designing a fast rowboat

Blackburn Challenge 2015

A great report about the race: http://www.surfskiracing.org/2015/07/2015-blackburn-challenge-a-race-to-remember/

Blackburn Challenge photos by Leslie Berchtold Chappell: https://drive.google.com/folderview...1hpcEMyUHI2dGd3d0F2WmwwSDA&usp=drive_web#grid

 

blackburn

Thanks for the congrats guys! Guess I better give a little "race report." This was about the best one ever, and deserves a book of tales. It will be interesting to do a full look at the boats, the times, and user feedback. But for now, here's a little non technical race fun reminiscing. It's only merit may be in planting the Blackburn Bug a little further under everyone's skin(?) :

"We're getting reports of four foot seas coming out of the river." This call at the starting line was our first real glimpse at what lay ahead - yesterday's weather report betrayed us into thinking this would be a fast year.

it was no joke coming out of the river. White caps, steep seas piled on top of each other, wind against current, and water piling up to eye level with that nice stormy grey color. Within the first mile of this open water, I passed a racing double split right in half, tended by a powerboat. The first of many scenes of carnage. Word is, a few boats broke up. Shells split, OC-6s lost outriggers, boats sunk, and a big collection of DNF tells the tale.

I played the angles and kept a steady pace into the wind and seas. I passed the two ferocious Guide Boat rowers along this north shore, and they were putting down any last doubts about guide boat seaworthiness. They had to bail a couple times (as no one was stopping breakers from boarding), but otherwise looked more intent on racing and not overly concerned with the seas. They looked good in the chop, and put in times at the top end of all rowing classes.

Coming around Halibut Point put the seas (a little more moderate here) on the beam. I went further offshore to change my line into a little more down wave than straight beam, and looked for some big ones to surf. I think my course change, even though longer on the miles, paid off, as I caught the first place racing single (which started in an earlier heat) along this stretch.

The home stretch along the south side was more protected, and had moderate waves topping out no more than 2 feet. Still steep though, making great surfing conditions, and an intriguing technical row. The WRS surfs like a dream, and I was in a fun surfing duel with a surf ski all the way into the harbor. Amazing how much ground you can gain or lose depending on wether you catch each wave or not.

Coming through the harbor to the finish was less fun. Its still a surprisingly long stretch of water. Without the waves to focus on, it was just a slow slog into the wind and current. Luckily, I was still amidst a bunch of surf skis, so let them define the straight course to the famous "greasy pole" finish line.

Its going to be hard to top this one!

 

Great report and great race. Awesome.

 

As a veteran of 23 Blackburn Challenges I followed this one closely when the weather people forecast NE winds. When they blow from that direction it's a day's work just getting around Halibut Pt. And then you've still got about 2/3 of the course in front of you! The currents, chop and groundswell all coming from different directions combine to make very difficult conditions. The race becomes secondary, you just want to get around the damn point without swamping.
And from watching the videos it is clear this year's race was the most challenging, worse than any I encountered. Part of me wished I were there and part of me was glad I was at home. For anyone who finished this year's race it is a huge accomplishment. Howard would be proud.
The fact that Ben Booth finished first in the recreational sliding seat division and only seconds behind the first place winner in the single racing sliding seat division in the boat that he smoked everyone as a fixed seat last year is beyond remarkable. The fact that he designed it and built it himself adds to the accomplishment. He is not a boatbuilder or designer by trade, but a great rower with some very well thought out, maybe unconventional, opinions as to what makes a boat fast or seaworthy. It's a little hard for us older guys with our own ideas and our commitment to traditional stuff but Ben has made things exciting and generated some new interest in this open water rowing thing that we all love. Kudos.....

