building vs buying...

Discussion in 'Boat Design' started by tugboat, Jul 14, 2013.

  1. pdwiley
    Joined: Jun 2008
    Posts: 1,004
    Likes: 86, Points: 48, Legacy Rep: 933
    Location: Hobart

    pdwiley Senior Member

    Oh yes, radius chine hulls - double the time needed to weld up and grind back the longitudinal butts as you now have 2X the length to do. Plus any 'darts' to get the steel to lie fair. Plus the added time to cut & fit the plates.

    I agree that the shape looks nicer but you pay a lot for that 'look' and really that is all you're getting for the time & money.

    PDW
     
  2. MikeJohns
    Joined: Aug 2004
    Posts: 3,192
    Likes: 208, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member


    That might be for one specific design available in chine or round ? But you design a boat to a stability requirement and that requirement is no different whether its hard chine or radiused chine it's dicated by the righting moment, that is the immersed shape and the centre of gravity. Either method of construction and it's easy to get too much stability and produce any amount of excess stability ( resulting in an an overly stiff uncomfortable boat).

    I've tank tested various hulls in both round and chine form and with refined chine placement that doesn't interfere with flow there is no measurable difference. Some tank testing has found chines actually reduce resistance.

    In your tug form I'd be inclined to opt for a small radius from a split pipe if you had to round the chine. Otherwise I'd look at a single chine for that sort of hullform you have it at the stern either way. With a deeper forefoot the single chine is invisible at the bow.
     
    1 person likes this.
  3. tugboat

    tugboat Previous Member

    buying is probably the way to go with this design...its 45 x 12.5
    The owner of that one states that the hull is "better than it looks"...its hard to get this design anywhere for under 70k... if its got some thin plates it could be replated...

    despite the extra work I'd still be willing to do it...if I could do it for less than buying one- I plan on steam anyway so a diesel power plant in the tug is actually an extra cost. id be paying for that inclusive in the price..

    it sure would be nice to find a bare hull of this design,..
     
  4. tugboat

    tugboat Previous Member

    yea that would be a good estimate...
    see enclosed...its pretty close...
     

    Attached Files:

  5. pdwiley
    Joined: Jun 2008
    Posts: 1,004
    Likes: 86, Points: 48, Legacy Rep: 933
    Location: Hobart

    pdwiley Senior Member

    Replating thin bits shouldn't be a drama, I'd agree. The topsides look a bit battered, shrug, adds character and can be worked on. Blast back to bare metal, epoxy paint, good enough for years to come. Factor a repaint into the initial cost.

    I'd try very hard to look at the interior of the hull anywhere that might have trapped water.

    If it's half decent and you can get it for a reasonable price - say the cost of hull raw materials or less - I'd say it's a deal worth pursuing. A hull that size is a hell of a lot of work to build. I would have bought a Colvin GAZELLE hull instead of building my Witch if the owner hadn't been so determined on getting their price - which I may add they never did get, ended up selling it for what I'd originally offered which was half the initial asking price.

    As for the engine I think you're nuts thinking of fitting a steam plant. I quite like old engines etc but the logistics of fitting a steam plant with its boilers, fuel storage etc etc is enough to make me want to lie down with a damp towel over my eyes. Not to mention the testing & certifications needed to run a steam plant in the 21C - you've got a very large bomb in the hull when the boiler is under pressure.

    Diesel engines supplanted steam plants for a number of very good reasons.

    Where are you going to get the steam plant & boiler from anyway? Do you have one tucked away? If so, can you please post pictures etc? I may not be interested in fitting one to a boat but I'm an incurable enthusiast for elegant old machinery in general.

    PDW
     
  6. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
    Likes: 1,042, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

  7. pdwiley
    Joined: Jun 2008
    Posts: 1,004
    Likes: 86, Points: 48, Legacy Rep: 933
    Location: Hobart

    pdwiley Senior Member

    Biggest one seems to be 10HP, correct?

    Somehow the term 'underpowered' comes to mind when I consider a 10 HP engine fitted to a 45' tug.....

    PDW
     
  8. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
    Likes: 1,042, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Nothing more than 10 hp ? I didn't look that closely, steam propulsion is so inefficient ( maybe 10-15 %) feeding a substantial steam engine at today's coal and fuel prices would be totally uneconomical, not to mention laborious. The romance of it seems to been overblown somewhat, I have spoken to old locomotive enginemen who regarded the transition to diesel as similar to going on holidays !
     
  9. brian eiland
    Joined: Jun 2002
    Posts: 5,067
    Likes: 216, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Tug Boat styles

    The real problem I have with a lot of small tugboats is there real lack of space inside. You know with the orginal designs their BIG engines took up the great majority of space inside the hull,...it was just a pilot house and a 'covering' for that big engine.

    I'm sure you have looked thru a number of Jay Benfort's designs, particularly his tugs and tug-trawlers?
    http://www.benford.us/index.html?lists.html

    It seems to me there were a number of tug type vessels in various states of disrepair down along the big St John's river in upper Fla. I doubt that a number of them are even 'listed for sale' unless it is in some sort of commerical trade publication. Proboble some deals to be had there for someone really willing to get down into the real dirt.
     
