designing a fast rowboat

Great to hear from you Gerhard! Although you don't build boats, I'm sure you will have a lot to contribute to this because as you said, you sure can row them! I think all design is a theoretical challenge that only gets real proof once the boat is wet and in various conditions. So I imagine more rower commentary will be invaluable for this forum. And as you've probably noticed, the guide boats have been a bit of the standard for fast rowboats- i.e. "is this faster than a guide boat?" is a good benchmark from which to start.

My original plan was to row the Blackburn fixed seat this year and sliding seat next year, but right after the race last Saturday I knew I would have to do fixed seat again! You guys inspired me and as you said, it will be very interesting to do this race again in what will probably be rougher conditions than this years bathtub calm. Will my boat be faster in waves? Interesting stuff.

I'll second your Pat Brown endorsement. Your guideboat looks much more refined than others I have seen. Nice lean lines on that.

On NoEyeDeer's comments: I agree entirely. Its a good point that the wherry is a different boat entirely. I do think it is still interesting though, because the boats have similar specs, with the wherry being much more traditionally shaped. On a general comparison of the new boat with the more traditional take, the new one is better all around.

And right, I don't think I'd go out to say my boat is faster solely because of the transom and transoms categorically are faster. There are so many factors here. I do think the full run aft (like a surf ski) helps a lot. I suppose I could carve out of balsa or foam a pointed stern extension and bolt it on the transom and do some compare and contrast that way.

So far, as is, I've clocked this boat on a gps at 9.3mph in a sprint on a calm inland lake and don't feel like it was bogging down yet. Just under 9mph can be maintained on longer sprints. This is fixed seat, set with a light pull for long rows. I hope to fit her with a slide at some point to see what happens.

 

paulownia

Checking out this Paulownia wood more… found my wood for the next build! Great tip.

 

It's getting pretty popular over here. Locally grown and sustainably sourced, and at a reasonable price too, with an excellent strength/weight ratio.

One drawback is the species can turn weedy in some areas, which needs to be watched (Australia already has enough problems with introduced flora and fauna going feral). Also, apparently some of the stuff sourced from China can be of variable quality. The Australian-grown stuff is fine AFAIK. I'm thinking of grabbing some if I get round to building another boat (have to finish the current build first, dammit).

I have to say you guys are keen with your 20-30 mile per day races. I'd be hard put to get enthused about anything longer than 10 miles, and even that would be pushing it for racing. Past a certain point I start thinking I could go a bit slower and enjoy it more.

 

I'm impressed by Ben's speedy craft. He avoided issues inherent in this design which I only belatedly tried to modify.
I row in a marina, in circles, and wanted to get past the breakwater to the open bay. I almost bought a used Wayland Merry Wherry 2. The guy selling it, a wonderful artisan boat builder, persuaded me that I could build my own boat....

So, I just finished a Firefly Double designed by Ken Basset. It seemed a good choice at the time I (utterly clueless) started building it some 5 years (!) ago as a fast open water boat. Since then I've learned a lot, much of it from this thread. It remains a great design for its intended rec use. I omitted the wooden skeg, hoping to reduce drag and weight, and used thinner ply than called for. I stretched it, and added sheer, per Ken, and stiffened it with flotation chambers and decks. I played around with changing the stern shape to reduce drag there but finally just went with a racing fin. Without the row rigs it weighs 85lbs but with them about 125lbs, which is not ideal for speed. A five-minute test row -- all I had time for the other day -- yielded a 6.1 mph speed at 75% pressure with a growing wave wake. Not sure how much faster it'll go. As the guy rowing with me said (he's used to racing singles), "It's a f#@%&n' tuna boat!"

I'd like to figure out how to tweak it so it can go 7 mph easily, for long distances, but that may be dreaming. Didn't manage to attach a short video -- it's at: https://www.flickr.com/photos/slowslide/14492042752/
It looks like the stern, despite the huge rocker, may be dragging a bit which could be helped by putting the heavier guy -me- in bow. Beyond that, I don't know.

