Ever seen a towboat out of the water?
SKIN COOLERS are welded to the sides of the hull. Another type of cooler is a series of pipes on the bottom of the hull called KEEL COOLERS. GRID COOLERS are like radiators for the engines, gear boxes, and generators placed in recesses in the hull.
Building a simple frame hull.... "Towboat" Joe's technique
Here's a basic frame work for a 1:48 scale triple screw towboat 200' x 54'. With a hull so large ( 50" x 13 1/2" ) I prefer to do the stern section separate from the main hull. I "break" it where the deck meets the angle for the raised stern. That is usually where the tunnel stern starts flattening out for the bottom of the hull. Notice that the hull side extends 4 1/4" past where I stopped the bottom sheeting. That is where the flat part of the bottom starts the rise to the tunnel stern.
Here shows the framing of the tunnel stern. Notice the three tunnel areas cut into the framing. This will be the end that will be mated to the main hull. Small sheets will go from here to the flat bottom frame. Offsetting the joints like this will also make a stronger joint.
Here is an overhead view of the tunnel stern bottom and the port side showing it partially sheeted. Notice reinforcing angles on the cross frame to increase strength. Always build framing so that each sheet will glue together on a supporting frame.
Here are the two parts joined together. Next thing is to glue 1/2" blocks into the outside corners. This not only increases strength, but also gives you wood to sand into when rounding off the corners. Next I like to glue a 1/4" or 1/2" sheet of Styrofoam to the bottom with a sheet of 1/4" or thinner plywood on top of that. It gives me something to screw into if needed plus adds more strength to the bottom.
Another frame hull can be viewed on the Bruce Darst page.
Here's the hull of the Bruce Darst (a Jeffboat design hull) I carefully mark off the placement of the steering and backing rudders and I usually install the sleeves for the rudder struts first thing. Then I measure for the shafts and drill holes for them. That way I can line up the shafts to figure the center line placement of the Korts. If I use a can with a seam I usually epoxy the seam to the hull. It's far less noticeable in that location.
Building a Foam Hull.... "River Bill" Zumwalt's technique
Using the Hot Wire- Foam Cutting "Bow" .... this drawing shows how "Two Templates" from your plans - Side Hull Profile, are made, then placed - "On Each Side" of the foam block. The templates must be straight and aligned correctly, meaning directly across from one another, to insure the hull is cut square. The two - templates, must also be cut correctly, allowing for the thickness of the coverings of wood and Fiberglass materials too. This is a must do - task, in order to keep the model in its correct scale size!
ADJUSTING THE TEMPLATES .... By this - I mean, if you chose 1/8" thick balsa sheeting to cover the foam core hull - for example. Then you must ( Remove ) this same amount from all 4 sides of the Foam Block, prior to adding the Side templates Plus you must remove an additional 1/16" off each of the foam, to allow for the fiberglass & Resin materials, in their thickness - as well. These two adjustments to both - foam block and templates, insure the finished hull will be exactly to scale. "So this is critical in required tasks, before your ready to use the Hot Wire and carve the foam hull. Once the templates are adjusted, its time to heat up your - HOT WIRE foam cutter. And Draw the Bow - Gently along the templates - slowly with a steady pull, to carve away the excess foam.... ( SEE NEXT STEP BELOW )
Using the Hot Wire- "Hand Wand" ....Once the foam Hull Core - is cut out with the hot wire knife & bow, gently sand the hull core and check measurements, the block of foam has got to be - Square in Shape." The next task will be to carve out the "Tunnel Stern" for the "Wheels" = Props and Rudder systems to be installed later, by changing to the Small - HAND WAND. REMEMBER, the Tunnel Hull - Stern, must also be carved out & adjusted in correct depths, to allow for the thickness of woods & Fiberglass Covering too, since this area will later be covering too. In this drawing, you can see the "Tunnel Hull" is being "SPOONED OUT" with the hand wand. Note ... The wand ( Its Wire ), may want to bend out of shape - as you use it. If it does, your pulling a bit to hard, so adjust the voltage a bit higher, as needed. "Just don't get the wire - TO HOT, Noting the hand wand uses a shorter - wire, that will heat faster, than a longer one!
SPECIAL NOTE..... Another way to make a Hand Wand, is to use some heavy "Solid Copper" wire, mounted into an old solder gun. Shaping the wire to required cutting shapes, then heat it the solder gun and use it to shape foam objects or sections of the hull!
The "Thomas K." as the Foam - Hull, was being Built
The Deck Plate - awaits the 1/8" balsa sheeting. Bottom, side, Bow & Stern Plates already installed already, the deck plate - Frame Work, is completed. Note the area the r/c systems will be installed into, hasn't covered in wood sheets - yet!
