WeeLassieII thwart and seat

[essaunders]

My extremely slow building of my canoe needs to wrap up soon. The only item that I haven't figured out is the thwart-gunwale attachment.
The kit manufacturer (Newfound Woodworks (http://www.newfound.com/) ) suggest the thwart be bolted on under the inwale - they provided bolts in the kit for that purpose.
Mac McCarthy says to

"Notch the thwart to fit under the rails and epoxy it in place. After the epoxy sets up, reinforce this joint with a long finish nail in a drilled hole through the rails and into the thwart"Here is where I am now:
http://www.imagestation.com/picture/sraid191/p52d2aa86e1650e24ded0318e725f904d/f1cb476a.jpg

If I were to use the Newfound instructions I would just need to drill a hole and bolt in place.
If I were to use McCarthy's instructions I would need to something like:
http://www.imagestation.com/picture/sraid191/p8947a1de429d913a6f7fb3e5e7d713c5/f1cb4a80.jpg
The black colored wood shows approximately where notches in the inner rail are.
Here is the mock up in an 'exploded' view (the rail has been tipped up to show the joint):
http://www.imagestation.com/picture/sraid191/paba40a0c6f3501780009f726f3a77cfb/f1cb4a93.jpg

I think the end result I am looking for is a thwart that is flush with the rails...and I'd think I have to do this half lap to get that effect. Is this an acceptable way to make this joint? What problems should I be anticipating?

Also, I know making the half-lap on the bottom of the rail may be difficult. I think I can do it with my little router... However, if making the lap on the top of the rail is better that may be easier to cut. (Once this is all epoxied together, does it make a difference structurally whether the thwart half of the lap is on top or bottom?)

Any suggestions or comments would be most welcome.

[Uncle Duke]

Lovely boat. Years ago my step-son and I made one of these for his use when he was about 11. The deal was that if he helped with every step, then the boat was his, but if he skipped any steps, then he had to ask permission to use it. Lots of fun.
Regarding the thwart - you really just need to determine what direction the stresses are going to be in. During use most stress will be towards aft, as you lean back into it. But if you will be portaging, resting the thwart on your shoulders, for example, then the stress would be 'down'. In that case the lap would be better on top.
Mac's method 'tab a into slot b' covers you in all directions, but isn't essential. More important is to make sure that the tabs/slots, etc., are pre-coated with epoxy first, so that you don't lose any of the bonding layer to 'soaking into the fresh cuts'...
Have a great time!

[Todd Bradshaw]

That's the absolute worst possible place to put a notch in the gunwale. I'd be willing to bet that within a couple of years you'll have a kink in the gunwale and hull there - assuming that the gunwale doesn't break first (which is quite possible). If you want to notch something to bring the thwart closer to flush, do it to the ends of a thick thwart, not the gunwale.

Ash thwarts don't always weather too well and it's nice to be able to remove them if needed for refinishing, so just bolting the thwart under the gunwale instead, does have it's advantages. Another possibility which dates all the way back to birchbark days is to cut a small mortise in the gunwale and a tenon on the thwart's end that fits snugly into it, but they normally used bigger inwales where cutting a chunk out wouldn't remove half of the gunwale's wood. I've had to remove enough thwarts over the years for one reason or another that I don't think I'd ever glue one into a boat. A couple machine screws and finish washers or Old Town-style diamond headed bolts do the job just fine.

The only boats that I've built or used with glued-in, flush thwarts were Hazen Micmacs which had a rather strange looking, but effective, yoke/centerthwart system built by installing two big fir dowels as thwarts about 15" apart in the middle of the boat and running slings between them. The dowels were essentially just butted into the inwale with some glue and a couple of #10 by 2"-2.5" flathead wood screws were screwed from the outside through the outwale, hull and inwale and into each end of each dowel. The screw heads were countersunk into the outwale and plugged over. It sounds flimsy as hell, but was strong enough that you could pick up the 60 lb. boat by the end of a dowel without a problem. There were sometimes problems though with the outwales eventually breaking at the plugs because so much original outwale wood had been removed to sink the screw heads. This happened mostly on mahogany outwales which tend to be rather brittle in the first place, but if you want flush, glued-in thwarts it would still probably be a lot stronger than cutting notches in the gunwales.

