designing a fast rowboat

Long time since i posted but a successful launch day is a good enough reason! This afternoon we launched my Seax rowing Gig, she is 27ft 6" long x 4ft 6" beam, GRP foam sandwich construction with wooden fit out, a lot of research & thought has gone into her & i have learned an awful lot along the way. I would say much of it was learned from reading this thread!
She is the first boat i have designed though i have built quite a few so today was especially nerveracking. However all went well & once the scratch crew got into their stride we went for it a put the power on. Looking astern at the wake ripping aft i was a very happy man. The story & photos are on my blog
, http://eastcoastrowing.blogspot.co.uk/, Once we have a road trailer sorted she will join the racing circuit on the East Coast. That should be interesting!

 

those are some sweet looking boats in your blog!

 

Thank you, the Gig was designed using delftship pro & is one of a series of designs i did, Thanks are due to Rick willoughby who offered to run the Mk4 design through Michlet/Godzilla to check hull performance, this was very useful as it allowed a comparison check with the resistance plots produced by delftship. In the end we went with a later design that was a bit longer due to the need to carry a passenger for racing in the Great river race.
Thanks also for advice from Tunnels on foam sandwich construction practicalities!
All i gotta do now is find somewhere to build her a sister ship or two!

 

Drake 19 and Drake Raceboat on horizon

Hey all I have been busy expanding my Drake line up to include a Drake 19 for tandem rowing and voyaging. Also my winter project will be a 4-strake per side, go-for-speed version that I'll just call the Drake Raceboat for now. Fun stuff. Drake 19 attached.

 

Looks fast! Are those the Finnish style seat rails for a single or double rowing set-up? Interesting idea to make them one piece -- my only question is whether someone like me (200+ lbs) might bend the rails over that length if they don't have some other support, perhaps beneath?

 

We have been experimenting with longitudinal supports too. It adds rigidity to boat with little extra weight, and rowers have been pleased with the system. To my view, it is also quicker to build, than normal frames.

Jarmo

 

Back in post 1217 DickT put out an interesting concept using "vertical chines" which would involve laying the planking transversely.

The more I look at it the more intriguing possibilities I discover; as an example the plank developments are almost rectangular as a latter post of mine on the subject shows, and a planking kit would be very compact for shipping, with no scarfing required except for longitudinals like gunnels.

A further simplification occurs when the gunnels are designed as a circular arc in the plan view and a constant chine profile is used for the midships; these features are seen in some design schools. The midships planks then all have the same profile, just the end planks at each stem are different.

The idea seems to suit building with a bottom plank like an Adirondack guideboat. I am continuing to work on the concept, I may build a canoe to demonstrate the building method later. I goofed up big-time on a model but I think I know how to tackle that now. Gardening chores first . . .

 

I would think the vertical chine concept lends itself to foam sandwich construction especially if there is a bottom panel. The Gig i just built had vertical joins in the core & it was easy & quick to lay the core. She was however built on a substantial jig. Working the other way from a CNC cut pile of core panels the jig could be far simpler & lighter.
Only thing i would worry about would be the hungry dog effect showing through the paint particularly if plywod panels were used.

 

I've seen it done in foam sandwich construction and it looks very easy, simple to smooth out too. Of course, you then get into glassing, something I don't like and won't do, so the plywood is a better material for me.

Just for interest, the height between the flats and peaks of the "dog rib" facets varies as the inverse square of the number of planks, for a given radius and length. For a typical canoe it reduces to 0.5 mm or less when the plank count gets over 20 or so. At that point it wouldn't be a big deal to sand it smooth with a long board, but I don't think I would bother. As DickT wrote, I kinda like the effect. As the facet run around the bilge down to the waterline they get less noticeable, but even at 0.5 mm you'd have to be moivng aweful fast to create a ripple.

Of course the proof of the paddling is in the floating to use a really tormented analogy . . .

 

These rails are supported in the middle by the bulkhead itself. So the 100" long pipes have a support in the middle; it is two 50" sections unsupported. I might add more...I am also 200 lbs.

