This is an internet forum, whoever that was.
--- On Tue, 17/5/11, Paul Napper <pnapper@pathways.org.au> wrote:
From: Paul Napper <pnapper@pathways.org.au>
Subject: RE: [harryproa] Theory is for bits of paper, on shelves or in waste paper baskets.
To: "harryproa@yahoogroups.com.au" <harryproa@yahoogroups.com.au>
Date: Tuesday, 17 May, 2011, 13:45
this is the real world of give and take , exchange of ideas etc Contributions can be made in a number of ways by a number of methods . Most developments in the 3d world of aircraft or naval design are done in part by sophisticated modelling assisted by highly sophisticated software . It is not the whole story but is a very quick way of generating new concepts / hypotheses which can equally be tested
. No one is claiming a mortgage on method or ultimate wisdom re issues being discussed . It's called the scientific method at work , everyone's contribution has a role in a larger conversation . Not that difficult to grasp Grow up.
Paul Napper From: harryproa@yahoogroups.com.au [mailto:harryproa@yahoogroups.com.au] On Behalf Of Doug Haines
Sent: Tuesday, May 17, 2011 1:31 PM
To: harryproa@yahoogroups.com.au
Subject: Re: [harryproa] Theory is for bits of paper, on shelves or in waste paper
baskets. Apparently you are abit insulted or upset by something I said about the fact that your "models" are not actual models as I though of first. Modelling is doing maths with equations which give you predicted velocity for different inputs. Right? So okay, at least I know that you are not using small model like TOdd. Well, um, I don't really have an argument, with want you are doing. But If you did make small models couldn't you narrow down your optimum solution by just doing enough different ones? It is a bit like the Sailing Anarchy motto of show us some proof of what you are claiming is or we remain somewhat sceptical of you. Anyway, I have been asked to apologise to you beacause we need you on our forum to help us. I have been way over the top about something or other and should probably not have bothered with your posts at all.
From: Rick Willoughby <rickwill@bigpond.net.au>
Subject: Re: [harryproa] Theory is for bits of paper, on shelves or in waste paper baskets.
To: harryproa@yahoogroups.com.au
Date: Tuesday, 17 May, 2011, 12:48
I can develop the software from first principles so I am not trusting anyone but what a lifetime of observation and education has given me. The polars I produce are just Excel files with a bit of visual basic. You can see my progression with pedal boats here. It mirrors my education on hydrodynamics and aerodynamics over the last 10 years: Plus better understanding of materials for light weight
construction. But looks have not been high priority. Some boats never got used more than twice. My main interest in these boats is validation of the mathematics that are used to predict the results. On 17/05/2011, at 11:50 AM, Doug Haines wrote:
Serious?Wow, just trust the computer hey? Any credit
to the programmers and engineers? Or just trust the software company? Okay, so when I want to look at pretty lines on a graph then I know who to call. A few real world examples of how this amazing analysis has improved things for you would be nice.
From: Rick Willoughby <rickwill@bigpond.net.au>
Subject: Re: [harryproa] Theory is for bits of paper, on shelves or in waste paper baskets.
To: harryproa@yahoogroups.com.au
Date: Tuesday, 17 May, 2011, 9:37
One good one. It is inside my computer. This overcomes some of concerns you raise. There are no scaling issues or no need for radio control. I choose the control parameters and the computer takes care of that. It takes about 2 minutes to derive the speed polars over a range of wind conditions. So very fast at testing ideas. On 17/05/2011, at 8:55 AM, Doug
Haines wrote:
So how many model proas do you have? The scale would need to big enough to be able to see stuff clearly. You need to catch up with your model as it speeds away across the pond. I think Todd should be contesting other RC models if there are any around nearby to narrow things down a bit. Different camps will try and maximise their own take on the problem. I am totally confused with Todd's models, your numbers and lots of things in these forums. Who thinks that the harryproa is beyond any theorising, because they actually are working quite well for him now.
--- On Mon, 16/5/11, Rick Willoughby <rickwill@bigpond.net.au> wrote:
From: Rick Willoughby <rickwill@bigpond.net.au>
Subject: Re: [harryproa] Theory is for bits of paper, on shelves or in waste paper baskets.
To: harryproa@yahoogroups.com.au
Date: Monday, 16 May, 2011, 21:34
It no doubt helps to have hands on experience. It helps put issues into perspective and what factors are important and what are not so important. The best theory is the least complex construct that has all the important parameters in perspective. If the theory is sound it is the fastest way to develop new ideas. For a few minutes effort you can
try a dozen ideas rather than having to build and test them, waiting for the same conditions you tried before to get valid comparisons. I got to #11 pedal boat before I was confident about my theoretical model of these boat. That design currently holds the world distance record for human power and has been described as the most efficient human powered boat on the planet. Many of the components that went into its optimisation apply to any sailing vessel. Low drag hulls and efficient foils being the most notable. However taking my efficient pedal boat design and testing it in the Murray Marathon raised a whole lot of other challenges that needed addressing. Having sound theory behind the design helped developing
new ideas like folding prop, compliant curved shaft and dipping rudders. These were all aimed at reducing the speed loss due to fouling and impact damage from logs. I expect my proa model would lead you to the same conclusion about the different rigs that you spent a good deal of time, effort and expense to arrive at. At this stage I do not even know if I want to build a proa. I think I can achieve the cruising I want to do with a solar powered boat. But then I am curious about certain things that have not been tried to get the best from a proa. Of all sailing boat configurations they Harryproa makes most sense for value for money. On 16/05/2011, at 8:40 PM, Doug Haines wrote:
One point that you bring up here is the idea that maybe the sail geometry is causing the rudder to have to work too hard to get the boat tracking straight oncourse. This was the basic idea that had me rebuilding and trying a single mast ballestron even after enjoying my nice easy to use double main schooner set up. The up shot as I am trying to express continually here is that that change seemed to do nothing at all to help my steering. It was only when I started chopping down and then re-adding on about 30cm of blade length that any real change in handling occurred. I wish now that I had stuck to the original two masts in the beam to mast cross beam design that was detailed on Rob's plans I bought from him oh so long ago these ages past. What a lot of hassle that would have saved. I am trying to point out that you can theorize and
tell us what we should expect to find wrong or right with our harryproas, but I don't think you really have the faintest idea untill you make one yourself.
