View Full Version : Planking Twist Problem

02-25-2002, 12:03 AM
Hello All,

I'm currently building a Weston Farmer designed launch, 10 foot in length. The construction method is glued plywood(6mm) clinker(lapstrake).

I have both garboards and the next strake in place and glued. This is the first boat I have built.

My problem is with the amount of twist and bend on these planks at the stem. The boat is round bodied and quite beamy which I think adds to the problem.

I broke one plank trying to get it on, basically three planks are fine, but one of the second strakes is off the in the middle by about 1/8'. A bit of thick epoxy has fixed it(I know I will have to do some fairing on this).

My questions is is there some sort of clamp that anybody uses to pull these together? My "C" and finger clamps pop off.

The original plans call for 3/8 planking stock, I assume this would have been steamed. Is steaming viable for plywood or is there another method(I tried liberal amounts of Windex which seemed to help a little).

Thanks in advance

Mark S.

Art Read
02-25-2002, 12:27 AM
Welcome to the "zen" of plank clamping. You're going to need lot's of patience, ingenuiety and improvisation to get all the various bends and twists in a round hull "home"... Having lots of various sized and shaped "pads" handy helps. Especially wedges! "Shores" off the walls and ceilings aren't to be overlooked either. (And you'll get to learn all about patching drywall if your garage/boatshop is semi-finished like mine is...) I've not heard lots about steam bending plywood, but some here have mentioned wrapping it in towels soaked in boiling water with some success... Windex, eh? That's a new one on me. I did see something once about a production shop using ammonia, so you may be on to something there. Where'd you get the idea?

02-25-2002, 12:56 AM
Thanks Art,
I used to build models. Windex works well for bending thin balsa and wood.

I know that large furniture manufacturers soak wood for bending in anhydrous ammonia(gas). They do this at several atmospheres of pressure. It apparently only takes a few minutes for the wood to come out like cooked pasta.

As far as my planking goes it seems it may get easier after I have gone around the turn on the bilge?

Mark S.

Art Read
02-25-2002, 02:23 AM
Yup! ('Cept maybe the hood ends when you get up by the sheerstrake, but maybe that was just me...)

Wish I'd heard about the "windex" trick before I planked my models!

ken mcclure
02-25-2002, 10:54 AM
The only thing I can add is that you should start fastening the plank at the end that has the greatest bend. Get it attached, clamped, braced, pushed, screwed or whatever and then work the rest of the plank in.

In the descriptions for other craft using 3/8" ply, I see several people have used pan-head screws to hold the plank temporarily and then filled the holes with either bungs or thickened epoxy.

Alan Peck
02-25-2002, 11:31 AM
I have had good luck using towels and boiling water. I covered the area with towels and then poured on boiled water. I reapplied the water about every 45 minutes for about six hours. During this time I slowly increased the bending pressure.

I was using 3/8" plywood and it worked quite well.

Don Maurer
02-25-2002, 11:33 AM
I cut my planks a little long and put screws in the outboard corners. I then used a spanish windlass to pull the planks into place. If you go slow, you will hear when fibers start to split. As soon as you hear it (or before), back off a little and use your hot towels or ammonia. Sometimes it helps to let it sit overnight under tension before continuing with the bend.

02-25-2002, 11:35 AM
...and don't try to rush the job. Bend the plank to a point just before it breaks and tie it off. Let it relax a while, over night maybe, and have another go at it. On the other hand, I've done that and had the piece snap during the night.


02-25-2002, 06:14 PM
Thank you all for the good suggestions.

I have been using pan head screws. Fastening the plank at the area of greatest bend will I think alleviate most of the problems. When I think about it is obvious. "Can't see the forest for the trees"

The ply is five ply Indonesian stuff stamped BS1088. I'm pretty sure it's not though, it has no voids but AB face. One sheet out of five had a small(1'x1/4') patch. The price was good though($50.00AUD sheet).

Mark S.

02-26-2002, 07:44 AM
If it's still too tough maybe you could laminate the garboard out of two 1/8" sheets?

02-26-2002, 09:28 AM
We need some clarification from Ken, Mark. If you run fasteners in at the point of greatest bend you are making a weak point and perhaps making it more likely the plank will break. I read Ken's advice to be to fasten the end then bend.



ken mcclure
02-26-2002, 10:57 AM
The scheme is to start fastening at the end where the plank will have its greatest bend. Then as you work the plank onto its lands, you continue to fasten past the bend area to the point where there's less stress.

As you get to the other end, you'll need to begin working on the plank again to force it down to its marks using clamps, braces or whatever.

This has worked fine for me in architectural wood projects, and I suspect it will work the same on a boat. I'll find out for myself this summer. (I hope!)

ken mcclure
02-26-2002, 10:59 AM
By the way, since we're working a relatively wide plank, the plank itself is not weakened significantly by the fastener holes. Fasteners at the "bendy" part will be close together (maybe 4" ?), and the accumulation of fasteners will provide the strength to hold the plank until the adhesive kicks off.

Tom Dugan
02-26-2002, 11:30 AM
Ken, Alan, and Don's advice is all spot on for solid wood, but does steaming really work for plywood? What steaming does to solid wood is heat it enough to soften the lignin, and allow the fibers to move past one another. We know from Forum members' tests that steaming marine plywood does not delaminate it, hence the glue holds everything in place, so I'm not convinced that it'll really do any good to steam in MarkWW's case.

And is it really critical now, after the garboards are on?

-Skeptical T

Bruce Hooke
02-26-2002, 11:39 AM
There are times when, in my experience, it makes sense to drill a small hole (later filled) in the planking to aid in pulling the plank into place. A trick I used to pull some planks back in after replacing the stem on a rowboat was to use a screen door turnbuckle (those long thin ones that run on a diagonal across the lower part of the door). A 1/8" hole perpendicular to the centerline of the boat, in the same plank on each side of the boat, would allow me to feed in the turnbuckle wires and connect them at the center. To anchor them I put a big wooden washer over the end of the wire and then grabbed on right outside that washer with vice-grips. That done, I could turn the turnbuckle on the inside and draw the planks in tight. Putting the turnbuckle holes above the centerline of the plank took care of applying the twisting action to the plank end.

ken mcclure
02-26-2002, 12:08 PM
Dale Hymanyk's Alistego (http://www.alistego.com/) website has some pics of how he fastened the garboards. Look in the planking section, and see his discussion on using screws to fasten it temporarily.

02-26-2002, 12:18 PM
Extrapolating from unrelated experience is a dangerous thing. Oh, well...

When son Wes and I were making mountain dulcimers it was said that wood bent with steam would spring back while dry heated wood would not. We use dry heat. Now the relevant? part. Is it the heat from steam primarily that allows wood to relax and bend? If so steaming plywood would then make it easier to bend. (It would be difficult to use dry heat on anything very large so I'm not advocating dry heat in the boat shop.)


Don Maurer
02-26-2002, 02:05 PM
Wetting the plywood does work - to a degree, as does bending it part way and letting it "set" to its new shape overnight. My guess is the moisture allows the outer layers to flex, which makes the entire plywood construction bend easier. I also think there must be some elasticity in the adhesive which allows the plywood to take on a temporary set.