Model Boat Mayhem
The Shipyard ( Dry Dock ): Builds & Questions => Yachts and Sail => Topic started by: labougie on September 09, 2009, 07:23:59 pm
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I've recently made a start on my first r/c model boat - a Colin Archer. The big Billings (414) was going to be too large to transport (and I also fancied plank and frame construction) so I had the idea of acquiring the small Billings kit (606), taking the lines off and blowing them up 200% to give me 72cm LOA. 'Longshanks' kindly provided me with the David Petts article describing his adaptation of the 606 to an r/c sailing model, which has been a great help.
The stage I'm at atm is the bulkheads (6mm ply) have been cut down to ribs and the internal keel (4mm ply) cut down to allow space for the gubbins. I've got the ribs glued in to the keel and we're currently looking like this:
(http://i17.photobucket.com/albums/b58/labougie/Portsidegluedup.jpg)
The plot is to plank it in spruce and use a two-pack clear finish (I've used Rustins Plastic Coating before now in a different application and it seems to be pretty tough so I'll probably go with that). Petts fibreglassed the inside of the hull and I figure that would make sense - I've seen some woven 120gsm tape at 75mm wide, which would fit nicely into the gaps between ribs (60mm) leaving a little on each side to go up the ribs. Does 120gsm sound about right? Any input much appreciated.
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Hi
I think you said you were using 3 x 10mm planks which should be quite firm. I would be tempted to use tissue instead of 120 tape unless you have to do a lot of sanding to fair the lines.
Save weight, more weight low down - better sailing :-))
longshanks
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Idly thinking about planking while waiting for glue, timber etc to arrive. A few questions:
1/ I'm assuming the garboard strake ought to be a longish plank, starting and ending on a frame station. As a planking philosophy on a double-ender, should one subtract from the amidships width of each plank as one goes fore and aft, or keep them parallel and end up with shorter planks coming towards the garboard?
2/ I could make my life much easier by using 2mm planking, not 3mm. Would this be strong enough (on 65mm frame stations) with glass reinforcement inside?
3/ Should the planks meeting the stem and stern posts be rebated into the posts, or faired away to nothing (from the inside) as they meet?
There are going to be many questions........
Think I'll draw up a king plank tonight - curved deck planking would be nice. I've also half a mind to cut away the (straight) deck beams after I've planked and replace them with cambered ones. The beam amidships is 250mm - how does a 5mm rise to the centre line sound?
I've only just noticed that this posting is in the 'Masterclass' section which is not exactly apposite - if the mods would like it somewhere else, please move it. Thanks
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Hi Labougie
Are you talking about deck and hull planking here?
1/ I am not expert, but my garboards run from stem to stern.
2/ Depends on the wood. If using balsa then 3mm would be stronger. If using cedar or other 'normal' timbers, 2mm with FG reinforcement is more than adequate. IMHO.
3/ Rebated. It actually makes the job of planking easier. And it gives you a good straight line of plank ends.
Re: Curved deck planking.
What did the original boat have? Working boats generally had straight planking.
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Don't worry about placement of this thread.
It is under Yachts and Sail.
Yachts and Sail is a separate board under the heading Dry Dock, along with the Masterclass Board
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Thanks for the input. I've just now come home with my spruce so I'll have some planking pics in the next few days. If I were going to put a motor into her, what size motor and what diameter propshaft?
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A progress report. I'm having problems trying to get pics up so I've just given the URLs.
I got my spruce in 3" x 36" x 3/32" sheets and cut it down to 10.5mm strips on the bandsaw, cleaned up the edges on my magic little hand operated thicknesser and wound up with plenty of nice clean 9.5mm x 2.3mm planks.
