Folding SOF Expedition Rowboat

[IanHowick]

I've been thinking about a folding SOF expedition rowboat for quite a while now. I have a SOF folding kayak I made, thoughts around trying a rowboat are based on the idea that you can go bigger and wider once you're not restricted by the need to keep it as narrow as possible for a paddling stroke.


So, my design brief is:


Big enough to take two people, either both rowing or taking turns, big enough for one to sleep in at a pinch, big enough to put a (folding?) bicycle in. Still a good size for solo rowing. Small/light enough to tow behind the bicycle to the beach, pick up and get on the water on my own. Capable of being taken apart, put in a bag to go on an airplane, a bus, the back of a motorcycle or in a car boot. (No, I don't anticipate being able to fit the motorbike in this boat)


With sliding seat and outriggers. If possible as seaworthy as a sea kayak with a zip/velcro on fabric deck - i.e. capable of doing a multi day trip along an open coast. Reference point as to what is possible would be Colin Angus's row around Vancouver Island, though I realize that, as with a sea kayak, there's a lot of experience and acquired skill in managing a row boat or kayak along such coasts.


Very similar aims to what Colin Angus has already achieved with his rowboats, but lighter and fit in a bag capable.


I first fiddled with my kayak design making it bigger and wider, changing this and that, but was never happy with how it looked so I left it for a while. Some inspiration came from Dave Gentry's Ruth, I thought about a similar Whitehall with transom, just a bit bigger and wider? I had a play, but transom plus skeg or a wineglass transom started to look like too much of a pain in the butt to manage in folding SOF, so I went back to double ended.


A Norwegian Faering like Clint Chase's Drake or Iain Oughtred's Elf? Problem is, especially in folding SOF it's hard to maintain too much of that beautiful upward curving sheer line.


I finally spotted some pictures of the Finnish rowboats, those I saw were more like the picture I had in my mind - the right size, nice clean lines, chine and gunwale lines that can be bent from a stick, so I had another go at drawing. Results are here, still some fiddling to do, but I'm getting closer to being happy with the looks and lines than before.


6100 mm (20 feet) long, 1120 mm wide, so about the same size as a big double sea kayak. A bit more rocker at the front than the Finnish rowboats, but keel line reasonable straight at the back for a bit of a skeg effect. First chine moved out quite a way compared to the Finnish Rowboats, so less deadrise and a wider beam at the waterline for more stability and load carrying capability. Profile still reasonably low for less windage - I'll rely on a deck to keep the water out in rougher conditions rather than the upsweep at the bow and steer of the Faerings and Iain Oughtred's double enders.








It'll be some time before I can build it, in the meantime I'll work on a "virtual build", see if I can get all the structure defined in CAD with a view to getting the ply cross frames CNC cut and the plastic snap in connectors between the cross frames and the stringers done on a 3D printer I have access to.


More on construction methods soon in another post.


Ian

[IanHowick]

Ok, a little on construction method:

Similar to my sea kayak, but 7 stringers (Gunwales, 2 chines, keel)
Keel and gunwale stringers of about 28 - 30 mm dia / 1.4 mm wall fiberglass tube (about the size of a kayak paddle shaft)
Chine stringers recycled from the 20.4 mm dia carbon tubes off my SOF kayak.


Cross frames from 12 mm Meranti ply.


Plastic connectors like this:



In cross frames like this: (These are for my kayak, ones for the rowboat will be minus the deck beam but with an extra chine)


This is an example of an early prototype corner connector I drew and had printed in ABS plastic on my sisters 3D printer:


Ian

[peterchech]

I like the concept. Why no transom though?

And do u have a source for those glass rods?

[IanHowick]

My thoughts against a transom were that a pointy stern leaves a simpler single vertical seam at the back for the skin, and I already have it figured how to do the construction back there with a built in skin tensioning system. I also don't have to worry so much about designing it/trimming it so the transom is only just out of the water. A transom allows wider/flatter lines at the back, but seems to rely on a skeg to provide some grip back there, which can be done on an non folding SOF such as Dave Gentry's Ruth but I don't think works on a folder. I think I would draw it with a small transom a bit like Colin Angus's Camper Rowboat if I was doing it in ply, but a transom in folding SOF raises more design issues than it's worth trying to solve.



Yes, I can source custom mandrel wound fibreglass tubing at a reasonable price. I can also source mandrel wound carbon tubing at a much less reasonable price. Think I'll go with a larger diameter fibreglass tube to save $, it works out at less than a fifth the price. If you are free to go up a diameter size or two, the glass tube ends up about 50% heavier than you could do in carbon, but the stringers are perhaps one third of the weight of the whole boat or less, so overall weight penalty is probably around 15% of total weight.

