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

    Wow--im envious of your shop. sounds like you have some awesome love to have my own lathe...if i did i'd probably do something foolish like build a working steam engine for it...

    thats great advice ill look around and when i am ready to have the shaft machined, ill bring the prop and any specs i need--yes it is a tapered prop. takes 2.5 inch tapered to 2 inches...(i think)
    also my caterpillar has a MG 61 trans. 3:1 reduction gear. so Ill just make a template of the coupling. I wonder how many hours to do the bore for that taper? for a flange--is it feasible to just cut out a 1/2 inch flange from mild steel? weld it to the shaft?
    I just sent my plans in to be looked at by an N.A. I wanted to downsize the hull as mentioned so he has sent me back some info on it--i may have to let go of that design...sadly. It seems i just cant have what i want...I really dont want a 45 ft boat -its way too big for what i want to use it for. Thats been the issue right along. Im not comfortable in a larger boat skippering her etc. I thought 40 ft was the largest one i wanted but I just havent seen any plans i like as much as it puts me In a dilemma of comprimise. I am mulling it over now--I have three choices as mentioned on this thread...
    1. the 45 ft'er(but this is too big)
    2. my own design(which has hard chine and i dont i am a round bilge guy)
    3. there is a smaller tug i like almost as much as my 45ft'er.
    a Mal Low designed "pintle". (It has no accomodations however)
    so it seems stuck once again. no matter which way i go i have issues....ugh- i just want to get the build going...
  2. pdwiley
    Joined: Jun 2008
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    pdwiley Senior Member

    Feasible, yes. Sensible, no. Consider what's going to happen if the shaft gets damaged for any reason. How do you get it out of the boat? I'd never do this, you're not going to save any real amount of money and it'll be a big headache. After the flange was welded to the shaft, the entire assembly would need to be put in a lathe and the flange face machined square to the shaft anyway.

    As for the taper bore, if the shop has a lathe with a minimum 2" hollow spindle and a taper attachment, most of the time will be taken up getting the taper attachment set to the correct angle. They may well have to make up a short dummy shaft first to use for trial fits in the prop. That's what I'd do anyway. I'm not an expert machinist (I can get the accuracy, not the speed) but I'd reckon on 2-3 hours. The inboard end is going to need a keyway cut (or whatever is specified for the HP).

    I think it was George Buehler that said it was better to have a smaller boat finished & in the water than a larger one sitting in the driveway. I thought of building Colvin's GAZELLE but decided it was just too big for a first project. Given where I'm up to I still think that was the right decision...

    Probably easier to add accommodations to the Low design than screw with another one. I found his Web page, which design are you looking at? Never mind, I didn't realise 'PINTLE' was a design, I just saw it.

    Last edited: Nov 1, 2010
  3. tugboat

    tugboat Previous Member

    that makes sense about not welding the flange...ill just do it proper.
    i was toying with the idea of using double universals...this lessens the accuracy of lining up the flange perfectly..considering my engine is a monster.
    weighing about 3100 lbs, and the gear about 650.00 ...
    i mena to taks --does Colvin have a site with the plans and specs?

    Lows design is a definite option....and i had thought the same thing --that i would be on the water sooner..funy you quoted Beuhler--i just bought a set of riverwaker plans. and got his book free...we have been communicating via email. I like his ideas even though ill never be a wood guy.
    He also talks about how one guy who got his plans got brainwashed by the others around him in the boat yard he was building his boat in...
    how big is the Gazelle???.ill look it up...brb
  4. pdwiley
    Joined: Jun 2008
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    pdwiley Senior Member

    If you use double universals, you MUST put a thrust bearing assy in the drive line between the prop and the first uni joint. Uni joints are not meant to take thrust and will die. Marine g/boxes have heavy thrust bearings inside them to deal with this. For the HP you're talking about you need to talk with an engineer who can design for the thrust AND HOW TO ANCHOR THE THRUST BEARING ASSY IF YOU USE FC OR FAL because both materials are weak.

