14' Welded Aluminum Skiff

[Kevin Morin]

We live in the Cook Inlet in Alaska, and seasonally my wife runs a bed and breakfast in Seldovia Alaska, which can only be reached by air or water. The area has a very nice little bay extending south off of Kachemak Bay and was the site of one of Imperial Russia's original settlements in this area of South Central Alaska.

Our family has recreated in the Kachemak Bay for fifty years, including when our now thirty something children were pre-teens. During that period, our family built a little 10' dinghy for the kids and their cousins for use during our camping years, before we had a house in the Bay.

This little dinghy was rebuilt a few years ago to add new wood seats, paint and some other details.

The skiff is about 20 years old in these photos, but she cleaned up pretty well.

The bottom is 0.100" topsides 0.080" and transom is 0.125" but reinforced to hold an 8hp 2stroke leg that moves the little skiff nicely. You can see the bangs and dents from all those years with a 10 year old crew driving her onto Alaskan beaches.

Fast forward to '06, my wife and I were in Seldovia and the little skiff shown was in the harbor with our friend's family boat. We'd given the boat to a family with younger people who would use it, and one afternoon, my wife asked for the first time in 30 years if she could pilot the little blue skiff around the harbor?

Naturally, I jogged to the harbor and warmed up the engine and she spend a few hours putting around a walking speed and when she got out of the boat she said the most romantic, but kind of frustrating phrase, I can recall.

After I'd cleaned up this old skiff, remodeled and painted and given it away because none of our family would even look at it, my wife gets out of it for the first time and says; "Honey, I'd like one of those."

This thread is about the skiff I designed and built for her in the next two years in response to her new found, after thirty years, interest in having her own boat.

This is an image of the mostly complete skiff that I built to give my wife 'her new boat' to enjoy the waters around Seldovia Bay. What started with an old 10' skiff we built for the kids to pirate the rocks when we camped in K'Bay- inspired the new boat shown here.

I'd like to start with the design concept, show the construction and the finished boat more completely in the next few posts. None of the designs are for sale, these boats are not commercial products, we no longer build full time, but I hope those of you who enjoy designing and building skiffs will also enjoy reading about this one.

The 10 dinghy was built by eye but the green and yellow skiff was designed in Delftship Pro, a marine design software application with free version available, and built using that software's output.

cheers,
Kevin Morin

 

[Kevin Morin]

14' Welded Aluminum Skiff: Design Concept

14' Welded Aluminum Skiff: Design Concept

As a commercial builder, I usually begin with some other boat as reference, a set of plans from another designer or a description of the boat we're building from the owner.

In this case, I wanted a small boat that would be seaworthy enough to run safely with an inexperienced skipper in the tidal waters of the Kachemak Bay and Seldovia Bay. This boat would need to be a little deeper sided than the same size Lund, Gregor, or Starcraft.

I decided to use an outboard engine well so that my wife wouldn't be sitting at the stern in a following sea and would be [more] surrounded by the boat to give her more sense of security. I drew the sides quite a bit taller than most open 14'ers to give more reserve buoyancy and a raised, sealed and air tested deck that would give some flotation if the boat were swamped.

Because I didn't want the boat to be fast, the forefoot was somewhat sharper than might be seen in a planing skiff of the same size, and the motor well's cutout of the bottom would also reduce the planing area and raise the bow's pitch when running. The skiff was planned around a gear motor with a 3:1 reduction so the flatter prop would move the boat slower but still push her along in any swell with an over sized load.

Seating in a skiff this small is critical because one adult of normal size will heel the skiff is they're sitting off center, and since the skipper would be sitting aft and to one side of the tiller, a round center seat pedestal was chosen to allow crew to be moved to trim the little boat with body wt.

I wanted the battery and fuel tanks to be out of the way, and not underfoot so they would have to fit in the stern seats which were designed as lockers with a lift off top.

Since I wanted to provide a very secure feeling and 14'ers are a bit tender if you stand up, I decided to add hand railing fore and aft so that getting in and out was less a balancing act.

This area of the Gulf of Alaska has plenty of rain, and even on a nice day there might be a shower to wet the open skiff crew so I added a canopy to the design. This gave the skiff a kind of 'African Queen' look and I admit a canopy on a 14' skiff is a hard look to carry off, but it does keep you [mostly] dry in the rain and works as a very tall hand rail too.

here is the concept sketch showing the rough lines from many views.

