Ken,
I want to give my $0.02 on passages like Tenass. My opinion is based on experience, I recently retired from running an oceanogrpahic research boat. In that capacity I was called on to make these kinds of passes often with minimal information. I don’t want this to come across as preachy or lecture-y. I know a lot of the members have decades of experience. Some however do not. I don’t know where you are on the spectrum.
Here goes…..
Deciding to run Tenass Pass is like everything else on a boat, a risk / benefit calculation. Risk here being the key. As others have mentioned you will be in a remote area with little help available if something goes wrong. You are running a twin screw boat with little or no protection for the running gear. A tiny bump on the rocks and a lot goes wrong in an instant.
Many here have already mentioned it, the most important thing is survey the pass from your small boat. Preferably with a good sounder. I prefer to make my survey at low water. If you’ve got a good GPS even better. If that GPS can be mounted on the bridge of your big boat so you are dealing with very similar system errors as you make your passage and following the GPS track line better still.
Make your passage 1 – 3 hrs before high water. The exact timing will depend upon anticipated currents in the pass. You want as much rising tide left under you with as little current as possible.
The survey is made at low water so you can see more of the dangers. The passage is made near high water for obvious reasons, before high water so that you might float free if you get stuck. A note on that. Ak is a mixed semi diurnal tidal cycle. Two highs and two lows per tidal day. Often there is a considerable difference in height between the lower high tide and the higher high tide. If you are transiting the pass on one of those days, especially during spring tides consider that you can be aground for a day or more if you get stuck near the higher high water. And with Ak’s extreme tidal ranges you could be high and dry perched on a rock doing considerable damage to your hull and running gear.
If at all possible time your passages so that you are stemming the current. This allows you to move more slowly over the ground and to be able to stop and back away more quickly.
As you gain experience and local knowledge with Tenass Pass your transit window times widen. But on your first few passages be very careful, even if it means transiting the pass at inconvenient times.
Now I want to talk about charts, electronics and judgment. Again, not trying to be preachy.
Sounders.
I would not make a pass like Tenass without a good sounder. However, in places like S.E. Ak the bottom is so vertical that some times the sounder will tell you that you are aground as you strike the rocks. Go slow. Be careful. Know what the transducer offset, what the indicated depth is. Under the keel, under the transducer, at the water line? It is usually best to not run the sounder on auto range and auto gain in these situations. You don’t need it getting confused and trying to find the bottom just when you need it most. Choose an appropriate range and adjust the gain before starting in. I prefer to have a sounder that charts the bottom as well as gives a digital depth reading. Sometimes the numbers get jumpy and there is no good way to make sense of the information. A chart of the bottom shows the trends even when the signal gets a little noisy.
GPS.
All non-survey grade GPS receivers are subject to error. There are no exceptions. Do you know how accurate yours is? How repeatable yours is? If the “wobble” in your system is 3 meters (not at all unusual despite manufacturer's claims) that means the confidence in your track line is 6 meters, 20 ft. GPS error increases in narrow steep sided channels. I know, the experts say it isn’t so but I’ve seen it many times. And what GPS are you using? A purpose built marine unit or a tablet / phone GPS? The tablet / phone units are damned good but I won’t use one for narrow tricky passes. The short version is that well designed marine units prioritize accuracy over speed of fix. Most tablets / phones prioritize speed of fix over accuracy. And worse yet, the phone / tablet won’t tell you when it’s doing that!
All of this is to say use the GPS, but don’t trust it blindly. I don't have good charts of Tenass Pass here but it looks like there are some skinny spots that at low tide are 11 meters, 36 ft. If I'm right about 20 ft confidence and 36 ft wide safe channel that's just 8 ft of sure safety on either side of the centerline of your boat. If your boat is about 13 ft beam take 6.5 ft away and you're down to almost nothing. Oh yeah, and know where your GPS receiver is. If it's off to one side of centerline......
Charts.
In these kinds of places I will only use official charts, in Ak that would be NOAA charts. Cartographers have to make decisions when creating charts. They have to reduce a massive amount of data to a usable chart which means they throw out some data. Then as other chart makers use the NOAA charts to create their versions even more decisions are made resulting in more data loss. Generally non NOAA charts are very good. But I’ve seen more than a few instances where important features were missing.
And, things have been missed. A few years ago I found an uncharted pinnacle in a narrow pass I’d transited dozens of times. That time I was a bit to the right of my usual track line. I can’t recommend that as a way to get your heart rate up.
Paper vs electronic charts. It’s your choice and often a financial decision. I like having both aboard but then my employer required it and paid for them. These days I’m a little stingier with the number of paper charts I carry. However, if I wanted to transit the little passes around Prince of Whales Island to my favorite fishing holes frequently I’d buy the relevant paper charts.
RNC (raster) vs ENC. In US waters NOAA provides them free of charge. Carry both. They offer different strengths and weaknesses. I have found in some less traveled areas they don’t 100% agree. In those cases I put more trust in the RNCs for the same reasons I trust NOAA charts over other charts.