Jon Aborn

 

Great thread here! Ive learned a lot and I have been playing around with an idea for a simple to build two man, long distance, row boat. it would have drop in sliding seats and be able to hold gear, food , and water for two rowers for 3 - 5 days. If any one would like to look at the attached numbers and linespan I would greatly appreciate any input. Thanks

 

Stability

sbirddog

The transverse metacentric height and the longitudinal metacentric height are all to low.

see more on:
http://sassdesign.net/Design of a fast rowboat.pdf

js

 

Hi sbirddog
Good to see someone else designing their own row boat. Listen to the experts but dont let them stop you! Looking at your dxf file I did wonder about the long thin stern you have drawn - having relatively more displacement in the ends, espeicially the stern, rather than concentrating it so much in the center would slightly reduce wetted surface and improve longitudinal stability, i.e. increase longitudinal metacentric height as HJS points out. I shall not say much about the transverse metacentric height since some rowboats do seem to get by with almost zero form stability, but looking at rowboats designed for sea use they do on the whole seem to have rather more form stable midships sections than flat water row boats and I guess there must be a reason for that.

Actually, as I mentioned in a previous post here, I have designed a new rowboat myself and I am now about to start building it. We have been away sailing on our other home designed boat for most of the past three months but before leaving I took some sheets of plywood and a dxf file to a firm that does waterjet cutting then when I got back they had ready for me a pile of weird shaped pieces ranging from long skinny panels for hull planking down to tiny packing pieces and the like, some of them not much bigger than lollipop sticks. It was all wrapped in cling film and stacked on an 8ft x 4ft pallet which I brought home on my roof rack - photo shows what it all looked like after 'unboxing'. So far I have only had a chance to trial fit a few of the smaller pieces and everything looks good so far - the real test may well come when I start to fit together the main hull panels - we shall see. But before I can even start on that, I will need to clear all the junk out of our garage to make space for the project, I also need to finish installing a new central heating system befor winter sets in!

I was fascinated to read the excellent article by Jurgen Sass for which HJS provided a link, thanks HJS. I would have been interested to read that before starting to design my boat but actually I can say (with considerable smugness!) that the same thinking expressed in that artical was incorporated in my design. Although I have never in my life rowed a sliding seat row boat, I had a feeling that a transom that is fairly wide at the base as opposed to a canoe stern or a wineglass transom, would give somewhat better pitch stability, slightly lower wetted surface and would spread displacement more towards the ends of the boat, some of the same thinking as Jurgen expresses. Hence my design has such a transom and the general underwater shape of my design does to me to look similar to that of the chined plywood boat shown on the final page of Jurgen's short paper. Mind you, I had anticipated only a very marginal performance advantage, probably too small to measure, so I am astonished that Jurgen has measured an approximately 20% performance improvement over a traditional Whitehall hull form, both with same length, weight, radius of gyration and transverse stability.

One further comment on sbirddog's design, which in any case is only an initial hull form sketch, is the use of twin sliding seats on a boat intended for long distance non-competitive travel. My design is intended to carry either a single rower or a single rower and a passenger, it was quite a challenge finding an arrangment and hull form that would allow that in a hull short enough for roof rack transport on a small car! We will have to wait to see how feasible it is in practice. When two persons are on board, one would row and the other would be a passenger, then after a bit they would swap round. My thinking was that having two row together would provide only a marginal speed advantage but would be tiring out two people at once, so for best average speed over long distance one person should row and the other rest, then swap. Not having twin rowing positions does also make it a lot easier to fit everything into a hull of limited length. I wonder whether people who actually do have some practical experience would agree with me?

 

Cool! Thanks for the awesome fast responses!

I had read the Sassdesign article where it showed up earlier on this thread and I tried to put a little more flare into the stern area (kinda above the waterline) just because of that article. I also read some of the debate over the accuracy of the 20% speed increase. It makes sense to me though, think about a torpedo, they probably have Cp of 0.8 or something. So I will try to add some more volume to the ends, especially the stern.

