25' Double Eagle aluminum build (placing stringers)

Barry - Yes, I am aware of the need (and have been practicing) to backchip the other side of a butt weld, before welding it up.

re: backhipping the ends of weld sections, before welding the next leg of a continuous weld - I am aware that you need to do this. Have not practiced it much yet, but was under the belief that a die grinder (best with an aluminum specific bit - larger "teeth" than the ones for steel) was the best choice. I am comforable backchipping with the skill saw, so if it is as acceptable for this, I will try both on a pratice continuous weld and see how I do.

 

Re the query about welding the frames to the side panel.
This is what prompted the starved cow comment

This is where we have seen the greatest issue for the weld distorting the sheet. Especially in the area where there is no curvature or preload in the sheet.
A new welder will pour excessive heat and weld into the joint and distort the areas between the frames. Perhaps Kevins auto Tig set up is a solution though it is new to me.

Kevins skiffs show no vertical (chine to gunwhale) welds of framing in his skiff and rarely do we against 1/8 plate. But occasionally we have to for a watertight bulkhead or certainly the engine bulkhead if it is to be kept separate from living areas.

Northeaster , we back cut the weld with a skill saw with a 80 tooth carbide in a 7 1/4 inch skil saw as well as take the crevice crack out with the same.

When you are making up your plates, and I assume that you will make these up on the ground rather than making them on the frame, when you cut into a butt joint you will see a very small black thin line at the juncture of the two plates appear until you have cut into the solid weld

Adhoc
Why use only 0 temper? Rather than work hardened H suffix alloys?
Certainly when you weld up the joints the weld areas strength gets back close to the 0 temper strength but areas outside of the HAZ can still maintain additional strength without a weight penalty.

What do you normally use for stringer extrusions, assuming that you do or other structural members that are extrusions

I will draw the criticism from welders to be sure as almost always you push an aluminum weld for good penetration and filet control.

But we normally weld down hand when attaching frames to the sides, keeping the pool just behind the arc so we get penetration. The weld appearance exhibits a bit of a cold weld ie higher bead but we have not ever had an issue with this.

We weld continuous on one side and skip weld the back side

I am not recommending this to anyone as it does fly in the face of normal practice but it works.

I learned this from a rather large aluminum builder who has more than 1,000 boats up to 45 feet under his belt and this was their procedure.

 

For the same reasons noted in the Proboat article. The formability of the plate is reduced significantly once you go away from “O” temper. Once you start delving into the strain hardened tempers for hull plating the capacity for easy deformation is reduced. And from a design point of view…er.. why use higher strengths? In going from an “O temper to a H116 or even H321 for example, the yield/proof stress may be higher but its doesn’t translate into thinner plating, not on small boats. You only start to see benefits on vessels over 50m and even then 1mm on hull plating or 2-3mm by the time you get to 100m size. If you wanted to reduce the scantlings on a small boat, then you can do that much easier by changing filler wire, from 5356, which is easier to weld to 5183. But the end results is almost always the same….it’s a scale issue. If you calculated that you needed say 5.15mm plate using class rules, what would you buy??..of course 5mm plate. But if using H321 or changing to 5183 filler wire, that 5.1mm may reduce down to around 4.9mm. But what plate would you buy…yup..5mm. Thus there is no real gain.

On much large vessels this may turn out to be a 12.1mm to a 10.9mm change, thus its worth while, but this is on vessel circa 100m in length, not a 10m or under RIB etc!

I really never understand the desire to use H321 or similar strain hardened alloys…it is a myth that it’s a better boat. The only region it really helps is buckling. Its higher strength means there is a higher resistance to buckling for the same arrangement as one with O temper, that’s all really. I do not know of any plater that prefers H321 or similar strain hardened temper to O temper for rolling/forming plate of a hull. By hull, I mean one with shape, not simple 'flat panel' types.

6082 – T6

Indeed, at least on smaller boats one can get away with a lot more and often not so “standard” methods are used and often successfully too.

But…

Agreed….which demonstrates the importance of:

1) Training and procedures
2) Quality control

Also, don’t let the newbiies weld such locations!!

