building a 25 ft Tug

Back in the mid 80's, in Florida. Tom has built many of his own designs and was finishing up a 40 footer under a carport type structure behind his house. I had tracked him down
as a friend of mine was building a "Gazelle" and had some questions that I couldn't answer. Called him and was invited to visit. Great guy. Had lunch and dinner with Tom and family.

A couple of open "C" shaped hunk of plate tacked to the plate to be moved or positioned
and also to the adjacent receiving plate may be brought close by driving a wedge shaped hunk of steel between them. Effectively pushing the out of position plate toward the already welded (receiving) plate.

 

One of the problems ive noticed when i unroll a developed surface in my rhino is that it shrinks. if you are not perfect with the frames and set-up-forget those plates ever fitting--this is the main reason i would never get cnc cut plates..i think its better to template it then cut the plate--

btw i cannot afford a plasma cutter--1100.00 u.s. plus the compressor which ill need anyway, but i cant justify that cost for one build-

but i did have a question-

prior to the invention of plasma cutters- how would metal workers cut out things like the chine slots, scuppers, plate etc?..the issue is i know to use the torch- but after you cut the slots i.e. circle portholes etc the jagged edges need to be made smooth
**how do you clean up the edges if you cant get the grinder into the space just cut-i.e. like a porthole circle or scupper..how do you clean up and make the edges nice inside the circle?? same apllied to the chine slots?..i figured a drill press for the chine slots...likely ill cut my plate sections using a compressor and a grinder or a torch...?
but how to smooth the edges of a closed circle-or other shapes too small to get a grinder in...??????????????????

 

Got Tom's books, in fact I'm building one of his designs. I've swapped a lot of emails, me asking dumb questions, he patiently supplying very useful answers.

Keep in mind I have a fully enclosed shop to work in, with a full concrete slab. This influences what works for me & what doesn't for someone else.

I tried Tom's technique using wedges but found using a porta-power much more efficient for the bottom plates. I also tried Gil's technique using threaded rod etc & pulling from the inside. This also works but is slower IMO and you need to cut the rod off & grind back. PITA. Some ways work better in some places than others and the only thing to do is try, if it isn't working go & have a coffee & try a different way. Something will work. For the topsides plates I tacked heavy angle from the deck edge pipe to the chine then hammered in hardwood wedges to fair the plate against the stringers. That worked pretty nicely.

If you're working outdoors then yeah, flux cored is the only way to go if you're using a MIG. Otherwise your welds will be full of holes. Nothing wrong with the weld from flux-cored if your technique is OK.

NFI what 10 gauge is, I only work in metric and sorry but I'm not bothering with units that are obsolete and used by maybe 3 countries on the planet.

I go through about 2 E cylinders (4m3 gas more or less) per 15kg roll of wire. I've used up a lot of gas & wire, more than I thought, but a lot of the wire has ended up on the floor after grinding back so a better technique would have saved me time & money. Next boat maybe.

There's no right way, upside down or rightside up, whatever works for you. If I were to build without any overhead cover at all (which I wouldn't ever do, I'd knock together a temp shed first) I'd build upside down so the crap etc falls away. I don't agree with the argument that the welding is easier, you need to weld both sides of the seams and welding plate to stringers overhead is going to be a king sized pain in the neck. If you need to push the plate to the stringers, good luck because you don't have a skyhook whereas pushing against the ground is easy. There is a technique of wrapping a chain around the hull & pushing with a jack, this does work but it's easy to push too far if you're not careful.

The Lincoln welder sounds like it'll be OK. Not a lot of metal in flux cored so I'd want to be running wire bigger than 0.8 or 0.9mm, at least 1.2. Cold laps are not what you want. Practice and cut your practice bits apart until you're confident the welder settings and your technique are right.

Don't expect anything except going over time & budget. I have.

PDW

 

Plasma cutter cost me $600 AUD. I already had a small air compressor; great for using staples when pattern making too. I would NOT build a steel boat without a plasma cutter. A 50A unit is sufficient. Claims that it will cut 16mm plate should be ignored but no problems on 6mm, adequate on 10mm, 12mm is marginal but will work. Buy lots of cutting tips and an air dryer for the compressor.

