Motor cavitation. Prop or Boat?????????

I had about the same problem you are having now. No push at low RPM
prop would spin and not bite in the water when throttle was opened up.
I used a prop with more pitch and the rear of the boat went down into
clear water with less RPM and took off with a good hole shot and planed
off.
I also would raise the cavitation plate on the motor to the bottom of the transom.
 
The pitches were all the same. But the factory prop has no cup. The 4 blade and the SS prop do. That was why I tried them to get more bite. I have a feeling I am going to have to spend some more $ and get the high dollar PowerTech wide ear performance 4-blade. I'm still waiting on a response from them about this.

I have one of the top prop guys just north of me. He does all kinds of modifications to them to get them where you need them. I might run this up there and see what he thinks.
 
Like Capt. Jeff asked...what was the pitch of the props you tried? How many inches? The prop's pitch is very important. You are running a very heavy wooden home made boat...bow heavy you say too. You are trying to make that boat run with unknown loads using a very small 4 stroke outboard. 4-strokes are miserably slow out of the hole to start with and a 15 horse just isn't going to have the power to get any large load over several hundred pounds up and running. Playing with the cup, and rake aren't going to help a whole lot on a very small outboard...especially if the pitch of the prop is totally wrong for the load. If you are getting 22mph out of it...that is actually pretty darned good for a 15. Please realize that factory props are for the average boat that a particular motor is going to be put on...many companies these days don't even ship a motor with a prop...you have to try several and decide on the one that suits your boat the best. Just guessing but if that factory prop is a 12...see if you can find a 9 or 10 and put it on and try it. Go to the shop you bought it at and ask to borrow it...make sure you don't ding it...and see what it will do.
God luck with it. If you have a buddy that has a 25 horse 2 stroke...see if he will let you borrow it and run it on your boat and see if it does what you want it to do.
 
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They were a 9'' pitch. The pitch only will not help carry a load. The rake and cupping do. High rake helps lift the bow. Cupping helps grab the water. It also depends on where the cupping is at. These have the cupping on the rear edge and not the tip. So it is more for carrying a load.

The SS also has a progressive pitch instead of a fixed pitch the alum 3 blade has. Once the SS prop is hooked up, the rpms are a little lower than the alum 3 blade.
 
I got the jack plate on today. 4.5" of set back. I tried the two props I have on hand. The factory alum and the Solas SS. Both are 9.25" dia x 9" pitch. I tried it with and without the fin. It ran the best with the factory alum prop. It slowed down a little to 21 mph. But, it runs way better when the livewell is full. 19 mph. I tried with out the fin and it would not even get on plane with the SS prop.

For right now I am going to leave it unless something happens. I want to extend the keelsons next. I am going to need about a week of nice weather to do that. The way it has been raining here it might be a while.
 
When I did the break in on the motor, I borrowed a friends 14 foot wide Alumacraft. The riveted light one. It was doing the same thing now that I think about it. And the other thing it is doing is if you look back at the prop wash, it has a rooster tail coming off the lower end on both sides. It is about 3 feet high for each. Water is being sprayed up to the higher plate and that is where the rooster tail is coming from. It only does this once the prop bites. I don't remember any of my other motors ever doing this.
 
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