"...with the lagoon full, the low water slack will be later than expected and the incoming tide will be weaker or possibly non existent and the high water slack will be earlier than expected and the ebbing tide will be stronger."
Yep, super geek. Direct link to the article (free) here.
First, I want to say that we are viewing Navionics charts on iNavX on our iPad. I don’t know for certain whether the issues are with Navionics charts or with the software we are using to view them.
Problem #1: In some areas that we’ve visited that have not been hydrographically surveyed Navionics has depths marked. This sounds like a great thing, right? I assume (but can’t confirm) that Navionics is using satellite imagery to mark obvious shallow areas in those non-surveyed areas. I love the idea that they are using the satellite imagery to enhance their charts – this is fantastic – but what is odd to me is that in some of those places they have assigned a depth of 5m (16 feet) to all of those shallow spots.
Take this view of SE Tahanea in the Tuamotus – one of our favorite places. You can see that all of the blue dots are marked 16 feet. Having spear fished and snorkeled a number of those blue dots close to the anchorage and having sailed very close to some of the others, I can say with absolute certainty that many of those dots are shallower than 16 feet – in fact, some are at the surface. Why assign an arbitrary and unverified depth and worse, why assign a depth that is a safe depth for most cruising boats to transit over? I hope no one is naïve enough to sail blithely over these 16 foot marks in bad visibility, but still, the charts become actively misleading when they present specific (but inaccurate) depths.
Problem #2: The shallowest depth is not the depth that shows on the chart when zoomed out. The depth when zoomed out is the depth of the outer ring of a shallow spot (the deepest) rather than the inner ring (the shallowest).
Here is an example of three shallow spots from Taravai in Mangareva, Gambiers showing that at a fairly normal level of zoom, they are all marked at 32 feet.
At a closer level of zoom, one shallow is now shown at 19 feet and one now at 16. The third remains at 32 feet.
At an even closer level of zoom, the third shallow reveals a 26 foot depth.
Obviously in this example, we could sail over all three (if we trusted the charted depths) but in others we have found shallower marks hidden.
On a positive, several countries past French Polynesia we are still finding the Navionics charts to be the most accurate. Of course, not always as this screenshot from Tonga shows us sailing right over a reef (track in yellow dashes) which was in fact to port the entire time.
In French Polynesia are 5 archipelagos. One archipelago, the Easternmost, is called the Gambier Islands. The only island of the Gambiers with a pass to enter for cruising boats is Mangareva. Thus, Mangareva is the name of a single atoll in the Gambiers but is synonymous in cruisers’ talk with the Gambiers.
Like many atolls, there are small islets called motus on Mangareva’s encircling reef. Mangarevas reef is mostly open to the ocean on the entire Southern side of the atoll with another large pass on the West making for little current inside of the atoll or in the main pass. Depending on the direction of the swell you may get incoming or outgoing currents in the false passes but not in the large navigable passes.
While book writers disagree on the subject, most Frenchies and Mangarevans consider Mangareva to be outside of the hurricane zone and along with the Marquesas are a common spot for European boats to cruise through the hurricane season. We are the only N American boat here this austral summer and most of the European boats are either staying here for the entire hurricane season or splitting their time between here and the Marquesas.
Most N American boats visit during the austral winter, arriving usually from the Galapagos, which is also the time of the worst weather in the Gambiers. It’s storm season here then, and the low pressure systems from the Southern Ocean whip up the seas and the winds when they pass through. Reportedly, the weather is often squally and less sunny and pleasant than the summer average. The good news is that when it is squally here, as mentioned above, there are a lot of anchorages, in close proximity, to switch between to gain protection from various wind/fetch directions.
The only downside to Mangareva so far for us is that most of the anchorages are deep – 40 to 60 feet. While we have anchored in shallower water here, we are usually cranking like crazy people on our manual windlass to raise an enormous amount of 5/16” HT chain and our hefty Manson Supreme. We have started using a single pearl farm buoy at 2-to-1 before dropping the rest of the scope to help with the weight of the chain.
Supply ships come regularly but not on any particular schedule and there are at least 5 small grocery stores that we know of that each offer their own selection and each have different arrangements with the supply ships. The offering is similar to the Tuamotus with perhaps even fewer vegetables on offer. Thankfully there are a lot of opportunities to exchange or be gifted fruit and vegetables.
There are “false passes” in some atolls in which there is a spot in the encircling coral reef just low enough for snorkelers, or surfers, or even small boats to exit to the open ocean.
Well, in the middle of a BBQ on the beach in the afternoon a group of us had the great idea to head out the pass for some fishing (trolling style) even though the tide was a little low and even though the light was already fading.
On the way back, surrounded by the light of a stunning sunset, we worked our way back, through crystal clear water that the sunlight was glancing off of, allowing occasional peeks at the what lay beneath:
Sometimes the sunset obscured everything except what poked out of the surface:
In each dinghy it was a team effort to spot the coral heads just below the surface before they ripped into the pontoons or broke the prop:
Is it possible to be stressed when you are looking at this scenery? Yes…but then no…but then yes…
First, if you want to know how to set up a real iPad system, and who is a fan of iNavX (with some caveats) read this post and this post by Tucker on Convivia.