Main plus of the fibreglass tubing over alu is you don't get corrosion/binding issues at the joints between sections. It's easy for these joints to corrode/weld themselves together in a salt water environment. The other big plus is you can specify just what you want in diameter and wall thickness. Alu tube comes in a limited range of sizes and given the need for ferrules that will just fit inside the main tubes, there's not much choice in sizes.

Ian

[IanHowick]

Here is a quick look at the likely frame layout with outriggers in place. Orange ones in the middle for solo rowing, dotted in green is the placement for rowing two up. 700 mm between all the middle frames, so 1400 mm between front and rear rowing positions in double mode. 1600 mm across between rowlocks. I still have to get my head around rowing geometry, does anyone have some opinions as to whether I am in the ballpark with this, and or a good reference to the required geometry?

Here is a PDF version of the picture below, it maintains resolution as you zoom in on it rather than going blurry like the JPG

Thanks,

Ian

[upchurchmr]

Ian,

Whats the weight delta going from aluminum to glass, and also the cost of course? I was looking to get into my first SOF kayak and thought about aluminum, but it is pretty steep compared to wood I have sitting around. I really like the connectors with the 3D printer, this is one of the few practical uses I have seen, great idea. Have you thought about using the glass tubes instead of ply, putting two sockets into the connector?

I have seen some bent tubing used as the frames, my first idea was to just make saddles with a 3D printer - a simpler form of copying your idea.

My thoughts against a transom were that a pointy stern leaves a simpler single vertical seam at the back for the skin, and I already have it figured how to do the construction back there with a built in skin tensioning system. I also don't have to worry so much about designing it/trimming it so the transom is only just out of the water. A transom allows wider/flatter lines at the back, but seems to rely on a skeg to provide some grip back there, which can be done on an non folding SOF such as Dave Gentry's Ruth but I don't think works on a folder. I think I would draw it with a small transom a bit like Colin Angus's Camper Rowboat if I was doing it in ply, but a transom in folding SOF raises more design issues than it's worth trying to solve.



Yes, I can source custom mandrel wound fibreglass tubing at a reasonable price. I can also source mandrel wound carbon tubing at a much less reasonable price. Think I'll go with a larger diameter fibreglass tube to save $, it works out at less than a fifth the price. If you are free to go up a diameter size or two, the glass tube ends up about 50% heavier than you could do in carbon, but the stringers are perhaps one third of the weight of the whole boat or less, so overall weight penalty is probably around 15% of total weight.

Main plus of the fibreglass tubing over alu is you don't get corrosion/binding issues at the joints between sections. It's easy for these joints to corrode/weld themselves together in a salt water environment. The other big plus is you can specify just what you want in diameter and wall thickness. Alu tube comes in a limited range of sizes and given the need for ferrules that will just fit inside the main tubes, there's not much choice in sizes.

Ian

[johngsandusky]

Interesting thread, thanks for posting. I've tinkered in my head with a collapsible SOF tender. I'll be interested in your results.

[timo4352]

In cross frames like this: (These are for my kayak, ones for the rowboat will be minus the deck beam but with an extra chine)


Ian

Might I suggest - if you're giong to be partially decked - to keep two of the frames WITH the deck beams intact. I think you'll get alot of frame sturdiness from this.

Your idea is very interesting. I'll be watching to see what you come up with.

[IanHowick]

Might I suggest - if you're going to be partially decked - to keep two of the frames WITH the deck beams intact. I think you'll get alot of frame sturdiness from this.

Yes, exactly, frame one and two, seven and eight will have deck beams. Cockpit opening will be more or less a big oval extending from frame two to frame seven, with a bit of a side deck. I'm thinking I'll put an inflatable rim around this whole opening, with a velcro and or zip all the way around so I can go from a partly decked boat with a good raised cockpit rim to a completely decked boat depending on what I'm planning.

More on the questions from other posters when I get the chance.

Ian

[IanHowick]

Ian,

Whats the weight delta going from aluminum to glass, and also the cost of course? I was looking to get into my first SOF kayak and thought about aluminum, but it is pretty steep compared to wood I have sitting around. I really like the connectors with the 3D printer, this is one of the few practical uses I have seen, great idea. Have you thought about using the glass tubes instead of ply, putting two sockets into the connector?

I have seen some bent tubing used as the frames, my first idea was to just make saddles with a 3D printer - a simpler form of copying your idea.

