Foil Alignment

23/01/2010 11:29:34
Anyone know how the boatbuilders get the centreboard and rudder aligned and vertical?

24/01/2010 10:54:09
I've always used tape measures, lots of care and attention, and mk 1 eyeball. Rudder of course just has to be in line with the board, so turn the boat upside down: simple enough. Locating the plate case can be quite a can of worms, because boats - especially if one is rebuilding an oldie, are very rarely absolutely symmettrical and it may be necessary to compromise. I figure the relationship with the mast is probably the key one.

24/01/2010 15:08:40
Thanks Jim, was thinking along the lines of a string line from stem to transom, setting up level side to side on the thwart (upside down) and dropping a plumb line down the transom from the keel to the transom top. 
On a hog stepped boat, I suppose you could put a plumbline down from the middle of the step to the middle of the mast gate. On a deck stepped boat it maybe less simple.

Getting the foils absolutely perpendicular may be less critical than getting them both in line? Or is the opposite true?

24/01/2010 20:20:04
The question is - How will you tell if they are not aligned?  The answer is by looking at them.  use the same technique to align everything.  I take the centreboard out and replace it in the box the otherway out with the boat sat on the trolley.  I then line the rudder up with this.  I initially stick the pintles on with double sided tape.  Once in place i then carefully drill, taking time to check things as i go.  Measure three times, drill once....

I think the hardest and most important thing is to get the mast in line with the cboard. I also do this with the board removed and then placed the case upside down.

24/01/2010 23:29:52
Thanks for the good advice 'eyes' - I acknowledge the idea of a visual alignment check (or backed up with string lines) - the problem I was struggling with was getting the relevant bits arranged for comparison - the idea of putting the centreboard in from outside hadn't occured to me to set the mast / vertical 'datum' - thanks for that. Once that is set, the comparison with c/b and rudder is more reliable.
Knew there must be a practical way of doing it!

25/01/2010 11:08:36
If you are turning the boat upside down why not set it on carpeted trestle - a couple of workmates eg. and then push the centreboard up from underneath.  Then you will have the precise alignment of the board as it will be when it's in the water.  Get the rudder alignment from that.

25/01/2010 13:10:04
Hi Puzzled, 
I think the point that the previous contributors were making is that it's important to first verify the mast and centreboard are both on the centreline of the boat and that they are vertical. Once that's done as you say, its straightforward to invert the boat and compare foils by eye or by string.
I'd originaly thought of using the thwart as a horizontal datum, but others reccomend the mast is used as a vertical datum - I'm happy to accept thats a better way of doing it.

25/01/2010 13:17:21
Keith Callaghan
Laurie Smart builds the case into the hull jig, so he can guarantee that the case is vertical in the boat. Unless the builder of your boat can tell you he did likewise I would certainly not assume that the case is vertical - and I would definitely not assume that the thwart is horizontal!

25/01/2010 13:24:03
Richard Battey
The case is the first bit of the boat to be built. Everything else is built around that, as Keith points out, to guarantee vertical alignment, etc,etc.

25/01/2010 20:54:51
2 points

if you do it upside down the rudder has an annoying habit of falling off the pintles - and they are only gently affixed themselves. Right way up having got mast and board in line first is best.

I doubt Winders build the centreboard case first for their tupperware boats.

25/01/2010 21:37:38
Andy Hay - 3626 Business as Usual
There was a photo sequence in a recent magazine showing the Winder build method. This showed that the case went into the hull moulding at skin stage on the plastic boats. That way it is structurally part of the hull skin. The case capping is part of the internal moulding that includes the bow tank.

26/01/2010 09:09:46
I would have thought it very unusual for any Merlin to have foil alignment problems, as they are generally built so well as the boat builders reputation hang on their craftsmanship. If the boat is very old, I can imagine you would have doubts.  

But if the hull is a modern design by one of the reputable Merlin builders, I would have a time issue going to all the trouble, when there's time out on the water getting mileage under the hull. Am I missing something, but what drew you to the conclusion that your foils could be misaligned?..

Or is it just the usual Winter of discontent/paranoia/bimbling disease gnawing I get it too, my buoyancy bag straps are the wrong colour, as they clash too much with the toestraps. Worse, white dyneema is so last year, black/grey is this years' colour, as it matches the hull. mm, must put some texture into the colour combination somewhere too.

Yes too little sailing time does this.

26/01/2010 09:45:48
What colour are your toe straps Tim, that they clash so badly with your buyancy bag straps, and who chose them in the first place? LOL

26/01/2010 13:12:36
Here are some snaps of me doing this on my 12 ... maybe useful

26/01/2010 14:32:35
err..the bag straps are red..and the padded toes straps grey..the yellow bags are a colour clash disaster

I don't want to hijack this serious thread though with winter frivolity, however I thought about covering the toe straps and bags with some zebra print stretch lycra, to offset the carbon It's London fashion week soon...

26/01/2010 20:51:18
Thanks for sharing the pictures Rick - thorough job and as they say, a picture is worth a thousand words.

26/01/2010 21:52:28
I knew I needed a garage - now I know why!

27/01/2010 10:17:22
Andrew M
One one occasion when I was taking Heaven Sent to Laurie's shed he had Luka, the retro Passing Cloud in being redecked etc for Mike Stephens.  Several things were not in line and the shroud attachments were not in the same place.  He was using the string down the centreline method to align everything.  I have previously described a simple way of determining if your mast is perpendicular to the side decks.  Cleat your main halyard at the point you can just touch one side deck by the shroud attachment with the end of the rope.  Go round to the other side and see if you can do the same.  Adjust shrouds till this is achieved.  If you do this and then check the C/B by eye you will not be far out.

27/01/2010 12:25:08
Garry R
Provided your older hull isn't twisted then the halyard method works well!!

27/01/2010 23:49:07
>  I have previously described a simple way of determining if your mast is perpendicular to the side decks. 

That considerably begs the question though doesn't it? If the boat has moved over the years then, especially in a boat as open as a Merlin, the side decks are probably about the least useful datum points... If the board case is fixed I'd use that as the datum, but if you should be replacing the case then you probably want to level up the boat using a good number of points below the waterline as reference (one situation where your clinker construction eases the task considerably), averaging them all out, and then use a spirit level to get the case perpendicular to the averaged waterlines. I'd then look to position the shroud anchors symettrically to the case without worrying what the actual decks were doing.

27/01/2010 23:49:42
Oh yes, a laser level is a dead handy bit of kit for these alignment games...

28/01/2010 10:44:27
Ask yourself these question, do I keep the boat upright all the time, the answer will be no, so does it matter if the mast is a bit off? What is vitally important and in so many wooden boats that were not built with the case in the mould the answer is no. is is the plate case in line fore and aft. Thats the big one.
If the rudder is a bit off centre does it really matter given we are always wobling it about anyway?


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