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Author Topic: Stand off scale yacht 'Force 8'  (Read 14100 times)

roycv

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Re: Stand off scale yacht 'Force 8'
« Reply #50 on: November 21, 2012, 09:52:01 AM »


The frames are going to be 4mm (or is it 3.6mm??) ply, just the covering was to be balsa. I will look into liteply though - I think the shape will be fairly easy to plank along the length of the hull (long planks though the boat is about 936mm long -

I know balsa is easy but it is mainly soft and smoothing down will flex the balsa as you do it and it is difficult to get good curves.  Another point is that the adhesive will probably be tougher than the balsa.

The way I have seen the lead keels bolted was holes right through the lead pieces with a wider hole about half way through (or at least enough to recess the nut and bolt) - washers fitted both sides then nut tightened up. I think the builder may have filled the recesses with resin or epoxy adhesive, then glassed over the lead and painted -

Are you going to cut up lead sheet for the keel.  A good safe way.  Then you can bolt it together in layers.  I do not think you can glue lead!  You can of course surround it with epoxy and filler etc.


I am going to step the mast on the keel, one idea was the widen the keel at that point as well as make the keel higher, then a hole drilled in about 2/3 down the depth of the keel at that point, then once mast inserted drill a hole through the 'step' and mast and bolt it in. Actually I will have to make the hole a slot so the mast can lean back a bit.

Stepping the mast on the keel will work, it works better if you can secure it as well at deck level too.  This helps the mast resist the bending induced by the wind on the sails.  May I suggest that you mount the mast in a simple way until you find the right position for it, then fit a tube that the mast can slide into.  The tube can be fixed at the keel and deck level.  It is best if you can then also fit a tube around the mast base that slides into the tube in the hull.  I had experience of a wooden mast in a tube that got wet and took 3 weeks to dry out before it could be removed.
Brace the mast opening at deck level with extra beams between the frames and across the deck.  This is where the drive from the sails transmits the power to the hull.
The benefits are a water seal at the deck level.  It is very easy to rig the boat at the pond side, wind etc. when you can put the mast in and it stays there. You can also reduce adjustments to the mast stays.  These can be fixed wire with a very strong spring in the base of the mast so that the spring tensions the stays.

The mast gooseneck can be a problem, if you can machine items you can make your own but they need to be strong and act like a u/j.

Another idea was to widen as before and use a ring like a washer with a collar to fit the mast foot into

Work out where any strong points (shroud connecting etc.) have to be on the deck and strengthen them before the deck goes on.

Have you worked where you will need access into the hull?  for instance adjusting rudder servo connections, if using a sail winch sometimes the string gets tangled.
regards Roy




Please do not use Blue as it is reserved for the moderators

Cheers

Ken


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goBulawayo

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Re: Stand off scale yacht 'Force 8'
« Reply #51 on: November 21, 2012, 11:49:04 AM »

Thanks very much for your help Roy - I had forgotten about marking up strengthing points for the stays etc.

I see liteply isn't all that expensive so I will get some for the first layer on the hull. I suppose as I am going for an overall smooth finish I could use the liteply for the second layer too? If I do the first in long strips along the length of the hull and the second layer in shorter strips at 45 degrees to the first?

Re the keel, I had planned on shaping the two sides in wood and then cast the pieces in lead. But on thinking about it, thats probably too much for my limited capabilities and budget - Your idea of layering the lead (fixed with epoxy glue?) and then shaping it sounds much better.

I was going to run the mast through a brass ring with collar that could be fixed to the deck. I will remember to strenghten the area around where it comes through the deck. As to the gooseneck I will probably buy one. For my stays I have some fishing trace covered in a plastic tube, I will also be using shroud stays that look similar to the ones used on yachts, expensive I know but I am trying to get as much of a scale look as possible. I have not worked out as yet how to connect them to the mast - One thing I am strugling with is finding a streamlined tube for the mast, the original is that shape and works out to about 1" along the long side, I have found tubing about 3/4" but only in short lengths, I cannot recall off hand but I need about 1800 mm length for the mast - I may have to compromise and use a different shape, I know Sailsetc have a sort of half round tube with a slot up the back, or I just go for round, though a 1" round tube is quite big, so would have to reduce it to say 3/4"

Access to the hull is to be through the cabin and cockpit, its not a huge opening but I can get my hands in. I will have to make sure I place servos etc where the screws are accessible once the deck is on so that I can remove them if need be.

