Asking too much from a 9.8 Evinrude?

[njsignman]

Hi all,

First, thanks in advance for any input. I have a 14' Sea Nymph FM 146 that i bought a few years ago. TBH I don't recall the year. For the boat I bought a brand new Evnirude 9.8 tiller motor. This boat has a flat wood floor, bow mounted trolling motor and also a stern trolloing motor, a couple of swivel seats, etc. i I have it set up with three batteries. One for each troller and one for starting the motor. When I last used it i was on a lake in NJ doing some bass fishing. According to my GPS I was able to get a top speed of about 7.5 mph in calm water with little wind. Even if I eliminated two batteries and trolling motor, put in minimal fishng gear, etc. i still couldn't get going any faster. I did experiment with different trim positions, raised/lowered the motor mounting, etc. but can't get any more speed. The motor is a long shaft which matches the transom height, etc. I fully understand that i'm not going to fly with a 9.8 but am I expecting too much from this boat/motor combination?

 

[nytebyte]

Check for spark on both cylinders. Sounds like its only running on one cylinder. What year is it? Are you sure its not a 9.9?

 

[Still Afloat]

You might want to check the rpm’s as well. It could be propped wrong.

 

[LDUBS]

That is a nice boat. Seat of the pants, that hull might be rated for a max of 30 HP. So, you are right not to expect a lot of speed with your 9.8. But 7.5 mph does sound low to me. Investing in a tiny tach seems like a good idea to check rpm's at wide open throttle. Other than confirming what you already know, I'm not much help I'm afraid.

 

[airshot]

Definetely a problem somewhere....I had a 14' Starcraft with a 9.9 Evinrude that would do about 15 mph with two batteries and a bowmount electric. Unless you have some serious issues with the hull, you have a motor problem !!

 

[njsignman]

Thanks for the replies.

I will check the plugs, I hadn't thought of that. And I'll see about a small tach. It has the factory prop so I'll have to investigate to see if I was given the wrong one. I bought it before covid so whatever I do will be on my dime. It was bought brand new in late 2019 from a dealer (shorts marine in DE) and was labeled as a 9.8. IDKY they don't call it a 9.9 but yes it's a 9.8. TBH i never even took it out of the box until early the next spring and didn't have it on the water until fall of 2020.

i did the breakin as close to the instructions as possible. I let it idle in a 55 gallon drum (with hose to refresh the water) for two and a half - three hours, then on the first trips didn't take it above half throttle, etc. It has a total of perhaps 15 hours on it in five trips (including breakin) and that's probably a bit generous, all in one freshwater NJ lake. I only took it out once last year (too busy at work, family, etc.) and am itching to get back on the water once we get through winter.

It's kind of a long story but this 14' boat did come with a 25 HP merc. I took that motor and put it on a 16' Crestliner to use for flounder fishing in back bays and inlets. But in a moment of weakness (insanity?) I sold the Crestliner to an old friend before ever getting to try it out. I still regret selling that boat because he loves it in the back bays etc.

The main reason I got the Evinrude was that on the phone, the dealer swore to me that it was USA made. When they brought it out, right on the box it stated "made in japan" and I almost told them to take it back inside the store. If it hadn't been a two and a half hour drive I would have told them to keep it. IIRC it's actually a Tohatsu which I could have just bought for a few hundred less with a much shorter drive to the dealer. Oh well.

 

[flatheadsteve]

Somethings not right I get 9mph with a 5hp merc on a loaded down 1436 flatbottom. The 9.8 is 209cc vs 9.9 333cc that's a huge diffrence but I'd bet your prop is all wrong for your boat and at full throttle your a good 1k-1500 rpm below max.

 

[nytebyte]

I was thinking 9.9 2 stroke. but still a good idea to check for spark on both cylinders

 

[MrGiggles]

Weight distribution makes a big difference.

I had a 14' Alumacraft with a 9.8 Merc. With the trolling battery in the back (and nothing but an anchor up front), it would plow at 8-9mph and never get on plane. If I moved that battery up front it would pop right up and cruise right along at 15-17mph. That 60lbs in the right place made all the difference.

Three batteries is a lot for that size boat. I had a similar setup and ran everything on one group 29, including the outboard. The 9.8 would still plane it but top speed was reduced some with all the extras I had.

 

[Buster]

Weight distribution makes a big difference.

I had a 14' Alumacraft with a 9.8 Merc. With the trolling battery in the back (and nothing but an anchor up front), it would plow at 8-9mph and never get on plane. If I moved that battery up front it would pop right up and cruise right along at 15-17mph. That 60lbs in the right place made all the difference.

Three batteries is a lot for that size boat. I had a similar setup and ran everything on one group 29, including the outboard. The 9.8 would still plane it but top speed was reduced some with all the extras I had.

Similar experience. I have a '66 Lund C-14 with a 2021 Tohatsu 9.8. Alone, balanced, and trimmed, 17mph but 12ish if it isn't balanced. Add a buddy in front, 12mph. And a second, 10ish. Depending on the year, that Sea Nymph empty is 200-300 pounds more than my Lund, so it's like having another guy and a half in the boat right off the bat (Your friend size may vary.) And it's got a foot more beam. I think you're just underpowered, but a tach will tell. Really like my tiny tach, although I wish I'd gotten the long lead version.

 

[Pappy]

What is the model number of your engine? Lets see what prop that came with and what is available.

 

[LaqueRatt]

I'm no expert, but I suspect the motor is performing just fine. I'd be curious to know the total weight of boat with gear and also what the owner weighs. If you're a large guy, have 3 batts, a bunch of stuff, a fuel tank....or two? you may be asking a lot for more speed out of that motor.

