Repowering 18' Potter
 

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.

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

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.

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.

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.

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

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.

Power to da' People
 

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

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.

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.

Hello, Boca. I have an 18 with a Suzuki 140 4 stroke and love everything about it, BUT, the weight. At 436 lbs., it's a lot back there. However, after moving batteries forward and careful weight placement, I use mine with no worries. My biggest problem, I think, is that the boat will fall off plane at around 3000 rpm. I think it's just the excessive weight and possibly the 21 pitch prop I'm running. When the time comes, (meaning money), I'll be doing several changes. I plan on raising the floor, getting all the plywood out, except the transom, and replacing with composite, then moving the console forward about 8". Moving the console has a twofold effect. It'll give me more forward weight to offset the weight of the motor and give me more fishing room. With all that said, I've been to the Gulfstream twice with her and had a ball. Planning on going back soon while the dolphin are getting thick! Good luck with her!

Wasn't there another 18SF here in Boca Raton? I think he was running a older Yamaha 130 and was considering a Suzuki DF140.
That makes at least 3 18s and a lot of 20s.

With all the modifications to my 18 I'm thinking of a 150 Merc or Suzuki.
I fish loaded down and offshore mostly and I want to be able run lower rpms in the slop and cruise in the 30s.

My brother has an '87 or '88 Tracker 18 purchased in '96 with an OMC 120. Upgraded to a '95 OMC rebuilt 150. With the 47 gallon tank it would damn near keep up with my '79 MA with a '99 OMC 175, very close to 50 mph boats without gear.

When that engine crapped the bed he went with the 140 Zuke. He is very happy with a little less top end, but significant fuel savings.

My SeaCraft rarely sees the light of day because of the simplicity of my recently sold 1982, refurbished myself in 2005, Boston Whaler Sport 15. Went with an '05 F60, mounted on a Bob's fixed jack plate. She was a 44 mph boat but weighs less than 500 pounds plus 18 gallons of fuel, and a forward mounted 48 qt. cooler.

My next project is an '88 BW sport custom center consul. I have everything I need to rig an F70, minus engine and prop. They're freaking expensive!

As you can see we tend to overpower. But I earned an arse of respect for the etecs this weekend!!! IMHO, I would never contemplate a 70 horse on an 18. Just my two cents.

Vezo, Part II

Great information from everyone. It seems we all have different setups aimed at satisfying different needs. We're lucky our Seacrafts are such versatile boats. I'm still on the fence about power. My cousin is a marine mechanic and tells me the F70 is a fine motor with great power to weight ratio. Now, if Yamaha would just run a sale on these things.

You should consider the new 115 mercury 4 stroke. Pushes my 20sf to 45 mph easily, hit 46.1 with a light load. This with the motor mounted to low and it weighs Less than the new yamaha 4 stroke and much less than the 140 zuke At around 360 lbs

The 150 merc on these hulls would scream

I'm not a Merc guy but would have to agree. My ten years with my F60 were flawless minus three broken steering tubes, and I do not trailer far. Of course, my neighbors delivery three weeks ago, I discovered she is "making" oil. Hopefully a bad thermostat causing it to run on enrichener mode. We shall see.?.?.!

Yamaha re-power
 

BocaSeacraft

I just repowered my '76 18' with the new Yamaha 115 a couple of weeks ago. I did not move batteries under the console and wish I had plus I had put a 40 gallon Moeller which I don't regret. She squats a little but not too bad.

I decided before I did anything else I would try putting 50# bag of sand in the front and it helped. I had a Merc 2004 115 hp and I like this new one a lot better.

Good luck

making oil on a four stroke is an easy fix.... Run it at 5500 for about 10-15 minutes on the way in every trip. Reduces coking as well and keeps everything running well.

Thanks T-Man. Nice looking 18.

I hear you clearly on the light weight, but at the risk of spending your money, I would seriously consider a little more umph to get out of tricky troughs if it gets sketchy in those southland inlets.

I think the the 90 etec, 90 zuke, and the new 2.1 Liter 115 Merc 4-s are all good calls. Nice mix of appropriate weight to power for a V-hull. They all have gearing available to spin more prop and can probably get you out of a jam in a jiffy. Not so sure about a Yammie 70.

If you're a Yammie loyalist and thinking new, their 115 has dropped 20 lbs into the first run etec 115 weight class (375lbs i think). I think new etec 115 is over 400 lbs. Mercs Optimax is in that 375 weight range too, but once you've run in relative silence, its hard to go back.

Adding ballast is not the best solution. I'd suggest moving the batteries to console and maybe adding 20' of chain to your anchor line, which will dramatically improve holding power of your anchor. And maybe consider adding trim tabs. Any of the Moesly designed SeaCrafts will plane at about 12 mph if balanced right. Other bandaids you could consider to help the stern-heavy condition would be an AV plate fin and a stern lifting 4B prop.

I'm still researching the F70 and its use on similar weight boats to my 18. Boston Whalers Montauk 170 weighs in dry at 1400# and the base motor on that boat is shown as a 60 Merc. 90 is max. The more I read about Seacraft 18 and 20' boats and a lot of the advice on this forum stresses weight and center of gravity, etc. If the boats are designed to plane out at 12 mph if balanced correctly, the additional 47-75 pounds of weight (over the design weight of 300#) seen on the latest 90 and 115 four strokes is kind of a big deal. Maybe it's not a big deal if added to the center of the boat, but hanging out over the transom... I'd really like for my scuppers to be above the water line as designed. Maybe I'm crazy but I'm still leaning towards the 265# Yamaha with like a 13 or 14 pitch prop.

