bertram31.com

I took the boat out yesterday for some performance testing. I'm still not convinced I have the right prop on the engine, but I'm always looking to change things (personality defect). Hopefully this helps others that are considering an outboard for a B25.

Weight estimate as tested - 6500lbs. 2 guys, 70 gallons fuel. Chines are just kissing the water at the stern (could use more weight back there).
Prop - Evinrude RX- 4, 15 x16, vents closed.

Wind was quartering at about 10 knots.
Seas calm, no boat traffic on the ICW (cold day!)

Acceleration tests - just in gear to 30 mph. 0 deg. trim, with various jackplate heights: Average of all runs - 7.75 seconds. Range was 7.3 seconds to 8.04 seconds.
Notes: Felt very quick. She gets up and goes. Jackplate height does not affect this performance, provided the prop is in the water...

Top Speed runs - with the wind I was touching 6000 rpm and 45 mph, against - 5900 and same speed. I played around with trim angles and jackplate heights...minimal impact to speed or mph. I did one run with the automatic trim feature turned on...scary...very difficult to control...turned it off.
Notes: Rides very high in the water at these speeds. Steering very light. Slight breeze will push boat off course. Not enjoyable at all. With a full load she would be right in the middle of the max rpm range - 5700.

Cruising - played with heights and trims. She likes about 2.5" of lift and 20 deg. of trim. 30 mph at +/- 4300rpm seems like the best cruise. She is happy up to 40 mph, but above that, hang on.
Notes: Boat never finds that obvious happy place where the sounds mellow and you can tell all is right with the setup. She is mean and angry at all speeds.

Low cruise - drops off plane at 20mph.

Reverse - very poor at all trim angles and heights. I think this is an issue with the 4 blade prop.

I'm working up some options for 3 blade props. Will report tests results when available.

Cam

Maybe the three blade will get the transom down some into the water and help with handling. You won't know if you don't try it.

That's my thought as well. The prop I have evidently has lots of stern lift.

Cam, what engine have you got on the back?

Evinrude G2 300

Thanks for the info, Cam. I can’t be of much help, but enthusiastically following along as you work this out. I know you will.

How’s the bow thruster working out? Do you find it useful?

Ok - I'm launching mine next week (single diesel CMD 320hp / Bravo 2).

Seems like pretty good numbers your getting there - I managed a massive 21 knots on the pre-purchase sea trial, but hoping for at least 30 knots after cleaning her up, changing the turbo and a few other things.

The bow thruster is completely awesome. Makes docking and other tight maneuvers very easy!

Good luck with that diesel. Post some pictures!