So I may have overpowered my SIB for my uses?

Joined
Jun 8, 2017
Messages
23
So, I purchased a cherry condition 15HP 2 stroke Mercury short shaft with a 6 gallon tank for my Mercury 340 Air Deck and while I kinda dig it I gotta say it might be more than I need. It can be a bit scary if you let er rip. And I have found that learned that this thing can drink the fuel and I prefer the 3 gallon tank size over the 6 gallon due to space being at a premium.

The wife is tiny so I keep her up front on the cooler to get me on plane, but she does not let me open the throttle up on a lake (it's always choppy) and going slow in an idle zone is still noisy and we seem to do that a lot. Would a smaller 4 stroke be quieter? Also, I doubt we ever use it on a flowing river. So I am thinking it's overkill for my needs.

We do like to spend time in Florida and we like to Christmas in Fort Myers and park our camper right at a boat dock. We have rented boats there in the past and figure the 340 SIB is bigger than a lot of dinghy's we see being used by the full timers on the sail boats and after bangin around on a flat bottom skiff last year this boat will do fine to go to the bars and get dinner, the dog beach (Boston Terriers love the water) and a few other beaches, I plan on doing some fishing out just a little ways and also in the back bays etc..

The boat is rated for a 20HP and this 15 weighs in at somewhere in the mid 70# arena, I found a smaller 6hp Tohatsu 4 stroke that weighs 55lbs and also has an internal .29 gallon tank for short trips with the option to use an external tank, (I don't know if I can swap back n forth with the gas tanks however?) and I would think that my 3 gallon external with the little 6hp 4 stroke would last as long as my 6 external gallon on my 15hp 2 stroke and save me some space and weight? Thoughts on the fuel consumption? Do you think I can get the boat on plane with the 6hp 4 stroke with about 350 lbs in the boat? And what are your experiences with the brand?

Thanks folks.
Alex
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,306
a 4-stroke would be quieter, and quite a bit heavier if you stay with the same power

dropping to 6hp from 15 would be a significant drop in power. I probably wouldnt drop below 10hp
 
Joined
Jun 8, 2017
Messages
23
Well, a 10 would be a twin cylinder and much heavier than my current 15 (and really expensive) so I cant see much point in doing that. I think I am looking at this as getting a gas powered "Trolling" motor that might just barely get on plane. I am just curious if the smaller 6hp 4 stroke would let me cruise back bays without needing as much throttle or noise at the same low speed I cruise on my 15. Going faster than plane may not be used out in the real world.
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
The small single cylinder 4 strokes tend to be louder and vibrate more, so extended use can be come annoying quickly. You may be able to get on a slow plane with a light load, but you may just be plowing through the water with two people and the cooler.
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
So, I purchased a cherry condition 15HP 2 stroke Mercury short shaft with a 6 gallon tank for my Mercury 340 Air Deck and while I kinda dig it I gotta say it might be more than I need. It can be a bit scary if you let er rip. And I have found that learned that this thing can drink the fuel and I prefer the 3 gallon tank size over the 6 gallon due to space being at a premium.

The wife is tiny so I keep her up front on the cooler to get me on plane, but she does not let me open the throttle up on a lake (it's always choppy) and going slow in an idle zone is still noisy and we seem to do that a lot. Would a smaller 4 stroke be quieter? Also, I doubt we ever use it on a flowing river. So I am thinking it's overkill for my needs.


Alex

Howdy Alex,

Welcome aboard!

I did a little research on the Mercury Airdeck 340. It has a max HP of 20, so I would say you're definitely NOT over powered.

I have a Zodiac Zoom 310S SIB I have had since I bought it new in 2003. I originally used a 6hp Evinrude "Fisherman" outboard and it ran well and was fairly fuel efficient . Since the boat was rated for 10hp (max) i eventually bought a new Tohatsu 9.8 4-stroke. The performance increase was significant! (and uses much less fuel than the 6hp Rude 2-stroke)

At high power settings, the Tohat is quieter than the 2-stroke. You can hardly tell it's running at idle and very low power settings.....

I originally used the 3 gallon tank that came with the engine and switched to a small 3-gal tank that mounted to the transom but I didn't like the extra weight on the back so I went with a Todd Automotive formed 6-gal bow tank.

edit: http://www.iboats.com/Moeller-6Bow-...8862150--session_id.357640220--view_id.729914

gpft01.jpg


I absolutely LOVE this tank because with 6gal and the 9.8hp 4-stroke engine, I can run every day for nearly a week and not run out of gas!! It also puts the right amount of weight in the bow for operating with one person! Plus, I have a Bow "Bag that fits perfectly on top of the tank!

If I had your boat, I would opt for a 4-stroke Tohatsu/Nissan 15 or 20hp motor. (they weigh the same 117lbs) My 9.8hp Tohat weighs 81 lbs and my little boat just fly's with it!

Let me also add that your boat is definitely bigger than mine. I would NOT go with less than 15hp. the 15, 18 and 20 short-shaft Nissan/Tohats weigh the same. 115 +

You would probably be "OK" but marginal with a 9.8. But, the 340 is a full 1ft longer and wider than the 310 and the 310 (Airdeck) is rated at 15hp.

If it were mine, I would definitely find an 18 or 20hp 4-stroke


Cheers,

Rick
 
Last edited by a moderator:
Joined
Jun 8, 2017
Messages
23
Thanks gang. I guess at this point I will keep the 15hp 2 stroke Merc, as I mentioned it runs really strong but the weight difference to go with a 2 cylinder 4 stroke is kind of a deal killer for me as I set up every time I use the boat, not to mention I haul the motor on it's side in the basement of the motor coach and wrestling this thing in & out is hard enough with a 75lb motor... 25 more pounds could slip a disc :)


Also, thanks for that link on the tank, I am going to look into that for sure!
 

Pack Rat

Petty Officer 2nd Class
Joined
Jan 18, 2011
Messages
186
I think the Tohatsu 6 hp comes either with the internal fuel tank or external fuel tank connector. The place I was looking at gave a free 3 gallon tank with purchase. A cherry condition 15 hp 2 stroke would pay for a new Tohatsu 6 hp I would think?
 
Last edited:

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
A cherry condition 15 hp 2 stroke would pay for a new Tohatsu 6 hp I would think?
I don't think I give up 15 hp for 6hp.

With the former 6hp 2-stroke, my smaller SIB would barely plane with one person in it. IMHO, A larger boat would be a real dog with a 6
 
Top