Force by mercury 90hp

[TexasDan]

95 Force 90 hp on 19' spectrum pro angler (aluminum)dual console, propeller selection.
Have 13 x 19 stainless, 23 mph @ 5200 rpm , boat looses plane around 4000 rpm, very slow too plane or seems that way. This is my first boat. Boat is rated for 150 hp
Looking at 4 blade aluminum 12 3/4 x 17 or 13 X 17 , have just rebuilt motor so I am trying to get it right the first time .
Any recommendations appreciated .

 

[H20Rat]

4 blade isn't going to help you, it seems like what you have now is probably as good as it is going to get. A 4 blade prop takes more power to spin since you have another blade to drag through the water.

Normal recommendation is around 75% of the recommended motor at a minimum, you are well below that at 60%. (Force motors weren't exactly known for being over-rated either...) Max rpm for that engine is 5250, so you are right there already...

How is the rest of the setup? How low is the motor mounted on the transom? Trim? Can you move weight forward? (IE, do you have a couple heavy deep cycle batteries for a trolling motor in the back?)

 

[TexasDan]

I'll answer what I can ,
1.trolling motor on front ,
2.batteries not yet installed but will also be near the front.
3.there is a lot of structure in the front of the boat , live well ,storage compartments, anchor compartment , there is nothing in the back of the boat (motor and cranking battery)
4.motor appears to be mounted correctly from seeing some of the other post here, but I have not had a chance to look at while underway
5. motor does have power trim
6. I only assume that a boat 22 years old there would be some waterlogging of the flotation foam

I am not looking for speed ,I know the boat is gong to be a slug , the performance from idle to 4000 rpm is so poor , Is there no slow speed benefits to reducing the pitch? I want a peppy slug !

If 13x19 stainless is 5200 rpm what would the correct diameter be for 17 pitch or 15 pitch ?

Thanks,Dan

 

[flyingscott]

The problem with lowering the pitch is you will start to overev the motor. Try a Doel-Fin or similar on the motor may help, they usually have really good effects on underpowered boats. You can also try to move weight to the front of the boat.

 

[SkiDad]

Something is wrong. A force 90 should get that boat up to 35 mph with no problem. Have you verified spark on all 3 cylinders ? Also 23 at 5200 doesn't compute.

 

[Chris1956]

Falling off plane at 4000RPM is unusual. Normally boats start to plane at about 3000 RPM. Perhaps your tach is reading high by 1000 RPM? If so, you have too much pitch int he prop. You might verify operation of the tach.

 

[steelespike]

Is the speed by gps? Do you know the gear ratio?I'm guessing 2.30.It does appear that the prop slip is about 40%.
Normal would be around 12% Perhaps you could borrow a shop tach to verify the rpm.