Boats hit rocks all the time, often snapping off deep keels.

[Jackdaw]

In the Chesapeake we like to say, ‘There’s them that’s been aground, and them that’s going aground’ but man, you really have to work at it to hit a rock in the Chesapeake!

A hard grounding is my absolute nightmare, I spend hours at chart study when we sail the thorny path and still I fret. In the early years we easily spent 75% of our sailing time confirming our location and reconfirming. First with LORAN and later with first gen GPS handhelds I filled my bookshelves with lists of lights and cruising guides, carefully entering the lat Lons for each and every rock, coral head and shoal in my cruising area. I set guard waypoints.... Our locating effort dropped to maybe 20% of the sailing day. I had more screen time than a teenager with a new iPhone. When the first of the helm mounted chart plotters came out I was an early adopter. I would not be without a GPS plotter at the helm. If I am on a strange boat I have a type of RAM mount for my handheld. There is still a chart on the seat, but there is always a chartplotter at eye level.

A counter thought.... I’m not a huge fan of helm mounted plotters. I’ve seen too many times that the ability to see it all the time can create an over dependence on the plotter and the accuracy of the chart. In almost all close quarter piloting, I want to depend on my eyeballs, not some electronic chart.

 

[Gunni]

A counter thought.... I’m not a huge fan of helm mounted plotters. I’ve seen too many times that the ability to see it all the time can create an over dependence on the plotter and the accuracy of the chart. In almost all close quarter piloting, I want to depend on my eyeballs, not some electronic chart.

Close quarter navigation is one thing, general situation awareness is another. If you will be spending 24 hours transiting a shoal or reef edge you want each watch to instantly know how they are doing relative to that no-go area. Better to have the driver seeing that real time.

Some traditionalists don’t like the look of a big ole chartplotter mixed up with their bronze and mahogany cockpits, but I noticed that even on Hermione, La Fayette’s replica 18th century French frigate there was a full compliment of digital instruments and chartplotters hidden in a cabinet just behind the helmsman’s wheel on deck.

 

[Will Gilmore]

In almost all close quarter piloting, I want to depend on my eyeballs,

Let me include myself in that thought. If you are close enough to consider it an imminent danger if the heading changed at all, you should have eyes out. If there is the possibility of traffic, you should have eyes out. If you are relying on a chart and calculations to know your position, you should have a second and third, if possible, method of confirmation. Sight being the surest for piece of mind.

- Will (Dragonfly)

 

[dlochner]

Some traditionalists don’t like the look of a big ole chartplotter mixed up with their bronze and mahogany cockpits, but I noticed that even on Hermione, La Fayette’s replica 18th century French frigate there was a full compliment of digital instruments and chartplotters hidden in a cabinet just behind the helmsman’s wheel on deck.

Likewise on the Draken, a replica Norwegian Viking ship, there was a full complement of modern electronics. Docked alongside it was the Hokulea, a Polynesian catamaran that was on a circumnavigation using only traditional Polynesian navigation techniques.

 

[Gunni]

I understand if you are a Polynesian navigator you spend about 30 years in training and a lot of second-seat time!

 

[TomY]

Years ago, grounding threads drew big crowds. I thought this thread would never get off the ground.

Every body has their own systems of coastal navigation.

My first 20/20 hindsight for prevention of this accident; I would take my own portable device, with a GPS Nav. app.

I'd not be comfortable with the only CP, below decks. Just a tablet that I could keep tabs on that I could view from the helm, and another device, a phone in my pocket, that I would have for back up.

This works well for us on our boat. I especially like the phone CP back up. I'm rarely behind the helm so have no CP binnacle mounted. Instead, we have one dedicated CP in the companionway (can be seen from anywhere), and usually also have an ipad under the dodger(or on the bridge deck). #3, the phone is always in my pocket for instant checking of location, or having it track our location in tricky areas.

I know this area well - all the hazards. It's my boats location, that causes me problems.

Underway, I can't keep as accurate a position of the boat with e-charts below, or on paper in the past (I don't carry paper charts anymore), as accurately as I can on a CP in the cockpit.

And this particular, common hazard - I know - cannot be seen by the best eyes(I don't stare exclusively at the screens, nobody does).

It's invisible mid to high tide. I give it a wide berth these days, and I know exactly where I am in relation to it.

But the occasional boat, even with todays new tools that show the location of the boat and these hazards, hits these rocks.

One thing is for sure, nobody was looking at the screens on these boats, when the screens showed the boats,.... hitting the rocks.

 

[jssailem]

Having just been inundated with my granddaughters movie Moana they show measureing progress at night by measuring the height of the stars above the horizon with an out stretched hand. Or testing the current cold vs warm by dragging a hand in the water. No need for instruments when you have those skills.

