View Full Version : REmodeling a Welded Aluminum Skiff
05-08-2010, 09:22 PM
Alaskan coastal rivers mouths provide ocean access for salmon 'runs', as they're called, with so many fish returning to spawn inland that they can be harvested commercially. Commercial fishing for salmon involves hook and line along the coast with Canada, called trolling, and almost everywhere else with gill nets. For those not familiar with that type of gear, it amounts to a nylon mesh curtain hung in the water with diamond shaped openings about the size of whatever species of salmon is anticipated or permitted in that region's catch. There are salmon seiners too, but this thread is about the rebuild of a welded aluminum skiff originally an 18' LOA salmon set net skiff used in the Cook Inlet to handle salmon gill nets anchored to the shore in tidal areas.
In order to look at the original skiff and understand her build, it’s important to think of a gill net as a huge wall of lace curtains otherwise the boat's structural elements will seem odd in the extreme. Handling a net that has been 'set' or placed on anchors in the water in the path of migrating salmon, is a matter of leaning over the bow, picking up the net's cork line that floats at the surface and then gathering the 12' deep lace curtain in your hands and pulling the entire bundle over the side of the boat. Once the cork line, web [net mesh] and lead lines [they make the curtain hang vertically] are all 'roped' into a 3-6" diameter bundle they are pulled along the top of the net skiff to the middle of the boat. When a gill net is over the skiff's amidships area the leads and corks are be pulled apart, fore and aft, to open the web allowing the crew to remove the fish.
Each crew member has to stand in the skiff, more or less facing fore and aft, holding the cork or lead line with their legs spread toward the chines on a relatively flat bottom and pull the net along - more exactly- the boat is pulled along sliding sideways to the net's ends. If fish are trapped in the web, 'gilled', by swimming into this nylon curtain from which they can't back out, they get pulled over the sides of the skiff and have to be 'picked' from the web and released into the bottom of the skiff.
One of the most important features of this type of boat is that salmon range from 3 to 75 lb. , depending on species, and enough fish in the skiff may add up to weigh more than the boat. In fact the sole purpose of using metal boats is the loaded skiff my increase wt by ten times.
If you add a following sea, a little surf to the gravel beaches where the fish are landed, and picture landing a few tons of fish on that beach; then, you'll be able to understand why the skiff in this remodel was built somewhat stronger than would seem needed. This type of commercial fishing may be done in sheltered waters or in more weather exposed locations so the boat has to carry the fish onto a beach in a potentially dry-breaking sea on a loose gravel beach. Most other boat building materials don't last very long in this service.
Suppose you needed to figure out how to build an open rigid boat weighing less than 500lb. that can haul three tons or more, is stable in a sea working nets, where all the structure didn't tear or snag the net anywhere? The upcoming pictures will explain why I built the original boat in the manner shown. The skiff in these pictures has ribs made of 0.125" sheet that are rounded along their bent edges forming hollow box beams once welded continuously to the bottom and sides. The sheer is lined with a full round pipe and the missing motor mount was surrounded by a slop tray of splash well to keep the side mounted outboard from the net when it was payed out over the stern. That is why this skiff is nearly flat bottomed but has 34-40" sides and a platform to stand over a very modest V in the bow.
If you're still with me, (?) I'll be explaining the reconstruction of a net skiff originally built in 1979 for net fishing salmon, which was converted to a college graduation gift for our daughter in 2004-05. I'd built the skiff when building full time, sold it but the owner offered it back in the late 90's for less than I could have re-purchased the metal, naturally I bought it intending to resell and 'make a killing'. Instead, I used the net skiff as originally built for a few seasons, just to burn gas, then leaving it sit on a trailer in the yard for several years; finally deciding it would be the quickest way to get a skiff for a graduation gift.
Unfortunately, I don't have any pictures of the original skiff before I put her in the shop and cut the transom out. Here, then, is the story of a Cook Inlet Salmon Set Net skiff converted to a [sort of uniquely shaped] runabout, with a stand up helm but remaining an open boat.
Using the aft most upright line of the topsides we can see the transom plane of the original skiff. The slop tray was cut out to the starboard and the full ht transom removed from the port.
A 1" pipe shaped like a hand rail but located about 6- 8" below the sheer pipe has been removed and the sanding marks to fair the former weld locations is evident along the topsides. This pipe was used to secure lines and hold on when the fishing, but won't be needed in this configuration in the remodeled skiff.