So, I've decided on the Tohatsu TLDI 90. The weight is decent at 337 and my research on the web and talking to some marine mechanics has shown the motor to be fairly bullet proof. I was liking the Suzuki 90 but found the dealers around here to be lacking in the follow up department. Like, nobody wanted to give me a price after several attempts. the Tohatsu dealer was the exact opposite. He spent a bunch of time with me running through all the details. I wiol report back after the motor is rigged and run. Thanks everyone for all your input, knowledge and advice. If anyone out there runs a Tohatsu 90, it would be great to know what prop you are running. I'm thinking 13.25 x 15 Stilletto.

Please give us a report when you get your motor on.

Thanks.

BocaSeacraft once you get the boat setup I would love to go for a ride. I have been looking for 18 but never actually rode one. I will bring your beer of choice. Cheers!

Fishfullthinking

Boat Motor
 

Hi Boca, if it were my boat, I would go with a motor in the 115HP range, maybe a little bigger. like up to 150HP. It's nice to have the extra power, in case you need to carry extra weight, like dive gear, big cooler, or extra people. You don't need to run WOT all the time, and when you do it should get up and go. I have a 1971 20' CC with a Mercury 225, 25" shaft, 90 gallons of fuel under deck, and I can cruise all day between 3200 and 4000 RPM's all day long depending on the load I'm carrying. Once or twice a month I go out into the Gulfstream and collect 110 gals. of salt water, so I can do a water change in my reef tank, and this is when the larger motor really preforms to its max. Good luck with whatever size motor you decide on, but I always believe, go with the biggest motor your boat can handle, you never now when you will need it.

"I will bring your beer of choice. Cheers!"

Really?? How many? I've got a 23'er you can ride in. :) :)

I finally purchased the new motor and am bringing the boat in today to have it installed. Hope to be back on the water soon. Ended up getting a Suzuki DF90 for the same price I would have paid for a Tohatsu. Had to go 4 stroke. I will report back once I have some hours on the new set up.

We're still waiting !

Sea Trial
 

Well, motor is installed and went for the sea trial this afternoon. I just want to say the guys at Drummond Outboard in Deerfield Beach did a heck of a nice job installing the motor. Joel and Zach are a great father and son team who really spend the time to get it right. First impressions of the motor are very favorable. I'm still in the break in period but the DF90 gets the boat up on plane with ease, even with 4 of us aboard (about 750#) and half a tank of fuel, all equipment, etc. It holds plane down to about 3200 RPM with the 14x16 Suzuki prop. At idle it is so quiet I can barely tell it's running. The wife and I are taking it out tomorrow for the day to put some hours on it and get ourselves familiarized with the new setup. I will report back once we get a chance to put it through its paces after break in.

Another data point proving why "light is right" on the very efficient 18/20' SeaCraft hulls! Maybe someday folks will finally start to believe us old timers that actually ran these boats with 300 lb motors back in the 70's! My experience is that the poor balance with heavy 150-200 hp motors really hurts the amazing ride, load carrying and 12 mph planing capabilities that these boats were famous for back in the day!

Had a great day out. Put about 7 hours on the new motor. This thing is sweet. Boat likes to run at around 4000 rpm (17 mph or so). 5000 is about 26-27. The motor gets the boat on plane instantly. With me and the wife aboard with full safety gear, fishing gear and about 20 gallons of fuel, we could hit 6000 rpm. The faster you go the lower the bow dips. The boat makes the captain feel very secure in all situations. We ran from Boca down to Fort Lauderdale and back. Stopped at the Nauty Dawg for lunch. The motor never missed a beat. I would highly recommend a Suzuki DF90 if you are thinking about re-powering your SeaCraft 18. Cheers!

Perfect!

Looking good! I knew you would like that motor, it transformed the way my boat handles. It's great how flat it runs, right? I run the factory Suzuki 3 blade stainless 14x18 with a cup added. I can spin that prop right to the limiter. I usually cruise at around 4800 rpm 26-28 mph. Motor seams happy there. Enjoy and put as many hours as possible on it!

Meet up?
 

Me and my wife go to Naughty Dog for breakfast all the time. If you ever want to meet up let me know. Located in Boca also. Cheers on the new motor! I love my 140 Susuki.

Nice!!! Looks great on the back of your boat. I'm looking forward to hearing some mpg reports.

Well, we had the opportunity to head down to the Keys for a week with the boat. The boat performed flawlessly. We rented a house and kept the boat in the water all week so it was easy to just jump in and go for a ride. I don't have the ability to get real GPH or MPG since I don't have electronics to support that. I did fill the boat up before we left and when i put it back on the trailer there was still a quarter tank. We had it out 5 of the 7 days we were there and we ranged offshore to Alligator and over to Cheeca Rocks and everything in between. On the bay side we did the same. We visited Lignum Vitae and Indian Key State Park and had a great time. The Suzuki never missed a beat. I passed the 20 hour mark and reset the oil change reminder light on our way back from one trip. I had done the 20 hour service before we left. Very happy with everything. The boat did great in seas up to 3-4. As usual.