Where are you locating the waterline on the guideboat modeling?
Where are you locating the waterline on the guideboat modeling?
Without knowing the weight of the boats I'm comparing, I've assumed that they weigh about the same (within the range of Clint's target weight for his design of about 30 kg (65 lbs)).
For the hydrostatic calculations, I assumed a displacement of 135 kg (300 lbs) for one person and 225 kg (500 lbs) for two for all boats. This results in a slightly different draft for each boat.
For example, the first boat in the table (AGB Ghost S&G): 11.3 cm draft (4.5" waterline) at 135 kg (300 lbs) displacement and 15.4 cm (6" waterline) at 225 kg (500 lbs).
That is, the waterline results from the given displacement.
Interesting Flo-mo - I just sent you a PM.
With the comparisons in both Hydros form and in 3D to overlay, it will make an interesting study.
Regarding Cp - it is tricky - if I were making a purely competitive boat I would go higher - my current hull shape is at 0.55 which seems about right.
Speed-power curve comparisons would be quite interesting, as well.
The guideboats which are working boats seem to run higher than .55. Should be possible to get VIRGINIA into Rhino which would help set some baselines. Nick Schade is running .61 on his stripper based on VIRGINIA. https://guillemot-kayaks.com/catalog...ack-guide-boat
Ben Fuller
Ran Tan, Liten Kuhling, Tipsy, Tippy, Josef W., Merry Mouth, Imp, Macavity, Look Far, Flash and a quiver of other 'yaks.
"Bound fast is boatless man."
Ben,
Nick's AGB model has a high Prismatic coefficient because he has set the DWL at 404# - like Flo-mo's numbers show, the GB's pick up volume in the ends when it is sunk and so Cp goes up. Most of the racers are running pretty light - probably around the 135 kg that Flo-mo is using in first column. I'll be digging more into all this later, but it will be fun to keep making observations and thoughts. I have some already and ideas about what to do with my hull design, but want to go through the due diligence first.
One other observation about the AGB's is that there is more deadrise amidships than many of the other boats with the bottom narrow and sunk down a bit more. I'd like to go for a row in one.
Looks like the river wherry holds its own and is in the ballpark of the GB at 5-6
I have added three more boats to the table, eliminating the S&G variant of the Herreshoff 17, whose values are almost the same as the original.
The three new boats are designs by Clint Chase.
Two are 3D models of designs he is working on that he kindly sent to me. One is Clint's version of the Monument River Wherry (MRW 17) - see post #1 -, the other is Clint's version of the St. Lawrence River Skiff Annie.
The third is a 3D model I created of his Drake Raceboat 18.
Since the models I have used for my calculations so far represent the inside of the hull of a boat that was built using lightweight construction, I have stayed true to my approach with these three boats as well so that the comparison is not distorted.
I would like to point out a peculiarity of the resistance calculation according to Kaper, which I have already noticed in earlier comparisons.
In the calculation, there is a drop in resistance in the speed range of 6 knots, which cannot be in agreement with reality. The diagram clearly shows this inconsistency.
It is not clear to me what is causing this.
Possibly it is an operating error on my part of which I am not aware.
Or it may be a bug in the algorithm on which the calculation is based. It seems that even the author of this program, John Winters has his doubts, because he now also uses an additional program (Michlet by Leo Lazuaskas) for his design work.
https://www.scribd.com/doc/45959057/...y-John-Winters
Obviously it would be nice to know how a boat will perform before we build it. We find out by using KAPER, a performance prediction program created by me. The only program of its type designed expressly for mathematically predicting canoe and kayak performance it is used by SeaKayaker magazine for their boat reviews. With KAPER I can analyze a design (those of competitors as well as my own) and adjust the hull shape to optimize performance. Recently I have begun using another program called Michlet written by Leo Lazuaskas of the University of Adelaide to augment KAPER.
Independently of this, I would like to quote from the manual of ProSurf 3, the program I use, to make clear what there is to consider in principle with this kind of calculation.
Kaper – This calculation type uses a formula developed by John Winters [published on the web – search for Kaper and John Winters] that can be used for kayaks, canoes, or any other lightweight, small craft. It is included here with the permission of John Winters.
......
The program needs only the velocity for input to perform the resistance calculations, since all of the other input is obtained from the hull model at the final balance condition, even if the boat is heeled over. Please note that these calculations do not use the exact 3D shape of the hull. They just use a variety of basic shape values, like waterline length, weight, wetted surface, center of buoyancy, and angle of entrance of the waterline. The program calculates these values from the shape of the hull at the final hydrostatic balance condition.