A two inch (2-3/8" OD) sched 40 6063 T6 pipe was rolled to the radius of the distance between the original skiff's beam at the sheer nearest the transom. The butt joint is about 8" forward the transom end of the original sheer pipes to use the topsides for support while the new form is tacked up.
With our point of view closer to the floor from the previous pictures we can see the lines of the rounded stern that will be hull extension create the new look. We're going to add a counter or a bustle stern and sometimes called a tugboat stern.
There was a boarding foot step on the transom that was a 2' wide bent of pipe butted to a pair of plates near the bottom aft. The listing waterline shows the engine was always off center and about what the skiff drew empty.
Looking aft across the starboard forward quarter into the cut out stern a sloped line is evident in the sanded topsides on the starboard side. That is the approximate outline of the splash well that kept the transom cutout from allowing a following sea into the skiff when surfing in to the beach.
In the image the ribs construction is more obvious- they're about 6" to 10" deep in 60" of span and almost all of them have a 4" to 6" flat top. These are all 0.125" 5356 bent on a sheet fold with a 1-1/4" diameter bead bar to insure there was no stress cracking in this bend and more importantly that if you fell on this box beam's edges you'd get bruised not broken. Also, this surface will NOT hang any web when it was worked side to side.
The ribs are transverse to stop a layer of fish from shifting fore and aft, which can plunge a bow or stern into the water. These ribs help with level flotation when swamped, although they are not adequate to that job alone, and they're very stiff but about as light wt as can be found for the combined weight of the final skiff. Being smooth sided they're easy on the crew when they slip in fish gurrey, so they're worth the effort to fit and weld.
Looking just a little closer at the bottom of the original skiff at the beginning of the remodel; the side ribs sit on the fully fit and welded bottom ribs. The bottom ribs have a 2" x 3" limber hole under them all to allow water's movement rapidly from rib set to rib set in order to level the boat if she takes a green one over the sides.
The limber holes are made of an extrusion of the shape shown that is cut and fit to the ribs before they are tacked down. When the fit is complete the ends of the limbers are tacked in the four corners to the bottom. By removing the rib used to locate the limber 'liner' a permanent full length weld can be placed along both sides of the extrusion where the legs lay to the bottom.
If anyone welds aluminum they realize these two welds will completely distort the bottom downward and the rib fit will be lost. Since the boat is cambered in the stern and transitions into a very light V forward, the fit of each rib is unique.
The method of regaining the bottom's originally fair form is to clamp the rib to the, now welded, extrusion ends. By putting large C clamps fore and aft the fitters can pull the heat contraction distorted bottom back to the rib's lower edges and the resulting added tension between these two elements actually increases the tensile strength of this alloy of aluminum.
A trial look at the new deck surface is being discussed by using the cambered plywood riser. Is that too much? Will the deck drain if we make it less curved?
In the bow is a deck surface supported along its aft edge by a pipe that fits to the topsides just above the chine flat. There is a single leg to break that span and take the bounce out of the deck but there is no after bulkhead. In a more expensive and complete model of skiff this volume, under the bow deck, was used as an additional air chamber to contribute to the level flotation if swamped.
The chine flat is not full length in this skiff but only at the bow 1/3- 1/2 of the bottom. The flam is somewhat wide for a skiff this size but that is because of its purpose, smooth ride was not as important as load carrying and being able to get beyond the first few swells out to the nets.
The interior also shows the topside were convex as the edges of each vertical rib is curved outward. As the ribs are viewed for and aft it’s obvious the skiff's topsides have less lean out [flam] toward the stern as compared to the bow.
05-08-2010, 09:25 PM
This is where the project is headed; here is a repeat picture of our Skipper at the helm in a lake during our first test launch.
The Skipper's brother watches the lake shore bottom, shoaling ahead, so her new wheel doesn't get shined, I think the motor is coming up and I notice the painter looks secured inside to a cleat below the gunwale.
Obviously the stern changes added the [nearly] six feet to the boat; some in the rounded counter stern [4' approx] some in the 2' engine cantilever.
The entire surface of the boat, old and new have been buffed with a ScotchBrite (tm) like hook and loop abrasive series to remove the mill scale on new metal, and to remove old oxide layers from the old boat. The whole boat was acid etched and alodyne wetted before the next photo.
This is why we usually hire the paint work done, its slow, produces super fumes, and I'm not as good with a spray gun as I am with a MIG or TIG gun, and I'm not very dexterous with those either! It turned out the paint sales people had given us the wrong mix of chemicals for the PPG system and the reason for my dry overlaps was the hot mix. Just the same, I'll let the auto body guys shoot the paint; they already know how and obviously I don't!
