Still need help with Legacy prop, boat got sluggish

[cloumar]

Here is my problem, last year I bought new boat Princecraft 176 2007 with a Merc 115-HP 4 stroke. Of course it was slow to get on plain - out of the hole, the engine was mounted on the top hole and the AV plate was at about 11/2 inche below keel. So I raise the motor one hole at a time and finally got the best setup at the second last bottom hole - hole #4 out of 5.
I gained some speed and the hole shot was better, but it had tendency to ventilate like cruising at 3800 - 4000-rpm and just triming up a bit could cause the prop to run free a bit like extra slippage expecially with more load like rear livewell full of water and 10 to 14 pounds of fish - I could see the RPM raised for 700-800-rpm more and not getting any faster... by triming down a bit it was returning to good grip, and also was slipping in turns with the original Black Max prop.

Since I had no spare prop I went and got a Legacy from Turning Point of the same pitch - the hole shot didn't improve that much but the grip is a lot better, no more ventilation - BUT it took down my max RPM of about 400 to 450-RPM down and also slow me down to 38-mph when I was doing 40-mph the first time I got the boat and 42.5-mph after raising up the engine with again the Black Max.

One thing I noticed the prop are different not only in shape but the blades are different also - the Black Max has shorter blades but wider compare to the Legacy on which the blades are more narrow but longer.

Here are some specs:

Boat: 1400-lbs - 17.5-feet long
Transom at bottom: 80-inches
Engine: 400-lbs - 115-hp - 4 strokes
RPM range: 5800- 6400-RPM
Gear ratio: 2.07
2 people: 300-lbs - most of the time
Fishing gear and others: 345-lbs
Gas tank is kept at 25 to 30 gallons most of the time
The engine now sits with the AV plate at about 3/4 of an inche above the keel
The TACH was check on the water with computer to compare ECM reading of the engine and it is showing to good value.
The boat is used for fishing mainly
When new - top speed 40-mph aprx. at 6000-RPM with Merc. prop. WOT
After raising engine to max. possible hole top peed 42.5-mph at 6150-RPM with Merc.Prop - WOT

With Legacy prop at same engine height ( 4th hole ) - top speed is 38.5-mph at 5700-RPM - WOT

Prop original is - Black Max 13.25 X 17 pitch
second prop is - Legacy 13.25 X 17 pitch

So the Legacy prop is holding better but acting like a 19-inches pitch by taking down my RPM and like a 15-pitch by taking down my max speed.

Any ideas ?

Thanks !

MC

 

[hwsiii]

Re: Need help with Legacy, boat got sluggish

Re: Need help with Legacy, boat got sluggish

Mc, actually your prop slip is worse for the legacy prop than it is for the black max. But it does appear to be creating less slip in the corners for you. But you still do not have a better prop for your setup as you just traded prop slip in corners for prop slip in general all the time.

Prop Slip

H

 

[cloumar]

Re: Need help with Legacy, boat got sluggish

Re: Need help with Legacy, boat got sluggish

Well the Black Max is not only losing grip only in corners but in straight line also. As I said it will kind of break loose a bit and getting up to 800-RPM with no change in speed.

On the other hand the Turning Point grabs better but with less good performance, should I go with a 15'' pitch turning point or SS.

Thanks


MC

 

[cloumar]

Still need help Please with Legacy prop, boat got sluggish

Still need help Please with Legacy prop, boat got sluggish

Any suggestions ?


MC

 

[steelespike]

Re: Still need help Please with Legacy prop, boat got sluggish

Re: Still need help Please with Legacy prop, boat got sluggish

Other than the venting It seems your original setup was pretty good.
Almost exactly the same numbers as a bunch of similar setups I checked like yours My experience with Turning Point is only with the Hustler.It generally shows overall improvement when changed pitch for pitch.Fights ventilation well. I feel it could get you back closer to your best speed
with less venting.

 

[cloumar]

Re: Still need help with Legacy prop, boat got sluggish

Thanks for the reply Steelespike,

So you believe I should try a Hustler same pitch or 15-pitch ?

I have been told that Legacy and Hustler are of the same quality and design - the only difference is the hub.

I understand that my original setup 17'' pitch Black Max had the best performance in term of overall slippage but when under load it doesn't hold that good,

MC

 

[hwsiii]

Re: Still need help with Legacy prop, boat got sluggish

Mc, if you change to a 15" Hustler your RPM are going to go to about 6,400 RPM, and that is too high in my opinion. And if you hold the throttle to about 6,100 RPM I expect you will be getting close to about 37 MPH. Whereas I believe if you go with a Solas Amita or Rubex 4 blade in a 17" pith I would expect you to be able to reach about 41 MPH at 5,700 RPM and you shouldn't have the ventilation that you are getting now and your hole shot and acceleration ought to increase very much. I will have to say I can't guarantee that you won't have some ventilation in the corners, but I don't think you will.

Prop Slip

H

 

[cloumar]

Re: Still need help with Legacy prop, boat got sluggish

Thanks Hwsiii !

That is may be the option for me - I will try to find something in my region here - will let you know the result.

MC

 

[cloumar]

Re: Still need help with Legacy prop, boat got sluggish

H,

Forgot to ask - are you sure for a 4 blades it is 17-pitch I need to have - should we go down in pitch when going from 3 to 4 blades ?


MC

 

[hwsiii]

Re: Still need help with Legacy prop, boat got sluggish

Mc, with the 17" Black Max you are turning 6,150 RPM and when you change to the Solas 4 blade you will lose about 300 RPM, which will bring your RPM down to about 5,800 RPM. You say you use the boat for fishing mainly, and this will work fine. You will find this prop will increase your hole shot and acceleration throughout all of your RPM.


H

 

[cloumar]

Re: Still need help with Legacy prop, boat got sluggish

Hi Hwsiii,

Following your suggestion I went and buy a Solas Rubex 4 - 12.75 X 17 and I tested yesterday Monday October 12- it is a night and day change. Hole shot is good, handling perfect and planing at lower speed I was capable to stay on plane at 3500-rpm - at 23-mph and I could even go low as 3000-rpm at 20-mph which was impossible for me before.

Also the max RPM at one point was 6300-RPM and the speed was 44-mph this is with my regular load of two adults and fishing gear, I could really feel the stern lift and I believe this is what improve the top end performance. Of course I know that those results will change next summer with hot temperature ... of how much I don't know ? but still the engine never deliver that kind of performance last year at the same weather and temp.

Next step will be to get rid of the SE300 foil that I put on last summer and see, because I have a bit of ventilation at 4000-rpm in a sharp turn and I wonder if it is not that foil creating that, but at least there is no more ventilation in straight line and with rear livewell fill.

Recap of the results:

AV plate at 3/4 to 1 inch above bottom of keel, with SE300 foil:

Black Max genuine prop - 13.25 X 17 - 6150-rpm WOT - 42-mph - easy to vent in straight line and turn;
Legacy ( Turning Point ) - 13.25 X 17 - 5700-rpm WOT - 37-mph - grip was good - but drop down performance and engine runs below min. range (5800 - 6400-rpm);

Solas Rubex 4 - 12.75 X 17 - 6300-rpm - 44-mph - no vent in straight line - hole shot better - stay on plane lower speed - stern lift *** at colder temperature - outside temp at 48-F and water was at 47.5-F


So H thanks for your help and suggestions.

MC

 

[hwsiii]

Re: Still need help with Legacy prop, boat got sluggish

You are very welcome Mc, I am very happy to see you even gained speed. And that stern lift usually helps in the right application. And I think iy would be a great idea to get rid of the foil.


H