Stability of Strange Canadian Boat (pictures inside)

Discussion in 'Stability' started by CatBuilder, Sep 11, 2010.

  1. CatBuilder

    CatBuilder Previous Member

    I have some nagging questions I've always wanted to ask about these very strange looking Canadian fishing vessels.

    (pictures below)

    These vessels are (or were) in service in the Great Lakes.

    1) Given the shape of the hull, how would these boats react to rough, open ocean conditions relative to a Nordhavn or some other trawler?

    2) Do you think stability would be compromised if you were to add a yacht's worth of interior fittings (wall partitions, berths, galley, water tanks, etc...) and such to one?

    3) In general, do these seem seaworthy, or not? I can't quite decide...

    4) How could I do basic stability calculations for one of these boats, given I have no plans and all that steel up high has to have an effect?

    http://www.boatquest.com/photos/304708024728_50216_1.jpg
    http://www.boatquest.com/photos/304708024729_50216_2.jpg
    http://www.boatquest.com/photos/304708024746_50216_1.jpg
     
  2. alan white
    Joined: Mar 2007
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    alan white Senior Member

    Actually, the significant attribute in terms of seaworthiness appears too be the enclosure. Tiny ports and all fore/aft travel inside rather than on narrow side decks. Must be a tad uncomfortable in high winds and steep seas due to the low displacement and tall superstructure.
    You can make a simple steel box and float around the world without mishap as long as you can survive the motion.
    There are many definitions for the word 'seaworthy'. In this case, it seems the definition runs closer to the word survivable. Keep the doors shut and stuff something in the crack underneath...
     
  3. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    1) Wildly.....

    2) Yes....

    3) not.....

    4) Do an inclining to ascertain VCG, measure flotation, take the lines and make a computer model, run hydrostatics.....

    The illustrated vessel is very dangerous...not to be trifled with....That steel box is free flooding but not quick draining...free surface will roll the boat over right now!
     
  4. apex1

    apex1 Guest

    A floatin coffin even on a windy inlet.
     
  5. CatBuilder

    CatBuilder Previous Member

    Ok, this boat is considered deadly and not well founded. I have a couple of follow on questions. I ask these because I don't know a lot about power boats or their stability principles. To me, they *all* look dangerous! :) But, I'm sure the stability has to do with how much weight is down low vs. up high and the shape of the hull.

    1) Tad, when you say the free surface would roll her right now, do you mean if there were water inside the box? Otherwise, I'm not familiar with the type of free surface effect you are talking about. The free surface effect I'm familiar with is typically inside a tank without baffles.

    2) Ok, that boat was bad. What about the following boat that is the same design principle, but different dimensions? Are all of these boats that have been plying the Great Lakes since the early 1900's death traps? If so, what, specifically about them makes them unsafe?

    3) What is the story with the stern of the vessel in the pictures below??

    4) Why are these boats sitting at their waterlines with no fish in them??

    5) What makes the boat in this post any better or worse than the boat in my original post?

    6) What would happen if you added full cruising amenities to the boat in this post? Same thing as the previous one?


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  6. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Those are/were "fish tugs", used for commercial fishing on the great lakes. They are enclosed to protect the fisherman in the winter. My understanding is a common way of fishing with them is the nets are shot off the stern and retrieved through the doors on the sides. Some were built as production boats by larger yards to plans.

    Fish tugs were developed decades ago for almost all season fishing on the great lakes. I have trouble imagining the fisherman would have settled for "floating coffins", even if they do look slightly odd to folks more used to looking at yachts and recent powerboats.
     
  7. apex1

    apex1 Guest

    Maybe a second look at the second picture above lets you see why that vessel IS a floating coffin, no matter how a fisherman thinks about it.
     
  8. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    You have no idea.......Commercial fishing is a very dangerous occupation.....in BC waters 160 fishing vessels have capsized between 1975 and 2008, an average of 5 per year.

    Great Lakes fishermen have not suffered the same fate because commercial fishing on the lakes has almost completely disappeared....thus these boats...mostly built pre 1970....are for sale cheap.

    I have a paper on Great Lakes Gillnetters written by Tom Colvin in about 1960 and published in the FAO book Fishing Boats of the World 2. The paper mentions neither stability nor safety. He does mention that the fishermen were concerned with motion, thus the low freeboard and deck levels. The smaller boats actually had the working deck below DWL!!!

    To address Cat's questions....

    1) Yes, I'm talking about free surface effect of water on deck enclosed by solid walls with no interior divisions....scary stuff.....Note the small scuppers visible along the rail, and no door sills to the outside aft deck? Water piles up inside and can't get get away (small scuppers are easily blocked with loose crap), no one notices because they're in the pilothouse yakking, the boat rolls just a bit.......and keeps on going......