05-08-2010, 09:29 PM
This image which I copied [but hope to have kept their credits] “says” what the skiff was originally designed to do. Oddly enough, this may be one of our skiffs(?) Lots of signs that it could be, but even if I didn't build this one, I think it conveys what we were building the original skiff to do.
The engine was mounted directly on the transom but off to one side, the net was “shot” or set over the stern because it was first tied to a buoy then the skiff driver had to get the other end of the net and his bow man to the other buoy in a 10 knot tidal run cross current.
In this picture they're actually hauling [round-hauling because they're not picking fish out the web] this net aboard after one end has been turned loose from the buoy. Still a bit of a chore if there's fish in the gear and a little swell running.
This picture shows a view looking aft with the net across the gunwale, the motor man, aft, has just pulled a flurry of reds over the pipe under her(?) left elbow, and the bow man to the left is keeping tension on the cork line so the skiff won't drift and pull the fish and web from the other crew.
Looks like they're all recent hits as they're moving a bit, and again it looks like this could be one of our skiffs by the details in the background but I don't know that for a fact.
The outboard is exactly behind the woman's (?) head and the slop tray or splash well is lined on top with 2" pipe and the starboard topsides extend all the way aft to the plane of the transom. There is a net post or setting post of 3" capped pipe showing over the motor man's shoulder used to keep the gear off the engine while setting out the net chute.
The seat box on the side, aft the coil of line on the net pin, and the vertical panel under the slop tray were distinctive elements of the Cape Kasilof Boatworks skiffs so I'd wager this was one of our skiffs but longer by a few feet than the boat I'm remodeling in this thread.
And this image of two young Alaskan men working their gear in one of our 18’ skiffs is about my favorite, and shows what these sort of unique welded metal boats were designed and built to do.
So that was all to explain why the boat in this remodel was designed as shown.
05-08-2010, 09:30 PM
We didn't have floor space to put a skiff in the shop during the earliest dates of the remodel, but we knew there would be a stand up console and windscreen and a couple of 22-24' gallon tanks. This post introduces the console by itself since it can be confusing to figure out how some of these fabrications are built. Let's start by looking at exploded view of the console parts then the welded results may be more informative pictures.
I like to use light metal when possible for consoles by folding the sheet into boxes, angles an various other press braked shapes; fitting them and welding the edges into a more or less cube. Using this method even 0.080" is strong enough for the helm console but won't add too much wt to a boat.
Here is a typical helm 'box' where the main structure is based on a 7 sided fold [pink w/blue interior] that provided the main upright and is cut for a top and face coaming that holds the door seal inside the pan broke door.
I usually sketch these illustrations with colors that are there to make part visually separated. I'm not suggesting a paint scheme by drawing this way, (!) just making screen shots a little easier to understand as a view of sheet metal shapes.
The door coaming is roughly equivalent to a wooden cabinet face frame, except it had to be welded inside the console, it's shown assembled in this image and the lower sill or deck coaming of the console is also shown in place
Here, the top or deck is on, and all that remains is the door mount, note in the photographs of the finish welded work below that there are control mounts to both sides of the top surface.
The door is riveted using aluminum 'piano hinge' and aircraft style rivets to avoid trying to access the hinge area with a weld. The result is a nice smooth console of light material but very strong and stiff construction.
The welded version from the sketches, showing the windshield frame and the shift throttle control cut out and box. Its always a pain to have the stiff cables run into a helm station so we ended up with a side box that allowed the deck mount style of engine control to receive cables from the almost straight down.
There is a pipe conduit under the welded deck that carries the controls, electrical and battery cables aft so all they're all run down from the floor of this console.
By using the plate mounting glass rubber extrusion the windscreen plate can be welded completely before cutting out the glass opening. Behind the top deck or slanted surface is an H of 2"x1" angle that is bolted to the top to act as a stiffener and helm pump mount.
A rebuilt Hynautic hydraulic steering system was used so we could skip a steering cable connection to the outboard. This system has been very reliable even if we did have to make our own brackets in most cases to use the hardware on the Honda.
05-08-2010, 09:32 PM
Last few items about the console
The instrument housings are kind of retro looking more or less from a 50's era automotive design influence that was a bit of humor on my part for the Skipper. I used a pipe section let into the top surface at an angle with a donut or recessed flange below the after face that will mount the instrument's bezels.
