Half Patterning

[timtheboatguy]

I have read here that some of you folks only make a half pattern for boat tops, covers etc. How do you maintain a perfect center line so that when you flip the pattern to make the other side everthing is correct?

[Peppy]

When I'm making an enclosure I like to make the frame myself. I can do every step perfectly and that makes it way easier when it comes to 'T'ing it up.

I mark the center of the bar precisely then the bend marks.
I bend the bars and make sure the crown is symmetrical and the legs are equally flaired and parallel.
When I cut the bars I make sure to cut flush or undercut so my kerf doesn't wander and cause the bar to grow 1/4".
I make sure the deck mounts for the main bar are parallel to the back of the boat (or splitting the difference with the window if it's goofy)
I make sure all the bars are fully in the fittings and not hung up on the set screw or some shavings and the jaws slides are set the same.
When I tension the frame I make sure I haven't put more tension on one side than the other, and haven't pulled down one side by accident.

Usually ( if you've done every step rIght) it'll line right up with tape strung down the center lines to the window. Even if it is little off (the line bends from bar to bar)  it'll still work out as long as you haven't slid off center. Then it'll be too small. A bent center line makes wrinkles. But, if its all T'ed up and you see something out of whack fix it before you make the pattern. Figure out which bars are good (centered) and figure out why the other bars don't. It's probably something you did wrong earlier.

A lot of it too is the laser eye. It's right when it looks right. You can measure all day but if the line of tape looks straight/centered it probably is.  

Oh and you don't flip the pattern. You lay the centerline on a fold and cut out both sides at once with a hotknife. What did you think we were making 1/2 a pattern for anyway?

;P

[Mike]

A mooring. COver or snap on  cockpit. Cover ill half pattern it if its on a boat lift  the only way working from inside the boat. I find the center of the bow center of the window or console window and then the stern i run a piece of strapping tape from the. BOw to the window or. Center console  then the transome  pulling the pattern the tape can be deflected to one side , so some side  to side tape to bold it center will belp.  

[Tejas]

Establishing a perfect center-line probably assumes a perfectly symmetrical boat, which might not always be the case.

Assuming a close-enough symmetrical boat, measure the same distance from the same port and starboard features such as cleats to a foot or two off-center on the aft- or fore-most frame-bar. The midpoint between these two points should be on the center-line. Repeat for the other frame-bar, and these two midpoints should define the center-line.

[timtheboatguy]

Thanks for the input here, and Peppy, that heart just says it all!   ;D

[DBR1957]

Mike - You must live in canvas Utopia where the previous canvas riggers put snaps in the hull
in the exact same spot on each side.

If I did a half pattern on a bow or cockpit cover one side would be way beyond the snaps or
fall very short.

[Peppy]

Just like cutting snowflakes, eh Tim?

DBR- you just need to make sure to make it on the 'big' side. If its really terrible then you just need a trim on the non pattern side. 95% of the patterns I make are 1/2. It's really only the goofy dodgers or bow covers I make whole patterns for. Come to think of it life is pretty idyllic.

Establishing a perfect center-line probably assumes a perfectly symmetrical boat, which might not always be the case.

Assuming a close-enough symmetrical boat, measure the same distance from the same port and starboard features such as cleats to a foot or two off-center on the aft- or fore-most frame-bar. The midpoint between these two points should be on the center-line. Repeat for the other frame-bar, and these two midpoints should define the center-line.

Why don't you just measure to the center mark on the bar? Why a foot to each side? And if you use this method to find a center line it seems like you might find a line that isnt in the center of your bars. It's really terrible when that happens, if you're a 1/2" off center of the bars you're main top will be 1" to small. I always stick to the center marks on the bars and manhandle the bars to the center of the boat or close enough.

Yes boats aren't perfectly symmetrical, yes the previous canvas guy was maybe drunk installing the snaps, yes it takes time T'ing up the frame and making everything right but it's worth it for the time saved patterning and drawing the lines on the non-pat side and you only have to cut out half the boat top.

