Lund Crossover/Mercury 150 Four Stroke

[Minnesota Fats]

Hi all

I picked up a Lund Crossover with a Mercury 150 Four Stroke. So far, I love the boat.

I had a question that I thought someone might be able to help me answer:

WOT throttle RPM is exactly 5000. It's spec'd at 5000-5800, and I'm wondering if I should be running a little higher. It has a Mercury Marine Laser II stainless 21P prop on it. Not sure if anyone else out there has this combination, but thought it would be worth an ask to see if anyone is running a 19P prop and what RPM they are seeing.

Thanks!

[boatfixer]

What kind of load? Full live well? How many people, how much gear?

If your really light and only turning 5k I'd say drop in pitch.

[Minnesota Fats]

Thanks for the response. It runs at 5K either way, loaded or unloaded. It's almost like its electronically limited at 5000, although I don't think that's the case. I had it out last week with a full livewell, cooler of beverages, bunch of gear, 3 people, and it tops out at 5K. It's still doing almost 48MPH, so its plenty fast, I just don't want to lug the engine if I don't have to.

[delcecchi]

Are you sure the tach goes above 5000? The reason I say that is my old 115 had a 21 pitch and did like 42 at 5000. I don't know what the gear ratio of your motor is so can't calculate speed from rpm. Also you don't say whether this is the new 150 4stroke or the one before that was like a verado. Did you buy it new?

It is strange the WOT doesn't change with load. How many hours on it? Do they have some sort of break in mode?

OK, found gear ratio 1.92. If I calculate speed I get 46.6 at 5000 with 10 percent slip. So I am a little suspicious about the 5000 rpm at 48 because that would be like 8 percent slip which is low. But it is possible.

I would still double check the tach.

[Minnesota Fats]

Thanks for the reply Del. That's a good thought - do you mean "does the tach needle stick at 5 grand even though the motor might actually be over 5 grand?" I will check that, I should be able to back the throttle off slightly and hear the motor lose RPM and verify that the tach needle moves too. That would actually explain everything, and I agree that speed seems pretty high with a 21P prop at 5000 RPM. The gear ratio is 1.92. I think that if it was actually doing 5500 RPM and had 15% slip, that would be about 48 MPH, right?

It's a new motor, just bought it a month ago. It isn't the Verado, its the new naturally aspirated 150.

I probably have 10 or 12 hours on it, so should be past the break in, but I also had that same thought. The fact that there was no RPM difference between loaded and unloaded made me think that maybe it was that way, but I think it should be past that now. I'm not sure, but if you are right about the tach needle sticking, that would explain it.

[clKiekhafer]

The RPM difference between mine (not like your motor)is only 200 between light and fully loaded and I run a 21" SS. The top speed at WOT between the different loads is barely noticeable on the GPS (~1 to 1.5 MPH).

[BoxMN]

Just my two cents (and worth exactly that ) is that the Laser II is not a good prop model for that style boat. Meaning, an alum hull that is not exactly a speed demon (i.e. light fast bass boat). We have similar style hull and 150efi (2 stroke) and tried a Laser II, in a couple pitches. Just didn't work well. I think (I may be wrong) the Laser II is for a fast light hull. Any alum hull (usually) doesn't fit that category, IMHO.

I sound like a broken record but try a 19" Tempest, or whatever new model Merc has that is like the old tried and true Tempest II. Still great top end, but with bow lift and plenty of grunt, as much as our high-five used to have, but with more top end and actual power in reverse.

Good luck, you will need to test more than a couple to really find the one you want. We went through the standard old SS, Laser, Trophy, High-5 and Tempest. Used high-5 for years, but Tempest is on now. Have fun testing!

(btw, we can get higher top speed (GPS speed) with more pitch prop, but rpms are too low. Get to middle or high end of your range and I think you will like it better and maybe better on the motor.)

edit - oh yeah, if your motor is mounted low on the transom, you might want to try lifting it a hole. Made a big difference for us, we actually went up two holes [middle], but we have 20" transom if that matters, most now have 25" in these style boats. The tempest just can't blow out, nor would the high-5. Laser or Trophy would blow out in tight turn, high or low on transom. Something to consider.

[Minnesota Fats]

Thanks for the replies all. Next time out I'm going to check on the tach needle sticking, and now you gave me something else to think about, Box. The Laser II was the prop that came on the rig. I think I'm going to try the Tempest. I have noticed that in a tight turn it ventilates a bit, nothing too extreme, but I can definitely pick up the change in sound as the motor spins up a bit. I should try it in both 19 and 21 to see how it works out, depending on what I find out about my (potentially) sticky tach needle. The fun of a new rig!

[BoxMN]

On the Tempest, you will need to remove the trim(torque?) tab, that little fin that hangs down behind the prop from the top. The Tempest blades are BIG and will likely hit it. You can run it without the tab until you decide if that is the prop for you. If so, you can get a flat plate that fits there for like $15. Big motors don't need that little tab anyway. Good luck in your testing! Also, if you have a torque wrench make sure to torque the nut properly. Once I actually used one, I realized that I have never been tightening the props tight enough. Basically, tighten them down GOOD!

