GBR1524 TLC and control line changes

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EdS
Posts: 188
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Boat Number: GBR 1524

Re: GBR1524 TLC and control line changes

Post by EdS » Fri Dec 06, 2013 10:33 pm

new tiller extension mount
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EdS
Posts: 188
Joined: Mon Aug 06, 2012 12:06 pm
Boat Number: GBR 1524

Re: GBR1524 TLC and control line changes

Post by EdS » Fri Dec 06, 2013 10:41 pm

the surface needs flatting back to make it look better prior to clear coating.
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EdS
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Re: GBR1524 TLC and control line changes

Post by EdS » Tue Jan 14, 2014 10:34 am

The boat has been put back together with the shroud purchase replaced with the strops shown below.

A new to me high aspect rudder is now on along with a stiffer rig.

Mark and I had our first sail with the new configuration on Saturday and what a difference.
It is a completely different animal and much more powerful, sensitive on the steering and she feels faster.

Hope everyone had a good break over the new year.
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The boats hiding away from the Gales and flooding.
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Mast base with cleats and jib track support mounted
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Old vs new on the shrouds. Large difference in weight and cost. There is obviously an increase in friction
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Shroud extensions and friction ring
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EdS
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Re: GBR1524 TLC and control line changes

Post by EdS » Tue Jan 14, 2014 2:28 pm

Rudder foil query.

Does anyone come across the issue where the rudder lift ends up the foil forwards around the biscuit.

i.e. the force to hold the rudder on the purchase system is 0 or negative?

The solution is either to move the pivot point forwards on the biscuit of go stronger on the bungee, but wanted to see if anyone else has this issue?
Roaring Forties GBR1524

Andrew P
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Location: Melbourne

Re: GBR1524 TLC and control line changes

Post by Andrew P » Wed Jan 15, 2014 2:34 am

EdS wrote:Rudder foil query.

Does anyone come across the issue where the rudder lift ends up the foil forwards around the biscuit.

i.e. the force to hold the rudder on the purchase system is 0 or negative?

The solution is either to move the pivot point forwards on the biscuit of go stronger on the bungee, but wanted to see if anyone else has this issue?
I believe you have discovered the limitation of the "bungee" tensioned control system. In bumpier locales such as the east side of Port Phillip bay we have found that no amount of tension on the bungee will overcome the dominance of the water and foil combination over the hull system.

We found that the foil system stays relatively stable at higher speeds and the hull moves around it. Most often characterised by the tiller moving up and down as yuo travel through the waves.

The closed loop tensioned rope system appears to be the accepted means to remove the problem.

EdS
Posts: 188
Joined: Mon Aug 06, 2012 12:06 pm
Boat Number: GBR 1524

Re: GBR1524 TLC and control line changes

Post by EdS » Wed Jan 15, 2014 8:40 am

Andrew,

Thanks for the response.

I see that as a problem, but that wasnt quite what i meant in this case

However i have the issue where the foil actively puts itself on in flat conditions without any changes.
I think it is due to the location of the biscuit (rocker) pivot and the centre of lift of the foil moving forwards with increased angle of attack.
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Dan H
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Re: GBR1524 TLC and control line changes

Post by Dan H » Wed Jan 15, 2014 7:49 pm

Ed,
Had that problem before when putting a new tfoil on mounted further forward.
As you wind it on the total force vector of the foil can act fwd if the pivot, meaning it jumps on to the limit - not great.
You can only really move the foil further back into the rudder (massive ballache) or nice the bolt back in the biscuit, or the rudder pin further away from the rudder le in the stick. Bolt further back in biscuit is by far the easiest. As long as it doesn't hang out the back a dangerous amount, structurally speaking.
You can also find a way to stop it going on any more than you need.

Think the rudder banging about in an elastic return system can only really happen in fairly neutral states as long as the foil ain't a silly long way out the front of the rudder.

Reckon you should ditch the vernier completely and lash the caps to the shrouds or Antals.

Dan

EdS
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Re: GBR1524 TLC and control line changes

Post by EdS » Fri Jan 17, 2014 3:38 pm

Dan its amusing isnt it, you spend your year moving the pivot closer, switch rudder and now it needs to be further away.
There is enough meat to move it about 3cm so should be fine, Seasure should sponsor me for the number of bushes i have bought.

The max angle on it limited by a bit of string otherwise it would only be limited by elastic.
Quite odd when you go to let it off before a bare away and nothing happens.

Not sure about lashing the caps, how often do you adjust the tension on them? Plus repeatability, maybe i can use a single row verier and make the main shrouds captive.

Before you say, the reason the shrouds are different lengths is because until i put the new spreaders on and move the trapezes onto them the main shrouds are in a T slot about 10cm below the forestay.
I dont think the trapeze should be below the main shrouds at the hounds because the will wear on each over.

Maybe if i swap the caps to dyneema/carbon lashing will make more sense
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EdS
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Re: GBR1524 TLC and control line changes

Post by EdS » Mon May 19, 2014 9:09 pm

So what wind speed and boat speed do people find they are getting the most out of the foil?

I am able to pull on enough foul to destabilise the balance on the foil. As far as steering balance that is.
So it ends up v twitchy well before it stalls.
O
Comparing to my old rudder the lifting foil is narrower and smaller and thicker.

In 15 knots we are quick but I notice we don't get the bow down as much as Julian or other boats at Weston and the limit is it becomes a nightmare to steer.

Ideas?

