I've had a fair bit of boating experience in the past and owned craft up to 30 foot motor cruisers but have been out of it all for about 18 years so both knowledge and memory is a bit rusty to say the least.

I want to buy a smallish open boat that I can use for fishing the (dammed) monster lakes/Rivers such as the Zezere & Cabril here and have been offered a 3.8 metre, cathedral hull fibreglass boat with flotation chambers (similar to the old Dory designs) on a trailer for a more than fair price but for some bizarre reason Portugal limits the size of outboard one is allowed without writing a boat handlers exam and as the exam is in Portuguese which I have yet to learn, that's a problem for me.

Water conditions whilst not usually flat calm are not far off of that. The rivers are dammed and surrounded by steep mountains on both sides so although deep & wide, current is fairly minimal and wave not much more than a few inches....... and of course, I don't intend to use such a boat in anything approaching bad weather.

As to speed: I don't need to break any speed records and if I can get the boat to move at around 7 or 8 km per hour across the water when laden with 2 adults and a bit of fishing tackle, It'll be more than enough.

So the question is do you guys reckon a 6 hp 4 stroke outboard will be enough for such a boat please?

I appreciate an 8 or 10 would do the job a lot better but I'm restricted by my inability to take the Portuguese boat handlers exam.

If my math is right, 3.8M = 12.5 feet, and 8km/hr = 5 mph.

I think a 6 hp motor could push a lightly loaded boat that size 10-20 mph, so even if loaded up pretty good your 8km is pretty attainable.

Here is a youtube video of a guy who made a 4hp lawnmower conversion on to a 10' boat, just so you can have an idea of how fast it will run:

http://www.youtube.com/watch?v=fgQO4RvfUiY