can you decrease plate thickness or use FC for a tug?

Discussion in 'Boat Design' started by tugboat, Apr 17, 2010.

  1. tugboat

    tugboat Previous Member

    ok so- the design is a round bilge design 45 ft army /navy st tug- a 1943 US Army design, their size came about as being the maximum length that could be transported as a unit aboard a railroad flatcar of the period. Mass-produced for the war effort, they served both Army and Navy, designated as YTL by the latter. Several are still in service with the Navy.

    dimensions- 45 loa, beam 12.5 ft, depth 6 ft. designed for steel 1/4 inch i believe (perhaps 3/16th - i have to check the plans and re-ordered them since the last set got ruined- *Laughing*- my ferret ate them!)

    the hull is beautiful- one of the nicest working platforms i have ever seen with low freeboard counterstern for working lines...

    question: do any pro-ferro-cement advocates think ferro-cement could be used as a viable alternative in working commercial operations if built strong?...and what about getting a commercial inspection..would it pass?....the only other thing i could do since i cannot afford 1/4 inch plate, AND rolled(would it even need to be rolled?- coudn't it be strip planked or clinker style?) is to buy 3/16 plate and ballast it a little more...

    Tug National, built in 1951 is owned and operated by Curt and Jenn Muma of Rebellion Tug & Barge Co.,

    what do you steel advocates think about using 3/16 rather than 1/4 inch?...i personally dont think the stability or characteristic of the hull would be much of a problem using slightly lighter guage..*(i also really love steel since its so easy to build and attach things to and i can weld)

    with ferro i could use thick hull forms which could make it very strong...but question its ability in banging around on a tow or while "towing on the hip" in moderate weather...wouldnt want the hull to crack or spall..but i do know that tugs have been successfully built with by samson marine in B.C.!

    btw -this is also a response to an older thread i started about 4 years ago--
    the othe rone is "help on tug plans" or soemthing like that...
    to see large size pics click on picture...
    consructive -happy criticism is welcomed.

    Attached Files:

  2. messabout
    Joined: Jan 2006
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    messabout Senior Member

    Stiffness of a plate is roughly proportional to the cube of the thickness. So 1/4 inch plate, compared to 7 gage (3/16) is on the order of 2.4 times stiffer. This ball park figure is also applicable to planking including plywood, FRP, etc. I don't know about ferro. That is a different breed of cat. With ferro I would think that we could not tolerate much panting, although pre-stressed concrete structures do have some elasticity. But the FC armature is not a pre-stressing arrangement.

    Concrete ships, of WW2 vintage, were produced in considerable numbers at McCloskey Shipyard in Tampa, Fla during that time. They served the purpose well enough. They were said to have less chance of being destroyed by magnetic mines. I suspect that economics and material availability had more to do with the selection of concrete, than magnetic mines. That, and the fact that one set of formwork could be used over and over.
  3. Tad
    Joined: Mar 2002
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    Location: Flattop Islands

    Tad Boat Designer

    "I have a design that's just perfect except I want to change everything, do you think it will be okay?"

    No, it won't! Any one of the changes you mention require a new design.

    Commercial Canada CSI...involves far more than you are prepared for.....see http:// Then there are stability requirements and operator/crew certifications as well.

    Cement will shatter with every point impact...which is what you get all day in a working tug. Ever see them back into a speeding barge to stop it? BLAM....

    Half the cement structure is steel might as well go the full course.
  4. erik818
    Joined: Feb 2007
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    erik818 Senior Member

    If you intend to use the boat as a heavy duty tug to bump into into barges and other boats, steel is best material. Steel is ductile and easily repariable. If that's not the intended use, the usual arguments over hull material applies.

    The engine you're going to install in it will be a lot lighter for the same power compared the WWII original, so some engineering will be required anyway. Would you trust that a WWII design is up to date, and spend all the money building it, without going over the engineering first?

