Plywood planks on batten seam - anyone tried it?

[JimD]

So I'm building the Witholz catboat dinghy designed for cold mold but modifying for glued plywood lap a la Iain Oughtred and others. Have made necesary modifications to the design to accomodate wider planks as opposed to narrow strips. Had to sacrifice some of the nice curve at the transom (original design looks very whitehallish at the stern) but oh, well. Also have decided to brace all the lands on the inside with permanent DF battens. The battens are now set into the station molds and am now ready to lap plank. So far so good.

But it occurs to me that straight forward batten seam with the ply plank edges meeting at the middle of the batten as per tradition could be an easier way to plank in plywood, especially if you wanted to use sawn frames or bulkheads instead of bent ribs. Yet there are more and more boats being designed for ply lapstrake and I don't know of any for batten seam. Any ideas why?

[WayGray]

I used batten-seam with plywood planks on my last boat. It worked fine. I close-butted the planks on the midline of the faired batten and then went over the joint with a light epoxy putty to penetrate and fill any discrepancies. The battens help define the plank widths and helped in clamping.

On the boat before that I used no batten, but epoxy putty and fiberglass cloth, ala stitch & glue. On that one I intentionally left a small "V" gap between planks to insure that the heavy putty would thoroughly wet the joint.

On the boat I am building right now I plan to use batten-seam with plywood planks. The stability of the plywood allows the glued seams. The battens define plank shapes- no fancy spiling. To me it seems easier than lapstrake which you usually rebate to achieve flush joints at the ends anyhow.

[imported_Steven Bauer]

I don't like the idea of leaving the stringers in as part of the finished boat. The Arch Davis Penobscot 14 down at the local marina had a cover that didn't fit very well and each stringer had a little puddle of water trapped behind it. Isn't this just asking for rot eventually? Tom Hill's method uses the stringers but you leave them on the molds, you don't make them part of the boat.

Steven

[ken mcclure]

I'd think the plywood edges would suck up water (as plywood is wont to do) if you didn't get them absolutely sealed.

[Ian McColgin]

I used the seam batten approach building Leeward - a chamberlain gunning dory - all per John Gardner's instructions in "Building Classic Small Craft." Also in his "The Dory Book."

A long used technique and very easy to do.

If you make a side bar for your plane it will automaticaly allign as the plank does and you can thus plane the battens above and below the center line so that the planks can land exactly.

After beveling the battens to accept the planks but prior to hanging any planks I planed the top and bottom edges of the battens in about 30 degrees so that they would not hold water or dirt. I also relieved the two inside corners.

I cut the planks normal and filled the narrow V gap between planks with thickened epoxy. I used my plastic trowel to make a fair hard corner of epoxy running down the center of the crack, which I then sanded to a pleasant curve after it set. This worked better than troweling the epoxy flat over the mouth of the V and then sanding the curve into the wood.

I was originally going to leave the battens bright but it made for a cluttered look and promiced to be a real pain to maintain.

I think seam batten is a lovely way to go for one-off production, especially if you are, as I was then, a bit intimidated by lapstrake construction. For professional work, lapstrake will be far more sellable.

G'luck

[stevenj]

ply on battan seams is the method Gardner calls for on his 12' semi dory in the Dory Book.... go fer it.

stevenj

[Keith Wilson]

I see no technical reason why it wouldn't work. It has the advantage (over lapstake) of being relatively easy to sheath outside with glass and epoxy if you want. However, I can see several disadvantages, both practical and aesthetic:

- Fitting the planks will require considerably greater accuracy than lapstrake planking. Edges of lapstrake planks don't need exactly fitting curves, just fair curves that are close enough. Edges of pseudo-carvel planking have to fit pretty exactly, unless you're going to just fill gaps with googe and glass over it.

- The hull will have a "faceted" appearance unless you use quite narrow planks (more work). Standard carvel planking (with natural wood) is thicker, and is planed down considerably to get a smooth round curve in cross-section. You can't do this much with plywood, both because it's thinner to start, and because you don't really want to plane through the face veneers. A lapstrake boat is not expected to have smooth curves in cross-section - dories are an extreme example because the planks are so wide.

