ADAGIO’s long range wifi configuration: options for antennas, routers and local wifi

This post is for cruisers who are interested in a very convenient and easy to operate way to translate land-based wifi into your yacht’s local wifi zone. We are very happy with this configuration – this is “generation 3” for us – technology has improved since our first-generation rig installed in 2000. The first section is on antennas, the second section on routing and our local wifi bubble.

 Antenna options:

External antenna: historically we bought our antennas from L-COM. But recently we’ve bought omnidirectional antennas for for both cellular and WiFi from RF Industries (Australian company, often abbreviated as RFI). An excellent New Zealand source for RFI is Paul McKnight +649 537 2683, Paul may have difficulty advising you what will satisfy your needs – it isn’t just distance, it depends very much on what gear the WiFi base station is using (the router, the antenna directionality, quality and gain).

We are using the RFI COL2410 which is their highest gain omnidirectional. Note there are 3 smaller (cheaper!) versions. I’m not an antenna guy so I won’t speculate whether you would be happy with less gain. Maybe ask Paul McKnight for advice? See pricing of the range of RFI sizes. The 2 dBi is $99, 6dBi is $120, the 10dBi like ours is $170. Telco Antennas is an Aussie company.


Router options:

For your external WiFi router (to communicate with land-based wifi access point), the options have improved very dramatically in recent years. All of the expense and trouble we endured to install low-loss microwave cable from wet to dry is no longer needed. The reason is outdoor routers that convert the analog signal to digital – so we only need ethernet cable from wet to dry. And we use POE (Power Over Ethernet) to supply power to the little router. We did a good bit of research amongst contacts in the communications biz – the consensus recommendation for our needs was the Ubiquiti Bullet M-2 running AirOS on linux.

Because the WiFi connectivity is often so important to us, we now have 2 Bullets – live and backup. The live/active Bullet was bought from Amazon for about $75. Later I discovered this first Amazon unit was the N. America version which locks out the international channels 12 to 15 where the best wifi is in places like Noumea. You may not care about the extra channels as the cost is slighty higher. If you do care, I ordered the second one from HD Communications for USD $78.50.

To bring the ethernet from the wet to dry we are using the L-COM ruggedized flange mount (when we go to sea we remove the cable and close the gasketed cover).

I also bought an L-COM POE injector that allows us to feed regulated 13.8V into the cable instead of using the AC wall wart that ships with Bullet. If you haven’t dealt with L-COM before, they are my go-to place for anything communications (high quality, low price).

Once you get the ethernet cable inside, one option is to connect your computer’s ethernet port directly. Then have the PC create a WiFi zone inside the boat for your other devices. Another option is to spend another $30 – $40 for the convenience of our setup. For the in-boat WiFi we repurposed our old external WiFi router, an Engenius ECB3500,  configured as Operation Mode = Access Point, fixed IP (Note the other fixed IP addresses must be carefully chosen – ours are Bullet IP and Bullet-router DHCP range – 99).

The ECB 3500 has no auto collision avoidance AFAIK, only fixed IP or DHCP. So I used the Bullet’s site survey to assess channel collisions, then assigned the 3500 to CH4. I adjusted the ECB 3500 transmit power to minimum 9dbm and removed one of its 2 antennas. That got the 3500 down to about 7 dbm below our wifi ISP as seen by the Bullet site survey. Speed tests using an iPad to sample various areas around the boat are OK at around 2Mbs.

Russell Coutts on AC72 short courses

In case you are wondering how the America’s Cup is going to fit the AC72 cats into San Francisco Bay, here is a 16 Jan 2012 Daily Sail interview with Russell Coutts:

(…) “You have to recognize that these 72s, they are probably only going to be on a tack or a jibe for two and a half minutes, maybe three, so it is not like the old format where you had boats straight lining for 10 or 15 minutes. And maneuvering will be critical because if the boat is doing 35 knots and you slow down to say 15 knots in a jibe, obviously you had better make sure it is a good jibe because [if not] the other boat will be gaining a lot on you very fast.”

