Question for the converted(4 to 6 hp that is)

[Sushiboy]

I am curious to hear some examples of improved performance from the Tohatmercissan(Tohatsu mercury nissan)4 to 6 hp carburator change.I see lots of questions but not a lot of follow up.I want to swap the carb and add the alternator to run lights,FF and a small bait tank on my 9' Boston Whaler tender.Alone I can get 11mph according to the GPS with my 4 hp 2008 mercury.I would like to see 14-15 alone and about 12mph with my 2 small kids.Thanks for any input you guys may have.

 

[qzyn]

Re: Question for the converted(4 to 6 hp that is)

Hi!!

I did the carb swap last year on my Merc. 4hp
Also I put 9" pitch propeller in place of original 7" and used external tank 12ltr.
(Fuel consumption is 50% higher and frequent refueling i.e. every 30mins could be annoying.)
My Merc 2008 4 stroke 4hp was converted to 6hp and used with quicksilver 270 inflatable, V-bottom, wooden hardfloor.

4bhp was enough to get on plane with one adult on board (160lbs),with 2 adults top speed abt. 6-7 mph only!!!
6hp was ok with 2 adults, ie abt 15mph, but with my boy (80lbs) and some gear no more planing!!!, speed 6-7 mph
Figures for hard body boat are different probably, drag coefficient for inflatable is much higher and more power required to get on plane.

Big advantage of this engine is weight and ext. fuel tank connector, power increase from 4 to 6 hp is also noticeable.
Total cost of conversion (carb, prop, tank) was a little bit less than cost of buying "original" 6hp.


CU

 

[Sushiboy]

Re: Question for the converted(4 to 6 hp that is)

Thanks for the input.So If I understand you correctly with 2 adults and the 4 hp you were going 6-7 kts and the 6 hp got you back on plane with 2 adults?I know performance will be different for me as I weigh 230# and my boat about 150#(Built like a tank!)
Also did you do the prop change at the same time or was that after you swapped the carb and still felt you needed to do a little more?
I allready hooked up a 3 gal tank because refueling on the water is a PIA.

Also If anyone knows the true origin of this boat, let me know.I know its not a true whaler but a knock off.I had no paperwork and the lady at the DMV refused to register it until I named the manufacturer.I said "Its like a Boston Whaler" she said "I'll ask you again,who is the manufacturer?" "Boston Whaler" I replied allthough all whalers I have ever seen have gelcoat inside too,and this one doesnt even though dimensions are the same as their 9' tender.

 

[qzyn]

Re: Question for the converted(4 to 6 hp that is)

Hi!!!


I did prop swap after few trips,
9" gave me definitely better performance.

In my case total load (boat, engine, etc) was abt 450lbs


Tohatsu prop chart for models MFS4A MFS5A MFS6A

load dia pitch
Light 7.8/ 9
(5/6hp) Mod 7.8/ 8
(4hp) Hvy 7.8/ 7


7" is standard on 4 hp, 8" is standard on 5/6hp


Definition of Loads Gross Weight
Light 100 - 500 lb. range
Moderate 500 - 1500 lb. range
Heavy 1500 - 3000+ lb. range


Finally, this year I went even further and replaced my really beloved Mercury with 9.8hp 4 st Tohatsu.
I didnt want to pay for sticker, Tohatsu was 15% less, being sold in Poland through Volvo Penta network for many years.
Top speed is 18 kts now ( sea miles) with two adults (300lbs) on board,
16 kts with 3 adults ( live load 460 lbs)!!
Two days ago I fiited Smart Tabs ( thank you, eBay!!) and Im really impressed after first ride .
(I know, it is overkill to put tabs on 9ft inflatable, but I like them!!)
Getting to plane much easier and faster, I need more test rides to set them properly


good luck

 

[Sushiboy]

Re: Question for the converted(4 to 6 hp that is)

Thanks for all your helpful answers,thats just what I was looking for.As for my boat,I am wondering if someone pulled a mold from a whaler hull and made these?