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

    Pierre R- twin outboards??...i paid 2000.00 for my diesel..this engine will last longer than me-- the twin outboards?... good for anchors...they break down often, are way too complicated with special valves, electronic fuel ignitions etc ad infinitum... they are expensive to run and they dont have the torque of a diesel... and to buy-try about 10 000 minimum for good reliable ones...whats more financially realistic?-

    i wont discuss my financial situation...i have enough money for my needs.

    the tug is not for commercial use its for light duty and pleasure--ive mentioned it earlier... btw what does an N A charge?

    im guessing about what a lawyer would charge...but its a guess...i wouldnt even know who could help in my area...

    about the knowledge..what exactly are you looking to find?- perhaps thats an assumption? that i dont know too much?

    --i know enough to feel confident to build one...but thats my opinion-

    perhaps you could tell me where reducing the plate thickness - proportionate to my reduction in hull size is not realistic?...
    thats what the thread is about...
  2. Pierre R
    Joined: May 2007
    Posts: 461
    Likes: 32, Points: 0, Legacy Rep: 458
    Location: ohio, USA

    Pierre R Senior Member

    In a steel boat you have to build in for plate errosion. You could very well get by with thinner plates, especially if you don't care for a fair hull. Warp will be much more of a problem and the boat will not last as long. The boat could still outlast you though depending on how old you are.

    Building from scratch is expensive even if you get a lot of things cheap. $2k for an old engine of that type is not that cheap in my mind. Outboards are not that expensive to run overall unless you will be traveling thousands of miles a year.

    I would imagine you can find a decent tug in that size range for between $40k and $75k. I doubt you will build for less than that. The hull is usually only 20% to 30% of the cost of a build. You are also looking at two years plus full time work if you are any good.

    The cost of a NA varies considerably depending on reputation and work load. There are lots of NA's reading this thread and not responding. Many work cheap and many do not. You have to find one you like at a price you can afford. This is the place to find em. With the internet they can work anywhere.
  3. tugboat

    tugboat Previous Member

    Id definitley like to speak to a NA...see what they charge. I am not saying your incorrect about warping...but i just cant see that happening unless there is some major forces that are unusual. Ive got plans for many tug vessels and most up to 30 ft call for 10 gauge. one well known designer Ken Hankinson uses 11 guage for a 28 ft'r. if i do the ratio and proportion equations for that tug compared to the one i want including hp, the difference in strength in comparison would be much greater favouring leats thats what i can tell...also i personally know a guy who builds tugs professionaly..he probably builds about 3 a year up to 50 ft. from scratch. he sells them to contractors etc. he has no NA background but he does design and build them himself. too rich for my blood but i learned a lot from him.
    i have seen how he designs his boats... he simply draws up the plans on small square graph tools- no cad- he used intuition...and he is VERY succesful...i asked him about the ville class...that hull i could buy for 5000.00. i priced the steel for the 45 ft'r- 218.00 per sheet for the hull plate for 1/4 inch..its better to build new. at 5450.00 for 25 sheets needed. plus framing 1000.00 plus misc another 1000.00.decking can be 10 guage 1000.00- i have the engine, and gear.-0- the prop 500.00 deckhouse etc...i figure i could build her for 20 000 using well sourced cheap parts...doing the labour myself. using basic systems...meaning im not going to use hydraulics or anything fancy. think pleasure craft. but cheap...not going to make the cabin in teak..etc...
    anyway...if it costs more then it costs time rich so it doesnt matter about build time.

    if you know any NA's ask them what they charge?..i am not looking to have plans drawn up--just to see if i can modify the existing design. i still am not convinced that ferro couldnt work...i have seen some hulls and been told by a lot of owners that they are nearly indestructable. but i actually dont feel as confident using that material as i do just welding up a hull. the diff on 3/16 and 1/4 inch plate--it cannot possibly be so great that it would warp out of fair.but you never know i not an NA.
    For what i want--outboards just arent an option.
    really want a true tugboat design....also my tug is fresh water based. they tend to last years and years on the lakes. so plate erosion is not the same problem here. as you know since i believe you are in ohio...? close to michigans beautiful great lakes area?. many a good tug still in service.

