What size

[Dingydiver]

Could someone help with some advise on what size outboard would probably the best.
I have just purchased my first 12 aluminium v hull boat an older Princecraft Springbock.
I was thinking along the lines of 2.5hp/3.5hp or 4hp Mercury/ Tohatsu.
Is the extra money for the 4hp with it's reverse gear and extra hp be worth it, and would the 1.5/0.5hp be noticeable.

 

[Bob_VT]

Welcome to iboats!

Normal rule of thumb is at least 75% of the maximum rated power as per the data plate. 12 aluminum boats as an example are usually rated max 7.5 to about 10 hp you will get decent performance at the 75% point and the 4 mercury/tohatsu will still move the boat and a "ok" speed.

Better to have the power and not use it

 

[garbageguy]

Good rule of thumb and advise above - then, it depends how, where and when you plan to use the boat in the water, and how much/how far you intend to move it out of the water

 

[JimS123]

It depends on how Fast you want to go. Regardless, not having a reverse gear will make sure you never are without one.

 

[Dingydiver]

Thanks for the reply's.
I only need to potter about, don't want or need to win any races, too old for that sort of thing.
Looks like the 2.5 is out.
Now, would the difference between the 3.5 and 4hp be noticeable, personally I don't think so. So it's down to reverse and is it worth the extra dollars.

 

[racerone]

Find yourself a 6 HP 2 stroke Johnson / Evinrude.----1966 to 1979.-----Wonderful motors.-----Easy / cheap to maintain.-----visit ----leroysramblings-----To learn about older motors.

 

[JimS123]

The 3.5 is a smaller displacement, thus I believe yes the 4 would provide better results. Regardless, the F-N-R would make the deal for me.

The 5 is the same displacement as the 4, so that, IMHO, would make the 5 an un-needed choice.

I personally have both a 3.5 and a 5 (the pro-kicker extra long shaft) and i love them both.

My perception was that you are looking at a new Mercury 4-stroke. Awesome engines.

I also have several older 2-stroke 5-6 HP JohnnyRudes and they are excellent motors as well. I run them just for fun. But, when I want to go fishing and don't want to have to add oil or fiddle with carbs, I take out my new 4-strokes.

 

[Dingydiver]

Thanks Jim
Yes a new mercury 4 hp 4 stroke is one of my options.
Thanks for your experience and insights,

 

[mr 88]

I would be looking for a 8 hp Yamaha 4 stroke - Two Cylinder . Your going to have the torque - hp to move the boat along on a plane with a full load . 6 hp is a single cylinder and does not troll as smoothly as the 8 hp twin cylinder . The smaller engines will be worked to death and the vibration isn't fun in a aluminum boat.

 

[roscoe]

Definitely worth the $ to have a gear box with reverse.
If you plan on running the motor for more than 15 minutes at a time, you should really consider a 2 cylinder motor.

If you plan on trolling, definitely get a 2 cylinder.

 

[Dingydiver]

Thanks everyone you have given me lots to think about.

Lee.

 

[JimS123]

Definitely worth the $ to have a gear box with reverse.
If you plan on running the motor for more than 15 minutes at a time, you should really consider a 2 cylinder motor.

If you plan on trolling, definitely get a 2 cylinder.

I ran 2-strokes for eons. The smallest was a 2-cylinder. Never had a single cylinder. Then in 2017 I bought a 60 and a 3.5 4-stroke. That convinced me about 4-strokes so much that the next year I traded our I/O for a 150 and a 5.0.

I must admit that when I first fired up the 3.5 I was surprised at the sound and difference in "smoothness". But since its a kicker on a 2000# FG boat I can't really say I perceive much vibration. Nevertheless, I can understand the comments about a small tinny.

Of course, a 2-cyl 8 would be the best of all, provided that it doesn't exceed the boat's HP spec. Naturally, everything comes with a cost.

A Merc vs. a Yami is probably not debatable. When I bought the 60 and 3.5 I traded in a Yami 25 2-stroke. It was a good motor, but with 12 Merc dealers and only 1 Yami within driving distance, the choice for me was quite obvious.

 

[jimmbo]

4 hp is not going to put that 12 ft on Plane, so 6 or 7 is the minimum

 

[dwco5051]

I have a 12' Meyers V aluminum that I use on the smaller electric only lakes around here. A couple of years ago the oldest boy picked up a 5hp Merc 2 stroke. Ran it on the lake with the 5hp and it would plane guessing about 15mph. Your boat is probably a little heavier so speed would vary. Started running boats about 65 years ago. One 12' jonboat and the other 11' with two different 3.5 hp motors that not only did not have reverse but also no neutral. Go with reverse, you won't be sorry.

 

[rallyart]

Thanks for the reply's.
I only need to potter about, don't want or need to win any races, too old for that sort of thing.
Looks like the 2.5 is out.
Now, would the difference between the 3.5 and 4hp be noticeable, personally I don't think so. So it's down to reverse and is it worth the extra dollars.

Usually a 3.5 is a lot lighter than a 4. Check the weights and which have attached fuel tanks, if that matters. Not much difference from a 3.5 to 4 in performance. A 6 often weighs close to a 4 and that would give you more get up and go, especially if loaded with two people. A 3.5 will probably not get it planing so you are only puttering.

 

[JimS123]

When I was a kid my Dad and I used to fishing at a small lake a few times a year. We rented a 14' tinny with a 3 HP 'Rude with weedless lower unit. The lake was only a few miles long, but it still took us a looooog time to get to the other end.

When I was 15 Grandpa gave me his Mark 10. That sucker would make those little rentals howl. But alas, ALL forward gear. We had to paddle out from the dock and then start her up. One time I decided to idle in and then coast into the dock. Easy peasy, right? I guess I cut the throttle a bit too late. The rental shop owner chewed me out for ramming his dock.

Reverse gear was a requirement after that.

(Funny how some threads bring up old but good memories. I wish I could putter around with my Dad with that little "rude one more time)