----- Original Message -----

From: Doug Haines

To: harryproa@yahoogroups.com.au

Sent: Friday, July 02, 2010 12:35 PM

Subject: Re: [harryproa] Re: Rudder lift?

 

RUDOLF, why not enlarge the rudders 50 % or more and put them way out back? doug --- On Fri, 2/7/10, Rudolf <rpvdb@freeler.nl> wrote: From: Rudolf <rpvdb@freeler.nl> Subject: [harryproa] Re: Rudder lift? To: harryproa@yahoogroups.com.au Date: Friday, 2 July, 2010, 18:04   It seems you don't want to consider another difference being the rockered ww hull of BD while RB has a straight keel ww hull. This is a difference and even if it seems unlikely, untill this stuff is completely sorted I think it could make a difference. The amount of spray over the ww hull on RB at speed is something we haven't haven't experienced on BD. Rudolf --- In harryproa@yahoogroups.com.au, "robert" <cateran1949@...> wrote: > > Point taken, > I had not considered the hydrodynamics of the stern being pulled down and the bow being pushed up. > I am not sure how this would affect the overall drag, especially at higher speeds but Farrier uses this in his tris to good effect. > > Is it possible that with the long skinny Harry hulls, the extra induced drag from the transom being pulled down due to the rocker may contribute to the overall drag and exacerbate the luffing up, increasing the loads on the rudders, thus increasing the induced drag on the rudders,increasing the drive needed for a given speed and exacerbating the bow depression. > > I still don't understand why Blind date depresses its bow so much compared with Rare Bird; the only difference being the lighter and less windage ww hull. > > --- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@> wrote: > > > > I have done experimental testing and detailed hydrodynamic analysis > > on long slender flat bottom dory type hulls. > > > > These hulls have high block coefficients and trim bow up even at > > displacement speed. This is due to wave making pressure distribution > > not dynamic lift. Setting some rocker in the ends increases the bow- > > up trim at displacement speed and increases dynamic lift at higher > > froude number. > > > > With these hulls it is possible to counter the pitching moment from > > modestly tall rigs so the boat trims bow up or near level at speed. > > > > If you take a look at the sections of the amas on BMW Oracle you will > > see they are essentially flat bottoms. In the case of a tri the wide > > transom will sink the stern a little more than achieved with a flat > > canoe stern on a proa hull but it is still possible to generate > > significant bow-up trim with the canoe stern. > > > > Rick > > On 30/06/2010, at 1:20 PM, robert wrote: > > > > > The driving forces of the sails and the resistive forces of the > > > foils and hulls creates a torque that forces the bows down. This > > > can be compensated in small boats by moving people or even in large > > > boats with moveable ballast. There is nothing much one can do about > > > this except minimise the resistance by having smooth foils and > > > hulls and I think some value can be had from having the drag from > > > the foils more to lee of the vector of the centre of drive of the > > > rig to reduce the induced drag needed to compensate for an > > > imbalance of drag. Theoretically high aspect foils have less > > > induced drag for the same lift. These two points suggest having > > > fatter bows and the rudders more towards the ends with two leebords > > > and then lifting as many foils as possible. Having a high prismatic > > > coefficient reduces the depth of the bow depression as there is > > > more extra buoyancy on a longer lever arm for the same restoring > > > moment. This needs to be balanced against the reduction of drag > > > associated with a sharp transom when dealing with double ended > > > vessels and wave impacts. Wave impacts include vertical movement > > > coming off a wave and horizontal movement due to movement through > > > the water. I think the lee bows of the Vis are a very nice balance. > > > > > > > > > --- In harryproa@yahoogroups.com.au, Arto Hakkarainen > > > <ahakkara@> wrote: > > > > > > > > The bows of visionarry are just the way they should be. They have > > > enough buoyancy to be safe and fast. However, the force on the rig > > > will push the bow down more or less. Having as good balance as > > > possible is good for boat performance in all conditions. Having > > > bows up in moderate and heavy wind is better than having bows down. > > > Having bows up should improve the balance also. That is all I was > > > trying to say. Finding a way to both improve balance and lift the > > > bows should be good for both perfomance and seaworthiness. What are > > > the solutions for achieving those goals and compromises that come > > > with the solutions are the questions I was and still am wondering. > > > Even with the added complication of four foils (two rudders and two > > > boards) I think the improvements would be worth it IMHO. Next > > > question is