We have not set up a similar system and because our iPad isn’t our only navigation system running, we are not sure yet if we will add in the expense of the iMux or similar. Maybe someday...
First, the positive: We have limited experience because our iPad is new to us, but Navionics charts have been better than our other two chart types in the 3 islands in French Polynesia we’ve visited since we picked up an iPad. If friends’ reports are true, this pattern will stay consistent as we head West next year. The general consensus is that Navionics charts win in the South Pacific.
Here is where it gets awkward. Navionics charts are expensive (on a cruising budget) UNLESS you buy them through a single vendor, for use only with iNavX, only on an iPad or iPhone. So, if you want Navionics, you essentially are strong armed into buying an iPad and installing iNavX. The cost of the difference in chart prices essentially pays for an iPad if you can believe it.
So, is being strong armed into an iPad and iNavX so bad? We love our new iPad. It can be annoying because it assumes you are mainlined to the cloud at all times and as cruisers we are definitely not. However, it is fun. It is slick. We feel like part of the techie world again. My ereader broke and although I don’t love the iPad as much for reading I’m very glad that it serves that purpose as well. We have all kinds of other apps crammed onto it that we love. Generally we’re happy to have one aboard. The only real negative for an iPad with navigation is that because it doesn’t have an easy way to get files on and off the tablet (unless it is networked) it makes swapping files difficult and swapping tracks is a big part of the cruising community at this point. Not that file swapping is possible really with iNavX, but I get ahead of myself…
What I really don’t love is iNavX. It is a shame because it looks so pretty, and swiping your fingers around is so fun…but it cannot do so many of the things I am accustomed to being able to do, as standard, in every navigation program I’ve used. Simple, basic things really. To us it feels like an app, not a fully functional nav program. You can certainly use it to navigate around the world but it is missing the flexibility of a full nav program.
A few of the ways I find iNavX underwhelming:
Caveat: We are new iNavX users and so I’m hoping to be wrong about the above. I did send iNavX an email about each of the above and they responded to our email quickly (with links to specific pages on their online help which I was able to view the next time I was online). If you know how to fix any of those 5 issues, please dish here.
You might think that the charting flaws would be a dealbreaker but there are a number of reasons that we really love having a Garmin 76CX (actually, we have two): 1) The combination of a great internal GPS and high resolution tracks mean that we lay down very good tracks that we can then follow if we need to in an emergency, 2) They take very little power and even less power when you darken the screen, 3) They have a nice anchor alarm feature and 4) They have a convenient compass setting that we really enjoy using in the cockpit on passages to give us a running idea in the cockpit of where our windvane is taking us.
It is also a handy size to put inside of our oven, or in our v-berth, or wherever we convince ourselves might be less affected by lightning, and they are very durable in crappy weather or when dropped frequently in the cockpit (ahem).
Notice that I did not claim this was state of the art.
One thing I enjoyed about running the IWAC Project particularly when I was prepping, was reading about what cruisers are actually doing – not what someone says is the ideal, not what a prepper has carefully researched (and is probably the best) but what people “out there” have cobbled together and are getting along with.
In that spirit, this is the set up we currently have that allows us to get around where we currently are...and we aren’t dead yet.
I loosely divide charting philosophies for cruisers into “gold standard” vs. “variety of options”. Of course, like any interesting dichotomy, most people think they are striking a balance between two extremes. However, since everyone’s balance varies from one side to the other, the dichotomy is still useful.
We have definitely taken the variety of options approach to navigation. This is probably not so much because of planning as it is because over time we’ve accumulated different resources and over time the options have changed. Still, although it may not have been put together with a master plan in mind, now that we have all of the options, we are glad to have them. We really like to see a few different types of charts for an area, plus satellite imagery when planning a trip.
Fairly regularly, on a short sail, we will have 4 methods of charting running. These four methods are:
On passage we usually have either the Garmin or the iPad running, but not both. The Garmin and the iPad are low power consumers even compared to our old netbook. When we open the netbook for other things we will usually check in with OpenCPN as well but obviously for passages we rarely use satellite imagery – that would just show us a lot of blue water and clouds.
I’ll follow this post with a bit about each of the above.
Click on any image below to be taken to Google Maps at that location.
When you find your own little corner of paradise, away from a village and away from the guidebook waypoints, another boat will see you anchored and come over to investigate your spot. Not that I’m complaining too loudly because we’ve done that ourselves. Always wondering if the other guy found something good. We’ve become better at moving around and finding our own corners. Satellite imagery has made locating good spots a very fun game for the navigator.
However, it is a circular atoll and we found that the fetch wrapped around and so always seemed to hit the boat just a little bit off from the direction of the wind. Because the boat was facing into the wind, the fetch hit the boat at 20-30 degrees and caused, not a rolling motion, but a short little jerking motion that drove Carol and I bonkers.
