Joining longitudinals to the frames

Hello everybody,
I´m a new member but I´ve really enjoyed reading the forum.
You know what you are talking about and you answer politely.
Thanks.

I have a question:
Is there any significant difference in strength between joining longitudinals to the transverse frames by "backing" instead of notching?

By "backing" I mean butting the longitudinals to the back end of the frames.
(i.e. the longitudinals are welded to the hullplate and after that the frames
are butted "on top" of the longitudinals.)
Both the frames and the longitudinals will be made in angle iron.

I can´t ask the designer because there isn´t one.
I´m going to "smack together" a steelboat without plans,
although not without a plan.

Kind regards
Kaj Westergard

 

Not anwering your question cos I dont quite get it, but why invest in steel & time in some thing smacked together ?How about investing in plans from a designer with good resale value second hand and build that instead, it will be cheaper especially one day when you go to sell it.All[nearly] your questions will be anwered- you can just get on with the job at hand of building the boat-stock plans are terrific value- good NA's save you money & time.Best regards from Jeff.

 

There are no plans quite like......

I think you are right, but...

I´ll do the building seriously, but I don´t really mind what the "design" will look like.
I´m "designing" the boat from the inside. Meaning that I decide
what facilities I want , kitchen, double bed, etc. then I´ll build a shell
around everything.
I´ll make as much "boat" of it that I can but it is not my first priority.
Simplicity of build and liveability while in harbour are my first priorities.

I´m not going to take the "boat" very far -
Sweden-European channels-Turkey is quite enough for me.
(people are sailing on logs from Cuba to the US)

Nobody has such a plans for sale and I don´t want to pay for customplans.

Resale value for me, means "not daring to express yourself".

"I may be crazy, but I ain´t stupid".

Kind regards
Kaj Westergard

 

I beg to differ - have you looked at Jay Benfords boats
http://www.benford.us/ They certainly maximise living space, particularly his Florida Bay Coasters.

I'm with Jeff here - the money spent on a design will almost certainly be re-couped when it comes time to sell. And without wanting to cast aspersions on your own talents the results will probably not only look better, but will be safer too

 

Hello Jeff and Will,


You are absolutely right about the resell value, but I don´t care
about the resale value.
Am I rich? - not even close.
The aesthetics, well - "beaty is in the eyes of the beholder" but I think
you are right there too.
Safety - propably you are right there too.
Am I too stubborn for my own good - well - Your guess is as good as mine.

I am familiar with Mr.Benfords designs, I have a couple of his books.
His designs are far too complicated to build (according to me, nobody sane is saying that) and Philip Bolgers boats are too small.

I´ve read a couple of "steelboat-building-books" but I can´t find find the answer to my question:
Is butting the frames to the longitudinals significantly weaker than notching them together ?
By the way; Some people call "longitudinals" for "girders" or "stringers"

By notching them together both the longitudinals and the frames will be
welded to the hull plate. It may be that notching is stronger.
But I think that notching can create hardspots, and more possibilities for rust
to occur. The notches can also become stress raisers in the frames and lastly they are more work.

I was hoping for an answer like: "yeah sure you can use the "backing" method if you beef up the longitudinal and frame scantlings by 15%".

Anyway:
Thanks for your comments even if I´d prefer that you´d be less sane and more supportive - we only get to have our fifty-years crisis once.

Kind regards
Kaj Westergard

 

Kaj, if you want fast building the fastest "boat I ever saw built" was a pileing rig the basis of which was a box with swim end fwd & cutaway aft to house propulsion & rudders, framing was unequal angle set longtitudinally between watertight bulkheads, the longtitudinals left short of bulkheads & bracketed through slots then fully welded to seal. Bottom & deck plates overhung side plates for fillet weld both sides.Every thing was heavy, she was fabbed up in a fortnight, welded complete with gorgeous half pipe sponsons in short time, those boys just kept the triggers pulled- absolute poetry to see-so simple that she had a delightful industrial elegance of purpose- an aura even, I think.Best regards from Jeff.

 

Hi Jeff,
That sounds like something for me

I´ve been reading the postings at "boat design".
I found an answer to my question (kinda) they are
called "floating frames" too.

There is a marine arcihtect posting at boat design
and he had inspected a sixty-footer with floating frames.
Not good (according to him)
I guess I got my answer.

But I also got a new problem from the postings att boat design,
it´s called "cold feet".

Par, a senior member at boat design, told a story of a boatbuilder
(for thirty years) who designed his own boat . The boat was a total disaster.
(couldn´t keep her on her feet)

Here is the scary part:
It so happened that I was talking with a friend only last week
and we were discussin my machinery needs for the project
when he told me that there is (here in Stockholm) a guy who
designed his own boat and that when launched, the boat was
a total disaster so the guy just dumped the boat.