But I would perhaps suggest this may also be a cause

Having a continuous weld one side and then stitch the other creates localised imbalance in the heat input and thus the strain is imparted into the structure and hence the plate is pulled in unequal directions and unequal amounts.

 

Double Eagle's construction details

Ad Hoc, North, Barry,
thanks for the kind words for what is smaller than a life boat for Ad Hoc's typical work!

Barry, I know the sheets off coils are rerolled but I still find a 'natural lay' and so I still stand them up to see what the sheets 'tell' me.

Weld wise, I'm not familiar with any technique of a full weld opposed to a stitch so I can't remark. I draw a sketch of the entire boat's welds that are balanced. I include the main hull welds and put them in: inside opposed to outside; fore opposed to aft; top opposed to bottom. My goal it so slowly draw a 'noose' around the entire boat- to balance the weld contraction forces and add to them slowly and evenly, so I have not instances of a solid weld backed by stitching: EXCEPT that might occur in the rare fully sealed bulkhead in a larger (for me) project.

In that instance I'd 100% bevel the transverse element and add the weld to both sides evenly until the stitched side was done then 'fill in' the remaining welds to the continuous side.

Topic of welder's experience.
Younger, this term is not related to chronological age) less experienced welders are less aware of the final monocoque or solid structure they're building and therefore tend to think one connection point should be out of proportion to the parent metal.

This is a difficult concept to get across and fair (small boat) hull are dependent on proportional welds.

Barry the 25' outboard skiff has a vertical seam in the topsides at a butt between the 25' topsides and a 'tail' piece to form the stern extension. the little dink has lockers in the stern shown here.



The after locker/seats are bulkheads to the topsides as shown here. This weld was done down hill with TIG into the 100% beveled 0.100" (2.5 mm) into 0.100" topsides. And printed through but did not distort the topsides due to the tension of the shape and the position and size of the weld relative to the bulkhead or seat front panel.



The 25' outboard walkaround skiff has a vertical seam from chine to sheer but its kind of hard to see in this poorly focused image. The vertical discoloration about a foot or third meter from the stern is a vertical seam in the topsides. Both butt edges of the 0.160" (4mm) plates were beveled 50% at 40deg and back to back TIG welds were put in, top down with a face of about 3/32" (2.3mm) on both sides and not distortion.

A larger weld its seems to me, would be out of proportion and therefore this panel would not be fair due to weld contraction.

Ad Hoc, in skiff building the post forming aging and hardening is a blessing for shapes in that are easily cylindrical and conic ( I avoid all flats as too much work to maintain) as the stiffer material can be planned for and somewhat larger (15-20% !!) panels will remain fair and as you note; they still won't buckle.

I rely on the H-116 stiffness in 5086 for example in several basic small hull forms to allow the skin-first build methods I use.

The extent of forming in our skiffs are pressed flanges on straight members, and the increased tensile is welcomed where we can reduce one entire thickness of most of these elements.

North, if your stringers/longs/flat bars are not welded in take them out.

Lay them on a series of saw horses with some 2x6's (IP dimensional lumber terminology Ad Hoc) and batten the bow ends to a thinner depth/width.



This is how to taper your flat bar/Longs. With the bar, laying on a work surface and clamp the angle extrusion so it is exactly along the edge of the bar's inside surface 6' or 7' from the bow.

Read that again.



North this is the only handy image I have to give you the concept of a 'baseline' for you to establish along the edge of you hull long flat bar. The left of this image shows a drafting batten laying along a line until... at a tangent point it curves away to the right. Back to the left is the straight part. If you don't do this with the angle batten layout on your flat bar- the result will not produce a fair line and clean taper and therefore the long will KINK.

Once your the reference or baseline: Then pull the angle so it is at the end of the long/flat bar only 1" from the opposite edge. Leave the angle to bow 'naturally' and it will describe a fair curve. Now, with the two clamps at the 6'-7' parallel, and the tip clamped 1" from the opposite edge, mark with a magic marker.

Next scribe with sharpened tungsten and that will give a very nice high contrast line to cut with a jig saw. This is a difficult cut with a skill saw but whatever tool you use; cut the scribed line, now the long will bend to the ever increasing curvature and remain fair on its outside edge which you hope is the same surface as your frames.