.....
Please keep in mind that all of these calculations are done using empirical formulas based on just a few measurements or calculated values from the boat. They cannot be as accurate as the results from a sophisticated 3D computational fluid analysis (CFD) program. Because of this, you must be careful how you use the results. Always try to back up the results by comparison with known quantities from other vessels or other calculation techniques. In fact, the best use of these resistance calculation techniques is as a relative comparison tool. It is more accurate to use the resistance results to compare boat A with boat B, rather than to use the exact, calculated resistance to select the size of the engine.
DELFTShip uses an extended version of KAPER developed by Matt Broze, and according to the DELFTShip help file "while implementing this method in DELFTship two serious discontinuities showed up in the curve of residual resistance. These consist of a sudden drop in resistance of about 10% at speed/length ratios of 1.4 and 1.6 and are the result of a correction implemented by Matt." I'm guessing the ProSurf program probably has the same problem.
Ken
Those curves are interesting in that there is no difference for any of the boats in the 3 to 4 kt range where everyone rows. My LFH 17 and my much bigger Walkabout both row at about the same speed, even shorter prams and light narrow Natoma skiffs in our club all stay about the same speed on a rowing trip. The only time I have hit 5 kts was test rowing a CLC expedition wherry, and the only boats I have seen rowing at 6 kts are the skinny carbon fiber sculls in open ocean races. I think windage has a much bigger effect when evaluating real water ability to get somewhere.
- Rick
Windage is indeed a critical element when it is blowing. Why my little 15' ducker is pretty easy to drive above 4 knots. I don't know that for say a six hour row you might not find the Walkabout a little more work.
Ben Fuller
Ran Tan, Liten Kuhling, Tipsy, Tippy, Josef W., Merry Mouth, Imp, Macavity, Look Far, Flash and a quiver of other 'yaks.
"Bound fast is boatless man."
Been thinking about windage a lot and also why the AGB's are so fast....and been modifying the river wherry to suit my current thinking. The underbody is somewhat similar to the AGB in the current state and it is interesting to see that the hydrostatic numbers for both are nearly the same! That was not the intent but since I am trying to match performance of the GB I suppose it makes sense that the underbodies are similar. Above DWL they couldn't be different! I am pleased with version 10. Will let this one stew and simmer for a bit.
This really shows the difference above dwl - my hull is the green one.
The brown hull is the guideboat "Ghost". You can see how deep and narrow their bottom is...mine did the same on version 10 but not quite as far as the GB
Front view, bow to left - hard to see the asymmetry in my hull but it is there, the stern sections being a bit deeper and fuller. Less windage on the river wherry I imagine.
The bow is to the left. This is the "fish eye" view. My waterline is blue, GB waterline is red.
Last edited by Clinton B Chase; 03-10-2023 at 12:33 PM.
Thank you for this comparison. Interesting how little room for improvement there is in the underwater lines of low powered boats.
Looks good.
The narrowness of the guideboat, I suspect, has to do with the need to carry it as well as weight. You need to be able to go upside down and right side up under control. Having done this now a bunch with my solo w/c canoe about 35 inches wide and about 55 pounds, it isn't trivial to spin it and settle it on the yoke. Once on the yoke easy to handle. And I can see how the stem height would make all this easier, pivoting on a stem, as well as easier to rest it on a stem when carrying. The GB stem height also make plank shaping easier as I suspect that the rabbet is pretty close to the girth, making less shape needed in planking.
You've dropped the stems which cuts your windage but kept the height where water comes aboard when you have spray or stuff it, not at the stem but someways back.
Not constrained by carrying, you let the beam increase above waterline (see as an example some of Gartsides boats). May need a pad on the ground to roll her for cartopping like a friend does with his annapolis wherry.
Weight will be interesting. 16'gb 60-70 lbs are the glassed ribbed strippers like the AGB boats as well as the 3/16" ribbed originals. What it comes down to is skin area, and I don't know whether your software will give you that so you can compare it to an AGB of similar length.
Ben Fuller
Ran Tan, Liten Kuhling, Tipsy, Tippy, Josef W., Merry Mouth, Imp, Macavity, Look Far, Flash and a quiver of other 'yaks.
"Bound fast is boatless man."
Thanks for thoughts and observations, Ben.
