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Author Topic: J Class sailing  (Read 30538 times)

JayDee

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Re: J Class sailing
« Reply #75 on: August 13, 2014, 09:16:34 AM »

hello Brooks,

Have tried every setting possible with the sails.
 Time for alterations !!.

John,  :-)
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Brooks22

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dynamic centers and maneuverability
« Reply #76 on: August 13, 2014, 03:27:40 PM »

Can you slack the jibsheet to reduce weather helm in a gust?

Whoops, I wrote this BACKWARDS! To reduce weather helm, one needs to slack the Mainsheet. Or, tighten the jibsheet, or do both. Sorry.
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Sloops can be harder to manage than squareriggers when the vessel turns into the wind due to excessive heel: The long boom of the mainsail will hit the water, limiting the skippers ability to spill wind from the mainsail. I see this all the time with my sandbagger sloop. But squaresails can be squared in, spilling wind, even if the lower yards are in the water. I see this (with barque Pamir and brig-rigged Aldebaran) whenever I carry too much sail for the wind/gusts, and have to contend with a knockdown or near knockdown. The heel of a moving vessel automatically turns the bow into the wind due to the asymmetric thrust of the bow wave.
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When designing a hull/keel to match the scale sails and scale mast locations, I try to align the Dynamic Center of Effort of the sails (dCE) and the Dynamic Center of Lateral Resistance of the hull+keel+rudder (dCLR). When the centers are aligned, the rudder is most effective.

Many builders don't appreciate that the static CE/CLR is not in the same place as the dynamic CE/CLR. When the ship is moving, the dynamic centers rule, not the static centers. While the static values are at the geometric centers, the dynamic values are shifted forward to the 1/4 chord point. Example: static value for a 4 ft hull CLR is at the center, ie 2 ft aft of the bow. But the dynamic CLR is only 1 foot aft of the bow. This is per aviation practice; since sails and hulls and keels operate as lifting bodies, anything you know about airplanes will help you fix boat balance/maneuverability  problems.

The common method used by modelers to find the CLR is to push the hull sideways. Where their finger is placed to get the boat to move w/out turning is the Static CLR. Now, to find the dynamic CLR, measure from the bow to your finger, and cut that distance in half. This will give you the 1/4 chord point, a good starting place for your endeavour to get the CE lined up with the dCLR. dCLR can be anywhere from 1/4 to 1/3 chord point, per aviation experience. Its never at the 1/2 chord point, though, which I've seen gets builders in trouble if they don't know that.
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Brooks22

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Dynamic CE
« Reply #77 on: August 13, 2014, 03:38:39 PM »

The dynamic CE moves forward during vessel movement, just like the dynamic CLR. I do my figuring of sail dCE on paper: find the geometric center of the triangle (jibs and fore&aft mainsails). Then, estimate the 1/4 chord point by splitting the distance from the geo center to the mast. Then measure the distance of the sail's dCE from the bow. You will want to know the relationship between the dCLR and the dCE, so choose a common datum; I use the bow as the datum for both CE's and CLR's.

Since most vessels have more than one sail, find the dCE for each sail. Then, find the summation dCE for all sails by weighting each sails' dCE by the sail's area. I do the math just like calculating a center of gravity for a plane:

      (dCE1 X sailarea1 + dCE2 X sailarea2 +.....)/(sailarea1 + sailarea2 +...)=Summation dCE

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The same equation can be used to find the summation dCLR for a hull plus finkeel plus rudder. For my boats, the rudder is always way oversized vs scale size, so I include the rudder in my calculations.
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For squareriggers, which can strike sails (at least mine are designed to do that), I may calculate several dCE's to see how the vessel balance will change as I adjust for wind speed changes. These calculations are easiest with a spreadsheet.
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Brooks22

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Drag of the hull - why
« Reply #78 on: August 13, 2014, 03:57:00 PM »

"Drag" is the term used for hulls which are deeper aft than forward. Clipper ship hulls generally had no drag, but Schooner and Topsail schooner hulls usually did. A hull with drag starts out with the static CLR farther aft than the same hull w/o drag. Thus, the dynamic CLR will be further aft  (compared to a dragless hull) when the vessel is moving. I suspect nautical architects of the 1800's realized their ships did not balance like they expected, so added hull area aft to compensate. Many of the 1800's "rules of thumb" of ship design I've read unconsciously adjust for the fact that hulls are generating lift, thus are ruled by  then-unknown aeronautical physics.
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JayDee

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Re: J Class sailing
« Reply #79 on: August 13, 2014, 06:08:29 PM »

 Hello Brookes,

Yes, I spotted your "whoops" - easily done !.