    i think if you saw the old engine and saw how robust that engine is---you'd agree it wqas a good deal...youtubes got lots of the older engines in peoples tractors...they were made better than todays higher revving diesels...
    i would have paid less for a 6v -53n DD used (750.00!) but the tranny would have cost me more than this engine and the gear combined! needing machining to get it to mate with the engine--and this cat has more low end torque power.
    in the long run you get what you pay for i guess..but im happy with it..comes with 3:1 reduction. reverse etc. I plan to use a old but still in good condition d.o. tank for household use...this is how i plan to keep costs down by salvaging many things, buying used etc.
  4. tugboat

    tugboat Previous Member

    hmm i may have confused warp (i.e. welding distortion - with"twist"- torque force, exerted against the hull from the power or the engine or other forces)

    if so--plate distortion or "warpage" is eliminated or minimalized by sequencing welds and weld and applying equal pressure to bend in the steel P&S during the build....
  5. BayouDude
    Joined: Feb 2005
    Posts: 27
    Likes: 2, Points: 0, Legacy Rep: 46
    Location: Louisiana

    BayouDude Junior Member

    To the original poster

    I personally wouldn't go any thinner than 1/4" especially if this boat will see any salt water. Plus on plating that thin your boat will end up looking like a starving dog between framing. On a boat that size that is going to see any commercial use I would go 3/8" sides and half inch bottom from the aft engineroom bulkhead back. I design tugs and OSV's for a living and trust me you can't put too much steel into a workboat. I have seen owners punch a hole in a 1-1/8" shear strake. 1/4" plating doesn't give much room for wasting and after a few years a sand blaster will punch holes through your hull.
  6. tugboat

    tugboat Previous Member

    BayouDude--your reply was much appreciated!- the boat wouldn't see much salt water being on the great lakes-it will see ice!
    wow half inch!...really!?...that sure would put the project out of my reach financially. with the rolling and the size of plate..and the bigger welding equipment needed. the more expensive lifting gear, larger clamps etc...etc etc.

    the boat is actually not for full time commercial use mostly just for pleasure and the occasional tow or push. built for pushing my houseboat barge.

    I figured i could decrease the frame spacing about 6'' then use stiffer longitudinals to accept the 3/8th plate? stop the starved cow look

    i do also have a design for a smaller vessel (30 ft x 11 ft). it calls for 3/8th plate. or ten guage cor-ten.

    in the smaller tug- with the engine I have-(A D 4600 CAT 75 hp but huge torque! with an mg 3:1 twin disc reduction/reverse) - would I need a pillow block for the shaft? shaft will be about 3" or so...turning a 32" or more wheel?
    i am starting to think that i have bitten off more than I can chew with a 45 ft tug using heavy gauge steel and round bilge design...your input would be greatly welcomed. thank you
  7. BayouDude
    Joined: Feb 2005
    Posts: 27
    Likes: 2, Points: 0, Legacy Rep: 46
    Location: Louisiana

    BayouDude Junior Member

    I am not sure what your budget is but you could always find an older lugger style tug that has a model bow and some front deck space that you could convert into a lounge area if it will be used for pleasure. Most of these in the 50-70' range have a pair of 6V71 or 8V71 engines and dual generators. I would think it would be much cheaper to fix up an existing vessel than to start from scratch. Although the Great Lakes is a totally different animal than I am used to down here on the bayous of Terrebonne Parish. Most boats down here in that size range are more suited to protected water and it isn't till you get 80+ that you see anything good for offshore. Whatever you do make sure to beef up that bow for the ice. We designed the new 100' tugs for Vane Brothers and installed ice frames on 12" centers up front.
  8. tugboat

    tugboat Previous Member

    Hi BayouDude...i had in mind building a smaller tug --then using that tug to tow a huge barge houseboat...
    we have all kinds of waterways here- more than you could ever imagine!-- one really good one close to me connects to the great lakes and goes almost through southern Ontario..from Georgian bay to lake Ontario...and it has hundreds of lakes which connects it..known as the famous Trent-Severn waterway...with unimaginable beauty(in summer, spring and fall)!

    so- perhaps a tug for protected waters and the occasional great lake crossing would be ideal...i think 50-70 ft would be a bit more than i could chew...

    Mal Lows site has some nice double chine designs in the 25-30 ft range. I don't need too much space for the tug just a good towboat that is pleasing to me. the engine I have for my tug is an old cat d4600 with a mg 3:1 gear -today i got hold of a steel 36x32 prop for that engine and it will have no trouble turning that wheel! so it should be great in a smaller tug, provided i can get a hull that will have clearance for that the winter i probably wont need to break much ice -ill just winter in a harbour somewhere and live on the houseboat.
  9. tugboat

    tugboat Previous Member

    for those reading my other forums--well- practicality overulles passions- and I have abondonded my sub plans and i am going to build the tug--
    what i was hoping to get input with is again-as i have mentioned- I have not found a suitable tug hull to buy- that has economy, power andmeets my needswith the look i desire. That leaves me with one other option- to build. yes i may pay more inititially than buying since I have seen older g-tugs for sale on scruton marine for around 26 000 u.s. they are 72 ft and are 1912 hulls. It has 750 hp. but running costs and slip fees would eat away the pocket book. one outing at 30 gph would be a seasons operation with the
    D318 or the d 4600.

