designing a fast rowboat

Nice! The longitudinal views of the lines show what I think of as a kayak profile, very sharp entry with the maximum beam is aft of midships. Zero rocker, built for speed! It is very like the Inuit (Eskimo) hunting kayaks although they are rockered for manouverability. It looks like a hyperbola to me, which was the shape I used for my last - very quick - boat. I built that one with its maximum beam midships but my next one (waiting for its paint job) has its maximum further aft and more rocker, intended for exploring small inlets and streams.
 
Fixed seat is not a problem at all (actually, sliding seats were prohibited earlier few years ago). Outriggers? there are any.
 
I just went back to the design link in post #462 and took a look at another design "Vuorosoutuvene" and it seemed to have its maximum beam aft of midships, strage. Then I checked the underwater lines and the MB is midships for both boats after all; not as I first thought.
 
Vuorosoutuvene (shift rowboat) is a national speciality. On the back seat there is a paddler and they chance their roles every 20-30 seconds in fly. In fact, shift rowboats are the majority of small racing rowboats.

http://www.suursoudut.net/kuvat_07/sunnuntai/Suursoudut 2007 sunnuntai kuva 131.html

You are right about the center of bouancy, it is only slightly aft of midships. They have very different prismatic coefficient however, singleboat goes just below hull speed, shiftboat about in it and doubleboat just over hull speed.
 
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terhohalme--I'm very impressed with your boats. My 16'wl boat(pics on posts 296 and 301) pulls a transverse stern wave as I approach 5mph. Can you see any changes I might make to help that? I did 3 miles in 33 minutes in a race last year. I was out in a strong wind Sunday and was able to hold 7mph by my gps briefly downwind but could barely do 4 coming back. Boat weighs 85lbs, I'm 200, oars and other things put displacement around 300.
I'm 61 and don't expect to be getting any stronger, so I'm not sure how much extra waterline would be advantageous.
 
Well, you can't change the laws of physics. The boat will start to make waves when nearing the hull speed. The solution is to make longer waterline and proper prismatic coefficient. Here the science take a role, I have used Michlet software (not available at the moment) to optimise prismatic.

Your speed on 17' WL is a good one (Froude nuber is 0.35, so you stil have decent power). The waterline length of our wooden race boat is over 21'. I calculated also a race row boat for women (less power) and they didn't benefit WL over 20'. I think you can use 21' WL.

The weight of your boat is good.

Terho
 
Thanks! I'm happy with the way my boat feels in the water so guess I should accept the speed limitations, leave it alone, and think about building a light 21. Glad to hear you think I could make use of that much waterline. Is there any rule of thumb for optimizing prismatic coefficient/speed on a given waterline length from rower power output? I have an old Concept 2 erg that has can be set to readout in watts. I could estimate my sustainable power level, and go from there.
 
Dick, sent you an email.
 
responses

Terho, Your posts have given this thread a shot in the arm. You say you are "just" the designer. You deserve far more praise than that. I build boats that I concieve in my mind, but they are not "designed" as yours are. Again congratulationson a fine piece of work. Jeff
 
Thanks, I though get my praise: My uni pays me salary about teaching boat design...
 
terhohalme said:
Vuorosoutuvene (shift rowboat) is a national speciality. On the back seat there is a paddler and they chance their roles every 20-30 seconds in fly. In fact, shift rowboats are the majority of small racing rowboats.

http://www.suursoudut.net/kuvat_07/sunnuntai/Suursoudut 2007 sunnuntai kuva 131.html
Click to expand...

Sorry for the OT, but i have looked all over the internet for rowboats. This thread comes up when googleing for "fast rowboat"

Im looking for a moderate fast rowboat, for training and for sunny days, mayby for some weekend trips.

I have found many boat models, such as explorer, virus, vagabond, venture and many of the boats mentioned in this thread. My problem is that they are to expensive, and the second hand market in Sweden is non existing. I cant pay 3-5000 euro (4-6000 usd)

Therefore, i wounder if the second hand market is functional in Finland (or any other nordic/european country for the boats in the link and how much do they cost? Where can i found one?, for example:
http://www.suursoudut.net/kuvat_07/sunnuntai/Suursoudut%202007%20sunnuntai%20kuva%20159.html

I really like the idea with as slim, fast wooden rowboat with slidning seat.

I cant build one. :(
 
Terho, I think the shift boats are very cool. I love paddling and came to rowing after paddling, so this has totally "shifted" my worldview. My wife used to be a highly competitive rower (sculling) and injured herself. She has a hard time rowing hard, even in fixed seats. So, this shift boat may be perfect for us! Oh boy, another boat to start drawing.

I have a question. You say:

"The solution is to make longer waterline and proper prismatic coefficient. Here the science take a role, I have used Michlet software (not available at the moment) to optimise prismatic."

Could you discuss what you mean by "proper prismatic coefficient". I understand the concept of P.C. So far, I have gone by the rule of thumb that any more than 16' waterline length gets to be too much for a single fixed seat rowboat. My boat is 15 1/2'. How do you optimize prismatic and do so manually? I am primarily interested in single fixed seat rowing.

Your boat is great. Congrats.

Cheers,
Clint
 
Clint, Kanstenmarine has a paper of this:

http://www.kastenmarine.com/coefficients_of_form_equations.pdf

Shoud work for rowboats too.
1. determine your target speed (from results of the best rowers if you are fit enough)
2. calculate speed to length ratio
3. interpolate (estimate) proper Cp from givin optimum values of Cp.
 
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