How Safe Are Trawlers in Big Seas ?

[cat man do]

Originally Posted by Astrid

One can also have a fishing trawler that resembles a motor yacht:

http://upload.wikimedia.org/wikipedi...en_harbour.jpg

And a catamaran that is a trawler/fishing vessel, as per the definition of "Trawler" used here by some.
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[psneeld]

Originally Posted by ChristiGrab

jkleins got my point exactly!

psneeld: Bad fuel creates a catastrophic engine failure. Sucking in a jellyfish or plastic bag creates a catastrophic engine failure. raw sea water rapidly eroding your engine can create a catastrophic engine failure. My point is that you need a complete propulsion system that is designed to prevent the things that create catastrophic engine failures. You are kidding aren't you...NONE of those ever ruined one of my engines...and I've had'em all plus dozens of other boats I've repaired/delivered.

Now to address your comment about it being possible to never be in big seas... if you have an unlimited amount of time to wait for the perfect weather window and no concerns about visa issues, it could be possible. But, in the real world, visas expire and you have to leave even if the weather window isn't ideal. In the real world, where it takes 3 weeks to cross an ocean, the forecast can change in that three weeks. And while forecasting is indeed pretty darn good, more than once we got caught in a storm that was not forecast. When we crossed the Pacific, we had 15 - 20 foot seas virtually every day all the way from San Diego to Australia. It only got worse the farther west we went. And those were the "good" travel days! Several times we got stuck waiting out worse weather!

Again...many cruisers routinely avoid bad weather ...maybe not totally but enough to miss the worst of it.

Oh, and my cousin is a merchant marine. He gets stuck in LOTS of bad weather. They stick to their schedule no matter what.

Merchies DO have to stick to schedules and routes to a point...many lose their lives when they stick to it and shouldn't....

[rgscpat]

(all ye ancient mariners who already know this can skip over this stuff or just nitpick it for fun)

As my limited brain and limited experience understand the issue:

There are various numbers that purport to have some relationship to the stability of a vessel, and these have probably been talked to death on other threads or forums -- people who know their way around the forums might be able to dig up appropriate links. They generally work better for discussing relatively similar hull forms, such as monohull displacement sailboats.

Very simply, a couple of the simple ones are the Capsize Screening Formula and Angle of Vanishing Stability.

The CSF (in feet, beam/cube root of cubic feet [or lbs. displacement / 64.2]) only looks at displacement and beam and hence overlooks a whole lot of the characteristics that make one boat more stable than another. All it says, really, is that big deep boats won't capsize as often as little flat boats. A CSF below 2 is better than a bigger number.

AVS (or limit of positive stability), as it implies, is the angle beyond which a boat, in calm conditions, won't return to upright. Even in rough seas, a boat with a high AVS, such as 135 degrees or more, will tend to get rolled back upright, whereas a boat that had an AVS of less than 90 would tend to be happy to stay upside down. The AVS formula is a smidge more sophisticated than CSF in that it considers a vessel's draft and proportion of ballast in addition to beam and displacement.

Obviously, these are only beginning approximations to what a real boat would do in the real world, and fall short of many of the issues that naval architects and physicists would consider -- centers of gravity, moments of inertia, effect of weight distribution, chines & various hull form details, roll dampening from sails and spars, interaction of different types of motion, blah, blah, yada yada, etc.

You could get even more sophisticated and real-worldly by subjecting a vessel to a inclination test -- actually measure the response of a boat to being heeled/having weights put on board in different places to learn about the vessel's center of gravity. A naval architect or builder may have also arranged for a "curve of static stability" (GZ) to be drawn for a loaded vessel. And no doubt there are more sophisticated measurements. Now maybe the experts can come in and tell us if they have any numbers that they believe predict something about stability in the real world.

[hummingway]

Originally Posted by Astrid

One can also have a fishing trawler that resembles a motor yacht:

http://upload.wikimedia.org/wikipedi...en_harbour.jpg

And I thought I had a problem with seagulls crapping on my boat!