The skiff has reverse chines, more to hold the bottom shape while building than to effect planing. The stern is rounded and the cambered bottom to stern shape changes required a 'step'. This is like a large angle with curves cut onto both legs' outer edges. The lower edge fits the camber of the bottom and the after edge curve fits the shape of the transom's lower edge.

There isn't much flam but the bow is full up near the sheer and the chine plate helps make a more sharp shape change from bottom to topsides.

cheers,
Kevin Morin

 

[system-f]

Re: 14' Welded Aluminum Skiff

more pictures?

 

[Kevin Morin]

Re: 14' Welded Aluminum Skiff

For those who like to look at the lines of a boat, here is the preliminary lines set and my thinking as I progressed to the final lines and shape.

These lines won't show up all that well in terms of exact details but this plan view shows waterlines every 4" up the hull. If you notice the forward 25% of the chines and sheer-there is marked lack of fairing -the lines are almost straight in this view.

One [black] line in this view can be confusing, the the sheer clamp or guard deck is a flat plate about 8" wide along the topsides sheer. This line shows up following the sheer all the way aft, but it crosses the chines in the after 1/3 of its run so at the stern the plan view of these lines can be confusing.

The Body Plan shows the bottom has a reasonable entry but is highly warped, and that is because the boat is designed to run in displacement mode not to fully plane. In a planing skiff running at 14-16 knots or above this fine and entry might make this small a skiff wobbly or veer off the helm. At slow speeds it just makes here helm steady and the entry smooth.

The topsides flam (lean out) more than we'd see in a typical freshwater prodction boat of the same LOA, but wind spray in an open skiff is bad enough we don't need to let the spray run up vertical sides and make her 'wet'. She'll be wet enough as an open skiff in a salt water with a breeze.

The look of the small skiff is generally set by her sheer line, and in our area there is a small commercial fishing boat that is used by seiners to pull the net off the deck of larger boats. This little skiff type, called a seine skiff or snag skiff, naturally, is a small tug like shape, often of welded aluminum, that has been around for a very long time.

I admire this group of skiffs and I wanted to give these lines that feel so I used the Western or Powderhorn or reverse curved sheer line. I didn't return the sheer line as dramatically as most seine skiffs here, but I did want to hint at that heritage in this skiff so that is the most influential design element in this view.

This Perspective View only displays the panel outlines and the stations but does show what I was after in this little boat. I wanted something that was as dry as we could get in an open 14'er, something with a fine entry to keep from slewing sideways in a wave face so the helm wasn't tricky and something with good flam forward so it would lift the bow well in a following sea. A fine forefoot and wide transom can make the helm tough in a following sea if the forefoot digs and the stern lifts too much then the hull can broach. I wanted to make sure the bow would only go down a relatively short depth and that is why the forefoot is fine and the topsides more full.

Since I intended the boat to travel slowly I anticipated it would not outrun weather or swells, so it needed to be able to 'cork it out' and that is why she's beamy than most 14's, deeper and has more flam forward, and she's fine under her chine warping out to a few inches of cup or camber in the bottom aft.

The outboard well is not shown, neither is the deck, seating, structurals or hand railings or canopy. The purpose at this point is to convince myself that I could send my wife, an inexperienced skiff driver, out in this skiff and not worry about her safety in any weather she'd consider leaving the harbor.

cheers,
Kevin Morin

 

[Kevin Morin]

Re: 14' Welded Aluminum Skiff

This post is about the process of laying out the cuts in sheet aluminum. In this case I skipped the standard builder's modeling step of making a plate model. This was the first skiff I'd modeled in a PC without confirming shapes in a plate model but it was not the first skiff I'd built in welded aluminum.

This is a screen shot reduced and cropped to fit here, of the Delftship Pro software's output of the plates that was used to draw the outlines for laying out the cuts on the 0.100" 5052 aluminum sheet.

I'll make some remarks for those who are interested in this process. The software makes this page [shown] automatically but if the underlying model is not 'fair', if the model has hogged lines or has kinks int he curves then these panels will have rough, hogged or kinked curves on the edges.

The software does have tools to help you clean up the lines, to 'fair' the shapes and edges of surfaces BUT..... that is somewhat limited even if you have a large, high resolution CAD screen. In fact, the smaller the boat, the more caution you need to give relying on the output controlled by your visual edits on a PC screen.

