Portable outboard power question

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Hey everyone, I'm trying to max out power for a Zodiac inflatable boat. So, considering only these two factors, which engine is a better option strictly from a power i.e. potential top speed standpoint:

A new 4 stroke 9.9hp, or a 2 stroke 15hp with about 85-90% of the original compression?

Again, for this question, ignore other factors like year and brand of the 2 stroke, price etc.

Interested to hear thoughts on this. Thanks!
 
I kid you not, but my dad had a 47' Chris Craft with an inflatable dingy on it. One day we got it off the boat and fired it up.

To our surprise, the little soft bottom inflatable had a 25HP 2-stroke Johnson on it!!! Holy COW was that thing fast and fun!!!
 
85% of 15 is bigger than 9.9 plus the 2 stroke weighs less.

UD
 
This brings up something I've always wondered about. How the Navy SEALS launch their inflatable boats from submarines underwater. Inflate them, and keep the outboard motors attached to them from becoming waterlogged?
 
Originally Posted By: CT8
Why the apples and oranges comparison?


Ok, you asked for it. Here's the long version.

I have a '78 Evinrude 15hp, the one in my sig. Rolled the dice on it a few years ago, and it's probably toast at this point...been chasing problems and has left me SOL on Lake Erie too many times at this point. My marine mechanic also agrees it's time to move on.

The older two stroke outboards...the 8, 9.9, and 15hp blocks were all the same in many cases, and the same weight...about 80lbs. This weight is pretty much the max for me as far as pulling the outboard off and on the transom on a regular basis like I have to do.

So I'm looking at replacement. There are a small handful of older outboard options. 2 that I looked at (15hp) and did compression checks on were about 85%. So was the one I'm bailing on.

In the newer 4 strokes, the 9.9hp is a smaller engine than the 15hp, and they weigh about 81lbs and 97lbs respectively. The 15hp 4 stroke is out in this case. Why a new 4 stroke? The weights have come down in the last few years, and every lb counts.

When I take my wife and daughter out, the 15hp 2 stroke gets the boat on the plane. My brother's 2 stroke 9.9 struggles. So when finding a replacement, I'm right at the cusp in terms of power, so I don't want to lose any. I just can't do the 4 stroke 15hp, so I would have to do the 9.9hp 4 stroke if I go that route. And a 15hp 2 stroke if I go down that road again.

And then of course there are cost considerations. Used would be about a third of a new 4 stroke. Maybe I get a good one. Maybe I get someone's problems. Marine repair costs add up fast.

The ultimate question, which I tried to word in the OP, is will a new 9.9hp 4 stroke match the output of an older 2 stroke 15hp with what seems to be a normal decrease in compression from age/use?
 
If the 15 hp 2 stroke runs well, it will trounce the 9.9.
Will it last if compression is down?
Can the engine be brought back to life with a ring job cheaply?
 
Originally Posted By: thunderfog
I have a '78 Evinrude 15hp, the one in my sig. Rolled the dice on it a few years ago, and it's probably toast at this point...been chasing problems and has left me SOL on Lake Erie too many times at this point. My marine mechanic also agrees it's time to move on.

Sounds to me like you need to find a new mechanic, or at least a second opinion. Of course he would want you to replace a motor that has stumped him, eventually you are going to take it somewhere else.

EDIT: Everyone is going to tell you to keep the 2T because any gearhead loves a 2T because it is lighter, more powerful and easier to fix. It seems that you need the 15hp without the 4T weight penalty, so you need a 2T 15hp outboard. You could just buy a newer used one, but I am afraid it would be a lateral move unless you pay a premium for a low hour dreamboat in mint condition. You could probably find a nice one in the offseason if you can limp it through, just wait for a really nice one to come up for a good price around Christmas.

I'd fix what I had but if you have been stranded by it multiple times, I would consider purchasing a nice one especially if you have more money than time. I actually drove a water taxi that had a newer Yamaha 15hp 4T tiller for a summer and it was very smooth and reliable, that was nine years ago and the motor was probably early 2000s.
 
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It depends how old the 15HP two stroke is. Old ones were measured at the crank where the new 9.9 four stroke will be measured at the prop. If it's in good running order I'd prefer the 15.
 
Originally Posted By: maxdustington
Originally Posted By: thunderfog
I have a '78 Evinrude 15hp, the one in my sig. Rolled the dice on it a few years ago, and it's probably toast at this point...been chasing problems and has left me SOL on Lake Erie too many times at this point. My marine mechanic also agrees it's time to move on.

Sounds to me like you need to find a new mechanic, or at least a second opinion. Of course he would want you to replace a motor that has stumped him, eventually you are going to take it somewhere else.

EDIT: Everyone is going to tell you to keep the 2T because any gearhead loves a 2T because it is lighter, more powerful and easier to fix. It seems that you need the 15hp without the 4T weight penalty, so you need a 2T 15hp outboard. You could just buy a newer used one, but I am afraid it would be a lateral move unless you pay a premium for a low hour dreamboat in mint condition. You could probably find a nice one in the offseason if you can limp it through, just wait for a really nice one to come up for a good price around Christmas.