[Schubie]

MNFats,

I sent you a PM.

[Moose-Hunter]

Hi all

I picked up a Lund Crossover with a Mercury 150 Four Stroke. So far, I love the boat.

I had a question that I thought someone might be able to help me answer:

WOT throttle RPM is exactly 5000. It's spec'd at 5000-5800, and I'm wondering if I should be running a little higher. It has a Mercury Marine Laser II stainless 21P prop on it. Not sure if anyone else out there has this combination, but thought it would be worth an ask to see if anyone is running a 19P prop and what RPM they are seeing.

Thanks!

From what I know, your engine was made to run in the upper end of your WOT RPM range. That said, anything less is lugging the engine... yada-yada-yada... You most likely heard all that before.

The Laser II prop is, for all intents and purposes, a stainless copy of a aluminum prop design. Geometry that "may work" in may boat/engine combos but isn't always the best suited for each application. In my opinion, this is the case for ALL props that come on your engines from the dealers. Oh, they can get close. And sometimes they luck out and hit the right one. BUT... how is the dealer or factory going to know how you load your boat? Your driving habits? Do you want holeshot or top end? What kind of water you're going to be in, rough or calm? As you can see... It's a best guess scenario.

The 175 Verado that came on the back of my 2012 Pro-V had this same Laser prop. It now sports a 19P Tempest. Gained holeshot, as a lower pitch prop is expected to do, but gained top end as well with the added revs and better holding power...

Back to your dilemma...

Without knowing the rest of the details, I'd say you're over propped. Which is to say you're running too much pitch. A 19P will get your higher in the RPM range with a 17P a little higher yet.

First things first... Have you checked your engine height? When running WOT, where is the cav plate in relation to the surface of the water? If it's submerged, it's too low and you'll need to raise the engine a hole or two. If it's visible, just at the surface, you may be good to go for prop testing.

Let's leave it here for now and see where this takes us. OR... contact Ricky at Brainerd Prop. He's helped me prop 3 boats now and is a absolute magician when it comes to his trade!!

[Minnesota Fats]

Good idea - I will have it out this weekend and will report back. I'm going to check the sticky tach idea, and if I can get a hold of one, the 19P tempest. Good thought on the motor height as well. I'll check that too.

What length pro-v do you have?

[Moose-Hunter]

Good idea - I will have it out this weekend and will report back. I'm going to check the sticky tach idea, and if I can get a hold of one, the 19P tempest. Good thought on the motor height as well. I'll check that too.

What length pro-v do you have?

When/if you check the engine height, you'll need to do that first, out of the water. Verify that the cav plate (directly above the prop) is at or above the bottom of you hull. Any deeper, you're giving up performance in most cases. Next... On the water. Rev her up and get her topped out or very close to it. BE VERY CAREFUL!!! Have a trusted companion pilot your boat while you CAREFULLY!! WHILE WEARING A PFD!!! Look over the transom and check to see if the cav plate is, in fact at the surface or just above it. You want it being "splashed" not submerged. Again... BE VERY CAREFUL!!

I fish from a new 2012 Pro-V 1875. Roughly a 19 footer, sportin' a 175hp Verado. I run the 19P Tempest Plus. Remember, I'm setting my boat up for top end. I don't ski or pull water toys. And with a kicker and electric trollers, my main engine is a "get me there quick" device.

My boat originally came with a 21P Laser and it was not a match for my boat at all. I could blow it out almost at will with the torque of the mid sized V-Rod and to make matters worse, it had ZERO holding power in the corners. It was a fast prop IF I could get it hooked up. Managed 54mph and change. But that's IF I could get her to stick.

I tried a number of props from different manufacturers and different configurations... 3 blades and 4 blades. High rakes, low rakes, too much pitch, not enough pitch... Well you get the picture. So far, the Tempest Plus in a 19P is the best suited prop for my boat. I have two others here in the shop I still need to test. A 3 bladed Powertech in 19P. They say P.T. is "stout" on pitch and I may get a couple more MPH on top end. And a 17P, 5 bladed monstrosity. This thing is a beast! However, I'm not expecting any top end gain but a HUGE hole shot.

Propping a boat is a science, but there's a little magic that goes along with it. Have fun, be careful and keep us posted!!

[Minnesota Fats]

Great advice. Mine is also a 2012 model, same length - 1875, same beam 95" (I think), so hopefully your setup is a decent proxy for mine. The dealer is going to get me a 19P Tempest plus and I'll report back when I get that.

In the meantime, I'll check my cav plate height tonight on the trailer and then go put it on the water and check the sticky tach needle idea and where the cav plate is actually running in the water.

Thanks for all the help.

