Bjorn:
My post was intended as a bit of gentle teasing. I had assumed that as you said the number on the right was tonnage, and the upper group were monohulls. Presumably the X axis is some unit representing drag. Y axis remains a mystery to me. The Y axis goes from .10 to 1.00, and yet the x axis spikes and dips at multiple values. Without understanding what I am looking at, I had just as well be looking at Rorschach ink blots in some shrink's office.... I may be if I stare at this too long ;-)
Every boat should have a mission statement. This boat was designed to fulfill this mission, the design being driven by these criteria, each weighted as to it's relative importance. A Westsail 32 cannot be meaningfully compared to an M32. They have entirely different missions
Rob's innovations interest me as I've said before. I love outside the box thinking and unconventional solutions. While the proa will not fulfill my boat's mission within the parameters I've set, other features and innovations of his boats could be incorporated into the project. His intelligent infusion techniques obviously. His fore and aft rudders rather than a fixed foil or keel or centerboard, and rudder offer a possible solution to the problem you describe in tacking. Deploying the fore and aft rudders in opposite directions should in theory at least achieve at least double the number of degrees of rotation per meter of forward travel. In other words, you should be able to complete the tack before running out of inertia. Rather than rotating about a center fixed by a centerboard, you are in a centerless rotation more or less, particularly where the design I'm talking about has shallow draft and a flat bottom.
The other solution worth considering is placing the mast in one hull. While placing the mast on the bridge deck offers more mast height perhaps as much as 1200mm, and that is not insignificant in terms of weight and cost in the context of a small cat and a carbon fiber mast, placing it in one hull offers the option of setting the mast farther forward, which is desirable in terms of boom length & sheeting angle for the junk rig, which has sheetlets at the end of all but the top batten. It is desirable to have a low aspect rig or several reasons........ obviously speed is again not one of them. Low aspect equals reduced capsize leverage for a given sail footage, and again it means a shorter mast. As a single hander, the probability that I will NOT be in the cockpit with my hand on the sheet clutch or whatever I use for sheeting is far higher than on a fully crewed boat. While the aspect ratio will be lower, total sail area ideally will be greater. The net result being probably less overall speed in many situations, but the ability to ghost in extremely light wind due entirely to lots of footage, and the fact that a junk rig will not flog due to all the battens.
I intend to build two "identical" mirror image hulls, not because I have a prejudice in favor of symmetry, but because I have a prejudice against work ;-). Each of the two main hull forms will produce two hull halves. Ideally the main portion of the sail should be carried over the boat when reaching and running, keeping the lateral center of effort fairly constant. There are two approaches to accomplish this. One is shunting, but I have no intention of resorting to this for a number of reasons which need not be repeated yet again. The other is reversing the flow over the sail, which is not as unreasonable as it sounds, though the camber would have to be located at the center, instead of 30% or so. How much real world difference would this make? I suspect far less than some might imagine. Sheeting might be interesting, but as the boom would be tracking out toward the starboard hull with the mast in the port hull on a reach or a run, and we are talking about a beam of close to 6M, some creative rigging with some line and blocks could control the sheet more tightly when the wind is from leach to luff............. a traveler line. As there is no sheet tension needed to shape the sail on a junk rig, this could be simple and work well. In some situations, one might simply carry the main sail outboard just to get more sun on the solar panels for example. In sailing as in most endeavors, convention is enforced by habit and by peer pressure. Again, I appreciate Rob's outside the box thinking for getting me to look toward alternative solutions. Just a few days ago, I suggested that a mast in one hull would not work out well on a cat. I'm moving away from that hard and fast prejudice, and looking at how to make it work...........
H.W.
On 05/30/2018 01:53 AM, Björn bjornmail@gmail.com [harryproa] wrote:
My post was intended as a bit of gentle teasing. I had assumed that as you said the number on the right was tonnage, and the upper group were monohulls. Presumably the X axis is some unit representing drag. Y axis remains a mystery to me. The Y axis goes from .10 to 1.00, and yet the x axis spikes and dips at multiple values. Without understanding what I am looking at, I had just as well be looking at Rorschach ink blots in some shrink's office.... I may be if I stare at this too long ;-)
Every boat should have a mission statement. This boat was designed to fulfill this mission, the design being driven by these criteria, each weighted as to it's relative importance. A Westsail 32 cannot be meaningfully compared to an M32. They have entirely different missions
Rob's innovations interest me as I've said before. I love outside the box thinking and unconventional solutions. While the proa will not fulfill my boat's mission within the parameters I've set, other features and innovations of his boats could be incorporated into the project. His intelligent infusion techniques obviously. His fore and aft rudders rather than a fixed foil or keel or centerboard, and rudder offer a possible solution to the problem you describe in tacking. Deploying the fore and aft rudders in opposite directions should in theory at least achieve at least double the number of degrees of rotation per meter of forward travel. In other words, you should be able to complete the tack before running out of inertia. Rather than rotating about a center fixed by a centerboard, you are in a centerless rotation more or less, particularly where the design I'm talking about has shallow draft and a flat bottom.