I output this file into the AutoCAD format *.dxf [drawing exchange format] so that I could print from AutoCAD onto a large format plotter; 3' wide roll plotter referred to as E-sized Roll Plots. This allows you to print a full sized panels 3' wide and however long.

I did this to see what level of smoothness my panel outlines would be? They weren't clean enough, there were flat spots and kinks or angle points in the curves that were visible at full size but not clear on the screen. May locations needed 1/8" more 'curve' for a few feet here and there along the computer generated outlines.

I'm sure my lack of ability to use the software well contributed to these slight irregularities but I still needed to 'clean' the curves so they were fair.

I took the file of outlines and used the Spline /Polyline tool to smooth the curves then I drew a grid onto each panel outline. The grid was the 'size' of the sheet that each part would be cut from and the grid gave us a baseline and a piont on the curves above the that base and back from one end.

By 'cleaning' up the curves I created a table of X,Y coordinates that would map the curves for the hull panel shapes. I will look up some illustrations of this step to post next.

cheers,
Kevin Morin

 

[Kevin Morin]

14' Welded Al'm Skiff; Batten Panel Outline

14' Welded Al'm Skiff; Batten Panel Outline

With the output of the software very close but not as fair or clean as we needed I used AutoCAD to 'spline' the curves. This allowed me to get more even curves with fewer hard spots and get ready to layout onto sheets.

By creating a layout grid then reading each point on the layout you can easily take off a table of points, then mark them out full sized onto the sheets. Now the marking process induces errors, small but potentially important, and the overall process of scaling the model from CAD to real plate also adds some possibility of misreading and marking.

Here is one method that can help clean up the lines. Since the 2x2"x1/4" aluminum angle extrusion won't bend too easily it won't copy the kinks or tiny hardspots that might be in your measurements. In other words, regardless of your measuring and drawing scaling errors, and even some of your model's fairing errors as well- by using an extrusion as a huge drafting batten you can clean up or 'fair' a curve through the layout points.

You might be off a little here and short there, but the best approximated curve using a batten will give a clean edge to all the panels. This clean edge allows you to tack up fair and that is the beginning of a clean welded skiff.

cheers,
Kevin Morin

 

[Kevin Morin]

14' Welded Aluminum Skiffavis Skiff Jig

14' Welded Aluminum Skiffavis Skiff Jig

I don't know if your back is still young enough to support all that you want to do? If it is then I hope you enjoy it that way, and for the rest of us this post shows the way I deal with an old welders' back.

This is a concept sketch during a design exchange with a friend from Oregon, Jack Davis who wanted to build a skiff but didn't want to rely on his back.

Jack decided he needed a rotisserie style jig to put the skiff on and roll it to all the countless positions needed to get welds everywhere they need to be. The sketch shows a garvey shaped hull on the fixture because we were discussing that form at this stage.

This is what I ended up building in order to work on welded boats without the flexibility I used to use to get into all the corners. Notice that the large chain gears are not here as I roll the Davis Jig using an overhead monorail and chain falls.

Close up of the pivot on one end, the jig is almost all concentric pipe except the long box beam and end uprights.

Looking down on one end where the vertical extension is lowered compared to the detail above.

sliding clamping system to grab the main beam and hold skiffs at different points in their build.

This is a rowing dory done on the Davis Jig, the first I'd built this way, and shows the idea of a "skiff on a spit" making all the welds and most of the fits and tack up at about belt or shirt pocket ht. That means that bending kneeling, reaching, odd contortions and many other semi-acrobatic bodily positions are reduced to standing flat footed and working -just like the whole project is on the bench.

I needed to introduce the Davis Jig to make sense of the building photos to follow.

Cheers,
Kevin Morin

 

[Kevin Morin]

14' Welded Aluminum Skiff:Tacking Up

14' Welded Aluminum Skiff:Tacking Up

We have built skiffs using the skin first method since 1977 because we couldn't afford the labor to put frames up and compete with other builders from the Seattle area. Skiffs built with frames, then covered with hull panels are fine, but the frames take alot of work, and may not be absolutely needed in a welded skiff.

Since the shape of this group of hulls is almost always 'developable' all the hull panels can be cut from flat sheet and cold formed into planes, cylinders, cones or parts of all the above. By cutting the edges of the hull panels to a clean scribed line using a wood working jig saw you can make a line along the edge that is smooth to within 1/32" pretty simply.

