Repowering 18' Potter

[BocaSeacraft]

I'm in the process of choosing a new outboard to replace my old Evinrude 90 (1987) on my 18' Seacraft (1975) and am intrigued by the 2015 Yamaha 70 four stroke. In their performance bulletins they have one bolted to the back of a 1400# center console that's 18'10" long with a 7'-6" beam. This boat and motor combination gets better than 8 mpg at cruise and gets on plane in a bit more than 4 seconds. The motor weighs in at around 265 lbs. I'm having a hard time talking myself out of this motor. Does anyone have experience with a 70 on their 18'? I know several of you guys run 90's on your 20' boats. I run offshore and only run about 22-25 max in any seas 2' or over here on the south Florida Atlantic coast. I don't pull tubes or skiers and 35 is plenty fast. It swings the same size prop as my Evinrude (13.25") What do you think? Yamaha 70? I know one other member mentioned that they used to rig the 20' with 85's in the old days. Will a new 70 be sufficient? I'm turning it over to all you guys who have been running these boats for years. Thanks for your help.

[otterhound]

I'm interested in this also as I just snagged a nice unmolested 18 last fall as well. Mine has an old Evinrude 120 hp looper on it and it's a thirsty bugger lol! I was thinking a 90 Etec or Optimax would be a good fit but the lighter weight of the 70 would certainly be nice if it's enough power.
Rod

[Blackfin26]

Make it three...just picked up a '79 18 and will restore it eventually. I was thinking a Suz or Etec 90 for weight and performance.

[Fr. Frank]

I used to rig the 20' hulls with JohnnyRude 85 hp V4's. They were adequate power. I'm not knowledgeable about the Yamadog 70's. They're the same block as the F60 & F50 motors at about 260 lbs. My concern would be the rather small alternator output of only 17 amps, compared to 81 amps on the ETEC, and 35 or 60 on the Mercury, Zuke, or Tohatsu.

Personally, I'd like to repower with the 2.0L Mercury Diesel 150 VGT with AlphaOne. It's only 6 lbs heavier than my current 3.0L with the old MR-1 drive. Fuel economy in testing down-under with a 800 kg 19' cuddy-runabout produced an astonishing best of 7.4 NMPG at 28 kts. That's nautical miles per gallon! 8.5 statute miles per gallon at 32 mph!

The same boat achieved 4.2 NMPG at 36 kts WOT.

Drool.

[DonV]

Ya need to do some research on this engine. There is quite of info on the Maverick Boat Company forum with guys who use this engine on 16 -18 flats boats. Seems it works very good with the "technical skiffs" that are very, very light that normally fish only two people, however borderline on power with the heavier boats. I think it's a 1000cc engine, from what I've heard a motorcycle type engine, that does very good on gas. Good luck.

[PigSticker]

I asked a Yamaha dealer awhile back which is the worst engine they make now and he said the 70..

[Old'sCool]

My fishing bud has had his on new 20 Carolina Skiff jvx for 2 1/2 yrs. Fantastic everything and 7 mpg. I don't think it would be quite enough (for me) on an 18 SC.

[Terry England]

Originally Posted by BocaSeacraft

........... I know one other member mentioned that they used to rig the 20' with 85's in the old days. Will a new 70 be sufficient? I'm turning it over to all you guys who have been running these boats for years. Thanks for your help.

My old cut up 20' bow rider is probably lighter than your 18 if you have a standard console and tee top. If you have an electronics box up there in the fresh air too I know my drag coefficient is better. I usually run my '06 - 90 E-tec at 32-3600 which is probably only making 60 HP and it lopes along at 18-20 knots. You could get by with a 70 but you will probably be running at 80% throttle all the time and there is a lot of extra stuff "framing" around in a four stroke to make the same HP.

Think about a 90. Find a good, reliable, nearby marina and pick a color. Nobody makes a bad one. A lot of 4 -S are de-tuned 115's. The E-tec is a three cylinder 78 Cubic inch motor that is rated at 5,000 rpms. At 5,500 they actually make 101 HP. Do the math on the service intervals to keep the engine within the warrenty specifications for the warrenty period. $6.00 or $7.00 per hour required service plus fuel changes the picture somewhat.

Fr. Frank, Otto and Tiny's right - Almost everybody way overpowers these boats.
The Miami to Nassau race is over - go enjoy the sweet ride, Brother

[BocaSeacraft]

Thanks everyone for all the informative responses and experience. That's what I love about this forum. I will be taking your advice and moving my search up a notch to the 90-115 range. My main concern is weight on the stern of my old girl. Yamaha is at 366 for their 90 and another 10 pounds for their new 115. Suzuki is about 20 pounds lighter. Etec 320. I've moved my batteries up to the console, installed a new Moeller tank (smaller) all the way forward in the coffin box, so I'm guessing I will be okay with any of the above motor choices. I will keep studying my options and checking back for everyone else's opinion or experience with this great little 18' center console.

[FishStretcher]

Personally, I would opt for the lightest you can find. Which might mean an ETEC or F70.

I have the F100 (basically a F90 rebadge) on a 20 footer.

I don't have any experience with an 18 footer or the F70. If the F70 is like the F100, then you won't run a lot of pitch. Maybe a 15" pitch prop. Maybe less. Too much pitch just destroys holeshot and overall drivability.

I do my own work and the F100 is cheap to maintain, parts-wise and in terms of intervals. (Mine has carbs). But I can work on motorcycles, too, so the labor rate for checking valve lash is $0/ hour, along with timing belts and oil changes.

I like the thought of an ETEC, but the one on the RIB ( 40 hp?) at work never started or ran as well as I thought a new outboard should. It didn't have an easy life, though, and I don't know that it was regularly maintained.

I'd really like a 260 lb motor versus a 320 or 360 lb motor on an 18 footer.