The other solution worth considering is placing the mast in one hull. While placing the mast on the bridge deck offers more mast height perhaps as much as 1200mm, and that is not insignificant in terms of weight and cost in the context of a small cat and a carbon fiber mast, placing it in one hull offers the option of setting the mast farther forward, which is desirable in terms of boom length & sheeting angle for the junk rig, which has sheetlets at the end of all but the top batten. It is desirable to have a low aspect rig or several reasons........ obviously speed is again not one of them. Low aspect equals reduced capsize leverage for a given sail footage, and again it means a shorter mast. As a single hander, the probability that I will NOT be in the cockpit with my hand on the sheet clutch or whatever I use for sheeting is far higher than on a fully crewed boat. While the aspect ratio will be lower, total sail area ideally will be greater. The net result being probably less overall speed in many situations, but the ability to ghost in extremely light wind due entirely to lots of footage, and the fact that a junk rig will not flog due to all the battens.
I intend to build two "identical" mirror image hulls, not because I have a prejudice in favor of symmetry, but because I have a prejudice against work ;-). Each of the two main hull forms will produce two hull halves. Ideally the main portion of the sail should be carried over the boat when reaching and running, keeping the lateral center of effort fairly constant. There are two approaches to accomplish this. One is shunting, but I have no intention of resorting to this for a number of reasons which need not be repeated yet again. The other is reversing the flow over the sail, which is not as unreasonable as it sounds, though the camber would have to be located at the center, instead of 30% or so. How much real world difference would this make? I suspect far less than some might imagine. Sheeting might be interesting, but as the boom would be tracking out toward the starboard hull with the mast in the port hull on a reach or a run, and we are talking about a beam of close to 6M, some creative rigging with some line and blocks could control the sheet more tightly when the wind is from leach to luff............. a traveler line. As there is no sheet tension needed to shape the sail on a junk rig, this could be simple and work well. In some situations, one might simply carry the main sail outboard just to get more sun on the solar panels for example. In sailing as in most endeavors, convention is enforced by habit and by peer pressure. Again, I appreciate Rob's outside the box thinking for getting me to look toward alternative solutions. Just a few days ago, I suggested that a mast in one hull would not work out well on a cat. I'm moving away from that hard and fast prejudice, and looking at how to make it work...........
H.W.
On 05/30/2018 01:53 AM, Björn bjornmail@gmail.com [harryproa] wrote:
H.W,
I was not trying to brag about my skills or show my superiority. I could barely understand the graph myself when I had a look at it yesterday, because I had nothing to go on except the very cryptic labeling and my slowly recovering memory. Took me a while to remember that the numbers in the end was the displacement. I do happen to be pretty talented with numbers, which comes with a lack of skills in some other areas.
Anyway, what I thought was so interesting with that graph. was how the "humps" completely disappear on light boats. I've been sailing keelboats, and it is so obvious on those boats that they will reach a certain speed, and then not go faster. You may be able to push it 0.2 knots faster when the wind picks up. But I was once on a pretty long and light keelboat under spinnaker in a breeze, and it starting to go faster! it was very exiting. That boat had about 10m waterline length, and a displacement of 4 tonnes (so just like the purple curve), and we reached 12 knots or so on a broad reach with a 90 m^2 spinnaker and 34m^2 mainsail. So it is possible, under the right conditions, to climb the hump and reach a higher speed. But I have also watched the M32 sail in almost no wind, but they are still moving in a decent speed. And then it just takes a puff to lift the WW hull and reach 12 knots instantly.
If we look at the numbers of the Harryproas, it looks like they will have a almost as good performance as to the M32, but as cruisers!So that is one of the things which excites me about these boats! Even though they don't tack or gybe. But from watching the M32, and Sailing the H14, I can say that it is very hard to make a good tack. A lot of the times the boat stops completely, and with me on the rudder, even sail backwards. So I believe Rob when he says that shunting is not that much slower then tacking. And then of course, with the H14, I have experienced the "zone of death" while trying to gybe in a strong wind, and capsized it completely forwards. Even just starting to sail the boat from a stop has capsized it because the sails hit the shrouds and can not be eased further. So I understand a lot about how unstayed masts must make life so much easier aboard a big boat.
But still, there is something very rewarding to making a good tack/gybe and maintain the speed.. But I guess when sailing on the open ocean, you do those maneuvers less than once per hour, so not much of a reward or time difference at the destination... =)
On Wed, May 30, 2018 at 7:52 AM, Doug Haines doha720@yahoo.co.uk [harryproa] <harryproa@yahoogroups.com.au> wrote:
The length of the lw hull is not necessarily the measure of the size of the boat.
If it is a problem for mooring or trailering, then design a folding bow like Ian Aitken did. This seems like the best solution to get a decent length and still fit a trailer.
My opinion was that lw hull should be even longer than as shown in some of the HP designs.Bucket/Sol is a good benchmark: 15m lw hull and only minimalist ww hull.
For the constraints on cost and weight etc it is easy to add as much length onto hulls, especially lw hull without increasing cost.So for better speed and safety, make hulls even longer.
One big advantage of HP's. Why not make the most of it?
Doug
On Wednesday, 30 May 2018 11:37:08 AM AWST, StoneTool owly@ttc-cmc.net [harryproa] <harryproa@yahoogroups.com.au> wrote:
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Posted by: StoneTool <owly@ttc-cmc.net>
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