Did you consider running the Mirage prop for a true like for like comparision or would it be over propped for the ProXs?

was looking into this a few weeks ago as am lookking to put a 200hp merc 4 stroke on the new boat. ddint realise there were different types to choose from! for an average fisherman, any benefit in going the sea pro, or pro xs over the normal 4 strokes?  i got quite confused by it all... pro xs obviously v8, more powr, but heavier etc.....

was suggested as being a better prop.  If I were to use the 19pitch Mirage on the ProXS it wouldnt reach the required revs of 5,500 to 6,200.  In theory it would give higher speed at lower revs, so assuming the gearboxes were the same ratio, the performance I guess would be similar.  I tried an 18pitch prop on the ProXS it pulled 5,500 revs so dealer changed it for 17 pitch themselves.  I understand the V6 225 and 200hp are gutsy in comparison the the other makes, but that is advice is only from the dealers.  A point to remember is that the V6 has a smaller gearcase so less drag and this should be an advantage..  I had difficulty choosing, only chose the V8 as it is meant to have a bit more torque and I figured that if the V8 can now produce 450HP (with a blower) then the v8 225 shouldn't be working too hard, whereas the V6 at 225hp is the top of the range for the V6.  The weight difference I understand is only about 15kg or so.

Those figures make me feel quite good about my tub burning two litres per Nm @ 20 kts . Not too bad for a 5 ton 28 ft cat !  

AWESOME.

JUST A QUERY. THE BoaT I AM LOOKNG AT IS RATED FOR 150-200HP, I CHOSE THE 200 EVEN THOUGH I VERY MUCH DOUBT THERE WILL BE MANY OCCASIONS WHERE will be able to reach top speed, but figured that having higher hp than necessary would put the engine under less stress? is this thinking accurate, or am i mistaken?

cheers!

 You'll be spinning less rpm with the larger motor , until you get past the smaller motors' max speed. Given that the new V6 Mercs are very light, the added weight won't really come into it.

To wagyl--your higher speed at lower rpm was nothing to do with "the greater  torque of the 2-stroke". You were running a larger pitch, which will always give you more speed than a smaller pitched prop at the same rpm. Simple physics, as long as you have the same reduction ratios in the two gearboxes. Your peak rpm (5300)quoted for the 225 Opti was almost midrange of recommended max  (5000-5750).. But the current max of 5700rpm for the 225 pro Xs looks a bit low--they have a recommended max rpm range of 5600-6200, so you are right at the bottom of the recommended rpm range, and getting closer to being overpropped. Did the dealer say this was Ok? Merc will keep giving you props until you get it right, at no cost--avail yourself of this, because it is free. I accepted what the dealer said, after trying one change, and left it at the original. 18 months down the track, I was overpropped, and had to buy a second-hander of the right size.  Maybe you need to look at a different diameter, rather than just focussing on pitch alone.

There is a misconception around correct propping--not saying you are guilty of this,  wagyl--that a prop which makes you go faster at cruise rpm, but won't hit the max, is somehow better. Boats and their physics are nothing like cars, there is no such thing as overdrive.  You have to think of a boat as something  which spends its whole life driving uphill in top gear--the load is never off it.  So if it is overpropped( overgeared) the load is higher than necessary, even at medium cruise rpm.  The fact that yoiu can hit max recommended rpm isn't about how fast you can go, it about having the right prop to allow the engine to be loaded right at all rpm.

The dealer tried an 18p prop and then reduced it to a 17p prop after the test run.  I will give it a squirt the next time I go out and see exactly what it does and then refer back to the dealer if unhappy.

Silver fox, my friend has a 60 foot boat weighing 25 tonnes and burns 2.5 litres per nautical mile at 7knots, but 250 to 300litres/hour at 28knots.  If you are getting 2l/nm though, that sounds good.

 I spec'd a prop ( 14.5x17 Enertia) , dealer supplied. Was only hitting 5650, IIRC, light. He wanted to see how a 14.5 x16 went. No more revs, just slower, dropped 2 knots. Weird. he talked to the Perth dealer, who told him the original 17 was the best for that motor/hull combo, so i accepted that. Wish i'd asked around more and tried more options, they were there for the asking. As I added to the fitout, including a scoop for the water intake, revs kept dropping. So after talking to a bloke over east, I took a chance and bought a 15 x15 s/hand. Pretty well fixed the problem, get 5650 loaded now (5800 max) with the same top speed as i had with the overpitched prop.  Good speeds, and you can load up for the Monties with 300 litres of extra fuel, dinghy, all the gear, and it doesn't feel it.

that the same motor produces much higher horsepower (300hp plus and 450Hp with a blower) just by supplying more fuel from the computer.  So surely the 225hp is more than capable of taking the load and is working a lot easier than the higher HP motors.  In the V6 range, to achieve the higher HP of the 225, they just allow it to rev higher with more fuel.

 With the same block, there might be more to it than just more fuel. Different valve sizes, camshaft timing, compression? if you have exactly the same internal configuration for two not hugely different HP outputs from the same block, it is usually done by getting them to rev harder, ie, 130 yam vs 115, 115 suzuki vs 140. With motors such as those, you really only gain any advantage at the max rpm, cruise will likely be similar or the same as you will be running the same size props or thereabouts. I think that if you look at the actual power curve of the 225 vs the 300 in the v8's, the 300 will be pushing more HP right through the range. And the 225 V8 such as yours, is actually pushing MORE RPM than the regular 300 V8 ---  225 Pro XS is 5600-6200, as is the 300 Pro XS.  300 regular V8, same block, is 5200-6000.  Although, of course we know that the Merc  Pro XS version in any given nominal HP rating is " cough" somewhat more than what is written on the cowling, to get around transom ratings, for those who want a little bit more bang . 

Looking at the V6's, which run from 175 to 225, they probably just are running them harder ( more fuel, more advance?) to make the extra rpm --from the website  175 is 5000-5800, 225 is 5200-6000. 

awesome info. certainly not my field of expertise, but great learning!

is 3years plus 3 years (last 3 years if dealer serviced) I understand.  Same for the V6.