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Mon Feb 15, 2016 12:40 pm

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PROBLEM SOLVED - Thanks for the suggestions. In the process of trying to make a new center line with laser,I found the out of line bulkhead!!!
Only discrepancy now is about 2mm. I guess I can live with that. Pretty much within my margin of building error.
George C.

Building a jig from plans out of 3/4" OSB is a lot of work only to find that after meticulous measuring to the millimeter, my diagonal measurement (corner to far corner) is off by 14mm, about 1/2". I cannot determine where the misalignment is exactly. Everything checks out from bulkhead to bulkhead and end to end but that diag. is off a bit. What I am wondering, since the boat is built on the bottom plank, is it safe to proceed?
I would have to take extra care in aligning the stem to spine, etc. since I cannot trust the centerline I have drawn.
All I can figure is that the jig bottom plank was off slightly when I did the join for a longer piece - even though I aligned with a laser line.
Thanks - George Cunningham

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George Cunningham
Franklin TN


Last edited by GeorgeC on Wed Feb 17, 2016 2:39 pm, edited 1 time in total.


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Tue Feb 16, 2016 8:33 pm

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George,

Sorry it has been so long without a response. I kept hoping someone with more knowledge would jump in, but....

1/2" not sure if that is enough to to make a difference in performance..., but I can say there were plenty of times during the build that in my mind I reverted back to, well I know that the jig was level and square, so .... So given my experience I would do everything I could to ensure that the jig is correct before moving forward. For me it almost becomes a piece of mind thing other than anything else. However, I am not sure it is necessary to be that particular. Probably some of my own OCD coming through there. Hopefully someone with more expertise will jump In here.

Marty



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Tue Feb 16, 2016 10:12 pm

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The side and end pieces can be exactly right but the matching diagonal measurements are what indicates you have a proper 90 degree rectangle.

How the pieces are joined will dictate if the bottom piece can be removed and things re-positioned.

If you proceed with the jig as is, then perhaps the following will be adequate:

If you shoot a perpendicular laser line forward from the true mid point of the aft end of the jig, it will hit the forward end of the jig slightly to one side or the other. That would be the mark upon which to align the center-line of the hull bottom sheet.

The center-line of the stern end of the hull bottom should be centered and square to that end of the jig.

The bottom rocker should still be accurate, and there would be a slight more hull overhang (of the jig) on one of the sides but that should not affect the garboard first set of planks.

Below are a couple of photos taken using an early jig design (Dec 2010).
Note, the stern end of the hull bottom sits on the high end of the jig's rocker.

Don't know if you would end up with any issues that I haven't foreseen.
Hope this is of some help.

Simeon


Attachments:
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fwd-IMG_4652.jpg [ 49.45 KiB | Viewed 1901 times ]
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-aft-early-jigIMG_4650.jpg [ 46.95 KiB | Viewed 1901 times ]

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Voyaging with Noddy, #11

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Wed Feb 17, 2016 10:35 am

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Simeon - Thanks for the suggestions and pics. So far, I plan to proceed as you suggest. I was just going to align the stern square with the bottom plank but shooting a laser line forward is an excellent idea. Actually shooting the dot forward might be more accurate. I find that, when projecting a line, the slightest rotation/tilt of the level skews the line one way or the other. I will try with the dot and see. Now I see the value of a self leveling laser level! - G

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Franklin TN



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Wed Feb 17, 2016 1:55 pm

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Location: USA Midwest Wis.

GeorgeC George take a square and check if the stern end of the jig is square to the sides. If that is reasonable square you are off to a good start. You know you are going to get this boat built one way or another I guarantee...

Next the stern first, see that your jig is level side to side. if it is, proceed every several feet and check level. If every thing is copostatic I think you are good to go.

The center line falls into line if at least one side of the jig is square to the stern. The bottom plank should even with the stern part of the jig.

Square and level and you are good to go.

Write on the wall " I am building a boat not a watch " Remember it it floats you succeed.

It is good to see another SCAMP built in the Midwest. Pete



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