What size outboard for my 10' Inflatable Tender

Hi,
I am buying a new 10 foot (3100mm) tender for my cruising yacht. This tender is a rigid bottom inflatable with a dry mass of around 45kg (95 lb). I want to select a 4 stroke outboard that will get this tender on the plain with myself and my wife and maybe some miscellaneous sailing gear, so a payload of a little over 200kg (440 lb). The inflatable is rated for upto a 10HP motor, but I wanted to get the absolute minimum size, say a 4 stroke 6HP motor. Will this size motor be able to get us plaining? I know there are some formulas to work this out, but I am really after some practical experience and advice.
Thanks,
Dale.

 

Practical experience won't help unless you happen to get it from a person with the same boat. There are too many variables in design to assume that someone else's design will perform the same as yours in similar conditions, that's why the formulas exist -- to give you a general idea of what you might need.

Jim Michalak's formula is one HP for every 50 pounds, which means you'd need 10.7 HP. I think his formula is conservative for small boats, so you may not need this much power to get on plane ... but this still indicates to me that you should go with the 10 HP engine, not something smaller that 'might' work but probably won't.

Sicne it's a new boat maybe the dealer has some 'real world' information to share with you about this topic, or maybe he can direct you to someone who does ...

 

Hp

I have a 5 horse on my 10' inflatable. It will get one person on a plane but not two. It does not have a rigid bottom, but does have a plywood floor so the bottom is pretty stiff. Different boat but a point of reference. My guess would be at least 8 or 9 HP as a minimum to plane with 2 + gear.

 

My inflatable 12' needed all 9.9 hp to plane with just my 220 lb carcass onboard + trolling motor, deep cycle battery, 6 gal of fuel topped off, and fishing gear. It had plywood floors, so it was semi rigid when assembled.