We purchased our first cruising boat last winter. Until this year, this was always an inland lake boat and we have been busy getting her set up for cruising the east coast and hopefully the loop in 2021. One of our last upgrades left to do is adding a tender and a way to store/launch it. Never owned a dinghy but we are leaning towards a very lightweight 8'2" or 8'10" fiberglass RIB with a 5 or 6 hp motor that we will store on a Hurley swim platform mount. Total weight under 150#. 95% of the time it will need to carry two adults and two small (15#) dogs. Obviously, the smaller & lighter, the better, but how small becomes too small? We don't intend to anchor out a lot, maybe one or two nights over a week of travel. Recommendations on size? Is 8'2" too small? Thanks!
I think too small. You have the capability of carrying a larger dinghy that will serve you well without being too unwieldy.
We too cruise with dogs, and typically anchor out. The dogs have to go to shore. Night, day, in weather. Sometimes the anchorage picks up a little. Even a protected anchorage will pick up, and a little larger dinghy/motor will help. Also, as others have pointed out sometimes the mothership will stay and the dinghy becomes a longer range exploration vehicle, so having something that will plane comfortably will help. the 8' 6 hp won't get you there with two people.
Think too about guests aboard, and taking them along. My guess is that you have a guest cabin and might ocassionally do that. While you can always ferry guests, its nice to take all four of you at once.
A couple things to help you sort out what will be best for you: How will you cruise? Will you exclusively go dock to dock, and only occasionally ever use the dinghy to go a very short distance from ship to a dock? Or will you be going exploring? Will you go land on unknown beaches/shores of varied makeup? If you are going to be at mostly docks and rarely use the dinghy, then maybe you are on the right track. If you are going to use it a lot, and be landing on beaches with the dogs frequently, then think about maybe a 10ft RIB. RIB is more durable on rocky/barnacle beaches, but very stable. They will plane well with the HP people have talked about (15).
A couple things we have found useful for us. The dogs have no grip on most gelcoated (even non-skid) surfaces and RIB tubes. We use some step treads and outdoor carpet mats from Lowes that have square tread blocks the dogs can get their grippers around to help them feel secure jumping into/onto the dinghy and boat.
https://www.lowes.com/pd/Blue-Hawk-Black-Rectangular-Stair-Tread-Mat-Actual-9-in-x-35-in/999946338
We take the dogs to beaches before bed; sometimes they haven't been able to go and get desperate just at dark in a crowded anchorage. We found the NaviSafe Dinghy Complete system (around $150)
NAVISAFE | Navisafe Dinghy Complete
that gives us a portable but mountable battery operated USCG approved nav lite set up on our dinghy, which otherwise does not have an electrical system. We also have an anchor buddy system, which allows us to anchor the dinghy off the beach, then pull it in to us when we want to leave. It lets us keep from the dink being either stranded high up on the beach or battered by waves/wakes while we are onshore.
As for your choice of davit, there is some discussion here about putting the dinghy on the swim step and the dangers of following seas. My boating is inshore, and my dinghy is on the Seawise davits others have posted about here. While massive (for me) following seas can/could batter it, that is a known to me and a decision point for me as to whether I go out in that weather. The bottom tube of my dinghy is about 18 inches off the water. Not sure how far your system will have your dinghy off the water, or what the risk is for having following seas slop into it. Something to consider if you haven't . Having a lot of water in it in rough water would be scary; with the Seawise system I worry about waves bashing into it and smashing my lower mounts loose.
Good luck in your search!