How to level a cambered surface ??

Discussion in 'Fiberglass and Composite Boat Building' started by pescaloco, Jan 1, 2009.

  1. pescaloco
    Joined: Feb 2006
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    pescaloco Senior Member

    Ok, thanks in advance guys

    Here is the senario, I want to fair the crown / camber in the front of the trunk cabin on my one off pilothouse. I can see visually that the line is not right

    the pilothouse is foam core over a male mould, that sits on a wood platform.
    Over the considerable time I have worked on this, the platform has saged, and I think the frame jig may have got a little out of square from draging it.

    So I need to establish level, would you take say a long aluminum bar, ballance in the front center (like a teter toter) then put a carpenter level on the aluminum, Then measure the gap at the outer edges of the aluminum.
    I hope that makes sense the way I have explained
     

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  2. Eric Sponberg
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    Eric Sponberg Senior Member

    Pesca--
    Another way to do it is with a water level. This may work better because you can get to any part of the structure and see if it has sagged or hogged. You need a large jug or bucket of water and a long clear plastic tube. The jug is placed at some point near to the known reference point that you want to call the master level point. Set the water jug on something near in height, but a little below your master level point. Fill the water jug with water and place one end of the plastic tube in the water and suck water into to the tube like you would a siphon. You'll see that the water level near to the other end of the tube, which you hold next to the jug is at the same level. Take the free end of the tube to your master level point, and continue filling water into the jug such that the water in the free end of the tube is at the level of the master level point. Now you are set with where level is and can check any other point where the tube will reach. Take the free end of the tube to any other point on the structure where you know it should be the same level as the master level point. The structure may be above or below the water level in the tube. Mark the structure with a pen at the water level and measure how far up or down you have to shift the structure at that point. Go around the structure until you have marked all the level points you need to, and this will show you how the structure has moved. Adjust the structure accordingly bringing it back into line until all the level points are at the same level as desired, according to the water in the free end of the tube. You can keep checking with the tube until you are back in alignment.

    I hope that helps.

    Eric
     
  3. pescaloco
    Joined: Feb 2006
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    pescaloco Senior Member

    Eric,

    Thanks for the heads up, I have never used the water level meathod. I have heard of it but was not sure how it was employed.

    I think I now understand the concept, and will give it a try.
     
  4. PAR
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    PAR Yacht Designer/Builder

    I use to use water levels all the time, marking soles, aligning stringers, painting LWL's, etc., but now I've been using a laser for several years and couldn't think of an occasion when I'd want to dig out my old vinyl tubing and fill it with water.

    When working with a surface and the level is sitting on it, you just measure down from the beam to the surface. Subtract the height off the surface the beam is and this is the amount you're out. It's more difficult to describe than actually do.

    You can use a cheap torpedo level, but you have to manually level this, which is a pain, plus it just shoots out a pin point or beam. This isn't particularly useful. I have a couple of lasers, one is a fancy rotating, self leveling deal, that cost a lot. It's dead nuts accurate, can be raised and lowered, still maintaining it's level and it swings a line 360 degrees, which is darn handy. I bought this for use on larger boats and in direct sunlight.

    The laser I use most often is much cheaper, is also self leveling, but doesn't revolve. It can cast a line about 10' in daylight or about 50' at night. It can be adjusted to throw a pin point, crosshair, vertical or horizontal line. This cost about $50 at a big box store and though not as accurate as the high dollar rotating version, is just fine for about anything a boat might need.
     
  5. TollyWally
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    TollyWally Senior Member

    I own 5 different laser levels, they've totally changed the way I work. But that being said, I often use a water level, depending on the situation it is often more accurate and easier to use. You can use it around corners, in bright sunlight, etc..

    You can get an adequate laser for $100.00 or so and build a bitchin water level for $10.00-15.00.

    I prefer 5/16 to 3/8 clear hose. A little food coloring is nice. If you leave the water in the hose too long you may get some funky algae growth. A little bleach will cure that. I get the syphon going and then add bleach.

    Once you get the hang of a water level or purchase a laser you will use it all the time. Probably more information than you need, good luck with your boat.
     
  6. pescaloco
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    pescaloco Senior Member

    Thanks guys, I will look into a lazer as well

    To give a little more insight into my concerns. I don't like the looks of the top front of the trunk section the slope of the lines doesn't look even, my 2 front most corners measure with in 1/8 inch or so by using a straight edge and tape measure down to floor. But when I look at the lines it looks much more so off.

    My big concern is that the slight out of level of my floor combined with any out of level or square of my frame jig, then combined with any hills or valleys that were induced from installing the foam panels and then glassing, that I may have messed up.

    It measure close but looks way off, is the best way I can describe it
    So how at this point does a person go about grinding a fairing I feel like it is seat of the pants aproach, and ofcouse the looks change depending on the angle at which it is viewed (even worse my work area is a tight space and is hard to get a good perspective)
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    It sounds as if you have two basic issue to solve. The first is to restore the "square" to the build. This makes using the laser and water levels accurate. The second issue is fairing curved surfaces. The short answer is filler and a long board. Using a notched trowel to apply the first lavers of filler can speed things up considerably. Working the long board along the axis of the camber will insure it levels nicely.
     
  8. pescaloco
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    pescaloco Senior Member

    thanks Par

    I just want it a perfect as possible, I think lack of ability to stand back a get perspective on all sides is making it hard.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Unfortunately, fairing surfaces (making them smooth) is a matter of lots of practice. Learning how to identify high and low spots, techniques to deal with them and methods that help eliminate making more as you attempt to smooth the surface, all require a bunch of prep time. If you spend 100 hours to prep and finish a surface, 95% of the effort will be the smoothing process, with the remaining 5% priming and finish coating.
     
  10. pescaloco
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    pescaloco Senior Member

    Par,

    Thanks for the help.

    for flats I have allways used a 45/45 cross hatch with a long board.
    On a crown or camber I have little experience, when you say the axis do I start at the front most corner of the trunk section then stroke in tword the middle at a 45 degree angle, then move higher up the side and then again draw the long board in a opposite 45 degree motion ? Or do I need to sand from the edge at 90 degress working into the center of the crown ?

    Mark
     

  11. Dutch Peter
    Joined: Aug 2004
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    Dutch Peter Senior Member

    To get a good read-out, put some whiskey (just a little!!!!) on top of the water. I was told they used to do that in the old days with the inclination test of a vessel.
     
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