Issue is in your BoatTile controller. When you set params at the point of firing the event, you need to set it as an id not an object type.

Example,

({
    onBoatClick : function(component, event, helper) {
        var BoatClick = component.getEvent("boatSelect");
        var boatId = component.get("v.boat").Id;  
        BoatClick.setParam("boatId" : boatId);
        BoatClick.fire();
    }
})

Issue is in your BoatTile controller. When you set params at the point of firing the event, you need to set it as an id not an object type.

Example,

({
    onBoatClick : function(component, event, helper) {
        var BoatClick = component.getEvent("boatSelect");
        var boatId = component.get("v.boat").Id;  
        BoatClick.setParam("boatId" ,boatId);
        BoatClick.fire();
    }
})