A seascape is essentially a landscape featuring the sea instead of land. This means that the focus of the painting is the water and background, although the seascape may also feature animals, boats or even people. The challenge of painting a seascape in acrylics, as with nearly any painting done in acrylics, is in getting the paint to blend before it dries. Once the paint begins to dry (this happens in only a matter of minutes), blending is much more difficult -- and blending is important for creating a realistic illusion.
Set up your materials. Because you're working with acrylics, you don't need to worry about ventilation--acrylic paint doesn't emit a smell or harmful vapours. Place your easel in front of you and a palette to your side. You'll need jars of water for mixing water with paint. If you have a picture to look at for inspiration (this is recommended), tape that to your easel or place it somewhere nearby where you can look at it.
Draw a line on the canvas to represent the horizon, where the sea meets the sky.
Dip a flat, medium sized paintbrush in blue paint. Start at the top of the canvas and paint downward in horizontal strokes. The paint should become lighter as you move closer toward the line where the sea meets the horizon. Mix the blue paint with white, if necessary, as you proceed downward. This part you are painting right now is the sky.
Clean the paintbrush and dip it in paint that is a slightly darker blue than what you used for the sky. If you're not sure how to make a slightly darker blue, dip the paintbrush in a little bit of the blue you used for the sky and mix it with a little bit of brown. There should be more blue than brown in the mixture.
Paint the sea in horizontal strokes, starting at the top where the sea meets the sky. Paint down to the bottom edge of the canvas.
Dip your medium sized rounded paintbrush in a light blue/nearly white colour paint. Paint little horizontal tufts of white distributed throughout the water you just painted in step 4. These tufts of white represent the surf on the waves in the sea. As the tufts come closer to the bottom of the canvas, they should become larger and wider. The tufts of paint that are closer to the horizon line should be thinner and shorter. This is a trick to create the illusion of depth. Use a dry paintbrush to blend the edges of the tufts into the blue paint behind it. If the blue paint of the ocean has already dried when you are painting on the white tufts, you may need to add some fresh blue paint to the area around the white tufts, in order to make blending easier.
Clean your medium sized round paint brush and dip it in a darker shade of blue than the dark blue you used for the water. You can darken this blue with a little bit of brown. Use this paintbrush to paint little strokes of darker blue throughout the water, randomly distributed in much the same way that you randomly distributed the tufts of white throughout the water. These darker splotches of blue represent the variations in the surface of the water. As the strokes come closer to the bottom of the canvas, they should become larger, darker and wider. As the strokes of paint are closer to the horizon line, they should be thinner, shorter and less dark. If the blue paint of the ocean has already dried when you are painting the darker blue strokes, you may need to add some fresh blue paint to the area around the darker blue strokes, in order to make blending easier.
Once you've painted the sea, add some details to the piece as desired. These details could include a sailboat in the distance, birds in the sky, clouds or a sun.
Acrylic retarder is a product intended to slow the drying time of acrylic paint. Acrylic retarder is available at art and craft stores. Another trick you can use to prevent the acrylic paint from drying too quickly is to spray the painting with a very fine mist of water. You can also try mixing the paint with water before applying it to the canvas.