Twist Grip Mechanism

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mwattsi14
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Twist Grip Mechanism

Post by mwattsi14 » Mon Mar 31, 2014 3:18 pm

Feels like deja vu.. i posted a similar thread back in 2010.

First sail in the new boat after a couple of months at home fitting the new rig and overhauling. Bit of a baptism of fire in gusts over 26 knots but good to see we haven't lost what we learn't since we last sailed the B4.

Anyway its the first time with a rudder controlled from a centrally placed rope control and it felt completely wrong. I cannot get a twist grip based control on to the boat fast enough..

Last time i went down the Ovington boats route for the mechanism. Before i take the same route again what are views on the other alternatives out there.

Hope to see some of the UK fleet on the water soon.

Cheers

Mark
Mark Watts
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Dan H
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Re: Twist Grip Mechanism

Post by Dan H » Mon Mar 31, 2014 3:29 pm

Just use string Mark, even if it's just a case of placing it on the aft beam.
Never met a twist grip I liked!

joe.bersch
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Re: Twist Grip Mechanism

Post by joe.bersch » Tue Apr 01, 2014 2:01 pm

Kris Henderson also makes a twist grip assembly, but without the Ovington clicker. It is simpler and smaller. Just a delrin cylinder machined to take a 3/8" shaft and bored out on the ends to take your choice of flexible universal material hydraulic hose, torque rope, etc. Mounted on top of your tiller through a piece of carbon c channel. Easy to make yourself actually or have done locally. Have Kris send a picture.

In contrast to Dan, I am a fan of the twist grip. Really just a preference thing. As he has pointed out before you don't need one to win the World s but it sure improve s my sailing experience.

mwattsi14
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Re: Twist Grip Mechanism

Post by mwattsi14 » Tue Apr 01, 2014 5:26 pm

Thanks Dan, Joe.

Agree its totally personal preference but having now used both i am a fan of the twist grip. Far easier to fine tune.

I am debating working on a system to have both.. fine tune/general trim on the twist with a coarse tune led to a cleat for upwind/downwind changes.

Whilst out last weekend wave conditions meant one tack needed less foil than the other, with a twist grip these subtle adjustments were much easier.. with the current system it meant reaching down to adjust.. It's also in the middle which doesn't help making it crew adjustable only (as if the crew hasn't got enough on in the front of a 14 anyway!)
Mark Watts
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Dicko
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Re: Twist Grip Mechanism

Post by Dicko » Tue Apr 01, 2014 9:35 pm

Billy Devine out of Perth makes a nice solid unit. I don't have any pics currently to post up though.

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Re: Twist Grip Mechanism

Post by Dan H » Wed Apr 02, 2014 12:28 pm

joe.bersch wrote:Kris Henderson also makes a twist grip assembly, but without the Ovington clicker. It is simpler and smaller. Just a delrin cylinder machined to take a 3/8" shaft and bored out on the ends to take your choice of flexible universal material hydraulic hose, torque rope, etc. Mounted on top of your tiller through a piece of carbon c channel. Easy to make yourself actually or have done locally. Have Kris send a picture.

In contrast to Dan, I am a fan of the twist grip. Really just a preference thing. As he has pointed out before you don't need one to win the World s but it sure improve s my sailing experience.
I've probs never had the patience to make one work properly. Tried a few times mind.
So if there is no clicker, what sets the drag and stops it unravelling (which it usually did with the clicker anyway hence my preference for string!)

joe.bersch
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Re: Twist Grip Mechanism

Post by joe.bersch » Wed Apr 02, 2014 2:17 pm

Dave: I am an avid fly fisherman with many reels- both click and pawl and various disc drag systems. Based on these ideas I experimented with various discs to create a smooth even drag on the system. Of course the problem is, unlike a proper reel, the drag is in both directions. Nonetheless, surprisingly little resistance is required to keep it from unwinding. Cork or soft (low durometer) rubber against a stainless or delrin tiller adapter works great.

Currently, we are using a positive wind on and wind off mechanism brought to North A!!merica by Dave Hayter. The rigging is a bit different but doable on most gantry set ups and eliminates the bungee from the system. As a result there is virtually no load trying to unwind the system.. So far I like the set up on my latest B6 although with no lines running through the boat it is a bit harder to to accurately determine foil position as you have to look back at the tiller to do so.

Finally, others have utilized both a coarse line adjustment and fine tune twist adjuster. This seems like a good idea but in my opinion is just further complication of an already complicated boat. The older and less skilled I get, the more I am focused on reducing controls to the bare minimum and focusing back on the basics. Maybe I should just stick with flyfishing.

mwattsi14
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Re: Twist Grip Mechanism

Post by mwattsi14 » Mon Sep 29, 2014 9:57 am

Hi Guys.

So i took the plunge and converted to a twist grip control using the Ovi barrel adjuster and the Katie system of positive on and off..

The system works (ish) and controlling from the wire again is fantastic (as i had on my previous B4)

The issue is despite setting it up as per the photos of Katie's system I seem to have too much load when winding the foil on.. Its a two handed operation even in 10-12 knots.. so something is clearly not right.

Any clues what could be the issue?