[Todd Bradshaw]

Are you sure Mac was giving you a formula for making the gunwales and thwart flush? That's a pretty unusual feature on a canoe. It is, however, quite common to cut a very shallow notch or beveled spot on the underside of an inwale or to bevel the tops of the ends of a thwart a little so that the mating surfaces of thwart and gunwale meet properly, since the underside of a gunwale isn't always level.

[Stephen Hutchins]

How about two #8 FTSB screws each side screwed upward into inwale from underneath?

[essaunders]

the thwart is cypress and the gunwales ash.
The least intrusive method is clearly the bolt. I wonder though, is the half-lap is really going to weaken much... the whole boat is just held together with epoxy anyway.

[Todd Bradshaw]

Well, if you remove half of the wood from the most highly stressed spot on the entire gunwale I think there is a really good chance that it will weaken it a whole bunch, which is probably why nobody in the canoe industry does it that way or ever has in the past as far as I know. I suppose you can always cut the gunwales off if it fails and replace them, but I can assure you, that's not a lot of fun.

p.s. I've seen several inwales break at the center thwart bolt holes on boats with only one thwart over the years, so you don't have to remove an awful lot of that long strip of wood to make a weak spot in that area.

[ 10-21-2005, 06:08 PM: Message edited by: Todd Bradshaw ]

[Bob Smalser]

Originally posted by Todd Bradshaw:
Well, if you remove half of the wood from the most highly stressed spot on the entire gunwale I think there is a really good chance that it will weaken it a whole bunch, which is probably why nobody in the canoe industry does it that way or ever has in the past ....Most traditional canoes I've worked on have the thwart bearing on a frame...their structural purpose is to hold the frames in place under load...and are indexed to the underside of the rails and bolted ala your kit manufacturer's instructions. The advantage is that they can come out easily when repairs or maintenance is required, and the carriage bolt alone in a butted assembly is more than sufficiently strong.

Your boat doesn't have frames, but the thwart serves the same purpose, holding the wales open, as do the wales themselves in keeping the sheer fair. The stresses involved in portaging the boat and pounding in a chop under load are the same, and it’s questionable whether lighter epoxy composite construction ameliorates those stresses any more than a traditional cedar and canvas canoe built heavier would.

I wouldn’t mortise the wale, either.

[Steve Lansdowne]

Have you really figured out whether the height of the thwart will be comfortable for you at that location and height? Boat strength aside, a backrest at the wrong height can really be a pain in the back. I learned the hard way that positioning the thwart/backrest in the correct fore/aft location is critical. Otherwise you can end up sitting on the wooden frame of the seat rather than on the woven part. Likely as not, your rear end is somewhat larger than that fine woven seat you made!

Once you're sure you want the thwart at a specific fore/aft location, one suggestion I'll make is to screw each of the ends of the thwart into small blocks, perhaps two screws per end, then epoxy these blocks to the underside of the gunwales while they are still attached to the thwart. That way you can remove the thwart if needed by removing the screws. This may not be traditional, but it does allow you to remove the thwart later on if needed for any adjustment and it doesn't weaken the gunwale at the point where the thwart connects to it. Of course, this method does lower the height of the thwart by a distance equal to the height of the block. On a light canoe such as this, I imagine you could still use this as a carrying yoke if that is your intention.

[ 10-21-2005, 08:49 PM: Message edited by: Steve Lansdowne ]

[JimConlin]

Posted in error.

[ 10-22-2005, 12:24 AM: Message edited by: JimConlin ]

[Badley Built]

What I've done is screw through the outside into the thwart. With the thwart landing on the spacer blocks, as you have it laid out, you can get two screw per side in. Plug the screw holes and you're done. Be sure to put a little epoxy in the joint. Like you, I like the thwart flush with the top edge and this is the most tidy way I've found of doing it.

