designing a fast rowboat

Outrigger canoes

As Terry knows I'm trying to figure out a project for a stack of 13" x 60" 3mm 3 ply Baltic Birch. The grain runs in the short direction in the outer layers. I was thinking of a kayak, but maybe the annelid segmented approach would work on an outrigger canoe. I'll do a search and maybe start a new thread, but if anyone knows of good plans for a medium performance example suitable for a 200lb 64 year old, I'd be interested.

 

I looked up annalid and got worms!

I think of it as vertical chines: that idea goes back to your post #1217 in this thread. Currently I am considering it for a new sailboat design I working on at http://www.boatdesign.net/forums/boat-design/kempenfelt-12-1-2-a-42130.html

As you know I looked at it earlier in this thread and tried it out on a paper design for a canoe. I came to the conclusion the ply would not bend tightly enough to make a stable hull narrow enough for a canoe.

However, for an outrigger canoe that restriction is removed; you can have a semi-circular body plan shape with enough buoyancy. Ply bends easily to a radius 100x the thickness or 12" for 3mm ply and a bit tighter at some risk of breakage. It varies with different woods, I can get 9" from 4mm Okoume ply or R = T x 57, and it will do better with heat. So you should be able to build a narrow, fast boat with really low wetted surface. The ama could be built from the same ply, it wouldn't matter if the face grain went the 'wrong" way for that.

A rowing shell may be a good place to start for a design if you cannot find an outrigger canoe design. I suggest you start a new thread if you want to pursue it further.

 

Annelid

Yes worms with their segmented bodies is what I was getting at. I ripped one sheet in half and it easily bends to a 19" circle or various ellipses. I did start a new thread, but if I build this thing maybe I can figure out a way to row it.

 

There simply isn't a really good solution for ocean rowers. I have a system in mind, but it's relatively simple and as no one has done it, there must be a flaw that I can't see.

I do think that for the system I have in mind, building a scupper gate just above the water line and putting a strong electronically controlled gate which would prevent water coming in from following waves is doable with new, DIY electronic technology. If curious, see this forum (but be warned only a few comments seem to understand what the clean sheet bilge design is intended for):

http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/dumping-bilge-through-oar-power-38356.html

 

I doubt the speed of a rowboat is likely to be high enough to operate a regular auto-bailer except for a racing shell, where the additional drag would be unacceptable.

Using the acceleration of the rowing cycle is an ingenious concept, but one problem is the transom of a rowboat is raised above the bottom; even as little as 3" requires a speed differential of at least 4 fps to overcome even with 100% efficiency and I don’t think any rowboat would have that much speed variation. Some kind of venturi device to exchange speed for pressure somewhat on the principle of a steam-powered water injector may work to elect water either above or below the waterline, but I would want to be convinced by results.

A more fruitful approach might be a foot-operated pump of some kind, perhaps using ankle rotation to avoid wasting energy when the boat is dry.

Theoretically the best approach is be to find a way to stop the water reaching the bilge in the first place so you don't have to work to get it out again. Kayaks are mostly decked to keep the water out and kayakers can use skirts to seal themselves into the cockpit. That's inconpatible with a sliding seat, but it should be OK with a fixed seat craft and should also work with the sliding outrigger rigs discussed earlier in this thread.

 

I'm going to quote you on my thread. Thanks for that. I'd like to know more about how to get the numbers you gave. Could you reply there? Many thanks.

 

rowing solo

I've signed up for two races: one in Essex on May 19th and one in New Bedford in mid June. As it stands now, I'll be rowing solo in my skin on frame boat. Just celebrated (?) my 68th birthday and am determined to keep racing and competing if not winning as long as I'm able to. New boat projects are on hold untill I can settle on a good looking design. Does any one have any thoughts on a 20' St. Lawrence skiff as a good double boat?

 

I thought I read somewhere the St. L skiff wasn't as fast as the guideboat in the Blackburn...maybe a 20' guideboat?