See attached pic. This is how I cut my plates. Template from hull, transfer template to sheet of steel, draw around it, move it 4mm off the cut line, then cut with plasma cutter. The HAZ is so small, you can ignore it. Repeat for each side, clean up edges and you're done. Good luck doing this with an oxy torch....

As for cleaning up small openings, I use a die grinder.

PDW

 

Exactly what PDW said. I have a decent plasma cutter and didn't know how much it was really needed/useful until I used it for the first time!

 

There's no right way, upside down or rightside up, whatever works for you. If I were to build without any overhead cover at all (which I wouldn't ever do, I'd knock together a temp shed first) I'd build upside down so the crap etc falls away. I don't agree with the argument that the welding is easier, you need to weld both sides of the seams and welding plate to stringers overhead is going to be a king sized pain in the neck.

**** the idea of building upside down is that you do most of the plating flat position because with the inside welds-overhead- you just are doing tacking to the stringers..if you do some stringer welds- then you can right her and again use flat position welding -the inside can then be welded up...truth is with this hull built upright-your welding largely overhead...

Don't expect anything except going over time & budget. I have.
****my last boat i built underbudget-but of course i always overquote for the budget so there are no surprises...but thats me.



I have a quandary- I have been doing a lot of thinking--this hull was designed for flat bottom -and i am told its very seaworthy. im guessing adding the v hull to it is more work, has some unknown variables and for sure more time --so i thought id build her flat...but-HTH would I build her right side up??
the problem is this- the frames because they are simple square frames must be supported by the strongback of some type- hence how do you plate the bottom?- on my modified version- I simply would have set up the 1/2 inch keel and stem in the ground as colvin suggests...but you cant with this design unless you use a large unnecessary inner keel frame which then wouldm protude through the floor...
so for this hull if built flat- my thinking is- you plate the sides first- and the deck- to give rigidity to the hull- then the hull can be blocked and still assume the shape needed...this allows me to plate the flat bottom in sections- however, another way is to do the bottom first--ie. cut it to shape
block that into position- and mount the frames right to that - again huge hassles--so to me easier to plate the bottom in one large plate (if i have hoisting equipment) while inverted..tack it to the sides and perimeter and tack it to the stringers- then right it for the major welding inside the hull..??

 

Good luck doing this with an oxy torch....
**** yeah- for plate like that- i could still use cutting disks --yep-it would take me a hell of a lot longer and id go through a lot of disks maybe- but still not 600.00 worth! i agree though -a plasma cutter is the way to go--i am looking at some cheaper chinese ones..how big a compressor do you need for a 50 amp plasma?


As for cleaning up small openings, I use a die grinder.

AHA~!..I have never used one--maybe my inexperience showing here but -now i get it...

****so how would Colvin have done it prior to plasma?..they are relatively new in mainstream- even ten years ago no guys i knew had plasma's- in fact the tug company i worked for still used cutting torches-of course the guy i saw doing the work could cut a 1/2 inch plate like butter and needed no cleanup-or very little--i bet you -he could cut that plate out without much distortion or clean up- but- he was a pro..im not.

 

The cheap Chinese plasma cutters are perfectly adequate, that's what I have.

Oxy torches aren't great on thin material. You use a sheet metal tip which helps but there's still far more cleanup AND you can't cut to a template AND the cut is slower. All in all, not great. Not worth it IMO for a tool that costs about the same as a single sheet of steel.

Cutting disks work but I think your time budget is going away, plus you can't cut complex shapes as I can with a plasma cutter. Also they're not cheap in bulk. I have used hundreds of cutting & grinding disks.

Horses for courses. I use an oxy cutting torch on 16mm and up, plasma on 12mm and down. No way I'd part with my plasma cutter, in fact I'm thinking of buying a bigger one and ditching the oxy gear altogether. Bottle rental is a killer and I can't own them (don't ask).

People used cutting torches in the old days because there wasn't an affordable better tool. Like using a MIG vs a stick welder. Both work, which is faster & easier?

