designing a fast rowboat

Yup, of course I have figures. Been fussing over the damned things too much.

Designed displacement is 118 kg in salt. That's at a draught of 84mm (which is just what it turned out to be). Minimum freeboard is 235mm. Prismatic is 0.590. The important bit though is that the metacentre is only 360mm above the waterline. This thing would actually be tippier than a guideboat. I'm fine with that but some people wouldn't be.


Cool pix of the guideboat. You're right in that post about most of the strength being needed at the rowlock pads. If you want to go lighter on the next one just make sure there is adequate strengthening of the gunwales there and taper it out so you don't get hard spots.

 

My canoe has a metacentric height of 35 cm, very similar to J. Henry Rushton's Wee Lassie which is 37 cm. That type of canoe typically have freeboards as low as 11 cm and are designed for a single paddler seated virtually on the keel. If you sit any higher than that you may have to ride it like a bicycle, but that is easier with oars than a paddler.

 

Oh don't worry, I know all about that. That's 360mm from the waterline, which is 390 from the CB. The last skinny one I built was only 300 from the CB. That was fine for me (I even used to stand up in the thing if it was calm) but when carrying a passenger or a lively German Shepherd in a chop things weren't quite so good. This time around I want something with no more wetted surface, more waterline length, more reserve bouyancy, more initial stability and heeled stability, no reduction in metacentric height when heavily loaded (that gets nasty) and no pounding or chine drag from a flat bottom. It's tricky but it's possible and the result should go well.

Boats like these are fine if you follow Shakira's advice: the hips don't lie. Balance them properly and they're stable as anything. Get a bit off line and you'll be dragging the gunwales. The good thing though is that in rough water you can choose how much you want the boat to heel to waves on the beam, just by shifting the weight from one side of your butt to the other as the waves pass under you. I'm sure as a kayaker you'd be well familiar with that trick.

 

That's needed if the boat is stable but a tippy canoe will ride over most waves and stay upright We of the paddling fraternity do heel our boats to turn them and compensate for a crosswind. The trick to feeling comfortable in my canoe is to be wedged into the boat; that is easier in a kayak, with the cockpit, than in the open canoe. I used to spread my knees out to grip the gunnels, but I was younger then and my hip joints still worked as advertised I designed the boat for a geriatric paddler - extra light, comfortable seat with high back, easy to enter and leave - but I forgot to install thigh pads

 

So put thigh pads in then.

 

nothing is free

So, I've got my pile of FREE western red cedar and I'm going to start milling it this weekend. Ripping it to width is no problem but geting everything the same thickness is. The strips will be 1" and 1-1/2' wide. I don't have a thickness planer and am wondering if a planer blade on my Makita 8-1/4" table saw will work. Next item will be bead and cove cutters. I've got a router with a 1/4" collet. The strips will be 3/8" thick, is there a cutter set that will work or do I have to improvise. If I have to buy a planer and 1/2" heavy duty router, the free wood starts to get expensive. Any thoughts?

 

I routinely cut strips from plank edges with a typical thickness variation of 0.014" with a skilsaw. I use a thin kerf finishing blade to reduce wastage and get a glue-ready surface that only needs minimal sanding for finishing. The tricks for doing this are: fit it with a zero clearance baseplate, use a long and perfectly straight guidance strip, and get the blade runout as close to zero as possible. You should have no problems matching these results on a properly set-up table saw with a good blade.

Checking and adjusting the runout is the most important: on a skilsaw all one can do is attend to cleaning the arbor and change the blade if necessary, but runout should be adjustable on a table saw.

It took me a while to get these results: I improved my accuracy x3 when I realized my guidance strip was minutely curved, so double-check the fence.

I haven't been able to find a combined bead and cove cutter with 1/4" shank, I can find separate bits (pairs) but they are for 1/4" strips, but keep trying! Flute and round-over bits may work if you can't find what you need.

 

Do you really need the bead and cove? I've edge glued with WEST epoxy and haven't had issues filling gaps on square cut strips.

 

I wouldn't bother with it myself. Square edge seems fine in most places and planing a bevel in a few spots isn't hard.

 

millwork

I checked my table saw ( small Makita ) the fence has a bit of belly in it. A longer auxillary wood fence might help. I'll try the zero clearance insert too. How much of an issue is it to keep the strips aligned with square edges? It seems to me that keeping them aligned to one another to create a smooth surface could be a challange.

 

The advantages of the cove and bead edge treatment are, it keeps the strip edges aligned between the frames (the strips can be stapled to the frames) while the glue sets, and the edge treatment provides enough surface area in the joint that a regular wood glue can be used, which is faster than epoxy.

Without the cove/bead engagement along the edge, I'd guess you'll need a fair number of clamps of the parallel sided kind. And patience too, as the epoxy will be slower than the usual wood glues used.

However, you might be able to put on 2 or 3 strakes at a time per side which should speed things up, provided the clamps have enough jaw width - and you have enough clamps for both sides at once. If not, the extra prep time and tool cost for the cove/bead work will pay dividends IMHO.

 

Check out any of the many books on strip planking- lots of stuff on line too- for miriads of different ways to approach these problems. Every one seems to have a different take on it so find what makes sense and try it - go back to the books if it doesn't. Most of my reading says not to use epoxy to glue strips together. The new water proof (brown) Titebond is TOTALLY water proof. Soaking tools for weeks does not soften it whereas regular Titebond falls off in a day. Using epoxy will be expensive, messy and wasteful as you will constantly be having mixed up batches going off on you. Plus think of the clean up! If you were doing really thick strips I can see where a thickened epoxy would help. The water proof Titebond does take a little longer to grab. I would think that you could make some little clamps to help with the alignment. I wonder if old fashioned clothes pins might work. I bought a bag of cheapo plastic clamps from a home improvement center for this. Various books show slots the width of the strips with the addition of a shock cord to apply clamping pressure. If this all sounds like a pain - just think of the drag milling all that bead and cove!! Noisy and dusty.
The long table saw fence will only help if your boards are straight. First things first - loft the boat then build the forms. - Have fun!

 

A few more notes:

Titebond is not gap filling; if it fails to hold because only the edges of the strips are in contact, the joint will have to be reglued.
Titebond III will not adhere to dry Titebond III, very few glues will, so a failed joint must be cleaned down to bare wood.
Titebond III sets hard enough to remove clamps in 30 min.
The glue between the strips doesn’t have to be waterproof because the boat will be glassed.
I believe most folks use ordinary carpenter's glue with cove and bead strips.
Glassing is essential to provide cross-grain strength unless you are going to install ribs.
Coves can be cut on a table saw, I understand, but you will probably need a thin kerf blade.

Epoxy is hard and tends to clog sandpaper! Sanding prior to glassing will be more work if epoxy is used in the joints unless you are stringent in cleaning up as you go. If you use epoxy, a dusting of talc will reduce the clogging.

 

Any good glue will exceed the strength of the cedar with a standard side grain butt joint.

I've only done a couple of stripped hulls but found that with adequate form spacing nothing extra was needed in most places. You definitely wouldn't want to edge clamp the strips though IMO because that would do nasty things on a curved surface. If I wasn't using epoxy I'd use a polyurethane glue. Easy to apply, easy to sand and waterproof. I personally do not believe this stuff about the glue not needing to be waterproof. What if one of the glass skins is damaged?

 

WEST epoxy with 403 filler is a lot like welding. You can mix it thick enough to not sag and it will bridge gaps. On a small boat you won't go broke filling gaps. Sanding it is awful, It will plane when green, but that's tricky for a lot of reasons..