A 2.5 minute leg at 35kn is about 1.5nm or 1.73 miles or 2.8km. Roughly the distance from the SF city front to Treasure Island. The pictured course layout above is not from an official source – but it does give you an idea of how the bay could be utilized for racing that is highly visible from land viewing points.

More on America’s Cup San Francisco.

Model Tests to Study Capsize and Stability of Sailing Multihulls

Thanks to Beth Leonard for reminding us to study the captioned paper from the Wolfson Unit MTIA, University of Southampton, UK [PDF download]. I found the wind tunnel and tank test work to be of the most interest. Contrariwise, the analysis of 124 stability instances was of very limited utility, because there was little reliable data on the yacht and wind/wave characteristics. The Wolfson team attempted to assess by objective testing catamaran and trimaran capsize sensitivity for the wind, breaking wave and pitchpoling cases.

More to follow when I have time to do the numbers on Adagio…

Elastic anchoring

During the ADAGIO design phase one of my top priority projects was Ground Tackle. This seemed to be the area that brought more cruising yachts to grief than any other. Over time I found a number of technical sources that were very generous in sharing what they had learned from empirical work and theory: Chuck Hawley at West Marine, Earl Hinz, author of The Complete Book Of Anchoring And Mooring, and William G. Van Dorn, author of Oceanography And Seamanship, Second Edition.

I learned a lot about anchor testing, about the design of elastic anchoring schemes. And I just realized that the results of all that effort did not make the transfer to our new website. So this post is intended to restore some of that research. I’ll do more when I have the time.

For several years we had a vigorous discussion on the old Compuserve Sailing Forum — one of the predecessors of the modern Internet. That means it is a silo, so the content is no longer available. For laughs I just Googled for “compuserve sailing forum”. The second result was my little paper on Anchoring Theory which still exists in the old Adagio Marine website. I have just uploaded Anchoring Theory.PDF to this website. The anchor testing analysis is dated, as the new generation of anchor designs either did not exist or had not been tested. But the principals remain sound, especially the methodology for evaluating anchor performance relative to weight (often neglected in anchor tests).

I’ve found a copy of one of my last bits of correspondence with Dr. Van Dorn — his reply to my queries on the physics described in Oceanography And Seamanship, Second Edition.

Research Oceanographer Emeritus, Scripps Institution
of Oceanography, University of California, San Diego
April 28, 1997

Dr. Stephen Darden
Te Wahapu Road
Bay of Islands, NZ

Dear Dr. Darden:

Sorry about the delay; your problem caught me at a busy time, and it has taken me two weeks to go back to my files of 30 years ago and find out how I did the early calculations. Now I think I am up to speed and find that the corrections are relatively minor–albeit important. I thank you for bringing the problems my attention. I am sending an errata page to the publisher and this longer discussion to you.

It might be best to first clear up the errors in my book (O&S) before responding to your questions about elastic anchoring:

p.276 change coefficient of equation from 0,004 to 0.0034. This changes Hinz’s 0.00238 from feet/sec to knots; viz. 0.00238*1.69^2*(l/2) =0.0034

p.388 Eq.(3) should read: lo+O.8lc=5.8h; an overlooked typo that verifies the scope of 7.2 for an all-chain rode on p.389.

p.390 Eq.(4) should read: Fh = 0.18*V^2*W^(2/3).

This equation is a special case of the general wind force equation on p.276, whose solutions can be found graphically from Figs. 114 & 115 on pp275 &276. Eq.4 is derived in the attached spreadsheet labeled ANCHORS, for the special case of an anchored sailboat at a swinging angle: A(30)= 30 degrees, a wind gust factor, Fg=1.5 (see p88), and a yawed drag coefficient, Cd=1.0, corresponding to a displacement/length ratio D/L=28.6/(.01*60)^3=277 (see below). Eq-4 now correctly gives wind force and rode size from fig. 155 and functions of displacement, subject to the conjecture at the bottom of the spread sheet.