The windscreen sides have two pipes, this ends up being a truss to keep the glass panels stiff and since folks naturally stand along side the helm while running, these are hand rails as well.
The day we put the skiff inside we tested the console by putting a piece of plywood over the original ribs and standing the console in place to see if the sketches ended up with a usable design.
1" butt weld 90's of 6061 T6 were TIG welded to the pipes that truss the forward leaning glass panel and the tops of the pipe framing the glass panel are 90's as well. Bent pipe radius's are too long to make these tighter corners. We could have used bends but the top line of the windscreen would have had a more tapered look- we chose the 90's.
05-08-2010, 09:34 PM
With all the work we planned to get a nice round stern for this skiff remodel I needed to use hydraulic steering because the normal cables are so stiff they'd hang out in order to enter the tilt tube on the engine mount.
I found an old refurbished system on eBay for a fraction of the new SeaStar systems, so I ended up with some bracket work to use the mis-applied Hynautic brand pressurized glycol system.
This image is looking aft from the starboard side over the top of the engine cantilever and shows the cylinder bracket is a 2" angle with a 'pipe collar' at the other end.
The fittings are SS Swagelok, thread cap and double ferrule tube fittings with NPT male-to-tube 90's on the cylinder and bulkhead unions on the top of the engine mount.
Dropping lower in this view, which is the same angle to the keel as above, its clear how the cylinder was reused from its original single post style mount in a inboard lazarette. The interior tubing is all SS 3/8" 304 and 316L using the same fitting type- this eliminates leaks, wear, sparks, and fatigue; and is almost impossible to damage without the full swing of a large hammer.
On the right near the top a compression fitting made of 2" PVC cap and a welded threaded nipple provide a cut foam block surrounding each cable individually. The cap compresses the foam and the cables are sealed like a packing gland on a shaft.
A jack plate was needed because of my welded transom ht guess- the T stern, more on this later, rises the wake more than I figured. So, we jacked the engine mount 4" with this clamp on shown in bare aluminum under the engine's mounts.
Inside the after port corner of the curved stern section this hydraulic pressure reservoir has two lines aft and three from the helm [I think]. The tank is down near the deck, that is the blue patch at the bottom of the photo, and the Zolatone was shot inside the whole boat.
Square housing with bolt on cover [gasket showing] is the access to the engine mount cantilever. This is a water tight pressure tested void where the controls and 'dry bilge' runs.
The side strut supporting the after curve of the sheer clamp rises at an angle from the top of this sealed hatch coaming up to the bottom of the inner guard deck liner pipe. That pipe is the bare 1" in the top half of the photo.
From the stern, our remodel is on the right, the engine's added ht and the shape of the cantilever are more evident. Behind the tie strap's winch, inside the hull is the can shown in the photo just above.
On a later modification of this skiff the T bottom cut away areas were filled in in order to begin another future bottom change to the entire skiff. One reason was the amount of water on the outboard cowling in a turn; it was wet but turned better than most slalom boats.
05-08-2010, 09:36 PM
Not knowing what a Honda 90 needed for an hour's run pushing this skiff I guessed that whatever volume we built it would mount forward of the console to balance the hull.
From the previous shots you can see she's narrow aft and the rounded stern has to float the engine so I figured the tanks just aft the fore deck. I didn't want to leave a permanent bench seat in front of the console so the deck had more load space and that left the bilge and sides.
These sketches show the tanks that were built to lean out the same as the sides and bolt in to the boat. With a narrow guard deck around the hull I figured we'd tuck the tanks under that but leave the wide enough to fill directly.
This sketch introduces the two bent sides and the end plates with baffles to make the tanks' interiors stiff and keep the fuel slosh to a minimum. As with all these sketches the colors are there to make the parts easier to see as separate pieces.
Same set of parts from a rotated view point outboard to starboard and above like we were looking down into the skiff from the side. All plates, parts and braked panels were 0.125" 5086 H116 and welded with 5356 wire using a cold wire feed TIG gun.
This view of the tank in cross section through the skiff shows the position under the guard deck and essentially sitting on the deck. The mounting hardware is not shown but the fill and draw pipes are included as they attach to fittings on the top of the tank.
View point here is below the sheer and above the chine, and the boat has been cut through port to starboard; the camera is at the starboard side looking forward.
By rotating the view upward and rolling inside the boat hull toward the middle, this view just clarifies details added in the cross section sketch above.