(http://i17.photobucket.com/albums/b58/labougie/DSCN3770.jpg)
There were several false starts before I found a way to plank her. I had it in my head that I should start from deck level and run the planks parallel to the deck which simply didn't work. There were abrupt changes of direction and orientation and the planks just wouldn't sit fair and had to be broken off. After five tries at it I gave up and decided to let the planks go where they wanted to go, so I started 3 planks down from the deck amidships and let the plank follow the rib shape and rise up towards the deck at stem and stern.
http://i17.photobucket.com/albums/b58/labougie/DSCN3767.jpg
I’d also found that number 5 rib was almost 2mm proud of the line and was therefore creating a lump (no idea how this happened – I thought was fairly accurate with the cutting and sanding but........). Things were much smoother after I'd sanded it down.
(http://i17.photobucket.com/albums/b58/labougie/DSCN3758.jpg)
This was infinitely better, I'd previously made a classic cock-up - after trial fitting the ribs to the keel I thought it would be a smart move to put an approximate chamfer on bow and stern ribs before they were glued which I did, then promptly glued the port side number 4 rib into the starboard side keel and vice versa. It's a good job epoxy fills gaps. Rebating into the stem and stern posts works well.
(http://i17.photobucket.com/albums/b58/labougie/DSCN3762.jpg)
The fourth plank down was starting to exhibit symptoms of the “I don’t want to go there” syndrome which I’d encountered at the start of things – I had to make up a little jig to get the plank to close up to its neighbour. Narrower planks from here on down.
(http://i17.photobucket.com/albums/b58/labougie/DSCN3773.jpg)
I think I’ll get the same fourth plank glued in to the port side then get a few planks in at the bottom. There isn’t a garboard as such – the central ribs come all the way down to the bottom of the keel.
(http://i17.photobucket.com/albums/b58/labougie/DSCN3775.jpg)
I envisage a shaped spruce board flat across the keel base – probably extending all the way up the stem and stern posts. The more spruce the merrier! No, I’m not that bothered about the weight – she’s not a racing boat. It seems to me that I should plank in a straight line from the stern at the bottom of the keel and let the planks fall off the keel as it curves upwards. I could curve them up, but wouldn’t I just be decreasing the space available at the bow and thereby giving myself more shaped planks to make?
Any input appreciated. What do people think about a motor and shaft size for this?
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Looking good.
I love the home made thicknesser.
Letting the planks take their own route is a good way of doing it, but you will end up with stealer planks around the sharpest turn of the bilge. You should think about starting planks at the keel as well and work towards the bilge to meet those you are already working with.
When you come to bending the planks you have a couple of options to think about:
1. steam the planks for 10 to 20 mins, offer up to the line you want to plank to, allow to dry thoroughly then remove and refit with glue! Traditional way, but time consuming.
2. soak plank in v hot water for 10 to 20 mins, bend around the curve required, clamp, allow to dry, remove clamps and glue in place - again slow.
3. use a hot air stripper, run the plank in the hot air stream (mind your fingers) backwards and forwards while inducing a curve. Go slowly and dont let the wood scorch - if it does it goes brittle and will probably snap. Have a practise and you will see how quick and effective it is. I used this method on my current build - Bourbon Orca - lots of difficult curves at the bow.
I agree with tigertiger, 2mm is plenty thick enough, you will be surprised how strong it is when glassed up
One thing I noticed - there is only half a hull :o
Ian
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Hello Labougie
Great job on the boat so far but I noticed your not tapering your planks towards their ends. They should be wide at the midship section and taper towards the bow and stern otherwise your going to end up with odd shaped holes to fill with the final planks.
I wrote an article here that might help
http://www.modelboatmayhem.co.uk/forum/index.php?topic=19469.0
Its a bit involved but I'd be happy to help with advice.
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Thanks Boatmadman - Plot No 3 above is WAY TO GO! Works a charm. Glad you like the thicknesser - I've often thought it might work even better if I substituted a nicely hooked card scraper for the plane blade - just never got around to trying it.
Greggy - Yes, I had tapered ends in mind. I was going to stop at four planks down, put a few on the keel then start measuring to find out how much I needed to taper them by. I'll have a look at your article tonight.
As to only half a hull - I thought I might make half a Thames Sailing Barge for the other side and start a new whacky trend in composite models, but I'm having problems with the rig. If I can't figure it out, I may just have to use the other half of the Colin Archer. %%
Cheers, Chaps.