    I bought plans off of George Buehler but decided I liked Tom's boat philosophy better. One day I might build an ARCHIMEDES.

    A GAZELLE is 42' LOD, just under 12' beam and its design displacement is 18500 lbs IIRC. Mostly as-built they run over 22000 lbs because the original design didn't have an engine at all. Tom is a purist about sail boats sailing. He did a lot of power boat designs as well.

    I'm happy to talk about engineering details machinery and the like but I'm going interstate for a week or so and may be off-net most of the time.

    Final thought - even a small tug seems to displace 25000 lbs. Boat costs seem closely related to displacement so the heavier it gets the more it'll cost you.

  5. tugboat

    tugboat Previous Member

    Thanks--if you ever do get some pics of the build-it would be invaluable to me. I have my 45 ft design in with an NA to see about what chnages I need to reduce everything by 10% was pointed out to me that this means a reduction of about 27% of the displacement since it means adding each plane
    i.e. .9 of the beam.9 of the Loa and .9 of the depth takes away 27% displacement..this menas the displacement is quite a lot lighter.

    Yea for the universal..-i have a diagram showing how to set that up with a thrust bearing. or self-aligning bearing. i guess the idea i thought it would be good for the vibrations in case the shaft coupling is out more than .002

    doesnt leave a lot of room for error does it?

    have fun on your trip!
  6. Pierre R
    Joined: May 2007
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    Location: ohio, USA

    Pierre R Senior Member

    You reduce by 10% overall. That leaves 90% So you take whats left, cube it and thats what you lose? Looks like politician math to me.
  7. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Indeed....sounds 'fishy' to me.

    Is the NA you are consulting a real NA (ie qualified professionaly) or just a 'boat designer'. BIG BIG difference between the 2, especially in the US.
  8. tugboat

    tugboat Previous Member

    funny thos efigures came form one of the most repsected NA's on this me and you can argue with him./..ill just copy and paste his message to me but keep it anonymous
  9. Pierre R
    Joined: May 2007
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    Location: ohio, USA

    Pierre R Senior Member

    Hmm, guess it does come of fairly close when I do it more than one way. mea culpa
  10. tugboat

    tugboat Previous Member

    yes--based on the west coast, he is a regular poster to this site...i looked at his site and contacted him since I ve seen pics of his vessels...
  11. tugboat

    tugboat Previous Member

    it made sense to me when he put the number sout--it really threw a wrench into my plans ..I am not sure how to compensate for the loss of displcement..any this worth doing even?
  12. tugboat

    tugboat Previous Member

    I had another quote to do a new design- it was quoted at 5500.00 me a fair quote...but just not viable financially ---one way or another ill have my tugboat but just still figuring it out when all i want to do is start the build--I may just buy a hull --
    its 15 000 cdn.

    Attached Files:

  13. apex1

    apex1 Guest

    A lot of money if it is in a condition as bad as it looks.
    But possibly it is better than it looks, and has some of the important gear running with no, or little effort?
    Replacing a plate or two is a much easier task and much cheaper than building the same area from scratch.

    You have to be aware though, that if there is no substantial value in that boat, like engine, gear etc. you will end up with a costly restoration.
    Then you will not save much money, if any, compared with a newbuild.
  14. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Hi Richard, Well done. I noticed that your replies have become pleasant and to the point. I start liking you and if you carry on with replies like this one, I may even ask you for advice in the future.

    Tugboat, should you ever take a loan out from the bank, you have to manipulate it in such a way that you get at least 30% more money in your pocket. Just to enable you to finance any unforeseen hiccup. The last thing you want is to have a hull or boat and you run out of money to have something repaired or modified. It is different in my case, I like to experiment and if it goes wrong, bad luck I had fun. But in your case, if it goes wrong, the last thing you want is to have to pay month in, month out to the bank without having the pleasure from your purchase. Enjoy your dream, go for it, but be careful is my advise

  15. apex1

    apex1 Guest

    You are 6000 posts late buddy. I did not "become" pleasant, I am, and always was, frank, honest and straight, but never polite or pleasant.
    And that will remain so.
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