The place to start is your eye height when looking thru the glass.
Standing , sitting , for you and the bride.Mark the spot looking at the horizon and measure.
That will give the location you need swept.
The parallel arm units will allow the blade to be verticle and allow a wider sweep.
Multiple speeds is nice , and the better units will come with a parking feature.
The controls should be really EZ to reach sitting or standing as the unit will be turned off and on frequently in a light rain .
A cheap auto store FW washer should be installed as salt will destroy glass very quickly.
NEVER use wipers on plastic.
The marine units from IMTRA are sold at Defender , and IMTRA has a great web site to figure it all out.
Marine units are required if the boat will see salt water.