How come my boat cant reach 50MPH?

[Legend188]

Ok, I hjave a Legend (canadian boat, incase u havent heard of them) fishing boat and its 17'10". We put a brand new 2002 Mercury 115 4Stroke EFI on it and we have run it now for about 3 hours. Mercury manual says we can now go full throttle. WE figured at max RPM we could hit atleast 50MPH, but we can only do 43MPH. Is this because we need to put more hours on the motor to break it in more? We have the trim set properly too...so dont tell me its that. maybe a new prop would help? any help would be great<br /><br />thanx guys.

 

[JB]

Re: How come my boat cant reach 50MPH?

Howdy, Legen.<br /><br />You didn't tell us the weight of the boat or the rpm at WOT.<br /><br />Need to know that to give you useful answers.<br /><br />Let us know.

 

[Legend188]

Re: How come my boat cant reach 50MPH?

center line length is 17'10"<br />hull weight is 1120 lbs <br />the rpm was about 5400 at WOT<br />The boat hull is actually a Smokercraft 178<br />it has the gullwing deep-v hull design<br />we had 35 gallons of fuel on board plus our gear and two adults

 

[wilde1j]

Re: How come my boat cant reach 50MPH?

Sounds like you're close to the max you'll get from that motor. You might tweek a few more MPH, but not too much.

 

[JB]

Re: How come my boat cant reach 50MPH?

Howdy, Legen.<br /><br />I agree with Wilde One.<br /><br />I calculate your theoretical top speed at between 45 and 50, with a gross weight of 1800, and 43mph with a gross weight of 2000, which is more likely with that 425lb engine.<br /><br />Good luck.

 

[steelespike]

Re: How come my boat cant reach 50MPH?

L188,These guys are probably right.But you could try adj. the virtical height. As little as an inch can mean 2 or three mph.

 

[Legend188]

Re: How come my boat cant reach 50MPH?

well what about a new prop? would it make a difference? or size of prop?<br /><br />dan

 

[JB]

Re: How come my boat cant reach 50MPH?

Howdy Legen.<br /><br />Your engine's operating range is 5000-6000rpm. You can probably drop your prop pitch a couple of inches without too much risk of over-revving her. <br /><br />That would give you a better hole shot, but is unlikely to increase your top speed more than a mph. Most likely would be no increase in top speed.<br /><br />Good luck.

 

[FlyBoyMark]

Re: How come my boat cant reach 50MPH?

Ifer' ready to spend $500.00 on a cupped 4 blade prop and $135.00 on a jack plate and fiddle around for a week with tweeking, you can get almost 5 MPH. Hull condition should be examined closely too.....(dents bulges, warpage, rough paint, ect.) That's still less than 50 MPH....When all this is done with jus two guys and no gear.....the speed will go to h e l l soon as you start loading gear. Weight will become super criticle when your working on the edge....

 

[Legend188]

Re: How come my boat cant reach 50MPH?

ok thanx guys, guess ill just have to buy an Optimax....jokes...<br /><br />later