This photograph taken at the level of the gunwale/guard deck/sheer clamp shows the starboard tank mounted to the hull with the fill fitting and draw tubing. Behind the fill cap, taken from an old outboard can and rusting away nicely, is a second SS tube existing this frame to the left. That is the vent line which runs forward under the sheer clamp at the bow where there is an aluminum bottle to take up forth and release vapor.
The tank mount is a section of aluminum angle welded to the tank and bolted to a tapped block of 1/2" plate welded to the inside top of the rib- all hidden behind the strut pipe in the middle of this view. A 3/8" full port ball valve, fuel shut off valve is located upper right under the narrow guard deck.
05-08-2010, 09:40 PM
The post above explains the tanks' design; two leaning parallelograms that fit between existing ribs and under the new guard deck. The fill from the top surface and have a vent tube running to a higher location forward and SS draw tubes run aft to a filter and then to the engine cantilever.
The tanks were welded inside with MIG and outside with TIG. Before showing the welds I'd like to disclose that I use a TIG gun, this allows me to weld nice beads with less skill, by far, that those who are good enough to use a torch and filler rod - or 'twohanded' TIG.
Like a clumsy carpenter who puts both hands on the handle of his hammer to reduce smashed thumbs- I put two hands on the handle to TIG weld. Anyone who welds will realize the difference between using this tool and a hand torch.
In this picture of the wire case open, all the parts are visible and probably self-explanatory to the welders. The torch is rigged for steel wire not aluminum in this shot.
With the case closed and a hand added for scale you can see how simplified this would make TIG welding? An [system] on/off switch is covered just above my thumb, the tip of that chubby digit is on the wire speed and the amperage control is under my thumb on a black plastic knob. The trigger finger cups the trigger to turn on the welder's contactor and gas flow timers, and water, gas and power are connected to the torch inside the ribbed cover to the left.
By avoiding a foot pedal control a welder can weld in more positions without loss of control, so with all the weld controls needed at the torch on the right hand- the left hand can cup the torch, the case or the black ribbed cable cover and steady the weld.
This is an end plate to side seam weld done with the TIG gun.
This closer view of the top shows the fill pipe socket welded to the tank top doubler and two, 1/2" pipe, half couplers one nearest the camera has the draw tube socket welded below and the other is the vent. The doubler is used to insure no flex of the fill or draw tubes can effect the tank top surface and the vent tube half coupler is just butted to the top so all gases can exit under the top surface.
The gas cap screw-on fitting is not on, but can be seen in the previous post showing this tank installed in the skiff along the starboard sheer clamp. We got the weld on fitting from the aircraft supply house, they are thin but fit all our old metal can caps just fine.
Since we remove the tanks periodically and wash them to keep the water corrosion down, they have drain fittings even though gasoline tanks are NOT supposed to have fittings below the top surface. A SS socket recess pipe plug fills this 1/2" pipe coupler half and leaves the tank side smooth but allows improved washing and flushing.
This is a closer view of the drain fitting weld which holds the half coupler inside the tank so the pipe plug will be completely flush outside.
Each tank carries 22-24 gallons of fuel and the few hundred pounds located about 60% forward seems to help the light load trim of the remodeled skiff. Tanks were painted with Zolatone and clear coated but spills and 'gas rinses' have generally degraded the original paint job in the last few years.
05-08-2010, 09:41 PM
As a net skiff the sheer was lined with a single round pipe but as a recreational skiff we wanted a guard deck or sheer clamp in order to stiffen the remodeled boat and to make working over the side more comfortable.
To put a nice looking plate around the sheer I had to predict the shape of the bow deck first since the rolled pipe at the stern, shown above, was already tack on. The plate would be roughly flat in the stern and incline increasingly as along the topsides forward until the little short deck near the bow.
This picture looks forward along the port side over a plywood template of an aluminum transverse deck frame.
Once the metal frame was in place a blank was clamped over the bow and trimmed to fit the original pipe's centerline where it would eventually weld. Also the inside of this deck piece was cut to a radius that would echo the stern roll and begin the side deck/sheer clamp.
To hold the rectangular blanks of 0.125" used in this narrow addition at the sheer, scrap wood was laid over the gunwales to give the approximate level of the final plate. Looking at the port port bow you can see the butt joints are being marked while the blanks are in the approximate slope of their final position.
This image taken along the starboard after quarter looking over the bow shows outer line of the deck at the centerline of the original sheer pipe liner and butt joints of each plate blank in the sheer clamp; cut and tacked up.