By using a Vixen or non-ferrous metal file those cuts can be cleaned up to leave very clean edges with little or no contamination sources for the future welds that will fuse them together.

The entire hull is tacked up here, inside edge to inside edge, without any frames except a bottom camber former, coming in a few pictures, and the occasional temporary stiffener to keep one or another tension area smooth.

Here the hull is rolled to the port so the chines are more or less vertical.

A closer look at the stern step and transom tacked up. Tacks are very short duration fixed in time by the welding power supply with tack timer feature. By making the tacks very short, single puddle or 'one dime' tacks that are narrowly spaced the edges of the sheets fit together 'knife edge to knife edge' along the inside of the hull panels.

There is no weld heat to contract the seams and they remain as clean as the cut and filed curves mentioned above. This method is much like plywood stitch and glue except the temporary ties are later welded through after dressing.

Here is a shot under the hull, more or less opposite ends from the previous image. It may be a bit confusing to see in the many shades of gray that result from photography of aluminum sheets to pick out the bottom former jig from the bottom plate and stern step.

This image closes in on that same area but might not give the color separation needed to see there is a set of transverse hollow curved frames that are tacked to the bottom panel to begin the cylindrical forming. This is used to get the entire after bottom shaped until the well, interior framing and other permanent structural elements are at least tacked into the hull.

Looking into the forefoot, chines nearly vertical again for photography, a pair of chords or collar ties are tacked between the inner chines of the bottom panel. This area had so much outward force remaining when tacked up that the chine plate, which is very narrow this close to the bow stem would bend if tacked to the bottom without these ties.

If I were to do this particular hull again I would draw the chine flat wider all the way to the stem in order to get more lateral/transverse stiffness in this piece to better hold the shape before weld out.

Last in this series outside the forefoot just after we tacked up. In this image there is a 1" x 1/4" flat bar tacked and even distance below the inner chine on the bottom. This bar was used on the port side as well, and the tacks are still visible slightly above the other inner chine line at the bottom of this picture.

Because I wanted the hull to be as light as possible, a view I no longer hold, I made the entire boat of 0.100" which isn't available in the more stiff and rigid 5086 alloy very commonly. 0.100" is most often rolled and milled in 5052, admittedly a marine alloy, but one that requires 'fairing' as in this case in order to tack up adjoining pieces in a fair intersection of curves.

This post was to illustrate the importance of fairing the hull panels as they're laid out and cut. Once cut, cleaning the edges to the scribed line with a Vixen file can result in a tack up that is clean. This is important to begin fair as welded boats can be wrinkled, crinkled, bent and distorted by the final weld out without starting out that way during tack up.

The layout and cutting took about 24 manhours and the tack up took three men two hours beginning with mounting the bottom into the camber jig/bottom former that was already built. In two-three days three people could have progressed this far given the layout tables and modeling already complete.

These sheets were put through a 50" wide drum sander wrapped in 3M Scotchbrite (tm) abrasive to remove the mill scale so the boat won't corrode. The 'buffing' lines show on all the panels because it was much simpler to buff them before they were tacked than to go back with a hand held 4" or 7" grinder to get the mill scale off.

Cheers,
Kevin Morin

 

[Bob_VT]

Re: 14' Welded Aluminum Skiff:Tacking Up

Re: 14' Welded Aluminum Skiff:Tacking Up

Beautiful Work.

 

[Kevin Morin]

14' Welded Aluminum Skiff: Still Tacking Up

14' Welded Aluminum Skiff: Still Tacking Up

The stern is held into a camber or cupped bottom form of about 3" in nearly 5' by this temporary set of female frames mounted to the Davis Jig by the temporary clamps.

There are a series of 1-1/4" x 1-1/4" x 1/8" angles between the two formers that will keep the bottom panel in a cylindrical shape as it is tacked to the camber frame.

From the aft end the jig is little bit less obvious but the after former is about 3/4" forward of the end of the bottom just before it tacks to the vertical half of the bottom to transom 'step'. This step is curved to the bottom camber and aft [in the plan view] to the lower curve of the transom. The transom is a very slightly tapered cone so the top curve is larger radius than the bottom.

The outer edges of the transom are not straigth lines, they're bulged by about 3/4" in 33-34" to make the topsides have a very tiny tumble home. The purpose is to stress the side sheet so it has tension between the sheer and chine and that works to reduce weld distortion later in the build.

