Rowboat geometry

[seo]

I just bought an old fiberglass 12' canoe to use to go out to my boat on its mooring. Going off of a beach, I'd rather portage a canoe down to the water than drag one behind.
The idea is to rig it up for rowing. I've done this with bigger canoes, and they make great rowboats, very fast and easily driven, and when you get the weight out of their ends they're a lot less prone to driving their noses underwater. This 12' boat is a fat little thing 44" wide amidship, and paddling it single is about impossible. Maybe with a skeg or rudder... But rowing seems a lot better.
In the past I've just used a box for a rowing seat, and put the oarlocks where they looked about right. With this much smaller boat, correct placement and geometry seem like they might be more important.
Are there any rules of thumb for height of seat vs height of rail (9"on this boat), placement of oarlocks vs position of seat.

[robert666]

Seat 6'' below the rail, rowlocks 7 1/2'' aft of aft edge of seat seems to be the standard on 14ft rowing boats.

Robert

[Candyfloss]

On my dinghy, the seat is 150mm below the gunnel, the rowlock is 250mm aft of the aft edge of the seat. Works pretty good.

[Bobcat]

I just got back from rowing my canoe. I would recommend trial and error, starting with the measurements above. I put a box seat a bit aft of amidships and clamped on the oar blocks and went for a row. I would then adjust both seat and oarlocks until it felt right. Once I was happy with the set up I mounted the oarlocks to the gunwale.

[seo]

Thanks, all. What Bobcat says makes great sense, because the length of oars, personal preference, phase of moon, price of pickled newt's eye, will all influence my decision. And the hesitation to just go ahead is of poking holes in the hull, which a movable box and clamp on oaklock pads eliminates THAT excuse for inaction.

[Bobcat]

Just make sure the clamps are tight. There's a lot of force with an oar prying on an oarlock. One of my oarlocks is in the mud in Lake Washington. I did not lose the clamp, but the oarlock made a nice expensive plop on the way down

[seo]

Thanks for the advice. I shall rig them with tethers. I'm curious to know what kind of canoe you have, length of oars, etc. Canoes that I've had rigged for rowing are a very big 19' Aluma Craft "Y stern" motor canoe. It was a good motor boat, able to cruise right along with four people on board, pushed by a Neptune Mighty Mite. It was a heartbreaking sloth to paddle but would go along pretty well under oars. I've also had oars on my 17' Old Town Guide, which will go fast. My observation has been that a canoe well rigged up for rowing, with good oars, will go about as fast as the same boat paddled by two people of similar ability to the oarsman in the other boat, particularly after half an hour or so going upwind.

[Bobcat]

I have an Old Town Camper, a 16 foot Royalex canoe. I bolted wood blocks to the gunwale with oarlocks on them and row with 6 foot oars. I sit on stool and in turn sits on a wooded rectangle with foot stretchers on the other end. The end of the stool is notched to sit on the rails of the rectangle and whole thing just sits in the bottom of the boat. My weight hold it down. The oarlocks are set up so with a passenger, I can get on the front seat and row (I row the boat stern first usually) and put the passenger on the stern seat.

I have also rowed with 8 foot oars and a homemade set of outriggers. It is successful, but I have given it up since I got a sliding seat

I am currently rowing with a Piantedosi Scout sliding seat rig. It is made for canoes. It works great. I move right along with 9 1/2 racing sculls

[seo]

I have often looked at the kind of weird, tweaked shapes of Wenonah kevlar canoes, which look like pregnant salamanders (or something). But that shape, skinny at the ends, fat in the middle, might be good for rowing. Your explanation of rowing positions for one/two person in your boat isn't entirely clear to my addled brain, but that's what I'm looking for-a good position for single, one pax, two pax (or a pax-load's worth of stuff.) I'd be interested to see some pictures, if you have them.

[Bobcat]

No need for pictures. I have oarlocks mounted about a foot forward of amidships. When I row solo, I row the canoe backwards: Meaning the stern is the bow and I face the stern, propelling the stern through the water. When I have a passenger, we row the boat the other way with the bow being the bow and the stern the stern. The rower sits on bow seat and rows. The passenger sits on the stern seat.

I hope that's clear

[seo]

Yesterday I took the canoe out with clamped-on oarlocks, and the proper spot was about exactly where Bobcat said it would be. The correct seat turns out to be a 5" thick piece of ethofoam, which I happen to have, so that's simple. Tried some 5' oars, which were too short, and some 7' spoon blades, which were a llittle too long. Six feet ought to be about right.
Which leaves the question of how to mount the oarlock sockets. The hull is conventional uncored fiberglass, the gunwale is a one-piece hollow extrusion, riveted to the hull with pop-rivets. Having replaced gunwales like this before, I'm pretty sure that there's a strip of aluminum inside the extrusion, which serves as a washer plate so the that rivets have something to "pop" against.
I have two kinds of sockets on hand, the strap-with-socket type that screws to the hull, and the spigot-with-flange type that's installed in a hole drilled vertically into the sheer.
The strap would mount to the hull, and so would be below the level of the top of the gunwale, and so would require a mounting pad of wood, and besides, they stick out and gouge at the sides of boats when you go alongside.
Which leaves the top-mounted flange sockets. It would be great to mount them in the PVC gunwale, but I don't thing it's strong enough. Which means an externally mounted strake, or reinforce the gunwale. Right now I'm leaning toward the latter. Drill the mounting hole, and use that as access to pack a foot or so of gunwale with reinforced putty, either epoxy or "Hull and Deck" polyester. Then maybe a 3/8" X 12" oak stiffener piece fitted on the top of the gunwale, attached with screws and urethane goo, drilled for the socket.
I had to take the center thwart out to give room to sit, and the hull sides flex quite a bit when rowing. A bit of stiffening is probably in order. If the oak piece on top isn't enough, I can put some longitudinal stiffeners on the hull below the gunwale. Either an internal spruce stiffner, maybe 1 X 1 X 50", or oak, mounted on the outside, as an additional rub strip.

[almot09]

To help with a psychological barrier of drilling holes, there are clamp-on oarlock mounts - I think by Old Town - they don't require any drilling. Probably a crap, in the long run. But you may try it before drilling.

Positioning of oarlocks... I saw numbers up to 20.5" from the center of the seat (16.5" from the rear edge) for wide canoes. A bit of difference from 7.5" (measured from the rear edge) suggested above, I don't know why. May be try first with temporary C-clamps in lieu of oarlocks.

Same with oar length - through trial and error - though this can be spendy if you don't already have pairs of oars of different length. You probably know 2 formulas for oar length, one is (0.5B)*25/7, another one is (0.5B+2")*25/7 where B is the beam. Round up to the nearest 6". Those +/- 2" make for 0.5ft of difference in oar length, i.e. in your case 6.5ft or 7ft.

Seat height - Duckworks Magazine suggests 6"-8" from the stretcher (footrest), rather than measuring from the rail.

Reinforcing the gunwale - can't help here, but again, the article that I mentioned http://www.duckworksmagazine.com/05/columns/welsford/5/free.htm suggests minimum 46" between the oarlocks. So if you add 2" or 3" thick pieces of wood on the outside (shaped somehow to make it flush with the gunwale lip?), you can mount those flush oarlock mounts on them and it won't be too wide. Well - may be just a little too wide, considering how short your boat is. I'm curious whether this reinforcing will eliminate the flex of the sides. May be internal vertical rib will be needed.