Eq.(4), combined with Eq.(5) p392, yields the revised Eq.(6): w/W=V^3*.079/Ca^1.5, as shown in the spreadsheet, which also gives the computed table from which Fig. 156 was plotted.

At this point, I began to worry whether scaling wind drag areas in terms of W^(2/3) was really appropriate in view of recent changes in yacht design; viz., the table on p291. The latter half of the ANCHORS spreadsheet compares the influence of drag coefficient and D/L ratio on w/W, from which I conclude that their product is roughly constant and about 30 percent lower than predicted by Eq. (6). I believe that this result is safe enough, considering that the wind force equation includes a gust factor Fg^2=2.25, which can be taken to represent the surge factor invoked by Hinz.

The same argument applies to the wind force equation, which includes both W^(2/3) and Cd. Here we must take the 2/3 power of 0.70 = 0.79% of the calculated wind force. For your 30,000 lb (13.3 ton) cat, this would yield a force of 3100*.79=2450 lbs, which is rather close to Hinz’s figure, and still includes the 2.25 surge factor and the 30-degree swinging allowance.

Re your question about Example 2, p393, you are right. The chart says you would need a 96-lb COR. But, if you believe the above caveat, you could reduce it to 96-30% = 67 lbs. This seems consistent with Hinz’s account (His pl 76) of holding a 10-ton Morgan in coral sand at Fanning. However, having dragged miles of CQR-tracks through coral sand in Pacific atolls, including Fanning, I would carry a 40-lb Danforth–just in case. Coral sand is light and has very low cohesion. It is produced by fish chewing the reef. However, it tends to re-cement in brackish water. So it can have a highly variable texture.

My personal experience with Bruce and COR anchors is that they are much the same, except for the tendency of Bruces to ball-up in sticky clay and having to be hauled up and washed clean before resetting. I like Danforths in sand, coral sand, and all lo-cohesion sediments. I have never tried a Delta.

Your Table B is quite interesting. However I must admit my table of anchor coefficients involves a lot of surmise and conjecture–and I have found no reliable data on coral sand. As with all anchoring problems, there is lots of room for improvement, and I believe you have made a considerable contribution by your analysis. Please let me know if you find further errors in O&S. The page of errata I am sending to the publisher will be sent out to future buyers, until they can be incorporated in the next printing.

With regard to your question about how much nylon to use as an all-chain snubber, I would approach it as follows. From the design wind force, find rode size from Fig.155. From wind speed and anchoring depth, find the anticipated max height from Fig. 153, p389. Take four times the wave height as the max stretch required. Divide by 0.38 to get the length of nylon required. Of course, you need to have enough chain slack to accommodate four wave-heights of stretch. I do hope you aren’t planning an all-chain rode for your cat.

With alI best and thanks for your interest,
William G. Van Dorn, Phd

New AC45 catamaran class takes shape

The first AC45 is under construction in New Zealand, hopefully launching before y/e 2010.

Boat No.1 slated to hit the water in December.

America’s Cup Regatta Director Iain Murray today inspected production of the new AC45 catamaran class.

The AC45 is the little sister with attitude to the AC72. Both classes are fundamental parts of the transformation of the America’s Cup.

A one-design wingsail catamaran of 45 feet, the AC45 has been created to fulfill three roles:

•   Fast-track teams for the 34th America’s Cup to a common level of catamaran sailing and wingsail technology at the outset of their campaigns.
•   Provide a class of boat for the 2011 season of the new America’s Cup World Series.
•   Provide a class of boat for the Youth America’s Cup commencing in 2012.


The AC45 was designed and engineered by BMW ORACLE Racing on behalf of the America’s Cup community. Manolo Ruiz de Elvira led the hull design development, Scott Ferguson the wingsail development, and Dirk Kramers the structures team.

Mark Turner and Tim Symth of Core Builders, Warkworth, created production tooling for the hull platform and wingsail, and will produce the initial batch of boats in collaboration with other New Zealand marine industry specialists including Cookson Boats and Hall Spars NZL. Steering and daggerboard assemblies have been sub-contracted to C-Tech Carbon Technology and Craig Stirling Composites Engineering.