Also visible in this image is the twist of the topside, where the forward section is curved around the turn of the chine and leaned outward [flam] and the after end is tapered inward at the chine as well as pulled more plumb and cambered outward. Thin sheet is a bit of a workout so these steps were done to make her more stressed before welding to keep her fair.

This corner tack up mainly shows the method of tacking fair at a butt joint in the sheer clamp. By putting stiffeners under the entire joint, at 90 deg to the butt joint, and 'tacking' them with vise grips, you can reach under and tack the strips before tacking the butted plates. This means the joint has a temporary structural element under it before the heat of the tacks is added to the butt joint. This will work to keep the butt joint from distorting downward away from the original tacks.

A bow on picture of the tacked up 14 hull without any weld or longitudinals added inside or outside. The powder horn sheer is more pronounced in this shot which is taken close by the port bow.

Finally, an outboard profile of the tacked up skiff looks like we haven't finished tacking the after sheer clamp to the transom plate but we did get the forward fairing strips off and sanded off the temporary tacks.

Cheers,
Kevin Morin

 

[Capt'n Chris]

Re: 14' Welded Aluminum Skiff

What fun that was to read your posts. I certainly appreciate that!

Captain Chris

 

[fishrdan]

Re: 14' Welded Aluminum Skiff

WOW, that's a lot different than what I expected from the title.

Nice work and I can't wait to see her finished.

 

[JB]

Re: 14' Welded Aluminum Skiff

SHAZAM!!

What a great start on a gorgeous skiff, Kevin. Can't wait to see the completed project.

 

[Kevin Morin]

14' Skiff; Tack Up Errors & Some Improvement

14' Skiff; Tack Up Errors & Some Improvement

Bob VT, Fishrdan, Captain Chris, JB,
thank you for the kind words, I'm glad that you like seeing this skiff go together.

All was not perfect due to my lack of familiarity with 0.100" thin material and the fact that 5052 is much softer and less stiff than 5086 which is the alloy I'd used almost exclusively before this skiff.

I'm a little out of focus here and no amount of Photoshop seemed to clean it up, but its only here to introduce the next few photos. We're looking at the chine(s) near the bow stem. From a distance there is no problem but when we get in closer and look under the forefoot to stem transition all is not as tight as I'd have liked.

If you look at the near chine plate between the bottom and topsides you can see a 1/2" curve along the most forward 8" where the chine plate is not really horizontal. Aft this, the widening chine plate was stiffer and kept its relationship of topsides to bottom in correct orientation; nearly horizontal. Here in the last foot or so forward the chine plate is so narrow, tapering to a 1/2" wide 'point' that it rolled down, allowing the topsides and bottom to align with an unintended overlap.

In a previous post I remarked that if I were to build this skiff again I'd make that reverse chine flat wider all the way to the bow stem, and showed the collar ties inside the bottom holding the curve at the inner chine. Well here is another example of why I came to see this narrow, thin strip as a design error.

All was not lost as this shift of topsides down the stem and the bottom inner chine upward, didn't make enough shape change so other parts didn't fit. It was a somewhat small error in shape but is an example of the types of design problems that don't show up as clearly using a PC instead of a plate model.

This photo shows two or three items that I think are worth a remark.

First; the chines, both of them, curve in toward the centerline aft the master station. This clearly shows on the right of this image and goes to further explain the speed I intended for this hull- slow. At planing speeds too much tuck to the chines would cause the stern to squat, this skiff will squat too if she is pushed too hard. Tapered chines combined with a motor well bottom cut out reduce planing surface lift dramatically.

Next, there is the flat bar tacked to the starboard after inner chine at the last three or four feet of the bottom. This area just wouldn't tack up clean and kept curving or bulging downward even with the bottom jig's angle under that section. We ended up having to put this temporary on one side in order to clean up that inner chine while being tacked.

Last item I'd like to call attention too in this image is the transom curve transition to the sheer clamp. There are several potential problems here and I call attention to them for designers and builders who may want to include more curves in their skiffs.

If you look at the top center of the transom, then follow the line along to one side or the other, and continue you eye along the sheer- you'll see there is a butt joint in the sheer clamp and a hard corner of the skiff topsides to transom.

It can be a difficult area to make a clean transition because there's a joint in the topsides and transom AND there is joint in the sheer clamp/guard deck.

