Well, if you're never leaving the dock then I guess you can't impress the judge with the way that navigation puts mathematics to practical use. Trig and even spherical trig make sense when you're navigating, geometry becomes practical, and math skills (will we make port before the storm?) become a matter of "gee, I ought to know that".
OTOH mother's do worry about kids falling in the water and drowning, simply having water around with constant adult supervision seems to be a greater hazard than all the equally real dangers we ignore in homes.
Does her home have natural gas or propane? Couple of those blow up every year, but we all ignore it. Got an attic? Attracts bats, which carry rabies. Same thing for any critters under the porch. Or poison ivy invading corners of the garden.