Opinions on if I should repower 18
 

It was a bad day today for my little seacraft. Its a porter 18 with a Yamaha v4 130. I’ve been keeping an eye on my steering arm for a while, it’s had the dreaded corrosion and I knew the day would come where it would become to brittle for me to chance. While inspecting it today I was actually able to bend it and it seems like I could break it if I really tried, so needless to say the seacraft won’t be going out again until it is fixed. My dilemma is should I go through the hassle of trying to fix the steering arm (removing power head, most likely breaking bolts in power head, trying to find a new steering arm since I’m pretty sure they’re no longer making that part, etc) or just repower my boat. I love the boat and it’s always performed great with the 130. Unfortunately it’s still a 20” transom so if I was repowering I would like to go ahead and raise the transom for a 25” motor and I can see the snowball effect coming already. I really don’t won’t my boat down for the whole summer either. What would y’all do if you were in my situation? The 130 runs great and has good compression, but the mercury 115 pro xs sure sounds nice about now too?

Let me start by saying that I am super cheap (mostly because I have to be). With that said, I think the Yamaha 130 is probably the perfect motor for the 18. Its light, super reliable and fuel efficient for its horsepower. I just looked on ebay and you can buy a steering arm for a 115/130 for less than $200. I recently pulled the head on my 90 to replace a bunch of gaskets and was surprised at how easy it was. I built some gallows out of 2x4 and used an automotive jack on top with a chain to do the deed. My vote would be to keep the 130, change out the steering arm, put a new base gasket in there, and maybe repaint the cowl with some new decals. You'll feel like you have a new motor and you'll have almost 10K still in your pocket. You'll also have a great feeling of accomplishment.

That's my 2 cents. Good luck on whatever you choose to do.

Rob

Thanks for the reply Beaver. I think I’m leaning towards repairing it. I ageee that it is the perfect motor for the hull. I’ve nevwr pulled a powerhead before but your experience with your 90 is encouraging.

Same here. After everything I have read in the past few years, that seems like the perfect engine. I bought mine with a Yamaha 115 back in 1992 and would probably grab a 130 if I could find one. Hope you can make it work.

Giving an update on my motor situation. After a lot of thought I decide this might be a good time to repower. The four stroke is getting more and more appealing to me recently and I decided to go with a 140 Suzuki.

The 140 is a lot of motor on an 18. I have a friend with a 20 Seafari but the cabin and forward helm really helps with weight distribution. It flies that hull but in your case I did some research on weight and options going with a 90 hp. Below is the weight for each of the same HP. I was surprised to see who was the lightest...

Etec 90 - 390#
Merc 90 - 359#
Yamaha - 353#
Suzuki - 343 #

One of those "second opinions".....

I just sold an 18' Kenner Vision with the standard rigged "boat show" package from Tracker (yes I said Tracker, it was my friends boat, I bought it from him versus him having to give it back to the finance company, don't shoot me), anyway it had a 90 hp Merc OptiMax, great engine, however with the 115 being the same weight, size, etc. engine I wish it was rigged with one or even a 140.

Thanks for the replies. I understand the 140 might be a little over the target weight. I considered the 90 but I really loved the performance I had with the 130 two stroke so I felt like I would be sacrificing a lot going down to a 90 four stroke. That left the 115 which in Suzuki’s case was actually a little heavier than the 140. It seems like the mercury 115 command thrust motor would be perfect but I couldn’t work a deal out on one that I could with the 140, the mercury 115 was going to be significantly more. So that brought me to the 140. I have moved my two batteries to the front of the console to help offset some weight. I think if I need to work more weight forward I could go with a smaller tank now that I have a four stroke and mount it as far forward as possible. And I guess worst case is it really doesn’t work out and I find a 20 sf hull and mount the new 140 on a floatation bracket haha. I really do appreciate the help though. The 140 isn’t in yet so I still could go with the mercury 115 if I changed my mind. I believe it’s 360 lbs.

Y’all have really got me thinking about the Suzuki 90. I wish I could ride in an 18 with one. I’d hate to be disappointed with the performance. Not so worried about top speed but more worried about having ample midrange power since I’m coming from a 130 two stroke. The weight of that 90 Suzuki definitely interests me though. It would also save some money over the 140, which is also good. I honestly hadn’t really thought much about the 90 hp engines. I was more focused on the 115 line.

I’d do the 90. There are several guys on this site that have mentioned the 140 being too much weight. The Potter hulls do a lot better with a lighter motor (20” transom and they’re all a little ass heavy). It’ll plane a lot quicker and be able to keep it on plane at a lot lower speed.

