welded hull structure options

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chille51
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Joined: Thu Oct 20, 2022 8:09 pm
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welded hull structure options

#1

Post by chille51 »

Hello all, first time poster here.  Have been reading lots and searching past threads but so far haven't turned up quite what I'm wondering, at least in one place.  If this has been discussed before or should be posted in a different area please let me know!

So the situation is I am seeking to get a basic understanding of the various options for hull structure/framing, for the purposes of having an educated idea what I am looking at in my search for an aluminum fishing boat in the 22-26' range for use around Vancouver Island, BC. 

A couple of notes that might help about what questions I am not asking:

- I don't mean the options around different plate thicknesses etc. Plenty of info available on that
- likewise, I am not specifically talking about the shape of the hull, deadrise etc.  Again, it is easy to find lots of resources on that
- not planning to build a hull myself.  100% will be buying a hull already built, either used or new TBD, and assembly line vs custom build also TBD.  But I'm not a welder and not trying to be.
-- not really looking for another debate on Hewescraft vs Kingfisher vs North River vs on and on.  Plenty of those to read (and I have been).  Unless I guess we're comparing specifically the differences in how they construct their hulls, as opposed to just general opinions on quality, fit and finish etc.

What I AM trying to build is a basic understanding of is the inner structure of these types of boats and how they cone together, and the tradeoffs in different approaches.  The framing, foam or no foam, and other things I may not even be aware of yet that I should know.  Not so I can build, but so I can compare different designs and know what I am looking at when I look at a boat I could buy.

I'm relatively early in my search, and in research mode.  Realistically I'm probably 2 years out at least from pulling the trigger.  So mostly looking to understand the fundamentals and separate what really matters from the marketing.

As I said, this is for saltwater fishing off Vancouver Island, both east and west coast.  My priorities are safety, durability, and ride comfort in that order.  If there are other questions I have left unanswered by all means please let me know!
scoter17
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Joined: Fri Oct 21, 2022 9:15 am
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Re: welded hull structure options

#2

Post by scoter17 »

It's a fair question, although the priorities of safety, durability and ride comfort are more seriously addressed by hull shape/design IMO. That said, there's a good discussion on joint design and weld technique that begs to be had. In the matter of the critical welds--those below the water line--I have seen three different weld designs for the chine to side sheet set up: corner to corner, flush and t-shaped. I have heard Lloyds stipulates the T-shape as the strongest of the three, but I'm not so sure. I believe Kevin Morin has supported the corner to corner method as it allows for better hull shape(let me know if this is correct Kevin?). The problem here is if you weld inside first, you've got to dial back the machine or do a lot of weaving to keep from blowing out as there's no metal. Then you have to do this tricky and cold corner weld, using some sort of rolling brace is you're smart. I've been in a shop which prefers the flush technique--aka side sheet edge is flush with the bottom edge of the chine. This is welded from the inside first as a filet then the outside seam backgouged and welded horizontally as a groove weld. There is a question as to whether this leaves a void which is generally unacceptable. The last options the t-weld where the side sheet is inset from the chine allowing filet welds on both side of the side sheet. While unsightly, this one seems most rugged. Any thoughts from welders/designers as to these three methods? Also, what about the preferred sequence of these methods?, Inside first, then outside, or reverse?
chille51
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Joined: Thu Oct 20, 2022 8:09 pm
1

Re: welded hull structure options

#3

Post by chille51 »

Thanks for the thorough response and point taken regarding the importance of hull shape.  I don't dismiss or disagree, but just have found information on that topic, as well as the types of alloys, easier to come by.  Definitely have been reading up on both topics.

I'll admit, at this stage I only really follow about 50% of what you've provided on first read.  That's not a complaint, just an acknowledgement of my own very limited experience onbthe topic and terminology of welding.  I'll need to do a little more research on my own to fully understand in detail, but a conceptual level I think I follow and will be interested in others responses to the questions you posed.

What put me onto this particular topic is actually looking at the websites of various manufacturers and noticing what some of them choose to market as their competitive advantage. For example, from the website of one such manufacturer:

_________ Boats builds each and every boat using a fully integrated and thoroughly engineered stringer grid system. Unlike the common and much easier to build box girder design, a well thought out stinger grid will give each hull an unparalleled strength and in turn is much less prone to cracking or breaking welds.

Certainly sounds good to someone with no knowledge on the subject, and I don't doubt the claims.  But it got me thinking that there are probably only so many basic ways to put one of these boats together, and they probably all have pros and cons, so it wouldn't hurt for me to know what they are.
JonH
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Re: welded hull structure options

#4

Post by JonH »

Hi chille51

Here is the hull structure of my 28' x 10' (not counting the bracket) boat that was built by
Crozier and designed by Hunt.