Small benefit of the plasma cutter - my waste pile at the end of this job is going to be tiny. Most of the offcuts, I've been able to re-use for brackets, gussets, strips of plate etc etc. My waste pile if I were using a torch would be a lot bigger.

Compressor size - a little 2.5HP (joke rating) unit from the hardware store has proven adequate. Minimum 8 cfm air delivery I'd say. A bit bigger would be better; I bought this one to drive a nail gun originally. No way was I firing up the big compressor just to run the plasma cutter, not with a 25HP motor.

Some hull forms pretty much dictate how they're to be built so you go with the flow. With a full length keel, mine was easy to build right side up. There's very little o/head welding incidentally, mainly horizontal/vertical and the inside nearly all flat except the vertical seams and the deckhead.

I tacked most of the deck on first to stiffen the entire structure, then the bottom plates, then the topsides plates. Worked for me. That was Tom's recommendation for this hull shape. Other hull shapes need a different sequence.

Got to get back to it now as I've been working on another project for a few months. I moved the hull back 400mm from the big doors yesterday so I can add the bowsprit stub. That and the engine beds are all that's left to do other than some padeyes, cleats and lifeline rails etc on the weather decks. Fiddly jobs that take quite a lot of time but what the hell, I've spent some of the downtime planning the interior anyway.

PDW

 

I have a quandary- I have been doing a lot of thinking--this hull was designed for flat bottom -and i am told its very seaworthy. im guessing adding the v hull to it is more work, has some unknown variables and for sure more time --so i thought id build her flat...but-HTH would I build her right side up??
the problem is this- the frames because they are simple square frames must be supported by the strongback of some type- hence how do you plate the bottom?- on my modified version- I simply would have set up the 1/2 inch keel and stem in the ground as colvin suggests...but you cant with this design unless you use a large unnecessary inner keel frame which then wouldm protude through the floor...
so for this hull if built flat- my thinking is- you plate the sides first- and the deck- to give rigidity to the hull- then the hull can be blocked and still assume the shape needed...this allows me to plate the flat bottom in sections- however, another way is to do the bottom first--ie. cut it to shape
block that into position- and mount the frames right to that - again huge hassles--so to me easier to plate the bottom in one large plate (if i have hoisting equipment) while inverted..tack it to the sides and perimeter and tack it to the stringers- then right it for the major welding inside the hull..??

 

OK, it all depends (as usual).

If you build right side up, is the bottom going to be a single sheet of steel? If it is, no butt welds, fine, it's possible. If not, think about those butt welds in the bottom plate first.

Build a gantry. Plenty of examples out there. I needed one, Sandy & Gena needed one, Murielle needed one, you're going to need one. What you build will depend on available materials and the ground you'll be using it on.

I'd set up timber cribbing to elevate the plate to say 500mm off the ground, comfortable sitting height on a milk crate or similar. I assume the beam is fairly moderate so you shouldn't need that much timber. Lay the bottom plate down and tack the stringers/frames to it, then tack on the other plates in whatever sequence works. I'd probably do the deck plates for 2 reasons. First, it helps stiffen the structure further. Second, you can get inside easily from the side, cutting down on the climbing up/down. It's surprising how far you can weld leaning in from the sides towards the centre.

That hull might be better built upside down, though. The flat bottom would worry me a little, getting it flat because you'd be using it to erect the frames on. Good setup of the underlying timber supports would help but if the steel isn't really flat then pushing on it might be a pain to do. Upside down, with the frames & stringers done & braced, then laying the bottom sheet in place may well be a better way to go as you can push down by various means. Not the end of the world to have to turn one over.

Lots of angle iron for cross bracing is a really good thing. Leave it in place until it annoys you working around it or you're finished tacking the hull together, better still finished welding it together on at least 1 side.

What does the designer say? Has he ever built one (as opposed to designing it)? If not then unless he's supervised a build or 2 and knows from experience what works, he's doesn't really know which way is best either.