I am thinking of using a servo with a large arm to control the sails.

Regards

Wayne

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roycv

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Re: Stand off scale yacht 'Force 8'
« Reply #52 on: November 21, 2012, 05:32:46 PM »

Hi Wayne, Sounds like you are thinking through and should do well.  I would not use 3 mm for the diagonal planking just use some 1 mm thick wood.  The diagonal has to take more bending and will still result in a strong hull, but the liteply along the hull is fine.  45 degrees is good for the angle.
When you plank the diagonal keep the 45 degree angle as long as you can and when it gets greater start again at 45 degrees leaving a triangular gap.  This is easy to fill in afterwards as the gaps are all triangles.

I have some of that streamline ally mast 3/4 inch wide for a project I never completed.  Don't know who has it now and getting 1.8 metres through the post is difficult.
The large arm servos work well but the ones I have seen are fast in their action.  I have one in use with an ACTion servo slow down unit. 
Sanwa did a nice slow action servo arm, there are still some around.  I have used them myself.

I have a yacht where I have used an aileron hinge for the goose neck, round section, one end  is lodged in the main boom and the other end slots into a close fitting tube attached to the mast.  Works well and is cheap.

How far have you got now?

regards Roy





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Boomer

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Re: Stand off scale yacht 'Force 8'
« Reply #53 on: November 21, 2012, 06:07:12 PM »

Here is another place you can purchase a helm and helm post with compass in the size you are looking for. Very similar to the one on the Fairwind lll I mentioned in an earlier post.
The part number is PRB 3457 price is $9.99 USD here is the link to the web site http://www.horizonhobby.com/products/PRB3450?cm_mmc=BrandSiteReferral-_-PRB-_-ProductPage-_-PRB3450#t4
Boomer
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goBulawayo

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Re: Stand off scale yacht 'Force 8'
« Reply #54 on: November 21, 2012, 06:16:55 PM »

Cool thanks Boomer

Regards

Wayne

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goBulawayo

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Re: Stand off scale yacht 'Force 8'
« Reply #55 on: November 21, 2012, 06:20:09 PM »

Thanks Roy, I am no further than the photo earlier showing the supports on the building board. I need to wait for payday to get some timber - I was at the hardware store today and had a look at 3.6mm ply and I think its too thin for the frames so I am going with 6mm.

Thanks for the info about servo arms and the goose neck, I will look at the aileron hinges

Wayne
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goBulawayo

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Re: Stand off scale yacht 'Force 8'
« Reply #56 on: November 21, 2012, 09:09:53 PM »

Had a look tonight at deepening the keel - See attached pic - Pink shows the original keel , yellow the keel twice the depth - It then looked a bit strange so I changed the angle of the leading edge (hatched area), the new angle is random, I just drew what looked about right - Any thoughts please

Thanks, Wayne

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roycv

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Re: Stand off scale yacht 'Force 8'
« Reply #57 on: November 22, 2012, 09:05:53 AM »

Hi Wayne, I am sure others will want to comment. 

My thoughts are that the centre of area of the new + old keel should lie in the same vertical plane as the centre of area of the old keel.
The sails are to some extent fixed and the c of effort of the sails should be 4% ahead of the centre of lateral resistance at the waterline of the under water part of the hull.  I have used this successfully in several yachts before.

I would say that the lines you have drawn are pleasing to the eye and maybe a tweak to adjust for the above suggestion would leave them looking much the same.

Do you know how to work out the centre of area of the sails and the centre of lateral resistance for the hull?
You may need to increase the area of the rudder by 40 % or so if you do, take the rudder blade dimensions a bit lower.

It is worth doing some sums early on, including the displacement of the hull with the method of planking you are going to use.

I have used the above to good effect in several sailing boats.

