Author Topic: How do I adjust imperfections, what is normal?  (Read 3563 times)

Offline narvik

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How do I adjust imperfections, what is normal?
« on: July 28, 2013, 02:03:47 PM »
OK, bottom is placed on the stringers, sides are on. The building jig and stringers were perfect and the bottom went on without problems. When checking the chine to shelves distance at various points I found the first imperfections. (I measured left versus right, or port versus starboard) A couple of rounds with a straightedge and level + laser helped, but there are still some imperfections. I can live with that, but I want a somewhat good looking boat with nice lines. Most of the chines will be underwater (at rest), so what....
But while I continue the build, I will not see the shelves anymore, they are covered by the side panels. I do not know how to adjust for possible imperfections.
My idea is, that the spray rails and the shelves should give a fine and harmonic line. How do I place the spray lines without seeing the shelves? I am afraid that the chine is not the most reliable reference.
Next question: After turning the hull, how much can I adjust when capping the shelves with ply? I stretched the hull and there is some sagging of the shelves in-between molds. I placed some clamps to adjust, but still not perfect. Will the capping adjust for smaller problems with the shelves?
Might seem like a paranoid question, but normally I am used to work with very small details, even 1/10Th of a millimeter matters. Maybe I am not relaxed enough.
What are your reference points to get a fine finish?
How do I react to possible asymmetry or imperfections?

Thank you
Peter
« Last Edit: July 28, 2013, 02:21:53 PM by narvik »

Offline Dave Wright

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Re: How do I adjust imperfections, what is normal?
« Reply #1 on: July 28, 2013, 05:16:30 PM »
First, congratulations on getting the bottom on without any problems. When I placed the bottom on my old standard I couldn't believe that using my weight for a force fit was a good way to go. Now after doing the same thing on my widebody, I still don't think it's a good way to go, and I wouldn't do it again. Same with the bow stem fit up. If you get an exact bow stem fit prior to securing the bottom, your weight forcing the bottom onto the stringers up forward will ruin your perfect bow stem fit.

There are all sorts of ways to get symmetry, but since no one can see both sides of your boat at the same time you should relax and let things go a bit. These boats are not set up to be exacting pieces of art. On my standard I had visible differences from side to sided on both the chines and the shelves. The only person who noticed and commented is a friend who is a naval architect and a perfectionist (almost crazy perfectionist) no one else noticed. On my current widebody build I'm taking side to side measurements of chines and shelves from centerline, and up from my reasonably level concrete floor. If it's any consolation, I've decided that any measurements within  3/4 of an inch are good enough. And when I'm finished I won't be dissapointed if I've done worse than this in places. Keep on building and call it good enough.
« Last Edit: July 28, 2013, 05:20:58 PM by Dave Wright »

Offline adam_k

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Re: How do I adjust imperfections, what is normal?
« Reply #2 on: July 29, 2013, 06:08:08 PM »
Peter,

Re; spray rail symmetry.  I measured from the chine, and was happy with the result.  I made a mistake on one side, and ended up grinding off the entire spray rail.  That was a bummer.  I agree with Dave's comment about 3/4" tolerance.  My hull isn't entirely symmetrical, the only way you would know is if you measured it.

Offline kenF

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Re: How do I adjust imperfections, what is normal?
« Reply #3 on: July 29, 2013, 07:18:14 PM »
Spray rails- measure from the chime. Too many reference points and it get too much to keep track of. Pick either the top or bottom of the chine radius an stick with it. Close your eyes every so ofte an run your hand across, feel for a smooth transition. this is also a good technique for fairing and sanding.

Offline Dave Wright

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Re: How do I adjust imperfections, what is normal?
« Reply #4 on: July 29, 2013, 09:47:22 PM »
I'm at the point where my next task is to put on the sides. I haven't scarfed or glassed the insides of the sides yet.

How I came up with my 3/4 inch acceptable tolerances:

Right now when I take measurements at the middle mold for the heights above the shop floor and the measurements off centerline for the chines and the shelves, all dimensions are within a 1/4 of an inch for right side versus left side. However, I know that when I put the sides on there'll be lots of pushing, pulling and twisting. It may well cause a deviation of a quarter of an inch on one side, and a quarter of an inch in the other direction on the other side.

This would easily give me 3/4 of an inch deviation from side to side. If it's a real hot day and I'm hurried and frazzelled there might be a hell of a lot more twisting going on. I think anything within 3/4 of an inch side to side is very good on this sort of amateur construction.

Offline AlasKen

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Re: How do I adjust imperfections, what is normal?
« Reply #5 on: July 30, 2013, 02:55:07 PM »
I have to laugh as when I built my Jumbo I would often tell my son cut it just under 5" or just proud of 2 1/2".  My eyes got so in the shadowed confines of my shop I could not see my tape well enough to see more than the inch marks.  3/4" tolerance sounds good to me.  I think you will find that after you get it out of the shop ond on the water that the lines look perfect.  Enjoy.  Ken 
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Offline pfithian

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Re: How do I adjust imperfections, what is normal?
« Reply #6 on: August 08, 2013, 06:33:54 PM »
When I placed the bottom on my old standard I couldn't believe that using my weight for a force fit was a good way to go. Now after doing the same thing on my widebody, I still don't think it's a good way to go, and I wouldn't do it again. Same with the bow stem fit up. If you get an exact bow stem fit prior to securing the bottom, your weight forcing the bottom onto the stringers up forward will ruin your perfect bow stem fit.

This is one of the problems that is completely eliminated with the Alternative Build Order method that I used.

The fit of the bottom panels with the stringers and stem required almost no forcing into shape.

See https://fishyfish.com/boards/index.php?topic=701.0
Made It Jumbo 25
Skiffkits No. 7025 1/2009
Build Start:  3/2009
Hull Flipped: 1/31/2010
Maiden Voyage:  9/16/2011

Offline Dave Wright

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Re: How do I adjust imperfections, what is normal?
« Reply #7 on: August 08, 2013, 08:06:23 PM »
When I placed the bottom on my old standard I couldn't believe that using my weight for a force fit was a good way to go. Now after doing the same thing on my widebody, I still don't think it's a good way to go, and I wouldn't do it again. Same with the bow stem fit up. If you get an exact bow stem fit prior to securing the bottom, your weight forcing the bottom onto the stringers up forward will ruin your perfect bow stem fit.

This is one of the problems that is completely eliminated with the Alternative Build Order method that I used.

The fit of the bottom panels with the stringers and stem required almost no forcing into shape.

See https://fishyfish.com/boards/index.php?topic=701.0



Agreed, the entire build order could be adjusted to simplify, reduce labor, eliminate built in force fits, and take full advantage of stitch and glue methods. On the other hand, the very loose form and procedure allows builders to increase length to almost any degree without input from the designer. Same with house and interior arrangement. In some cases side height has been increased too.

I think the way things have gone, the definition of a Tolman hull is now any ply / glass hull with forefoot and transom formed per book dimensions, everything else is open. It's probably part of the attraction and appeal, anything goes. ;D