View Full Version : Stuck on Fairing molds

06-06-2014, 02:02 PM
me again..."building a 17' whitehall" guy.

I am absolutely stumped on the fairing process right now. I have my strong back set up, my inner stem carved, the keelson tacked on, the molds all perpendicular and smoothed, I was super careful tracing the patterns on the MDF, and now I'm trying to fair the mold


I have no means of clamping a strip to my molds at every station and so sighting along a full-length batten for fairness doesn't really work. I am therefore attempting the method described in Canoecraft by Ted Moores. This method essentially uses a piece of planking on edge (so it's stiffer) sprung around molds by hand - in my case a 1/4" x 3/4" piece of straight-grained cedar. For my 12" station spacing and my 6' arm span, the comfortable way to go about this is to hold the batten with my hands 5' apart, spring it around 5 molds at once and look for clearance between the batten and the mold at the middle station.

This is where I get stuck, and I have 3 "situations" to ask about.

on about 75% of the mold, the sprung batten either touches or is within 1/16" of the centre station (ie the centre station relative to my hand positioning). In almost all of the cases where the clearance is greater than 1/16", I can move 1 station forward or aft and the clearance disappears --- what gives? It's fair in two positions and not in another...does that mean it is fair or not??
Toward the bow of the whitehall, there is quite a bit of twist applied to the planking. On the 3 forwardmost stations, if I spring between the stem and Stn 3, I see no clearance. Great. If I spring between stations 1 and 4 however (ie moving 1 station aft) then things look positively awful on stations 2 and 3. Huge clearances. Laying the plank on its flat side and adding the twist seems to reduce the clearance somewhat. ----is this fair? I'm trying to figure out if this is just the result of some reflex curvature near the bow of if something is royally f**ked with my mold.
I have one station that is seems to be unfair in a manner similar to situation 1) above, but the clearance *doesn't* disappear when I move one station forward or aft. The whole garboard area of the mold is off port and starboard, so I assume this means it needs to be raised slightly. I tried this and it completely messed up all the surrounding molds. Should I be trying to raise this mold then, or would it be better to just glue a thin strip of wood to just the garboard area?

For 1 and 3, I think the main problem is coming up with a systematic trial and error method of raising and lowering molds. What should I be looking for in a mold that might need to be raised or lowered?

Resources for this are scant. Most books (even comprehensive ones like Moores') basically amount to "grab a batten and fair it"...FFS...

Any help you can provide, or a link to a comprehensive article would be much appreciated and then some.



Gib Etheridge
06-06-2014, 03:40 PM
Hard to help without pics, probably difficult with them also.

How about if you add all of the battens lining it off for the planking? You'll have to do that eventually anyway. Screw them into the edge of the molds with pan head screws. If the molds won't take the screws glue on a block at each intersection that will. You might find that all is well and no need to fret.

06-06-2014, 04:10 PM
You really do need to extend your batten, and as above, if need be, glue or screw blocks where needed to ake a clamp or a fastening. What did you make your molds from and how thick?
I personally wouldnt sweat a 1/16. Your point 3. does sound like the mold is set too low, or the rest are too high. Just shim it where needed to get the plank to lay fair. Worth paying attention too as this can dictate the difference between a sweet boat and one that.....er.....isnt.
I have not checked your other thread, is this build going to be strip or clinker?

06-06-2014, 05:46 PM
You could hole saw some holes into the moulds for your clamps too.

06-06-2014, 05:59 PM
It's important not to get confused by multiple results. If you made the moulds carefully and set them up carefully then the presumption is that they are correct.

Remember a batten will not pass fair over a set of moulds in any random direction. Waterlines are fair, buttocks are fair and diagonals are fair. Generally, when fairing moulds (which really shouldn't be necessary today), the batten needs to lay along a waterline. So if you feel that you have to fair them in, set out the waterlines on each mould (you probably have them already marked on) and make sure that the top edge (or the bottom edge) of the batten lays along the waterline marks.

A long batten is much better than a short batten. Something like ⅜" thick x 1" wide should be about right. Tack it gently to the moulds and then you can eye along it.

I well remember the first cold moulded boat we built (strip planks + diagonal veneers). Because the strip planks followed a line we weren't used to seeing it looked like the boat was unfair. As the surface filled in of course it became fair as a 3-d shape. But the lines followed by individual strips were not "fair" in the usual sense that we were used to.

The final run on to the stem is the most likely place to be unfair – even making the apron marginally too wide can produce unfairness here because the angles are getting quite sharp and the hull lines straight, or possibly hollow.

Finally don't change anything unless you are absolutely certain that something is wrong and absolutely don't change more than one thing at a time – that just leads to confusion!! I know – I've been there!

The strong probability is that everything is OK and correct.


06-06-2014, 07:43 PM
@Gb Etheridge (http://forum.woodenboat.com/member.php?36292-Gib-Etheridge)

I would absolutely do what you suggest if I was clinking or carvelling the hull, however it's a cedar strip hull (see response below) and does not receive a "lining off" in the traditional sense before planking begins. It probably isn't a terrible idea to add a few clamping blocks so that I can spring a full length batten around the molds and sight the entire curve anyway.

@skaraborgcraft (http://forum.woodenboat.com/member.php?26620-skaraborgcraft)

It is a stripper (link to my blog in the OP below my name if you're interested). 1/4" thick strips, glassed inside and out. Note, the plans were purchased (bear mountain) and intended for strip planking of this type. I will definitely glue a shim to the "bad" station as you suggest. Worst case I can just sand or plane it off to recover the status quo.

@andrewpatrol (http://forum.woodenboat.com/member.php?29797-andrewpatrol)

I wish I'd done that while setting up....even if I'd taken the router with a straight bit and put a groove for clamping. It's too much extra work to disassemble now, but I will be definitely following your suggestion for my next build.

@debenriver (http://forum.woodenboat.com/member.php?29372-debenriver)

Your words are encouraging...I did take my time setting up, tracing and sawing, then sanded with my disc sander & with a block by hand to make sure I was sitting right on my traced lines to the greatest extent possible.

WLs were not noted on the full-scale plans, but it would be easy enough to add this to every 3rd station for reference when lining up my batten. Thinking back, I suspect I was measuring a version of the diagonals, but not in any repeatable way. If I mark the WLs, at least I can go back to the exact same spot and get a bit more systematic with my adjustments (should I deem them necessary)

Good advice on the apron too. I'll pay close attention that my bevels are true in that area.


Thanks for the suggestions. Keep them coming too by the way!