Thought I had props figured out - I was wrong.

[McLoki]

Well, did my research and thought I knew what to expect with the purchase of my new prop. I was sooooo wrong.

So I have a Tracker V-175 Combo (with 90hp optimax). (about 17' long, approx. weight 1500#) - add in 9.9 bigfoot motor, 5-10 gal of gas plus maybe 40# of random stuff)

My second trip out on the boat (still in the first hour of use though) I chewed up my stock prop something fierce (Black Max - 19p) To the point it looked like this...

I asked the dealer about it and he said it was fine to run (would not hurt anything) but may lower my top speed by a few miles per hour.

With the prop in that condition (with the boat as loaded above + 600# of people) I got:

• decent mileage.
• ok holeshot
• 25mph at 3600 RPM
• drop off plane at about 20mph or 3000 RPM.
• Top Speed at WOT was 35 @ 5400RPM.

putting that info into the mercury prop selector it suggested a bunch of props in the 19p range
but - I always hated the way the prop looked......

I recently replaced it with a 19p Laser II. (supposed to be for smaller deep-V boats as well as bass boats) I expected RPM to drop a bit (maybe 100-200 RPM due to going to stainless from Aluminum) and top speed to increase slightly (maybe 1-2 MPH - although I was secretly hoping for more due to the condition of my old prop) This is what I ended up with (boat configured as above but only about 400# of people)

• planes VERY fast. (much faster than the black max)
• Fuel usage seems to have increased but not enough time to know for sure
• falls off plane at 20mph (as before) but now at 3800RPM.
• 25mph is still a comfortable run - but now at 4300 RPM
• Top speed is now 34mph @ 5900 RPM.

Putting that in the mercury prop selector - it now suggests just 3 props. (black max in 21p, Laser II in 20p or 21p and a trophy plus in 21p)

Based on the chewed up black max I started with - this seems like way to much pitch, but seems about right based on the 19p laser II I have now.

Without trying a TON of different props, what do you all suggest?
Thanks for any help - A very confused,

Michael

 

[jestor68]

Re: Thought I had props figured out - I was wrong.

Interesting:

If I run the numbers for the old 19 at 5400 rpm, it shows 17% slip at 35 mph.

If I run a 17 at 5900, it shows 17% slip at 34 mph.

Are you absolutely certain the SS prop is a 19? The numbers indicate it's a 17. Better double check.

You would not usually raise rpm by putting the same pitch SS on there.

BTW-I wouldn't have advised you to run that mangled prop with all the material missing off one blade. It would be pretty much out of balance.

 

[McLoki]

Re: Thought I had props figured out - I was wrong.

it seems the same to me, but mercury does not make a laser ii in lower than a 19p. (And the serial number does end in -19)

I did purchase the prop used, would there be any way to tell if it had been reworked to a lower pitch?

 

[jestor68]

Re: Thought I had props figured out - I was wrong.

Yes, by the numbers you're getting. A 19 putting down those numbers equals 26% slip.

There's something fishy about that 19" SS prop. Your slip should be less with a like size SS.

The fact that it's a used prop raises a redish flag. Used props can be a crap shoot.

A more cost effective solution is put a Solas Rubex 19 on there. It will out perform the original Merc prop and not cost a ton of dough.

 

[etracer68]

Re: Thought I had props figured out - I was wrong.

I purchased a used 19p SST(painted SS) a few years ago, put it on, and the numbers didnt make sence. I then looked at the prop again and seen a 17 stamped on the barrel, and looked close where the blades join the barrel, and could see it was repitched. You may want to look real good at the prop again, or have it checked by a good prop shop. The prop in your pic, I would not run, Im sure its out of balance, but could be repaired, for use as a spare.

 

[WIMUSKY]

Re: Thought I had props figured out - I was wrong.

Those Lasers are great performing props. I wish they made a 17p, I would put one on my boat. I see your original prop is a 13 dia, is the Laser? Unless you can fix the above prop, all it's good for is a wall hanger. As it is now, it will vibrate the heck out of your drive which will give you more problems down the road.......

 

[McLoki]

Re: Thought I had props figured out - I was wrong.

I am calling a local prop shop to get my aluminum black max repaired (or at least get an estimate).