The beauty of doing it this way is that the allowance for scale is just a few % and the designer of your boat would still recognize his child!

Looks good and an interesting thread,
regards Roy
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Landlocked

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Re: Stand off scale yacht 'Force 8'
« Reply #58 on: November 22, 2012, 07:48:04 PM »

Wayne,


In addition to calculating your new centre of lateral resistance, don't forget to calculate your new centre of gravity.


After I extended my schooner's keel for all the usual scale factor reasons, I float tested it with the major components in place to determine the ballast's weight and centre of mass.


I gridded by keel to help calculate the volumes.


After the first pass through the math, I realized that my keel didn't have enough volume forward for the required lead.  So I added a Dutchmen and recalculated.


Unfortunately, I mis-estimated the weight of the masts and deck so while I nailed the fore and aft, I was heavy overall.  Fortunately, since I knew where the centre of mass was, it wasn't "too" painful to drill out some weight (If you have to do this, use spade bits and not twists.  The extra friction from the twists will turn the lead greasy and seize and snap the bit -- learned the hard way).


Pictures show the general sequence.


Good luck.


Ken
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goBulawayo

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Re: Stand off scale yacht 'Force 8'
« Reply #59 on: November 22, 2012, 08:10:54 PM »

Right so there is alot more to this than just making the model - I know nothing about working out centres of gravity, centres of area etc etc - I have a copy of Model racing yacht Construction by R. Griffin - I will have a read through it to see if it can help - I take it a lot of things will only be calculable once the boat is actually built?

Wayne
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Landlocked

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Re: Stand off scale yacht 'Force 8'
« Reply #60 on: November 22, 2012, 09:04:24 PM »

Wayne,

While it's a joy to build a scale model of a real boat, the realities of physics will quickly get in the way and the modeler will be challenged to make compromises to accommodate them.

I apologize if this is all known to you but if you don't make adjustments, a model yacht will be at much tippier than the full size yacht. 

Stability is an interaction between righting moment (which is a combination of hull shape/weight, ballast weight and location) and centre of effort and size  of the sails.   Hull size and weight is a factor of its volume/displacement and centre of effort is a factor of the size and shape of the sails.

You indicated that you were building in 1/15th scale.  Your sail area will be 1/225th the real boat (H X W) but your displacement will be 1/3375th the weight of the real boat (H X W X D) so the scale modeler must make adjustments.

For the large square rigged models, an extra drop keel is often added that hangs way below the true keel.  It is removed for display.  The higher square sails will not be set to reduce the sail area.

For scale yachts, slightly deeper keels (as you are planning) are usually used.  The "J" class allows 2 extra inches.  For sail area, slightly shorter masts and booms will reduce sail area without looking "wrong."

Traplet publishes several books dealing with these challenges.  "Historical Sailing Ships -- Remote Controlled" and "An Introduction to Radio Controlled Scale Sailing Models" are two I have.

The fore and aft location of the centre of lateral resistance can reasonably guess-timated by cutting a thin plywood profile of all the underwater portions of the hull and then balancing on a thin dowel.   If you have highly detailed copies of the full size plans, you may find a circle divided into quadrants located somewhere in the keel.  This is the naval architect's calculation.  If you balance your area adds in front of and behind this location, you won't disturb things -- same thing for sail area. 

There may also be a similar circle marking for the centre of mass (and buoyancy).

If you have the centre of mass marking, keeping you fore and aft ballast adds/removals will keep you in the ball park but battery, receiver, and servo locations (and lack of engines) and difference between building methods can disturb things.  Keeping your internal design options flexible to allow some shifting around after pond testing is desirable (but if strict scale modeling is desired, location choices may be limited.

If you're not a racer, adding some area to the rudder will allow you to make up for small errors in the relationship between centre of lateral resistance and centre of effort (sail area).  You'll go a little slower.

With respect to early discussion on frame spacing.  Feel free to use only every 5th or so frames.  As long as spacing is around 10 cms  or less, you should have enough strength.  Add some in between frames if needed for strength in key areas (e.g.,  if your mast step is going to be on deck instead of the keel) or you have a complex shape transition area (not likely looking at your design).



