    so-I figure i could build a new 45 ft'er for that price using used parts and scavenging some others. keeping the hull a real work hull..almost bare
    i.e. no major electronic or hydraulics or industrial pumps gensets refrigeration etc..just the basics. so the choice is -I rescale a nice smaller design..or i build the 45 ft'er as shown on my first post of this thread.
    I am leaning towards the st boat . But how difficult would it be to bend in plates on a gradual radius?..i.e. look at the hull out of the water and see the round bilge design--would i need rolled plate?
    the build would take me 3 years.
  10. tugboat

    tugboat Previous Member

  11. BayouDude
    Joined: Feb 2005
    Posts: 27
    Likes: 2, Points: 0, Legacy Rep: 46
    Location: Louisiana

    BayouDude Junior Member

    Most new tugs being built have a single hard chine. It simplifies construction and doesn't take much away in performance due to the low speed requirements of tugs, it also makes for a more stable boat. If you are looking to build from scratch a hard chined tug design may be worth looking into.
  12. tugboat

    tugboat Previous Member

    Bayoudude,- your posts are appreciated.

    There is a smaller design i like--its 27.5 ft loa and it has a single chine.
    built out of 3/16th plate. would be excellent for pushing and towing my house-barge!

    Now im not an NA- and I know you are-- but i did alter the plans.(i know your eyebrows are probably raised like Spocks right now)

    The original plans were for a simple flat bottom hull- plumb sides and plumb stem...inboard canting bulwarks at the stern and forward at the stem. very nice design. although i dont like the pilothouse, and would change that.

    I wanted a straight shaft output, so the original 11 degree offset for the shaft and depth of hull did not meet my requirements.
    so- where the chine is, i simply added a spoon shaped "v" hull. I based it on other hulls I have seen. In fact I do experiment with some amateur designing myself. and have been designing tugs for a 7 years.
    I don't know- but it seems it would simply need a little more ballast to bring to the DWL but because it is a full displacement hull and that it is not going to go faster than displacement speed, the added depth and ballast should not hurt the bollard pull or towing performance.
    the extra lift from the amidships to the bow section should keep the spoon shaped hull from being slow to respond in returning the bow from a wake??

    Bayoudude- also may i ask your professional opinion? do you think a round bilge design in a tug is unstable or flawed? or was there any severe problems with these 45 ft st designs? my guess is it would roll more than a chine hull?..but i wonder why the architects used a round bilge design?..would it have been for fuel economy??

    Also- for the dry exhaust/heat exchanger, could i build a keel that could be water ballasted and then run my keel cooling into the keel section thereby protecting the piping from impact damage should i hit a rock (great lakes Georgian bay is like navigating a minefield of rocks)- how much pipe would you estimate for the cooling system would be needed?
    if your willing to help i could pay you for some services?.. let me know what you would charge and ill see what i can do...(pm me)
  13. tugboat

    tugboat Previous Member

    oh yeah-- why bother lofting out the three views? couldn't i use the offsets and loft out just the frames and stations(the body plan and stations)?

    the stem is straight..the bow is plumb..?? therefore, why need all views? wouldn't it be OK as long as you take extreme care in setting up the frames on a good strong back to exact heights above and below the DWl? plus i could scribe the body plan on a building platen? and later use the platen as plating?
  14. tazmann
    Joined: Aug 2005
    Posts: 329
    Likes: 17, Points: 18, Legacy Rep: 215
    Location: California

    tazmann Senior Member


    It depends on how accurate the offsets are but you should double check by lofting, you need the top view to make sure the shear and chine are like they should be, no hooks or hollows then do a side view for the same, Then do youre end views and if all looks good build the frames to the end view drawing as patterns. Only surefire methed to make sure the lines are fair. Lot of time and money to spend and take a gamble ?

  15. tugboat

    tugboat Previous Member

    Agreed Tom-I figured I might have to loft out the full size hull(sigh..)...the plans are drawn up by naval arc's from the U.S. Army. I thought they might be good enough- but most books say to loft the whole boat.

    one thing I didn't get when I was researching this was- how they actually make the templates for the frames off the full size lines?...I have seen people use nail heads pressed into the wooden mold loft lines. the tacks were laid with the heads half set into the wood. and then plywood pressed into the tacks?...the plywood was then there a more accurate way of doing this?
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.