The AC45 is a versatile, one-design class with controlled costs and ease-of-maintenance a priority. The hulls and cross-beams are designed for simple and fast assembly to accommodate the active racing schedule.

The one-design wingsail consists of two elements. It is a scaled down concept of the 223-foot tall wing that powered BMW ORACLE Racing’s trimaran USA to victory in the 33rd America’s Cup Match.

The wing will have simple, manual control systems. There will be two headsail options, a gennaker and jib, but no Code 0 headsail.

“The AC45 is small enough that it doesn’t need hydraulics. The loads drop quickly when you get down to a boat of this size,” said Ian Burns, design team coordinator for BMW ORACLE Racing. “There aren’t even grinder pedestals. The winches will be powered by top-handle grinding.”

Keeping with the simplification theme, the AC45 will have straight daggerboards. No articulation beyond raising and lowering is permitted.

Crews are likely to number five at an average weight of 85 kilograms (approximately 187 pounds) to fit the AC45’s future role in the Youth America’s Cup.

Cookson Boats and other key suppliers have been engaged to work with Core Builders to ensure swift production of the first batch of boats at a rate of two a month. Another designated boatbuilder in the USA or Europe is envisaged.

Boats will be delivered in sequence of ordering.

After use next year in the ACWS, the AC45 will be used for the Youth America’s Cup, a series to be run in 2012 in conjunction with the ACWS.

[From New AC45 catamaran class takes shape]

Morrelli & Melvin wins Americas Cup design competition

Click the thumbnail for the AC72 photos

This is really exciting for us. Gino and Pete have done an outstanding job on the design proposal for America’s Cup 34. The new “AC72” is a 72-ft solid wing cat manned by only eleven crew. The cup is once again going to be really exciting! Here’s an excerpt from the Sept 13, 2010 announcement:

(…) Technology returns to the fore with the AC72 wingsail America’s Cup catamaran, capable of regularly exceeding speeds of 30 knots.

The AC72 will excite fans as it zips around the racecourse with one hull in the air. Equally important, it will leave the crews exhilarated and drained after a day of adrenaline-fueled racing.

Crucial to the new boat is its ability to be raced hard in light and strong winds, a necessary development to do away with the frustrating delays of racing because of not enough wind or too much.

Fast to grab and retain the attention of a new audience, it also had to be technically stimulating to design and physically demanding for the crew to sail.

There will only be 11 crewmembers, six fewer than the heavy-displacement ACC monohull it replaces.

“The AC72 Class adds a new dimension to America’s Cup design and technology,” said Pete Melvin, a chief architect of the rule and champion multihull sailor. “The AC72 will place exacting demands on the helmsman, crew and support team that the vast majority of us who call ourselves ‘weekend racers’ could never hope to develop.”

The new class of America’s Cup catamaran is a tightly defined “box rule.” Certain parameters have been set, such as overall length, beam, displacement and sail area. Other factors are limited to keep the competition close across all wind speeds.

So that no team would have an unfair advantage by creating the rule, US SAILING and Morrelli & Melvin Design & Engineering authored the rule.

“Near the beginning of the process we were requested to look at a catamaran instead of a trimaran because it’s easier to transport, assemble and disassemble,” Melvin said.

“The difference in the performance characteristics is not significant, and a cat was judged less expensive to build. From there, the experience of two America’s Cups in which wingsails were used (1988 and 2010), coupled with the latest developments in wingsail technology, made it natural to morph the design rule into a catamaran with a wingsail,” said Melvin.

(…) “It’s been challenging to have the cat fully powered-up and flying a hull in light winds, yet also able to sail in 30 knots,” Melvin said. “We put a lot of time and effort into sizing the wingsail and the platform dimensions in order to sail in that full range.”

Read more » Note: Morrelli & Melvin are the designers of our ADAGIO. We are hopeful that San Francisco Bay will be chosen as the venue for AC34. Below is the Skidmore rendering of the proposed America’s Cup Village.