[Tejas]

Peppy,

The purpose of the technique described was to establish the center-marks on existing frames. These center-marks should be on the center-line of the boat. If the boat is not symmetrical, including the reference-point features used, or the frame-bars are not symmetrical, then the boat center-line might not be all that useful for half-patterning.

[Peppy]

When I make a pattern on an old frame I always measure the bars from each end cap to center, on each bar. I check the bars at that point for symetricality, flair, and that the legs are parallel. I also stack the bars with the centers lined up to see if anythings out of whack. Then I put them back on the boat and proceed as normal. Some times I find the last guy cut 1/2" (or more) extra off one leg. How do you know that if your just measuring to the bars from the boat? If you only measure from the boat you might be off on the bars, which as I said before, will multiply your error.

I worked with a guy that worked in a boat factory as the guy who put on trim pieces and cleats and whatnot. I can assure you that there was no science to his instillation of anything. If you were measuring from cleats he installed you may be better off picking a number from a hat. That's also why I say you can measure all day long. Shoot your laser eye on it, when it looks good it's good. Remember we're not making it out of sheet metal.

[Mike]

Mike - You must live in canvas Utopia where the previous canvas riggers put snaps in the hull
in the exact same spot on each side.

If I did a half pattern on a bow or cockpit cover one side would be way beyond the snaps or
fall very short.

DBR most bost i do is a mooring cocer snf ill pattern half the bost and depending on the eind if sny eill determine wich side.   A cover like this ill do on a lift or on a trailor its just faster.

http://i782.photobucket.com/albums/yy102/Mike8560/covers/4940ae83.jpg
And most dont have snaps  yet on a new job that never had a cover.if there was  one  i.  Check the snaps if they are questionable i do hafl each side  from inside the boat  in the lift if its on s trailor i like to blank but have made full plastic patterns.  Somtimes the snapr
Look good snd ill half pattern like tbis deckboat i did half sorking crom in the. Ost Nd to instAll snap i had to work sitting on the canal side  lift i beam.
http://i782.photobucket.com/albums/yy102/Mike8560/covers/c79ff1fb.jpg

A full top and enclosure i to the whole thing
Oh and yes boats in everybodys backyard and yearound boating. Ya canvas utopia

[Peppy]

You must live in canvas Utopia

You know, I never really thought about it but you're right! Looking through my old pictures I found one to prove it!



Them cherubs must be why it turned out so well.

[fragged8]

man i'd give my left knacker to be able to work inside all year !

Pepster, when cutting two pieces of fabric together how do you overcome the lower layer shifting and ending up bigger than the top ?


you'll laugh at this but I only just realized this week who Devin is on my facebook contacts hehehe

Rich

[Peppy]

man i'd give my left knacker to be able to work inside all year !

Pepster, when cutting two pieces of fabric together how do you overcome the lower layer shifting and ending up bigger than the top ?

Use a lot of weights to hold down the pattern and cloth and cut with the hot knife. You have to go slower and pull the waste away as you cut. If it's topgun or something you don't hot knife cut the top layer first then the bottom layer. Of course you loose the 1/2 cut for free aspect of the double cut, thats why we use so much sunbrella.

  you'll laugh at this but I only just realized this week who Devin is on my facebook contacts hehehe

Ha! It works perfectly then! A customer will never find a 'Peppy' in the phone book!

[Mike]

Well heres. Y first full enclosure half pattern.
I bent the frames so i knew where the. Centerline on the. Owa were a s due to winds it was easiers to only balf pattern
Photo
photo2

[Peppy]

Go Mike! You didn't let fear or common sense hold you back! I'm real proud of you Mike!

Did you double cut it too? Baby steps.... there's always next time.

So what'd you think? Is it worth doing it that way? I know you get the anxieties after the pattern, did this make it worse?

Any trims?

Will you do it again?