should it be two daggerboards like Ono or some other > > > system. > > > >  > > > > Arto > > > > > > > > --- On Thu, 6/24/10, Rudolf vd Brug <rpvdb@> wrote: > > > > > > > > > > > > From: Rudolf vd Brug <rpvdb@> > > > > Subject: Re: [harryproa] Re: Rudder lift? > > > > To: harryproa@yahoogroups.com.au > > > > Date: Thursday, June 24, 2010, 12:35 PM > > > > > > > > > > > >  > > > > > > > > > > > > > > > > > > > > The new rudders of BD seem to show that thew minimum distance for > > > the large rudders is the old position. > > > > Also I would say that lateral balance in a sailing hull is a nice > > > thing to have, and that seems to lead to rocker imo. > > > >  > > > > rudolf > > > > > > > > ----- Original Message ----- > > > > From: Rob Denney > > > > To: harryproa@yahoogrou ps.com.au > > > > Sent: Thursday, June 24, 2010 8:09 AM > > > > Subject: Re: [harryproa] Re: Rudder lift? > > > > > > > >  > > > > > > > > The bows may be narrow, but they have far more buoyancy, much > > > further from the mast than any other boat I can find with the same > > > sail area. > > > > > > > > Most boats sail bow down when pressed hard.   They don't have > > > control problems. > > > > > > > > I can see how a daggerboard/ leeboard/ fixed keel have lower > > > loads than an oversize rudder, but I cannot see how they do > > > anything to the centre of lateral resistance that the oversize > > > rudders don't, apart from moving a component of it (the rudder > > > drag) a metre or so to windward.    Given the extra work, cost > > > and danger of the fixed foils, I will stick with oversize rudders, > > > built strong. However, keep experimenting, the more data, the > > > better. > > > > > > > > rob > > > > > > > > > > > > On Thu, Jun 24, 2010 at 8:37 AM, Arto Hakkarainen > > > <ahakkara@yahoo. com> wrote: > > > > > > > > > > > >  > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > This reminds me of some of the model testing Todd did a couple of > > > years ago. When the boat is pressed hard with high rig the bow > > > seems to be pressed under and knocked down and/or luffs to wind. > > > Seems quite uncontrollable and violent incident based on the model > > > tests. You should find the test videos from youtube. My current > > > connection is too slow for youtube search this week... > > > >  > > > > It seems that the high rig and narrow wave piercing bows will > > > cause the boat to sail bow down at high speed when it is not > > > wanted. Bow down may be good for light weather work for boats with > > > wide aft sections since it reduces wetted surface. In heavy weather > > > and higher speeds bow up would be best choice but how to get that > > > is the problem. > > > >  > > > > My favourite boards for proa are the twin bruce foils developed > > > by Fulgencio and demonstrated at the proa file. In his system the > > > bow foil is canted to give more lift up for the bow and more > > > lateral resistance at the aft end. Foils are linked so that canting > > > one foil to more horisontal will cant the other foil to more > > > vertical position. Canting forward foil to more horisontal will > > > lift the bow and move the lateral plane aft which will lead to > > > better balance and better hull position. > > > >  > > > > Downside of the system is that IMO it needs also rudders for > > > added control when sailing and all control when motoring. Also > > > making the system strong and simple enough is a challenge and with > > > also rudders means four moving foils on the boat which is hardly > > > simple anymore. > > > >  > > > > Arto > > > >  > > > >  > > > > > > > > --- On Wed, 6/23/10, Rudolf vd Brug <rpvdb@freeler. nl> wrote: > > > > > > > > > > > > From: Rudolf vd Brug <rpvdb@freeler. nl> > > > > > > > > Subject: Re: [harryproa] Re: Rudder lift? > > > > > > > > To: harryproa@yahoogrou ps.com.au > > > > Date: Wednesday, June 23, 2010, 10:45 AM > > > > > > > > > > > >  > > > > > > > > > > > > > > > > BD has a rockered ww hull while RB has a straight keel to ww. > > > That is a difference that might change something. > > > > On BD at the test sail with new rudders sailing with just the the > > > main was hard enough. Lots of rudder angle to keep course. > > > > Raising the jib (20 m2 on a total of 76m2) gave a lot of extra > > > power, we felt the drag, the boat didn't accelerate and rounded up > > > uncontrollable. > > > > We have always been surprised by the bow down attitude of BD in a > > > bit of wind, maybe from 14 knots upwards. Also we haven't seen speeds > > > > over 14.5 knots even at winds where you would expect more. > > > > With the old rudder set up we tried lifting the front one and > > > lots of different positions but it didn't seem to make a lot of > > > difference. > > > >  > > > > Rudolf > > > >  > > > >  > > > > > > > > > > > > ----- Original Message ----- > > > > From: Rob Denney > > > > > > > > To: harryproa@yahoogrou ps.com.au > > > > Sent: Wednesday, June 23, 2010 2:07 AM > > > > Subject: Re: [harryproa] Re: Rudder lift? > > > > > > > >  > > > > > > > > > > > > Hard to get really high prismatics with rocker, but they may not > > > be required. Something else to test. > > > > > > > > On Rare Bird in the Gladstone race we were hit with a pretty good > > > gust and the boat took off on a broad reach. Huge amounts of > > > spray from the rudder, but the bow barely went down at all and > > > steering remained easy. It was pretty near the comfort limit if > > > we had been cruising. Doug put a video of it on You Tube. > > > > > > > > If you are immersing the bows further than this on Blind Date > > > (which is lighter, but has the same lee hull), you must be > > > putting some serious force into it. How much wind was there? > > > What sail did you have up and were there any waves? Anything else > > > that might be relevant? > > > > > > > > On Elementarry moving my weight fore and aft does not make much > > > difference to the bow trim as I can't move far and it sters pretty > > > well bow up opr bow down, except when it is going slowly. Upwind, > > > I sit amidships or aft if I need to be near the mainsheet cleat. > > > Really pushing it downwind, I sit on the aft beam, but have still > > > managed a summersault. .  > > > > > > > > What was quite noticable was the difference in bow down trim > > > between having the front rudder (reasonably well shaped and faired, > > > but nowhere near perfect) up or down. Up and the nose lifted > > > noticably and the boat went much quicker. This happened both up > > > and down wind, which is one of the reasons I switched to using a > > > single rudder. I guess the drag would also add to the tendency to > > > luff, but the rudders are still pretty close to the hull, so it was > > > not noticable. > > > > > > > > Still plenty to learn! > > > > > > > > rob > > > > > > > > > > > > > > > > On Wed, Jun 23, 2010 at 6:51 AM, Rudolf vd Brug <rpvdb@freeler. > > > nl> wrote: > > > > > > > > > > > >  > > > > > > > > > > > > > > > > > > > > > > > > The buoyancy would be there, but located differently. > > > > Changing the lateral profile can change the behaviour of a boat > > > dramatically. > > > > It could be the boat would seem to have a more bow down attitude, > > > but the truth would be the deepest part of the hull moved forward > > > just a bit instead of all the way to the bow. > > > > High prismatic coefficient is good to prevent nose diving, that > > > doesn't change if the hull has rocker. > > > > Leeboards have advantages, but I don't know of leeboards at high > > > speed( say over 12 knots). > > > >  > > > >  > > > > > > > > > > > > > > > > ----- Original Message ----- > > > > From: robert > > > > To: harryproa@yahoogrou ps.com.au > > > > > > > > > > > > > > > > > > > > Sent: Tuesday, June 22, 2010 5:28 PM > > > > Subject: [harryproa] Re: Rudder lift? > > > > > > > >  > > > > > > > > > > > > I don't see that rocker in the lw hull really helps. It will > > > still require similar extra buoyancy in the bow to counteract the > > > sailing loads. (it would also give more vertical load vectors form > > > the sail, but this is pretty marginal) A rockered ww hull would > > > make it worse. > > > > A higher prismatic coefficient giving greater extra bow buoyancy > > > for less side area should make it better.I am working on 8.5-9 > > > prismatic coefficient, depending on the payload > > > > > > > > Your work with a single leeboard is dominating my ideas at the > > > moment with the rudders at 9m apart just out from the hull, though > > > I am wondering about two leeboards. This is starting to look a bit > > > excessive. > > > > > > > > > > > > --- In harryproa@yahoogrou ps.com.au, "Rudolf vd Brug" <rpvdb@> > > > wrote: > > > > > > > > > > Hi, > > > > > > > > > > The steering problems on BD to me seem related to the bow being > > > pushed down so it becomes the deepest part of the boat. > > > > > It took me some time to realise that this seems to be happening > > > and that it relates to experiences on other boats. For a non-proa a > > > solution may be to trim the stern down. For a HP that would mean > > > pumping water ballast. Another solution for a proa might be to > > > design rocker in the lw hull. > > > > > A rockerless lw hull of a HP in my opinion needs its rudder as > > > far aft as possible. The small ones like Harriette are easily > > > trimmed by shifting weight, which is a instictive reaction when > > > sailing a small boat at speed. > > > > > > > > > > regards, > > > > > Rudolf > > > > > > > > > > > > > > > > > > > > ----- Original Message ----- > > > > > From: Gardner Pomper > > > > > > > > > To: harryproa@yahoogrou ps.com.au > > > > > Sent: Tuesday, June 22, 2010 2:58 PM > > > > > Subject: Re: [harryproa] Re: Rudder lift? > > > > > > > > > > > > > > > > > > > > > > > > > Hi, > > > > > > > > > > The leeway is not my primary concern. I am worried about > > > steering. I have heard several mentions about Blind Date and also > > > about Sidecar, that they lose steering control, can't shunt, or > > > head uncontrollably up into the wind before their rudders were > > > enlarged, moved, etc. > > > > > > > > > > I don't see the advantage of a shallow draft boat if I need to > > > have my rudders down 5' in order to steer. I have been trying to > > > find out if this is just a problem when the boats are overpowered, > > > or strong winds or something, but no one has admitted to that, so I > > > am worried that I won't be able to sail in less than 4-5 feet of > > > water. I will be able to drag my boat up near the beach, but the > > > last mile will have to be done under power. > > > > > > > > > > - Gardner > > > > > > > > > > > > > > > On Tue, Jun 22, 2010 at 8:05 AM, robert <cateran1949@ ...