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Very nice job of planking. :-))
And like Boatmadman, I love the thicknesser.
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Having mentioned it in a previous post, I thought I'd have a crack at putting a scraper blade into the thicknesser instead of the plane blade and it doesn't work nearly as well - I think it may be because the scraper is too flexible. Planking away like a good-'un - more pics later.
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I'm new to all this, and building a double-size version of the 606 Billings Colin Archer - http://www.modelboatmayhem.co.uk/forum/index.php?topic=19525.0
Before I get too far I need to decide what sort of auxiliary power to have. She'll be 720mm LOA x 250mm beam. Essentially I need to cut a slot for and glue in a propshaft before gluing the two sides together - could anyone advise a suitable shaft diameter and a suitable prop? What does one do about a thrust bearing? Given the astronomical rpm figures I've seen for electric motors, I assume a reduction gearbox would be required - is there a thrust bearing in one of those? Would a 540 motor at 6V be around the mark? Do I need any cooling? Any pointers gratefully accepted.
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Photo links sorted. :-))
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It depends how fast you want the motor to be able to propell her?
Bob
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Hi,
To give you an idea on my pilot cutter (1140 x 300mm) I fitted MFA/Como 919D motor with 2.5:1 reduction. Through standard M4 prop shaft to 30mm dia 3 blade prop. Battery 6volt. Control through 15amp Mtroniks speed controller. Speed/power more than adequate.
Re prop size I guess your boat/rudder being smaller you will have to gauge against your rudder. Dont forget you will need to increase your rudder size by approx 30% - scale boat meets non-scale water!
All available at
http://www.shgmodels.com/acatalog/
longshanks
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It depends how fast you want the motor to be able to propell her?
Bob
Don't need fast - just to be able to get her back it I get stuck somewhere or if the mast folds on me for pushing her too hard!
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If it is just for plodding around a direct drive 385 motor on 7.2 volts and a around a 35 mm prop will provide this.
If you want more power go for a motor that will drive a larger prop a such as a MMB 550.
You wont need any more than 5000 rpm so you could look on the Graupner site for a motor to physically fit.
Bob
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Thank you, Shipmate60 - Jerome at SHG says the exact same thing so that's a goer. Got a few planks on the keel -
(http://i17.photobucket.com/albums/b58/labougie/DSCN3782Small.jpg)
The gap remaining to be planked is 106mm amidships, 81mm at the stern and 80 at the bow so 11 of my 9.5mm ish planks, thinning down to 7.3mm ish at the ends should do it.
Got to put a new steering rack on my Polo this w/e so more next week.
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With inspiration from Greggy1964's article on planking, I worked out the size of plank I should be using from here on in. I measured up the open ribs using paper strips - pretty accurate since it's easy to get a razor blade into bottom of the rib/plank joint. You also get a graphic of what's going on.
(http://i17.photobucket.com/albums/b58/labougie/DSCN3784Small.jpg)
This below has 11 off 9.5mm planks amidships (Station 5) as a given - a couple of mm shy but I'll cut the next lot of planks a little thicker. When I'm halfway, I'm going to be doing the sums again anyhow to check the percentages still hold.
(http://i17.photobucket.com/albums/b58/labougie/PlankWidth0001Small.jpg)
Is it going to make any difference whether I thin them top or bottom? Or should I be tapering from each side? Or does it matter? And if it matters, does it MATTER that it matters? Exit muttering........
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Here are some excellent photo's of Vigilance during her 2009 winter maintenance
You can clearly see the run of her planking to give you inspiration.
http://www.vigilanceofbrixham.co.uk/gallery09.shtml :-))
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I’ve been asked for a sketch of the thicknesser jig – my sketching ability is almost zero so herewith some pics and info in case anyone else fancies it. I used beech but any hardwood would do.
It’s simply a base board with two posts screwed and glued into it at an angle of 55-60 degrees.