In this photo from aft the transom we can see the line of the transom and its transition to the sheer line. This area, or lines flow, has given me fits in the past and I have seen lots of other boats that have hogged or rough transitions here other than my own boats. So, I know that I'm not the only one who needs to pay attention to their skiff form in this sheer to transom area.

There is no question I've improved this skiff's lines in this area if I compare it to many of the square stern skiffs we built for commercial net fishing. [But] I might have improved it further by rounding the corners instead of working off the angled joint shown here.

Cheers,
Kevin Morin

 

[Kevin Morin]

14' Welded Aluminum Skiff: Bow Stem

14' Welded Aluminum Skiff: Bow Stem

Small skiffs metal skiffs often have a sharp stem formed by the topsides sheets coming together in a cut edge. This is a strong and clean way to end the topsides in the bow stem but since I was looking for a little more rounded appearance I wanted a bow stem that was rounded too.

I'll reuse this shot of the stem tacked sheet to sheet to begin the look at the bow stem 'snuff nose'. The term snuff nose is used in Scandanavian metal boat building because they cut the bow stem intersection of the topsides plates and put a flat plate across the stem. That is an attractive stem treatment for some.

I liked the idea of a rounded stem but needed to find a way to form and fit one that looked clean but was within the capacity of our limited forming equipment. I drew the lines of the skiff with the topsides/stem intersection about 3" more raked than I wanted. I would be able to cut that much off the topsides at the sheer and add the rounded piece of bow stem and still retain the topsides sheer in plan view and the profile of the stem would fit the forefoot curve more cleanly.

this is another photo of that same area, this time I'd call your attention to the rake of the stem in relation to the curve of the forefoot.

Another photo we've seen before but this one seems to capture the two different lines better than the others. The stem from the chine to the sheer is not as cleanly related to the curve below it as could be drawn and that is because of the extra rake to the stem.

This means I could cut 3" out of the topsides along the sheer, taper that cut to the chine an add a rounded piece to fill in the space now cut between the topsides sheets.

Here is the profile of the bow stem and forefoot as modified to curve the stem in all three views; profile [shown here], plan [by using a rounded piece of metal] and bodyplan or section view by making the two vertical cuts bulged or cambered outward.

I used a piece of 4" Sched. 40, 6061 T6 pipe an cut a 1/4 section from the cylinder as the blank stock. The 1/4 round section was then bent along the original pipe centerline axis so from the side a curve was permanently held in this 1/4 round 30" long, 1/4" thick piece of aluminum.

The topsides cuts were laid out as straight lines from the sheer to the chine and the bottom gap would be 1" and the top as much of the 1/4 round pipe as would form a smooth intersection between the topsides at the sheer clamp outer, forward most edges and tip.

By holding the 1/4 pipe on top of the top plate at the sheer the original outlines or offset points were drawn. Then these lines were connected to the 1/2" per side offsets at the chine. After the straight lines were drawn on the topsides a 5/8" inch curve was drawn to that 15-17" from the chine the line was bulged outward instead of straight.

When this was cut and dressed the opening was actually hour glass shaped INWARD since the topside now longer had a tack point along the stem and they sagged inward slightly.

The bow stem or snuff nose piece was marked for width at the top and bottom and a similar bulge or cambered line laid along the cutline. When cut the 1/4" material was wider by almost 1" in the middle than the boat's topsides opening.

We rabitted the sides of the slightly conic section of pipe so 1/8" of each side had a shelf to accept the topsides forward edges. Then the stem piece was forced into the bow from the inside of the tacked up skiff. The bottom was pushed through and tacked at the forward end of the chines and bottom seam. Pushing more and more, finally using a hydraulic jack and some termporary tacked in bracing the stem piece pushed the topside outward until it was flush with the outer surfaces of the sheets.

This picture is taken slightly more forward and moving to the left of the previous picture and shows the two curves are now resolved into one and the 1/4 section of pipe is becoming more clear.

The focus on this set of images is not very clear so you'll have to bear with the fuzzy information they present. If you look at the right side of the photo at the port side vertical weld seam of the curved stem- you'll notice the topsides and pipe don't intersect in a straight line.

Next post will continue this detail exploration.