Beware of the dangers of overzooming electronic charts, no matter who made them or created the software. It leads to a false sense of accuracy that simply is not there.
A comment on the accuracy of charts. Know the dates of the survey the charts are based upon. I am not saying the surveyors and cartographers of old were sloppy and inaccurate. I am saying they and the mariners the charts were created for used different tools. Bearing and range were the tools of the trade “back in the day”. Early in the days of GPS and electronic charting it was not uncommon to find significant errors. Almost without exception the errors I noted were a displacement of the charted areas on the earth’s surface. That is to say the bearing and distance between two points were nuts on, but might not be accurately placed on the earth’s surface. An old pilot would round Pointy Rock Shoal day beacon at a known distance and bearing, set the course for Bent Tree Point for a safe clearance, make adjustments for set and drift and all was hunky dory. A GPS user like we all are these days would round the day mark by eye, point and click a waypoint off Bent Tree Point, activate the route, mash the autopilot button and if the charted area were displaced on the earth might wind up parked on the beach.
Hydrorgraphic services have been very diligent in correcting these errors but some of the less traveled areas are still not quite right. Be careful. I found one not too long ago. Slipping between an island and a peninsula, a narrow but deep channel and almost straight. Piece of cake, plot my course, look out the windows and keep ‘er in the middle. I glanced over at the electronic chart and saw by that we were on the logging road on the peninsula! A friend found a rock awash the hard way a few years back putting too much trust in a GPS chart plotter running non NOAA charts.
Putting it all together.
Here’s how I would approach my first transit of Tenass Pass. Assuming from your first post that you have considerable experience with El Capitan.
- Head over to southern El Capitan the day before. Anchor as near to Tenass Pass as you can and be confident in leaving the big boat for some time.
- Survey Tenass Pass at low water. Take your time. Find all the scary spots. Use your eyes as much as your GPS and sounder. Do you know how to spot natural ranges and how to use them? If not that’s another subject.
- Your survey line will be all zigg zaggy, not a usable track line. Using what you learned run the pass in your small boat as if you were running it in the big boat. Same speed you intend to run the pass in the big boat. Repeat until you are confident you have a trustable track line and good familiarity with the lay of the land. Both bottom and land marks on the shore line. I like to carry a waterproof note book and make sketches and notes.
- Back aboard the big boat chart your track line. If possible on both electronic and paper. Note where turns need to be made, courses to steer, safe distances off hazards, anticipated water depth at key points adjusted for tide height and transducer offsets. Work it all out in your head before you go. When you are in the pass is not the time to be figuring things out.
- When time and tide are right, probably the next day, make the run.
- LOTFW. Older captains, I guess I’m one now, like to remind the youngsters who professionally grew up on electronic navigation Look Out The F...ing Windows! Not just stare out the windows but know your courses, bearings, ranges and land marks. Use ‘em all.
- Stay ahead of your boat. A key to successful navigation and piloting is thinking ahead. Where you are now was solved a while ago, where you are going next is what you are thinking about. Electronic navigation encourages thinking only about where you are now. I can be as guilty of that bad practice as anyone!
Local Knowledge. There are two kinds, yours and theirs. Yours comes from experience with Tenass Pass. The more you run it the more you know it. Just don’t get complacent and sloppy. Theirs is not to be trusted until you know for sure. Listen to the locals, particularly with respect to cautions and warnings. But do you own homework before you head into the pass.
The tools I like to use
- NOAA charts. All 3. Paper, RNC and ENC
- A quality marine grade hand held GPS that can save trackline, routes and waypoints. Can output them to my PC. Can connect to my PC to provide GPS position data. I trust Garmin units.
- Plotting software that will accept track lines, waypoints and routes from my GPS. Use NOAA Rnc and ENC charts accurately. Take position data from my GPS. I’m a big fan of Rose Point’s Coastal Explorer.
- An accurate heading source for use with the courses, bearings and ranges you learned form the survey. The heading source can be an accurately compensated magnetic compass or any number of electronic gizmos. I’m a big fan of a quality magnetic compass properly compensated. They are not subject to electronic / electric failure.
- Radar. If you’ve got a good unit that accurately determines range use it. You can use it to keep a safe distance off a hazard abeam, know the range to a landmark ahead where you make your next course change. If you’ve done your small boat survey well, done your chart work and see the small boat GPS track line does not plot in the good water on the NOAA chart you don’t need to be alarmed. You can still use the ranges, bearings and courses from the paper chart.
- Dividers, compass (the drawing kind) and a rule of some sort. I prefer for small boats like we all run the Weams and Plath rolling plotter. These tools are used with your paper chart to plan your route.
If these techniques of inshore piloting are new to you then you might consider practicing first is some less demanding passages. I see at the southern end of El Capitan a bay called Kosciusko Bay. Skinny with rocks but straight and short. Should be a straight forward small boat survey. And when you’re ready plenty of room to turn the big boat around in there and head out. Too bad the bottom charts as rocky. What a secure anchorage that would be to ride out a blow!
I hope you and all reading this find it helpful. And if any of the experienced boaters here can improve my post please jump in! We’re all here to share and learn.