- The biscuit moves freely
- There are no obvious friction points in the system and the barrel is winding up cleanly..
- I have 2:1 inside the tiller.. debating if i could fit 4:1 in there but that could lead to a lot of tiller spinning to make adjustments.

Any thoughts appreciated.. in the meantime i will continue to investigate..

Cheers

Mark
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Tom Heywood
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Re: Twist Grip Mechanism

Post by Tom Heywood » Mon Sep 29, 2014 11:33 am

It might be that your lifting foil might not be balanced - i.e. the line of action from the lifting foil falls behind the pivot point in the biscuit (same logic as balance on a rudder against the rudder pivot point but in a different plane), this means that when you try and twist the foil on you are effectively having to pull the foil down through the water against it's lifting force.

If this is the problem, the simple answer is to go 4:1 - it's not that bad.

You can adjust the balance of the foil, but it's more effort..:

-Move the pivot point on the biscuit - easy if you can, but can be a hassle if the biscuit doesn't have space, or the stock is already right against the pivot point and so gets in the way

-Move the foil forwards on the rudder -hard as basically means chopping your rudder in half and re-gluing it, and high risk as getting the balance correct is tricky, and overbalancing it would make it impossible to sail. But an absolute pleasure if you get it right

mwattsi14
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Re: Twist Grip Mechanism

Post by mwattsi14 » Mon Sep 29, 2014 2:37 pm

Cheers Tom..

Experimentation with 4:1 it is..

I am certainly not cutting the rudder to bits.. absolutely love the rudder from Sam.. has transformed the boat. As to moving the pivot.. possible but concerned i will just end up chasing round in circles (i.e. working out where to move it to.. ).

Hopefully i will be at Itchenor in 2 weeks for some further opinions.. fingers crossed i can get it operational enough for then.. worst case it is positive on and Bungee for off to get the purchase in for the short term.. In fact the more i think of it that might be the way forward.. whilst being an easy job to plug the string system back in that way if i am still struggling to make it work..

Cheers

Mark
Mark Watts
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mcghan
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Re: Twist Grip Mechanism

Post by mcghan » Sun Nov 16, 2014 8:03 pm

I've decided to move from the bungee + friction system originally on the red B6 from Henderson to a homemade clicker with wind on/off. The current system is 8:1 wrapping on a 3/8 inch shaft so requires a lot of winding (>10 full rotations) to go the full range.

I made a pretty simple conversion to Hendo's friction system. I made the clicker using a delrin cylinder which mounts on the 3/8 inch shaft in the middle of the C-channel. The cylinder is about 1 inch diameter and it is machined with dents every 45 degrees. I then added a plastic block with a 1/4 inch ball bearing sitting in a 1/4 inch hole in the block and resting on an elastomer "spring" underneath the block. The block simply mounts in the bottom of the U-channel. The idea is that if necessary I can later change the force between clicks by changing to a softer or harder elastomer under the ball bearing.

For now, the line still wraps on the 3/8 inch shaft and I intend to reduce the purchase to 4:1 or maybe all the way down to 2:1. I could also make a new cylinder the full width of the C-channel to adjust the diameter and optimize the number of rotations.

Here is a picture. Unfortunately, our sailing season is done and I can't make it to Geelong so I won't be able to report on success or failure of this experiment until spring. Let me know if you have comments or suggestions. I still have all winter to modify this.

Doug
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home made clicker

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Re: Twist Grip Mechanism

Post by Hendo » Mon Nov 17, 2014 8:47 am

remember that when I designed and built this, we have milled the 3/8" shaft with flat spots were set screws can tap into as well
for friction as you twist.
Doug, the ratchet is cool.
Hendo.

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Re: Twist Grip Mechanism

Post by Northshore Pirate » Tue Nov 18, 2014 5:40 pm

Hi:

How do you eliminate the hysterisis in the system as the line winds on and off at different layers?

Ed Chimney
US 1112

mcghan
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Re: Twist Grip Mechanism

Post by mcghan » Sat Nov 22, 2014 4:13 am

Some hysteresis is inevitable but shouldn't be a real problem. In the end, I hope there will only be about 6 wraps on or off so there should only be one layer if I use a small diameter line. It may also be possible to keep the whole system under some tension and take up any slack with a bit of bungee. I did make a mistake in my previous post. The current system is actually 16:1 and that's a lot of winding. I'm hoping I can take that down to 4:1 but I don't know if that is realistic. Assuming the geometry of the T-foil itself is ok, it will depend on how much friction there is when the rudder is under side-load from normal sailing.

Of course one of the most important requirements in tinkering with this is that I can easily revert back to the setup that Hendo designed. It does work well and is nice and simple. I got spoiled by a very easy and fast twist adjustment system on my previous boat so was hoping to achieve something similar. If not, the B6 hull with more volume in the bow is more forgiving so we seem to be able do a bear-away with the foil still mostly on in some breeze without instantly pitchpoling the way we would have in the B3.

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Re: Twist Grip Mechanism

Post by mcghan » Fri May 29, 2015 3:49 am

The mechanism is working very well and 4:1 purchase is enough. I used stacked rubber washers under the ball bearing for the ratchet and that is giving a solid click now which is enough to keep the foil where I set it.
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