jet booat design

Discussion in 'Boat Design' started by tugboat, Dec 30, 2013.

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  1. viking north
    Joined: Dec 2010
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    viking north VINLAND

    Agree on the tugs. Back in the early 80's I almost bought a small 39ft.wooden hull working tug in Mulgrave N.S. It Had this huge Cat engine which kind a scared the hell out of me visualizing fuel consumption and maintenance. A few years ago I had first option on a 34ft. Polish lifeboat which had that bluff bow and rounded fantail stern of a Tug. Would have made a beautiful Tug or heavy motorsailer. Oh well water under the bridge-- One boat at a time and in the long run I think my present build/conversion will prove out the best choice.
    Building a jet boat from scratch, my choice would be alum. It will take one hell of an impact before punch thru due to it's ability to absorb the load by stretching. 5052, 3/16 in. is beautiful to MIG with a good unit. Less thickness is tricky for a non professional welder and lends itself to slow but less susceptible burn thru using TIG for the less experienced. If one can weld with oxygen /acetylene Tig should be a fast learn. Tigging alum. and stick weld using stainless rods are my best beads. This comes from many hours of experience with stick on steel and oxygen/acetylene bronzing. Welding is like music , practice practice practice. Worked for the welding but I still struggle with the "get box" after 40 yrs. It's why I seldom play onboard, some of my notes could set the whole thing into it's natural resonance :D


    A yacht is not defined by the vessel but by the care and love of her owner ----
     
  2. tugboat

    tugboat Previous Member

    Viking north, do you have a link to your present conversion/build?. Did you see the vids I posted for Barry??
    check out on youtube just type in aluminum vs fiberglass...watch the impact test at around halfway...you'll be surprised at the results...

    economically speaking they are roughly the same if using standard frp layup's like biaxial.
    but I wanted to go with carbon fiber and Kevlar which adds about 4000.00 extra to the hull build which puts it out of reach.

    I am thinking of using a light wood then coring it with biaxial.

    and epoxy is smooth and great abrasion resistance. Al would beat it in that dept tho. but not the impact dept. if done correctly.

    beside core wont deform.

    overload frp and you reglass it later- overload AL and you bend it back with some 2x4's and some jacks.

    the sad fact is I don't have the required 220v's right now to weld Al. so it is going to have to be in core. unless I pay 700.00 for a genset and another 1200.00 for a welder...
    how hard is it to learn to be effective at tig if you never brazed? I never did a lot of brazing but I did learn to weld very easily? Could a 115 v. miller or Lincoln mig 3/16th Al? I can get a good tig in the 550.00 range. its an inverter type. 115 v.


    I had to laugh at your earlier quests for a boat when you came across the one with the cat- you made the right choice. I dabbled a little in cats for my tug design. I bought a cat d318. it weighed in at around 3500lbs! had a huge 3:1 gearbox. I suspect it would have run a good 6-8 gph. but they are pretty good for maintenance...better than the old 2 stroke gms. such as the 6-71.
    my cat turned a prop at 1500 rpms but geared down 3:1, would turn a 36 inch fan.
    keep on playin'...I was a pro musician. made a living in Toronto.
     
  3. Barry
    Joined: Mar 2002
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    Barry Senior Member

    You can use a Miller Multimatic with a spool gun to weld up to 1/4 inch material with a 110/120 volt single phase input source, 20 amp. Might be some other 110 220 combined units as well

    The multimatic can also do stick, and with a contactor, Tig as well,

    About tig vs mig

    While tig is fine for thin metals say 1/8th or less, the speed at which you weld with tig as compared to mig is a lot slower, which means that the HAZ, heat affected zone, is larger and sometimes will cause more distortion. Aluminum will lose much of strength properties when you heat it, up to 50%, so you really want to minimize the HAZ zone if you can. More impact to 6000 series heat treated material but also affects 5000 series hardened series aluminum. Some good time spent googling this issue


    We rarely used tig, though we had several tig machines in the shop, to weld a boat.

    Note when you weld aluminum plate together, you will almost always weld both sides, you would weld one side, then get to the unwelded side and take a circular saw and back cut the seam down into the backside of the weld until the you are at the point where the weld is complete. You can see this pretty easy, as there will be a thin line where the plates are touching when the weld is not complete.
    This can be a little dangerous when you are in a valley and backcutting the weld as you have to expose the blade quite a bit out of the saw. Often the saw will buck back so be careful. Then you can weld the back side.

    The other area that we see rookies make mistakes is the grinding of exposed welds that you want to clean up for appearance.

    If you use a 7 inch grinder, you must lay the ENTIRE disc flat so that the disc is in contact with the entire 7 inch of the disc.( So you need a depressed center disc to make this happen) That way you will not undercut just the area near the weld, which when painted will show up as a dished surface. Before you take a grinder to your boat, take a 12 inch by 12 inch square plate and weld a high bead in the middle. With the method above, grind down the weld. Then take a can of high gloss black spray paint, and paint over your grinding job, if you have dished the welded area, then you did not hold the disc flat when you were grinding.
     
