Drawing the strongback centerline

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David James
Posts: 223
Joined: Tue May 11, 2004 9:04 pm
Location: Glenview, Illinois

Drawing the strongback centerline

Post by David James »

Hi folks

I just came up with what I think is a good idea (it worked well for me) for drawing the strongback centerline:

Monofilament is fishing line stretched nice and tight down the center of the strongback, held away from the top surface at each end with a shim about 1/16" thick. This enables one to check for "sag" in the middle (prevented, in my case, by eight 3/8" bolts in just the right spots) and also keeps the line away from the surface along the full length, thereby ensuring its center position at any point. Next, and this is the cool part, a strip of carbon paper, say 1" by 2', is slid under the fishing line wherever the center line needs to be marked. Then I took a pice of hardwood about an inch wide and six or so inches long and smacked the line down against the carbon paper. Then it was an easy matter to join the carbon lines with a straight edge.

What do you guys think? I'd be glad to know I made a contribution for a change.
Dave in Glenview Illinois
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Dean in Eureka, CA
Posts: 267
Joined: Mon May 10, 2004 10:23 am
Location: Eureka, CA

Post by Dean in Eureka, CA »

Hi David,
That sounds like a pretty fast way! One thing I found out though, is a sharp crisp line made with a mechanical pencil is much easier to reference to. Something I had to do with my centerline was to extend the string line out past the ends of the strongback and I clamped the string to vertical plumbed stations about 30' apart. After setting my forms up the first time, I noticed that my stem stations were warped. What I like about this new set up is, I can change my string line height at will.
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Dean in Eureka, CA
David James
Posts: 223
Joined: Tue May 11, 2004 9:04 pm
Location: Glenview, Illinois

string line height

Post by David James »

hey Dean, thanks for the feedback

if I understand you right, you're able to vary the string line height and in doing so, as you set up the stations you can adjust the height of the string to just over the station being positioned and therefore be more accurate? And did you use a plumb bob to check the stem molds? I've read a lot of what you have posted and I appreciate your help. Thanks also for the "pecan floorboard for stems" advice.

Dave
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Dean in Eureka, CA
Posts: 267
Joined: Mon May 10, 2004 10:23 am
Location: Eureka, CA

Post by Dean in Eureka, CA »

Hi David,
Since I had previously set everything up, I had a good idea how to go about this when I relocated my strongback to get the one end away from the sun coming through a window.
I set my string line stations up first 30' apart. It took some time getting both of them trued with a plumb bob. They go from the floor to the ceiling. Then I set the string line at the height of the top of the strongback and moved it into position, then anchored it to the floor. Then I moved the string line up to the height of the #0 station. Next, I set up my stem stations and now with the string line extending past the stem stations, I could see that one of them was way off center out at the bend of the stem, the one that had been exposed to the sun. It had a pretty good warp in it. I made the adjustments, then worked my way in towards the middle of the boat. I used a 3' level to set my stations up, along with using the string line as a top reference point. After everything was set up. I checked the centerline, by sighting down the string line. I also checked the rocker by measuring down from the string line to the top of the stations. Then I attached a scrap piece of wood to the top of the stations to make sure the spacing was right with 1" finish nails, leaving the heads expossed to remove them easily when the time came. I then moved the string line up 3/4" so that it didn't catch on any of the nail heads.
Hope this helps.
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Dean in Eureka, CA
David James
Posts: 223
Joined: Tue May 11, 2004 9:04 pm
Location: Glenview, Illinois

string lines

Post by David James »

Hi Dean

thanks again for your time

I was out in the garage attaching my station blocks this afternoon when I thought, what the hell, let's see how things are looking so far: I set the first four station molds in position and was suprised how far off things look. I spent a good bit of time over the winter carefully cutting and sanding these seventeen stations, (Freedom 17, with #8 being the center station) so I was a little bummed out by what I saw. I do realize that I'm not building a rocket after all, but I like things right. I think I understand your method and will give it a try when the time comes to fasten the station molds. You're sort of setting up a "plane of reference" to go by. I'm not afraid to spend the time needed to set things up. I keep hearing that the stripping of the hull is the fun part; this is my first boat, so we'll see!

by the way, I got a nice crisp line from the fishing line-carbon paper trick!

Dave
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ealger
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Joined: Sat Aug 14, 2004 5:14 pm

Strongback center line

Post by ealger »

Another way to mark the center line on a strong back is to stretch some 60# monofilement line, from end to end flush with the top of the strongback, and then lightly spray over the line with black (or the color of your choice!) spray paint. Cotton string will work as well but I think the mono makes a crisper line.
Ed..
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Bryan Hansel
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Location: Grand Marais, MN
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Post by Bryan Hansel »

I'm with ealger and the spray paint. I just use standard construction yellow nylon string and stretch it as tight as it can be, and then I spray paint it. Works like a charm.
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