gmane.culture.transportation.humanpowered.boats

Re: Sounding off on the 40 % bit

Giuseppe Carignani — 2008-08-29T08:50:27

Hi everybody (this is a post I have just sent to Boatdesign forum, so the colleagues that have already read it can skip it, while the others may be interested in having a look at that forum, that holds interesting conversations about pedal powered boats) you may not remember the exact value of Plank's constant, but we all are certainly familiar with Rick Willoughby's constant of 40% more power required by catamarans than monohulls. Rick is a fine PPB builder and an inventor, and he doesn't miss the engineering point that choosing and architecture means to address a trade-off between different goals, and comparison ar well done if all the specifications are stated. Rick's constant is correct (if a bit crude) for boats of the same displacement boats without any other constraints. If length is a constraint (it is if you need to transport the boat on a car, for example), the cat architecture can be the better choice (it depends on the other specs) as Rick himself noticed. Other issues can be user friendliness, stability, maneuverability et. al. Comfort, too, can be an issue. Monohull require lower seat level, and this can lead to less-comfortable and inefficient positions. So, Rick's constant is not a constant after all; the issue is more complex and for a start we need a set of specifications. We are trying to do just that within the Open Waterbike Project here: http://www.openwaterbike.com/archite...e-requirements. We believ these specifications are just common sense for recreational high performance PPBs. Please give us your opinion. Best regards Beppe Founder, The Open Waterbike Project On Thu, Aug 28, 2008 at 5:39 AM, public.gmane.org> wrote:

Sounding off on the 40 % bit

2008-08-28T03:39:35

Attention all readers, If you stick with a "constant" that you think may apply to all nature you may run a risk and come across as being a dufuss (dufiss?). Ther ARE contants that occur in nature (like Plank's constant or G) and two of the most common constants in nature both apply to what we're doing here. Anyone want to guess what they are? One of them is arguably the most common... Hint: one applies to anything that oscillates; the other is involved in the solutions of differential equations and pops up in trancendental functions. Anyone want to guess? Anyway the "dufiss_risk" is trying to paste a constant onto a ratio of monohull to catamaran. Especially without any mention of initial conditions. Are the hulls like bathtubs? Are they as long as they structurally can be? Are we talking about power? Speed? Are there any other hull parameters ? Like the ability to turn? What about hull wave interference and how far they are apart vs. how much structural weight for the catamaran? Next exercise will be jumping to conclusions.....Ready.....BEGIN, ...........and one and two and..... The last thing I have to sayt on this subject is that after all the sophist crazy-talk, nobody has yet mentioned that the fastest time in an IHPVA/ Hydrobowl type flying start time trap is held by "close to perfection" with a time of eighteen seconds and some change for 100 meters by a pedal powered propeller boat. Perhaps a short-term-archive, long-term-chatterer would like to tell us what type of boat she is!!!!! Yup. Close to Perfection is a catamaran. jake **************It's only a deal if it's where you want to go. Find your travel deal here. (http://information.travel.aol.com/deals?ncid=aoltrv00050000000047)

re:Hpv-boat Archived files

Rick Willoughby — 2008-08-15T23:22:30

Bruce Been a long time since you posted here. Any submarine developments? Did you ever make your test boat? You might care to go to this link and provide an opinion: http://www.boatdesign.net/forums/showthread.php?p=221464#post221464 Rick Willoughby

V11J

Rick Willoughby — 2008-08-09T13:59:38

I posted some pictures of my latest variant of the V11 hull on the bottom of this page: http://www.boatdesign.net/forums/showthread.php?t=23345&page=6 The boat hull is made with glass/epoxy on 3mm Klegecell foam using the old hull as a male plug. Total weight is 23kg. It has twin "dipping" rudders that I am pleased with. Rick Willoughby

(unknown)

Rick Willoughby — 2008-08-05T21:52:47

Rick Willoughby rickwill-bzGI/hKkdgQnC9Muvcwxkw< at >public.gmane.org 03 9796 2415 0419 104 821

Mono vs cat (both optimized)chart?

