Proa Questions: Atlantic vs Pacific

"can you tell me of any conventional catamarans that have held this record?"

I'll answer that myself: D Class catamaran Beowulf V of Steve Dashew's (a man maybe two decades ahead of his time) set a North American speed record of 31 knots back in 1961. But since then - zero cats, mostly proa types or .... foilers like Longshot and lHydroptere - not talking boards.

 

No Gary. You appear confused. The boats you mentioned are more efficient in one direction than the other from memory. Ie they have sterns?

Unlike the symmetric proa with four bows. Or is that four sterns?

Possibly truer to refer to them as lop sided multi's, than proas. Then again maybe the proa can come under that label as well?

 

Bruce. I said "one way proas" - is that confusing?

 

Slender is not always faster; one sample.

After I have first seen Thai longboat racing was really excited to see what is their hydrodynamic efficiency. I did a simple spreadsheet for resistance estimate of such boat, and calculated series of lengths. So the results were: with increase of length residual resistance was decreasing, but frictional resistance is growing; so there is optimum length of boat, as I expected. Amazingly the measurements of real Thai longboat matched my calculations for optimum! The conclusion is that during centuries of races they have developed optimum type of boat...

 

Well yes Gary I am now very confused. Not only don't I see that phrase articulated in your post, but now I'm thinking that in your world a catamaran is a "two way proa" . Huh?

Any way here's some pictures of boats you define as proas. The original crossbow was a trimaran configuration from memory and they could move the crossbeam across the boat , to really make the whole lot lopsided.

Regards

 

What defines a proa? Shunting & therefor sailing in both directions.....
So isn't a one-way "proa" really a tacking outrigger?
But i suppose a proa could tack if it wanted or not too windy?

 

Older boats don't really tell us much unless they are very similar to current optimized designs. Otherwise they are often just leaps forward on going further down a dead end path than others at the time dared with different designs.

 

- "slewed cat (Crossbow 11) which was really a Pacific, one way direction Harryproa;"

Bruce, this is an area where pedantry and straw splitting arises - but imo, a true proa is what you describe, shunts, 4 bows etc, and then there are variations of that theme, one way proas like Crossbow 1 (by the way you are wrong about the sliding beam proa/tri, that was Slingshot) different rigged slewed cat/proa like C2; my interpretation is that if the crew are stationed in/on the outrigger the boat is a proa, not a true proa but a proa all the same, as is an outrigger, as is an Atlantic, Pacific, Harryproa and Daniel Charles designed proa .... all different but broadly speaking, proas. The Charles design is Harryproa-like but with the rig near the smaller hull, and very similar, but not the same, as an Atlantic proa, which has acccommodation in the equally long windward hull, whereas there is accommodation in both hulls of the Charles boat. Earlier he designed an Atlantic proa named Tahiti Douche. Then there are other French designs which are both Pacific and Atlantic at the same time and others like Guy Delage's 2 flying proas, the last, lost one with the huge wing mast and with crew working on and in between the outrigger, actually pretty much like Russ Brown's designs, but with accommodation in the longer hull. And so it goes. Did I start off saying this can get pedantic?
Alex, the Crossbows were not tacking outriggers, they could only sail one way, then lowered their rigs and got towed back on the other tack/shunt.

 

My apologies for doubting your thoroughness.

Please let us know how much you allowed for:
Area, fore/aft and athwartships location of the rudders
Height, section, flexibility, thickness and taper of the mast
Windage, prismatic, sections and bow bluntness of the hulls
Forestay sag in each breeze strength
The jib and the slot working at all wind angles on the ballestron.
The absence of daggerboard slots, and daggerboards.

Some of these have more impact on performance than the difference in hull weight. All of them have some impact on harryproa performance and are very different to the F40.

Of course. Which I why people who sail treat computer numbers for novel boats (both harryproas and excessively overloaded race boats) with circumspection until they are confirmed by real life numbers.

You agreed that the proa in the video is sailing at windspeed under main and jib.
Do you have any evidence (actual, not theoretical) of either the overloaded F40 or any cruising cat sailing at these speeds?