I wouldn't screw with the bottom for a first build where serious money is at stake. I thought of a lot of changes to my hull I'd like and resisted every single one of them below the WL. The one change I did at deck level is causing me to chew up a lot of time redesigning the steering position and I'm not happy. I didn't ask the designer first and am paying for it but at least it doesn't affect hull form or stability.

PDW

 

I figured that doing a build upright would be harder with this design because if using a keel-you can just do it in like Murielle did it. I figured that upside down would be easiest. The designer having built one is a good question-by the tutorials that came with it it sounds as though he has some metal boat experience...but i cant say...The gantry- yep- ive been thinking about this one- i liked Murielle's- so i think ill base it on hers. The gantry shouldnt be too hard the only real issue is what axle to use and what wheels to put on it...
I will need lifting equipment --since ithe steel supplier tells me i must lift the steel myself with a rig or ramp or something...seems odd but true- so ill have to make on--maybe though if i made two it would be cheaper than having it craned at the flip day?..might be able to use chain falls...?

whats your estimates on time regarding not having to do the larger hull?..the actual sq f'tage of the v hull is actually less by a few feet than the flat hull but the v hull has the extra centerline keel/stem/keelson to it- one thing that confuses me is he says the vessel (flat bottomed) has a full keel, but is he referring to an inner longitidinal running the centerline? or is he referring to the skeg deadwood etc and calling it a keel? in colvins book the flat bottom designs dont really have a centerline inboard keel they have stringers same with a barge....so this tug hull is essentially a curved bottom barge with a model bow and fantail stern...

 

the following images are the Mal Low designed "porker which is the hull form I have been basing my boat on.

I have have recieved written permission from the designer to post these renderings-which i have done up in rhino using the offsets given in the plans i bought.

In my opinion this is the nicest looking tug ive ever seen perhaps as nice as the 45 ft Alden tug. The plans can be had for a mind boggling small fee through his website. He send the plans with tutorials and considering these are designed for amateur builders, they are incredibly seaworthy from all accounts that i have read including the designer. so flat bottom it is...

I chose this design because of the ease of construction-the ease of build and the lower fuel savings while underway due to the easy run of the hull.
It is seaworthy and i trust the design. It has an added bonus of being beachable- in the plans are bilge keels but I will use two long keels and a center skeg. I also have omitted the twins since i have violated my own rules of k.i.s.s. so im doing away with twin screws based on advice from two n.a.'s.
and becuase its a hassle for little gain.
- if your reading pdw, there is a nice example of a cruising st pierre type dory not unlike this in Colvins book. range 1000 miles designed to go to the carribean.


ive added a few things and subtracted a few things-
1. changed the wheelhouse accomodation for more deck space by decreasing beam
2.removed the twin screws..
3. removed the v hull
4. followed the designers plans more closely.

I have decided to build inverted and have it turned.
Ill use 10 gauge on the sides and 3/16th plate on the bottom.
and 10 gauge checker plate for the deck.
Im waiting for noront steel to get back to me regarding doing a cnc cut for the four panels- the deck-the bottom and the two the sides. ill weld them up origami style and add stiffeners after.ill plan to use heavy stiffening on the bottom to allow pounding and eliminate or reduce oil canning.

the bottom of the hull will have wooden floors to cut costs. and add a bit of warmth in the living spaces.
there will be a v berth forward, a tiny galley- and head, and a small shower ...
after she is built ill fit out my barge and push it with the tug..
itll be a month ortwo before the first full size sheet is ready but the sides will be pulled together first..ill investigate origami more...i know of a guy doing a 74 ft'er in that style and have seen a nice 65 ft'er in that style--

should go fast...
ill have alot of downtime and i plan to sand down the hull plates with flapper disks...i have discovered i can do about 1 sq ft of steel to white metal in about 45 seconds - this means for the plate- doing 1100 sq ft (550 sq ft for four surfaces) x2. I can get enough flapper disks to do this for about 180.00 u.s. this means that it will take me around- 13 hours to do..
thats a weekend of hard work compared to sand blasting. ill paint with coal tar epoxy....

the plan is to launch her after then hull is done and live on her while fitting out...

 

i moved the wheelhouse forward i like this better