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

    Hey Tad--yea i hear you and Richard...I dont have those figures. i.e. hydrostatics and weight studies. but then again the designers of all the 14 sets of plans, i own, sadly did not present me with those the case of my own design, its all guesswork...i did look at your site-- i know your an NA and have some really beautiful designs(!) and I understand an NA needs to work out everything on paper...but i am from the the pseudo Colvin School of thought that "you really wont know till you actually build itl"-based on what works for hull form and scantlings -choose previus scantlings and then design by those parameters- then I am able to design a reasonable vessel without the not saying those things dont have a place--but i also think - our western society tends to overcomplexify everything wayyy too quite sure my boat could work--it may not win any awards or be the best performing boat but I am sure it could be a reasonably seaworthy design for its intended use. but of course one nevers knows...and its a gamble...
  2. tugboat

    tugboat Previous Member

    this is my UNCORRECTED single chine hull in steel deisgned after some other designs i loved but couldnt get the plans for..
    particulars for "The Ironwood"
    30 ft loa,
    beam 11 ft 3 inches (molded)
    depth 6.5 ft
    draft 4.5 ft
    single screw
    3/16th plate
    36 inch prop.

    This hull is uncorrected as viewed- I have the corrected plans.

    yes i know the shear is not drawn perfectly nor is it parallel with the rub strake here...the plans I corrected are fine.

    I haven't done stability calcs but i trust my design cuz its based on others of almost the same dimensions and scantlings. I have taken all the points from other tugs i liked and made it my own...
    please dont point out that there is no stability calcs with it or that it wasnt a pro design...i dont care- since i have seen vessels that are more poorly designed that work quite well...its beamy enough to be pretty stable...

    Attached Files:

  3. ACuttle
    Joined: Aug 2008
    Posts: 85
    Likes: 3, Points: 0, Legacy Rep: 40
    Location: UK

    ACuttle Marine Design Engineer

    Think that's the smallest image going there.

    I'm not sure turning away advice like that such a good idea. There's a middle ground between over-complication and ignoring too much. Working off similar vessels is often a good start for things but you'll always be making changes and with a small vessel the % of the change is larger.

    I don't want to lecture folk though and I recon you could likely get a way with 5mm plate (apx 3/16") but you're shorter on any safety factor.

    I'm happy to approximate things myself when I'm working but if I do I go the other way, if I'm estimating then I'd increase plate thinkness to account for error. You're going both ways estimating and minimising, I can see your reason for wanting the 3/16 plate if that's what you can handle but you might need some thicker stuff in key areas. It would be worth doing a bit of maths before setting off but keep it simple and you wouldn't have to take it to the n'th degree.

    That doesn't sound as positive as I'd intended - just if your spending the cash and chasing the dream, might as well makesure you're doing it right...
  4. tazmann
    Joined: Aug 2005
    Posts: 329
    Likes: 17, Points: 18, Legacy Rep: 215
    Location: California

    tazmann Senior Member

  5. apex1

    apex1 Guest

    Well, that was the deal with these free plans! The NA retired and does not provide any assistance.

    Tad was dead right, it is not as easy as it seems to be. What you are trying to do is not a minor change of a existing design, you try a new design without having the required data or educational background.

    The weight of the Atkin tug is unknown. All I know is what the internet site provides:

    You may have noticed that there is little input from the NA´s here. For good reason! They don´t like to be involved in a new design which they have no control over.
    So, in the end you will have to go for a existing and proven plan, or hire a pro.
    Minor changes can sure be discussed here, and possible solutions can be found without receiving any bills. But the way you like to go will not find the support you hope for.

  6. tugboat

    tugboat Previous Member

    good morning tazmann- yes thanks, i had looked at it--i called glen-l
    about the prop aperture- since either design I build needs room for my 36 inch prop. the aperture wasnt big enough and I wondered about torque and twist for my large engine. I didnt like the canted inboard tumblhome- not good for towing on the hip. need a flat mating surface to tow like that and its the best way to tow. so when i designed my 30 ft'er I made her with plumb sides...
    peace to you...

  7. tugboat

    tugboat Previous Member

    i guess it will come down to whether I want to take a risk or not. I do appreciate the input...
  8. tugboat

    tugboat Previous Member

    Hi Andrew- thanks for repsonding--i did not take your post as being negative at all--i appreciate your time to post. I do also apologize for the small thumbnail, i uploaded it as a jpeg but it didnt want to go full size for some reason...i can email you a pdf version?

    so if im correct- you are syaing that the 30 ft design would be better with thicker plate??..I used Mal lows scantlings for similar sized boats he drew- he suggests 3/16th plate? and says thicker plate would make his hulls too heavy.
    can you direct me to the math required?...
  9. pdwiley
    Joined: Jun 2008
    Posts: 1,004
    Likes: 86, Points: 48, Legacy Rep: 933
    Location: Hobart

    pdwiley Senior Member

    Just a comment on this - Tom Colvin does know what the various values are when he designs his vessels. Most of his designs, he also built in the past.