I did not think about the stems on the AGB helping to hoist her up on shoulders...makes a lot of sense. Jon A's MRW was 68 lbs bare hull built with 4mm topsides, 5mm bottom plank, and 2mm decks. I don't know what he used for the bulkheads. My plan is 4mm topsides, 6mm bottom plank (since I stock 6 not 5!) and the decks may be 1.5mm with 4 oz glass. Like Jon, I plan to have two bulkheads in the ends most likely 6mm with a doubler around the edges. The "rib" in the middle will likely be two layers of 6mm. Once I am modeling the structure, I will look at making a lightweight stem that makes it easy to land the planks. I figured 75lbs all up with a set of oars, boat bag, little anchor.
Once this is all modeled I can accurately do a weight estimate based on volumes of all the materials. Cartopping is not the priority, but it will be nice to be able to do it. Whether 68 or 75 lbs, the owner/builder will need a system to load the boat. Pad on ground is good idea, allowing to get the bow up on the rack and then push it into place. Got to wrap the racks in something easy on the gunwales.
Projected weight range the same as the Annapolis Wherry. What my friend with same does is slide the boat back on his roof rack where it it upside down and lowers the end to a pad. Then picks up the other end, rotates the boat off the pad and sets it down. A pad on the ground lets him roll the boat upright and onto a cart, then to the water. There are some other systems with tech, but this is about the simplest. Need to carry some pads and with experience know where to put them. Or for a much simpler system enabled by your flat bottom carry the boat upright. Slide it back onto a cart tie down then lift the other end off the roof rack. What you might want is some chocks or guides for the forward end and rollers aft, maybe one of those pricey extensions depending on the vehicle. And a drain hole in the boat in case of rain.
Ben Fuller
Ran Tan, Liten Kuhling, Tipsy, Tippy, Josef W., Merry Mouth, Imp, Macavity, Look Far, Flash and a quiver of other 'yaks.
"Bound fast is boatless man."
I created a table with the characteristic values of 7 other rowboats and also added the value for the surface of each hull.
If the boats are made using modern lightweight construction techniques (strip built, glued lapstrake or stitch-and-glue), this value gives an approximate indication of the weight of the boat.
As an example I would like to consider the two SAVO singles. On the Puuvenepiste website the weight for the "equipped" boat for the 575 Single is given as 39 kg and for the 650 Single 43 kg. The surface area of the hull of the two boats is 7.66 and 8.64 m² respectively. This means that if you divide this number by two and multiply by 10, you get relatively accurate weight in kilograms. This simple calculation also leads to a plausible result for all other boats.
Most of the 7 boats I have put together in the new table differ very clearly in terms of the length of the waterline and are intended to illustrate how this affects the resistance at different speeds.
The resistance curve for all 14 boats is completely confusing in this type of presentation, but nevertheless shows the extent to which they diverge in the higher speed range (I consider everything in the range above 9 kg resistance to be worthless).
Anyway, you have to be a top athlete to overcome a constant resistance of 6 kg over a longer period of time.
Last edited by flo-mo; 03-12-2023 at 04:07 PM.
This is the visualization of the 14 3D-models that are the basis for the calculations, including an additional model (original Herreshoff 17 rowboat).
Flo-mo, can you please clarify resistance in kg? That is a mass unit, not force. Does it mean in gravity, as the force to lift the mass?
As I understand it, the purpose of the resistance calculation is to determine which motor should be used to drive the boat.
The result corresponds to the thrust of a motor given in pounds or kilograms (1 lbs = 0.45 kg), where in this case the motor is the human body, which according to John Winters (https://www.scribd.com/doc/45959057/...y-John-Winters) can generate 0.1 to 0.5 hp.
OK. Not to get all pedantic, but in imperial measurements lb is confusingly used as mass (lbm) or force (lbf). In my physics education the metric system was much more consistent, kg was always mass and Newtons (kg*m/sec2) was always force. It is confusing because 1 lbm = 0.45 kg as you say, but 1 lbf = 1 lbm * g, where g is the gravitational acceleration which is 32 ft/sec2. So using kg as force I am still not clear on what that means. Not blaming you, Flo-mo, Winters must have got it from somewhere but I do not understand.
I don't see this as pedantic at all, in fact I'm glad you brought it up.
Since I followed the recommendation in the ProSurf 3 manual and only ever used the resistance calculation to compare different hulls, I never thought about the unit for the resistance.
Since the program writes kg next to the numerical value, I have adopted this for the tables.