Losing weight is Major factor, we have approaching 200kg over the back.
Working on that seperately.

Anyone in Europe have a medium to high aspect verticle rudder blade I can aquire?
No hydrofoil required.

I guess I could get brutal on my old rudder, but not sure I am confident fairing it down and not getting a mess in the foam shape.
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Shu
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Re: GBR1524 TLC and control line changes

Post by Shu » Mon May 19, 2014 10:16 pm

Hi Ed.
How is the control issue manifesting itself? Lee helm? weather helm? helm wanting to slam over during tacks or gybes?
I'm finding that in somewhere around 5 or 6 knots of wind I start to notice some help from the foil when going to weather. When going off the wind, it may be helping in as little as 3 knots. The biggest help seems to be in marginal 2-wiring conditions upwind, where having the foil on makes the difference between single-wiring and 2-wiring.

I had a rather poor (cheap) foil evaluation program which allowed me to assess parameters like lift/drag ratio for different foil shapes. It wasn't very easy to use, but I noticed that when I started with a basic shape, like a NACA 5 digit series foil, and started fiddling with the shape a tiny bit (a millimeter or less) the performance went downhill very quickly. Since then I've left the foil shaping to the professionals.
Steve Shumaker
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EdS
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Re: GBR1524 TLC and control line changes

Post by EdS » Tue May 20, 2014 5:58 am

Hi Shu,

It is the helm slamming across in the tacks and being twitch even in a straight line.
No issues with helm in the traditional sense.

I do think we could go for more foil on if the rudder didn't become unstable.

I guess I could modify the stock to move the rudder aft a bit and that would help.

As you say, in marginal conditions with the old rudder it made a huge difference. We haven't sailed enough with the new on but in a lot more wind we were getting that much lift.
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Shu
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Re: GBR1524 TLC and control line changes

Post by Shu » Tue May 20, 2014 10:40 pm

Ed,
I recall sailing a B3 that had that issue in gybes. I thought it was because the cassette had too much play and allowed the rudder to angle (sweep) aft relative it's center of rotation, the pintle. It seemed to happen when the foil was on (light to moderate and flat water so foil still on downwind) and when we let the boat heel coming out of the gybe. This particular rudder was a rotating axle design, so it wasn't related to any changes in the vertical angle of the rudder itself, which should have stayed constant. It was an inspiration to keep the boat flat, but not really acceptable behavior from the boat.

My current rudder, the latest Bieker/Brown version (currently built by Hendo) a solid t-foil on a rotating "bisquit" as you call it is well behaved, which you should remember, having sailed my boat. The rudder has no cassette. Rather, the gudgeons are attached directly to the rudder, so there is no play whatsoever. Furthermore, when I attached the gudgeons, I kept the pintle close to the rudder's leading edge and made sure the pintle was aligned with the upper leading edge of the rudder, minimizing the separation between the rudder's center of effort and the center of rotation (pintle).

My hypothesis on the behavior is this: With the foil on and the boat heeled to leeward, the foil wants to push the stern to leeward, which if you let happen (easy to do when you're changing hands coming out of a tack or gybe), then causes the flow over the (mostly) vertical rudder blade to further exert a turning force on the rudder. So it's a vicious cycle. The more the center of effort of the rudder is separated from the center of rotation (pintle), the worse the secondary turning effect on the rudder, hence our problem with the loose cassette and consequent slightly swept rudder in the B3. Also, the more the foil is "on" the more the primary effect of pushing the stern in the direction of heel, hence your observation that more foil = less control.

That's my reasoning. I welcome correction from those more knowledgeable about the fluid dynamics of the t-foil setup (I know you smart guys watch these threads).

If my reasoning is correct, then you should have less of an issue when you keep the boat flat through the tack. Is that your observation?
-Steve
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EdS
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Re: GBR1524 TLC and control line changes

Post by EdS » Fri May 23, 2014 7:05 am

Hi Steve,

Sailing flat will help no doubt.

The issue i am having is not helm though. although the result it a twitchy steering.

My rudder has a significant amount of its area infront of the pintle which results in a very light helm (balanced), however as i increase the amount of lift on the foil and therefore increased rake of the rudder forwards.
the light helm becomes unstable, even when flat.

Maybe i am putting on too much foil, which goes back to the lack of lift for our weight or our position.
because the biscuit rotates the pintle location doesn't so it shouldn't affect the helm.
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Shu
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Re: GBR1524 TLC and control line changes

Post by Shu » Fri May 23, 2014 6:20 pm

Sounds like you have negative helm, which I've always thought would be nightmarish, though I've never experienced it.

So you're thinking that if you can get just a little bit of sweep angle to the rudder, relative to the pintle, the twitchy-ness will go away?

Perhaps some shaping of the rudder head, where it's in the cassette (and not in the flow) as you were originally thinking would be a solution.
Steve Shumaker
USA 1183

EdS
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Re: GBR1524 TLC and control line changes

Post by EdS » Mon May 26, 2014 7:14 am

Hi Steve,

Potentially the solution, i am still struggling to get my head around the problem.

I have a flip down stock, so would either need to drill another hole or used a smaller pin to hold it down and packing at the leading edge to allow a small increase in aft rake.

Either that or i could make a new stock with elongated lower pintle attachments. Might be easier being in Norway.
I guess the other one would be to mod the pintle location on the stock but that might leave me without a rudder on one of the trips home.

Not as bad as you think just dont let go of the stick :)
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