The ( 6 ) Rudder Sleeve Tubes, are being added to the stern, plus the drive shafts have been fitted. Note the area of the r/c systems, is now also sheeted ( Inner - Rc Bottom Hull Plates ) and all wood seams have been filled, sanded and sealed/ So the hull is ready for glass cloth and resin.
The deck plate - sheets applied, work continues on the "Rudder Sleeve Tubes" to seal them and the stern - deck plate. Sealing the sleeve tubing, was done with J-B Weld Automotive Epoxy, because 50/50 hobby epoxy will not withstand moisture for long periods and can come loose!
The Thomas K. nearing completion, note its Structures - taking shape, made of mostly balsa wood, with some plastic's, the structures details include a fully Detailed - Helm, and All Working Nav. Lights & Radar.
The completed 1/48 Scale - 4 channel r/c operated model, after taking several "St. Louis Admiral Club" Awards. Powered by 12 volt - Gel Cell Battery, with twin "Homemade Electronic" Speed controls and Twin - Dumas motors, and prototype Duel - Rudder Steering. Capable of Pushing - over 30+ scale 200' barges, each barge = 50" in length, for a full scale tow, over 26 feet long - Overall.
Fiber glassing a hull
I start off by taping the cabins off so spray adhesive won't get on them. The mat I am using is 3/4 oz fiberglass mat. Spray adhesive to the hull and lay the mat out, cutting the contours as needed. After the mat is stuck flat to the hull with no raised places, it's time for the first coating of resin.
There are two types of resins for this job, Polyester Resin and Epoxy Resin. I prefer Epoxy Resin because it's virtually odorless and mixes 50/50. For fiber glassing use Finishing Epoxy for it is thinner and flows better than regular epoxy used for gluing. Polyester Resin is extremely strong in strength and smell. You have to estimate how many drops of hardener to add to each ounce of resin according to the humidity. Humidity affects the setup time of Polyester Resin. You'll need two measuring cups, a mixing cup, stirring stick, a disposable paint brush, razor blade, and a squeegee. Old credit cards make the best squeegee I've ever found.
After the hull is coated, use the squeegee to work out any bubbles or creases in the mat. Always work outward with the grain of the mat. When you've worked it to where you can see the pattern of the mat, then it's making good contact to the hull. If you get any creases that won't work out, use a razor blade to slice it and it will usually flatten out.
Set the hull aside to dry. keep an eye on it for the next couple of hours, especially if it's a big hull with overlapped mat. Sometimes, after it has set for a while, it may come loose or create a bubble where it has come loose from the hull. just take the squeegee and lightly rub it back down.
After it has dried, use a sharp knife to trim of any strings hanging. Next give it a light sanding and brush on another coat of resin. I usually apply two to three coats of resin after the first initial coating with the mat. Be sure to give it a light sanding between coats. After the second coat the hull should start looking nice.
Don't try to just coat a hull with resin and no mat. Either type of resin will become brittle and crack easily without the mat. I have found that the one layer of light mat is sufficient for most hulls. For large heavy hull, you may want to go to a heavier mat. I buy my mat and Epoxy Resin at Tower Hobbies.
Scratch Building Kort Nozzles
I make Korts out of anything I find that fits the diameter of the wheel I'm using on the model. I've used everything from 35mm film canisters to PVC pipe. Here is an anti-perspirant can I cut up with a moto-tool with a fiberglass cut off wheel. A good way to mark your diameter is to sit the can on the work table, stack some blocks and sheets of wood to the cut mark, then hold a sharpie in place and rotate the can.
Here is a Kort made from a plastic cap from an aerosol can. Here you can see the shaft support carved from bass wood. The wheel and rudders are scratch built. I use brass rod for a rudder shaft and grind it flat on one side to solder the rudder cut from sheet brass.
Here's a view of a finished boat. A larger photo can be viewed on the G. L. FURR page.
This is the front part of those cheap $1.00 flashlights that takes two "C" cell batteries. I just took the lens and bulb reflector out, cut it to the length I wanted, used a moto-tool with sanding disk to removed the threads inside and there you go. A 45mm prop fit perfectly inside. I made a couple for my American Viking.
R/C ADVICE... If you're building a Kort for an r/c model from a can or plastic that is flimsy, you should make it stronger by laminating strips of bass wood around the "Kort" to take the flexibility out of it. You're first choice may be in plumbing supplies or opting to go the expense of buying a production Kort from someone like Harbor Models.