I'd fix what I had but if you have been stranded by it multiple times, I would consider purchasing a nice one especially if you have more money than time. I actually drove a water taxi that had a newer Yamaha 15hp 4T tiller for a summer and it was very smooth and reliable, that was nine years ago and the motor was probably early 2000s.



Part of the consideration also... the unreliability of my current engine does not mix well with taking out my 3 yr old girl who *loves* the boat... and that is half the fun of the whole venture. I gotta think of her safety. A 30 min ride on Lake Erie in summer heat that could turn into 2 hours rowing in or even waiting for a tow...

I'm trying to avoid paralysis by analysis, but there are a lot of variables here.
 
Originally Posted By: thunderfog
Originally Posted By: maxdustington
Originally Posted By: thunderfog
I have a '78 Evinrude 15hp, the one in my sig. Rolled the dice on it a few years ago, and it's probably toast at this point...been chasing problems and has left me SOL on Lake Erie too many times at this point. My marine mechanic also agrees it's time to move on.

Sounds to me like you need to find a new mechanic, or at least a second opinion. Of course he would want you to replace a motor that has stumped him, eventually you are going to take it somewhere else.

EDIT: Everyone is going to tell you to keep the 2T because any gearhead loves a 2T because it is lighter, more powerful and easier to fix. It seems that you need the 15hp without the 4T weight penalty, so you need a 2T 15hp outboard. You could just buy a newer used one, but I am afraid it would be a lateral move unless you pay a premium for a low hour dreamboat in mint condition. You could probably find a nice one in the offseason if you can limp it through, just wait for a really nice one to come up for a good price around Christmas.

I'd fix what I had but if you have been stranded by it multiple times, I would consider purchasing a nice one especially if you have more money than time. I actually drove a water taxi that had a newer Yamaha 15hp 4T tiller for a summer and it was very smooth and reliable, that was nine years ago and the motor was probably early 2000s.



Part of the consideration also... the unreliability of my current engine does not mix well with taking out my 3 yr old girl who *loves* the boat... and that is half the fun of the whole venture. I gotta think of her safety. A 30 min ride on Lake Erie in summer heat that could turn into 2 hours rowing in or even waiting for a tow...

I'm trying to avoid paralysis by analysis, but there are a lot of variables here.


Here, in Toronto I was looking at outboards recently, and it seems like a used good condition modern 4T 9.9 is worth about $2000-2500 for a 9.9 where an old 2T 9.9-15 would be around $800 maybe $1500 for a good condition newer 15hp. I was looking last week, so those are recent peak season prices.

I think a newer one is better bet because they will hold their value better. I think a lot of people are in the same boat as you, as the old ones are all worn out by now. Why bother screwing with the carb on a 2T every season when you can get a 4T with fuel injection and a check engine light for an extra $1000.
 
I've used 2 and 4 strokes in this power range. Like said, even with some age, hours and wear on it, that 15hp 2-stroke should outpower the 9.9 4 stroke. A mint condition, super running/performing 15hp 2cycle should smoke the 9.9 four. Literally! lol.
 
More power is always good when it comes to boats. I find modern 9.9 4 strokes to be pretty sluggish compared to say an 80’s Evinrude 9.9 2 stroke. Also those old twins are dead reliable.
 
The 9.9 is a very nice motor...super quiet, no smoke, wide open it will sound like it's not even trying work. The 2 stroke 15 hp is a beast...light, fast, powerfull but noisy, smokey, and dirty. I prefer the 4 strokes and like how quickly they cold start and are so very clean burning. Just change the oil and go. I don't like mixing 2 stroke oils either. Before I bought my 2007 Lund Tyee Grandsport I had an 84 Lund Tyee with a 90HP Evinrude and a 6 HP kicker motor and they were both 2 strokes. Trust me, the 4 strokes are the way to go but the 2 strokes were good in their day. Resale will be much better with any 4 stroke powered boat.
 
Like said above, if this is for an application where you will be having to mount/dismount the motor nearly every time you use it, I wouldn't want to use a new 9.9-15hp 4 stroke for that unless it was an old Honda 4 stroke or something you got a deal on.

We've got an old 18hp Evinrude fleet twin (or sport twin?) that is almost too much for a small aluminum boat when you have it dialed in. Horrible thing about the 1950's vintage is the pressure fuel tank. I haven't used it in about 20yrs and I'm not sure which family member still has.. Gotta love that.
 
Go look for a Tohatsu dealer and talk to them. Maybe the best made outboards out there. They have made engines for Mercury, OMC, Nissan, etc. Zinc plated water jackets, light weight. They have a sterling reputation and they have light weights in your power range.

Tohatsu Lightweights
 
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