Firstly, if you're talking non folding skin on frame, I think it makes the most sense to stick to wood and follow the methods detailed on Tom Yost's website (and also Dave Gentry's) Ply cross frames and WRC stringers, if you're in the Southern Hemisphere perhaps substitute Paulownia for the WRC and save a little weight. Skin it with the Polyester or Nylon skin that Dave Gentry and Kudzu on this forum use rather than the PVC Tom mostly uses. These boats end up quite a bit lighter, stiffer and cheaper than the folding versions with alu stringers and HDPE cross frames.

If you are going the folding route, then you need tubes that sleeve together. I think the choices come down to aluminium, glass or carbon. With carbon you can achieve about one third the weight for equivalent stiffness compared to anything else, at about ten times the price. Carbon tube for a sea kayak will come in at a bit over $40/metre, you need about 25 metres of the stuff.

Alu versus glass tube - you won't save much weight going from alu to glass a the same stiffness. Two big advantages to glass tube: You can spec exactly what you want for diameter and wall thickness, so you should be able to spec close to the most efficient section for the stiffness you want, maybe because of this you can save 20% weight over alu. The other big plus, nice close fitting joints and no corrosion problems at the joints.

Big plus of alu - you can do the ends just bashing the tube flat, drilling through and riveting, screwing or bolting the bits together. Carbon or glass needs a lot more care at the end joints, if I can make these on the 3D printer that should solve that problem.

More later, have to put the kids to bed!

Ian

[keyhavenpotterer]

Great concept Ian. Ruud who builds the Finnish rowboats has some great hardware, especially his simple sliding seat design.

http://www.puuvenepiste.fi/

Here is the web site of the designer of the Finnish boats. http://www.planet.fi/~kcad/index.html He does post some free designs on the canoe forums, so I think he might well be interested and prepared to look over the ergonomics of your design for you.

Brian

[peterchech]

My thoughts against a transom were that a pointy stern leaves a simpler single vertical seam at the back for the skin, and I already have it figured how to do the construction back there with a built in skin tensioning system. I also don't have to worry so much about designing it/trimming it so the transom is only just out of the water. A transom allows wider/flatter lines at the back, but seems to rely on a skeg to provide some grip back there, which can be done on an non folding SOF such as Dave Gentry's Ruth but I don't think works on a folder. I think I would draw it with a small transom a bit like Colin Angus's Camper Rowboat if I was doing it in ply, but a transom in folding SOF raises more design issues than it's worth trying to solve.



Yes, I can source custom mandrel wound fibreglass tubing at a reasonable price. I can also source mandrel wound carbon tubing at a much less reasonable price. Think I'll go with a larger diameter fibreglass tube to save $, it works out at less than a fifth the price. If you are free to go up a diameter size or two, the glass tube ends up about 50% heavier than you could do in carbon, but the stringers are perhaps one third of the weight of the whole boat or less, so overall weight penalty is probably around 15% of total weight.

Main plus of the fibreglass tubing over alu is you don't get corrosion/binding issues at the joints between sections. It's easy for these joints to corrode/weld themselves together in a salt water environment. The other big plus is you can specify just what you want in diameter and wall thickness. Alu tube comes in a limited range of sizes and given the need for ferrules that will just fit inside the main tubes, there's not much choice in sizes.

Ian

Do you have a link for that tubing? For aluminum too?

I need a tender that can fit on my boat, was also thinking about an sof folding tender. Im sure it's been done before (everything has) but wonder if there is a link with pics. I could store an actual rowing boat that way, instead of a wet motor only inflatable...

[IanHowick]

Ian,
Have you thought about using the glass tubes instead of ply, putting two sockets into the connector?

I have seen some bent tubing used as the frames, my first idea was to just make saddles with a 3D printer - a simpler form of copying your idea.

I thought out and tried your first idea of making cross frames from plastic connectors at the corner, connected together to make the cross frame with tubes that fit into sockets in each connector. (Using half inch HDPE for the conectors) I didn't like it. Problem is the tubes can put a lot of leverage into each connector, there's lots of stress concentration and ways for cracks to start and propogate, also it's got no/low resistance to twisting forces, so I don't think it's an elegant solution. Scary thing also is if it come apart at a corner, there's two sharpish tube ends ready to poke a hole through the fabric at that point.

Bent alu tubing for frames: Could be made to work. I've seen a non folding rowboat done this way (over on boat design.net in that long 'fast rowboat' thread?) I think he just pop riveted the joins. I've seen an, I think, Russian made folder with cross frames made this way and plastic connectors at the corners as you suggest. Problems are bending the tube accurately and reproducibly to the shape you want so the corner connectors end up in the right place. I guess it could be done, but I also think you'd end up making each frame three or four times before you got it right. The other problem is attaching the corner connector reliably to the alu tube at each corner. I think you'd be relying on pop rivets or self tapping screws, again, long term it's easy for the plastic to start cracking at the point where the rivet goes through. I recall the Russian made folder I saw had problems along these lines. Other downside is that without ply cross frames, it would no longer be a wooden boat and we'd have to discuss it somewhere else!

