On Sat, Oct 18, 2014 at 1:47 PM, Matt Tucker matt.s.tucker@gmail.com [harryproa] <harryproa@yahoogroups.com.au> wrote:
Hi Rob,I hope this gets to you ok as I'm just replying through my e-mail (Yahoo account has apparently been deactivated due to lack of use...)Really excited to see this and and am really looking forward to the opportunity to have a go at a racing Proa before I get the chance to build one!I've just got a few questions having spent a lot of time thinking about and drawing pictures of a very similar design concept for coastal racing (coastal classic NZ, Three peaks Tas, That sort of thing) then having a go at the solo trans-tasman.
Sounds like a great plan
Anyway my thoughts...Have the Harry main hull shapes (all very similar) been tested in large waves at high speed in all points of sail?
The original round bilge hulls have been, with no ill effects, excelent tracking and no nose diving. Most notably was surfing the bar on the Mcleay (I think) river. Aroha (overloaded 12m) hit 15 knots on a large breaking wave, for a considerable distance.
The reason I ask is that it seems to me that despite the extended waterline of a Proa they could tend towards pitch-poling due to the lack of underwater rocker which promotes lift in the bow and little buoyancy in the bow for ploughing into the back of a wave when travelling at pace off the wind.
I have put rocker in a couple of proa hulls. They both sailed seriously bow down, as the boat would "rock" forward onto the front of the hull. Rocker does not promote lift in the bow. Quite the opposite. The bow has to submerge a lot further before the buoyancy starts to act. Check out any racing tri outriggers. They do not have to be compromised for wetted surface or for steering ability. They are almost staright along the keel.
There is always going to be a tradeoff between wave piercing and opening yourself to the risk of pitchpoling I suppose. Also the flat deck and bottom would inhibit its ability to pop back up once it was bow down.
True, if the bow was designed to submerge through waves. It's not. Bucket List is way lighter than any other multi, so submerging the bow will be unusual. If it does happen, it is a warning to throttle back. The flat decks will not help, but they are very narrow. The boat will almost certainly be flying a hull, so the flat will be inclined. The flat bottom will, according to the models, plane, which will add significant dynamic lift.
I've noticed in the photos I've seen that they do tend to sail bow down (Due to the Rocker?)
The important number is the prismatic coefficient, which is a measure of how the buoyancy is distributed fore and aft. Most cats are round 0.65, of which more is aft than forward. Harrys are around 0.75, equally shared. This means there is more, not less buoyancy at the bows. The only times I have had them sailing bow down is when I pushed Elementarry too hard and it pitchpoled. Could you tell me which photos? Videos would be better, as you can see when it is just a wave at the bow.
All of this is not an issue in flat water but once you get out into swell it could become a bit hairy.
No reason for it to be hairy.
The rig configuration is pretty close to what I had in mind except for a few little things. First raising where the wishbone attached to the mast like the Wylie cats to give more shape adjustment in the sail and also gives an auto flattening and ease of the sail in a gust as the boom tries to lift (like an auto outhaul and sheet release).
Not sure the boom height has much to do with this. The angle between the leech and the foot is more critical. An 18m mast will flex in a gust regardless of the boom height.
Also have you considered adding the ability to raise a screecher or Gennaker (also like the Wyliecat 44) http://www.wyliecat.com/models/wylie_44.html. Great for light off the wind conditions.
True, but not on the charter boat due to complexity, and cost. I doubt it would pay on a race boat either. You have to carry the weight of the furler, the sail, a couple of winches, sheets, halyards, turning blocks all the time, but only use them in light air. On a heavy boat, no problem. On a light one, the issue is not so clear cut.
There is nowhere to sheet it to, the mast and step would need beefing up for the compression loads, the lee hull would need reinforcing and I suspect the safety rules would require pulpits at each bow. Plus, they are a pain to tack or gybe on a proa.
Is the windward hull so bulky to give it enough buoyancy for getting caught aback?