[markpierce]

Originally Posted by ChristiGrab

jkleins got my point exactly!

psneeld: Bad fuel creates a catastrophic engine failure. Sucking in a jellyfish or plastic bag creates a catastrophic engine failure. raw sea water rapidly eroding your engine can create a catastrophic engine failure.

A sailboat's engine is more likely to fail than a motorboats since sailors don't pay as much attention.

Recreational trawlers have sophisticated fuel-filter systems:






Proper recreational trawlers have screens to keep junk from being sucked into the engine's cooling system:



Sea-water-cooled diesel engines have zincs to minimize erosion.

A broken mast or torn sails don't affect a motorboat's primary motive source.

[psneeld]

Originally Posted by rgscpat

(all ye ancient mariners who already know this can skip over this stuff or just nitpick it for fun)

As my limited brain and limited experience understand the issue:

There are various numbers that purport to have some relationship to the stability of a vessel, and these have probably been talked to death on other threads or forums -- people who know their way around the forums might be able to dig up appropriate links. They generally work better for discussing relatively similar hull forms, such as monohull displacement sailboats.

Very simply, a couple of the simple ones are the Capsize Screening Formula and Angle of Vanishing Stability.

The CSF (in feet, beam/cube root of cubic feet [or lbs. displacement / 64.2]) only looks at displacement and beam and hence overlooks a whole lot of the characteristics that make one boat more stable than another. All it says, really, is that big deep boats won't capsize as often as little flat boats. A CSF below 2 is better than a bigger number.

AVS (or limit of positive stability), as it implies, is the angle beyond which a boat, in calm conditions, won't return to upright. Even in rough seas, a boat with a high AVS, such as 135 degrees or more, will tend to get rolled back upright, whereas a boat that had an AVS of less than 90 would tend to be happy to stay upside down. The AVS formula is a smidge more sophisticated than CSF in that it considers a vessel's draft and proportion of ballast in addition to beam and displacement.

Obviously, these are only beginning approximations to what a real boat would do in the real world, and fall short of many of the issues that naval architects and physicists would consider -- centers of gravity, moments of inertia, effect of weight distribution, chines & various hull form details, roll dampening from sails and spars, interaction of different types of motion, blah, blah, yada yada, etc.

You could get even more sophisticated and real-worldly by subjecting a vessel to a inclination test -- actually measure the response of a boat to being heeled/having weights put on board in different places to learn about the vessel's center of gravity. A naval architect or builder may have also arranged for a "curve of static stability" (GZ) to be drawn for a loaded vessel. And no doubt there are more sophisticated measurements. Now maybe the experts can come in and tell us if they have any numbers that they believe predict something about stability in the real world.

Like many fishing boats that have capsized and sunk...it wasn't the design that did it...

It was operator error plus improper loading and often some free surface effect thrown in.

Theory is where you start but it's what the cruiser does or doesn't do that is just as dangerous in terms of stability.

[hummingway]

Does all this sail/motor is more likely to break then motor/sail seem a little poorly thought out to anyone other then me? I'm hoping you all have your tongues firmly planted in your cheeks and have forgot we have emoticons.

[psneeld]

Originally Posted by markpierce

A sailboat's engine is more likely to fail than a motorboats since sailors don't pay as much attention.

Thank you...nice response!

But I'll standby what I was inferring before....even the most neanderthal engine setup doesn't catastrophically fail for common reasons...usually it's long term neglect, old age, or factory defect...unless it's operator error from the git go....

[Blue Stocking]

Originally Posted by hummingway

Does all this sail/motor is more likely to break then motor/sail seem a little poorly thought out to anyone other then me? I'm hoping you all have your tongues firmly planted in your cheeks and have forgot we have emoticons.

Mark,

Don't let me down now- I complemented you earlier in this forum
But that last post has me agreeing with Hummingway.
Sailing vessels may not have as fancy a filtration set-up as yours because the engine is generally is considered the 2nd line power source.
But I have also worked in sailboat engine rooms with far more sophicated filtration and lube systems than you show.

