Anything approaching the 4,000 lbs mark requires good trailer brakes for the Ridgeline's brakes are just average and
tests have shown it to be poor when hauling heavy loads. Also, when you are towing close to the Ridgeline's maximum capacity, it is highly
recommended that you use 91 or higher octane gasoline; your transmission will thank you.
What type of terrain will you be traversing with this future boat? If it's even small mountainsides, such as the Appalachians, I would not exceed your Ridgeline's Gross Combined Weight Rating (GCWR). If you'll be traversing rolling hills, you'll be in trouble if you exceed 700 lbs of the GCWR. If you'll be traversing flat terrain you can do it if you don't go over more than 900 lbs of the GCWR. This has been my experience pulling different trailers and hauling different loads on different terrain up, down, and around the Mid-Atlantic Region with my 2009 RTL.
I would not recommend exceeding the GCWR, but if you need to the above is what I've learned.
Note: These numbers should not be applied to the 2006-2008 model year Ridgelines for the 2009-2014 model years have a different engine, a revisited transmission, and an integrated class III hitch.
You can read about my most adventurous towing trip to date with my Ridgeline at the following thread:
http://www.ridgelineownersclub.com/...club.com/forums/20-dear-honda-feedback-forum/62922-my-trip-lake-cumberland.html
For my "does and don'ts" about towing heavy trailers with the Ridgeline, read this thread:
http://www.ridgelineownersclub.com/...club.com/forums/71-problems-issues/92634-question-about-towing.html#post1347210
Keep this in mind, if you get a 4,100 boat (wet) a dual-axle anodized boat trailer with single-axle surge-brakes will be about 900-920 lbs. That combination puts the Ridgeline at its maximum tow rating. Now add your weight, the trailer's weight, and your Ridgeline's curb weight and compare it to the GCWR, let's say (175 lbs + 5,000 lbs +
4,491 lbs) - 10,085 lbs = 419 lbs; that's how much additional stuff you can put in your Ridgeline before you exceed your GCWR. So, if you're going to be traversing some mountains and carrying four or five people with their personal stuff, you may be okay depending on what you put in the bed.