Need Help, will a different prop help?

[dadanddaughterfishing]

I have an 16 ft aluminum boat with a Nissan 40HP 2 stroke on it. I have been pulling my hair out trying to figure this out. Top speed on it is only 15 MPH. I cant get it to get on plane. the bow rises and wont plane out. Takes off ok but when a load is put on it motor seems to not go any faster. motor sounds great. Seems like its getting fuel just fine. in neutral it revs up just fine and sounds great. I changed the plugs new fuel tank and hose. it feels like at any second the boat sounds like it will take off but just doesnt pick up anymore speed. Any ideas whats going on? would a different prop help it? it now has an 11.4x12x3.
Any help would be greatly appreciated

 

[SkiDad]

If you are sure the prop is not slipping...Then try putting your gear in the bow. If it planes ok the drop down to a 10 pitch. Just my thoughts.

 

[dadanddaughterfishing]

Im gonna try and move everything to bow. i just dont know why I cant pick up speed.

 

[82rude]

Sounds to me like your prop is spun.Basically your prop is hitting a certain load point then the rubber hub is slipping preventing any further speed gains.

 

[steelespike]

If the hub was spun it basically lets go at a specific power motor revs and boat slows.
I would confirm it is running on both cylinders. You wouldn't be the first to not realize
your on one cylinder except for the lack of power.
Is the throttle opening all the away?

 

[dadanddaughterfishing]

throttle is open all the way. I moved some weight to the bow and it did pick up 3-4 MPH

 

[steelespike]

Did you try a cylinder drop test,To see if both cylinders are working.