 

How to make it go 7 mph easily:

1/ Sell it.

2/ Get a Savo 650.

Seriously, the Firefly was never that great a shape.

 

Yes the Savo is speedy. Interestingly, the waterline beam on the Savo 650 Double is about an inch more than the Firefly's, and the waterline length is about the same (more overhang though on Firefly). The max beam is 39" on the Firefly but 50" on the Savo - which has oars-on-guwales, so no heavy riggers. The Savo is 20-odd pounds lighter too. Still, the Firefly shape looks like it should go faster.

 

Ok. So row it faster. Easy.

 

"Ok. So row it faster. Easy."

What's your problem? You clearly are more interested in rubbing someone's nose into his choice of boat than helping him understand the dynamics of why it's shape / hull form doesn't work as well as others may - which is what I was thought was the point of this thread.

 

Bad news is your Firefly sounds like it is hitting hull speed at 6mph, which means there is nothing else you can do to modify, change, trim, etc to make this boat go any faster. Good news is, you are now a boatbuilder, and as the photos show, a good one at that! So not a poor result in the end after all!

Judging by the photos, not a lines plan, the firefly is slow because:

-looks like a narrow entry that too abruptly widens out
-V-bottom, hard chine shapes in my experience as a rower just aren't as fast as more rounded hulls, even given similar specs
-the exit is bad. Even thought that wide transom is out of the water, it appears your waterline exit is still very chunky, and will drag and not release the water well no matter how high the transom gets. ***Be careful about over-weighing the bow of this boat in attempts to remedy the designs unavoidable wave making as you will find yourself broaching wildly and capsizing in any sort of following sea.***

That could be some reasons why the Savo is faster. On the other hand, despite the streamlined water shape of the Savo, looks like a whole lot of boat there out of the water, and I wonder how that will feel on windy coastal afternoons?

 

No problem. He says it's not fast enough. I say ok, perhaps he should get a faster boat if a faster boat is what he wants, and the Savo's are on record as sustaining the sort of speed he wants. I'd call that a useful suggestion, since I'm assuming he just wants an existing design that delivers the required performance.

He says his one looks faster. I say ok, go for it. Point being that if someone is determined to stick with what they think looks faster, regardless of whether it is or not, there may not be much you can do. Either way, it's up to him and I'm not worried.

The Finnish classes have a minimum depth requirement, which seems to be a leftover from the traditional (much heavier) boats they developed from. If not building to class rules, I assume it would be easy enough to lower the sheer a bit.

 

I have to agree with Ben's assesment of V hull vs rounded hull as losss of speed. Just did a local fun row yesterday and was checking out the boats to see what I could convert to a faster rower. As I explained my ideas to a man who built his own kayak , he quickly brought up the need to stay away from the hard chimes that his boat has.

 

NoEyeDeer- I see the "faster" sentence is unclear -- I meant faster than the Firefly currently goes, not faster than the Savo. I just finished the boat (actually it needs some additional paint yet) so it's just a tad early to toss it away and I think I'll stick with it and see if minor things improve it in minor ways. It's useful for conditioning rows at least.

If this thing hadn't taken so long given my nonexistent spare time I'd dive in and build something with what I've learned. In the meantime, I have an old Hudson T7 that I think can be made fairly seaworthy. I see one won the touring double in the Blackburn some years back. It has a flat bottom with rounded sides like the Alden 18s but it is 22' long. It also has a transom which would drag, and that gets back to cleaner exits...

So a question: I might be able to add a stern extension that would lessen drag. Ben notes the slight V of the upswept Firefly stern exit is not ideal -- is a flat upswept stern better, or as much as a taper (double-ender look) as I can put in it and keep it under the Blackburn length rules (23')?
http://bp1.blogger.com/_tKg2hGaEXYE/SDwVIJh7O4I/AAAAAAAAALQ/FGzN-yYkKrE/s1600-h/photo-720300.jpg
This is the T6 I think --- the T7 is same beam, a meter longer.

