Proa Questions: Atlantic vs Pacific

I think in terms of stability those ISO standards are too liberal. Say, most of 8m powerboats can be classified as 'offshore' for 4m significant wave - that is nonsense! For sailboats, if You look at required AVS=100 deg seems too low for ocean category.

For structure - ISO standards are quite reasonable; they keep 20% margin for materials properties but this can be reduced if laminates are tested.

Of course, nothing is perfect; but standards are mandatory and we have to follow them. For practising designer it is also convenient: they help to keep customer reasonable in his requests, and for responsibility issues.

 

Maybe for you. I try to be completely open with information (good and bad) about my boats. I also try to help anyone else with similar aims, whether they pay me or not.

Asking questions is great. Telling me they are no good, then conceding you know nothing about them while ignoring my evidence and not listening to my replies is not so great.

I would if I had them, but I don't. All the multi polars I have seen are hedged by ifs, buts and maybes, so not worth looking at. I prefer to show the videos, the drag curves and the most detailed specifications I can and let the client decide. Incidentally, I could not find any of this information about any of the sailing boats on your web page. Perhaps you could let us know the polars, drag, and specifications for the design of yours which is closest to the accommodation of the harryproa in the video?

I was not suggesting it as a hobby. If you can validate your claim that a catamaran has all the advantages I listed for the harryproa, you will sell a lot of boats.

Another area in which we differ. I design, build and sail boats to see if I can make them faster, cheaper or easier to build and sail. None of my clients are interested in a boat which is 2-3 times heavier and more expensive than it needs to be, just to satisfy a bureaucrat in Europe. There are 2 x 15m harrys sailing in Europe, one of which takes blind people sailing and 3 x 20m being built so it is possible to avoid the silliness.

rob

 

I have seen You posted drag curves in another thread, but for leeward hull only. Showing these curves without showing total resistance of proa is kind of marketing I have done simple estimate of proa drag, and the result is not encouraging... the resistance of shorter and heaver windward hull at certain speed range is more then double of resistance of catamaran hull, for same displacement. So if we look at hydrodynamic efficiency of proa concept, it seems to me not the best choice.

Hmm... if replies are supported by engineering data I would listen them with great attention. Basic maths is for advertisement booklets only. One should compare overall performance with polars to make a conclusion.

You can see such polars for Gunboat, on their website.

For our catamaran designs - they are just heavier because all of them are ISO-compliant, we can not develop substandard designs... And they are cruising designs - with aircons, genset, some teak, etc. To me, there is no point to have 50-footer with accommodation of 30-footer And yes, I have polars for them

Actually, I think I can calculate the polars for proa (hope my software will take it), will do it over weekend. It is interesting to see what happens.

 

http://www.youtube.com/user/marcodelmonaco#p/u/16/AfkiGEEdzqg

http://www.youtube.com/watch?v=m1dFQaTeT6c

 

This is very nice of You to post video of motorsailer here

 

If I was 30 years younger I would definitely be in the market for Robs 50' Harry. As it is if he were to build a larger version with a real washroom a full sized galley and two double staterooms, suitable for a couble and child to live aboard in Thailand ,for lets say twice the price quoted for the 50 footer,it would be the hell with the condo I am buying another boat. Who knows if he offered plans I might have time left to buid it myself .This thread has got my imagination on over load. That and an aversion to tackeling the maintanince tasks on my own boat got me messing around with my computer. Since I know little or nothing about designing a proa I took all the ideas I have read about in this and other threads about proa's and came up with a sort of fish head soup. Its not supposed to be the basis for an actual design. Its just a compilation of a lot of concepts that other's have proposed or in fact used with varing degrees of success that might accommodate my rather large wish list. Attached is a short animation for your amusement. "Fish Head Soup"

 

I love it! The fish head soup... name, boat and animation!

 

You are welcome, it looked like a sportfisherman to me. Great view from up there, but it is the only sailing vid of a cat I could find.

 

The drag data I posted on that thread was for a racing proa. If the windward hull is not flying, or nearly so, you are not sailing it properly.

Gunboats publish polars with a disclaimer which effectively states that they are approximations. This is supported by the only race a Gunboat 48 has entered with tracking, in which the Gunboat performed well below these polars. If Morelli and Melvin can't get the polars right on a multi million dollar program, there is not much hope for the rest of us.

I find it astonishing that you refuse to believe (or comment on) a video of a boat sailing at windspeed under main and jib solely because it is not supported by "engineering data".

I look forward to your proa polars, as it looks like we are not going to see any of your catamaran ones..

rob

 

Interesting boat, great animation. Twice the price of a Visionarry 50'ter would get you a lot of flat panel boat. Plans for a boat that size aren't "offered", they are drawn in close collaboration with the client. If you want to have a go, I am certainly game.

The way I work is that we discuss what you want and i sketch it until you are happy with the concept and the costings. This is the fun bit, so I do this gratis. Then you decide if you want to proceed or not. If you do, pay me some money for the drawings and off we go. Judging by the video, you are a much better drawer than I am, so we would probably change the responsibilities somewhat. ;-).

If you want to have a look at what is possible, I am certainly up for it.

Rob.

 

I do not refuse to believe, I believe! (For clarity: can You quote where I doubt that boat is sailing at windspeed? I never said that!) But it happens only in certain range of true wind angles and windspeeds, can be clearly seen on polars. On rest of range boat is slower than heavier cat.

Sorry to say, but such video is not engineering data... Measurements, calculations, drawings, specifications are engineering data.

I do not need to post polars of our designs here, because nearest ones are 49' that weights 8000kg lightship, and 45' that weights 8800kg. These are different catamaran designs - heavier, but with real accommodations and outfit, and both ISO-compliant.

And now good news: I have done polars already, will post them tomorrow (damned tired, just came back from boating on Chao Praya river), together with polars of Formula 40 catamaran

Regarding the software - I have developed some VPPs myself and for me it is not just a 'black box', so reliable predictions for multihulls are possible. The VPP I use now is from Wolfson Unit and is developed for multihulls. Of course, Your opinion on those predictions will be very interesting - pls compare calculated data with measurements from sea trials.

 

polars

So, here are the polars.

For proa estimate, I took sail area 72m2 and weight of 3000kg. Catamaran template was used and modified for dimensions of hulls (so now they are different) and stability data. Gennaker was excluded and replaced by main+jib combination.

For catamaran, I have just calculated built-in sample from Wolfson software for Formula40 catamaran (DSPL=4840kg; SA=113/167m2) .

Wind speed and boat speed are kts. Effect of waves is not included, in both cases.

I also played with proa parameters and there are some other interesting results, but it would be great to get comments and verify the ones posted.

 

Are you sure about the Formula 40 weight? 4,850 is more likely to be pounds than kgs as they had an ex crew weight of 1,800 kgs.

rob

 

Rob, weight is specified with crew and some payload, for both boats.

For Formula40, I didn't change source file - it is original sample from Wolfson with weight of 4843kg used in calculations.

 

Is it easy to overlay one over the other in different colours?