(http://i17.photobucket.com/albums/b58/labougie/DSCN3796Small.jpg)
My posts are 40mm x 20mm and set 55mm apart. Once they were in, I glued a piece of 16x55mm (with the bottom cut to the same 55/60 degrees) in between them, the gap at the bottom being the height of the largest piece of timber you’re going to put through it. I added an extra two of these so I didn’t have to mess about with packing pieces when clamping the blade on.
(http://i17.photobucket.com/albums/b58/labougie/DSCN3797Small.jpg)
(http://i17.photobucket.com/albums/b58/labougie/DSCN3798Small.jpg)
The blade is just a very sharp plane blade, ground angle outwards so it’s working as a scraper rather than a plane. Clamp as near to the bottom of the blade as you can consistent with still being to be able to get the work past the other end of the cramp which will be even lower on the ‘in’ side of the jig.
(http://i17.photobucket.com/albums/b58/labougie/DSCN3795Small.jpg)
Cramp the whole thing to a bench and use a packing piece to guide the wood into the jig so the planks can’t fall sideways on the way through.
What I normally do is clamp it up with the packing piece set for whatever number of planks are going through, put that number into the jig then rest the plane blade on top and clamp it. This will give almost no cut. Adjustment is by way of a light tap with a hammer on the very top of the plane blade but keep an eye on the squareness at the cut! Given that the idea is to wind up with all planks the same size, put them ALL through before adjusting the cut. Don’t try to take too much off – you’ll get a better finish with a light cut and multiple passes. Don’t expect it to do the job in one pass – I normally go through half a dozen times on each side.
The bugbear of the design is that you have to push the planks in for quite a way before there’s enough for you to pull out from the other side and thin planks (even in company) don’t like being pushed. Gently, or they’ll snap on you.
If I gave anybody the idea that it’s quick to use – it’s NOT! However, if you don’t have access to a thicknesser it’s the only route available. My planks come off the bandsaw pretty well so all I'm doing is taking off the saw marks - earlier today I was putting 12 teak deck planks through at a time and it didn’t take too long.
(http://i17.photobucket.com/albums/b58/labougie/DSCN3794Small.jpg)
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Still plugging away gently.
(http://i17.photobucket.com/albums/b58/labougie/DSCN3807Small.jpg)
A buddy gave me this
(http://i17.photobucket.com/albums/b58/labougie/DSCN3809Small.jpg)
which turned into this
(http://i17.photobucket.com/albums/b58/labougie/DSCN3801Small.jpg)
and I made a start on this
(http://i17.photobucket.com/albums/b58/labougie/DSCN3811Small.jpg)
which I reckon will look rather tasty when completed and finished with Danish Oil. Onwards and upwards.
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Tapered planks going in-
(http://i17.photobucket.com/albums/b58/labougie/DSCN3817Small.jpg)
and more pretty (but VERY slow!) deck-
(http://i17.photobucket.com/albums/b58/labougie/DSCN3821Small.jpg)
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Your hull planking looks great. I assume you are using 2mm planking on the hull.
On my model it said 3 mm and the planks have not fitted anywhere near as well as yours.
Excellent job. :-))
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labougie........suburb planking :-))....however a few questions .....I see the hull planking fitted into a rabit [as shown on my markup]
1) the planking whilst fitted does not appear to be supported by any bronze pins
2) will you flood the immeadiate internal bow area with epoxy resin to secure the construction?
3) tell us about the hull planking material....I could guess but would be wrong
Please keep Mayhem posted with .jpgs.............many are interested in a planked wooden build.....................Derek O0
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Another point about correctly tapered planks the novice model planker does not appreciate, is that by tapering the planks correctly towards the bow and stern the plank cross sectional area is proportionally reduced and so aides in bending the planks around the frames where it is most needed.
Great job Labougie - very tidy indeed, but you need to concider how you are going to marry the top side planking in the rabbet at the bow with the bottom planking that has no rabbet.