The transverse frame at the bow has a pipe liner below to help soften that edge, its visible below the bow deck just below the sheer.
Looking aft over the bow stemhead the pronounced shape of the top fore deck is more clear. Also clear in this photo is the transition between the slope of that fore deck to the flatter angle aft. At the transom, because the rolled pipe aft is inclined upward aft; the sheer clamp can be completely flat side to side and still drain so it won't need to be sloped overboard.
In this photo all the guard deck plates are cut to their outer shape and all the butt joints between the rectangular blank pieces are also cut and have weld back up strips tacked below to keep them from sagging before additional support is provided.
05-08-2010, 09:42 PM
A 1" pipe needs to be slit and forced onto the inner edge of the narrow guard deck that is tacked to the original pipe sheer liner.
This image of the guard deck at the bow shows the sides have been battened and cut and a rolled piece of prepared to be fit at the bow. A length of aluminum angle extrusion was clamped to the bow and stern curves already cut and a 'fair' curve drawn on the blanks. This line was cut with a wood cutting jig saw and cleaned up with a Vixen file to remove any burr and to insure the line was without kinks or bumps.
Because the narrow strip of plate already tacked on will be flexed up and down, and clamps will pull the liner pipe onto the inner cut edge; some preliminary welds of about 3-4" are already applied between the original pipe and the new remodel's sheer clamp plate.
The pipe above has been slit on a table saw using a wooden jig to hold it as an UP-right 'U' and here it's seen clamped and tacked onto the bow deck inner and after edge. Notice the butt joint in the liner pipe is not common to the butt joint in the plate.
At the stern another piece of 1" pipe is rolled and will be fit to the sheer clamp's inside edge.
Here is that rolled piece of 1" 6061 T6 pipe, slit along its length, clamped and tacked to the guard deck plate's inside edge seen in this cross section photo looking aft along the port side.
Looking aft along the starboard side, all the inner pipes have been installed on the plate's edges. The pipe strut legs are being installed one on each of the ribs and some at the bow behind the spray rail on the outside of the topsides.
Finally a view over the entire skiff from astern showing the rectangular plate blanks fitted to the original pipe shape at the topsides' sheer and a curve cut inside and lined with 1" pipe. This shape, along with the struts shown linking the new sheer clamp and the ribs, will keep the skiff rigid while the new stern is added.
05-08-2010, 09:44 PM
The original skiff had a hull shape that was fine for its purpose and size but in the remodel I wanted to add a rounded stern and mount the engine aft that shape.
Plans aren't worth the time to draw if you don’t have the original hull's plans to work from as a basis to add or modify. Our original net skiff was built by eye during a time when a series of similar skiffs were being built by a small group doing relatively the same boat over and over.
It is true each boat was 'different' because each one had more or less flam, some bottoms were wider than others and some topsides deeper; but overall they were formed to the same basic lines as all our skiffs for net fishing.
To match the hull above, a rolled pipe was added to the sheer after the flat transom was removed. This provided the basic curve of the transom's new shape and would be the base line for the remainder of the shape.
In order that the lower bottom panels be a cone with the top wider than than the bottom, and the top panel be a cone that was inverted- a median line between the two cones needed to be put on the boat first.
Along the sides is a 1-1/2" angle with both legs on the hull, this breaks up the topsides panel and deflects spray without taking fish out of the net as the come over the sides.
The first addition in stern framing was to roll a flat bar between the aft ends of this angle as the natural median line between the stern's two curved elements.
The skiff is on horses and pipe jacks to make working on the median flat bar easier.
Rolled bar wouldn't hold its shape without some stiffening, so holding metal over the bar to scribe and fit the sterns' curved shapes wouldn't work. The flat bar would distort without some filler to make it rigid.
By cutting a plywood scrap into the same curve as the panel and screwing 1" x 2" scraps of aluminum onto the outer/after edge with dry wall screws, a plywood stiffener can be tack welded to the flat bar.
This photo shows the median flat bar 1-1/2" x 1/4" 6061 T6, cold formed to the curve of the transom.
Above that bar is the T bottom which is an extension of the original bottom with short sides then a panel that is rounded like the sheer. This area would leave room for large trim tabs mounted to the original stern and still be under the boat fully when running. Large wide tabs take less movement to trim the hull and they would be driven by cylinders inside the hull.