[ChristiGrab]

In the real world, wouldn't you leave your boat in a marina and hop over the border into another country , get stamped, come back in and then leave on the boat when weather is more favourable? In the real world, can you be forced out into unfavourable weather conditions or are the powers that be more likely to give you an extension until the weather clears?

Obviously, you have limited foreign cruising experience. Nope, it is not always that easy. You'll be very interested in a story in my upcoming book about three boats having to leave Indonesia in bad weather due to expired visas--2 sailboats and us. One dismasted and had to return; they were allowed in. The other returned because the conditions were so unsafe. They were immediately arrested. The other boat was us. We pounded through and made it safely, but it was AWFUL.

You are kidding aren't you...NONE of those ever ruined one of my engines...and I've had'em all plus dozens of other boats I've repaired/delivered.

What would you do if you had 2,000 miles to the nearest port and bad fuel shut down your engine and you had no steering control? I stand by my statement that all the weakness I mentioned have the POTENTIAL to be catastrophic. They won't necessarily be, but why take the chance? Start with a system that is robust to start with.

[Capt Phil]

Hummingway, you got me LMAO again! On a more sincere note, it is a pity that sea chests have gone out of vogue... easy to clean, spot trouble and good protection for salt water cooled power plants. Best of all worlds is dry exhaust/keel coolers IMHO.
Fuel needs to be stored low, multiple filters/polishing systems and redundant transfer and pumping capabilities as well as the ability to examine fuel BEFORE being pumped aboard from questionable sources. Nice to have a get home for single engined boats as well. Capt Phil

[psneeld]

Originally Posted by ChristiGrab

Obviously, you have limited foreign cruising experience. Nope, it is not always that easy. You'll be very interested in a story in my upcoming book about three boats having to leave Indonesia in bad weather due to expired visas--2 sailboats and us. One dismasted and had to return; they were allowed in. The other returned because the conditions were so unsafe. They were immediately arrested. The other boat was us. We pounded through and made it safely, but it was AWFUL.


What would you do if you had 2,000 miles to the nearest port and bad fuel shut down your engine and you had no steering control? I stand by my statement that all the weakness I mentioned have the POTENTIAL to be catastrophic. They won't necessarily be, but why take the chance? Start with a system that is robust to start with.

I guess LIKE the weather...know before you go...

I know some countries just can't be dealt with but force majure has worked plenty of times for others...tough straightening out but better than dying...

Guess I inspect my fuel better....

[markpierce]

Originally Posted by Blue Stocking

But I have also worked in sailboat engine rooms with far more sophicated filtration and lube systems than you show.

I didn't show my fuel-polishing system because they aren't typically installed.

[cat man do]

Originally Posted by ChristiGrab

Obviously, you have limited foreign cruising experience. Nope, it is not always that easy. You'll be very interested in a story in my upcoming book about three boats having to leave Indonesia in bad weather due to expired visas--2 sailboats and us.

So thats one place
Across the ditch in Malaysia I know people who have been there for years and do exactly what I said.
Google Visa runs

[psneeld]

Originally Posted by ChristiGrab

Obviously, you have limited foreign cruising experience. Nope, it is not always that easy. You'll be very interested in a story in my upcoming book about three boats having to leave Indonesia in bad weather due to expired visas--2 sailboats and us. One dismasted and had to return; they were allowed in. The other returned because the conditions were so unsafe. They were immediately arrested. The other boat was us. We pounded through and made it safely, but it was AWFUL.


What would you do if you had 2,000 miles to the nearest port and bad fuel shut down your engine and you had no steering control? I stand by my statement that all the weakness I mentioned have the POTENTIAL to be catastrophic. They won't necessarily be, but why take the chance? Start with a system that is robust to start with.

Geez...I crammed my boating, cruising and pole to pole voyaging with the USCG into a measly 50 years.....