May I suggest you bring the topside rabbet out a little and sweep it down to just back from the nib ends of the bottom planking. This allows you to sand away the step you will get on the bottom planking as it matches the rabbeted planking which will be deeper set in the stem. This way you will be able blend things with the planks in the rabbet and present a smooth even face at the transition.
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Tiger - the planking is actually 3/32" which is 2.38mm. I originally bought a couple of 1/8" planks and it was obvious just by offering then up to the ribs that they were going to be much more difficult to fit. I'll use them for the rubbing strake.
Decoy - the rebate was suggested by Tiger and with hindsight it's essential for strength and aesthetically much more pleasant. There is already a fairly decent fillet of epoxy behind the rebated joints and the plan is (once all the planking is done) to cut the internal keel down to a bare minimum so that I can get good access to all the inside planking, give it a really good roughing-up and run additional fillets of epoxy into all the rib/plank joints as well as the rebated ones before covering the inside with glass tissue and polyester resin.
"No Pins" was a policy decision - given that I'm going to clear finish the whole thing, I wanted to keep the planking as clean as possible so I'm just using 1/ plenty of mini-G-cramps 2/ the wedging jig pictured further up this post and 3/ lots of time. I'm usually managing to glue up stations 4-7 at the same time, then working outwards one or two ribs at a time. It's slow, but I'm fortunate enough to have the time. I just now put three shaped planks on 4-7 at the same time because they fitted so well and it was a mistake - I'm going to have to invent some new clamping solutions to get the first and second of those planks down on to the outer ribs while the other planks are in the way!
The planking is spruce, bought in sheets from the local model shop then cut down and cleaned up as shown further up the post.
The latest plot is to forget about the Billings bulwark rail and extend the planking up above deck level by 20mm or so to make proper bulwarks (c/w scuppers) supported by fairly chunky spruce staunchions glued to and aligned with the ribs - the deck would simply be notched out where the staunchions come through. I'd plane the top parallel with the deck line and cap it with teak. This would also mean extending the stem and stern posts upwards (in spruce). There will be 1/ a spruce plank running flat along the full length of the bottom of the keel which will rise up the stem post and 2/ a spruce plank running along the side of the stem post from the point where the rebating stops up to the top of the post, so any extension will have good support.
As everyone will have gathered by now, this isn't a scale model, it's a one-off - I'm just putting in bits that appeal to me. The deck hatches are (on current thinking) going to be teak-edged cut-outs from the swept deck, flush fitted (I've discovered a source of M1.6 stainless hex key-headed set screws - should do nicely).
I've also been thinking about the rudder. I've ditched the idea of a motor, so the prop cut-out will be going and I'm wondering if (given that the leading edge of the rudder will be curved) it would make sense to put a similar (opposite) curve into the stern post so that they fit together nicely? The pintles would be recessed into the rudder. Hmm.
Greggy posted re shaped planks while I was writing this and yes, there needs to be a fairly serious twist in the planking particularly at the bow and the fact that the planks are thinned out at this point makes life much easier. I've described above the way the step is going to be handled - by means of a spruce plank on the side of the stem post. It'll make the stem post thicker, but I wasn't going to leave any bare plywood exposed anyhow!
Thanks for the compliments, guys.
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I'm in need of some input here chaps - I've been thinking about a keel and I'm hydrodynamically out of my depth. I've cut out something that 'looks' right but whether or not it's what I need is another question which I don't have the answer to.
(http://i17.photobucket.com/albums/b58/labougie/DSCN3825Small.jpg)
I'm figuring some kind of keel is a must for decent sailing ability - she's not a racing boat but I want her to move as fast as she can. My ideas so far have revolved around a metal plate pinned or bolted through into the hull with lead flashing either attached to the sides of the keel or formed into an elongated teardrop shape and attached to the base of the keel. I'm confused as to what comes first - do I have to consider the CLR at this point or simply get her watertight, find out what weight of ballast is needed to get her to DWL and add this weight to the keel? Should the weight be evenly spread along the waterline length or concentrated in one place? Any pointers gratefully accepted.
