Using a solar car battery charger to power a solar boat?
The power and energy levels mentioned below, if you cover most but not all the boat area with solar cells,  are 10 to 20 times as high as from your example panel. Pricing MAY be similar.

IF you are willing to work with bare PV (= photovoltaic = solar) cells then you can get much more Watts per $ than you get from a prebuilt panel like the one you showed.

ebay solar cell pricing 

This ebay listing offers free shipping from China and about $US19 for 20 Watts of cells (5 x 4-Watt 6" x 6" cells. ) Price falls to $0.50/Watt in 1 kW quantity). Chose Watts etc from "model" box. They also sell tabbing wire, flux pens etc. To use this you need to be able to solder and use reasonable care - the cells are fragile. Their is a vast amount on-web on how to do this.

The above products MAY be related to eco-worthy in San Francisco - or may not. The encapsulant bottle on the ebay page had eco-worthy on the label. They sell many sizes of PV cell pieces and related equipment and prices seem OK. 



"Best" energy for area are liable to be silicon wafers on ebay. Broken pieces can be as good if carefully joined. Higher efficiency the better. 15% - 18% range is target. You can get special ~= 23% ones but they are rare and costly.

IF you can cover whole area with solar panels you get 2' x 1.5' = 3 ft^2. 
3 ft^2 = 0.278 metre^2.
At 15% efficiency and 1000 Watts/m^2 insolation (full sun) you get
Power = area x insolation x efficiency
= 0.278 x 1000 x 15% = 42 Watts.
Reduce that by at least 10% for inter cell spaces and probably 20% in real life.
43 x 80% = 32 Watts.
As you MAY not want a rectangular boat top and as you MAY have surfaces that are used for other purposes the actual area may be lower again - scale accordingly.
I'd guess that 20 Watts is attainable in real life.  That's with full sun - say cloud free at midday. Less as sunshine level (insolation) varies. 

Using bare cells you will need an encapsulant or to cover them. For short term use you can use a thin plastic sheet. Semi rigid polycarbonate can allow you to make a cover that offers SOME protection by not touching the cells. You lose about 10% more light from a good clear thin layer of polycarbonate. 



Added:


  What's a tabbed solar cell? 


Tabs are the flat wires that connect between the individual cells.
Some cells come with tabs already soldered on, others you need to add them.
To connect multiple cells in series each tab goes from the top of one cell to the bottom of the next (or vice versa). Thusly:

  

Larger view

Note that you can see the tab wires going from one side of one cell to the other side of the next cell in each case.

I'm not sure what the "others steps" are in your recent question. Electrically, once you solder multiple cells in series, as above, you have a solar panel. It will be ultra-fragile and subject to corrosion. At a minimum you'll want to fasten the cells to a stiff flat non conductive surface (FR4 PCB laminate is a common choice) and you'll probably want some form of protective coating and maybe a housing. You have never explained the details of your requirement , so we can't tell how much power you need or whether maximising power matters. As a one-off, if absolute mx power was not an issue, I'd probably buy a PET covered PV panel that met the need. Far cheaper than the housed item you mentioned. A lot easier on getting a finished product than bare cells. Many such on ebay.