This photo mainly shows the plywood 'welded' to the flat bar in preparation for lower hull stern plating. A leg holds the bottom plane extension that will be the main running surface aligned with the engine mount.
Here, some of the bottom curved panel is marked cut fit and the port side (now on the right) still has the scrap pieced tacked to establish the surface of the new plate to be added.
Also clear in this photo is the somewhat difficult shape transition needed to plank this area into a clean shape. The original topsides can be seen as they are continued into the curved panel under the median flat bar. The upper panel's transition is more radical if it is to remain fair.
This picture is at the same stage as the previous one but from a more outboard view of the stern. Instead of creating a straight line butt seam with the original topside a half circle was used to help smooth the plate transition and increase the weld joints' area and length.
Cold forming 5086 alloy in 0.125" (1/8") thick material was a work out- the very tight curves would have been much easier to fit if they'd been pre-rolled or formed with an English Wheel. At the time this work was done we didn't a have any other way to form these panels, they were held to the temporary framing and tacked and pushed and clamped and tacked again. This shape of skiff stern was a pain in our sterns to plate.
05-08-2010, 09:45 PM
If there is no builder's model or plans to use for plate take offs, the only way to fit hull panels to their final shape is on the boat. To fit a panel that would butt to the pipe along the sheer, and fit to a flat bar edge at the median [lower edge of the top panel] we had to put up a forest of small 'sticks' of scrap tacked into the surface. These held the trial sheet blanks into the eventual surface of as the edges of the blank we marked, removed, cut and replaced to marked again. Slow and strenuous because the material was stiff for the curves.
Here is a photo from the starboard side aft looking toward port, of the lattice of sticks we tacked in to hold the blanks while they were scribed. We used heavy craft paper to make an original pattern so the metal could be put up and marked as little as possible.
Same view but from the other side of the hull,
This view, inside the hull looking aft at the temporary framing and the lower after panels tacked in, show the T bottom concept about as well as we'll see inside this skiff.
05-08-2010, 09:46 PM
Unfortunately for anyone that is curious about the final details of the stern I was too busy to take pictures so we'll jump to the final shape images.
The engine mount is plated up off the two previously seen bars that formed the basis for this extension. The top to corners are plated with 1/4 segments of 4" pipe to make the shape more rounded and look more in keeping with the rounded stern.
A pair of 3" x 2" x 1/2" channels were made by welding flat bar to an angle forming a channel not in the standards shape book then a router on the corners with a carbide bullnose bit to gave the round-over shape. THese were both welded to the transom plate on the aft end of the engine 'box'.
Moving outside and backing away from the boat but from the same angle as the previous image, the overall look of the skiff's lines flowing into a rounded or counter stern is well illustrated by this picture.
The trailer side board blocks the lines of the median and spray rail transition but the sheer and topsides shapes are shown here looking aft along the port side from under the bow.
Form aft the transom a view of the topsides transition that helps to see the finished shape of the remodeled skiff. On the top of the transom is a pair of 1/2" bars to be removed if the skiff needs a lower engine point- it didn't. We ended up with a jack, shown in previous pictures, about 4" high!
Here is a look under the flat bottom beach landing net fishing boat that was remodeled. This shows how flat the bottom is, and is the site of a planned remodel this year, to add V to this area so the ride is softened.
05-08-2010, 09:50 PM
I could only dig up a few decent pics of this skiff in the last few years' use, once out of the shop they don't seem to have the photographic attention they do still in build.
Here is the Skipper's Mom and the Ship's puppy spring of '09, on a ride out the mouth of Seldovia Bay but the reason to show this photo isn't my lovely wife - it's the hand rails, tanks and deck.
This is about all we have to show those items in any decent focus, so the lower left corner shows the tank to deck mount. This is a piece of 3/8" aluminum angle extrusion cut as an 'L' then drilled on the deck leg for a bolt and the other leg welded to the tank wall.
The deck has a 1/2" thick x 1" x 3/4" bar, tapped to accept the 3/8" coarse SS bolt, then welded to the deck. This is the easy way to install tanks- bolt the legs and their tap blocks together then block the tank in place with wood blocks. Once the tank is located MIG tack the tapped blocks to the boat while the other anlge leg is tacked to the tank. Remove and weld both parts of the mount to the tank or hull as tacked. The tank will fit right back where it was, and stay there.
In the eyes of the bow under the small foredeck is a triangular shaped aluminum bin that bolts to the deck like the tanks and the struts that hold up the sheer clamp/guard deck. This bin or anchor locker holds the ground tackle and a buoy to 'sky the hook' with the outboard- beats hauling line for a few hundred feet!