Honestly, after building several ply lapstrake boats, it seems to me that batten-seam ply has little to recommend it except ease of glass sheathing, which isn't really necessary on small boats made of decent plywood. Lapstrake is not at all hard, even for one like me of very modest skill. If you don't have Tom Hill's book I'd recommend you buy it, or at least check it out of the library for a week or two. His description of the modified plane to cut the plank bevels is worth the price; makes an otherwise fussy task dead simple. And cutting the gains is really WAY easier than people think.

I think lapstrake would be easier, and IMO you'd end up with a better-looking boat. If you really want a smooth hull, strip planking seems like less hassle to me.

I really like the little Wittholz cat, BTW. He had a good eye.

[ 01-09-2004, 09:49 AM: Message edited by: Keith Wilson ]

[Ian McColgin]

Ian's easy way to fit planks for seam batten:

Remember, you want the battens to have two bevels on the outside so's the planks will land fair. Trust me, it's easier to get a nice jog this way than by landing the planks on the edge of a flat batten and having a void to fill.

Anyway, poster board or something such makes an easy plank pattern. Tape enough together to get from one end of the boat to the other along two of the battens. Push pin it in place. From inside the boat, just draw a line along the inside of each seam batten. You'll expand these lines to the center of the seam batten later.

From the outside, mark by push pins that do not land in wood but right next to some obvious places - frame or strong back stations.

Take the pattern off and flip it to the other side of the boat, alligning it in place with the marking holes. Check the lines and see that the two planks will actually resemble each other. If not, ask yourself if it's close enough and if anyone will see both sides at the same time.

It's nice if you can have only one pattern for every two planks.

Lay the pattern down and double check the distance of the bevel from the center of each batten to the inner edge that you marked on the batten. If your work was good, this distance is very close to the same all along, but sometimes the changing bevel will mean that the landing surface is bigger in one place than another. Like the turn of the bilge amidships may well have a wider landing surface than at the ends. So make a bunch of measurements at regular stations - all labled and marked right on the batten - and transfer those points to the cardboard. Make a fair line and cut to that. Test the pattern against the space before you cut the wood.

I found that I liked hanging a plank on each side per gluing session. I also did not want to make too many planks in advance as I worried about mix-ups and real accuracy. If you've a plank already one one seam batten, you can lay the poster board over it's space and rub - like run the head of a hammer along it - the posterboard where the existing plank is. This will give you a mark to cut to that's spot on and you only have to the the measure and transfer bit on one edge.

Again, the only real trick to seam batten is getting the bevels on the battens right. As mentioned, a rod sticking out normal to the plan with it's lower edge flush with the plane bottom will do the trick as it will ride on the next batten and keep the angle right. Do not finish plane one batten face at a time. Rather, whack off the edges of each batten in turn, working your way around and up and down, so that each bevel approaches finish at about the same time. Otherwise there will be an annoying systematic error bevel to bevel.

G'luck

[JimD]

Thanks for all the advice. I will almost certainly give it a try on the next one.

[Meerkat]

The way to avoid rot problems of water laying on those battens is to run a fillet of thickened epoxy along each one of them - vastly strengthens the boat too I hear.

[Norske3]

I like it.... smile.gif ..lapstrake requiring bevels on thin plywood is not for me.

[ 10-09-2005, 04:33 PM: Message edited by: Norske3 ]

[JimD]

That was a while back. And one day I'm going to finish that boat. At the moment it consists of a stack of station molds collecting dust.

[Norske3]

HI Jim...posted it 'cause I like this method from what I've read...OK so the molds are dusty....that means you are busy building something else...eh? smile.gif

[JimD]

Originally posted by Norske3:
HI Jim...posted it 'cause I like this method from what I've read...OK so the molds are dusty....that means you are busy building something else...eh? smile.gif Just this kayak, lately

http://www.imagestation.com/picture/sraid188/pd4fcd3c8658b2d17a84b6a6c90bb545e/f21d20be.jpg

[ 10-09-2005, 07:10 PM: Message edited by: JimD ]

[Norske3]

Nice....and you're on the water. smile.gif

[JimD]

Originally posted by Norske3:
Nice....and you're on the water. smile.gif Yup. This kayak photo is fresh water but we are staying in temporary digs only about 15 minutes from the salty version and when we get settled we may end up even closer. After I build a 17 or 18 foot kayak I'll finally be in a position to focus on a long term project for a pocket cruiser. I'd start another pocket cruiser thread but I've already done about a hundred of them. :D