Rick Willoughby — 2008-08-04T21:37:57

Larry Too many options for a chart. Also I an update of Godzilla that produces very interesting monohulls that work well when operated below hull speed. So I can nor produce better shape monos with a length constraint. They are very odd shapes that I am trying to understand. Rick Willoughby r

Hpv-boat Archived files

2008-08-04T18:20:09

If anyone is interested, here is a link to a web archive server that has a lot of the early hpv-boat forum discussions: http://web.archive.org/web/20050403170308/www.ihpva.org/pipermail/hpv-boats/ It doesn't seem to have everything but there are a lot of discussions available. Also the server seems to get bogged down occassionally but try again in a few minutes. It's a great source for finding old web pages. Here is the link to the archive server: http://www.archive.org/index.php I also have about 2000 old posts going back to September of 2005 if someone needs specific information on a subject. Bruce Plazyk

Re: Mono vs cat (both optimized)chart?

Larry Smith — 2008-08-04T18:19:24

Part of the acknowledged trade-off for stability. The greater stability of an outrigger or cat when compared to a mono-hull is certainly much more than an appearance. To translate in "terms of feel", try to sit on a 10 inch wide racing shell, and then on an equal displacement cat with, say, a 5 foot beam. At equal seat heights (which will need to be somewhat high in both, compared to a kayak) You will have just about time enough to register the "feel" of the rolling shell before you hit the water,...whereas on the cat, you can ponder the (nice dry) "feel" at leisure. Re. wake scares: Any craft of wide-form based stability, with sufficient roll-countering force(buoyancy), will follow the surface of the water. If a large wave approaches from abeam, the boat will be at the same angle as the steep wave face. Add a high C.G., and even more uneasiness will result. ;-) Weight-aloft(mast, etc.) aside, a cat (or a narrow mono, i.e.racing shell) has the requirement to keep the rider's butt clear of between-hull wave-tops, and so the C.G. has to be higher than the mono sufficiently wide to let the rider's butt pass THROUGH the waves inside the hull. Score one for the kayak,...lower C.G. Small comfort if you are suddenly involuntarily swimming. :-) Cat vs. mono w/training wheels: For EQUAL form-stability, whatever the configuration, there has to be an equal righting moment. This means equal buoyancy at an equal distance from the C.G. (or some equivalent.), ...this means an equal tendency to follow the wave face,...thus equal uneasiness at a given seat ht. when struck abeam. Aim the pointy end at the waves is still the basic rule. An as-low-as-possible C.G. is usually desirable, and then design the amount of roll-stability to your needs. (A narrow kayak can be kept upright on a steep abeam wave-face. But it will be the attentive kayaker's skill that makes this possible. A narrow Kayak can also dump you in a flash.) My own Preference is to have a comfortably stable boat, and handle the rough water issues with seamanship. How much roll-stability do you need? An individual decision,...how relaxed do you wish to be,...or how situationally capable? My own cruising/utility standard is for my own weight + 100 lbs. at the gunwale, with 5 inches freeboard remaining. Say 300 lbs. (200# me and 100# halibut, or worst-case, attempting to drag person from water). I am working on a retractable outrigger(for dockside, etc.,) which is progressively deployable, to meet stability requirements up to this max, in a 17 foot hull. Light recreational use could be much less demanding. Body weight on gunwale with desired freeboard remaining, should cover most boarding stability requirements, and be more than adequate for operational security. Those willing to spend more time in the water, or more willing to constantly be aware-of and control balance, etc., can go as low as they choose. Best wishes, Larry

Re: catamarans 40% less efficient than monohulls

Larry Smith — 2008-08-04T17:08:13

Hi Roger, and welcome! :-) A few thoughts : First, let's assume your eye is good, and the sail-plans are equal(as well as skipper-skill, etc.). You don't mention displacement,...only "same length". We have to remember that a mono of the same length able to carry the same sail-plan IN THE SAME WINDS, will be heavier (greater displacement) than the cat,...no question. Additionally, mono-hulls are often loaded with more gear/people than "Hobie"-type(trampoline) cats (as opposed to "cruising" or cabin cats). The cat has what is called "form" stability, ...advantageous because the form can be, and usually is, very light and thus more easily propelled. The mono-hull, in order to carry the same sail in the same winds, needs "ballast" stability, and ballast means more weight(displacement), which means more wetted-surface drag, more wave-making drag, and slower acceleration. The two boats should not be sailing side by side in the same winds, unless the mono-hull is an "ultralight" (nearly as-light, or lighter-than the cat),...and the winds do not exceed the sail-carrying capacity of the mono.In stronger winds which will have the mono reefed or heading for port, the cat may be just coming into its own, with the flying windward hull lifted and thus providing "leverage"(outrigger)-stability, and only the somewhat-increased drag/wave-making of the single immersed hull as a penalty. When the cat, with both hulls in the water, is outrunning tha same length, equal sail-carrying (but almost certainly heavier non-ultralight) mono, it is because the additional drag of the mono-hull ballast(and load!) as increased displacement/skin drag and/or appendage drag from a keel, is making the difference, costing more in performance than the 2nd hull is costing the much lighter cat. Also there is the possibility that the mono-hull is not as nearly form-optimized for the particular displacement and speed as the cat hulls are. Larry