If you can't make the marker mark and scribe without additional clamps to keep the fair curve, add clamps.

I show furniture clamps, but then my onhand illustration was a sheet camber exercise not a longitudinal flat bar taper, it's what I had.

The result is a tapered longitudinal that will relieve more and more as you pull more and more on it so the bend will be only as FAIR as the curve you lay out and cut.

The inside/tapered edge of the bar should be Vixen filed to a fair and shiny surface indicating you've cut off all saw kerf imperfections.

(North, we're not going to explain the alternatives: laying out and cutting diagonals or roll forming the original full section bar!)

I know it will not longer fill the frame notches but that is not a big deal.

And going to an extrusion is possible as well, I'm just showing you how to taper the existing stock, it won't be enough 'weaker' to make any difference. The reason its not in the plans is because most people get excited if they're asked to taper extrusions.

remember not to weld them in, just leave them until you have plate and worry about their final position when more of the puzzle pieces are together.

Cheers,
Kevin Morin

 

Our hull lines are also concial, for obvious reasons, but clearly since our boats are much larger the assumption that I had does not translate when dealing with small/skiffs boats; re strain hardened alloys. Very interesting. All new to me, this small/skiff stuff. Hence asking the Q to begin with.

An equally poor picture, but this is more my thing. Bit larger than a skiff

 

The reason we use the H32 or 116 is to try to keep flexing at a minimum as you have identified. As we do not have to roll the side or bottom plate, we do not have to worry about degradation that the work hardening aspect that it can impart

 

Indeed, as I am learning from Kevin too, many thanks.
This line of thinking for selecting strain hardening alloys for you guys (with small skiffs) is very different from mine, quite unexpected!

 

Kevin - I have read and reread you detailed post a dozen times. I want to be sure that I am understanding, so I have attached a paint diagram (Sorry graphics along with boat building is not one of my strengths).

Please let me know if this seems correct, or if not, where I am astray. I believe I get the concept of using a piece of angle, which bends to a nice natural curve, without kinking easily, in order to get a line on the flatbar, which is to be marked, scribed and cut out, so that the good, original outside edge will be able to bend more easily while still keeping a fair edge.

On the topic of sheet material choices, I am looking at Ryerson's website before calling them for a quote : I see that in 5086 there are different available stock sizes for what they have listed as 5086 H32 and 5086 H116 -Marine. For my use, would either be acceptable, as what if H32 is available in a stock size I can use easily vs the other that may have alot of waste? Is the label Marine on their H116 material description more of a marketing thing wheras the H32 is also a good choice for Marine?
this is from their website:

5086-H32: ASTM B209 and AMS QQ-A-250/7
5086-H116 Marine: ASTM B209 & B928


From another supplier website:

5086 is also in inventory as H32 temper which is a good standard engineering alloy, but it does not have the corrosion resistance of the other special marine tempers.i.e H116

 

Interesting thread. Thanks for the extra information on using these alloys and all the little practices and pitfalls. I've done plenty of stuff as extrusions in the main 6036, 6082 and 6005 alloys generally and mostly but not always T6 condition. Interestingly I have discovered that small dinghy/skiff masts are usually in the T4 condition prior to cutting and welding ie creating the tip taper(s). On sheet stuff, the grain direction is important and the ammount of forming sort of determines the condition.

It is informative seeing how you do this in the real world for this type of application.Some good practice and experience coming forward at both ends of the size spectrum.

 

Northeaster,

Simple answer, no. As noted here too.

So you need to be sure you get a proper ASSET test cert from the mill/supplier showing it is "marine" grade. Same goes for the H32...

You'll be in for lots of trouble if you don't.

 

Seconded, I have had a few instances of the wrong alloy or incorrect heat treatment. Fortunately no one has been hurt and mostly the fault(s) have been discovered in prototypes. The drawings and material(s) called up were correct but the actual item did not conform. Mostly they were normal land based applications but several carried quite high risk, and in one case an item that could have been patented was dismissed, because it bent on test. The latter was a real shame as it was a neat usage, and over strength if anything in the correct alloy.

I personally would not take a chance with any hull where life may be at risk.

