Proa Questions: Atlantic vs Pacific

Yes, I know you are.

 

Where does a Tepuke go type wise? It's a pac proa but..... with a cabin over the center to ama. How could this be adapted to a cruiser - modern style cruiser? Both hulls are only bouyancy (possibly stoarge) and all else in the cabin. Sort of like Jo's toy - alibi arch - but shift the cabin over. Light boat. light load.

 

I lived on/cruised an Iroquois 30' cat for a couple of years 30 years ago. Kept very light, it was a great little boat for a young couple, would be pretty awful doing it now. You know my thoughts on small boats length, speed, safety and fear factor, so i won't repeat them.

If 30' is your limit and you want a multihull, then you don't want a proa. Good luck with the little cat, we can discuss it again again after your first storm (or when your back pain gets too much ;-)).

rob

 

The structure (ready to sail) of the proa (Rare Bird) in the video weighs about 3 tonnes. It's near sistership (Blind Date) in Holland weighs 2 tonnes incl rig. http://www.zeilenmetvisie.nl/EN/Blind Date.html Which multihull with similar accommodation, has a similar weight?

You are the only one comparing it with a 15m cat. I am comparing accommodation and speed, which, along with cost, looks and safety is what people ask for.

"Supposing" is a cop out. Let us know a cat of similar specifications, then someone who can build it for this price. And if you can find such a boat, add into the mix that the weight of these components on the proa is 360 kgs.

You asked for the advantages of a proa, not the disadvantages. These are: 2nd hand market size, nonconformity, marina fees and difficulty of installing a fixed propellor.

The supporting structure is far less than the main beam on a stayed rig. Less than 40 kgs on the boat in the video. The stayed boat must also add the chainplates and their bulkheads, the forebeam and striker, the traveller and it's supports and the sheet tracks and winches.

The rig in the video weighs a bit over 200 kgs. The weight in the ww hull is far more than that. Proas never sail in the "opposite direction" so this is irrelevant.

Your lack of experience is painfully obvious. If you approach proas with a catamaran mindset, you will never understand them. Start with a clean sheet of paper and no preconceptions or fears about how you will sail it. Design the fastest, cheapest (least material) boat you can with the accommodation of either of the boats at http://www.harryproa.com/visionarry.htm . Let us know it's speed, weight and cost.

A proa is never sailed the wrong way round.

More length (faster and safer, but higher marina bills) and more righting moment (faster, safer).

Be wonderful if it did, but there is no evidence to support this. What do you base this prediction on?

Please be more specific. How do you expect a seaworthy boat to behave at 15 knots boatspeed? Can you show us some videos of "seaworthy" sailing multis at this speed to illustrate what you are describing. There is no flare on the vast majority of fast cats and tris. It is slow and unsafe.

For a charter boat, true. For a performance cat, it is in the ball park. Look at the all carbon, 2 million dollar Gunboat 48 (fewer bunks, more toilets and interior space, diesel engines) weighs 8 tonnes plus 2 tonnes payload. No video evidence that it can sail at windspeed with main and jib in any conditions. At the other end of the scale, look at the Maine Cat 30 (fewer bunks, much less space), weighs 2 tonnes empty, payload 0.7 tonnes. Doubt it can sail much quicker than 60% of windspeed.

What are the hydrodynamic disadvantages of a proa?
Look at the video and answer your "Does it work?" question. If not, what is not working?
If you can supply polars of a cat with similar accommodation and weight, I would be happy to compare the performances.

Probably the same reasons (conservatism, fear of the unknown, scaremongers magnifying small incidents and making a big deal out of small disadvantages) that made people so slow to accept cruising cats 50 years ago.

For someone with no prejudices, you certainly have a jaundiced view of proas.
Maybe a practicing NA should be conservative. But an NA with vision and ideas should let them loose, sketch some concepts, build a prototype or six for himself, learn what he can from these and eventually, he may make a breakthrough and not be stuck designing the same boats that everyone else does.

There is not much chance of anyone ordering a proa from a designer who acknowledges he knows little about them, then sets himself up as an expert to demolish them.

It is not easy discussing things with someone who does not use specific numbers to support his arguments. The discussion very quickly goes nowhere. I have given you lots of numbers relating to harryproas. Please use actual catamaran numbers to back up your claims that proas have no advantages. Ta.

rob

 

Rob, I am not kind of guy who will be satisfied by promotional materials only; I see whole range of problems involved in proa concept.