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Landlocked

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Re: Stand off scale yacht 'Force 8'
« Reply #61 on: November 22, 2012, 09:10:50 PM »

Oops, somehow I posted before I finished.


Keep asking questions and read through the various build logs, on this forum and others.  You'll find a lot of people who are working through similar challenges and lots of usually helpful advice (and if you're working cross the pond, don't be surprised by unfamiliar terms (and spelling) -- took me a while realize what a grub screw was.


Good luck,


Ken 




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goBulawayo

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Re: Stand off scale yacht 'Force 8'
« Reply #62 on: November 22, 2012, 10:15:18 PM »

Eish you guys are speaking a foreign language. I will check the drawings tomorrow for any architects points

I am not looking to race the yacht, I just want something to sail around our boating lake, so it does not have to be perfect.

I had a quick read in the racing yacht book I have and I am even more confused!

I have drawn up the frames with as much open space as possible, so should be able to move things about a bit to help with ballast etc.

You mention slightly shorter mast and smaller sails, what percentage can I look at regarding reducing the size? I have a 1/30 drawing of the sail layouts which I can amend with reduced sizes.

Thanks very much for your help Landlocked and Roy

Wayne
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roycv

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Re: Stand off scale yacht 'Force 8'
« Reply #63 on: November 23, 2012, 12:19:43 AM »

Hi Wayne, as Landlocked says it is quite technical but a lot of it has been done for you by the guy who did the drawings.

When looking at a full size yacht you can work out the centre of effort on the sails by making a drawing of the 2 sails exactly where they are in relation to each other.  Then take one sail triangle draw a line from one corner to the opposite side exactly half way or in the middle of that line.  Do it again for another corner and the lines will cross, this is the centre of the triangle.  Do it for the other sail as well.  Then join these 2 points with a line.

Now you should work out the area of each sail triangle (Half the base times the height of the triangle).
bring these numbers down to a low multiple.  i.e. if the jib is 70 sq feet and the main 210 sq feet then it is 70 over 210 = 1 ; 3.
On that basis at the jib area centre point draw a line at right angles to the line you have already and measure off the main sail area, in what ever units you have chosen, and it is in this case 3 inches / centimeters etc.

Now go to the other area centre point and measure again at right angles but the opposite direction the other area you have worked out in this case 1.
You should now have a line (joining the triangle centres) with a line at each end going in opposite directions. At the measured points draw a line between them.  This will cross the first line you drew.  This is the centre of effort of the sails.

Drop this point down vertically to the keel of the boat.  This line will cross the waterline of the hull (at right angles) and this can be assumed to be 4% ahead of the centre of lateral resistance.  This will save the cutting out mentioned by landlocked.  What landlocked suggests is fine for a new or unknown hull but here we can work from known things.

You now know where the centre of lateral resistance is.  Now any alterations you make to include a deeper keel should have the same centre of area.

I don't think you need to worry about the centre of gravity, you can calculate it but I don't think it will influence your build.

landlocked mentions the J class.  I have a 1 : 35 scale  J class and you do have to reduce the sail area as the full size yachts were grossly over canvassed and only sailed in no more than a Force 4 wind.
For your model the sails and mast height are OK.  A rule of thumb for the mast length from deck to tip of mast is 1 1/4 times the length of the yacht.  But as I mentioned before a 10 % reduction in sail area will do no harm.  This is to accommodate the square and cubed rules mentioned by landlocked.

ALL YOU REALLY NEED TO KNOW IS:-
keep the extended keel centre of area in the same same vertical plane as the existing keel center of area.

What ever you do don't panic, it will all work.
best of luck Roy

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goBulawayo

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Re: Stand off scale yacht 'Force 8'
« Reply #64 on: November 23, 2012, 11:24:15 AM »

Thanks Roy, I take it the keel centre of area is different to the centre of lateral resistance? If so how do I work out the keel centre of area? Can I just draw lines from opposite corners and where they cross is the centre?

