Help With Prop Selection

[JFZ]

I Have a 1710 Lowe Fishing Machine with a 2015 Command thrust 115hp four stroke with the 2.38 gears ratio.
With a 4 blade Trophy Plus 21p it turns 5800 rpms at 32 mph.
With the same prop with a 23p at 5400 rpms it also does 32 mph.
On Mercurys slip chart the slip is low 30's, awfully high.
It sure seems the boat should be faster.
I would really appreciate some help on what prop I should use.
I was thinking of maybe trying a 3 blade, an enertia or tempest?
I would like overall good performance.

Any thoughts or advice would be appreciated?

 

[QBhoy]

Hi.
Amazing that you should post this. Is your engine defo a 2015 ? I’ve a 2016 CT 115. In 2016 these came out with the 2.1l engine.
Anyway. I have a tempest 19” on mine. The boat will run at 43mph gps with that and hit the limiter at 6100 approximately.
I tried a laser 2 19” just because I was thinking about getting a 21” laser 2.
The 19” laser saw 41 mph gps but higher rpm cruising and hit the limiter much easier. So I naturally thought the 21” laser would be idle. Would surely see a lower rpm cruising, mayne a little top end and be better on fuel.
How wrong I was. The 21” wouldn’t take as much trim and air out sooner than both the 19” props. Very similar cruise rpm at same speed...but most shocking of all..only saw 38 mph gps top end.
I think the much smaller diameter on the 21” may be the difference.
All I can say is the tempest must be some prop. I’m going to try my 19” enertia to see what happens but I doubt it will be as good as the tempest for this boat.
Otherwise. What a great engine and can’t believe how powerful it is for only being 115hp. It’s on a deep v 19ft cuddy as well. Good going.

 

[Texasmark]

Something is dreadfully wrong. Check your speedometer with a GPS instrument first. Go from there. I think your tack is recording properly since 200 rpm /inch change of prop pitch is the norm and you changed 2 and lost 400. Unless you have it loaded up with 4+ big folks and lots of gas and beer, about 15 ought to be your slip average.

Rig a Lowe built combo with no tweaking by PO? If not, what what was changed?

 

[JFZ]

Texas mark,
The speed was with the GPS, and with just me or me and a friend the tach and speed does not change.
No tweaking except for electronics and rod holders.

QBohy,
Definetly a 2015, I tried a Trophy plus in a 19 pitch, seemed to slip getting on plane and over revved.
I think I would have to go with a 21 in a tempest.
If the rpms increase because of the 3 blade maybe a 23?

32mph sure is slow but it's a fast hole shot and holds the water in rough stuff and turns.

 

[QBhoy]

Texas mark,
The speed was with the GPS, and with just me or me and a friend the tach and speed does not change.
No tweaking except for electronics and rod holders.

QBohy,
Definetly a 2015, I tried a Trophy plus in a 19 pitch, seemed to slip getting on plane and over revved.
I think I would have to go with a 21 in a tempest.
If the rpms increase because of the 3 blade maybe a 23?

32mph sure is slow but it's a fast hole shot and holds the water in rough stuff and turns.

Ah. Maybe it’s a different engine to mine then and can’t quite compare each. Is it a 2.1l or maybe not ?
Mayne they came out earlier in the US ?

Anyway. With your trophy plus..what pvs plugs did you have in it ? We’re they holed at all ?
the tempest plus I have seems to behave different to the norm in almost every aspect. I think it’s huge diameter does this. It also seems incredible at hull lifting ability and taking very high trim. It will take the maximum trim I have before trailer mode and enough that it will lift the relief valve on the pump if I try more.
The laser 19” was almost as good, but as mentioned saw higher less efficient cruising rpm and hit the limiter much easier and 2mph less.
Really disappointed at the 21” laser really.

Only draw back tk the tempest was that it seems a lottle harsh going into gear and at idle speed. Seems a little heavy for the engine. Lots of torque steer too

 

[JFZ]

I'm not sure if it is 2.1L. Do you know what you're rig weighs?

 

[WesNewell]

Forget about the prop for now. You've got other problems if you're running 30% slip or more. Check engine height, water logged foam. anything on hull to cause drag. live wells full, etc., or combo of all. That boat should weigh ~1718# dry, and you should get at least 37 mph with 2 people, gear and full tank of gas. Oh, the 2015 115hp ct is 2.1L (2061cc)

 

[JFZ]

As far as engine height. It was in the lowest hole when I got it, I moved it up 2 holes.