  5. tugboat

    tugboat Previous Member

    Tad- I did work on tugs here on the great lakes- so i do know a little something about them we pushed barges and did ship assist for the lakers...

    actually i talked to a tug boat builder i personally know because there was a ville class hull at a shipyard here. the guys wants 5000.00 for it but it needs lots of work so i called the guy who builds small tugs up to 50 ft- since his yard is loctated across the river from where the hull lies.
    since he knew the boat in question, he told me the bottom needed to be replated . - he suggested sheathing the hull in 10 guage--and i directly asked him if doing it that way would hurt the characteristic i.e. stability--he said it that should apply to a tug hull i build with different plate wouldnt it?

    from what i know tug hulls are very much like a barge hulls..its designed to bull its way through the water. i have seen every different type of below waterline configuration you could imagine-and they are all radically different... to me at least it doesnt seem like those changes i mentioned should have an effect that would be so dramatic it wouldnt work...but i do agree that perhaps i should just do it to the plans specs...

    the ville class has a very similar design to the "st" you think i need to roll the plate? didnt seem that i would need to do that as long as i plated in sections longitudinally...

    i get what your saying Tad--i thought the same thing--might as well just build it proper. but i did see this- and it made me think of ferro-..btw samson marine out there in B.C. built a couple FC tugs..i dont know how they faired.
    but check this out

    this fishing vessel was on a reef for a long time bouncing up and down and there was no major damage to the hull--steel probably would have been ripped open...

    see page 72 i tried copying and pasting but it didnt work...
  6. tugboat

    tugboat Previous Member

    Erik818 thanks for the reply-
    the engine i have is a cat d4600 marine 3:1 reduction. mg twin disk. circa 1944-47 aprox.
    the engine weighs around 3000 lbs slow turning diesel 75 hp at 1500 rpms 1800 rpms max.
    there is a 60 ft tugboat here where i live from that era powered by a d8800 and its 93 hp... and apparently my engine is newer. i estimate the torque on my engine would have equivelent to much higher hp on todays diesels..and be close to the d 8800 if not better.
    it can swing a huge prop- likely a 32 inch or more. maybe a 32x28 or higher.
    btw i should have mentioned that the tug is intended for light duty and pleasure use. most likely to haul around a huge housboat/barge i want to build about 50 ft loa and two 6 ft stories high...
  7. tugboat

    tugboat Previous Member

    thanks for the help everyone--i also thought if i could scale down the tug slightly--i.e. decrease L.O.A. to 40 ft instead of 45 ft then i could use 3/16th plate...i have no intentions on consulting a naval architect since those services would cost me as much to build the hull!(ok a slight exaggeration but not far off!) but glen-l talks about how to lengthen or shorten hulls

    quoted from Glen-L marine....
    "Changing length can be easy
    The most common change requests involve size. A most important thing to remember is that a boat hull is NOT a box - it has shape and form, and must do certain things; not just sit still. A seemingly simple matter of adding or subtracting an inch here or there can have complicating effects that the novice may not realize.

    For example, while adding or subtracting length is usually easy, changing beam and depth is usually not, and the effects can be serious. As a rule of thumb, most (but far from all) boats can be varied up to about 10% plus or minus (see Fig. 1). In other words, a 30' boat could probably be built as short as 27' or as long as 33' with little problem. But there are some exceptions as I’ll explain later.

    Fig. 1 shows a hull with equally-spaced transverse stations. Changing the length of the boat is simply a matter of adding or deleting an equal number of inches from each station space. Often these stations correspond to frames thus making length changes on most framed boats straight-forward. Note also how the boat’s center of buoyancy (CB) stays in relatively the same position (you’ll see why this is important later).

    FIG 1 - Changing length is most easily done by respacing stations or frames a proportionate amount to keep the CB and other elements in relatively the same positions.
    This 30' boat with ten 3' stations has been increased 30" by adding 3" to each station.

    When and why length changes should NOT be made
    There are some cases, however, where boat length should not be altered, at least without professional advice. First is sailboats. The problem here is that there is a definite relationship between a sailboat’s center of lateral resistance and center of effort of the sail plan in order to maintain helm balance (see Fig. 2). Also, the ratio of wetted area of a hull (drag or resistance) to its sail area (the "horsepower" of the boat), as well as stability, must be taken into account. Thus, if you alter length, you may also need to alter the rig and ballast to compensate.

    However, as also shown in Fig 2, it might be possible to add length to a sailboat hull ABOVE the waterline by increasing the overhangs, in effect, increasing on-deck length but not waterline length. Although not always practical or as simple as it may seem, theoretically an addition to the bow and or stern as shown by the broken lines would have little, if any, effect on the relationships just discussed.

