wave making

[nordvindcrew]

I read a description of the Herreshoff rowing boat "Althelas"(try Google). In the write-up, it was mentioned that the location of the maximum beam was calculated to reduce wave making. The stated speeds the boat could attain suggest that it rows easily at speeds well above its' displacement speed.
is any one familar with the design, and how wave making is reduced in displacement rowing hulls? I row in a fixed seat double in open water races and win or lose is by seconds in a 6 N.M. race. Any way to gain speed has to be explored. Althelas is too small for two of us and for the water we row in, so I'm working on my own designs. Any knowledge I have is seat-of-the-pants from 10 years of competition and studying other fast rowing boats. any sources of information or ideas would be appreciated.

[Leo Lazauskas]

Originally Posted by nordvindcrew

I read a description of the Herreshoff rowing boat "Althelas"(try Google). In the write-up, it was mentioned that the location of the maximum beam was calculated to reduce wave making. The stated speeds the boat could attain suggest that it rows easily at speeds well above its' displacement speed.
is any one familar with the design, and how wave making is reduced in displacement rowing hulls? I row in a fixed seat double in open water races and win or lose is by seconds in a 6 N.M. race. Any way to gain speed has to be explored. Althelas is too small for two of us and for the water we row in, so I'm working on my own designs. Any knowledge I have is seat-of-the-pants from 10 years of competition and studying other fast rowing boats. any sources of information or ideas would be appreciated.

Have a look at:
http://www.cyberiad.net/michlet.htm

and

http://www.cyberiad.net/rowing.htm

Leo.

[nordvindcrew]

Leo, very good stuff, a bit too technical for me at the moment. What I am trying to isolate is the suggestion that wave making is reduced or moved aft depending on the fore and aft location of maximum beam

[marshmat]

Leo! Long time no see!
Nord- regarding the location of maximum beam, etc. Yes this will have an effect, but it's not an easy one to put into a rule of thumb. The "Godzilla" mode of Leo's Michlet program mentioned above, is probably the easiest tool I've found so far for this kind of optimization. It won't build the boat for you, but if you're careful with the setup it can give you a basic hull shape that has all the key elements and all the right ratios for your target speed.

[Leo Lazauskas]

Originally Posted by marshmat

Leo! Long time no see!
Nord- regarding the location of maximum beam, etc. Yes this will have an effect, but it's not an easy one to put into a rule of thumb. The "Godzilla" mode of Leo's Michlet program mentioned above, is probably the easiest tool I've found so far for this kind of optimization. It won't build the boat for you, but if you're careful with the setup it can give you a basic hull shape that has all the key elements and all the right ratios for your target speed.

Hello yourself, Marshmat!

Godzilla can be useful for this sort of problem, but you need to optimise over a (weighted) range of speeds.

I've recently been working on designing some rowing shells and found that it is important to take into account dynamic sinkage and trim. Godzilla and Michlet won't do those calculations for you. However, for recreational (rowing) applications where the last 2% is not very important, they should give very acceptable results.

All the best,
Leo.

[Guillermo]

Nice to see you back again in these forums, Leo!
Behaviours have improved quite a bit since some months ago...

[nordvindcrew]

Just read Leo's technical stuff on serious rowing. It is stated that there is from 22% to 40% loss of energy in the oarlocks. Where? How? how to reduce it? any ideas out there. Remembering that I have to be oar on gunnels, no out riggers or any other fancy stuff

[messabout]

Leo's tech stuff knocks our hat into the creek. Thanks much Leo.

With only a quick (and fascinated) read, I get the impression that our boats should have adjustable lengths while underway. We will row at different rates during various parts of the race and boat speed will vary as a result. Telescoping boats will no doubt be beyond our practical limits.

Nord, you might root around in some of the kayak design studies. Kayakers seem to have their own tribal language wherin a max beam forward design is called fish form and max beam aft is called Swede form. I think most of the high performance types are designed with the swede form concept. Not to say that is the way to go for your project.

It has been noted that the upper body movement of rowers cause the boat to pitch with possible negative result. Particularly true of a short boat with fine entry and exit. Here's another wild brain fart. Suppose the two oarsmen were positioned far enough apart so that it would be possible to stroke/recover in opposite cadence.

