40hp Merc Classic

[Ron173]

Hello all,<br /><br />well got my new boat n Merc 40hp classic, the 967cc one, pretty good, got the initial 4hrs on it now, dealer recommended 4hrs break in against manuals one hr, also dealer said not to put tank of 50:1 thru first as not necessary and just smokes out, he did say 'dont baby it' varied revs but give it regular squirts, just dont hold full throttle for more than 10secs, which I have duly done.<br /><br />Hull is a Stacer 420 seahawk, she sits fairly low in water at stern, due to engine weight, but climbs out ok above 3000rpm, 4000 pretty brisk and dying to go, with a max of 4800rpm showing a speed of 30mph (50km/hr) or 26 knots, which I checked with gps, not held her at these revs long, just 10-20sec bursts.<br /><br />Its running a 15 pitch prop, no idea diameter, but does seem to have a bit of a cup on it, hole shot is almost instant plane.<br /><br />Dont know if its propped right or should be running a 14? or if it will rev out bit more once hours on it? max revs supposed to be 5500rpm.<br /><br />Also if not propped right, does dealer have obligation to re prop? It was a brand new boat and motor.<br /><br />Any Merc experts advise me here?<br /><br />As for fuel, on 4 hrs running we prob used about<br />the full 25ltr tank, as it was low and I topped up with a 9ltr refill, and now just showing tween half n quarter, but we did give her a few big regular handfuls!<br /><br />Any comments / advice, very much appreciated.<br /><br />Rgds<br /><br />Ron

 

[Moody Blue]

Re: 40hp Merc Classic

Hello Ron, I can offer a little info for you. It is best to run the motor in the max recommended RPM range with a typical load in the boat. That being said, you are about 700RPM low. The general rule of thumb is that for every 1" reduction in pitch there is an increase of 200RPM. Following this guidline, you would require a 12" pitch prop. That much reduction in pitch will do a couple things; a) give you whiplash when you hit the throttle and b) reduce you top end speed considerably. <br /><br />Took a look at your boat specs and the RPM's seem a little low for a boat of that size and weight. I have a F/G 14ft boat about the same weight and my 40hp with a 15" pitch prop was turning about 5400. Changed to a 13" pitch and RPM's went to 5700 but lost 5MPH. Where is the anti-ventilation plate relative to the bottom of the boat ? Motor might be mounted a little too low in the water ?<br /><br />Talk with your dealer and explain your concerns. He should be willing to let you try out different props to find the one that works for you. If not, he's not the dealer you want to be doing any further business with.<br /><br />As for fuel consumption you can roughly figure on 4 gal/hr at WOT or 15L/hr. Rule of thumb is (Hp x 10%) to determine consumption at WOT. This is based on US gallons. Reducing throttle to 3/4 will dramatically improve fuel economy but takes longer to reach the destination.

 

[Ron173]

Re: 40hp Merc Classic

Thanks Rod,<br /><br />Did I mention its only got 4hrs on it, well 5.5 now and its starting to open up a bit, trimmed right out, its just on 5000rpm at a tad over 30mph. Motor is usa spec and is the larger cc heavier engine, she sits low in water too, dealer says fit hydrofoil to lift earlier, as she only really fully gets up flat out at mo.<br />Might see if she revs out a bit more once more hrs on, but hydrofoil is looking a good buy.<br /><br />Will need to investigate cavitation plate to give you honest answer.....<br /><br />will get back to you<br /><br />thanks again<br /><br />Ron

 

[Mercathode]

Re: 40hp Merc Classic

It sound as if your dealer is giving "Break-in" advice contrary to the manufacturer.