I meant to do some races out here on the West Coast in the Firefly but the San Diego Bay2Bay evaporated, as did the Monterey to Santa Cruz, both while I was building. Before that, the MDR to Catalina race was discontinued. My family is originally from north of Boston and I still have a cousin in Essex, so I've always had a bit of an obsession with doing the Blackburn. Just need to solve the logistics and carve out enough time for driving the boat out, etc. That and do it before my age and my erg times increase much further.

 

I've never had anything to do with the double Firefly. I did row someone else's Firefly single years ago, and IIRC they're basically the same as the Liz. From memory: short waterline, so consequent high wave drag when pushed hard, and pitching when using the slide. Lots of wetted surface for the length. Lots of stability. It looks like they were meant to provide a very stable platform for people who wanted a sliding seat, but didn't want to row hard and were happy pottering around.

Single chine boats tend to have more wetted surface for the same displacement. This is probably as big a factor (maybe bigger) as any drag from the chines themselves. Wide flat sterns also have a lot of wetted surface for their immersed volume.

That T7 should go alright, judging by the pic of the T6. Ben Booth reckons his transom is fine.

 

"...was checking out the boats to see what I could convert to a faster rower."
hmmm… Mungoman do tell us more please!!!

"Ben Booth reckons his transom is fine" - well, partly because it is a pretty fine transom! Photo below looking aft shows there's not a lot of width there - plan was just enough transom to bump up top end speed with minimal added turbulence at moderate speeds.

Tallman: Yes, do the Blackburn!!! Looking through results and types of boats entered in the touring double class - these are boats that are probably no faster than one of the two you have. Best times are hovering around 3 hours. So you need about 6.5 mph to be very competitive. I'd do tons of time trials in your options and see which one is faster in the whole range of weather.

"Ben notes that the slight V of the upswept Firefly stern exit…" Its not about the slight V vs a more flat - its the upswept exit itself that is less than ideal. It seems from the photo that where the Firefly leaves the water, there is still lots of width, wetted surface, potential drag, etc. So I wouldn't recommend adding any stern extension to the t7 that sweeps up out of the water. And if you try to extend it to a double ender, you also need to factor in harmonizing the run with the rocker. So if that transom is already at waterline, rising from a slight rocker, there is no place further for it to go except up and out. If you have a dead flat rocker, you could extend the stern to be a double ended shape. But a boat is such a balance, if there is any unfairness introduced you were better off before. And the t7 as is already has speed competitive with the class. So if spare time is short, at this point time on the water rowing may be more effective than further boat work(?).

if you want to blow the class away, we could think about stretching the Westport Racing Skiff to 23 feet or so…

 

Ceconite.
http://www.aircraftspruce.com/catalog/cspages/ceconitefabric1.php

We use it on the decks of our racing canoes. Strong enough to take some tough abuse. People sometimes fall right onto them. Clips of the 120 mile non-stop AuSable Marothon start:

https://www.youtube.com/watch?v=VM6-DsfVFxg
https://www.youtube.com/watch?v=UsaDec4o5bE

BTW the boats are CarbonFiber-NomexHonecomb-CarbonFiber and weigh less than 30lbs. 18.5ft (5.64m) and 27" beam at the 3" waterline. 33" beam at gunnel 10" above the keel. Deep water paddle speeds are close to 7mph for winners(14.5hours), 6.4mph for me healthy, 5.8mph injured last weekend (17.5 hours 52nd out of 82).

This boat might make a great single place row boat for open water and two place for inland lakes. We paddle across mile wide dam ponds in fairly windy conditions sometimes. My nephew and I have paddled and surfed in Lake Michigan with 2ft chop, but that is something that almost no one else will do. We didn't do it for very long maybe an hour.

The seats are 7" above the bottom of the boat. A lower seat in the middle of the boat would be very stable.