You are very used to applying formulas to designs for full sized boats.
I have quite a few books on the subjects.

However, do all these rules and ratings still apply to a model boat ?.
My boat is at 1/22 Scale, it has to sail in full sized Water, it has to sail in full sized Winds.

Neither of these elements can be Scaled.

Picture this scene, an nice sunny afternoon, a nice large lake, a nice breeze blowing - - around 10 miles per hour, a few other model boats moving about - - very nice conditions !.

Or are they?, my boat sees this as a wind blowing at  Hurricane force, with huge waves, which they are, if scaled up 22 times !!.
 There has never been a full sized yacht that could sail in such conditions - - or a Lifeboat !!.

I am trying to make my boat sail in conditions which are way beyond those which real boats sail in.

John,  :-)
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Brooks22

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scaling wind and water
« Reply #80 on: August 14, 2014, 02:28:20 AM »

My CE and CLR formulas are not a scale/non-scale process. The physics of balancing where the wind pushes (CE), and where the water resists (CLR) is scale invariant. I mentioned them because solving a maneuverability problem is hard if you base your fix on 1/2 chord balancing.

When it comes to scaling the rest of the boat: opinions vary, hoho. As you pointed out, a 10kt breeze is ideal for a real ship, but strong medicine for a model :-)

I always make my squareriggers so that I can easily reduce sail area. Jimmy James figured out how to use lazy jacks to reduce fore&aft sail area (ie furl) on his vessels, eg. his brigantine Freebooter. I've admired his work, but never implemented his ideas. Mainly, that's because my sail cloth of choice is Tyvek, which does not furl.

Its easiest for me to just remove a squaresail and it's yard entirely from the mast (rather than furl them per real practice). Or remove a jib, or other fore&aft sail.  My schooners and sloops (no furling, no sail removal method) are definitely wind-limited in a way that my squareriggers are not. I've sailed my Pamir in 22 gust to 27mph winds, which requires reducing sail to what a real ship would set for a real gale. Still, it's challenging to maneuver in such "scale gale" conditions.

When a model is getting knocked down, or heeling so much the bow wave=>turn to windward is uncontrollable with rudder, I always recommend that the modeler figure out a way to reduce his sail area. This works for the real ships, and for models too.

Increasing heeling resistance by deepening the keel (placing the external ballast lower) also works: but you risk running aground farther out than you are used to, or snagging seaweed that normally you could sail over with no problem. The shrouds may have to be beefed up, also. I have formulas to deal with keel length and shroud strength if you are interested.
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mrpenguin

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Re: J Class sailing
« Reply #81 on: August 14, 2014, 03:29:06 AM »

@Brooks22:

Thanks for the info on dynamic Centre of Effort (CE).....

I am comfortable with locating static CE, but just struggling a bit with dynamic Centre of Effort (dCE)..

For discussion, can I propose one simple sail, aft of a vertical mast, attached to a horizontal boom (thus it is a right angle triangle). This mythical sail is 10 units up the luff and 6 units across the foot
As I understand it Static CE (geometric centre) of this sail would be 5 units up from the bottom and 3 units from the mast.

From what you have posted I gather the dCE would be at 1/4 chord; thus it should be 5 units up from the bottom and 1.5 units from the mast.... Have I got it right????

I would have thought that with heel (say 45 degrees) that the dCE would move aft of the static CE, not forward from it.....? I think I understand the bow wave turning the boat into the wind when heeled....
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Brooks22

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Mr Penguin's calc
« Reply #82 on: August 14, 2014, 03:52:15 PM »

Yes, you got it right wrt dCE on your test sailboat. :-)

I don't know how dCE moves with heel. It does not move on an airplane with bank, so I just thought that heel would not affect it. Unless you have some info I don't (perfectly plausible, I don't know everything), may I make the following suggestion: Heeling increases the strength of the bow wave asymmetry, which increases turn to windward. This would mimic a move of the dCE aft....so, maybe movement of the dCE is not needed to explain what we see happening.
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JayDee

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Re: J Class sailing
« Reply #83 on: August 20, 2014, 12:53:23 PM »

Hello,

Did a lot of sailing over the weekend with the modified keel on Endeavour.
The boat has been tranformed !, it handled a full Gale with ease!!.

One Metre boats had their storm rig on, it was so windy.