Same story, twice in a week -
"is somebody trying to tell me something?"

I´ll keep you posted

Thanks for listening

regards
Kaj Westergard

 

Notching the frames is better with steel building, the longitudinals will fair themselves, providing all is fully welded there is no problem with weakening. Your method is not recommended , nor is your amatuer approach without some professional input.

What sort of vessel did you want to end up with? I have some plans available for easy build seaworthy steel chine hullforms. Once the hull gets over 45 feet on the waterline you have many options for the internal layout for the do-it-yourselfer.

 

Thanks for answering

Thanks for answering MikeJohns.
I begin to really understand that "notching" is the way to go.

However I´m not sure what you mean by "fully welded"
Surely you don´t mean "continuosly" - or ?

I take it as meaning "when finished".

regards
Kaj Westergard

 

something like this

Hello MikeJohns,

Thanks for answering my question about floating frame construction.

I hope to end with a " wide-beam-channel-boat" capable to be taken from Stockholm to the European Continent on her own keel.
Size: (approx.) Loa. 54feet Lwl. 50feet w. 13feet d. 2-3 feet.

Priorities:
1. Liveability in port (99% of the time will be spent in port)
2. Ease of build . (It´s a question of time)
3. Manouvering under slow speed in confined channels.
3. Seakeeping meaning stability (roughness of the ride not a consideration although I ofcourse know it has to do with seakeeping)

"design": straight (flat) bottom, straight sides.

Scantlings will be taken from Dave Gerr´s " Boat Strength "
and similar boats.

Prototype: shoebox size 9 1/2 with one end pointed
No consideration taken to "nice lines" i.e I am not willing to put even one hours work to get the boat "good looking".

I have two problems with "my design" (as of today)
1. I don´t know for sure how deep she will float.
2. I´m not sure of the dimensions for a Schiller rudder.
Two minor problems of mine are:
A. I´m not sure how I´m going to "design" the pointed end.
B. I´m not sure about the after end either

Kind regards
Kaj Westergard

 

Kaj.
I live in Hobart, Tasmania which has a population of about 250,000 - not many.
I have personally watched two boats built by owner-designer-builders simply sink at launch time. Since I've probably only seen 1/2 a dozen such launches in total, that's not good odds!
The moral of the story is simple: the money you invest (and I use the word advisedly) in having a boat professionaly designed is money VERY well spent.
I would also suggest that if you are going to spend thousands of hours building a boat then you might as well make it look good. I'm not talking about fancy finishes or perfectly faired panels, just the overall look.
It's not simply a matter of how the thing is put together - there are other -not inconsequential - issues as well: weight calculation, centre of buoyancy, stability etc etc etc.

Alternatively, you could buy yourself a barge and fit it out yourself. You would save yourself a year or two in the build time and at least you'd know it would float!

 

With notched frames the resulting gap is completely welded if you like all the missing material that would have been there is welded back in. The frames then suffer no weakness at the notc points, in reality a fillet weld of radius equal to the thinner memebers thickness on both sides will give a stronger frame at that point than before it was nothched. One of the great advantages of steel over other materials is 100% weld strength.

 

Are you familiar with the design known as a Scow ? In NZ the timber scows were built all flat faces and hard chines basically as you describe. They added a centre board case and lowerable centreb. for sailing ability. As river cargo boats they were very shallow draft. You could use a similar bow shape.

As for floatation depth, that is down to the weight of everything aboard relative to the displacement of the hull at design waterline. Design your shape, work out your plating and framing on Gerrs scantlings ( if thats what you will use I think they are OK for steel ) find the mass of the hull from the metal used. find the volume of the hull below the waterline, the weight of this water displaced is your total mass of hull and interior fitout etc.

But you could do with getting hold of a book like "how to design a boat" by John Teale (I think), I find this book a very good one to lend to aspiring boat designers. Once you have grasped its content then start asking questions.

Good luck

 

Kaj, definatly get some paid for pro advice- proper engineering often means real material savings over "winging it" & overbuilding- steel although a "cheap" material still costsA$900-1800 per tonne- soon adds up & affects a whole string of other stuff, & you'd get heaps of peice of mind on structure + stability.She sounds a bit narrow compared to barges we have here, but we dont have canals like your talking of.Regards from Jeff.

 

I could put you in contact with fellow that built a boat very similar to what you are describing. It is a steel scow about 50' long that he lives aboard and has a machine shop aboard so he can pick up work here and there where ever he goes. It is reasonably attractive and he built it very quickly. I don't know offhand how to contact him, but he is usually somewhere here locally in the winter and wanders when the better weather comes around. If you would like me to contact him and see if he would care to share information about his vessel just let me know.