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I am a little lost here labougie........ O0..from the photographs.....I assumed you were building a 1/2 hull for display only
However with your questions re keel placement & design I wonder if I am off track........do you have plans for the Colin Archer?.........Derek
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Hi Labougie
What length is your CA? I probably missed the figure further back the thread. I'm in the middle of building the Billings CA 414 which is about 4 feet long. That is reckoned to sail OK with no external keel and 6kg of lead shot in the bottom of the hull. That's what i'm going to do with mine. I've cettainly seen at least two CA models of this size sailing without external ballast keels.
Cheers
Guy
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Quick follow-up to my own post. Pictures of models of CA and lots of useful reference pics of the original here.
http://www.randen.no/
HTH
Guy
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No,no, she was always going to sail! The reason for only half appearing at a time is that's the way the Billings 606 is supposed to be constructed and knowing no better, I just went ahead and did it like that. For the doubters-
(http://i17.photobucket.com/albums/b58/labougie/DSCN3826Small.jpg)
She's 720mm LOA (excluding a bowsprit), 250mm beam and draught (from DWL so including ballast) is about 140mm - I don't think that's deep enough for what I have in mind which is a BIG cutter rig. I know she's supposed to be a ketch but like I said, she's a one-off, not a scale model. I want her STIFF!!!
Thanks Wideawake, I'll check that out.
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OK...thanks labougie...I would be inclined to join the two halves NOW.......with the premise that what you do to one side of the hull is mirrored [mirror reversed] on the other.... O0 ...just to evenly stress the hull as a one piece unit & minimise any distortion :-))
I would also reflect on the comments from 'wideawake'.......re additional keel ballast...remember the pendulum effect of the ballast mass being lower...makes for a very 'stiff' vessel as compared to ballast in a higher metacentric axis which increases the natural PORT to STDB roll....then we still have not considered the FWD to AFT placement ...which is another 'kettle of fish' %% :o.........Derek
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Derek - I have been sighting along the length of each keel half from time to time to check if there was any distortion going on and being pleasantly surprised to find very little - that's even with the two halves off the building board. However, after your post I put the halves together and found that although the stem and stern posts and the bottom of the keel are still fair, the tops of the internal keel are about 4mm apart amidships and require rather more than finger pressure to persuade them to meet. Hmm. Making the join is for sure the next move. I think I'll be cutting some slots into the keel in between ribs and using bolts and wing nuts to bring them together (dry run first, of course) on some Titebond. Many thanks for your very timely 'heads up'!
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OK labougie........
"the tops of the internal keel are about 4mm apart amidships and require rather more than finger pressure to persuade them"
If both sides of the stem & the stern are square & the lower keel meet ........ thats OK..... :-))
1) consider the addition of a wooden spacer between the hull halves
2) consider ....not 'using bolts and wing nuts to bring them together'...but only to gently position & hold the two hull sections together & not distort the hull O0
Could be a good location for a mass of that lead shot ballast encapsulated in epoxy resin {-) ....please keep us posted :-) ..........Derek
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Hi Labougie,
May I suggest before you glue the two halves of the hull together, make provision for keel bolts to hang your new ballast keel to the hull.
With my sailing trawler I'm hoping to avoid an external keel with the model being so big . . . . . . . but I'm adding provision just in case I need ballast low down while sailing.
My plan is to have 3 or four brass tubes set vertically in the keel to allow bolts to be passed up from the false keel into the hull and bolted from inside. The bolts will be a permanent fixture of the false keel.
In my case, this is so I'm not stuck with an ugly lump stuck under the hull when the boat is on its display stand.
The beauty of your building system is that you could do this while the two halves of the hull are separate as it will be easy for you to cut half circular grooves in the keel halves for the brass tubes, where as I have to very carefully drill up through a solid keel.
Also I notice you have a nice wide keel area - great for clamping a false keel to! :-))
The top of the brass tubes should be above the water line in the hull but if you don't have the space for that, just put a rubber grommet and washer under the nut when fitting to the keel bolts.
See sketch below.
