement is sounding good right now.

Having said which, I've just found a video on YouTube (http://youtu.be/8cUjkANFfJw) from Waverley models where Mike uses a bit of Action trickery to increase the number of turns available on a hitec winch to seven!  That'd meet the drum size half way.
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gregk9

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Re: Mainsheet position?
« Reply #7 on: March 04, 2012, 07:10:10 PM »

Have you considered a "dutchmans purchase". If you have a 4fold purchase hidden under the deck, if you use a servo or sail winch to overhaul the blocks then the hauling part will move 4 times the distance you pull one of the blocks. If the hauling part now pulls on the hauling part of a two fold main sheet purchase........... If you get the idea ???
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Jimmy James

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Re: Mainsheet position?
« Reply #8 on: March 06, 2012, 09:06:56 AM »

One of our club members has just built a Nobby  on my suggestion he used a sail arm winch and a 3 to 1 Dutchman's purchase (See insert ) the vessel sails beautifully and the boom goes out to 85 Deg (Against to shrouds) it's a bit more complected to use a drum winch (Riding turns) but it can be done... I tend to use the simplest way as its less likely to go wrong and if it dose its easer to fix

Jimmy James
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