    2) Low freeboard means they run out of reserve stability as soon as the rail (main deck edge) goes under water, in this case it might be as little as 20 degrees heel. Water can flood in those little scuppers, reducing stability more, and VCG is already high because these are relatively shallow hulls with little inside and a high steel structure. For instance a UK north Atlantic ocean trawler which meets modern stability criteria might have 3-4' of freeboard on the same 60' by 20' waterplane, and she'll draw 8-9' of water. This Great Lakes boat draws 6' and has what appears to be 10" of freeboard.

    3) Don't understand the question.......

    4) They may have had some ballast added since they quit fishing, but I doubt it. These boats did not catch huge loads, a really good day (according to Colvin) might have been 500 pounds. The gear was light, they are not big load carriers, shallow hulls with flat (shallow vee) bottoms.

    5) It's bigger and the waves stay about the same size...thus bigger boats are somewhat safer.

    6) Adding an interior above the main deck will raise VCG further. Perhaps one could build in huge water ballast tanks that would remain full all the time....which will sink the boat reducing freeboard. They may be okay for sheltered water.....a houseboat....few understand the limitations of those either.....
     
  9. peter radclyffe
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    peter radclyffe Senior Member

  10. CatBuilder

    CatBuilder Previous Member

    Ok, thanks! I have studied the MacDuff ships and read Tad's comments a few times over.

    I see the clear difference between the MacDuff boats. The hull goes up with tons of freeboard and there is little enclosed space on deck. Nearly the opposite of the example boats in this thread.

    Now, speaking to the 2nd boat I posted pictures of:

    There are no scuppers or any type of entrance way for the water to get in. Wouldn't that mean that the rail of that boat is actually the top of the topsides, all the way up, assuming it's watertight?

    I can envision rolling this 2nd boat over all the way to the point where the the blue and the white/grey meet and not taking any water. (although it may keep rolling due to weight distribution issues)


    Said another way: Wouldn't the rail on the 2nd boat pictured above be the point where the blue and the white/grey meet on this boat? Wouldn't that make it somewhat more like the MacDuffs in that it has a very high rail?

    Or... am I seeing this wrong?
     
  11. Tad
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    Tad Boat Designer

    Lightweight, high-sided, shallow draft hulls can exhibit good high-angle stability, but they must be ballasted and fairly narrow. This concept has been publicized by Phil Bolger and Susanne Altenburger. Wider hulls with high sides and shallow draft act like barges, they are just as stable upside down.

    If the deck shelter is to be treated as hull topsides, it must be built to the same scantlings as those required for the topsides, as the roof becomes the main deck. This raises VCG even more. Any openings must be treated as those in your hull topsides...ie watertight in continuous immersion.
     
  12. CatBuilder

    CatBuilder Previous Member

    Ok, this makes a lot of sense to me now, thank you for the lesson in powerboat stability. After 20+ years of sailing and thinking about sailboats (and catamarans lately) it's hard for me to understand the different nature of the power vessel design.

    A follow on question (two actually), if you don't mind (sorry... trying to learn):

    Would the following vessel be just as much a P.O.S. as the 2nd Canadian one I posted pictures of? You know... the one with the blue deck? I see almost identical features, yet these vessels are note as roundly criticized as that Canadian one.

    Seems to me it has the same low underwater profile, a square stern, a similar bow and the topsides go all the way up high, too.

    Lastly, would the 2nd Canadian vessel be acceptable for coastal work, going no more than 10 miles offshore? Would the other vessel in this post I'm comparing it to be suitable for coastal work? What are some differences between the two I'm not seeing?

    [​IMG]
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    Bows


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    Sides


    [​IMG]
    [​IMG]
    Stern
     

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  13. srimes
    Joined: Sep 2008
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    srimes Senior Member

    How often does a barge flip? Seems like they'd tend to swamp and sink, not roll over. But if they did they'd be stable upside down, like a catamaran.
     
  14. peter radclyffe
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    peter radclyffe Senior Member

    the lower windows/ ports all need to be gone,
    the weather deck/freeboard must be higher,
    the draught must increase
    all weight must be as low as possible
    these are general requirements for offshore
    if that aft canopy bangs a jetty, it may disintegrate, so it must be narrower, or preferably be gone, as it looks flimsy
     

  15. DianneB
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    DianneB Junior Member

    I grew up on the north shore of Lake Erie and remember quite a few of those boats (in the original post) sailing out of Port Dover and the other fishing ports in the 1950's and early 60's, before the Great Lakes fishery collapsed. Even my father fished Erie in the late 1920's. The only incident I remember hearing about on a fishing boat was one that burned in the 1960's as the result of a propane leak and fire.
     
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