18SF Re-Power...New 2.1L Mercury 115?

Tim · #1 08-27-2014, 04:18 PM

Hi Guys!

I'm a fairly regular lurker here and own a 1979 18 footer I bought from a member here after a partial restoration...this one, if anyone is interested: http://www.classicseacraft.com/commu...ad.php?t=23572

I'm thinking about buying a nice, new, quiet, reliable four-stroke and wanted to get the expert opinions of some more experienced members here before I make my decision.

My boat has a 1998 Merc 125 2-stroke right now, and I really like the IDEA of the new 2.1L Mercury 115 with "Command Thrust," but will this hull be underpowered with that motor? Should I consider something like a Suzuki 140 instead?

The boat is really just used hopping from sandbar to sandbar along the intracoastal in West Palm Beach. We sometimes go out front to do some snorkeling, but only when it is nice and calm.

Any opinions?

Also, while we are on the subject, do any of you guys know of anyone interested in a strong running 1998 Mercury 125 2-stroke with a 25" shaft?

Thanks for any input...this community is awesome!

72potter20 · #2 08-27-2014, 09:14 PM

If a 90hp is enough for a 20, than this 115hp should be more than enough for an 18. The more I read about the new merc 2.1's, the more I like.

I'm curious what you would want for your 1998 merc

Bushwacker · #3 08-27-2014, 11:10 PM

The 115 is plenty of power for a 20, not to mention an 18! These boats are very weight sensitive, so the lighter the motor is the better. Optimum motor weight is about 300 lbs, which is what they were designed for; anything over 400 lbs on a stock hull will adversely affect balance and ride, and seriously compromise min planing speed, which is about 12 mph with a light motor!

McGillicuddy · #4 08-28-2014, 12:33 AM

bitsamonkey has a late model zuke 90 on his 18 and gets 37 mph and 6.7 mpg at upper mid-20s cruise. Certainly not under-powered and exceptional economy. Terry england runs a 90 etec in his hardworking 19, and Fr Frank ran a 90 Opti on his Seafari, currently owned another regular, not sure if he repowered so maybe he'll chime in. While I'm sure they wouldnt hesitate to run more power, I've never heard any of them claim they were underpowered. I run an 83 115 tower of power ande it does about 36 and gets on plane instantly. My only complaint is fuel economy at hull speed.

The new merc sounds excellent in weight to horsepower ratio. Its only 20 to 30 lbs heavier than the etec and zuke with more ci and ponies. I like 2 strokes, especially modern direct-injects, but I cant argue with a 4 stroke that has cut considerable fat...did they leave out any parts

Another thing about the merc is that your controls probably swap right in.

72potter20 · #5 08-28-2014, 10:59 AM

Quote:

Originally Posted by McGillicuddy

bitsamonkey has a late model zuke 90 on his 18 and gets 37 mph and 6.7 mpg at upper mid-20s cruise. Certainly not under-powered and exceptional economy. Terry england runs a 90 etec in his hardworking 19, and Fr Frank ran a 90 Opti on his Seafari, currently owned another regular, not sure if he repowered so maybe he'll chime in. While I'm sure they wouldnt hesitate to run more power, I've never heard any of them claim they were underpowered. I run an 83 115 tower of power ande it does about 36 and gets on plane instantly. My only complaint is fuel economy at hull speed.

The new merc sounds excellent in weight to horsepower ratio. Its only 20 to 30 lbs heavier than the etec and zuke with more ci and ponies. I like 2 strokes, especially modern direct-injects, but I cant argue with a 4 stroke that has cut considerable fat...did they leave out any parts

Another thing about the merc is that your controls probably swap right in.

From my readings, they went with a simple SOHC design in place of a DOHC. This accounts for a good chunk of the weight savings. Simpler is better imo

Tim · #6 08-28-2014, 11:13 AM

Thank you to everyone for their insights. I have a Mercury/Suzuki dealer telling me that 115 may not be enough, but from these comments, it appears he is wrong. I guess I could even look at saving a little dough (and stern weight) and go with the 90! Any of you South Florida guys have a Mercury dealer you like?

Bushwacker · #7 08-28-2014, 01:30 PM

Quote:

Originally Posted by Tim

. . . I have a Mercury/Suzuki dealer telling me that 115 may not be enough, but from these comments, it appears he is wrong. . .

Not too surprising . . . I'm sure he'd prefer the extra profit from the bigger motor!

Also, like most dealers and 99.9% of the current boating public, he probably doesn't have a clue as to how efficient the SeaCraft hull is compared to other deep V's! It was different in the 60's, when the Moesly 21 dominated the outboard classes in very rough offshore powerboat races running a pair of I-6 Mercs, often beating many of the big 30-40' inboards running 1000+HP! Back then knowledgeable boaters and most dealers were very familiar with the superiority of the SeaCraft hull!

When Moesly designed the 19/20' hulls in the mid-60's, the biggest outboards were only about 100-110 HP, and HP was rated at the powerhead back then, so they were even less at the prop! So the VDH was designed with a relatively narrow beam for a great ride and built light but stiff like an airplane for excellent performance with relatively small and lightweight motors. Pretty much the opposite of modern boats that are designed with lots of beam and lifting strakes to support the heavy 4-stroke motors!

FLexpat · #8 08-28-2014, 01:51 PM

In the 1980's I used to fish w a friend on an 18 with a 2 stroke 150. It was scary fast at WOT; I'm guessing well over 50. In 'normal' chop conditions you couldn't really get the motor up to where I thought it should be running. The boat is rated for 150 but I don't think it needs anything like that.

mnwnvc · #9 08-29-2014, 07:34 AM

I run a Merc Opti 115 on my 20 CC and could not be happier. Will run 41 gps with a light load. Gets up on plane very well. Boat is super sensitive to weight distribution.

jdm61 · #10 09-05-2015, 02:01 AM

There is a video from an Aussie boating mag where they did a test of two identical little 18 foot cuddy fishing boats, one with your 125 Opti and the other with the new 115 Command Thrust 4s. the 115 ate the Opti's lunch in every category inducing a much faster hole shot and 3-4 mph higher top end. Sounds like they are underrating the 115 with that big gearcase and prop much like they appear to do with the new 150 4S. The Mercury reps answer to why they were still selling that Opti ws "ummm, errrr, lots of people like the Optimax" The 115 Command thrust also weighs the same or a hair less as the 115 Optimax at around 365-375 pounds.