> wrote: > > > > > > > > > > > > > > > In shallow water, there is a some leeway resistance due to the > > > water having a hard time getting out of the way. The shallower the > > > water, the greater the effect for the same depth of boat. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > --- In harryproa@yahoogrou ps.com.au, Mike Crawford <jmichael@> > > > wrote: > > > > > > > > > > > > Gardner, > > > > > > > > > > > > Your Mainecat/5200 idea is safe with me. I'm building a > > > plywood dory > > > > > > this summer and will be doing the same thing. Even if it > > > doesn't work, > > > > > > the theory is comforting./ / > > > > > > > > > > > > So now you're basically tripling your submerged foil area for > > > a 1.5' > > > > > > depth: two rudders at normal width, and two mini keels that > > > I'm assuming > > > > > > would each be twice as wide as a rudder. You won't have ideal > > > steerage > > > > > > and leeway prevention, but my guess is that this is a moot > > > point. > > > > > > Either you have two rudders, or you have rudders plus dagger > > > boards or > > > > > > mini keels. Anything you do beyond the rudders will likely help. > > > > > > > > > > > > I'd try keeping the keels as close to each other, though. This > > > > > > wouldn't be idea for beaching, but as Rob pointed out, tires are > > > > > > probably better than keels anyway -- that way there's no risk > > > of gravel > > > > > > sanding off your bottom paint, or of bouncing in the surf > > > taking your > > > > > > keels off. In keeping the keels close together, almost like > > > Rudolph's > > > > > > tandem keel, the keels shouldn't impact steering that much, > > > and could > > > > > > even conceivably help. Two keels far apart, on the other > > > hand, might > > > > > > make it harder to shunt, particularly when you don't have as > > > much rudder > > > > > > in the water as you'd like. > > > > > > > > > > > > At least you'll have the option of two counter-rotating rudders. > > > > > > That's definitely going to help steering in minimal depths > > > when compared > > > > > > to a cat. > > > > > > > > > > > > - Mike > > > > > > / / > > > > > > > > > > > > On 6/21/2010 1:53 PM, Gardner Pomper wrote: > > > > > > > > > > > > > > Hi, > > > > > > > > > > > > > > Yes, your description of when to use mini-keels is what I > > > had in mind. > > > > > > > I would rather not build them, but I am unclear as to what > > > the minimum > > > > > > > rudder area needed when sailing in light winds. Here is the > > > scenario I > > > > > > > have in mind: > > > > > > > > > > > > > > In the chesapeake, or the bahamas, there are many spots > > > that are 2-3 > > > > > > > feet deep that I would like to glide along in relatively > > > light winds. > > > > > > > The waters are sheltered, and therefore flat, and the wind > > > is likely > > > > > > > to be less than 10 knots. When doing this, I would like to > > > have a > > > > > > > draft of 2' or less. I can't have my rudders extended to 4 > > > or 5' depth > > > > > > > to get the requisite 2% of sail area, so I thought that fixed > > > > > > > minikeels, maybe 1' deep, would give the boat a 1.5' draft. > > > That, plus > > > > > > > the rudders raised to 18" draft would give me more foil > > > area than the > > > > > > > rudders alone. I would not be looking to sail at > 5 knots > > > under these > > > > > > > conditions, because i really don't want to hit anything. > > > > > > > > > > > > > > In that scenario, with a boat about the size of a harry, or a > > > > > > > harrigami, would I be able to steer with just the rudders > > > (total > > > > > > > submerged area of 3 sq ft, vs 400 sq ft of sail)? Would I > > > be better > > > > > > > off with an additional 3 sq ft of mini-keels? > > > > > > > > > > > > > > My Maine Cat 30 had the mini-keels attached with 5200, for > > > precisely > > > > > > > the reason you mentioned.. in a severe collision, the keels > > > were > > > > > > > supposed to break off without ripping open the bottom of > > > the hull. I > > > > > > > have no idea if that would have worked or not, but it gave > > > me peace of > > > > > > > mind to believe it, so please don't contradict the idea > > > <grin>. > > > > > > > > > > > > > > - Gardner > > > > > > > > > > > > > > On Mon, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Rick Willoughby > > rickwill@ > > 03 9796 2415 > > 0419 104 821 > > >