 

[dlochner]

The history of navigation is quite interesting.

Jack Lagan's book, The Barefoot Navigator describes ancient methods of navigation. Two other worthy books are David Barrie's Sextant, and Dava Sobel's Longitude.

For a contemporary and philosophical look at sailing, navigation, and family history take a look at George Foy's Finding North

All good reads that will help us get to spring.

 

[Jackdaw]

In the later days of LORAN and the early days of GPS, the big difference was that LORAN gave repeatably locations, i.e., if your Loran said you were at X spot you may really be at Y. But if you went back to X coordinates you would always be at X. GPS on the other hand was more accurate, but not repeatable. If you were trying to find X coordinate on a chart, the GPS would almost always get you closer than LORAN, but when you went back you might in a different spot, but still closer than LORAN. This was back in the day when the GPS signals were degraded for commercial and recreational use.

The reason fisherman liked LORAN is that it would also put them over the same spot, GPS wouldn't do that.

That's it exactly. You have to keep absolute and relative accuracy separate.

 

[Brian M H23]

Fun fact - All the GPS in a pretty large area tend to be "drift" the same way. We did some stuff for geological surveys where we mount one GPS tracker on a pole on the roof and a matching units on the survey equipment. When you calculate the "correction" to make the stationary data actually stay still on that pole, and apply it to the roaming GPS's that are sometimes 100+ miles away, the improvement in accuracy of all units is unbelievable!

In the later days of LORAN and the early days of GPS, the big difference was that LORAN gave repeatably locations, i.e., if your Loran said you were at X spot you may really be at Y. But if you went back to X coordinates you would always be at X. GPS on the other hand was more accurate, but not repeatable. If you were trying to find X coordinate on a chart, the GPS would almost always get you closer than LORAN, but when you went back you might in a different spot, but still closer than LORAN. This was back in the day when the GPS signals were degraded for commercial and recreational use.

The reason fisherman liked LORAN is that it would also put them over the same spot, GPS wouldn't do that.

 

[jssailem]

@Brian M H23 are you saying the satellites up in space orbit are moving. There not fixed. So how does this miracle of science know where I am?

 

[Morgan donor]

I'm of the "those that have & those that will" school. Stating the obvious perhaps, were the "old" CCA & 70-80's boats more forgiving to groundings due to dead reckoning being the technology of the day? Has the need for speed and profitable production engineered in, made newer boats incurring serious damage more likely? The subject boat had a keel drawn up into wood. Pretty old school and repairable! What happens when an adhesive secured keel & structure grid under an interior floor pan comes loose? Sawsall?

 

[Jackdaw]

Fun fact - All the GPS in a pretty large area tend to be "drift" the same way. We did some stuff for geological surveys where we mount one GPS tracker on a pole on the roof and a matching units on the survey equipment. When you calculate the "correction" to make the stationary data actually stay still on that pole, and apply it to the roaming GPS's that are sometimes 100+ miles away, the improvement in accuracy of all units is unbelievable!

Yes, modern RTK (Real Time Kinematic) based GPS systems can have sub-centimeter accuracy, but only for an area the size of a job site. But that's perfect for survey teams.

That '9 foot' fix you see so commonly today is part of a GPS-based systems that the FAA asked for call WAAS (Wide Area Augmentation) that does the same trick on a much larger area. It uses the error feedback from a GPS signal received at a fixed KNOWN location and broadcast as an error to be added to the fixes generates in that area. Also serves as a QOS (Quality of Service) indicator that the FAA also needed. Clever.

 

[LeslieTroyer]

Fun fact - All the GPS in a pretty large area tend to be "drift" the same way. We did some stuff for geological surveys where we mount one GPS tracker on a pole on the roof and a matching units on the survey equipment. When you calculate the "correction" to make the stationary data actually stay still on that pole, and apply it to the roaming GPS's that are sometimes 100+ miles away, the improvement in accuracy of all units is unbelievable!

This drift is call dithering an previously was on all non-military gps units for “national security”. The base station method you describe is call differential gps. Dithering was turned off by Jimmy Carter and is no longer an issue

Mahalo

 

[joker460]

I wonder if forward scan sonar would have helped in some of these incidents as I have grounded twice in sand. No damage but embarrassing that a power boat had to help pull me out.
The units now can give a distance of 8 x Depth.
6 knots would be approx 11 feet per second.
Say a depth of 100 feet, that would give you 72 secs to respond.
At a depth of 50 feet, that would give you 36 seconds to respond.
They need to increase the range.