When I ran it there was no difference except it seemed noisier.

I moved it back down 1 so I'm now 2 holes from the lowest position.

The only drag I can see is the size of the CT lower and the total scan transducer.

Thanks for all the replies.

 

[QBhoy]

Seems so strange really. Your speed is way out compared to the rpm, pitch and speed I’m seeing. So much prop slip it’s crazy. A 23” would be out of the question. Is the hub ok on the prop ? Are you using smart craft data or a normal tach ?
id have thought your boat would be far lighter than mine too. All seems weird.

 

[JFZ]

I think it's the hull. Right ahead of the transom the hull is concave. I didn't measure the area yet.
Hopefully I'll get some time on Saturday to check it out and take some pics.

 

[Texasmark]

I think it's the hull. Right ahead of the transom the hull is concave.

Bingo!!!! "Hook" Since at speed the transom area is what's driven and what is mostly in the water, the center of the hook tries to flatten out.....lower to be flat with the oncoming water so that there is more of a straight line between the driving part at the transom and the center of the hook. (My idea as to how it works and physically makes sense to me,)

In doing so, it forces the bow down which causes more of the boat to be in the water and increases your drag. Anybody that ever saw a picture of a high performance bass boat hooked could plainly see that the only thing in the water was the "pad" and not much of that.

No telling how many times or people have been at a 90* trim position, speed maxed out for their full throttle position, only to hit the trim button, "when in doubt trim it out" (Faztbullet), watch the bow lift, spray onset move aft, and speedometer and rpms run on up. Hull drag. It's the name of the game....gotta get rid of it.

Now on getting rid of hook, no idea! As of right now, somewhere on this site, posting within this last week, is a guy who is having this problem with his aluminum boat and he said he is a metal worker and thinks he knows how to straighten out. I have no idea.

 

[JFZ]

Thanks for the advice! If it was just one spot it would probably be repairable.

When the light is right and you look under the boat it looks like waves or ripples up the whole bottom.

It's fast enough for fishing, I'm wondering if it's even safe.

Lowe gives a lifetime warranty to the original owner, unfortunately I bought it used, it's a 2015.

 

[JFZ]

Definetly a hook, deepest part of it measures .413. Can't get at it from the inside.

There is another concave area toward the bow. The waves are real shallow less then a 16th.

So it looks like 2 areas need some work.

I'll have to do it from the outside, as soon as I figure out how?

 

[Maped]

Another thing to check which I had a problem on is making sure your tach is calibrated to the motor. I was having high slip problems and my tach was set to show higher than actual speeds.

If that checks fine you should see if u can borrow a 19p prop to try, it may cut your slip enough to increase speed without changing rpm too much.

 

[JFZ]

The tach seems ok, a 19p really slips.

 

[Maped]

I'm assuming this is an aluminum hull boat, ignore me if I'm wrong.
for your safety concern check all the areas that are 'wavy' for cracks. If you can't find a single crack then sinking should not be a concern.
Even tho the warranty doesn't transfer it may be worth contacting Lowe with your problem, they may work with you some with how new the boat is and they may already be aware of that year having an issue.

If not, I don't know everyone's opinion of fillers in water but if it's a ripple issue with the deepest ones only .5" then skimming it with a product like Bondo may be an option but only if there are absolutely no cracks in the aluminum

 

[JFZ]

The boat is aluminum. Lowe said only the original owner is covered. Good idea on the cracks
I'll have to look closer at everything.

I was thinking of Metl Weld. It's real strong, non sagging and slightly elastic. As long as the surface is
scuffed up with 80 grit and cleaned epoxies are really strong.

 

[QBhoy]

The tach seems ok, a 19p really slips.

Do you have the smart craft gauges ? Don’t suppose the trim needs calibrated ? I had to re do mine.

 

[JFZ]

No smart craft gauges. I did have the trim checked, the mechanic said it was ok.

 

[JFZ]

I fixed the hooks in front of the transom, using metl-weld epoxy as a fairing compound. It looks like the previous owner
tried to use roller bunks, there are concave areas evenly spaced on the bunk line. I will have to fix them over the winter.

The previous WOT was 32mph@5800rpms. Now it's 37mph@6000rpms.