Re: re: Back & Forth vs Rotary motion - of your feet.

Alex RIchards — 2008-08-04T16:42:17

Rick thanks for that, after a few scetches it all made sense. I'd wondered about fixing the "drive cables" to the hull aft of the swing arm and not the swing arm as in your design, and then looping them forward over pulleys fitted to the swing arms and then back to the drive. This would mean for every swing-stroke you'd pull twice as much "drive cable". Yes, the effort needed would be greater, but I wondered if the potential increase in prop speed, possible decrease in prop size and/or possible reduction in swing arm length would more than make up for this. Also can I find roller clutches anywhere in deepest darkest Brittany? Nope (mind you I don't know what one is in French) so I'm considering using single speed bike freewheels in their place and running bike chain over them. In my mind I could see that a single piece of chain could be looped round one, then over a jockey-wheel and then looped over the second. Yes there'd be slight twist in the chain, but not a great deal and I think it'd handle it. Then this would be attached to the "drive cable" using cable eyes to attach to the chain link pin as in the existing system. And of course it means no slip and no reeving - hoorah. Now, I await the potential problems. Alex

Re: Mono vs cat (both optimized)chart?

Alex RIchards — 2008-08-04T16:25:55

Whilst on the whole Cat vs Mono debate, one thing springs to mind. Won't a cat typically weigh more because of the spars, extra hull material etc? This would surely mean a cat will have a higher displacement than a monohull, and so we're back to ineffeciencies again. Also, whilst a cat would at first appear to offer great stability compared to a monohull, I'm not so sure how this translates in terms of feel. I've had the pleasure of sitting on a becalmed Hobie Cat when hit by a wake and it wasn't a hugely comforting experience. Ok the oscillating mast is something we don't have on an HPB, but being further above the water than when inside a monohull did leave me feeling a tad queesy. So I'm wondering, from a pleasure/recreational boat whether a mono hull with "training wheel" amas wouldn't actually have a better comfort/feel factor. And that's before we move onto aerodynamics.

RE: Efficiency & Marketability

Larry Smith — 2008-08-04T16:11:25

Sounds very good Michael!! Making a great boat even better.:-) Best wishes, Larry

Mono vs cat (both optimized)chart?

Larry Smith — 2008-08-04T16:01:07

From 11/13/06. 12:10 PM +1100: [[Of course the whole situation changes once you consider hulls of different form. For example if you apply the same length constraint to both the mono and the cat the penalty for the cat may not be as great. I did an example for Cory based on a length limit of 4.3m optimised for 10kph and the power required for the cat was only 15% higher than a 4.3m long mono. So if you have a length constraint and want good stability then it is hard to go past a cat. The 15% extra drag translates to about a 5% reduction in speed for the same power input.]] From 8/03/08. 10:53 AM -0700: [[You may also be interested to know that a minimum drag catamaran requires 39% more power than a minimum drag monohull for the same displacement. ]] Hi Rick, If I had been more awake, I might have thought to ask this last night: Looking at the two different % penalty for two equal hulls compared with one with the same total displacement, in the two posts quoted above, i.e. 15% vs 39/40%, am I correct in understanding that the difference is the result of the constrained vs. un-constrained length? And given that practicality more often than not does induce a constraint, can you comment on a general rule-of-thumb as to the degree of change in the %penalty as the constraint lengthens? This could take the form of a twin-hull penalty chart, showing the drag/speed-loss figures (ideally, I suppose, there should be a cross-column with displacements shown along one border,...a lot of figuring, no doubt ;-) For example(s): %penalty(s) for 225 lbs/1 hp at 10 ft /12.5 ft/15 ft/17.5 ft/20 ft/22.5 ft/25 ft? If this info could be expressed as in the first quoted post above it would be helpful --- i.e., %extra drag / %speed reduction at equal power. ( for my own purposes,I assume displacement (rider/craft and equipment load) at #300 lbs.,max sprint power at +/- 1 hp., "work-out" power at .33hp and cruise at .10-15hp) Using the first-post example, the form would be 4.3m optimized for 10kph (displacement not given)-15%/5% Such a chart would enable users to decide whether the speed change over-rides the cat stability gain for their purposes at their displacement/power within their length constraint. Thoughts? Thanks, Larry