 

[Jackdaw]

This drift is call dithering an previously was on all non-military gps units for “national security”. The base station method you describe is call differential gps. Dithering was turned off by Jimmy Carter and is no longer an issue

Mahalo

No, while the precision of GPS in theory would be perfect, it is effected even with SA (Selective Availability) turned off by:
GPS Clock errors
Satellite drift (location error)
Atmospheric effects.

WAAS serves to remove most of this to the common 9-foot circle of error we now see. SA was turned off by Clinton in 1999.

 

[Will Gilmore]

With xtra-light spectrum camera technology and good computer mapping algorithms, simply pointing a camera at the sky, no matter the weather should beable to yield as precise a location as any satellite technology. Celestial navigation in the Information Age. And, it can't be shut-off or dithered.

- Will (Dragonfly)

 

[Pendragon35]

Yup. I hit rocks too. I had Mystic for all of a month and I cut too close to Fort McHenry and CRRRUNCH. I did not see the bottom previous to the grounding so I am not sure which of the dings in the keel and scrapes in the rudder were attributed to this. I am sure several were. We we absolutely stuck between several rocks. I swung out on the boom and tilted us out while the Admiral steered us out. We did not hit it dead on, more like scraping into an underwater rip rap embankment. We were lucky as I think the tide was rising as we were trying to figure out how to get free.

I've almost run aground there. i sail out of Anchorage Marina, so every trip means going by Fort McHenry. It's so easy to focus on what comes next rather than on where you are and drift out of the channel.
That's how I grounded last summer. Pendragon is an Alberg 35, 5.5 foot draft. I was doing a lazy tour up the main creek portion of Bodkin Creek, as I began to go back east, my navigation app on my phone was doing something strange. I got so busy looking at that I drifted to the right of the channel. It was such a soft grounding I didn't notice; I just suddenly realized I wasn't moving. After a few minutes, a friendly power boater pulled me off. Not a big deal but an important lesson to PAY ATTENTION TO WHERE YOU ARE!

 

[dlochner]

I'm of the "those that have & those that will" school. Stating the obvious perhaps, were the "old" CCA & 70-80's boats more forgiving to groundings due to dead reckoning being the technology of the day? Has the need for speed and profitable production engineered in, made newer boats incurring serious damage more likely? The subject boat had a keel drawn up into wood. Pretty old school and repairable! What happens when an adhesive secured keel & structure grid under an interior floor pan comes loose? Sawsall?

If the old full keel designs were more forgiving, it would be the shape of the leading edge and the length of the keel. A sloping leading edged might allow the boat to ride up on to the rocks instead of driving into them with a vertical leading edge.

With a longer keel stump the forces from a grounding might be distributed over a larger area thereby reducing the force in any given area. When a fin keel has a hard grounding there are tremendous forces transmitted to the aft end of the keel stub, forcing the back of the keel up into the hull while pulling down on the forward edge. The forces are amplified by the lever action of the the keel. The aft floor timbers can be cracked, furniture dislodged and bulkhead tabbing broken. Also the hull at the aft end of the keel is often delaminated.

Fiberglass floor pans and headliners are used because it keeps production costs down. Stick built boats, like Sabres and old Tartans were always much more expensive than boats built with fiberglass pans because of the increased labor costs. I'm not sure if it is any easier to repair a stick built boat than one with a fiberglass pan. Removing and rebuilding the cabin sole is easier said than done. Cutting and fitting individual floor timbers and reinstalling them is a time consuming and tedious process.

 

[TomY]

I'm of the "those that have & those that will" school. Stating the obvious perhaps, were the "old" CCA & 70-80's boats more forgiving to groundings due to dead reckoning being the technology of the day? Has the need for speed and profitable production engineered in, made newer boats incurring serious damage more likely? The subject boat had a keel drawn up into wood. Pretty old school and repairable! What happens when an adhesive secured keel & structure grid under an interior floor pan comes loose? Sawsall?

Interesting point. Cost certainly determines some of keel attachment strength. But I think the bigger factor is design. Racing designs, were the design brief is to get the last enth of speed, can have keels that simply won't take a severe grounding without major structural damage to the boat.

On this same blog, here's an interesting piece on one way to design the keel to hull attachment, to better handle a grounding in a boat with a high performance keel.

https://stephenswaring.com/marine-engineering-for-ups-why-my-keel-does-not-fall-off/

GINGER's keel was designed with a grounding in mind. Pretty boat that looks like fun to sail! This low boat is 50 feet long.

I especially love this part of the blog about the raked keel. It's refreshing to see keel design that fits actual use:

"We custom-formed this keel so the tackle from fishing gear trails smoothly over the keel, hull, rudder and off and away from the boat. We did give up performance by angling this structure. But those few feet per hour were nothing compared to being parked for untold hours unfouling a nasty lobster pot."

I mean come on, let's not design keels solely on that last, "few feet per hour", gained.