Ok, this might actually sound a bit harsh... but after reading through some of the threads in this forum it seems like very many people who writes with a lot of confidence about how-to-go-fast with your Futura probably doesn't know much about how to use the fantastic hull for speed in real life.
I made a small video with my GoPro HD from a couple of this saturdays 41 knot runs:
(I will make a "real" vid this spring when I've got the 60 hp on the boat with a real prop etc)
Anyway, basically you will have to sacrifice some things if you want to have serious fun (i.e go *fast*) with your Futura Sport. First of all; get rid of all unnecessary weight. Anchors, large batteries and all other crap just has to go. Secondly you have to get *all* the weight as far aft in the boat as possible (oh, this point will probably generate a lot of posts ;-)). Put the tank right against the transom. Move the jockey-console as far back as possible. I.e don't have *anything* in the front/mid part of the boat.
As you can see in the vid I haven't had time to move the console as far back on my boat as I want yet but will do it in the coming days. This is why I sit behind my console when I get the boat to go seriously fast. Your goal is to get the boat to only have the last centimeters of its speed-keels in the water + as little of the engine in the water as possible.
On the vid I only had a crappy alu-prop with a bad shape on the blades, so I couldn't lift and tilt out the engine as much as I liked. So the anti-cav-plate was only 1-2 centimeters above the water-surface at full speed. Ideally (i.e with my 60 hp) I will have a surface-cutting steel-prop and will then have the surface just above (or at) the level of the prop-shaft. That will really open up for high speeds.
You also need to tilt the engine out from the transom. Having it push the nose of the boat down is a huge no-no. It will really destroy the top-speed completely.
Yes, having it tilted out will give you cavitation when going up unto plane the "wrong" way. You need to get a good feel for how to do it effectively without cavitation (and without flipping your boat backwards :-))
Another thing is that you must have the correct pressure in your boat. If it is to low the boat will just bleed all the energy and "stick" to the water. Also you can get oscillations in the boat where it sticks and then "unsticks" which have a good chance of making it dangerous at high speeds.
When it comes to selecting a suitable prop you also have to consider your engines gear-ratio. My Yamaha 40 has a gear-ratio of 24/13 (1.85) which gave me around 40.8 knots at 6000 rpm with my crappy alu-prop (10 3/4 x 16). However, when I will switch to my 60 hp the gear-ratio it has (28:12, i.e 2.33) will make it necessary to have a prop with roughly 26" of pitch to get the boat over 50 knots. Which is basically what I will start with and then work my way up. ;-)
When it comes to shape of the blades; try to get one with a straight leading-edge as possible. The "standard" cabbage-shaped blades are only there to make the prop "all-round". I.e providing you with the possibility to get good power when reversing etc. Since our boats are very light it is of little or no concern to us.
This page is pretty useful for calculating which prop that might fit:
http://www.rbbi.com/folders/prop/propcalc.htm
You can put the prop-slip very low since our boats are super-light. I think I calculated something like 0.02 in slip...
You basically need to make you boat fly; the less wet surface you have the faster it will go.
However, YOU NEED TO UNDERSTAND THE RISKS HERE; you will need to be *VERY* aware of how to drive your boat. Flipping the boat in 40-50 knots will most likely put you in the hospital with smashed ribs etc.
When you add a little head-wind and also some waves you will fly for quite long distances and you will at all times need to balance the boat on a knife-edge.
So start experimenting with the advice above if you want to go fast. Make sure to keep a steady eye on the rpm, you don't want the engine to over-rev more then, say, max 500 rpm's if you want it to survive longer periods.
When you start learning how to balance your boat on the last few cm's of the speed-keels it will give you a huge rush... just be sure to take it slow in the beginning since it can become quite scary quite fast. ;-)
And yes, I am very aware of that people want to use their boats for other stuff as fishing, diving etc. That is of course fine too and not something that has anything to do with my personal goals with my futura sport. I bought it to go fast and give me a serious thrill.
Have fun!
Sula