RE: Re: Efficiency & Marketability

2008-08-04T14:50:04

I've retained what I thought were the most useful posts from the past "n" years. If there is any way to post these in a searchable mode on the web I'd be happy to do so. Michael Lampi

RE: Efficiency & Marketability

2008-08-04T14:47:38

You should try a Cadence with outriggers, Larry. The amount of flotation is adequate to let people stand in the cockpit and access the hatches without worry, too. The outriggers can be positioned so they are both several inches above the water, allowing you that much tilt (at the end of 3 foot akas) for leaning turns, allowing small waves to pass without impeding the boat, etc. It is possible to unlock the akas while under way so that if you want to have them in the down position, where they brush the surface. In this mode there is no twitchiness regardless of how little sense of balance you might have. When I'm going to be alone out on the Sound for several hours and there is a chance the conditions will change for the worse I typically have them deployed in the raised "high speed/training wheel" mode. When I'm doing demos for newbies I have them in the "low/more stable" mode. Regardless, I still love my Escapade for its ability to carry up to 3 adults in totally dry conditions and its enclosable cockpit. Its slower speed is just fine for herding swimmers in races, which I'll be doing in a couple of weeks, or cruising around the houseboats in Seattle, or keeping up with the typical recreational kayaker. As an aside, I took the Cadence on a couple hour excursion with a bunch of relatively newbie kayakers, most in double kayaks. I don't think my heart rate went over 79 while keeping up with them. Michael Lampi

Re: Efficiency & Marketability

Larry Smith — 2008-08-04T07:51:39

From 11/13/06. 12:10 PM +1100: [[So if you have a length constraint and want good stability then it is hard to go past a cat. The 15% extra drag translates to about a 5% reduction in speed for the same power input.]] I had only a poor recollection of this item from your older discussion, Rick, but it helped form my foundational understanding that stability could be had, if desired, at a speed-cost that was sufficiently small not-to-bother someone whose interest was not racing. ( I'm sure I could have worded that more succinctly. ;-) Thanks for the reminder of where-to-look, in my files. Your 5% speed-reduction figure is a small price to pay, IMO for the peace of mind offered by the "good stability". Speed record seekers will of course feel differently, but for my own recreational uses, 9.5mph with more stability beats 10mph with considerably less. In any case, at 68, achieving either "max" would be an extremely short-lived anaerobic exercise that no longer fits this senior's definition of re-creating on the water. I have not re-read all the pertinent exchanges, but a cursory look suggests that your comments about which designers know what are well founded. It is a shame that all the old posts are not available, both to newcomers, and to forgetful old-timers. I'm sure I could learn a great deal from more re-reading, not to mention seeing some that I never got around to when they were current. Thanks again for all your many contributions to this list. Larry

Re: Efficiency & Marketability

Rick Willoughby — 2008-08-04T04:43:25

Larry One of the current problems with this site is that we have lost history and are continuing to do so. A few years ago I would spend hours perusing the archives to take in the well trodden ground. We seem to have lost that ability. That is partly why I have suggested the Boatdesign forum. There are now a few participating on the pedal boat thread. I have kept my own HPV posts and you would need to go back to November 2006 to see the exchange on cats I am referring to. Sadly I do not know whether the archives have been lost. It means people coming to this site fresh have no history to scan. I believe you give more credit to boat designers than they deserve if you believe most understand the fundamental advantage of displacement monohull over displacement catamarans. At the limit though a sailing catamaran is a skinny mono so it will perform exceptionally well at that point. Certainly the average boat buyer would not be aware of it. Rick Willoughby

