Auxiliary engine (kicker) pitch problem

[shingo]

I recently bought a mercury 3.5 hp (tohatsu) to use as a kicker on my 16 ft princecraft aluminium semi deep v boat.

The boat is around 1200 pounds and with me and I I fill the live well it's around 1500 pounds.

The 3.5h hp seem to had some difficulty at low RPM and wouldn't go very high in RPM.

It's equiped with the standard prop which is a 7 pitch.

According to the manufacturer, the standard pitch is 7 and considered for light use (100-500 lb.)
I have the choice to either go to the moderate load (500-1500 lb) or the heavy load (1500-3000+ lb.)

Since my boat is around 1500lbs with me and the live well, would you go for the moderate or heavy prop?

TECHNOLOGY : 4-Stroke
Model : MFS3.5
Prop Type	Load*	Diameter	Pitch	Blades	Standard Equip.	Part #	Comments
ALUMINUM	LIGHT	7.4	6	3		3F0B645120
RESIN	LIGHT	7.4	7	3	Y	3F0641010M
RESIN	MODERATE	7.4	5.7	3		309641060M
RESIN	HEAVY	7.4	4.5	3		314B641030

 

[Georgesalmon]

heavy if used for trolling

 

[shingo]

I'm going to use mainly fro trolling and also I want to use it as an emergency engine in cas my main fail. Will the heavy bring me to maximum hull speed if needed?

 

[crb478]

Go with the heavy load and don't worry about maximum hull speed, neither prop will get you there. The heavy prop will give you better trolling speed control and will get you headed back to the dock under some power, not fast, but steady.

 

[Scott Danforth]

with only 3.5hp trying to move 1200-1500#, get the smallest pitch you can. you dont have enough power to worry about speed, however you will be able to move it

 

[shingo]

With the current prop, I go at 2.5 mph at 1/10 throttle, 4.4 mph at 1/3, 4.4 mph at 1/2 and 4.4 mph at full throttle. The engine RPM do not seem to change between half throttle and full throttle under load.

I'l try to find a 4.5 prop, the current prop is definitely a miss match for my boat size and weight.

My main 50hp outboard get me at a minimum of 4mph which is way too fast.

I guess with the 4.5 prop I will be able to go slow enough.