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A thought on the position of the lead ballast at the bottom of the false keel.
Until you get the correct sailing trim by adjustment, make provision for the lead so that it can be moved forwards or backwards along the keel fin.
This way when the model is completed and sailing, you can fiddle about getting the correct trim by moving it forwards or backwards till your happy before fixing the lead bulb to the fin keel permanently. :-))
This whole false keel thingy means you could try different fin profiles and different depths of lead bulb below the water line simply by making a new keel to fit the boat.
Tons of variations but no alteration to the structure of the boat with each fin profile/lead depth change! :-)) ;)
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"consider ....not 'using bolts and wing nuts to bring them together'...but only to gently position & hold the two hull sections together & not distort the hull"
Derek - last night, I clamped the halves together at stem, stern and keel base and gently clamped at the keel top to bring them closer. Today, they're almost touching - in fact I think the only thing stopping them is the epoxy seepage from gluing the ribs into the keel. I'll clean that off and try again but you were right that the idea of bolting them together was a bit savage!
Greggy - splendid idea - I'll get some tube on Monday and let some in to the keel - if there's trial and error involved in setting up the keel/ballast then removable makes perfect sense. Thanks for the input, chaps.
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Cleaned up the epoxy seepage round the ribs and there's only a 2mm gap at the top of the keels amidships so perhaps I'll live with that and join them together with epoxy rather than Titebond.
Slots routed out for B&Q's very best 6mm brass tubing tomorrow. :}
(http://i17.photobucket.com/albums/b58/labougie/DSCN3831Small.jpg)
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Something else I need to know before cutting hatches into the deck is where the mast will step. The 606 drawings are of course for a ketch and have the mainmast at 37% of the way back from the bow, corresponding to frame station 4. I’m pretty sure I want a cutter rig – (undecided on bermudan vs gaff atm) – which I imagine will mean the mast being further back down the boat. Are there any guidelines for where a single mast ought to be?
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The simple belt and braces approach is to work out the centre of balance of the under water profile including rudder and balance this with the total centre of effort of the sails.
Trace the under water profile including rudder from the plans and cut it out of stiff cardboard. You need to balance this on a knife edge by laying it across the edge so that the knife edge is oriented 90 degrees to the water line.
With your hull shape it should balance roughly half way between bow and stern at the water line. Don't let the profile sag over the knife edge, fold concertina type creases forward and aft to stiffen it up if needed. Balance it horizontally and you have found the centre of effort of your underwater profile.
Next choose your sail plan and take moments about a convenient point (sail area times distance from chosen pivot point), say the end of the bowsprit. But first you need to find the centre of each sail as this is coincidered to be where the driving force of that sail acts from. So the moment of that sail is its area acting from its centre of effort times the distance from the end of the bowsprit.
Do this with all sails and the sum resultant is a distance from a point dropped vertically to the waterline at the end of the bowsprit. The resultant will be a distance from this point aft along the water line.
The centre of effort of the under water profile has to balance with the centre of effort of your sails and for your boat I would guess they should be close together with the sail area in front of the under water profile by a small distance.
This is called the 'lead', it is the distance between the plotted centre of under water profile and the combined centre of effort of the sails. It is usually expressed as a percentage of the water line length. With your boat and a chosen rig of gaff mizzen, gaff main with topsail, foresail and jib on a bowsprit, the sail C of E will be just in front of the under water C of E by 0.7 to 0.11 of the water line length.
Play about with sail areas at the drawing stage until you have this small lead of sail area over underwater profile.
If the sail C of E is too far forward the boat will turn away from the wind with the rudder central (lee helm) and if the Cof E of the sails is too far back the boat will constantly want to turn into the wind (weather helm) Slight weather helm is good, any lee helm is bad i.e. the need to put the tiller to leeward to keep the boat on the wind.
By altering the underwater profile of the completed boat, by changing your detachable fin profile fore and aft you can correct the above problems by experimentation - this is the fun of playing with sailing models :-)) ;) Or you could shorten or lengthen the bowsprit or change sail areas.