This structure is basically a scaled down pilot boat, probably overkill in some ways -
12 frames / 8 longitudinals plus CVK, using 5086 H116 Alu.
The side shell plating to bottom platting joint is T-welded.

Jon


 
 
 
 
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chille51
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Re: welded hull structure options

#5

Post by chille51 »

Thanks JonH. Definitely would be interested in seeing what the finished product looks like. Sounds like a solid boat to me!
JonH
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Re: welded hull structure options

#6

Post by JonH »

Here are a couple of photos, it's definitely a solid boat. 


 
 
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chille51
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Re: welded hull structure options

#7

Post by chille51 »

Looks like the kinda rig I have in mind, scaled up. Nice one!
kmorin
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Re: welded hull structure options

#8

Post by kmorin »

chille51,
I've shown this build before but repeat it here in part to help you see the different structural elements that can be used to frame a plate hull in the size range you've discussed.

This skiff is 25'-26' LOA and built for a local lake that is 50 miles long and the occasional salt water trip.  The walk-around cabin is well aft and she has no bunks by design.  This skipper fishes his bow deck not the stern as is more common in this size skiff.

Image

Notice that there's a 'chine line' above the actual chine? The weld line just 8-10" above the hull's chine?  Will make more sense in a few images below.

Image
This shot, bow on, shows there are not vertical transverse frames connecting to the deck just pipe knees 'boxing' or triangulating the guard deck to the topsides immediately behind the tapered, external, unequal legged angle used as main stiffener of the topsides panel AND as a spray rail.  Also notice the sheer has a 1/2 pipe on the outside and a vertical 2" bare inside?
Image
In the post above there's a framing method using ring frames and longitudinals - the skin is put onto that type of frame after the frame is tacked up. The keel and bottom halves with chine plates are all cut out and tacked edge to edge and there is no initial internal framing.  Building on a rotisserie facilitates this method- IMO.

The top of the 'lower topsides' shown here, are where the weld in the topsides shows up in the first image above.

Image
All the hull bottom framing is longitudinal there is only one main transverse bulkhead - forward.  So this type of framing is somewhat different than the more traditional type shown above in the CAD image. Pipes and conduits are for fuel lines, cabin heating propane and main control conduit under the deck from main helm.

Image

here's the main forward bulkhead where the longitudinal framing changes and become flat bars laid to the radial legs on the conic bow halves.  The Vertical Keel Bar is a 1/4" X 12" to 16" deep plate that intersects between the two bottom halves to form a '3-way' weld zone outside and two fillets inside.

So this skiff was built from the deck to the keel first- and has no main bulkheads, except on partial bulkhead forward, below deck or continuous from cabin down to keel. The framing was fit a 'buttock' lines or radially to the bow cone, not wrapped as would be the case where ring frames hold longs notched into their outer edges.  Some builders prefer this method as its saves some framing layout and cutting- if NC cut frames are used there remains significant cut file prep and cost of cutting compared to skipping that element in the frame?

Next post I'll show a few more items to make this concept clear.

Cheers,
Kevin Morin
Kenai, AK


 
 
 
 
 
 
kmorin
kmorin
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Re: welded hull structure options

#9

Post by kmorin »

chille51,

I did use transverse deck beams but.... they don't touch the hull directly so they're dropped into notches in the hull longs or were extended down to shorter hull longs w angle legs laid against each angle and flat bar intersection in plan view.

Image

Image

So decking could be keyhole drilled and fit without any tall sides and work was at shirt pocket height, instead of having to work down inside of the full height of the topsides.  The deck to hull seam was welded while the entire boat was a big surf board- so to speak.

Image

This method allows a very low hour but complete air test of the entire below decks, hull seams, deck and keyhole welds while there is nothing in the way of the inspection and TIG floating the leakers.   In this build I had failed to adequately clean a transverse seam on the deck between two pieces that met on a deck angle supporting the back of those transverse welds. Those were the only leaks, but it was TIG welded using a cold wire feed gun - not a commonly used welding torch but one that does produce extremely high quality welds.

My purpose here, has been to illustrate that welded boat framing really doesn't have to be one way or another?  Of course, like any aspect of building there will be lots of opinions and closely held beliefs about which way is right or wrong- I am simply showing that #1 this class of boat doesn't absolutely have to have transverse framing, #2 They don't need to be build keel to chine and chine to topsides in single plates (5 panel hulls), #3 once the hull is cut to the correct outline of the hull panels, the skiff can be assembled and framing installed after (cold) forming the hull.

chille51, hope these images and notes help as you explore the different building methods of this class of welded aluminum boats?

