Prop swap lost 10 mph

[gfleenor]

Hi all. New to the forum. A little background on my issue. Bought a 2018 Bentley 243 cruise tri toon (3/4) center tune with lifting strakes and a Merc 150, in March. Boat would run 33 at 5,000 rpm WOT. I thought that was a little slow for 2 people, half tank fuel load and bimini down. Have been searching for a prop that would get me more speed. I recently damaged the prop that was on the boat. It was a factory aluminum 3 blade 15 in. x 17p. I replaced the prop with the same part number and spec's from black Max..... Now my boat runs 23 mph at 4600 and ventilates badly when I try to trim up? Looking for all feedback and suggestions.
thanks
Glenn

 

[Chris1956]

Some props hold the water better than others. What is the difference in design between the two props?

 

[airshot]

Little things like rake, cupping can make a big performance difference. I have found that going to a prop specialist store pays off in the long run as I can try various props and keep the one I like best. Sure it costs more up front but in the long run, I am nuch better off with a great performing boat!!

 

[jimmbo]

Exactly how did you Damage the old prop? What damage was done to the Gear Case/Skeg?

 

[gfleenor]

Some props hold the water better than others. What is the difference in design between the two props?

Same exact part number 3 blade aluminum 15 diameter x 17 p

 

[gfleenor]

Little things like rake, cupping can make a big performance difference. I have found that going to a prop specialist store pays off in the long run as I can try various props and keep the one I like best. Sure it costs more up front but in the long run, I am much better off with a great performing boat!!

I like that Idea. Going to have to check around. I've asked questions at the local boat dealerships but haven't got a line on any. Do you know of any that ship?

 

[gfleenor]

Exactly how did you Damage the old prop? What damage was done to the Gear Case/Skeg?

I hit a sunken log. Took about an inch off of 2 blades but didn't damage the flo torque hub or the skeg.

 

[gfleenor]

Wanted to clarify my original post a bit. I added the new prop with the same spec's. Speed dropped 10 mph. (gps) and I am getting very bad ventilation when I try to trim up any. I bought a prop bore sleeve and installed it. My thought process was that: exhaust gases coming around the back of the prop and into the blades could be causing the ventilation issue. Once the bore sleeve was installed my WOT RPM is 4,600 and minimal trim is still causing extreme ventilation.

 

[jimmbo]

The new prop is the same Part #? or the same Diameter and Pitch?

 

[gfleenor]

The new prop is the same Part #? or the same Diameter and Pitch?

Both.
I ordered the same part number, diameter and pitch from Black Max.
Part number, diameter and pitch are all stamped on the new prop.

 

[Chris1956]

OK, SWAG time. Is the new prop installed correctly? The hub is pushed fully into the housing? The thrust washer is installed correctly? The OEM did not change the thrust washer? The nut is properly tightened?

When you say prop bore sleeve, you mean an adaptor to make the prop hub fit tightly into the gearcase? Did the old prop have one? Why would you need one?

Also, is the motor trimmed all the way down? 'toons do not usually use much pitch.

 

[gfleenor]

OK, SWAG time. Is the new prop installed correctly? The hub is pushed fully into the housing? The thrust washer is installed correctly? The OEM did not change the thrust washer? The nut is properly tightened?

When you say prop bore sleeve, you mean an adaptor to make the prop hub fit tightly into the gearcase? Did the old prop have one? Why would you need one?

Also, is the motor trimmed all the way down? 'toons do not usually use much pitch.

Yes, everything installed correctly. Motor trimmed all the way down. My thought process with the bore sleeve was that: exhaust gases coming around the back of the prop and into the blades could be causing the ventilation issue. Once the bore sleeve was installed my WOT RPM is 4,600 and minimal trim is still causing extreme ventilation.

 

[QBhoy]

Sorry to ask again …but is the prop definitely on right ? The thrust washer still in place ? Prop exhaust bore sleeve ring definitely where it should be ?

 

[Chris1956]

You didn't raise the motor on the transom, or install anything near the prop on the hull, right?

 

[gfleenor]

Sorry to ask again …but is the prop definitely on right ? The thrust washer still in place ? Prop exhaust bore sleeve ring definitely where it should be ?

Yes

 

[gfleenor]

You didn't raise the motor on the transom, or install anything near the prop on the hull, right?

I did not.