The Beam on my sketches goes back and forth. Trying to find that perfect balance is tough. I’ve gone pretty narrow for a couple of reasons and maybe y’all can find a reason for me to widen her up. I know she will be tender but I thought having some rocker would be good for choppy coastal rowing. If I put rocker in the hull then I have to put lots of weight in it to take advantage of the water line length. In order to get past that, I just keep making it skinnier. The 'drop in' rigs I built have outriggers on them so I don’t have to worry about the beam at the gunnels.

Speaking of beam and transverse metacentric height I am wondering how Freeship or any software calculates that. Metacentric height is GM. The center of gravity would be dependent on the gear and crew’s centers of gravity. I bet lots of canoes and kayaks have a negative GM, or close to it, relying on the crew to actively maintain stability. Im thinking that the “metacentric height” that shows up on Freeship is possibly the height of the metacenter, KM. if that is the case widening the boat would increase KM. Also taking weight out of the boat might increase KM.

John, I am really excited to watch your boat go together! I am about to go back through some of the older posts to look for your drawings. Really cool finger scarfs btw. I like your idea for switching out rowing. Basically how the ocean rower pairs do it. My cousin and I plan to do some long distance coastal stuff. I think we will both want to be on the oars.

Thank you both for your input. I'm going to add some volume aft and play with the beam some more.

 

John, I found your drawings on page 125 of this thread. It’s a great looking design with tons of work put into it already. Time to get that garage cleaned up so we can see it go together!

I also read your post about oarlock ‘spread’, seat height, and oar length. I have been getting my CLC northeastern dory dialed in with my own drop in sliding seat and can take some measurements if you need them. I built it with lots of adjustability options and Ive got it pretty close to perfect for my size, strength, and the open water conditions I usually row in.

Worked on the two man boat drawing a bit more last night, trying to take some of the advice y’all had for me. I added about a foot to the beam and put more volume in the ends. Took a little bit of the rocker out and added some freeboard amidship. Definitely raised the transverse KM so she wont be as tender. Please, Id like to hear some more input.

Heres the link to a Joe Dobler design that I like and probably inspires my plan a bit

http://duckworksbbs.com/plans/dobler/millenniumfalcon/index.htm

 

Hi JS,

Where can I find more information on the 5-panel butterfly plywood version of this boat shown in the pdf? It could almost be built from the flat panel layout shown. Are the transom and thwart geometries available? How about other basic specifications - Length, LWL, BWL, designed displacement, longitudinal location for the rower, etc.

It appears to fit nicely onto two sheets of 4'x8' plywood to make a boat somewhere in the 15'-6" range.

I'm learning my way through the basics of rowing boat design and would like to include this hull in my comparisons.

Thanks
Matt

 

The “butterfly" boat is constructed from two plywood sheets 1.52 x 3.05 meters. The overall length is 6.00 meters, the width of the deck is 0.98 meters and the displacement is 140 kilos. This boat was adapted to customer requirements.

A new boat with five panels has been designed to another customer. The intention is that it will go better than the previous round bottomed boat that was presented in the report mentioned above. The new boat is decked and designed for exercise and long trips on some more open water. The intention is to provide kits later. Right now a prototype is under construction. That boat will be tested before the ice settles. Boat's dimensions are 6.00 x 0.91 meters.

JS

 

Whenever there is a reason I like to revive my favorite thread.

This time there is a very good reason because by chance I found this photo of Jon Aborn's Monument River Wherry #3 at Walter Baron's website.



Jon reported about the build of his design (somewhere between post #1680 - #1723) but I have not seen the finished boat until now.

Congrats on the build -- great looking boat and excellent photo.

Some more from Walter Baron's facebook page:

 

Monument Wherry

Flo mo, thanks for posting.

I am curious about Jon's outrigger/brackets. That is always a trick on the racing circuit because they will put him and anyone with these sort of brackets, in the "open" class.

 

John got away with that on all three monument river boats he's raced.
I raced Essex river in a boat with similar oar lock mounts and ended up in the unlimited class

 

Wow! That is one sweet rowing boat! I'm sure John A is proud the way it all came together.

John A, how is the boat holding up with just taping the inside seams?

Thanks,
Woody