While there I will find out what is up with my new SS prop. What pitch it currently is and what it would take to make it work better for my boat. (we will see what he says). I may end up just selling the SS prop and picking up something different, but I am not one that likes to sell something that may have an issue. I want whoever purchases it to know what they are getting. (if the pitch has previously been altered or whatever....)

WIMUSKY - if I find out it is actually a 17p prop, I will let you know... (BTW - I think my Laser is 13-1/4" diameter)

Anyway, I will let you all know what they say.

Michael

 

[dazk14]

Re: Thought I had props figured out - I was wrong.

As noted above, that prop should not be used and a common cause of gearcase failure.

With a Solas Amita costing only $100 here on iboats, your damaged prop should NOT be repaired. Although the shop will make it look new, it'll never be as strong as original.

The amita comes standard with a rubber pressed in hub (no kit needed) and some sophisticated geometry (read performance) for the money.

You can keep the amita for a spare if you choose to stay in the hunt for a stainless prop and you'll have more rpm/speed data to work with.

Are you trimming out until it ventilates? You should be able to trim the laser II further out.

 

[McLoki]

Re: Thought I had props figured out - I was wrong.

Are you trimming out until it ventilates? You should be able to trim the laser II further out.

As I trim it up, the RPM's increase, but the boat does not really go any faster. Since it is running to high an RPM already, It ran best pretty much level (rather than trimmed up). keep in mind, this is only with an hour or so running on it - I really need to increase the pitch before trimming up much. Also - I think the motor needs to come up a hole. When looking down I can see about 1/4 of the plate above the prop when looking on the passenger side of the boat. I cannot see it at all from the drivers side of the boat.

Michael

 

[dan02gt]

Re: Thought I had props figured out - I was wrong.

McLoki,

I think your motor needs to come down a hole not up. The Laser II does not like to be ran high. If ran too high it will slip and perform poorly. I don't really think you can compare it to the aluminum prop either because by your numbers I don't think your boat perform well with it either. I think you should be in the hight 30s with that rig setup correctly. I have a Laser II so I may be able to help. My rig is quite different from your but the same concept. I have a Nitro 188 Sport (1675lbs) with a 150 opti and a 6" jack plate. I have a 21P Laser II as a backup prop. With my prop shaft 3.75" below the pad it will run 50MPH (GPS) at 5800RPMs with no bow lift. With the prop shaft 4.25" below the pad it will run 55.1MPH at 5600RPMs with good lift. Big, big difference a 1/2" makes. The Laser II has small ears and not a lot of cup, and doesn't like to be ran high. So if you can drop your motor a hole or 2 on the transom or install a small jack plate you may be really surprised with the results. I hope this helps.

 

[McLoki]

Re: Thought I had props figured out - I was wrong.

With the original black max prop chewed up (with the boat as loaded above + 600# of people) I got:
decent mileage.
ok holeshot
25mph at 3600 RPM
drop off plane at about 20mph or 3000 RPM.
Top Speed at WOT was 35 @ 5400RPM.


With the 19p Laser II I got:
planes VERY fast. (much faster than the black max)
Fuel usage seems to have increased but not enough time to know for sure
falls off plane at 20mph (as before) but now at 3800RPM.
25mph is still a comfortable run - but now at 4300 RPM
Top speed is now 34mph @ 5900 RPM.

Well, sold my Laser II and picked up a 19p Quicksilver Nemesis aluminum prop. (same as the Mercury Spitfire) I took it out for its first run today and this is where I ended up.....

mileage unknown (did not run it far enough, but I assume it will be similar to Black Max).
Decent holeshot (better than the blackmax - a little slower than the Laser II)
Acceleration slower than the LaserII - just did not hit as hard in my opinion)
Will have to play with it to see where it drops off plane.
Top Speed at WOT was 36 (GPS) @ 5400RPM.

For now it seems fine. I will be heading on a fishing trip to Wisconsin soon (19 days) where it will see use every day. I will have more to report after that. I will say this was my first trip out in the boat this year and the motor fired right up with no hesitation at all. (both the 90 optimax and the 9.9 bigfoot) I think a 17p would work at little better if I was pulling tubes or skiers, but for a running around fishing prop - the 19p seems like it will be fine. (and maybe get a little better gas mileage in the process)


Anyone have any other thoughts? For now - seems to be running ok. I did calculate to be at about 14% slip. Unsure if that is high, low or average for a 4 blade prop on a deep V boat though.

Michael