 

[wis bang]

While not a speed demon, the 3.5 Tohatsu moves my 14' at close to 6 mph, even against the wind.

I'd love to see what a 9.8 would do on that hull

 

[Buster]

While not a speed demon, the 3.5 Tohatsu moves my 14' at close to 6 mph, even against the wind.

I'd love to see what a 9.8 would do on that hull

Had 2.5 on my 14 and saw 6mph, which is about max displacement speed. A 3.5 isn't a big enough jump to plane it so won't go much faster. Over its nearly 60 year history it's run with a 4, 5 and two 25s (a 50s Johnson and a 90s Merc.) The 5 would partially plane. The 25s would hit 30+mph and felt dangerous. I was fine buying a 9.8 for it. I went with it because it was 15lbs lighter than the 9.9 and it's hard to do anything to counteract that weight on the transom.

 

[njsignman]

I'll get a chance to check the motor/prop probably this weekend and will report back.

 

[flatheadsteve]

Tohatsu lists a pretty broad range of props for the 9.8. Your boat is on the heavy side so you will probably wind up somewhere on the bottom of this chart. An rpm reading at wide open throttle and your current props pitch will let you know for sure.

 

[mirrocraft16]

I had an older, but new the time, 9.8hp Mercury and a 1978 Mirrocraft 16ft Lake Fisherman. It was a tiller only boat, no console, a simple wood floor in the middle, two plastic fold down seats atop 6" pedestals, two group 24 deep cycle batteries, a 3hp transom mount trolling motor, a 24 qt cooler, two tackle boxes, and four rods and reels, two grown guys about 230lb a piece, and what ever bait we were using that day. That combo would do 10mph tops with no headwind or current.
I moved it to a 14ft Starcraft Seafarer with one less battery and no cooler and we got 13 mph.
I bought a new Grumman 14ft Champ in 1983, with Stik Steer remote kit up front plus a new Yamaha 15hp and with the flat bottom mod V hull I got 20 mph with 2 group 27 batteries, two 6 gallon gas tanks, and a Mercury Thruster front trolling motor. It took very little weight to make a big difference in top speed, A third fuel tank and a filled 5 gallon live well dropped top speed down to 17 mph.

I still have the 79 Mirrocraft but with a 35hp Evinrude on it and it has no problem doing 29 mph, which feels a lot faster in that boat for some reason. I've been thinking about swapping out the 35hp for a newer 50hp but can't se taking off a good running motor.

 

[Hardpan]

I have a 14' Sea Nymph "Muskie" with a 9.9 Suzuki 2-stroke. With two other fellas aboard it's fairly zippy.... I seem to recall having her up to nearly 15 mph. Different engine altogether, but your 7.5 mph is surprising.

Like some above, my first thought is "prop." Be sure to let us know what you figure out!

 

[Pappy]

Had asked for a model number on this.
Looked up the 9.8 and found the specs on it.
The engine is only 209CC and has an operating range of 5-6000RPM.
The only propeller I saw for it was a 7p.
With this small displacement and the onboard load plus the fact the boat is a V-bottom it is very possible the engine is doing the best it can.
There is a 25" version of this engine that is used for sailboats and has a 4-blade high-thrust propeller. This propeller may do a better job on this combination.

 

[mirrocraft16]

I've found with several boats I've owned that the ticket to gaining speed is simply either reducing weight and drag or increasing hp.
If your going to gain speed, you have to get on plane.
On my first 16ft V hull, an earlier Mirrocraft, I ran a 1967 Johnson 6hp, while I never checked the speed with anything other than taking a guess, it was no more than walking speed. I thought I was doing something when I found a cheap 7.5hp, but I gained basically nothing. I then hunted down a cheap used 9.9hp Evinrude, that was better but still not much faster, certainly not enough to plane out a 16ft boat with two big guys onboard, and we had to carry more fuel. I wasn't able to get that boat on plane and gain any significant speed until I found an old 18hp for it. It got it on plane but just barely, but it nearly doubled the speed I could travel at vs plowing through the water. I blew that motor up not knowing any better about max RPM, so I found a used 25hp, and that woke that boat up like no other swap I had made. Years later I bought a new 16ft, and a new 35hp, it was a nicer boat but not all that much faster. A small prop, small motor combo will always have its limits. A buddy has the same boat as me, he's got an older Mercury 50hp inline four cylinder on it, and its maybe 2 mph faster on top than my 35hp, but it gets to top speed faster.
From past experience, with a V hull type boat, to get on plane, the boat has to be at or under around 200lbs.
That's 200lb hull, 3 gal of gas, and your motor, plus one normal size person.
I'm a big guy, 6ft 3in tall, 300lbs in my senior years, and a 12ft Duranautic with a rope start tiller 9.9hp with a 3 gal. tank will not get on plane. Its close but it rears up and plows water bad even if I sit in the middle and use a throttle extension. A flat bottom mod v hull would do better.
My 14ft Starcraft has a 35hp max rating, and I run a tiller steer 1981 Johnson 35hp on it. Its a pretty quick boat but top speed is still only around 23 mph. Prop changes make 1 or 2 mph differences but mostly just create cavitation issues or loss of rpm.
The problem with a lot of set ups is that with a single person, a tiller steered boat is way off balance and unable to get on plane even if it has the max hp. Weight distribution, seating position, current, wind, and the shape of the hull all have a major effect on how a boat performs.