Nice work by the way.

RonB.

[essaunders]

Ok. No mortising the inwale. that was going to be very difficult anyway.
The thwart fore-aft placement is directly from McCarthy's instructions... but the thwart is noticeably behind the CG - I'd need some additional portage rigging to portage comfortably. The seat gets secured to a rail (cleat) epoxied on the centerline. I am already planning on testing seat locations with temporary fastenings until I am happy with the seat/thwart relationship. (this will mean starting in the most aft location and moving forward, trimming the ends off the 'legs' of the seat where they rest (padded with felt) on the bilges).
I hadn't thought about moving the thwart... I was kind of hoping Mac knew what he was talking about....
I did look as a few canoes (heavy commercial plastic) in a store and yet, all the thwarts and hung from bolts.
The suggestion of using screws in the the ends of the thwart through the gunnel would result in the 'flush' attachment. I expect if I did this the screws would be accompanied with epoxy for this joint. [yep. that's what RonB wrote] Anybody know how cypress behaves when attached in the end-grain like this?

thanks

[ 10-23-2005, 10:51 AM: Message edited by: essaunders ]

[Bob Smalser]

Originally posted by essaunders:
...The suggestion of using screws in the the ends of the thwart through the gunnel would result in the 'flush' attachment. I expect if I did this the screws would be accompanied with epoxy for this joint. If I'm reading you correctly, running screws into the thwart end grain isn't a good practice. End grain simply doesn't hold screws, as the threads are in short grain that eventually turns to sawdust, a split point and a rot pocket as the boat works. Glues don't hold in end grain for the same reasons, so the failure of an epoxy joint there is also just a matter of time.

Use the 150-year proven carriage bolts so you can remove the thwart for recaning, varnishing or whatever. That's why you see them on almost all old canoes....a condition your boat should aspire to.

If you ever do have to fasten into endgrain, use a captured nut and machine screw instead.

http://pic3.picturetrail.com/VOL12/1104763/2594265/101714043.jpg

[ 10-23-2005, 11:55 AM: Message edited by: Bob Smalser ]

[Todd Bradshaw]

Anybody remember the original WB article on building Piccolo? As I remember it had some sort of small thwart-mounted, swivel backrest that looked a lot more comfy than just a wooden bar stuck in your back.

[Rick in Pender Harbour]

Hi
I attached the thwart on my first wee lassie with thickened epoxy only, although I now drill through from the outwale and set a screw into the end grain (I'm a belt and suspenders kind of guy). While I was exiting that canoe I lost my balance and fell onto the thwart, the boat cracked along the grain of the scupper block, no failure at the glue line... I would be more concerned with the way the grain runs on the thwart in your picture, I think it might be vulnerable to splitting where it bends and shows short grain.

rgds Rick

[JimConlin]

This is a Wee Lassie II with another approach to a backrest.
http://conlin-boats.com/wl2-rotc-haulout-2.jpg
It's glued to the inboard and bottom faces of the inwale. I came across a very light piece of WRC and would only do this again if i had equally light stock.
I can report that it's very comfortable, but doesn't encourage active leaning to affect the boat's roll, so it's hard to get the boat to do anything but go straight ahead. This is a trade-off.
The front edge of the seat is at the boat's CG and the backreset is roughly 12" aft of that. This is a very approximate recollection.

For a boat this light, a carrying yoke is a bad idea. The CG will be where the paddler sits and the boat is light enough that it's a one-hand-on-the-rail carry anyway.

[ 10-23-2005, 04:48 PM: Message edited by: JimConlin ]

[Steve Lansdowne]

I think Todd was referring to a swivel thwart that I first saw in Tom Hill's book, though I recall it was a Hereshoff idea long ago. The thwart swivels through two holes in inverted bell curved shaped end pieces which are fastened to the underside of the "inwale". It would provide some tranverse support, though not as much as a rigid, fixed thwart.

http://www.imagestation.com/picture/sraid191/pe4c77feb1a348980b37933ba057cf0b1/f1c3acc3.jpg

[ 10-23-2005, 08:59 PM: Message edited by: Steve Lansdowne ]

[Todd Bradshaw]

No, I'm thinking more of a simple, curved horizontal swiveling backrest attached to a solid thwart. I know that Hazen has a similar one on his strip kayak models and plans, but thought I also remembered one on the Piccolo canoe. Could just be old-timers disease.