  10. waikikin
    Joined: Jan 2006
    Posts: 2,440
    Likes: 179, Points: 73, Legacy Rep: 871
    Location: Australia

    waikikin Senior Member

    Which is why you should look to buy an up & running boat for less than a build cost........ spend some dough & go enjoy, make it better & paint it how she wants it.
    & have fun!

    All the best from Jeff
     
  11. tugboat

    tugboat Previous Member

    Actually thee is a company in India that produces 5hp to 50 hp steam engines. I want to use a 18 hp single acting. This is NOT underpowered by any means. There is a 48 inch prop mounted beside the beach near where my land is- it was run by a 17 hp engine. pushed a 70 ft passenger vessel.
    btw steam is no longer inefficient. not by a long shot- Coal is now 15 times less than diesel to run- do the math- the efficiency of a modern steam boiler is now about 21%.

    diesels are about 32% and in fact there is technology now that makes steam approach 28% boiler efficiency.

    but even if diesels run at 32% or so efficiency,
    the cost of coal is 15 x's less...the steam engine itself altho there are losses due to piping,
    the engine itself is much more powerful per HP than a diesel. They produce more torque, are generally less complicated and break down less due to the fact that they are running at 500 rpms rather than 1800-2500
    they need no reduction gear-
    hp per hp (assuming no reduction gearing) a steam engine would tow away a diesel of the same hp. hands down.
    here are some stats for a modern (post 1935) era steam boiler locomotive...


    Thermal efficiency 21 percent At drawbar
    Maximum HP 5,900 At drawbar
    Maximum tractive effort 180,000 Pounds
    Driver diameter 60 Inches
    Full weight 1,500,000 Pounds
    Max speed 90 MPH
    Grate area 71 Square feet
    Average hourly coal 2.44 Tons
    Average hourly water 2,880 Gallons
    Tender: 4 axles
    Coal capacity 51 Tons
    Water capacity 10,474 Gallons
    2 water tank cars 50,000 Gallons total
    Running time 21 Ho

    now the issue with diesels is- that they don't have the same torque generated. nope- that's why locomotives nowadays are D. E. electric motors are roughly the same torque at 0 rpms as a steam engine - which is 100%.the diesels cannot pull the loads required so they need to run the loco's with huge electric motors to climb grades.

    so you can conclude steam still is cheaper - more efficient in cost vs work. and they are actually more simple..explosions don't occur now because the quality of steel is much improved over the 1900's iron type scotch boilers.
    but if you use a water tube boiler such as a yarrow type, which produces about 600 psi ( post 1890's), there is no danger of explosion. maybe a pipe bursting - but they are enclosed. so its a non issue.
    most people aren't informed about steam. Its truly the only viable alternative at present to diesel fuels. And I can run 3 days on a 95.00 full cord of wood.
    where diesels are efficient is- you push a button and they go. that simple that's why they do more work. the downtime of firing up a true marine boiler such as a scotch. however its about a ten minute wait using a yarrow boiler. so its not a big deal for me. however I like the steady steam of a scotch or fire tube type.

    http://internationalsteam.co.uk/trains/newsteam/modern50.htm
     
  12. brian eiland
    Joined: Jun 2002
    Posts: 5,067
    Likes: 216, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Canal-Trawler, about 40'

    How about something like this?
    ....only ~40 foot, with a saloon and back deck bigger than many other trawlers of this size,...and a U-shaped galley,....and an owners double berth stateroom, single engine 6 or 4 cyl.. 60-100hp
     

    Attached Files:

  13. tugboat

    tugboat Previous Member

    Peter read my post to Mr E.

    (laughing) no- I wouldn't use 10 hp- it would be 18 hp...
    even so I might be lucky to get 5 knots out of it.. but it could tow the queen Mary at that' speed..
     
  14. waikikin
    Joined: Jan 2006
    Posts: 2,440
    Likes: 179, Points: 73, Legacy Rep: 871
    Location: Australia

    waikikin Senior Member

    Insert cheesy line here..........." don't kid yourself" or others, get a price from "Damen" http://www.damen.com/en/markets/harbour-and-terminal or similar to see what your efforts should be worth, Tugs are for work & business of moving heavy floating objects for profit, they are cool, if you want one but don't want to work it, get one that's already paid off & ready for your needs.
    Regards from Jeff.
     

  15. tugboat

    tugboat Previous Member

    that is very nice...what's the price? where is it located? they have mad eit quite large by extending the typical tug cabin...thanks for that...

    one of the issues about buying a boat that's not in the same atrea as one lives is the added costs of moving- with todays diesel prices- add another 5000.00 maybe more to haul a 40 ft boat- unless you can find a hauler with a hydraulic trailer- (rare)

    it would mean a crane - and a haul, then another crane at the other end- this get expensive so the bargain boat ends up not being such a bargain in the end- unless you can actually bring her up on her own keel...
     
Loading...
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.