From: Rick Willoughby <rickwill@bigpond.net.au>
Subject: Re: [harryproa]
Assymetric proas - leeway, blade size. And getting spray in your face.
To: harryproa@yahoogroups.com.au
Date: Monday, 16 May, 2011, 16:04
With rudder ventilating it really does not matter much what is preventing leeway. The hull and the rudder are both working to prevent leeway unless the rig is very unbalanced. The hull and the rudder are planing surfaces producing the lift to reduce leeway. The highest L/D for the rudder is about 9 and will occur around 3 degrees to true course. The hull will have lower L/D up to about 6 degrees. So if leeway is not obvious then you are probably achieving less than 6
degrees. If this is the situation there is no point trying to reduce leeway further by making the ventilating rudder bigger. I need to point out that these figures will vary a little depending on size of boat, speed and other parameters but are good enough for discussion. I would not expect that you will improve anything by changing the section shape of the rudders. They could be flat plates with pointy ends and work just as well. Maybe something to test. The case where bigger blade might help is if the rig is not well balanced and you need a lot of steering input to hold course. If the blade is working
more than a couple of degrees off straight then its AoA is the steering input plus the hull leeway. At 6 degrees true AoA on the rudder (say 4 on the hull plus 2 on the helm) the rudder L/D will be around 7. So you are below the best and more blade area would improve result for that point of sailing. Over a course there is a lot of variation with the loads. To make meaningful comparisons you need reliable polars from an accurate model or you spend days match racing against a reference boat to find the optimum. For example increasing the blade area will slow you down off the wind unless you raise it. On 16/05/2011, at 2:59 PM, Doug Haines wrote:
I would think that - from what I have seen looking at my aft rudder - that perhaps it could be of some benefit to have assymetrically faired rudder blades. I do see the water level several inches lower on the ww side of the blade than compared to the other side. Obviously this is the action of leeway prevention. Should I see as much as that? Does this mean that I am actually drifting down to leeward? I don't notice much from looking back at
the hull wakes. And I don't automatically pick up that my course is askew off to one side. Measuring things out on your passage is difficult. Speed and some other basic effects are mainly the observations easy to notice. Heel, spray wetness, cold wind etc are also more evident. I am curiuos about this rudder size thing though - because if I had such a good result by increasing my blade size, then should I try going even larger and really getting that bite through the water and hold my course more truely?
From: Rick Willoughby <rickwill@bigpond.net.au>
Subject: Re: [harryproa] Re: Design your proa HUll exercise
To: harryproa@yahoogroups.com.au
Date: Monday, 16 May, 2011, 14:48
The V hull will produce lift but nowhere near as efficiently as a cambered
centreboard. I also doubt that it will be more efficient than a flat bottom hull. Using your numbers you have increased the wetted surface more than 30% just to increase the lateral surface area. There is a huge cost in terms of extra hull drag. The lift coefficient for a deep V section could easily be half that of a flat panel. So 18sq.ft V may not be any better than 7sq.ft flat. I have some reasonable models for flat panel planing and Savisky for planing V hulls but it stops at 35 degrees deadrise for vertical lift. I know anything steeper than 45 degrees deadrise will dig in rather than slip sideways. So if the deadrise is greater than 45 degrees it should be good at preventing leeway but still not as good as a slab side. On 16/05/2011, at 2:11 PM, tsstproa wrote:
Hull length for length. Hull displacement for displacement.
Say on a 20 foot hull with a 400lb displacement.
V hull with a 13'' draft and Square bottom hull with a 6'' draft.
V hull 38sqft wetted surface area, square bottom hull 28sqft wetted surface area.
V hull with 18 sqft lateral area and Square bottom hull 7 sqft lateral area.
V hull skidding out and not producing lift I doubt it!!!
V hull with more than double the area how do you figure it would and not produce
lift?
Also at high angles of heel do you see the difference in under water plane shape? The wider the square bottom hull becomes the more defined is becomes.
Placement of rudders on beam is more about convenience for the models. The rudder placement on the model in this clip is to close to the hull. If you look at the end of the clip. The same model with the reverse flow sail design on it you might see what looks like rudder ventilation. I use rudders to test balance of hull to sail. Not to test foil designs. Except of course the large leefoil and windward foil design models.
Todd
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