I keep waiting for someone to put an F70 on an 18. I bet it would push it fine

Not sure I've heard much in the way of negatives from guys who have actually owned and run an 18 with a 140? I put a DF140 on my 18' (was really shopping for a Yamaha 115, but got a crazy deal on the Zuke) way back in '02, and was very happy with it. True, it's a lot of weight hanging off the back, and washboards are advisable to keep water out when backing. I can't recall the specs on the prop we settled on (sold the boat in '07), but we tried a bunch and ended up propping for all around performance. Great hole shot, 42 mph in flat water, phenomenal "guts" at any speed, even with full tanks, four (or more) adults, dog, cooler, etc., and absolutely sipped gas. I'll admit that it was more power than I needed or used 90% of the time...I'm sure a 90 would work fine, but it was really nice having the extra juice available when going in or out of a rough inlet with a heavy load. I remember thinking that it was a little like driving a turbo Porsche - everybody best be holding on when you put your foot in it! I do miss that darn boat...

Thanks for the info. Just curious did your boat have the original 20” transom height or had it been raised to 25”?

Thank you for this info. I am really considering the 90. Just a little nervous spending that much money when I’ve never been on a seacraft 18/20 with that size power.

Another thing I found interesting in my research of the 140 is that the weight is less than the older df140s. The earlier 140s were listed at 410 lbs for a 20” shaft and the current df140a 20” is listed at 395 lbs. don’t know how accurate this is but 15 lbs is pretty significant.

Your call, however a 90 might be perfect for just you in the boat. Ya gotta think how you are going to use the boat, how many people, how much gear, coolers and ice, etc., as you add weight the performance will suffer if you're underpowered. Good luck!

I ran a '02 df140 for 8 years. I thoroughly enjoyed the power and performance and loathed the heavy ass end. What bothered me the most was that anything under 3100 rpm s and the boat would slowly fall off plane. I read all the threads on engine height and decided to move mine up a couple holes and discovered the transom was toast, soaked toast! That's what coaxed me into doing the transom and floor. Only got to splash it once after completing the work for about 30 minutes before the motor crapped out. However, after removing all the weight, she sits high and planes at very slow speed. Didn't get to run it long enough to stretch it out. Hopefully my NEW df140 will be in this week and I can give some more accurate performance numbers. BTW, mine was a 20" but I raised it 3" and installed a 3" set back jackplate for fine tuning without removing the motor. Good luck whichever way you go!

That’s a great point, I do agree a 90 would probably be perfect if it was just me in the boat. Thank you for your help

I’m interested to see your numbers with the new motor. What did you do to remove weight on your transom and floor rebuild? Composites instead of wood?

Bought my 18 that had a tired 96 115 Yamaha 2-stroke. Replaced it with a new 2018 Yamaha F90 4-stroke that I got on a can't pass up deal. Why? I'm on the West Coast where I do quite a bit of 2 kt salmon trolling and breathing 2-stroke fumes on a downwind tack is not the most pleasurable experience. The Pacific has typical running conditions consisting of swells with 12 to 20 second intervals as well as short interval head-high wind swells. There are only a few days when you could run a sustained 30+ kts. comfortably and safely on this short, beamy hull, so right now I'm not missing the potential advantages of 115 to 140 hp that can be applied to this hull.
This is still the ass-heaviest outboard boat I have ever owned, and I'm still trying to adjust to water washing over the transom while sitting in a chop or backing down. I did relocate the battery from the starboard rear compartment to the front of the console and religiously keep the baitwell free of water when not using it
BTW, the F70 and F90 are exactly the same in terms of weight, dimensions, etc. Only difference, I believe, are the stickers and ECU...and the price.

Yes, yes and yes. Check out my thread 'deck replacement'.

Just read through your thread, very informative. That’s a shame about your motor. But you did an amazing job on your boat. It looks great. Going to be a really nice setup with your new power.. Looks like your motor was a 25” shaft on a jack plate, is that correct? Or was it a 20” on the jack plate?