Of course you are right that kilogram is a unit for mass and not for force. Correct would be Newton or Kilonewton, as it is displayed here with this program (DELFTship).
In this representation, the curves for the calculation according to Kaper and Delft series are shown. It is noticeable that Kaper is only displayed up to 5.5 knots and the Delft series makes no sense above 6.5 knots.
Finally, I have no answer as to why ProSurf 3 has kilograms next to the number and whether this calls into question the result of the calculation.
I have developed myself a spreadsheetapplication dedicated to the drag estimation and the speed predictionof rowboats, developedwith OpenOffice Calc and open source, it is not possible to attache the file within this forum but you can download it within Boatdesign.net forum at :
Drag and speed prediction of rowboats | Boat Design Net
Thisapplication includes a drag estimation with 3 components :
- residuary drag, based on Delft series (parent models N°1 and N°25), and formulation as reported by Larsson and Eliasson in « Principles of Yacht Design » 2^{nd} edition 2000
- friction drag, based on ITTC57 formulation for the friction coefficient (L = 0,7 Lwl for the Reynolds number, as also recommended by above authors
- aerodynamical drag, with an average Cx= 0,5 applied to both the boat (frontal area ~ bow freeboard x beam) and the rowers (input the estimated area of rower(s) back(s) )
Thedata to input includes, for the the rowboat with its loading (rowers+ their roaming equipment if any) :
Lwl :waterline length
Bwl :waterline beam
Tc :hull draft
Disp. :boat displacement
Cp rismatic coefficient
Sw :wetted area
LCB :Longitudinal center of buoyancy (in % of Lwl, from aft Lawl point)
Sahull : hull frontal area (which can be estimated as bowfreeboard x beam)
Srower :rower(s) frontal area
Netpower : effective propulsion power (as equal to drag x speed)
Theapplication includes also a speed prediction (on flat sea, but withvarious head wind forces) through the input of a net power. Questionis what power can be introduced to represent the rower effort ?>> I think that for an average rower and an effort of one hour or more, avalue of 40 W can be a valuable order of magnitude (and so 80 W for 2rowers). Whatever one may think of this assumption, this value isuseful for comparing different designs or loads or number of rowersin terms of speed and not just in terms of resistance.
Theapplication proposes 2 sets of input data (named Hull A and Hull B) in order that you cancompared directly, through the curves automatical output, either asame rowboat with 2 loadings or 2 rowboat designs with the sameloading.
3examples are proposed thanks to your data provided (+ for LCB, I took an estimated 47,5 % Lwl (?) from aft Lwl point, for Sa hull 0,384 m2 and for Srower 0,37 m2 (one) and 0,74 m2 (two)) :
**Adirondack Guideboat Ghost, at 135 kg / 1 rower and at 225 kg / 2 rowers
**Monument River Wherry, at 135 kg / 1 rower and at 225 kg / 2 rowers
**Race Drakeboat 18, at 135 kg / 1 rower and at 225 kg / 2 rowers
For the AGB Ghost, examples of the output curves (in Blue : at 135 kg / one rower delivering 40 W net, in Red : at 225 kg / two rowers delivering 80 W net) :
** Drag in kg versus speed in knots (the points are your values) :
ADG Ghost - Drag.png
** Effective propulsion power required (i.e. drag x speed) in Watt, versus speed in knots :
ADG Ghost - Effective propulsion power.png
** Speed prediction in knots versus head wind speed in knots :
ADG Ghost - comparison 135 kg one rower and 225 kg two rowers.png
This is a fascinating discussion. I've become hooked on skin-on-frame boats due to their light weight and ease of construction. Using Dave Gentry's techniques, one might be able to build a Monument River Wherry or a version of Clint's new boat that weighs about 55 pounds. That's ten pounds less than the planked version, which would be nice for loading and unloading. How to translate these designs for planking into frames and stringers is of course another question, but these look like great boats for those of us who like to row.
I have enjoyed seeing Clint apply modern technology and his knowledge to my Monument River Wherry. My idea for the wherries goes back 40 years when a bunch of us boat guys from Maine and Hull and Cape Cod started rowing and racing fixed seat, traditional pulling boats. Having limited time, limited income and a desire to stay married to the woman who has now been with me for 51 years, I thought up this simple idea for a boat that might be competitive in these races. It was built from a half model that looked to my untrained eye that it might be fast and was built light because that seemed like an easy way to gain advantage and was built simple because my skills and temperament are not otherwise suitable. Double ended was a way to simplify and if it was good enough for John Gardner, why not. The boats have done ok but I might concede that there is still some magic in the Guideboats. I will also point out that Paul Neil and Gerhart Unger were very serious athletes whose dedication far exceeded what I was able to muster.