  4. viking north
    Joined: Dec 2010
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    viking north VINLAND

    There you have it in a nutshell and well said, but alum. welding requires a learning curve regardless, especially when operating on the edge of input power as a 110 unit will be. It can be done but what is easy for the experienced can be pure hell for a beginner even with the best of gear. Let me put it this way I've never seen 110 v powered Migs in Welding Trade Schools. :). While at 69yrs. i'm not exactly a beginner ,I've always found it more economical to pre cut all my material to a certain stage and then hire a pro to do the heavy welding using me as the helper /gopher. ( in your case he will have a small self powered 220v mobile unit)Better to put a few bucks into a used or new 110 V plasma cutter, a good basic air dryer, A big tank 110v compressor, and a good assortment of alum. specific grinding and sanding abrasives along with a few stainless wire hand brushes. In addition pick up a couple of circular saw/table saw metal cutting blades and stick coolant/lubricant (regular wood carbide blades are quazi dangerous in alum.) (the stick coolant/lubricant prevents alum. bonding on the cutting teeth and allows saw cutting of the alum. as if it were butter regardless of the thickness. The only downfall you'll need a specific cleaner prior to welding. Ok had to leave the post -- someone at the door -- To continue --This will allow you to pre cut your material and do the trial fitting and doing so,finally getting to use the 500 pairs of Vice Grips you had under the bed. If all is within 1/16th. tolerance :) Just kidding, 1/8 to 3/16th open seams should make it fun for Barry when he arrives, Ha Ha . getting serious --aluminium would be my choice for this project bar none--don't get hoodwinked into these space age material ads, they are bitches to work with and even bigger bitches to repair.
     
    Last edited: Dec 31, 2013
  5. Barry
    Joined: Mar 2002
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    Barry Senior Member

    QUOTE viking north Let me put it this way I've never seen 110 v powered Migs in Welding Trade Schools. :).

    Barrys comment; I have not used a 110 volt either but many manufacturers make them but Tug could fit and tack the components and then just have a welder do the welding. With this size of boat, it is unlikely that he would have any plate more than 1/4 inch

    A big tank 110v compressor, and a good assortment of alum. specific grinding and sanding abrasives along with a few stainless wire hand brushes.

    Barrys comment; not sure why you would need a compressor or a plasma cutter, as all cuts can be made with a circular saw and a jig saw.


    In addition pick up a couple of circular saw/table saw metal cutting blades and stick coolant/lubricant (regular wood carbide blades are quazi dangerous in alum.)

    Barrys comments; the metal circ saw blades are better but we never use a lubricant on a saw blade. There is too much risk of contaminating the weld area if you do not clean it up 100% for which you need a fast drying, ie high volatile hydrocarbon which will not leave any residue. Toluene, Trichloroethane, etc not paint thinner which is a diluent ( which thins) as compared to a solvent which reduces the lubricant and can leave a dry clean surface. But these high volatile liquids can produce unhealthy gases in the presence of an open arc and of course who wants something as flammable as gasoline in a welding area.

    If all is within 1/16th. tolerance :) Just kidding, 1/8 to 3/16th open seams should make it fun for Barry when he arrives, /QUOTE]

    Barrys comments: for the most part the welding wire can be a little more brittle than the host material so Viking is right. 1/16 clearance is about the maximum that I would have for a joint. Certainly in 1/4, maybe 3/32 of an inch. But no more.
    The Mig welding pass is fast on 1/8 to 3/16 material and a large gap will almost always blow through and then you have to rebuild with very short timed welding interval, like a second or so to build up the hole caused by the blow out.
    This can create porosity and a brittle spot in the welded seam
    Our joke around the shop for our fitters was that butt welds had to be "light tight" before we welded. Of course this is not really possible but fitting is the largest consumer of time when building a hull.

    There may still be a company in Red Deer Alberta that will sell a precut kit for the type of boat that you are looking for, which could speed up the process, Outlaw Marine
     
  6. viking north
    Joined: Dec 2010
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    viking north VINLAND

    Now Barry be honest -- Ya gotta just love the plazma for metal work. I especially like it on Stainless which other than aluminium I work alot. I make rather than buy most of my heavier deck fittings. The great bonus of this tool is it is very reasonably priced it can be used to cut alum., stainless, reg. steel with such accuracy. Wrote my name in 3/4 in. plate steel just for the fun of it. Along with a compressor every guy should have one --:)
     
  7. Barry
    Joined: Mar 2002
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    Barry Senior Member

    The plasma is nice for rougher work, but if you scribe your cut lines, you can work within 1/16 and closer to 1/32 of an inch with a circular saw if you are careful. The plasma leaves a dross that you then need to grind off and the created aluminum oxide can cause some inclusions within a weld which is not a big deal if you clean up the edge with a grinder but it is another process. Plasmas are a lot quieter though and do have their place. We had a 125 amp Hypertherm and never used it on a boat. Depending on the cut, you can have some heat distortion created with the plasma cut, ie the plate is moving as you cut it, while with a circular saw it is not an issue.

    Different ways of doing it, but as I mentioned before, a full 1/16 inch to fill on 1/8 to 3/16 inch plate is just to much.
     

  8. viking north
    Joined: Dec 2010
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    Location: Newfoundland & Nova Scotia

    viking north VINLAND

    We have a great service available here thanks to Halifax being a military town, I hear thru the grapevine the industrial park now has a couple of companies that do CNC cutting for a more than reasonable price. Walk in with a computer disc and a bunch of alum. sheets --walk out with a pre cut boat. Great services now that i'm retired --:) Ok Guys gonna sign off the thread , hope there was something in my two cents worth that will prove useful --- Geo.
     
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