    Another case where changing length is usually not recommended is with Stitch & Glue and some other designs where hull panel shapes are pre-determined, and where typical frames are not evenly spaced or even used in the boat. In these cases, there is no easy way to expand all the panel shapes proportionately so that they will match up exactly during assembly short of redesigning them which is much like creating a new hull.

    FIG 2 - With sailboats, the relationship between the center of effort (CE) of the sail plan and center of lateral resistance (CLR) of the hull underbody plane should remain constant. Changing length may alter this relationship. However, changing overhangs above the waterline is usually acceptable if the rig does not change.

    Altering length - how NOT to do it
    With boats based on pre-determined panels, some might want to add a foot or two to the aft ends of the panels, which seems simple if the boat is relatively parallel here. But the danger is that the designer may have planned the shape of the hull (especially the bottom) to have the boat’s hull entry area at a certain point, or have volume distributed along the hull in a certain way for balance, etc. If you simply add to the aft end of the panels, you could change the boat’s proportions and volume distribution in ways that could detract from the boat’s ride, balance, and performance. In other words, results could be questionable.

    Generally, adding or subtracting frame spaces should be avoided on framed boats too. Again, a boat is not a box - it has curves and shape. If you attempt to add or delete a frame space - say in the middle of the boat - unfair lines are likely (see Fig 3). Not only will this look ugly - assuming the boat can even be built - but could also affect performance."

    so if i shorten the hull 10% that 4.5 ft the tug would then be 40.5 ft l.o.a.
    and the 3/16th plate would then be the correct size in proportion to the hull??
  8. tugboat

    tugboat Previous Member

    the other question i have is how to develop the frames??...this design has less stations than it take the frames from the lines plans? only gives offsets for the stations...?????????????
  9. tazmann
    Joined: Aug 2005
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    tazmann Senior Member

    You would loft the boat with the stations, then after its all drawn and faired you would draw in the frames at whatever the spacing is
  10. tugboat

    tugboat Previous Member

    thank you Tazman---awesome!...i thought there may have been an easy way to do it...

    there is a site on the web that sells these exact models to 1;16th 1;24th scale etc..if i buy the model that should allow me to use that also to to both scale the hull down and to take off the frames...


  11. Pierre R
    Joined: May 2007
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    Pierre R Senior Member

    If you have no itentions of using a naval achitect and believe that they are a huge cost in comparison to what you intend to do I would advise you to just go out and buy a working tug. You will be many dollars and time ahead of the game. If you insist, the tuition for your education will be very expensive as you will find out.

    One of the major reasons to build is that you cannot find what you want. I am sure you can find an old small working tug in fair condition for less than the cost of building.
  12. tugboat

    tugboat Previous Member

    Pierre R- thanks for your input...

    i have built 5 other boats..i do know a little about practice (since i have worked on them)tugs are forgiving boats..i could build a barge and throw an engine in it, tugs are not much different...i might need to ballast it a little more but it should work...if not..well there's always Mcnaughton school of yacht design!
  13. tugboat

    tugboat Previous Member

    Pierre R, there is a nice ville class boat- built by Russel brothers 40 ft loa, but in very poor condition ...1/4 inch plate. need the whole bottom replated...there are other designs i like but too small. i have a big engine--a d4600 cat wieghing in around 3000 lbs! immense torque. so need a good sized hull. the best hull ive seen is the st class. I most likely will build in steel that way i can scale down the vessel, and use lighter plate. also my reason for a build is i dont need to borrow.i cna build as i go..its a three year build for me...
  14. tugboat

    tugboat Previous Member

    does anyone think i need to roll the plate??(if using 3/16th plate?)..seems to me i could get away with out rolling using some tricks of the trade. plating it up longitudinally for instance...? using longer plates, and perhaps clinker plated?..or maybe not..?

  15. Pierre R
    Joined: May 2007
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    Pierre R Senior Member

    With all due respect I am not seeing enough knowledge here to avoid taking a bigger hit in the pocket book than consulting a NA. It might surprise you what their fees actually are.

    Your plan seems to be more passion and not enough realism involved. You could easily just power the barge and forget the tug and its associated liabilites with maneuvering. You would also save a ton of money. Twin outboards would be much cheaper than a post WWII vintage engine to fit and operate. The insurance alone would save a bundle and you don't sound like you have nearly the budget for what you want to do and come close to realizing your dream. I know your passion is high, we can see that but the pocket book does not seem to fit the dream very well.
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