1993 370 Sundancer props

[hrynyk6]

Hello,
Please bear with me, I'm a newbie to this forum and inboard powered boats in general.
I recently purchased a 1993 370 Sundancer with twin 454's, I'm looking to upgrade my props for better cruising. The boat currently has 17" x 16" 3 blade cupped bronze props on 1.25" shafts. There is approx. 1.75" - 2" of clearance between the prop and hull. I don't know if these are the original props that the boat came with or if they have been replaced in the last 18 years.
My goal is to reduce the RPM's at cruising speed to save on fuel consumption. The boat currently runs 4400 - 4500 RPM's at full throttle, and stays on plane at 3100 - 3200 RPM's with between 128 and 175 gallons of fuel and 6 - 8 adults on board.
I have an opportunity to purchase 2 sets of reconditioned props. 1). 17"x17" Dymex Mr.Minus 3 blade nibral cupped ($500.00) and 2). 18"x21" Michigan Wheel 3 blade bronze ($600.00). Are either of these a good option to achieve my goal? And how do you feel about 4 blade props?

Thank you,
Dwayne

 

[hrynyk6]

Has anyone had any experience using Acme 3 blade nibral props?
Thank you,
Dwayne

 

[dpmulvey]

Long and tough math, science and ART.......

You want 15% to 20% clearance between the prop blade tip and the hull as it relates to the distance of the center of the shaft to the prop.

For example. If you have a 16 inch prop. The radius is 8 inches. 15% of 8 inches is 1.2 inches minimum clearance from the hull. This quells a lot of vibration and keeps the prop from from "eating" itself via air bubbles created by the prop itself.

You want to make sure the engines can reach the MFG recommended WOT. If not the money you save will be eaten up with new engines because of overload.

My recommendation is to get the props to a prop scan or similar technology shop. Get them scanned and balanced for your boat. Get them cupped for your boat. Some MRI stations are equipped to cup from the trailing edge to all away around to the leading edge. It's some really advanced stuff.