The handrail was added a few years later after much sniveling to the Skipper by the builder. I felt the sides were too low in the final skiff as we'd put an air tested, sealed deck inside to avoid bilge problems and to give reserve flotation if swamped. That raised the deck and 'lowered' the topsides and the guard deck down almost 5" Not much in the bow where the topsides are taller, but in the waist and at the stern I thought it wasn't enough depth.
The forward rail shown here was mounted to the 1" pipe liner of the sheer clamp, and the legs and top rail are of matching pipe so all the joints are saddled T welded. I use the TIG gun for 80% of the circumference but there were stretches of those welds that had to be hand welded, reminding me how much more skill is needed to weld in that method.
This picture was taken of the lovely fishing women but I'm including it to point out the lovely taft rail aft, and provide another view of the hand rail forward.
These hand rails are some of the nicest ones we've been able to add to any skiff in my opinion, even if the Skipper, black coat 2nd from right, did resist my "wisdom" for a few seasons; they're on now.
Finally, here is the remodeled set net skiff doing what it is now intended to do- fish for halibut. Even seated on stowage lockers, I think the hand rails are a welcome addition, good ht for working a line and increased safety for the whole crew.
We're looking aft through the console along the port side about 10 miles out in the lower cook Inlet.
This skiff will have added work this spring so I'll try to update when that work is done.
05-08-2010, 10:24 PM
WOW! What a well documented build. I totally appreciate what went into that, as a welder and former boat builder for Northwest Jet Boats. Alot of work. Nice job man!
05-09-2010, 01:19 AM
Great looking build. That looks like something I would love to get a chance at doing.
What was the skin thickness? And how did you split the 1" pipe?
05-09-2010, 01:30 PM
thanks for your kind remarks,
The original skiff's bottom was 0.187" 5086 H116 and we added a 0.125" 5086 H116 deck over long framing laid on and emdded into the original transverse hollow frames. The sheer clamp or guard deck at the top was 0.125" 5086 H116 and all the welding was done with 5356 wire in MIG or TIG.
The original sheer was 1/2 of a 2" pipe extrusion which is readily available in the NW, not sure about other areas, and is 6061 T6 we cold wrap that with a forest of 12" and 18" long furniture clamp outside then inside with a 'three way' joint at the top which is sanded fair to leave a 'whole' pipe at the sheer.
The one inch pipe is slit in one of two ways. If you have a table saw then clamp a secondary fence next to the original with enough room for the pipe to be slit, and a top cover, so you can feed the pipe and not loose control. A cut guide behind the blade or a line on top of the pipe matched to a point on the in-feed table's top cover will keep the pipe from rolling as its fed into the blade.
The second way is to weld a piece of slit 1-1/4" pipe that has been 'expanded' and welded to a plate the skill saw base is screwed to. The saw blade is then plunged into the plate and pipe and clamped upside down between saw horses and the pipe fed through. This requires deburring the inside of the original 1-1/4" pipe slit or that edge can gall the 1" and the fit needs to be fairly loose, and you need a top of pipe mark and a matching line up mark on the 1-1/4" pipe guide to keep the pipe from rolling.
I pretty sure about the line up marks as I distinctly recall our first split pipes have a distinct barber-poll cut pattern and having to buy more pipe to get the slit piece on the boat.
The last method is a skill saw method as well, #2A so to speak. In this method you arrange four or five saw horses with a pair of 2x4 or 2x6's laying on them. The pipe to be slit is laid between the two planks (three or four on either side butted end to end) with furniture clamp UNDER all three long pieces forming a plank-pipe-plank flat surface. Then an angle is laid on the pipe and a magic marker line placed at the toe of one leg so there is a saw line and this can be cut free hand using a skill saw. The skill saw table will stay level and controllable on the two side planks and clamps will hold the whole show stable enough to walk the 20 length and the method is pretty fast to set up if you already have a sheet (hand) cutting station set up; horses and planks.
Curved pieces of pipe are slit using the table saw with 6" or 8" strips of 3/4" plywood inside the original table fence and the secondary fence to keep the rolled/bent/formed pipe in a single plane through the blade. Two men usually handle these cuts because you have to keep the entire formed piece in in control AND inside the two ply fences so the cut is clean.
Powered by vBulletin® Version 4.2.3 Copyright © 2016 vBulletin Solutions, Inc. All rights reserved.