Longitudinal supports sound good, but the Drake 19 has plenty of longitudinal structure, especially with the keelson.

My limiting factor right now is finding v-groove wheels for the seat to run along the rails.

 

Me too. There's a lot of that going around . . .

 

The name 'vertical chine' just rubs me the wrong way. I know it's similar to cold mold planks in terms of dimensional inaccuracy but with butt joints. In my mind the error is (w/2) * tan theta where theta is the angle length of each chine of the curve. 0.5mm error means there is not much curve. On a 20ft canoe, 3 ft beam, constant arc, 20 chines I get 1.13mm error minimum (single 8.5deg arc). The other worry I have is that the chines need lots of positioning control (a big precise mold) to not be 'up here down there'. And for butt joints to be strong the gap must be controlled which means precise subtle curves -PITA work. And the longboard sanding you say it won't need much of is the most miserable part of boat building.

I look forward to your build because I can't see how it can be done without great difficulty. Maybe I will learn something but until then I will keep the water flowing along my chines not across them.
Good luck!

Ps if it doesn't work as planned toss it on the fire. Don't let it clutter your shop for a year. Your stitch & glue chine boats are great do more of those!

 

Ancient Kayaker, how far from Toronto are you? I'm often in TO.

The other conundrum about the Drake 19 is how to do a composite outrigger that is easy to make. The boat will be rowed oar-on-gunwale but for those who want to use sculls I'd also like an option for them. The drop in units are just so ugly.

 

Just spitballing...

For a sliding seat boat, the usual spread is what, 60"? So if Drake is about 48" wide, then those are relatively small outriggers. One option (which admittedly may not be that aesthetic) is to do a carbon-covered wooden wing, with Concept 2 oarlocks and pins, attached with wing nuts (for quick removal) to plates/cleats on the inwales. One (or two) of these would also act as a stiffening thwart (allowing lighter internals) and the outboard would be small enough to be very rigid. The ends of the wing could even angle down a bit if lower oarlock height is desired (beyond the moveable C2 spacers on the pin).

More aesthetic riggers that won't impede on the inside of the boat are harder to get rigid but perhaps could be a 12mm ply triangular plate (12" base, 6" outboard projection), carbon-covered, with the base attached with several wing nuts and a metal strap under them (or long hinges) to a beefed-up foot-long section of gunwale.

 

I agree; transverse planking sounds nicer and is technically more correct IMHO than vertical chines.

Should that be W(/2)tan(theta/2) BTW? I assume theta is the angle subtended at the center by a plank. However I agree with your 1.13mm value. A quick calculation: take the depth of the curve and divide by the square of the transverse plank count BTW, it's very close.

The 0.5mm result I got was based on a 32" x 16' canoe with about the middle 10' cross planked as I recall (didn't keep notes) and the gunnels were allowed to straighten toward to stems so as you say there was not as much curve for the transverse planked part.

I would not extend the transverse planking all the way to the stems. I think the end planking could be a conic section needing just 4 ply pieces - identical for a symmetrical canoe. Only 2 plank developments? I don't trust FreeShip for this design as it's hard to get precisely the hull shape you need.

I'm planning a 1/6 half model to test the build methods I have worked out, after gardening chores. There have been a lot of challenges working out the build and there is no prior art on this. Main challenges have been the math, getting the circular arc accurately on the gunnel planform, joining the planks along the keel - I decided to use a bottom plank Adirondack Guideboat style, ensuring sufficient longitudinal strength with some redundancy in case the plank joints were to fail, and joining the planks for which I will use narrow ply ribs acting as butt blocks. I don't think the method will require any more precision than any other build unless errors may show up more.

?? I've never done a S&G ?? I helped a guy do one, saw his hopes die slowly and I vowed not to even try. He was a retired cabinet make obsessed with perfect and by the time he got the fillets to his satisfaction he just gave up. I would have settled for less especially as it was a sailing canoe with decks. I might have hidden the evidence with narrow side decks. Such a shame, lovely hundred-year old design updated to S&G.

Clinton: I'm in Alliston about an hour north of TO.