The boat still heels and turns slowly into the higher speed winds, but in a very controlled fashion, gaining a lot of speed while doing it, very handy for racing !!.
This was happening with the rudder at neutral setting.
With the rudder correcting, a straight course could be followed.

I am now one very happy chappy !!!.

John,  :-) :-) :-)
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mrpenguin

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Re: J Class sailing
« Reply #84 on: August 21, 2014, 12:07:23 AM »

@Jaydee:

Any chance you could post a pic of the alteration to the keel please?
(Looked back through the thread and in all the photos I found the keel is hidden by water or stand  :-) )
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JayDee

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Re: J Class sailing
« Reply #85 on: August 21, 2014, 12:55:42 PM »

Hello mrpenquin,

Not got a photo of the "latest version" of the keel.
Here is the original, and the first modification, with the latest one shaded in as close as possible!.
Everything has been packed away.

John.


***typo corrected at posters request***
***TT***
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mrpenguin

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Re: J Class sailing
« Reply #86 on: August 21, 2014, 01:04:33 PM »

Thanks John, clearly a big increase in fin area and you have move the CLR back quite a bit. Good job!!!!
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JayDee

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Re: J Class sailing
« Reply #87 on: March 22, 2015, 06:41:06 PM »

Hello,

Been sailing Endeavour at our Club pond at Runcorn.
Last Wednesday and today, both days with hardly any wind !!.

Did some testing of the camera rig on the rear of the boat - - a GoPro camera.
The camera is on a device which keeps the horizon level when the boat heels in the wind.

BUT, there was not very much wind to test it !.
No pictures of the rig, not available commercially - - home made!, but works very well.

John.  :-))
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Skimmer Fan

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Re: J Class sailing
« Reply #88 on: March 22, 2015, 08:01:58 PM »

John
Your yacht on the lake today.
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Brooks22

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Re: J Class sailing
« Reply #89 on: April 17, 2015, 05:10:16 AM »

Oh Man, is that Beautiful, or what. We may not be able to live in the 1930's, but with models like this, we can at least experience the elegance and beauty of the era. Thanks JayDee!
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dreadnought72

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Re: J Class sailing
« Reply #90 on: April 17, 2015, 09:46:54 AM »

The modern ones aren't too shoddy, either!



Andy
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JayDee

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Re: J Class sailing
« Reply #91 on: February 12, 2016, 02:54:09 PM »

Hello,

Got the J Class Endeavour out of storage, big cleanup and some repairs, ready for the first sail of the season on Sunday.
Will be sailing at the Heath lake, Runcorn, which has had a major rebuild by the Council.
Much deeper than before, all new walkways, aeration devices in the water, childrens play area and a new Cafe.
Forecast is for good winds, so looking forward to it !!!.

John.  :-))
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roycv

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Re: J Class sailing
« Reply #92 on: February 12, 2016, 05:20:43 PM »

Hi Jaydee, Have you thought of having 2 fore sails as per the 1934 version?
A quadrileteral looks really good on Endeavour it will have to be cut back a bit so that it can tack across the jib though.  I see you have already cut the main sail back so that it does not overhang the stern,
Nice to see J's sailing.
best regards Roy
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JayDee

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Re: J Class sailing
« Reply #93 on: February 12, 2016, 05:41:46 PM »

Hello Roy,

See earlier pictures in these posts.

John.
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roycv

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Re: J Class sailing
« Reply #94 on: February 12, 2016, 11:43:53 PM »

Hi JayDee, here is my Endeavour at exhibition in 2004 / 5,

 My one is a little smaller at 1 metre loa, but you can see the overlap of the Quadrilateral, it is about 2 -3 cms.  It does seem to tack OK and cross the jib without much problem. The sails are drafting film and you can see a join on the main sail.

Can't find any sailing pictures on my laptop at the moment.

I did not expect to carry the quad in any sort of wind and it is easily removeable and a forestay put in its' place.  The extra keel was balanced with the sails for neutral running without the quad.  So sailing with the quad required some helm on the rudder, but there is so much sail area that it is not a problem.
The full size Endeavour after restoration is 300mms lower in the water and has a big propeller, such a shame.

regards Roy
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JayDee

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Re: J Class sailing
« Reply #95 on: November 05, 2016, 11:03:21 PM »

Hello,

This is probably not the correct place to post this, but I have got my Website back on line !!!!!.
Still needs a lot of work, but I have lots of goodies to put onto it.
Be gentle and have a look!.

www.john-dowd.co.uk

John.
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