See http://www.youtube.com/watch?v=5pOsgqrO59A The first frame of the gps shows speed of 16.9 knots. We had been going faster than this (max recorded was 18), but the cameraman was a bit excited so did not film it. This was in a 20-25 knot bullet from about 140 degrees (broad reach). How fast should it be going according to your polars?

Still waiting for your grading of the harryproa benefits vs those for cats, which was the topic we were discussing, not your software.

rob

 

I can't agree with highlighted statement. DLR has major effect on hull resistance in discussed speed range. Other factors of hull shape are only of few % effect on resistance - this is clearly shown in many research including Larsson/Eliason's book, Mercier/Savitsky, etc. Same refers to minor details of rig shape. As to efficiency of rudders on proa, for example - they are much less efficient because they intersect free surface; this effect is clearly shown by Sobolev, Kuhn/Scragg, etc. But again, these are not major factors for such estimate.

I agree that Aerorig has different properties, delivering more thrust in range of 110-140 degrees of apparent wind angles (I did a study of that); this gives about 15-20% more thrust and few % of increase of speed. But all these factors won't have major effect on polars, as rough ESTIMATE they seem correct.

'Actual' for me is only measurements. I never did measurements for F40, but I do not see any need to verify software that has years of proven record.

What true wind speed was that? Was the GPS held in hand or fixed (should be fixed), continuous speed should be taken (on video there are fluctuations in range of 14-15kts), etc. - there is a procedure. How about corrections for current? I do a lot of sea trials myself (mostly for powerboats), there are lot of tricks of speed measurements

That's not MY software

For proa, I would estimate:

aesthetics - 4 (good, but still matter of taste, not a mainstream product)
performance - 5 (excellent)
comfort - 3 (fair - just too small for boat of this size)
safety - 2 (poor - not ISO compliant)
cost - 3 (fair - higher marina fees, lower resale, no secondary market)

For something like Gunboat, I would put 4-5-4-4-3

Again, this is just my opinion, nothing else.

 

So, your polars don't include the "few per cent" attributes that make harryproas different to overloaded cats, despite how "childish" it would be not to? All you have done is compare a lopsided catamaran with an overloaded one, and deduced (drum roll) that the boat with more sail is faster. I can agree with that.

You cannot verify your results, which you have now downgraded to "estimates" and see no need to, despite neither you nor the Wolfson institute ever doing any tests on actual harryproas (probably not on overloaded F40's either) to verify their numbers.

You admit "there could be some differences in predictions with reality", that "You know nothing about proas", and "the boat in the video is sailing at windspeed", yet you refuse to concede that it performs well compared to a cat. You then give a $400,000 harryproa a 5 (excellent) for performance, the same as a $1,800,000 Gunboat. You are as wrong about this as you are about almost everything else related to proas in this thread, but at least you are erring on the correct side.

In the interest of helping you get your polars right (or at least seeing how far wrong they are to prevent you making similar mistakes in future) there was negligible tide (Moreton Bay, near Tangalooma), the wind was 20-25 knots (not that it matters, the boat won't reach 17 knots on your polars until it is 40 knots) and you saw how the gps was handled.

And
You say "proa shows faster at higher windspeed when the hull is flying. Before that, cat is faster" Yet the boat in the video is nowhere near flying a hull at the windspeeds in your polars. It might be, if the rig wasn't unstayed, but according to you this is not relevant.

Re your gradings:
ISO compliance is neither proa nor catamaran specific, nor is it a guarantee that a boat is safe. As you said, all it really does is "keep customer reasonable in his requests, and for (avoiding) responsibility issues" which is great for lazy designers copying what everyone else does (not that I think you are, I know nothing about your designs as you would rather reference an impossibly overweight race boat than something from your drawing board), but totally inappropriate as a means to improve and optimise sail boats

Please include the safety issues I mentioned in my earlier post, which are harryproa specific and would apply no matter how overbuilt the boat was.