Re: Efficiency & Marketability

Larry Smith — 2008-08-04T02:54:33

No, didn't visit the site. Was aware, though, as I noted, that speed did seem to be emphasized in the brief posted description of his proposal. If the cat's stability is not a high-priority item in his concept, then perhaps he should go with a mono,...but that wheel, and most of the stabilizing options, has been invented many times. Maybe more time spent in study would be beneficial before stepping out on such a well-worn path. Re. progress still-to-be-made, IMO, your own experiments represent some of the most innovative and informative recent efforts. This surprises me, if by widely known, we mean to serious designer/builders.I would expect such people would have a grasp of the basic geometric differences in surface area, the wave-making issues with regard to hull length/beam, and that they most probably, in the research I imagine them to have done, would have tapped into the multihull work of people like Leo Lasauskas, re. hull interference, etc. I quite possibly am making the common mistake of expecting others to use the approach I would take, and forgetting that cats are skinned in many ways. (Does/did anyone ever really skin cats? Where did this saying come from anyway? ;-) Don't know what to say about this. Unrealistic expectations as a result of swallowing sales-hype with insufficient salt, maybe? Or only wishful hoping on the buyers part, with no blame due the advertisers? Never in question Rick. No offense intended. I respectfully bow to your superior watercraft knowledge and abilities in most all respects (particularly your proficiency as a designer/builder). :-) An illustration of the difference in where we draw our lines. I have tried the Cadence and think it is an exceptionally nice performance boat, but prefer something more stable for my own more-relaxed water pursuits. Understood. (I made no mention of propulsion issues.) Best wishes, Larry

gmane boat link

Rick Willoughby — 2008-08-04T00:13:21

Peter Go to this link: feed://rss.gmane.org/messages/excerpts/ gmane.culture.transportation.humanpowered.boats The old IHPVA site is no longer supported and we seem to have lost a lot of history. The gmane link has some data. I have started a pedal powered boat thread at www.boatdesign.net. It is a very good site. Just register and away you go. You can post images and video on that site. It has a huge data resource. I have been on the journey of understanding for about 5 years now and am happy to pass on what I have learnt. I have spent a lot of my life on water for recreation and some work but I have not had as much pleasure as I get from my various pedalled craft. I think it is a largely untapped frontier of development. Hope you find it enjoyable. You have to dare to be different to get satisfaction from it. So there are no dumb ideas or questions. Rick Willoughby

re: Back & Forth vs Rotary motion - of your feet.

Rick Willoughby — 2008-08-03T23:49:00

Alex I have posted some pictures here of Warren's system at #75: http://boatdesign.net/forums/showthread.php?p=219124#post219124 Mine is a little simpler but almost identical geometry. I do not have photos at hand. We did a lot of analysis on the best set up. You need to be able to adjust the rest position of the pedals to get the best result. It is a very flexible drive system. It has an extremely natural feel. You only need to stroke as much as you feel comfortable with. I found I would stroke further when I was going fast. Rick Willoughby

RE: oar+some pedal paddled cataraman

Peter Howard — 2008-08-03T22:35:00

First of all thanks to everyone for the high quality, well informed and gracious comments on my (newbie) posting. I just wish I had appreciated the potential of collaborations such as this mailing list earlier on! In particular the level of expertise and experience in the domain of screw/paddle/hull efficiency. The design goals and constraints for Oar+Some, were (are): I tried to evoke this more naturally as: In the cold light of the scrutiny you guys have provided, maybe I should be more circumspect... What you have told me about the 40% cataraman efficiency hit, makes it clear that the emphasis is very much on 'aspire' rather than 'approach' the performance of a racing shell. The point I was trying to make in my blurb - to people who had never thought about HPBs, was that Oar+Some was aiming higher in performance terms than the novelty pedalos you can hire at the beach. I used the metaphor of a decent touring bicycle, rather than a racing bicycle delibarately. My mental model involves taking a picnic and admiring the view - and doesn't involve much puffing and panting :-) However to me, the key and vital point - for which I'm extremely grateful - is that I've based my design decisions on spurious assumptions about screw (and transmission) efficiency - which does raise pivotal (no pun intended) questions for me. By the way, how can I view earlier material from this list? - I subscribed successfully and have received around 6 or so mails since my post, but I can't find a way to view the history. I arrived via: http://www.humanpoweredboats.com/ , and followed the link to: http://bikelist.org/mailman/listinfo/hpv-boats to subscribe, but the link on that page to see the archives is broken. Regards Pete Howard