I've found the ply cross frames very strong and light, my kayak weighs 10 kg, but I could stand on any of the cross frames of they were held upright. The connection between the ply and the plastic corner connectors I've shown above should be very strong with the connector fitting into a semicircular cut-out in each corner and wrapping around the ply as well.

Big plus of the ply frames is reproducible accuracy. If making them by hand, you mark and drill the cutouts where the stringers/connectors will fit, then cut the rest of the shape from there, so the important dimensions are located to within a mm if you are careful.

I am doing all the cross frames and other ply bits as dxf cutting files that I can send to the CNC router folk, so all those bits will come back ready made to very high accuracy. I'm in the middle of setting up these dxf files so they are linked dynamically to the design, and update automatically as I make changes to the design. Once I've got it all sorted, I can get another set made just the same, or change beam, LOA, rocker, deadrise or whatever and all of that is reflected in the dimensions in the cutting files. I'm doing the same with my kayak, the payoff will be that having sorted a kayak for one of my four kids, I can knock out kitsets for the rest of them quite quickly.

Ian

[IanHowick]

Do you have a link for that tubing? For aluminum too?

I need a tender that can fit on my boat, was also thinking about an sof folding tender. Im sure it's been done before (everything has) but wonder if there is a link with pics. I could store an actual rowing boat that way, instead of a wet motor only inflatable...

SOF folding tender: I think would be great for once you've got somewhere nice in the big boat, and want to go off exploring smaller/shallower waterways in a nice light rowboat. Maybe something shorter, similar to Gentry's Whitehall? Put a sail rig in it too of course.

My source of fibreglass tubing and spars is Killwell Fibretube in Rotorua, New Zealand. http://www.kilwellfibretube.co.nz/

I've sourced carbon tubes and spars from C-Tech in Auckland. http://www.c-tech.co.nz/

Both good to deal with and indulgent of my various projects and capable of sending stuff worldwide.

As far as a utility tender primarily for getting between shore and the big boat on a mooring, I'd be inclined to stick to inflatable. If you don't like a motor, the inflatable canoes are good and surprisingly seaworthy and capable of making good progress with a double paddle.

One of these below has done Skagway to Vancouver Island. I managed to fit camping gear, food and my then eight year old daughter in one and paddle for three weeks around the lakes of Eastern Germany. With both of us on the double paddles we could overtake German couples padling double canoes with single paddles.

Ian

[IanHowick]

Ian,

Whats the weight delta going from aluminum to glass, and also the cost of course? I was looking to get into my first SOF kayak and thought about aluminum, but it is pretty steep compared to wood I have sitting around. I really like the connectors with the 3D printer, this is one of the few practical uses I have seen, great idea. Have you thought about using the glass tubes instead of ply, putting two sockets into the connector?

I have seen some bent tubing used as the frames, my first idea was to just make saddles with a 3D printer - a simpler form of copying your idea.

Here is a link to that Alu SOF Rowboat with alu stringers and bent alu frames, perhaps it could be done similarly with plastic saddles made on a 3D printer for the stringer-cross frame connections so that it would be a folder.

This guy is an aircraft engineer, so did everything in alu and some composite, no wood at all.
Ian



Ian

[upchurchmr]

Ian,

This was a nice build, I'm still leary of the price. Aluminum seems to have shot up, possibly while I was not looking.

[IanHowick]

Ian,

This was a nice build, I'm still leary of the price. Aluminum seems to have shot up, possibly while I was not looking.

I must admit I haven't looked at the price of aluminum recently. I think if you don't need folding, all wood is the cheapest and easiest. Cheapest pine you can find for stringers and whatever 12 mm ply you can find for cross frames, it should be possible to position around the knots if necessary, all ply is done with waterproof glue so it shouldn't fall apart.

I've been amusing myself playing with a virtual build. Cheaper again than building in wood and glass tubing!

Results here, I have the cross frames and stringers in place. Still to do the stem and stern pieces and the plastic connectors to hold it all together. (The stringers end about where they are shown, ferrules on the end of the stringers fit into sockets in plastic pieces on the end frames)

[IanHowick]

Another look at how I'm figuring on doing the deck. Red cockpit rim a sleeve that will take an inflatable tube that will act as a bit of a breakwater.

Ian