23 vs 20 Ride Characteristics
 

Hey all. I bought my 23 Tsunami with a Mercruiser MPI 350 (300hp) and Bravo 3 drive from a member here. Shes a great boat and I'm setting her up my way.

I also have a 20' Sceptre with a 175 optimax. It took me a while to get this boat set up how I think it should ride. Engine came up, 4 blade stainless prop. When I put the hammer down and trim out, this boat raises up out of the water and just glides so delicately its amazing.

The 23 is actually faster than the 20. I get her up to about 40 but she is plowing much more than the 20. It never seems to lift up nearly as much. The result is a fair amount of side/side movement as it catches the water and it doesn't feel nearly as nimble. I just discovered that my trim limit switch was adjusted wrong and I was missing some positive trim so I'm sure that will help. It was also suggested that a different prop should do it, but is that true of the B3 dual prop setup?

My question is, will the 23 Tsunami with a sterndrive have the same ability to lift out of the water as my 20 with an outboard? I know you guys know what I mean. It's part of what makes this hull great. I'm just hoping I can get that out of the 23. It's still a smooth ride, but I feel like it can be better.

Sounds like you need to make two changes:
First, add stern lift trim adjustment via trim tabs or something like a Hydro-Shield skeg-mounted hydrofoil.
Second, adjust bow lift either by changing the drive trim angle underway, or change the propeller to one with bow-lifting geometry.

For stern-drives, the propeller diameter is more important than with outboards. You didn't say what the diameter, pitch, cupping and rake progression is for your propeller set, but if you know the part numbers for your props, you can contact PowerTech or Prop Gods and they'll offer good advice.
I do know that the closer your propeller blade tips are to the surface, the more bow-lift they produce. Other factors are important, too, but that's a good place to start. I would also put the drive into neutral trim where the anti-ventilation plate is perfectly parallel to the keel and measure the height difference. Prior to the wide acceptance of heavily cupped propellers, the drives (and engines) were mounted lower in the hull and on the transom. Giving that height difference to the techs at either of the places listed above may affect their advice on propping.

The 20 is like an old bathtub Porsche.
The 23 more like a Jag XJS.

Jag on the highway.
Bathtub around town.

Thanks for the detailed response. I do have tabs, but honestly they seem to just push the bow down and make it dig in more. I do feel like I'm not getting enough bow lift. I don't know anything about the props other than pitch (22). I know I'm a bit under my RPMs, so I need props anyway. Ken set me up well with my 20 and that boat rides just the way I want it to.

Just eyeballing it, I'd say the vent plate is level with the keel but I'll take a formal measurement. Unfortunately that's not as easy to change as it is on an outboard.

Duoprop drives alway feel more connected to the water due to the double amount of blade surface in contact with the water. There are more “pros” than cons with a duo where it counts. Low speed planing in seas would be the biggest pro.

I seriously doubt a prop change will equate to a significantly more nimble ride considering a new set will run about $1500, the juice won’t be worth the squeeze.

Might be worth a talented prop shop visit.

Great control and min plane speed are marks to hit.

We used Accutech Marine for prop modifications on the Ghost when we weren’t designing them from scratch at Acme in MI. Accutech is on the seacoast of NH- I used to talk to Larry. That was some time ago.