Nice neat work Kevin, looks very sweet.

 

batttened long taper

North, yes your diagram does describe what I'm advocating.

The problem you will have is that the 4" or 3" deep long will remain straight if left alone, so aft the master station in the purely prismatic after planing form, the butt lines are naturally parallel. There the stiff straight extrusion is a good material to tie the honeycomb of x-verse frames and hull together into a panel that is mainly flat (but I have argued the scantlings can be reduced somewhat by using strain hardening alloys w/ tension on these alloys, reducing wt, cost and labor).

But forward, a 5086 or 5083 alloy with post production heat treating like H-116 will 'harden up' significantly where the forefoot of the bottom panels are pulled into a conic section. That means you can get by with a shallower long and still hold form (right up to section failure) so in reality, for a small boat, the hull longs can be tapered as you show them and that allows them to be pulled into the frame notches cold.

Not only will the taper allow the longs to pull in cold (due to gradually reduced sections) but the side to side 'wander' or distortion of the cold bent material is greatly reduced too.

So, taper the longs, smoothly in my description not a function of a drawing program without Bezier curves or even Arcs (!) and then the long will deform to the locations of your previously laid out notches.

The thing to recall North, is the vertical leg of your previous batten was 1" or 1-1/2" x 1/8" not... the same section as your final longs. So of course the angle extrusion as a long bent fair and worked as a 'lining off' tool. Where the longs are deeper and thicker so pulling them in is more work.

When the longs are tapered, and the inner most may need more taper than the outer most (using the keel as most inside, and the chine as more outside) the taper may need to be more for a greater curvature and still remain a fair cold bend of the 6061-T6 alloy flat bar.

Ad Hoc, SukiSolo, roll forming strain hardening alloys in cones or cylinders allows entire tanks, bow sections, and transom corners to be formed 'skin only' construction; where there are no other internal framing to support the structure. Of course not in the moments you're working with, but for a five to eight meter hull using cold formed strain hardening materials allows various small boat forms that completely ignore framing. Obviously these areas are subject to failure at the edge of the elastic modulus but that is almost impossible to obtain in a floating small welded boat. In 95% of the impacts there is insufficient vector angle- the incidence of the entire craft is so oblique the reflection of the entire boat happens before the momentum of the craft can bring about hull site failure.

The strain hardened alloy boats I've built have consistently bounced of rocks, logs and any other impact so the hulls have a somewhat 'bullet proof' performance largely due to the combination of the strain hardened alloys' increase tensile and their mass being so low that failure almost never happens. This applies to almost any hull panel of this class of small welded boats, and is the sole design basis for the inboard jet pump driven river sleds of the NW and Canada.

Cheers,
Kevin Morin

 

Thanks again Kevin! I will be working on the boat some this weekend, so will try tapering one to start.

On a related topic, hoping you folks can weigh in on a question re: increasing the hull bottom and perhaps side thickness from 1/8" to perhaps 5/32" or even more commonly available 3/16". Regardless of imperial or metric measurements, lets say I am thinking of adding 50% more weight to the hull by going from 1/8 to 3/16". In reality this would be an increase of about 300 lbs, or perhaps 400 lbs if I use the scraps for the decking, rather than buying thinner material.

At 1st glance, this doesn't seem to be a good idea to me, adding 50% to the hull weight. But, I have stretched the hull the allowable 10% and I assume that thus would obtain some additional buoyancy? Would it be enough to offset the added 300 - 400 lbs?
Note. The design plans have a nice small cabin but I will be saving weight by building a center console. I may decide to add a small cabin in later years though, if it performs well and meets our needs.

 

It's fairly easy to work out the displacement volume from your stretched hull. A crude but pretty effective quick way would be to get the under waterline cross section areas of every 'half station' and multiply by length, then add them all together. If you plot the area (not volume) on a graph it will give a rough curve of areas which will also allow you to guage the weight loading a bit better too. This will give you the total immersed volume which if it equals your weight is the waterline. If it does not match move the 'waterline' a bit to include or exclude a bit more area. Use the original drawings which should give a static waterline LWL position. You will need an all up weight calculation, ie including engine running gear, people etc to get a proper value for the required volume. SD of Al 2.7 to 2.8 btw. This is one area if you work it in metric, it is easier ie 1 cubic meter is one tonne....but if you prefer cubic inches and pounds so be it.
You can do it with half areas but don't forget to double it at the end!.