I see no connection between size and comfort, except that long (which is different to big) is more seakindly than short.

Cruising comfort is the motion of the boat in a seaway, all round visibility without having to move from the helm, easy view of the sails, non sailing crew being able to sit near the helm without being in the way, access to the galley and it's proximity to the centre of pitch, staying dry, even when handling sails, not having to clamber along narrow side decks or over the cabin to get to the bow, ease of handling the rig, ability to sit in or out of the sun, etc.

Cruising comfort is not about a huge interior with nothing to stop you falling, bunks for 8, but comfortable outside seating for only 4, someone sitting on the foredeck or motoring because you can't see under the deck sweeping genoa, regular gybing downwind because the main chafes on the swept back shrouds, a headsail that flaps back and forth as soon as you are on a broad reach or reducing sail in a squall rather than letting the flexible rig handle it.

Your cost comparison is incomplete as it ignores initial cost, maintenance and running costs, all of which are far higher on a Gunboat, and most other cruising cats, than they are on a harry. I appreciate that these are not issues one mentions to clients whose primary interest is likely to be how quickly they can sell the overweight boat they have bought, but they are far more important to harryproa people than marina fees and the size of the second hand market.

rob

 

No, that's You can not verify Your results - You design proas, so where are performance measurements, where are polars with real performance? All we see is some amateur video and hand-held GPS showing +/-2 knots of speed, no indication of wind speed and direction. This is just speculation.

I think for cruiser both boats are fast enough, so I give them same rating. This is my opinion, as I said.

Thanks, but You are definitely not qualified to correct my mistakes

These measurements on video are useless - fix GPS and take average speed, during time interval. Not maximum of speed fluctuations. Same for wind speed, also measured at standard height of 10m.

Not catamaran specific??? Tell this to European builders/customers

You can see some launchings on my web. And for most of them I have full record of sea trials, with measurements

Have You ever read those standards? I am sure You did not, but claim they are inappropriate
This time, ISO standards for structure and stability are referred in ISAF OSR Special regulations and applied to racing sailboats including multihulls.

How You can assess safety without criteria? Criteria are formulated in standards, so we check for compliance. No compliance - no safety; other is just talks.

According to ABS Comfort class requirements, comfort is:

a) noise (sound level, privacy level)
b) lighting
c) climate (temperature, humidity, airflow)
d) accommodation (layout, ergonomics)
e) motions (accelerations - MSI, MII, MIF, vibration)

So accommodation is there. These are generally accepted criteria of comfort; maybe Your personal criteria are different but then You are in different coordinate system.

Cost of 50' proa is less due to less equipment and accommodations. So in terms of purchase cost it should be compared with 30-40' cat; but marina fees are higher.

 

"How You can assess safety without criteria? Criteria are formulated in standards, so we check for compliance. No compliance - no safety; other is just talks."

I don't deny that is very useful. But engineers goof structures all the time until a large enough practical database is available to set up reliable standards. So experience tends to trump engineering wherre experience is actually available.

Also there has been some discussion of the problems of s shorter windward hull. Whatever the truth of the mater, it could be same length. I think the trade-off would be that at same displacement, the hull could end up narrow, but some would accept that.

 

For structures such statistics exists and there are some results of actual load measurements on sailboats, from production sailboats to Open60s and multihulls, results are published. These results are base of ISO12215-5. For stability/capsizing of multihulls there is almost no full-size statistics; for development of ISO 12217-2 standard tests were made with models on breaking waves, in tank. Results are also published.

 

We are in a new world were the latest big boats have strain gages built into the structures etc... So real numbers of the type that you like are available, and those boats were no doubt engineered from the get go. But the debt to the methods and experiments of the past should not be forgotten. The period of architecture is relatively short, and while it may suit you to emphasise it's current role since that is what pays your bills, people got along nicely for millennia. Architects are both necessary for, and supported by, large military and business projects, and would not exist as a class were pleasure craft the only outlet for their skills. In the pleasure field I doubt they would be much missed either.