Prop Data On Moesly 21'

[Islandtrader]

I was able to pick up a Mirage + 3 blade 21 from blue heron...I believe it is a 14 3/4 diameter.

All the numbers are gps smooth water and a mile run through each rpm range. Boat had one person and approx. 40 gals. of fuel. No trim was used (motor and tabs).

Let me say this: instant response and torque on demand. Pulls hard all the way.

Motor is new less than 3 hours in the test. I have a feeling that I may be under propped when the stroker loosens up. Not by much.

rpm- gph- mph- mpg-

1000/ 2.1- 6- 2.8

2500/ 6 - 23.5 - 3.9

3000/ 9 - 29 - 3.2

3500/ 12.5 - 34 - 2.7

4000/ 14.1 - 42 - 3.0

One quick blast up to 50 @ 4900.

It seems when you hit 2500 rpm the mph from there on up almost = rpm.

Interesting to note that at 4000 rpm the mpg goes up over the 3500 rpm.

So if the grouper hole is 40 miles out I can be there (in good water)in 1 hour and use 14 gallons...or at 30 mph be there in 1 hour 20 minutes and use 12 gallons.

All this is subject to change...more weight looser motor, smoother bottom and so forth. However it is nice to get a baseline for the future.

[cdavisdb]

Sweet numbers! That sucker is FAST!

Very interesting that the boat seems to do the best mileage once it is up to a solid plane and mileage falls off from there, on through the range where most boats are more efficient and then climbs again. Does the boat feel like it is getting higher in the water as you approach 4000? Maybe better mileage from less surface drag?

[Fr. Frank]

Sweet numbers! That sucker is FAST!

Very interesting that the boat seems to do the best mileage once it is up to a solid plane and mileage falls off from there, on through the range where most boats are more efficient and then climbs again. Does the boat feel like it is getting higher in the water as you approach 4000? Maybe better mileage from less surface drag?

Also, if you're using hydraulic steering, and assuming the motor is mounted at the correct height, to achieve maximum efficiency at cruise or WOT, your trim angle should be adjusted out/up until the propeller just begins to ventilate, and then trimmed back in until the excessive slippage stops and you get full bite again. The idea is to have the propeller pushing as nearly parallel to the surface as possible.

If you have single-cable steering, (assuming you have the correct torque tab installed), trim up-out until the steering torque is completely neutral, i.e.; you can let go of the helm in calm water and the boat will continue to steer straight/track the same heading.

[Blue_Heron]

It seems when you hit 2500 rpm the mph from there on up almost = rpm.

Terry,
It looks like the mph is tracking just below rpm/100 until you get to 4000rpm and it busts loose and mph exceeds rpm/100. Either that hull has lots of lift and the reduced wetted area at high speeds reduces drag so prop slip goes down, or you achieved lift off.

Either way, the grouper grounds are much closer with that stroker providing the go. Glad the prop is working out so far. Once you've had a chance to break in the engine and run the boat with a load in it, you'll know if it's enough prop.
Dave

[cdavisdb]

Fr. Frank: Great info. I can hear the prop when it stops ventilating. It seemed like that was the best trim, but now I know why.

[Fr. Frank]

that hull has lots of lift and the reduced wetted area at high speeds reduces drag so prop slip goes down, or you achieved lift off.

Dave, you've nailed it exactly.
This is the beauty of the Moesly VDH hull. I actually got my slip down to 8% when I was running a carb'd Merc V6 with speed mods and a custom made PowerTech prop. That was pushing my Seafari at a max speed (in cold weather) of 54 mph.

[Islandtrader]

Something I found on prop slip...


Prop Slip Calculator

So with the current prop I have, there is a lot of prop slip.

More testing is needed when boat is done and fully loaded.