I've been noodling away at a glacial pace on a Firefly 2 (by Ken Bassett) and recently picked up a little momentum.
http://www.flickr.com/photos/slowslide

It's stretched to 22.9' with half an eye towards the Blackburn should I ever get it east for their touring double division. I went with 4mm ply instead of 6mm for weight, ditto a ply transom over cherry. The sitka chines and keel, though, are wicked heavy (relatively -- I come from a racing shell background) and I hope to shave them down once I get the boat turned over. It'll use two Piantedosi rigs (wish they were lighter) and has to be okay for two guys to put on a roof rack (or special small pickup rack and front T support) as a trailer is out of the question. I'll have to figure out an ultralight decking/coaming to make it more seaworthy.

The plan is to put a thin racing shell fin on it rather than a fat skeg but I'd like any ideas to further clean up the tail drag on this - perhaps some shaped piece? I want to wring as much speed and efficiency out of this as possible.

 

Looks like a fast boat!

Just a thought: I also used chine logs on my canoe; I glued them to the sheer planks while they were flat. The logs helped stiffen the floppy (3 mm) planks for easy handling, and once they were hung on the building mold the ply supported the logs while I power-planed the bevels.

It allowed me to use lighter chine logs. It also meant I only had to plane one bevel per log and didn't have to worry about getting two bevels to meet along the centerline of the log.

The method is OK with 4 mm ply but they get too stiff if the ply is thicker. It can't be used if the garboard and sheer planks are at too fine an angle though.

Dora Canoe Build

 

I don't understand the comment "It also meant I only had to plane one bevel per log and didn't have to worry about getting two bevels to meet along the centerline of the log." Why would you have to plane more than one bevel per chine log if the chine logs were installed after the side panels were in place? Fasten/glue the chine logs to the installed side panel, then bevel the bottom of the logs to match the bottom panels. Same as beveling if the logs were installed with the side panels.

 

DC- normally you can't just twist the chine log in the molds to line up with the hull sides. The twist would end up different from the developed ply surface. So you install it squarish in the molds and bevel both faying surfaces. You can set the top edges of the chine log to the desired angle for drainage this way as well. It's no big deal either way. If the chine log is visible, that is an important sight line and that exposed edge can't just be left topsy turvy. Using the molds to locate that edge is important to a good appearance. Chine logs usually taper, and it is better to have the taper on the faying surface than the exposed one. And ply on frame construction often involves torturing the ply to conform to the rigid frame, unlike the stitch and glue techniques.

 

Notch the molds for the chine log. Install the chine log, twisting as necessary, after installing the side panels. Top surface can be given a constant bevel for drainage, same as when pre-attached.

Nothing wrong with you method of pre-attaching chine log with everything flat since it works for you. But it may not work for boats with more shape.

Frames will generally not be straight for developed surfaces. There are exceptions such as flat bottoms and sides with constant flare.

 

David, in post #1373 Tallman commented on the chine weight, and photo DSC00813 in the linked web site shows a nicely beveled but hefty chine log. I passed the idea on him in case it was of use for his next boat since it saves weight and effort. As I noted earlier it may not work on all designs, but then, what does? I think gluing the log to a flat plank would be easier than twisting it to fit a plank that was already installed, but each to his own . . .

 

Interesting chine idea! But if I ever do this again I think I'll try stitch and glue to save weight even if the sanding is a nightmare. This will have 4oz S glass on the outside and inside, with small extra ply ribs to stiffen the bottom panels.

This builder's photos show the Annapolis wherry with a sort of triangular structure below the skeg that would seem to clean up flow aft, like a mini version of a racing shell stern:
http://www.flickr.com/photos/trentschler/5738052069/in/set-72157626636048593

Is there a tapered short extension design or some way to clean up water flow at the stern in a more V-like manner that will lessen wave drag but not add too much friction drag? I'm thinking made of light ply or even shaped foam covered with fiberglass.

 

What are you referring to as the "skeg" and as the "triangular structure"?

In the photos of the Annapolis wherry I see a short skeg attached to the bottom plank. The garboard planks are twisted and become almost vertical at the stern, similar to some Jersery beach boats. My guess is the short skeg intended to improve tracking. I don't think it will do anything to "clean up the flow aft".