I am very comfortable in my current wherry. It rows easily, is dry and is capable any the rough water that I am willing to put it into. I do not have a skeg on this new boat but I do have to apply the power in a cross wind to keep it running straight. Most would probably prefer to have a small skeg.
It's been a lot of fun,
Jon Aborn
Thanks for adding that history, Jon, and thank you for making your original lines available to us! And in reference to Overland's last post, I have already received inquires for this boat to be done in SOF. I think that could work.
Project update: I have been diverted to taking care of other business, but intend to pick up on the Monument rowboat project sometime quite soon. I think my hull shape is as good as it may get -- in comparison to Jon's boats, mine is asymmetric fore/aft, has a bit more displacement (~300#) to support a bigger guy or a little gear, a touch wider on the waterline, and a bit more flare to allow an 8' oar length and a little more stability. I plan to do one more iteration on the hull to optimize displacement and some other design ratios in as much as they can be optimized.
After comparison studies, I think the GB's are so competitive because 1) the rowers were very strong, 2) the boats are very light with their rowers sitting low, powerful, ergonomic position with lots of hand overlap at the oars (more efficient stroke) and 3) the AGB's wetted surface area is quite low which helps very much in the lower speed range especially going around a course like the Blackburn.
I will report back out here when I get back to it!
There was an interminably long thread over on boat design about designing the fastest rowboat. I bumped into one of the frequent posters a couple of years ago and asked if they had decided which boat was fastest. He said - The one with the biggest gorilla on the oars!
Haaa...yes I know that thread - I particiated for a while. Learned a lot.
True - I was able to hold my own in my Drake 17 agains a good AGB rower so I am hoping to get even better speeds with this "Monumental" rowboat.
Clint
Very nice boat and congrats with the WoodenBoat article, that was a pleasant surprise this morning. Frank
If you're going to be consistent with units, then g = 9.8m/s2, which is near enough 10, so 0.45kg goes to 4.5N
Thanks FF....been so busy with other work but I got a chance to do some personal projects.
Today I optimized the displacement a bit on my MRW. She displaces exactly 300# now which should offer just a few reserve pounds for a little extra gear. If she sits right on her lines, 5 knots should be no problem.
RICK- funny quote by that rower...lotta truth to it. Once thing I have been thinking a lot about in hull design is eliminating the aspects that count against you when it comes to drag. Optimized displacement is one, the full ness in the ends of the boat is another, and LCB is another. The faster one wants to go the more important it is to be in the right range for these factors. But throwing a strong rower in there is probably the biggest factor in speed!
Here is a screenshot of bow. Starting to working bulkheads and thin coamings.
Looks like a good candidate for a short slide. That way the gorilla gets bigger. Weight goal? A dozen or 20 pounds makes little difference in the water but quite a little bit on land where this boat like most little boats will live for most of its life.
Ben Fuller
Ran Tan, Liten Kuhling, Tipsy, Tippy, Josef W., Merry Mouth, Imp, Macavity, Look Far, Flash and a quiver of other 'yaks.
"Bound fast is boatless man."
Yes the short slide would work. I have the boat down at 73 lbs with small anchor, oars and a bag of boat stuff. With my 225, we are at 298# thus the 300# displacement. Hull sides in 4mm ply, bottom panel 6mm and bulkheads 6mm w/ doublers. Aborn's was 65# and I think that was w/o anything in it. Should be able to hit that or better even thought I have a little more beam.
My boat is 68 lbs with no gear. The bulkheads are 4 mil and the decks are 2 or 3 mil, I forget. All real lumber is eastern spruce, hand selected fro the local lumberyard (a real lumberyard, not the big orange box)
Jon
HI Guys- following this thread. I have been rowing Gloucester Gull back and forth (1/3rd mile) each way to a small isand for years (like 50!) and it has been rugged and useful and uncomplicated. Jon A often rows by here on summer days. Is anyone thinking of a get-together for a number of these various designs so we can compare for ourselves? I am at top end of Cape Cod near the CCCanal. Can trailer. Cheers/ JC
p.s.-I have put a sliding seat in the G Gull ocassionally when rowing to Naushon or the Vineyard. (10-15 miles each way) Gets your legs into it-otherwise they cramp up.