Most of advantages You list are not due to proa concept itself, but due to lighweight construction (is it ISO12215-5 compliant? I don't think so) and dramatically reduced payload. Claimed performance and safety are not supported by any engineering-style data and comparision with cats and tris; ballpark numbers do not work here.

For example, it is evident how the resitance curve of proa will look: heavier and shorter windward hull will get on hump and resistance will incease dramatically. Same refers to running trim, there are well know relations. There are well written books by V.Dubrovsky on dynamics of such multihull craft.

So good luck in further marketing of proas, hope You can sell some

 

Not to disparage that book, but it says at the publisher's site that it is based on Russian research, and covers the gamut of designs from the small end to Swath. I was not aware of the depth of Russian research on pleasure yachts dating back to the comunist era that seems to be implied. Joeseph Norwood has written two books on high speed multihulls with heavy slant on proas, which he attempted to sell plans for. I just mention it because they offer the requisite heavy sledding for those so interested.

 

The research in Dubrovsky book covers basics of hydrodynamic principles of multihull craft; they are same for different countries and different craft. The authors (in Russian edition there are more than 20 authors, Dobrovsky is editor) cover different aspects of design of passenger, naval, fishing, etc. multihulls; presented are results of models tests for different configurations. If You take SNAME's PNA reference book, then Dubrovsky's book is its extention to multihulls.

Norwood's books are great as well (read one first time then I was 12), but hydrodynamics and aerodynamics presented there are too simplified (in my opinion).

 

That's a good heads up, because I found Norwood densely packed, and one very prominent designer told me he didn't understand what he was talking about most of the time. And he was an NA. So I probably will avoid the harder core stuff.

 

FYI: There were some research that can be used for pleasure yachts, just couple of samples:

- Systematic series of sailing yacht hulls ('NKI-series' consisting of 24(?) models) was published one year before Delft Series. Not much in use now but results themselves are quite valuable and is definitely a priority.

- Systematic series for planning powerboats ('BK' and 'MBK') are recognized and highly recommended - see references in ALMETER, J M: ‘Resistance Prediction of Planning Hulls - State of the Art’, Marine Technology, Vol 30,
Num 4, Oct 1993.

Of course, pleasure boats were not top priority for Soviets

 

This is easy to explain - Norwood used aircraft approach that makes NA's confused This is also where simplifications come from.

 

Alik,
You asked for the advantages of a proa. I listed some. You asked for clarification, I provided it, along with actual evidence. Now you are saying that everything is marketing hype and/or could be included in a lightly built catamaran.

I think you will agree that the advantages I listed would be assets on any boat? You are a naval architect with plenty of catamaran experience, but are apparently unwilling to have a go at a proa.

So, design a cat with the advantages, performance and accommodation I listed. I look forward to discussing it and reading all the engineering data.

Re building to standards: All the main components of harryproas have been engineered from first principles, then added to from my experience of 40 years of multihull sailing and building. So far, my approach has proven to be more than adequate. You can use a similar approach, or use the standard. Should make interesting reading either way.

rob

 

But it is true, the world is like this today - marketing in every 'technical' paper.

Not right; I am open to listern and found this discussion interesting. Please agree that sometimes someone asking questions gives You opportunity to show advantages and oppotrunity to see some potential problems.

So, You won't show polar plots for proa??
I do not design boats as hobbie now; will do once have an order. This time mostly busy with interceptor powerboats for navy

Experience is good, but... This issue is that designer is required to comply with those standards if he designs for European market. For instance, You used Gunboat as sample of heavier catamaran - yes, but its structure is ISO-compliant! Same can be said about stability assessment - multihull size factor includes weight, so seems 15m proa with 2000-3000kg of displacement will not comply with category 'A - ocean', pls refer to ISO12217-2 #7.7.

 

Size factor is not the problem:

For proa LWL=15 m, BCB=6.8 m, mMOC>2264 kg, Size factor is >40000 and capable to category A.

 

I am not sure if BCB=6.8m, because overall beam is 8.3m and boat obviously does not have much flare. Is it Your guess, or You take it from plans? If BCB>6.95m it will comply

For example, our 15m sailing cat design (Wasabi1500) has overall beam of B=7.96m, BWL=1.035m and BCB=6.57m. But our cat has reasonable flare...

 

Do you agree with those standards? The majority of people I have heard coment on those standards or USCG, feel they leed to overweight boats structurally, or over-equiped. Nothing one can do about them where they are the law...