Cheers,

Kevin Morin

 

[Kevin Morin]

14' Welded Aluminum Skiff; Bow Stem/Snuff Nose

14' Welded Aluminum Skiff; Bow Stem/Snuff Nose

Just above we were looking at the detail of rounding the bow in a welded skiff. One quarter of a 4" diameter pipe was cut to a taper with curved sides and rabbited to accept the topside plates for a better weld joint.

This photo shows more of the stem from nearly bow on and the vertical welds are complete. Curving this piece in three views or planes made the topsides more cambered or increased the flam [convex curvature of the topsides] and made the bow at the sheer rounded as well. And as we saw in the previous post the profile view of the stem is now resolved to the forefoot's curve.

This is just a closer view and helps make clear the intersection of the sheer clamp on top, the topsides along the two verticals and the curvature added to the bow by this 'snuff nose' bow stem.

Anyone who's built in welded aluminum, commercially, is reading this and thinking that the level of fiddle in this detail alone is foolish. Building strictly for recreational purposes makes metal details like this a nice way to spend the day, instead of a waste of labor.

The boat won't perform one bit different and the only impact is visual, but I introduced this skiff's reason for being at the beginning of the thread- it was built as gift for my wife so making it 'nice' was just as important as making it safe.

Besides, I've always thought this would be an interesting stem treatment but haven't had the chance to try before this build.

Cheers,

Kevin Morin

 

[Kevin Morin]

14' Skiff; gunwale design

14' Skiff; gunwale design

The photos of this next area of construction are 'all gray' like most welded aluminum progress photos tend to be. So we'll take a quick look at some ideas shown in PC/3D sketches [SketchUP exports] where the colors are chosen to make each part look separated from the others.

If we looked at the photos of the next phase first; I'm pretty sure all I'd add was confusion. These screen images are here to help everyone get onto my song sheet -so to speak.

For me, a good part of the enjoyment of designing in welded aluminum is exploring forms than can be cold formed out of commonly available extrusions which, when welded into the shapes of boats, look nice and are strong, clean and smooth.

I like to use a triangular "box beam" at the sheer of my skiffs, and do so whenever I can get away with it.

A look at my 'box beam' begins in this image of an example section of a skiff topsides to sheer clamp or guard deck joint. By slitting a pipe and forcing the slit pipe over the top edge of a skiff at the sheer the pipe will smooth the sides, create a rounded edge and become very good rub rail when welded.

By laying the sheer clamp onto the top of the pipe at 12:10 O'clock there is a natural fillet weld groove formed which can be welded downhand and either left or sanded smooth with very little loss of strength.

Looking at the inside edge of this method of building the sheer or gunwale of a welded skiff shows another pipe slit and forced onto the inner edge of the sheer clamp/guard deck.

Struts of 1" or 3/4" pipe are added in a butt T to the lower edge of the slit pipe edging and they are mitered to lay flat to the inside surface of the topsides. You may have noticed one last detail in this method that is critical to its stiffness; the struts end on the inside of the same path an angle longitudinal is on the outside of the topsides.

This last feature means the topsides panels are now 1/2 as wide [roughly] as the chine to sheer distance and therefore the panel is much stiffer than before. Also now that the topsides have become two sides of a triangular beam curved along their length- the topsides are extremely stiff regardless of the panel thickness.

After welding, this light wt. assembly becomes an extremely stiff section; in all directions. If you imagine a skiff from the plan view now- you're looking at a wishbone or Delta symbol that is so strong and rigid that most boats' sides don't need transverse frames.

There are a few variations on this theme that take into account the different pipe sizes. If you tried to slit a 1-1/2" pipe and force it around the sheer of a small skiff without rolling - the pipe's rigidity is out or proportion to the skiff's shape resistance. If the pipe is too stiff it will deform the skiff instead of conforming to the shape.

In this image a 1/2 pipe is shown wrapped to the sheer inside and out. There are extrusion companies on the West Coast that offer 2" and 3" pipe in 1/2 profiles but I used 1-1/2" pipe that we sawed by ripping it on the band saw.

1-1/2" sawn, half pipe will be shown on the next series of construction photos.

Underneath the same arrangement of shapes we can see this sheer clamp has a vertical bar tacked along the inner edge to 'accept' the 1/2 pipe. Inshore commecial salmon gill nets are floated at the surface by corks that are shaped like small footballs with holes in their long axis to thread them on the 'cork line'.

