Is it enough motor?

[JasonMay]

I purchased a 1989 16' bass tracker flat bottom boat last fall without a motor. The maximum horsepower rating is 50hp.

A buddy has a 40hp Johnson, 1994, that he's selling. I'm familiar with this motor.

Will a 40hp be sufficient for my boat? I'd like to pull my son on a tube this summer. I know we won't break any speed records, but will the 40hp be ok for this?

 

[boobie]

40 should be okay but don't go any less.

 

[GA_Boater]

A 40 is 75% of the boat's max HP rating. 75% is the usual minimum HP recommendation for a boat.

It should be OK.

 

[Scott Danforth]

The trackers always seamed under powered. However that being said, a 40hp will get you fishing

 

[82rude]

Actually unless ive totally buggered up my math GA its 80 percent of rating .10 percent of 50 is 5hp x2 =10hp =40hp.

 

[Sea Rider]

You mean 75-80% of max HP capacity to carry max stated passenger rated for on transom plate, right ? if usually boating with less passengers than stated on plate don't need to follow that % rule, a less HP-OB with a maximized less pitch prop will do the trick, just don't expect a speed machine.

You can always maximize a less pitch prop to take the max out of that 40 HP-OB while revs middle to max wot rpm range as loaded, will need to install an induction tach for that purpose to check achieved wot rpm on an ideal flat water test run.

Happy Boating

 

[Faztbullet]

Slap a set of 50hp carbs on it and wala!!!! 50hp.

 

[Sea Rider]

Slap a set of 50hp carbs on it and wala!!!! 50hp.

When upgrading a less HP-OB, say 40 t0 50 with same CC powerhead, the lower HP one usually comes factory adjusted with less time advance than the upgraded model. More fuel intake from a larger carb needs more time advance. A matter to check factory tech specs.

Happy Boating

 

[Faztbullet]

the lower HP one usually comes factory adjusted with less time advance than the upgraded model. More fuel intake from a larger carb needs more time advance.

No it dont....All your doing is increasing CFM and AFM to motor...like saying you have to change timing on a SBC when you go from a 650 to a 750 carb

 

[QBhoy]

Simple answer is Yes. Optimised ofcourse by a good prop selection.
My mother used to mono ski off the back of an old 14 foot Broom speedboat with a 35hp Merc on the back.
I recently kneeboarded off the back of a 3m rib with a 10hp mariner. That a bit extreme to be fair and wasn’t ideal, but the wee broom with the 35 was fine.

 

[Sea Rider]

While both HP-OB's Shares Same CC Power Head, there are different simple and complex ways to upgrade a less HP-OB model. Depends on each OB brand fabricator. Varies from reed valves, less timing and carb advance synch, carb restrictions.

Must check both models on Parts Manual and determine which common parts are being shared for both and which not. You can find carb timing synch data on any Service Manual. Tohatsu al least especifies such data for every 2 strokes OB they sell and carb/timing advance varies between them with same CC power head.

You can go for a prop maximization only after the larger upgraded OB is running with carb/timing advance synch spot on adjusted, If not OB will not deliver it's next full HP potential and probably need a much less pitch prop to compensate for OB to run towards middle or max wot rpm range.

Happy Boating

 

[JimS123]

Your 40 will be awesome, provided that you prop it to attain max spec rpm. The 75% rating is merely someone's opinion and has no basis in fact.

My first boat was rated for a 60 and I put on a 40. My second boat was rated for a 95 and I put on a 60. Sorry, I didn't know any better and back in the 1960's I didn't have enough money to go bigger.

As a kid we waterskied behind a wooden boat with a 25 on the back. I don't know what it was rated for but it weighed more than my first boat that had the 40.

 

[Faztbullet]

Ignore all the posted tech/engineer dribble. There is NO difference in the 40/48/50 powerhead other than carbs. Timing,ports,sync & link are all the same.