    What he doesn't know is what an amateur (or professional yard) will add, subtract or change without asking him, so an 'as-built' vessel to a set of plans might differ considerably. Adding or moving tankage is a classic example as is using something other than lead for ballast. I've corresponded with him over many years and this issue has come up in discussions.

  10. tugboat

    tugboat Previous Member

    PDW- technically--is it true that the lighter the hull for sialing- the better perfromance?
    and if so they need to ballast the vessel to bring it down to the lines if it a monohull and a large displacement one? wouldnt this same principle apply to a light powerboat hull like a tugboat? fact would ths lighter hull (if it was as strong as other materials)make a tug type vessle repond better going fw'd to astern? as well as being more agile?
    hence if this is the case then the ,material i have chosen should be awesome...if your interested ill Pm you about it...there is a thread here on it..very good stuff regardless of what the naysayers would have us believe...
  11. ACuttle
    Joined: Aug 2008
    Posts: 85
    Likes: 3, Points: 0, Legacy Rep: 40
    Location: UK

    ACuttle Marine Design Engineer

    No worries, I was suggesting that you might be able to get away with thinner plate in less critical areas, then increase the thickness around certain locations, but that's not the simple way of doing it. Simple way is to use adequate plate all over but to say what's adequate is what takes the training/experience.

    I'd be loathed to give too specific advice without knowing all the details etc. but it sounds from your other thread that you're going with a FC hull. I'm only a metals guy so I cannot really comment on that. Good luck with whatever route you take, get as much free advice as you can, then at the end choose where you need to pay for information just to clear stuff up.
  12. apex1

    apex1 Guest

    The lighter hull, when ballasted to come down to DWL, will respond similar to the heavier one. But fast response is not the main goal for a tug, the opposite. Hence the "odd" shape of the bow, you mentioned, for example.
    Being able NOT to be influenced by the tow, is one of the main objectives of a tug. Fast responding is the opposite.

    It seems you are going the fatal FC way anyway. (I assume following the claims of the "advanced" material supplier)
    If so, you once will remember this post, be sure! And you will regret having named some people naysayers, because you will be one of them by then. Especially for a tug, FC and its derivates, is the least sensible material.

    If cost of the steel hull is already a hindrance for you (incl. blasting / painting), then you can never afford the boat at all! There is no way round, believe me (and all the others which have been there).

  13. tugboat

    tugboat Previous Member

    Richard-- We shall see!-if so --great i have learned something... as the song says--"this aint nothing!! listen to the lyrics--so very true!!

    good luck to you too mate...please pm me sometime and id love to see some pics of your boats...i always enjoy good craftsmanship. ill send you some pics of the material ill be using - fer-a-lite. mayeb ill send you a small sample too...might just might change your mind once you see that it almost indestructable...
    Richard I wasnt refering you as a naysayer--i know you are trying to help...i appreciate the thoughts...I know thta you dont like the material--i understand why--but it has been used with success on tugboats. check out the c-logger 38 000 pounds displacement! 9 ft draft round bilge. see the attachment--one is fiberglass, 26 x 10 ft round bilge- the other is the samson 38ft c logger. I have seen pics of a C-logger on the west coast of Canada.


    Attached Files:

  14. apex1

    apex1 Guest

    Makes me sad to see, you are not to convince.
    I am aware of the fer a lite claims (we quite recently had a dispute with the distributor here), he already offered some test material. For a commercial yard not worth trying. It is far too labour intense, and the final product (boat) has zero value. A mad idea....
    But on top of that, it is expensive! You have to use well prepared steel armature (galvanized, better epoxy coated) to avoid failure due to microcracking. And that WILL happen, no matter what these people claim.

    No thanks, I stay with my Wood Epoxy and FRP boats for the production series, and metal for the Passagemakers. And not when I was paid for, or hull and engines came for free, I would build any boat in FC and derivates!


  15. Tad
    Joined: Mar 2002
    Posts: 2,321
    Likes: 213, Points: 73, Legacy Rep: 2281
    Location: Flattop Islands

    Tad Boat Designer

    I haven't seen any evidence of successful use of Fer-a-lite to build working tugs.....none....nor fiberglass......the samson design has been around for 30 years.....I've never come across one IRL.

    Doug you have made your choice and I don't write to dissuade you....only to correct possible misconceptions for others reading this.....My understanding is your tug-yacht is another version of a Nordic Tug and not intended for real 24/7 towing....thus the material choice is less are your construction hours in a owner-build situation.

    A photo on the internet does not make a successful boat....especially one intended to make money's not a yacht that just has to look nice sitting in the slip.........
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.