[Alixander Beck]

Very Nice looking canoe.
I agree Badley's method of the thwart on the gunwale. I have on occasion used a similar method to allow seats to be moved for and aft as balance is required.

One suggestion I have for the seat is to put a strip of wood under the middle of the seat that lies flush with the centreline. This will stop the seat from transfering body weight directly to the four legs and onto the planks. Under heavy abrupt seatings this can cause the planks which the legs are seated on to become loose.

[essaunders]

Thanks for all the responses.

This is my most probably plan forward:
attach the thward with kitted bolts (no epoxy). This will hang the thwart from the inner rail and be, hopefully, the least intrusive method.

The seat will be bolted (screwed, most likely) to a 'riser' that sits on the centerline. I anticipate that at least half of the user weight will be borne here. the 'legs' of the seat will rest (padded with felt or similar) on the bilges. I hope to rig some temporary securing system until I am happy with the exact for-aft placement of the seat.

[Alixander Beck]

One suggestion for the ability to have the seat for and aft is to make the riser longer. I drilled holes in the riser and glued pegs into the underside of the seat. this enabled me to lift the seat and move it forward or aft as required.

[Todd Bradshaw]

That might be very handy. I've owned kayaks with sliding seats and being able to adjust the boat's trim by moving the seat just an inch or two, fore or aft can sometimes make a big difference in how it behaves in a crosswind.

[essaunders]

Going to garage to get this work moving. I've thought about it too long. I want to be able to paddle this year ---- so I can bug you all this winter about a sail conversion....

erik

[Steve Lansdowne]

You're right, Todd, as WB #37 page 62 demonstrates in a photo. A curved backrest that is angled back at the top. Looks mighty comfortable, and lets you slide port or starboard as needed.

[Doug Canada]

Question?

Are the plans for the "Wee Lassie II" in the Mac McCarthy book, "Featherweight Boatbuilding"?

If not; where are the (on-line) plans available?

Thanks,
Doug

.

[essaunders]

Yes. as far as I can tell, the necessary plans are in Mac's book.

I didn't do my own stations... I thought it would speed up building. good thing too! otherwise I'd be taking 6 years... (shouldn't talk until the thing floats, though)

[Alixander Beck]

Originally posted by Doug Canada:
Question?

Are the plans for the "Wee Lassie II" in the Mac McCarthy book, "Featherweight Boatbuilding"?

If not; where are the (on-line) plans available?

Thanks,
Doug

.You can get the plans online from Noah's

[garland reese]

Hey Doug,

yes the plans, or at least the offsets for the molds are in Mac's book. Mac used to have patterns available for the Wee Lassie II for not much money. I found the book offsets to be just a tad off, though nothing that a bit of adjustment and fairing couldn't fix.

I just did my thwart per Mac's suggested method. I sit on one of those floatation cushions. When I first built my boat, my youngest was small and when she was with me I needed to be futher aft, as she would relcline up in the bow, facing aft and lying against the curve of the forward deck, which I made just a bit longer than the plans show. Ahh....those were the days. ;)

[Bruce Taylor]

Anybody remember the original WB article on building Piccolo? As I remember it had some sort of small thwart-mounted, swivel backrest that looked a lot more comfy than just a wooden bar stuck in your back.Piccolo's backrests (which are quite springy & comfy) drop into a pair of notched cleats bolted to the inner face of the inwales. The notches are cut so that the backrests sit at an angle. Since each cleat has several notches in it, the position of the seats is adjustable.

They don't swivel, tho'.

Lately, I've taken to leaving the backrest off. The aft thwart/mast partner is good enough for me.

[ 10-25-2005, 10:26 AM: Message edited by: Bruce Taylor ]