This was my take after a conversation with Minkota.
Pounds thrust is not relative to HP in any way because if you have either 30lbs thrust or 55lbs thrust you would still only have a maximum speed of 3-5 miles per hour, the main difference being that the higher thrust rating could keep you moving in strong headwinds on on a fast flowing river whereas the lower power would struggle in those situations, even 30lbs thrust is rated for 1500lb and under boats so it is more than adequate for a small craft.
The formula is Volt x Amp hour draw divided by 746 to work out HP to Lbs thrust (they really can't be compared but this is the best way should you care)
So 12v motor drawing say 30 amp hour (30lbs thrust at full power is same as amp draw) divided by 746 gives you about a half horsepower, You can take this one step further and work out how long the battery should last based on Battery Amp Hour capicity, so if you are drawing 30 amp hour off a 100 amp hour rated battery then it should last for 3 hours at full thrust, bear in mind that really only about 80% of battery capicity is usable. So if you are trolling at 1/2 power with a 30Lb thrust motor and using a 100 Amp hour battery then you would get about 5 - 6 hours. Clearly this time decreases as you increase Lbs thrust of the motor itself, by that I mean 55Lbs thrust will draw almost twice the power of 30 - but you could troll on 1/4 power and still get similar battery life.... well you can do the math from here forwards based on your motor and battery but you get the general idea!
From the models I have looked at Minkota look solid, always have Oars and a spare bettery if possible.
Wal-Mart as much as I can't stand them were selling the Minkota 30 cheaper than anywhere else when I was looking into it but at the time they only had them in Guilldford Mall.
If anyone knows more about this then please post as I am sure there is more to know.
Regards,
Tinhat