I think I need a prop change

[studlymandingo]

As some of you may know, I recently installed a jack plate with 10" setback on my 18'6" center console fiberglass boat. The jack plate and setback were a very nice improvement; the boat seems to ride and handle better with the setback.

I think I need a prop with more bow lift, or perhaps I need to have my current prop reworked. The other day I went out, there were 4 adults and 1 75lb dog, 40 gallons of fuel and a cooler seat half full. The boat ran nicely but it was porpoising a bit more than I would like. With 2 people aboard, it wasn't an issue, but with the additional 2 people it was more pronounced.

I currently have a 14.25X21P Rapture SS prop that is vented. I have a great hole-shot, and the top end is about 48 MPH at 5400 RPM WOT (on a good day). I know the Rapture isn't the best prop on the market, but it has been all around a decent prop; I feel like the boat could use something with a bit more bow lifting capability. Should I look at having this reworked, or should I be looking for something different altogether?​

 

[Dhadley]

Re: I think I need a prop change

Actually since the overall performance increased but the porposing came up, I might be inclined to talk to John about the Smart Tabs. You've done a lot to max out the set up, just need a stabalizer. Obviously he's a little bias (deservedly so) but get his opinion.

I know I should remember but what motor is on the boat?

 

[studlymandingo]

Re: I think I need a prop change

It's an '86 150HP Mariner. I haven't increased the actuators since I installed the jack plate. The last time I increased the pressure, it slowed me down just a bit. I've heard several people dogging the Rapture, it pushes the boat along well though. When there are only 2 on board, there is very little boat in the water and she scoots along nicely; once I had an additional 2 sitting further forward, she felt like she wanted to ride the same way but the bow kept falling off.​

 

[Dhadley]

Re: I think I need a prop change

So you already have Smart Tabs?

 

[studlymandingo]

Re: I think I need a prop change

Yes, I reduced the tension before the setback because it was pushing the bow down too much and I lost some speed. Do you think I should increase the tension now? It really feels good with only two aboard, the jack plate made a huge difference in the overall feel of the boat. It rides "up" on the water more and the boat feels lighter. I don't want to push the bow down so much that I increase the drag.​

 

[Dhadley]

Re: I think I need a prop change

That's the idea -- get the boat "up" or loose. Then use the tabs to hold the stern stable and use the prop & setback to carry the nose. A 21 rapture -- let me think about this a little. What other props do you have to try with the new setback?

 

[studlymandingo]

Re: I think I need a prop change

That's what I have right now. I'm looking for a direction to head. I think the local merc dealer may let me try a couple; I just don't know what will give me the lift I need.​

 

[Dhadley]

Re: I think I need a prop change

Thinking.......I'd like to try a 21 Turbo but I don't have one. Let me see what we can find.

 

[studlymandingo]

Re: I think I need a prop change

I'm certainly open to experimentation, and appreciate your help.​

 

[studlymandingo]

Re: I think I need a prop change

So would more cup or rake give me more bow lift?​

 

[Esox]

Re: I think I need a prop change

As I understand rake is what has an effect on bow lift - but I'm no expert. Even with the setback you still need more bow lift? If so your in the same "boat" as me. No pun intended ​

 

[studlymandingo]

Re: I think I need a prop change

In a way I feel like I do. After installing the jack plate, the boat rides nicely out of the water when there are only two aboard, when I get any more weight towards the front, it wants to "fall forward" and I have to run trimmed in to avoid porpoising.

With just two aboard, it runs at a great attitude and there is very little boat in the water, it really feels good. I just think with a little more bow lift I could reproduce that same feel a little more loaded. (The boat not me!)​

 

[Esox]

Re: I think I need a prop change

As far as I have read cup also has an affect on lift. If I recall correctly - cup on the blade tip adds bow lift and cup on the trailing edge adds stern lift. I noticed the same thing as you when I added setback on my 18' aluminum deep v. It completely changed the way the boat handled for the better. I have been using a ballistic 19p and a turbo1 19p for my testing. So far the ballistic has produced the better #'s as far as speed but the t1 blows it away in acceleration and is running where I want RPM wise (5500). I am looking to exchange the turbo1 for a lightning. I'm hoping that will get me to where I need to be with bow lift. One of the problems I'm having is finding a dealer in my area that will let me test some different props and I already have 2 props that I'm unhappy with. Hopefully Dale will pop back in here and give you some answers.​

 

[studlymandingo]

Re: I think I need a prop change

I haven't located a dealer willing to let me run props yet either; surely someone in this area will; I'll just have to keep checking.​

 

[studlymandingo]

Re: I think I need a prop change

Does anyone know what the rake is like on the Rapture?​