Fairing molds questions...

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Grumple
Posts: 108
Joined: Thu Jul 03, 2014 7:38 am
Location: Halifax, Nova Scotia

Fairing molds questions...

Post by Grumple »

Hi Guys,

So progress has been very slow since Christmas, but lately I've had some good time in on the Canoe project. I finally got my strong back together, and just finished initially setting up all of my forms.

In terms of measurements and eyeballing, everything looks great! Now comes the fairing process...

My initial checks on rocker, etc, seem to be fine, the strip I put in place along the keel line to hold the molds plumb follows a nice shallow curve as expected, and touches all mold tops along the way.

After a few slight adjustments, I was able to run a few scrap strips the entire length of the canoe at the approximate location of the first strips (ie starting at waterline on station 0, staying roughly horizontal towards stems). I used a few of my 'stapleless' wooden clamps at the bow/stern and center molds to hold these test strips in place, and they hug the molds nicely except maybe a few spots being out by no more than 1/16" of an inch.

I've ignored the stem here as I haven't shaped them at all and so wouldn't expect the batten to lay across them correctly.

However, when I use a shorter batten to test for general fairness (ir 6' long strip), I am seeing some strange things. For example, on the model I'm building (Huron Cruiser), there are 13 station molds (center mold, and 6 molds in either direction towards the stem molds).

If I place my batten roughly horizonal in various places along the curve of the canoe, and stretch out so that I am holding one end against station 1 (just past center mold), and holding the other against station 5 or 6 near a stem, I can see pretty big gaps between the batten and the mold edges in between (ie 1/8 - 1/4"). It's identical on both sides of the canoe. If I generally check along just any 3 molds (ie hold the batten on any two molds straddling one in between) then it follows the edges nicely.

I've double checked everything i can think of to account for this, and so far everything checks out. The strong back is leveled well in both directions, the molds seem plumb and I was very careful creating my upper and lower center lines.

I'm hoping this is just something like what I've heard described as 'cheeking', or maybe not accounting for the twist the batten would normally take along some of the tight curves, or maybe just generally misunderstanding how to check fairness. It seems strange to me that the battens follow the molds so well at keel and at the sides near where the gunwales would be, but be 'out' elsewhere, and in equal amounts on either side.

However, I'm also worried there is something I'm missing, and I don't want to get halfway through stripping to realize it is actually a serious problem.

Here are a few photo's I took last night of my setup so far. I didn't get any of the fairing issue itself though.

http://imgur.com/18KQQe2,k4dCDsU#1
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Grumple
Posts: 108
Joined: Thu Jul 03, 2014 7:38 am
Location: Halifax, Nova Scotia

Re: Fairing molds questions...

Post by Grumple »

Just to follow up on this, I did some more investigation tonight when I got home from work.

If I hold my strip against the edges of station 4 and 6 following what I think would be the right lines horizontally, the strip just barely comes up against the edge of station 5. There is more of a curve coming off of the previous stations, so when I am holding my batten at the edges of station 1 and 6, it floats of of station 5 because of this greater curve generated near the center of the canoe.

This seems less strange to me now, and it seems like maybe if I were clamping at each station, the curve would just shallow out noticeably between stations 4 & 5, then turn into a bit of a cheek from station 5 towards the stems.

Does this make sense? :thinking
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Patricks Dad
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Joined: Wed Oct 13, 2004 1:11 pm
Location: Warrenville, Illinois

Re: Fairing molds questions...

Post by Patricks Dad »

Just from skimming your descriptions, I think you're just fine. Try clamping at each station and see how it looks (both sides).

As for the first strip, I always line it up with the sheerline amidship and a 2 or 3 stations out from their (both directions). Then I let it droop naturally (rather than keeping it level or bending harder to follow the sheerline the rest of the way. I find this approach strikes a natural balance between the two extremes (exactly parallel with the waterline or banana shaped following the sheerline).

Have fun with your build!
Randy Pfeifer
(847) 341-0618
Randy.Pfeifer1@gmail.com
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Grumple
Posts: 108
Joined: Thu Jul 03, 2014 7:38 am
Location: Halifax, Nova Scotia

Re: Fairing molds questions...

Post by Grumple »

Hi Randy,

That is really good to hear, thanks! Sorry for the long-winded post but I wanted to make sure I was giving a good description of the situation.

After reading your response I realized I screwed up terms in my original post...my test strips were placed roughly as you described...starting at the sheerline amidship and traveling ~horizontally towards the stem.

It's been a loooong time getting to this point. My friends get a huge kick out of the fact that I've been 'building' a canoe for 6 months (not even counting book reading, garage prep, etc), and I'm finally just about the start actually building a canoe. o_O
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