Help with prop on 22 Walkaround

[ttimss]

Recently purchased 1999 Wellcraft 22 Walkaround. Boat needed some engine work, I decided to rebuild the Mercruiser 5.0 EFI(TBI) Alpha 1 gen 2. Just put her in the water yesterday. Seems to run good, smooth, no smoke. Topped out at 35 MPH 3600 RPM. Boat felt sluggish out of the hole and I was expecting a little more top end speed, not to mention the engine spec is 4400-4800 WOT. There could be something wrong with the engine, fuel pressure, timing, etc, but before I dive in, does anyone have experience with a similar boat and could tell me what you're running for a prop? This boat came with a Vengeance 48 16316 19P. I know nothing about propping boats so any help would be appreciated. Thanks

 

[alldodge]

Is your speed from a GPS?
What is your WOT RPM?

 

[ttimss]

Yes, speed was from GPS on phone. WOT was 3600 RPM, maybe 3650. I need to verify the accuracy of the tach, but I was expecting the boat to be a little faster, which would coincide with the lower WOT RPM

 

[alldodge]

Agree need to verify the tach, and if it is accurate, then you might need another drive. You should have maybe a 1.8 or 2.0 ratio and might have a 1.5 drive. Can go down to a 15 pitch but that is about it

 

[ttimss]

So I verified my tach, and double checked my timing. I think the engine is running strong. Do these numbers sound right for a boat this size? 36 mph at 3700 RPM?

 

[dingbat]

Speed isn't bad but your rpm is way too low. It must be a dog out of the hole

I'm running a 226 Grady White Walkaround with a 200 HP outboard turning a 15 x 15 prop. Boats shoots right out of the hole with very little bow lift. WOT of ~5550 rpm @ 39.7+ mph.

Pretty sure I could break the 40 mph mark on a calm day with the wind to my back but those days are few and far between

 

[ttimss]

Its seems sluggish but tis is my first boat and im not sure how it should perform. It is an inboard so i'm not sure it would compare to your outboard. I was just hoping someone had a similar boat/engine combination and could share their experience.

 

[dingbat]

It is an inboard so i'm not sure it would compare to your outboard. I was just hoping someone had a similar boat/engine combination and could share their experience.

The Grady White 227 and 226 share the same hull. The only difference is the motor, I/O verse outboard. Factory specs are the same for both boats.

People tend to keep their good props and throw whatever prop they have laying around on a boat when sold.

You need to find out what prop your running. Your WOT rpm should be in the mid 4000 range.

 

[ttimss]

See above original post. Its a Vengeance 19 pitch.

 

[ttimss]

Where could I find the specs on the original prop that came on the boat?

 

[dingbat]

See above original post. Its a Vengeance 19 pitch.

No specs per say on a prop. A 19” prop will push boat 19” per revolution less any prop slip. A 17” prop will push 17” per revolution.

To match your speed with reported rpm you have 21% slip which is pretty bad. I was running similar prop slip before changing props this spring.

Generally speaking, you get a 100 rpm drop for every 1” drop in prop pitch.

Even if you drop down to a 15” prop, your rpm would only increase to 4000-4100 rpm. Closer, but still not in your zone.

Still stuck around 36 mph assuming your slip drops to 10-12%

 

[ttimss]

So I could experiment with props, but likely top end speed will stay the same?

 

[dingbat]

So I could experiment with props, but likely top end speed will stay the same?

You really need to get the RPM up to get any appreciable increase in speed. Your prop's 21% isn't helping you any.

Current: = 35 mph
1.47:1 Lower unit
21% prop slip
19" prop
3600 rpm


Assumptions: = 41 mph
1.47:1 Lower unit
12% prop slip
15" prop
4800 rpm

Assumptions: = 44 mph
1.47:1 Lower unit
12% prop slip
17" prop
4600 rpm

Assumptions: = 45 mph
1.47:1 Lower unit
12% prop slip
19" prop
4200 rpm

https://www.marksmarineinc.com/choose-your-prop-with-the--prop-calculator