Props & wot

[Sailboattraitor]

Long story, but suffice to say I replaced both engines in my year 2000, 3700 SCR due to water intrusion. The new engines are 7.4 liter, 454's, which are about 320 actual horse power each. I was wondering what the specs are for WOT rpm's in the 3700? Also, what is the approximate top speed for the 3700 (I understand the premise about fuel tank fullness, the amount of fresh water/holding tank, number of people aboard, weight of equipment, etc.)? At this time, the original props are only giving me 3600 rpm's at WOT. I am thinking that different props with different pitch may give me more rpm's.

In addition, where would be a good place to obtain the new props?

Thank you in advance for any thoughts or suggestions.

[mmwjr]

Did you ask the mechanic that replaced the engines what the WOT should be? I would expect it should be the same for these engine no matter what boat they are in which is 4400 - 4800 rpm.

Changing pitch lower will help also how many blades are the props? If 4 or 5 you can also consider going down one blade.

[Sailboattraitor]

The mechanic did state the WOT rpm's should be around 4600. I have 4 blades on the props. Any thoughts on where to buy the new props?

[mmwjr]

Originally Posted by Sailboattraitor

The mechanic did state the WOT rpm's should be around 4600. I have 4 blades on the props. Any thoughts on where to buy the new props?

I don't have any experience with buying inboard props.

[TJK]

Your figures appear to be way off, i.e. over propped for those engines.

According to Power Boat Guide, "Twin 380 hp V-drive MerCruiser inboards cruise the Maxum 3700 SCR at 18 knots (26–27 knots top), and optional 370hp Cummins diesels
cruise in the mid 20s (about 30 knots top)."

Your new engines have less hp. Need to reduce the original prop pitch or replace them with new ones with appropriate size/pitch.

Any reputable prop shop will guide you to select appropriate prop size and pitch, if you can provide the info of your hull, engines, transmissions, etc. Try this;

https://www.miwheel.com/inboard-propellers/prop-it-now/

[shrew]

WOT on the 454, like almost all Mercruiser engines, is between 4400 - 4800. Ideally you'd like to be as close to 4800 as possible, without going over. Speed is irrelevant.

3600 rpm Max WOT would be overpropped. There is a balance between # of blades and pitch. Going to a 3 blade will increase max RPM's, so would increasing pitch. 4 blade props are not stock on that model. I would start with a 3 blad prop in the range of stock and see where are you are for Max. RPM's.