You should be able to use the information gained to compare it with any other known similar data for similar boats, and therefore be more confident in your design. My inclination is that 1/8" on any deck part that is stood on, is a bit thin for a deck, certainly if someone is jumping from a quayside it would dent it. For areas not subject to bodies walking about and no need for structural strength it should be OK.

300-400lb is 2 to 3 people?, sometimes a good idea to think a little sideways to envisage the weight!.

 

Added Wt to Double Eagle

North, there are couple of ways to understand the added wt to your hull design, in terms of 'sinkage' or increased depth of the keel.

One might be the 'wt. to sink and inch' of water plane. Here you'd figure out the volume of water that is displaced by one single inch at the current waterline of the design. The mass/wt of that much water is how much wt it will take to sink the hull by the inch of increased depth. So using this rough figure 'the wt to sink and inch' you could figure what the planned increase in scantlings will do to your hull's waterline.

This can be done accurately or roughly, and the accurate method is to make an area of each of the waterplane areas, from station to station, in the Plan View of your design. But to get a 'feel' for the number of lb. it takes to sink and inch?-- that is a little easier.

First just figure a rectangle of the entire waterplane aft the master station, this is about the after 2/3's of the hull. Say the water line is 6' wide or 5' wide and this after body is about 12 or 16' long? Use the numbers scaled from your design in Plan View. Next, to figure the bow just make a triangle of the ENTIRE plan view of the forward (remaining) waterline area.

Measure the ht of the triangle along the keel (distance from master station to waterline intersection at bow stem) and the width of the base is the previous width of the after rectangle. Multiply one by the other, divide by two and add that area to the stern's rectangle area. Added to the stern's area this is the 'rough' area of the waterplane with the thicknesses figured in the design. We're figuring its all one inch deep; so figure the volume of that many square inch of waterplane (one inch deep means the area is the volume).

Divide by the mass/wt of that same volume of water and you'd have approximated the "wt to sink an inch" ; this is the amount of increased depth the boat's keel will draw for every wt equal to this figure.

Since the even added thickness is not located in one place the distribution is not going to effect list or pitch so the main effect will be the inch or inch and a quarter down the hull rides/floats at rest.

If you can find the 0.160"-5/32"-4mm material and not have to move up to the 0.187"-3/6"-4.8mm material, I'd say that increase is adequate IF you're willing to work at your MIG bead in proportion to the material thickness. If that eludes you- then the thicker material forgiving in the final look of the print through and the 'hunger horse' sides that could happen more easily in 1/8" or even 5/32" if the welds were over sized.

As to deck thickness. The decks get a higher loading than even the hull panels on trailer rollers usually. So if you use thinner material it implies a good deal more framing to support the panels- to make the deck panel support size smaller in order to keep the deck firm and not to warp from welding the pocket/socket/keyhole/through welds which are another topic of method controlling results.

I'd use at least 0.160" or even 0.187" decks in a boat this size personally in order to reduce the framing work, and still maintain a stiff and rigid shape.

If I used 1/8" deck I'd want the panel supports to be less than 10" say 8" on a side and that is one dense deck frame lattice for a boat this size!

If the boat has an inboard and a shaft then a huge percentage of the all up displacement is at or near the waterline, therefore sinking her down a little is not going to change the hull's overall performance. A small weather helm on most welded aluminum boats has more moment contributed by the glass in the helm station/cabin/dog house than the aluminum !

I believe the hull scantlings can be moved up to 0.187" bottom and 0.160" sides without any more effect than increasing her depth to the waterline. She will be more stable, and a stiffer hull. (not that she would be flimsy as you've described her).

I've built hulls in this general class with 1/4" bottoms and 3/16" topsides and all 1/4" internal longs under the decks of 3/16" and they seem to do fine so I'm not concerned with the couple hundred pounds of added wt you're discussing.

cheers,
Kevin Morin
Kenai, AK