Thanks

Wayne
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roycv

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Re: Stand off scale yacht 'Force 8'
« Reply #65 on: November 23, 2012, 11:31:39 AM »

Hi Wayne.  Take the keel as a 4 sided shape and as you say draw diagonals and get the centre.  This is only correct if the 4 sides make a square or oblong.  But as it tapers down towards a triangle shape it should not affect what you are trying to do.
Extend the drawing as you have done and draw diagonals for the whole area, old and new keel together.  Do the crossing of the diagonals.  The new point of crossing should be vertically in line with the original keel centre.
There is another way but try this first.
Even approximately it will work.

regards Roy
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goBulawayo

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Re: Stand off scale yacht 'Force 8'
« Reply #66 on: November 23, 2012, 11:45:06 AM »

Thanks Roy, I will try that and try the centre of a trapezoid to see how they differ

Wayne
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roycv

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Re: Stand off scale yacht 'Force 8'
« Reply #67 on: November 23, 2012, 11:46:49 AM »

Hi Wayne, if you are OK with trapezoids then just divide it into 2 triangles and do it that way.
regards Roy
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goBulawayo

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Re: Stand off scale yacht 'Force 8'
« Reply #68 on: November 23, 2012, 12:18:23 PM »

Will do, I had a look at the plans, the sail and rigging plan has the centres of the sails and a spot called Total MA which looks to be the Centre of Effort of the sails.

The hull plan has a spot quite low down on the keel, you can see it on the drawing above, its in the pink section, a spot with a vertical line through it, could this be the centre of gravity of the keel? The main plan shows a note saying 4500kg at this point. I have just printed out a copy of the above plan and will work out old and new centres of keel based on a trapezoid

Cheers

Wayne
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Landlocked

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Re: Stand off scale yacht 'Force 8'
« Reply #69 on: November 23, 2012, 07:54:45 PM »

Wayne,


I'm guessing that dot IS the center of mass/gravity for the boat.    If the keel shape is a normal foil/teardrop, you would expect the centre of the weight to be forward of the centre of the trapezoid. 


Can't tell whether the 4500 kg is total boat displacement or just the ballast weight.


Going back a few lines, for a fin keel design with fairly symmetrical bow and stern profiles, the centre of lateral resistance will be very close to centre of the keel's area.  When you get to the old full keel designs with long overhangs, things start getting complicated.  You should be fine.


Ken
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goBulawayo

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Re: Stand off scale yacht 'Force 8'
« Reply #70 on: November 23, 2012, 08:08:40 PM »

Thanks Ken, I seem to recall the 4500kg is the ballast weight and the boat had a displacement of 14700kg

Wayne
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goBulawayo

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Re: Stand off scale yacht 'Force 8'
« Reply #71 on: November 23, 2012, 08:12:42 PM »

I have just printed out a copy of the above plan and will work out old and new centres of keel based on a trapezoid

The centre of the new layout is about 6mm behind the centre of the old keel, could I leave it like that?

Wayne
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Landlocked

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Re: Stand off scale yacht 'Force 8'
« Reply #72 on: November 23, 2012, 09:18:10 PM »

6 mm out of a model length of 930mm is 0.65% so it should not be a problem.  Using Roy's 4% rule would mean you're either 3.3% or 4.7% of the desired value (Roy, isn't the centre of effort supposed to be slightly AFT of the centre of lateral resistance to give you a trace of weather helm?).


Ken
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roycv

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Re: Stand off scale yacht 'Force 8'
« Reply #73 on: November 24, 2012, 12:05:23 PM »

Hi Landlocked, you are right a slip of the fingers!  C of E  should be aft of the C of LR.  I agree 0.6% either way will make very little difference.
Main thing is to have the boat balanced.
regards Roy
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goBulawayo

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Re: Stand off scale yacht 'Force 8'
« Reply #74 on: December 05, 2012, 06:44:42 PM »

Hi Guys, would you suggest 4mm or 6mm ply for the frames? Yacht it 936mm long and about 280mm wide at widest point - As the frames will stay insitu I am thinking 4mm will keep the weight down.

Thanks

Wayne
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