When these nets are hauled over the sides of set net skiffs they need an all rounded shape saned smooth and formed of fairly large diameter extrusions in order to avoid tearing the net twine lashings that locate the corks evenly along the cork line. This last set of construction details shows a simple method to make a smooth, incredibly strong yet net fair sheer for a welded aluminum skiff.

The last point that is made clearer here than in the photos to follow is the weld joint. If you look at the topsides, sheer clamp and half pipe joint, you'll notice the naturally occurring weld gap or groove formed by all three pieces coming together.

By turning the amperage of a down hand MIG weld up, the weld will not only fill this area and fuse all three parts together, the weld will 'sag' into or overpenetrate this weld zone. This works as a defacto 'back weld' where the root of the weld actually bulges into the voids behind the weld zone enhancing the final strength of this weld.

When finished the outer weld would be sanded smooth and traditionally the loss of the top or crown arc of a weld is not good practice. In this case the 'hot' weld makes that rule of thumb less applicable to the joint shown.

Cheers,
Kevin Morin

 

[Kevin Morin]

14' Welded Aluminum Skiff: Adding Rub Rail

14' Welded Aluminum Skiff: Adding Rub Rail

Now that the idea of the rub rail has been shown in color separated parts these photos won't be as confusing- I hope.

The combination of 1/2 pipe outside and slit full round pipe inside is the method I chose for this skiff. I wanted the larger diameter pipe outside for both the look and increased roundness and I only needed a nice clean edge inside the gunwale plate/guard deck/sheer clamp.

If you notice (?) the inner pipe is tacked to the plate edge but is not faired with the struts.

This port stern picture shows the pipes on, rough ended, including the transom's pipe. That pipe was left whole and rolled in a pyramid rolls to the shape of the transom's top curve and since the transom is inclined aft the pipe had to be rolled downward at the outside ends. We cut the pipe by hand to scribed lines to the sheer's rub rail could be continuous without making hard transitions at the corners of the transom.

This pipe looks as though it has odd curves nearest the port side transom corner but that is a combination of the lighting and reflections since the blank pipe was rolled of one piece in a pyramid rolls.

This bow on shot helps give some idea of the proportion of the pipe diameter to the sheerline and introduces the bow finished detail at the snuff nose.

More poor photography from your old welder who can't see. The two half pipes were orange peeled before the pipes were wrapped to the hull.

In this photo we have lots of new parts to consider, many of them so faint or indistinct they need explanation. First, point of view is looking aft and inboard across the gunwale plate toward the tacked up outboard motor well. In the near foreground or left side of this view are an example of the gorilla welds [big, strong, ugly] used to sink into the sheer pipe to topsides and guard deck weld groove.

The inner pipe is only tacked in place but the mitered segements of butt weld 90's are inplace in the transition between the transom liner's pipe edging and the sheer's.

It may have been better to press brake the well but its shape needed very large radius corners on the forward inboard edges so we used pipe segments and butt welded inside and out with full back chipped grooves and TIG.

Cheers,
Kevin Morin

 

[Kevin Morin]

14' Welded Aluminum Skiff: More Longitudinals

14' Welded Aluminum Skiff: More Longitudinals

In my experience with unframed boats confining the movement of twist of the very flexible hull is critical to the method's success. So after tacking up, we typically add the sheer or some pipe to the sheer, or some element that will help hold that shape, similar to the way a chine flat will hold most of the bottom shape until all the added structure is finalized.

We have seen the 1/2 pipe outside the sheer and a full round slit pipe added to the inside of the sheer clamp plate so next is the an angle tacked to the outside of the topsides. This angle has the sharp edge routed off using a carbide round-over bit and is added to the skiff using a clamp that looks similar to a loggers 'can't hook'.

By hooking one end over the hull inside the guard deck pipe and holding the middle of the handle nearest the angle, one man can hold the angle against the side while another tacks at premarked intervals in order to have good smooth tack-up.

This view of a hollow line of the spray rail helps make the sheer's powder horn or 'droopnose' a little more obvious.

A view of the same side from behind the transom shows the line of the spray rail and the return piece wrapping the transom.

Back to my poorly focused images, here a closer view of the transom piece of outside longitudinal/spray rail with the corner detail and the sheer pipe butt weld 90 installed as well.

These pieces help to give a continuity to the spray rail's line and also help to keep the transom fair when the well's cutout is removed from that panel.

Cheers,
Kevin Morin

 

[Willyclay]

Re: 14' Welded Aluminum Skiff

Beyond spectacular!