I have an 18 SF with a 20" transom and '09 Mercury 90 hp 2 stroke. Weight wise at 303 lbs it seems perfect for our 18. It will cruise all day at 25 -28 mph, plane down to 14 -16 with out tabs and top out at 36 -37 with one aboard. It has a 4 blade aluminum Apollo prop, a Doel Fin and the ventilation plate is 1 1/2" above the bottom of the boat. It previously had a '92 Evinrude 120 hp. When we got the weight out of the back of the boat and the motor height set correctly the boat absolutely came alive. Although it's not a rocket ship it's nicely balanced, great in a head sea and economical to run. Best of luck!
Rod

"BTW, the F70 and F90 are exactly the same in terms of weight, dimensions, etc. Only difference, I believe, are the stickers and ECU...and the price"

Not true, the 70 is 1000cc and the 90 is 1800cc, the 90 is much heavier, 100# more. The 70 is only available in a 20" shaft and the 90 comes in 20 or 25". The 70 is basically a motorcycle engine with great HP/weight ratio. It was designed for the 16 to 18' technical skiff market.

https://yamahaoutboards.com/en-us/ho...15-50-hp/70-50

https://yamahaoutboards.com/en-us/ho...115-50-hp/f115

Real quick, back on post #7, the Optimax I mentioned is a 1.5L 3 cylinder for both the 115 and 90, they weigh the same. If they are still available the 115 Opti would work nice on a 18' SeaCraft.

My '75 18 footer had the 20'" transom. Back in '02 the Suzuki four strokes hadn't built up a reputation yet, and I found a 20" DF 140 that the dealer wanted to move. This was in the West Palm Beach area, where there's a good deal of flat water on the Intracoastal and sometimes outside, so you have an opportunity to run fast - but also occasionally pretty rough inlet running and ocean seas. My boat didn't have trim tabs, and don't remember checking low speed plane, but I don't recall feeling that it was an issue. I did however scare the living heck out of myself the first time I tried backing down on a fish out in the open ocean with a little sea running (the boat didn't come with washboards). In short order I made up some hinged boards out of Starboard, which allowed the motor to tilt when folded, and they helped a lot in keeping water out of the boat. I knew the motor put a bunch of weight aft, so I moved the batteries under the console and tried not to load heavy gear in the stern. As Don said a few clicks back, it's a good idea to first try to figure out how you're probably going to be using the boat, and go from there.

I stand humbly corrected. I was using the F75 as a comparison. It appears that the F70 and it's weight difference between the F75 is better suited for lighter boats where 70 hp is the upper end spec for mfgrs. power and engine weight, i.e., skiffs. Pushing a heavier boat with a 70 at the 5800 Rpm powerband range would probably require smaller diameter and/or lower pitch prop to utilize full horsepower. I noticed that Yamaha does not divulge torque specs. but using the formula
Torque = Hp x 5252 / Rpm (5252 is a constant)
the F70 yields 63.4 ft/lbs. @ 5800 rpm, the F75 71.6 ftllbs. @ 5500 rpm

I think Terry has a 90 Etec on his 18 and it does fine.

20" transom, 20" shaft and I raised the transom 3". 2-1/4" would have been better due to hydraulic steering head, but, I have it worked out. I went with the 3" jack plate solely for the purpose of adjusting the height of the motor without removing bolts.

Some more info for the 90...

Bocaseacraft sent me a PM that said his 90 Suzuki goes 34 to 36 mph and has been averaging 6 mpg. In my book those are great numbers for an 18.

That’s good to know, I might send him a pm and talk to him about his setup. Thanks for the info.

That sounds like a good setup. Are your scuppers completely submerged when the boat was docked?

Not now, 2-1/2" above waterline. Before the diet, the bottom of the scuppers was at water level.

Just giving everyone an update. I had pretty much made my mind up I was going with a 140 Suzuki. Went to the local dealer and was not really impressed with them. Didn’t want to be tied to them if I ever needed any warranty work. So long story short, I ended up working a deal on a new mercury 115 pro xs with command thrust lower unit. I really like the dealer I got in touch with and feel like this will be a great motor for the 18. It’s about 363 lbs so almost identical weight to the 130 2 stroke I removed. And with the command thrust lower unit I’ve got plenty of prop choices so I should be able to get it dialed in perfect. I appreciate everyone’s help and I’ll be sure to post up the performance of the new motor along with pictures after I get it installed.

Good Luck with the new motor. It is soooo important to get a good feeling from the dealer who will service the motor later...sounds like you made the right choice.

I have the Yam 70 4S on a 17' War Eagle and absolutely love it! That said, I wouldn't want it on a 18' SeaCraft.

Well done Mr. Bandit!!!! :)

Nice!!! Please post some numbers after you get a chance to run it a while.

SF18 Props
 

What size propeller are you running with 90 HP and 115 HP ?

Not sure about the 90s but I know with the 115 command thrust motors a lot of guys are running 14.25 x 21 pitch props on similar sized boats. So I’m going to start with that and see how it does.

How much did the ride and min plane speed improve?