[tspeer]

Originally Posted by Leo Lazauskas

Have a look at:
http://www.cyberiad.net/michlet.htm
and
http://www.cyberiad.net/rowing.htm

Have you considered adding parameter that would allow the longitudinal center of buoyancy to vary? A mapping function that distorted the X axis would allow you to use your existing parabolic-elliptical-rectangular parametric forms, but shift the sections unevenly to adjust the lcb.

Or would it just optimize back to fore-aft symmetry because that is the theoretically best shape for minimum wave drag, since you don't account for boundary layer displacement, etc.?

[Leo Lazauskas]

Originally Posted by tspeer

Have you considered adding parameter that would allow the longitudinal center of buoyancy to vary? A mapping function that distorted the X axis would allow you to use your existing parabolic-elliptical-rectangular parametric forms, but shift the sections unevenly to adjust the lcb.

Or would it just optimize back to fore-aft symmetry because that is the theoretically best shape for minimum wave drag, since you don't account for boundary layer displacement, etc.?

Hi Tom!

I have several different ways of stretching hull shapes but not all have been included in Michlet. I also have other "families" I work with that aren't based on the parabolic-elliptical examples. I often do include boundary layer displacement effects as well as BL separation, so optimal hulls are not always fore-aft symmetric. It really depends on the application or research avenue: sometimes it's important, sometimes it's just an insignificant distraction.

For rowing applications (especially those with sliding seats) it is important to account for the moving masses as well as the effect of dynamic sinkage and trim (aka "squat"), so the location of the LCB, LCF and LCG are very important. The "optimal" relationship between LCB and LCF is still not clear to me.

The first attached graph shows the squat of a 16m long, 800kg displacement shell over a range of speeds. In this example the rowers masses do not move with respect to the shell: "dzb" is the position of the bow with respect to its static position, and "dzs" is the position of the stern. You can see that at about 3m/s the stern begins to drop and the bow starts to rise.

The effect of squat on wave resistance coefficients and total resistance are shown in the other two attached plots. The largest difference between the "static" (i.e. no squat) total resistance and the resistance where squat has been included ("dynamic") is only about 3% at most (at 5.5m/s), but these sort of differences are very important for top class competitions.

A further refinement is to calculate the squat and resistance during the rowing cycle. That's a computer intensive process given that the rowers' masses can move quite quickly (and so the stroke must be divided into many parts), and also because each calculation of the squat requires about 4 to 10 iterations so that equilibrium is reached at each speed and each position of the masses of the rowers, hull and equipment.

I've done this under for several existing shells. None of these shells are fore-aft symmetric and neither are my "optimised" variants. They probably would be symmetric if squat didn't play such a significant role: BL effects on symmetry are, in general, much smaller for these vessels.

I hope that you aren't planning on rowing Basiliscus to get it foil-borne!

Leo.

[nordvindcrew]

that idea of stretched stations and alternate cadence is one that sounds good butwould be very difficult to adapt to. After years of rowing together and srtiving to always match cadence, the change would be impossibly difficult. any way, the sight of the bow digging in on the power stroke demoralizes the opposition.

[Leo Lazauskas]

Originally Posted by nordvindcrew

that idea of stretched stations and alternate cadence is one that sounds good butwould be very difficult to adapt to. After years of rowing together and srtiving to always match cadence, the change would be impossibly difficult. any way, the sight of the bow digging in on the power stroke demoralizes the opposition.

I think you have misunderstood the purpose of the graphs where I show the "optimum" length versus speed graph. I certainly never imagined that anyone would consider building a telescoping hull. The graph is the result of a theoretical/numerical optimisation to answer a simple, semi-silly question posed by Prof. Ernie Tuck, i.e. "What is the optimum length of a boat"? As you have seen the answer depends on what speed you are optimising for.

Regards,
Leo.

[messabout]

Not proposing to build a telescoping boat. Yes, I suspect that I did misinterpret. I was merely thinking of the manners in which one thing can affect two or more others in a sort of synergistic way. That is the stuff of fascination.

Over the years I have come to know that the more I learn the less certain I am. That is to say; I have addressed the fact that I do not know what I do not know. What better reason to lurk on these forums? This is where we learn or at least attempt to do so. Prose such as this is not self flagellation, it is merely attempt to approach reality.

Philosophic stuff may not make Nords boat go faster, so I'll go home now.

Best to all.

[nordvindcrew]

the brain is the most important muscle in the body. If you think fast, you will go fast.

[melong]

Just tried Googling "Althelas" and the only link is this thread.