Opinions on if I should repower 18

[uncleboo]

Quite a bit, but, I didn't have the gps hooked up yet, so no numbers. Soon, very soon we will have numbers!

[Bandit91]

Giving everyone an update. I finished installing the new mercury 115 four stroke pro xs last week. Took it to the water and ran it for a couple hours. I’m very pleased with the motor. It’s so smooth and so quiet that I kept looking back while I was idling to make sure it was still running. This motor is almost identical in weight to the two stroke 130 Yamaha I removed so my scuppers are still just above water level. I’m running a basic aluminum prop, 14.25 x 21 pitch. With this prop I could hold plane down to about 16 knots. I was following the break in procedure so no true top speed runs but the break in did call for short periods of full throttle. With doing this my mercury mobile app recorded a top speed of 40 mph at 5900 rpm. I’ll be sure to keep everyone informed as I run it more to get better performance and fuel burn numbers after the break in.

[Beaver]

Quiet, fast and your scuppers are above water....sounds like a winner. Congrats on the new motor. Good job doing your homework.

[thealife]

What's the weight on the merc?

I am thinking about repowering my 18 with a new 115 yammi,

Anyone running with this setup?

[Fr. Frank]

Originally Posted by thealife

I am thinking about repowering my 18 with a new 115 yammi,

I repowered my '87 18' with an Etec 90. I have the factory 25" transom and the 25" 90 comes with the 4.75" lower unit gearcase. I'm running a 15x17. I cruise at 23 mph, and WOT is 34-35 mph. I can hold plane down to 15-16 mph and have no trim tabs.

The best part is an average 7.1 mpg. Over the course of a recent 122 mile fishing trip, of which half or more was trolling at about 7 mph, I burned 12.9 gallons, or just under 10 mpg.

I think my hull was re-placarded at some point. It says the right hull and manufacturer, but says max HP is 200. I lasered measured the hull which came out at 18' 6.4" LOA, with a beam of 7' 5.2"

I ran the numbers and the USCG algorithms show a legal max HP of 191.2 hp, (which is rounded to the closest 5 hp increment, i.e.; 190 hp) so the decal is wrong. BTW, it had the original Mariner 115 hp when I got it.

For those of you who want the numbers, it is LOA in feet, multiplied by the beam in feet, x2, - 90 = max HP.
USCG allows the LOA to be rounded up to the next higher foot increment, but the beam is always calculated to the nearest 1/10th of a foot including rub rails. If the boat is a sterndrive, the propulsion machinery (outdrive) outside of the hull is INCLUDED in the LOA calculation. Outboards motors are not. Swim platforms or outboard brackets are included ONLY if they include an amount of flotation that is greater that their displacement value.

[Bandit91]

Was going to give everyone an update. Got a stainless prop from ken at prop gods. He was great to deal with and recommended an 18 pitch quicksilver that is the equivalent to a mercury enertia. The boat performs fantastic. I can cruise at 4400 rpms at 28 mph and although I’ve only run wot for very short periods of time I’ve seem 43 mph top end. At 28 mph it’s burning right at 5 gallons per hour. Hope to get my most efficient cruise dialed in but Ken nailed it with the prop. The top end equals a 5% prop slip and only 11% at cruise speed. I’m very happy with this motor on the 18. And for those asking, Mercury lists this motor (20” shaft) at 363 lbs. my boat will still hold plane down to between 16-18 mph which I think will be fine for me. I’m sure I could get that number down with a different prop but I really like how it’s currently performing. I’m glad I went with the mercury over the Suzuki and saved the weight, as the Merc seems to have plenty of power for me. I just wish it would have been available in white.