No. Caught aback buoyancy should not be a problem, but if it is, there is plenty. The hull size was determined by the bunks, plus wave clearance for the beams. It could be lower, but the beam connections get complicated.
Would you consider making it more wave piercing and if required slightly longer?
Could do, but if the ww hull ever goes into a wave, there is something seriously wrong. I would not change the length as the ends are not usable. It would just be added weight, windage and beam twist.
This would give a much smoother ride in bigger waves when even if youre flying a hull you are likely to be ploughing through the peaks of waves.
I doubt it would be smother. The ride is best when both hulls go over a wave at the same time.
Just a few thoughts that I thought could be worth considering.
For sure, and I may well be wrong. We will have a better idea when the prototype is sailing. I look forward to taking you for a ride and discussing it further.
I reckon its a great Idea and will hopefully open the worlds eyes to the potential of Proas.Good on you for making it happen!
Ta.
rob
CheersMattOn Sat, Oct 18, 2014 at 12:34 PM, Rob Denney harryproa@gmail.com [harryproa] <harryproa@yahoogroups.com.au> wrote:On Sat, Oct 18, 2014 at 6:38 AM, lucjdekeyser@telenet.be [harryproa] <harryproa@yahoogroups.com.au> wrote:If you continue to pursue the pure essence of sailing, the next Harryproa model will be abstract enough to be displayed at the museum of modern art ;-)
Thanks. Not exactly what i am aiming for, but a nice thought.As expected, you cut to the chase with the following questions.I have a number of questions:- It is not clear what one sits on.The ww hull deck or the tramp. Pretty uncomfortable, so folding canvas deck chairs will be able to be attached to the deck. Also working on a seat inside the hull so you can sit under the pram hood.- the flat panel rudder would be shaped in a Speer foil?A slightly modified Speer foil, otherwise known as an ogive with rounded edges. How much round (none at water surface level) will be the subject of experiment. The rudders will be mounted on Elementarry while we wait for Bucket List to be finished.Side note: El has been getting an absolute hammering as a test bed for boat viable kite launching/retrieving/control systems lately. Unfortunately, no photos, but it has been flown up the beach a couple of times, with me hanging off the side, with my feet barely touching the sand. Landed with enough of a bump to snap the outboard bracket off. No visible damage to the boat. We have also tried it with a SeaGlider with the kite take off point and the Seaglider attachment point on travellers. Learnt there is a lot more to coe/clr control than meets the eye! Last weekend, tried it with a kite on each end. At one point, my kite depowered, at the same time as the back one powered up in the wrong direction (operator inattention), we shunted in a millisecond and the boat took off fast enough to drop me in the tide. Nearly drowned while laughing. Huge fun, and we are definitely getting closer to a system that will allow us to fit kites to large proas for offshore use.- the animation shows the trampoline being pulled to leeward during assembly. How is that done with a trapezium shape?It's not. The tramps will stay on the beams, be attached to hooks on the hulls. Got a tool which should mean it is very quick to tension them.- is the 2 double bunk arrangement for the more cruiser version more like the ww hull of the Sol?It is the ww hull from Sol. However, it introduces a lot of problems if it is for a charter boat, so at this stage it would be more suitable for private ownership.- are the rudders pulled up and pushed down using leads up to the ww hull?Could be, but by hand is the current idea. They will probably need a line connecting them to the boom so that their rake angle changes when the boat shunts.- how does one push the boom down in the water when righting a capsized boat?via a strut between the mast and the mainsheet, which is not shown.- the estimated assembly time for two is 1 hour in the animation and 2 hours in the text. Meaning it takes 1 hour to read the assembly instructions manual but watching it on youtube no time ;-)You got it! I will fix it. Both times are a guess, but if the tramp tensioner works, then 1 hour for 2 people will be quite achievable.keep them coming.rob
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Posted by: Rob Denney <harryproa@gmail.com>
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