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Author Topic: Re: J Class yacht ballast  (Read 6111 times)

regattarich

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Re: J Class yacht ballast
« on: February 25, 2013, 01:55:36 pm »

Hi
Can anyone help me please with some advice, ive just made a plank on frame model of a 1930's J Class yacht, the hull is approx 1.3m long but the mast is almost 2m high from the underside of the hull. Its kitted out with smart brass fittings and cotton sails. I filled the hull with lead shot to take the hull down in the water to the water line. Sadly when I trialed the yacht in the water it simply toppled over, luckily I saved it before the water got to the radio gear!
Should I be adding an additional lead ballust fin which fits onto the hull which balances the top load?
Any advice with sketches would be appreciated.
Many thanks
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JayDee

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Re: Re: J Class yacht ballast
« Reply #1 on: February 25, 2013, 02:52:39 pm »

Hello,
ALL of the ballast must be as low as possible, inside the hull will not do!!.
The real J Class had their ballast low down in the Keel, some Js had an extra ballast, which pivoted down from the keel bottom.
Your boat will need a lot of work doing to the keel to enable the boat to sail realistically.
Have a look at my Schooner, Bluenose, which has an out of Scale drop keel, but she sails very well with it!.
My J Class, Endeavour also has a low keel - - not to Scale, sails very well too !
My website is  www.john-dowd.co.uk
John.  :-))
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hmsantrim

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Re: J Class yacht ballast
« Reply #2 on: February 25, 2013, 04:08:51 pm »

Hi.
      there is a guy doing a kit for a J class this is how he fits the lead.
 
   http://www.jclasshulls.co.uk/home/the-canterbury-j-class-model
 
         frank  :P
 
 http://www.jclassyachts.com/
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JayDee

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Re: J Class yacht ballast
« Reply #3 on: February 25, 2013, 04:23:10 pm »

Hello Frank,
That is a very good way of fitting the ballast, it puts it just where it should be - - low down !.
The J Class in the USA have their keels lowered by just 2 inches, to help with stability, but watching them sailing, it does not seem to be enough, lots of heeling in not much wind!.
If a yacht sails well and looks like the real thing, out of scale under the water is some thing I can put up with !!.
Very few folk have commented in the drop keels, when explained why they are used, it is understood, we cannot scale the Wind, or the Water !.
John.  :-)
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regattarich

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Re: J Class yacht ballast
« Reply #4 on: February 25, 2013, 05:07:52 pm »

Hi
Many thanks I will do some more research and get to it.
Cheers
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tigertiger

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Re: J Class yacht ballast
« Reply #5 on: February 25, 2013, 07:25:11 pm »

It is pretty common to have drop keels on scale sailing models. Due to the effects of scale, area (squared), volume (cubed), and wind and water don't scale.

The J's were unstable in real life, one of the reasons why the J class fell out of favour was that they eventually became so highly tuned that they were only fair weather boats and many events were cancelled. As such they are hard to scale down without some cheating; either by making the hull deeper than scale or using a drop keel.

As JD suggested, a drop keel will sail better, in more wind conditions.




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alanh

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Re: J Class yacht ballast
« Reply #6 on: March 04, 2013, 11:45:39 pm »

The J Class is not and easy yacht to scale to a model as the temperamental handling of the full sizes yacht is only exaggerated by scaling down. You might want to have a look at the following.


1) Where is your waterline? I would suggest you try use sufficient ballast to make the boat stable and then adjust the waterline to suit. Have a look at the two tone finish on my website which will give you an idea of what works for Nottingham J.
The Nottingham/Canterbury use 4.3kg of ballast in a hull of similar length to yours. I use a moulded ballast which will be denser than lead shot and making a solid lead ballast to suit your hull might help. You may need more ballast than I use as a planked hull and deck are quite heavy with much of the weight above the centre of balance.


2) Cotton sails and brass fittings are also quite heavy and well above the centre of balance and you may have used other materials which create an attractive boat but work against you in a working model. You will want to keep the weight above the centre of balance as low as possible.
 If you have scaled the sails, its likely that there will be too much sail for the model and that the centre of effort of the sails will be too high.
Have a look at the Canterbury rules on my web site which give dimensions for three sets of sails (top, middle and storm). The Nottingham/Canterbury models sail very well in open, more windy conditions with the middle suit, and very well in sheltered waters with the top suit. In the first place I would suggest that you replicate the middle suit in a lighter material than cotton and experiment from there.