We spent a night or two anchored in front of one of the expensive honeymooner hotels and it was fun to have the same view and to be reminded of how much of a dream location we are currently cruising in.
You can always see where we are currently anchored by checking out our map. Switch it to satellite view if you wish to see images like these.
Did you know that some places are relatively unaffected by lunar tides but seriously affected by solar tides?
I (Livia) wrote an article that appeared in a recent issue of Ocean Navigator on the application of solar tide knowledge to navigating passes in the places like Maupiti, French Polynesia. You can read the article online here.
Thanks to Michelle on SV Cheers who first told me about the topic.
I’ve been meaning to write about two books that I read on our crossing from Mexico to the Marquesas that I had set aside just for that passage and enjoyed a great deal. Honestly, I thought I already wrote about them but I can’t find the post in my offline writer or on the blog so apparently I didn’t. Is there a cruiser version of senioritis or can I get senioritis before 40?
Both books are non-fiction and both are the type of books that, in my opinion, if you like the idea of the book, you will like the execution. If the idea of the book sounds boring, give it a pass.
The first is a book about rogue waves by Susan Casey called “The Wave: In Pursuit of the Rogues, Freaks and Giants of the Ocean". Although perhaps a questionable choice of book to read while surrounded by hundreds of miles of ocean with no port in sight, I loved the book. I particularly enjoyed the fact that she skips back and forth between information and viewpoints from wave scientists, big wave surfers, and shipping companies and insurers.
The second book was about the discovery of longitude, or rather, the accurate measurement of longitude on land and later on sea. The book is “Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time” by Sobel. It is a bit nerdy, engaging and concise and I really enjoyed it.
I’ll bet your local library has copies of both or if you are feeling flush pick up a copy for yourself when you are ordering your holiday gifts from Amazon.
Readers will remember however, if the wind was directly ahead of us, we have to zig zag and so we might only make 1 knot toward our destination even if sailing faster through the water (20 hours).The first day the winds were too strong for kayaking in the Polkinghorne’s so we did some boat maintenance.
First, we took down the huge 130% (150%?) Genoa on which we had blown the sunbrella stitching on the sail over. The sunbrella stitching was the only thing holding in the leech line (bad design IMHO, the leech line could have been stitched with stitching underneath the sunbrella and thus protected from UV). We replaced the genoa with our working jib. It has a much, much nicer shape when reefed because of its smaller size and we are definitely in reefing strength winds lately.
Before we put up the jib I wanted to do a few small improvements that came up in Carol Hasse’s sail repair course when we examined this sail as a class. Primarily, I wanted to put leather chafe gear on the head and the tack which would protect simultaneously from chafing on the metal furling and halyard attachment points hand also protect these two pieces of webbing from UV. Done. I also hand sewed a few places where the sunbrella stitching had rotted off (on this sail as well - *sigh* UV thread anyone?). While doing so I saw that the areas that had ripped were between areas that had already been repaired. At least the previous repairs were in great shape. I probably restitched 10% of the length of the sail, anywhere there was stitching coming loose. Hopefully the sunbrella will stay put for a while.
Carol was a boat working machine and finished the SSB backstay antenna by terminating the wire inside the hull to the tuner with a ring attachment and he also ran the foil from the tuner amidships.
Then he removed our broken hinge from the aft starboard lazarette and attempted to remove the seized pin. However, during this attempt the hinge made a successful escape from the Estrellita foredeck prison and is now free to roam the bottom of the E bay at the Polkinghornes. Any Pretorien owners have an extra upper hinge for that lazarette? I’ll post on the owners’ forum later.
The hinge still imprisoned:
Finally, he wired the AIS for power and the antenna splitter for it. So we now have AIS reception (non-boaters, this is so we can see large ships and know which direction and speed they are heading so we avoid being crunched). Here you can see our navigation program (NavSim’s SailCruiser), we are the pink dot with the yellow track (we are tacking upwind to Blunden Harbor) and I’ve clicked on a boat so you can see what information that it is broadcasting that we can now see. The little brown circles with M’s are markers we made when we dropped anchor so we could see where we were compared to where our anchor touched ground. The yellow arrow just below the box is the current at the time I took the screen shot.
All of that he did while I was still stitching a single sail. AND, after that we connected via SSB to email and downloaded some practice weather files, checked in with the Great Northern Boater Net, and listened to the Pacific Seafarers net.
At Lewis Cove I cranked Carol half way up the mast and he installed our starboard spreader halyard. Non-boaters, this rope allows us to fly flags on the starboard side of the boat. We fly our Canadian flag from the back but we have smaller flags that get flown on the starboard side like courtesy flags for countries we are visiting (small US flag right now) and also any club flags (aka burgees) for clubs we belong to. We also have some fun flags like a pirate and martini flag (THANKS SARAH & CRAIG) and a huge Wauquiez flag we picked up at a rendezvous.
This was supposed to be our relaxing few days of becoming more cruiserly, remember?
We’ll get the hang of this retired thing eventually. – Livia
50 47.68 N; 126 55.38 W