Cheers,
Kevin Morin
Kenai, AK
 
 
 
 
kmorin
chille51
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Joined: Thu Oct 20, 2022 8:09 pm
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Re: welded hull structure options

#10

Post by chille51 »

Wow, thanks for the very detailed responses Kevin! Like the previous ones, if anything they only reinforce how much I have to learn on the subject. Even basic terminology is mostly new to me, so trying my best to follow along. In terms of just getting up to speed on the basics, if anyone has a good resource to go to I'm more than happy with a "go read book X or look at website Y and then come back" sort of response. It might help me to better understand the purpose of each of the major components - ie the bulkheads, transverse and longitudinal beams etc. I can make some logical assumptions but this is something I can probably research on my own, now that I'm starting to pick up some of the terms.

So, though I mentioned I am not a welder and not planning to build my own hull - I think I follow the advantages of the method you posted - especially from a building/effort perspective. And just making things more accessible while you work. Would you say there are advantages to this method in terms of the end result and integrity of the hull or are the advantages more in the building and this method vs the more traditional one that JonH posted could result in an equally strong hull, assuming quality execution and workmanship? Does it result in a significant difference in dry weight between the two methods?

Are there keywords I should be on the lookout for from the main manufacturers marketing materials that would tell me which approach they generally take? Or questions to ask? Since I'll most likely be looking at either production or used boats, unlikely I will have the luxury of seeing it built or as much input into the design as JonH did. The boats I view will likely be fully assembled already.

Apologies for the barrage of questions - it is a fascinating topic and as you can gather, one I just scratching the surface of. Again, if it is easier to point me to any existing resources that are considered authoritative, I'm more than happy to put in the time with them.
kmorin
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Re: welded hull structure options

#11

Post by kmorin »

chille51, 
Welded boats’ hull panels are quite thin compared to the hull sizes they form. As a result there are a couple of different ‘types’ or purposes of framing elements. Not that all framing isn’t intended to contribute to a very strong, rigid hull but there are main frame elements and ‘local’ panel stiffeners.

In the first case with main elements like deep plates running fore and aft or box shapes in the bilge welded to the hull plates- these are main stiffeners. But next to them will very often be more longs of thinner scantlings or a combination of longs and transverse framing elements intended reduce the ‘panel size’ of unsupported aluminum. 

We could say, and there have been boats built to this theory , that if the plate were thick enough there would be little or no need from interior framing. I’m not sure if the “Strongall” boats are still being built? They were sailboats that were 1/2” and 3/8” thick and had little to no framing as they were so rigid with just thick hull plates! 

If you search for welded aluminum boat framing images you’ll very likely find ring framed hulls with somewhat small longs notched into the outer edge of the frames? That is an example of a main frame element with local panel reduction framing so the hull panels don’t flex or ‘oil can’. In general, welded aluminum boats are framed/stiffened using two main concepts. One stresses longitudinal framing the other ‘ring’ framing or transverse framing.

Both methods have both transverse and longitudinal elements, but they stress one type of framing over the other. To really confuse the discussion, but to reflect the truth of design and building; there are so many combinations of the two main focuses of framing that it would be a legitimate argument that these two are just an arbitrary set of categories? 

In the first design focus the primary depth of the framing elements are longitudinal and Specmar is great example of this where their (open) hulls usually feature two very deep longitudinal plates that run from the transom to the collision bulkhead and from hull bottom plate to the deck. These two main ‘longs’ are usually at about the 1/4-1/3 buttock planes and are combined with other longs and various transverse to create a very stiff boat. Added to this are very sturdy ‘guard decks’ or sheer clamps along the gunwale of most of their designs and they usually have a very deep (side to side) long midway up from chine to sheer inside the topsides. http://www.specmar.com/aluminum-boat-pl ... hull-boats  

While the boats do have transverse frame elements the main stiffness comes from the longitudinal framing elements. A ring framed boat will concentrate the main hull stiffness as transverse framing with longs notched into the outer edges and once all welded- become just as stiff or rigid as the long wise framed hulls. 

Most aluminum hull damage I’ve seen has resulted from trailering the boat. Rollers instead of bunks allows the owner to concentrate much more pressure in a narrow area by using a 10ton nylon strap and pulling the boat to the trailer frame- forcing the hull bottom to deflect under loads it can never experience in the water even in many cases of a collision underwater!  Add a highly stressed pressure point to the hull panel where it isn't supported inside by framing and bounce at 60-70mph highway speeds and you have a real crack potential.  Simply going over to bunks or carefully rearranging the rollers to fit under framing elements will cure these problems. 

Just some notes to go with the thread’s content and exploration of framing methods of welded hulls. 

Cheers,
Kevin Morin
Kenai, AK
 
Last edited by kmorin on Wed Nov 09, 2022 10:06 pm, edited 1 time in total.
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