3) You may find that even with alterations after considering the above, that a drop keel is required but this will have an impact on the centre of lateral resistance of the hull and either the mast position will need some adjustment or a redesign of the sails will be necessary.


Last of all...good luck! The J looks great on and off the water!

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regattarich

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Re: J Class yacht ballast
« Reply #7 on: March 05, 2013, 02:07:08 pm »

HI Thanks for your advice, see attached images of my model.
Cheers
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regattarich

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Re: J Class yacht ballast
« Reply #8 on: March 05, 2013, 02:17:53 pm »

attached another photo
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regattarich

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Re: J Class yacht ballast
« Reply #9 on: March 05, 2013, 02:19:19 pm »

and another!
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alanh

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Re: J Class yacht ballast
« Reply #10 on: March 05, 2013, 07:20:06 pm »

Hi. Great looking yacht! Good luck on the water and get in touch if I can help further.
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tigertiger

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Re: J Class yacht ballast
« Reply #11 on: March 06, 2013, 12:07:06 am »

very nice indeed :-))
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regattarich

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Re: J Class yacht ballast
« Reply #12 on: March 06, 2013, 11:46:28 am »

Thank you chaps
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Islander51

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Re: J Class yacht ballast
« Reply #13 on: April 03, 2013, 11:06:02 am »

I would have a good look at this thread where such things are discussed in detail:


http://www.rcsailing.net/forum1/showthread.php?6900-J-Class-versus-12Metre-Class


It's well worth a read, all 25 pages of it!


Edward.
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roycv

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Re: J Class yacht ballast
« Reply #14 on: April 04, 2013, 09:21:35 am »

Hi, I built a similar size J class from the Amati Endeavour kit which comes out at a bit over a metre.  All the above advice is good, during my research of the restored full size yachts I found that the full size Endeavour was floating a foot lower than the original and had a propeller fitted into the rudder area!  Lots of scope there

I chose to balance my model version without the quadrilateral jib and she sails very well.  I have to put another fore stay in place when it is removed.  With the quad jib she works OK in light winds with a bit of rudder applied.

regards Roy
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hmsantrim

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Re: J Class yacht ballast
« Reply #15 on: April 04, 2013, 01:13:50 pm »

 
  hi.
       Robbe make a winged keel ballast for the Comtess yacht which allows it to be attached with screws into the bottom of the fin
       putting the ballast weight where it should be.  if you could remove some of the lead shot which is higher up in the hull to the
       equivalent weight of the winged keel it may be a move in the right direction.  Think you have realised The ballast has to go on
       the keel. BTW have you fixed the lead shot inside the hull or is it bagged and removable?   
 
                            frank
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regattarich

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Re: J Class yacht ballast
« Reply #16 on: May 10, 2013, 10:22:56 am »

Hi
 
Many thanks for your reply, sorry ive just seen it.
The lead shot is resined in place, so I will need to cut off part of the keel and drill out the shot!
Im sure I will learn from this!
Many thanks
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cabman

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Re: J Class yacht ballast
« Reply #17 on: May 18, 2013, 11:59:39 pm »

Hi. A nice looking yacht. It is a very similar hull design to a Dragon. A model of it is produced by Billings and the one I built had a solid lead casting for the bottom couple of inches of the keel. I believe current kits now have brass keel bottom sections. Mine stays upright but does lean dramatically in a strong wind but looks amazing. The upper part of the keel is the same plank construction as the hull.
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rickles23

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Re: J Class yacht ballast
« Reply #18 on: May 19, 2013, 08:44:32 am »

Hi,
 
The J class is similar, although a lot larger, to the Dragon class yacht.
 
If all the ballast is in the hull it is useless.
 
The lead should be in the bottom third of the keel.
 
One way is to make a mould of the keel and cast your own lead.
 
Regards
 
 
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regattarich

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Re: J Class yacht ballast
« Reply #19 on: May 19, 2013, 08:50:24 am »

Hi, yes thanks will do, I'm just finishing a 1m scratch build model of an old Brixham trawler and then I'm going to attack and make the mould and then cast a lead keel. Will post how i get on Cheers
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