Changing sail plans on a completed boat takes more effort than changing the under water profile by means of altering the fin in my humble opinion.
The point I'm trying to make is that it isn't a total disaster if you get it a little wrong and the model can be modified by sailing the thing and see what happens and then take steps to fix it.
I did all the above while designing my model sailing canoe and found that I had goofed a little :o
To correct things I needed to make the mizzen sail area smaller to get the boat to balance (in my case it was easier to do this than move the dagger board and its case) I could have added a short bowsprit and a jib and this would have had the same effect.
Don't let your model building stall because your stuck for a sail plan and worrying if it all will work out! Choose a sail plan that you like and do the above so your in the right ball park and get the thing sailing! {-) O0
There two books I would recommend that describes things far better than I if you want to go into things at length, these are 'Yacht Designing and Planning' by Howard Chapelle and 'Elements of Yacht Design' by Norman N. Skene
Both are easy to read and with a little head scratching easy to understand. :-)) ;)
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To clarify my ramblings here's a worked example in my sailing canoe http://www.modelboatmayhem.co.uk/forum/index.php?topic=19576.0.
I did some research to find out what the lead was supposed to be for daggerboard type dinghies and canoes, I couldn't find an exact match but it was somewhere between 8% and 14% of the water line length.
Armed with this info I set to work.
My water line length on the model = 0.855m
The Centre of underwater profile using the cardboard balance method including daggerboard fully extended and rudder blade = 0.447m measured from the bow.
All my sails are triangular so finding the centre of effort means halving any side and connecting it to it's opposing corner with a line on me drawings, all three sides treated the same way cross over at the centre. This is the centre of effort or balance of the shape.
A simpler way of doing this is to cut out your sail profile from card (cereal box cardboard ideal and free!) and suspend it from a length of cotton, when the cotton is fixed at the centre the shape it will hang horizontally.
I took moments from the bow as it was the furthest point forward x the distance from the bow of each sail area centre as plotted on your drawings, all divided by the total sail area.
The fore sail is 0.044m2 x 0.136m from bow
The Main sail is 0.153m2 x 0.344m from bow
The Mizzen sail is 0.046m2 x 0.724m from bow
Total sail area 0.245m2
therefore 0.044 x 0.136 + 0.155 x 0.344 + 0.046 x 0.724 = 0.379m
0.245
This gives a distance of 0.379m from the tip of the bow dropped plumb to the water line and measure aft.
The lead is calculated as :- centre of under water profile - centre of effort of sails x 100
water line length
therefore 0.447 - 0.379 x 100 = 10.4%
855
The lead for this sail plan for my sailing canoe was calculated as 10.4%
In practice when the boat was sailed, this lead proved to be too small requiring me to reduce the mizzen sail area to 0.031m2 which when recalculated gave a lead of 13.2%
When chucked back on the water after the alteration, the boat sailed nicely with the helm central, when pressed she heeled and turned into the wind which I was happy with as this meant she'd rather go head to wind than capsize! :-))
All this ranting will give you the position of each of the sails and the masts they hang from and hence the position of your mast steps!
Phew! :-)) {-)
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Greggy - thanks for all that - plenty to inwardly digest. I may be having a bit of a break from the CA because I need to do a bit on my workshop - a heater and some weatherproofing in order to stop me working in (and thereby making a mess of) my kitchen!!
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Haaaa! I confess I'm a member of the kitchen table top builders brigade also.
K.T.T.B.B.'s unite! O0 :-))
I don't have a 'she that must be obeyed' :o as I've been single for years but do get the odd grump from the direction of my daughters when the wood shavings get to knee deep! {-) >>:-( <*<
The taking moments thing is easy after a little practice.
It's good to take a break once in a while on a boat building project, it can get a bit too intense!
Look forward to the continuing story when you next take up the batton! :-))
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The Dirty Deed is Done!
(http://i17.photobucket.com/albums/b58/labougie/DSCN3837Small.jpg)
Normal planking will be resumed as soon as possible.