[Minnesota Fats]

Got out and tried it all. First, the tach needle isn't sticking, its really maxing at 5000. And, I loaded up with 4 guys, a full livewell, a full cooler and a bunch of fishing gear and it maxed at 4900. So, looks like it is overpropped. The motor height looks right - its in the second hole from the top and the cav plate is right at the surface of the water when running wide open. When I get the 19P tempest I'll report back.

[Moose-Hunter]

Got out and tried it all. First, the tach needle isn't sticking, its really maxing at 5000. And, I loaded up with 4 guys, a full livewell, a full cooler and a bunch of fishing gear and it maxed at 4900. So, looks like it is overpropped. The motor height looks right - its in the second hole from the top and the cav plate is right at the surface of the water when running wide open. When I get the 19P tempest I'll report back.

Well done! It sounds like we're on the right track here with the Tempest. Or a reduced pitch prop if nothing else. Again... Time to test and report back!!

Good luck!!

[Minnesota Fats]

Moose Hunter - I have the 19P Tempest on the boat now and I'll drag it out this weekend and see how it runs. One question - did you mess with those PVS ports on the hub? Mine has the large hole insert in place, but I see you can get medium, small, or close them off altogether.

[Kyhl]

The vent holes help with hole shot. They allow the blades to slip at slow speed which lets the motor wind up faster, getting into the power band faster.

I would bet you could plug them without any problems, especially since you are going down in pitch. Going down in pitch should give you a better hole shot anyway. Having the vents open will add to it.

[Minnesota Fats]

Kyhl

Thanks for the response. I know what they are for, I was asking Moose if he changed insert sizes and and if it actually changed anything or why I shouldn't just take them out altogether to vent the most exhaust possible.

[Kyhl]

Kyhl, or why I shouldn't just take them out altogether to vent the most exhaust possible.

They shouldn't help with allowing more exhaust. After you get moving the water flowing over them will seal them off anyway so you won't get more exhaust flow.

My power tech doesn't have any vent holes. It does have a removable spacer ring to open or close the gap between the lower unit and the prop.

I tend to err on not enough pitch (great hole shot without venting) then have Soderblooms add more cupping to tweak the top end.

[Moose-Hunter]

Moose Hunter - I have the 19P Tempest on the boat now and I'll drag it out this weekend and see how it runs. One question - did you mess with those PVS ports on the hub? Mine has the large hole insert in place, but I see you can get medium, small, or close them off altogether.

As mentioned, the ports help in "tuning" your hole shot. At WOT, I'm told they are no longer in play due to water pressure closing them off.

I'm running the solid plugs in my prop. As in NO holes at all. If I could get this exact prop completely without the PVS ports I'd sign up in a heartbeat! In fact... I may look into having the holes filled on my current prop over the winter. Don't know if that's even possible. We'll see.

My read on the PVS thing is, since open ports allow your engine to spin up before hooking up I can see where you'd be at a loss of "control" in rough water where you NEED precise throttle response. With solid plugs I get exactly that. If I hammer down on the go lever... I go! As in right now! More precise throttle control means safety to me. Personally, I'm not too hip on the whole ideal of having to wait even a split second for the prop to hook up. Depending on your application, PVS may have it's place. But I don't see it ever being used on my boat. As always... Your mileage may vary.

Good luck on your testing!

[Minnesota Fats]

Got the boat out today with the 19P Tempest. Wow, did that wake it up. Almost 50 MPH and gained 500 RPM. And, I was on a smaller lake so I'm not sure if I really found top end.

Couple things:

1) Thanks for the thoughts on PVS. I'm going to try plugging them off and compare that with what I've got right now.

2) Seems like this prop vibrates a little more than the laser II did. Not sure if that's the prop "settling in" or not - I didn't get a lot of time on it, and the vibration did get less and less the more I ran it. I'm going to re-torque the prop nut before I take it out next just to be sure.

3) Are flo torq II and flo torq III/IV parts interchangeable? Is the aft adapter different lengths on the different systems? I think that when I gave the dealer back the Laser II, it looked like the aft adapter included with the Tempest was longer. That said, my aft adapter that came with the Laser was back home on my boat, so he kept the one that came with the Tempest and said to re-use the one I had at home. The insert he gave me looked like flo torq II, and now my mind is messing with me as I wonder if I have a flo torq III/IV insert and a flo torq II aft adapter. Maybe they are the same - maybe it doesn't matter. Not sure if anyone knows or not.

Thanks again for all the (ongoing!) help!

[BoxMN]

Hehe, who suggested Tempest at the top? j/k it is great for your setup.

Agree with Moose that you don't need or want the venting with your setup. I run completely closed plugs (no holes). I tried it, and I think those vents are for heavy boats that need help getting out of hole. You boat doesn't fit that category, nor does mine. It feels "sloppy" and not precise to me.

Can't answer the torq question, but know that you will continue to like how the Tempest works. I will say, that a 3 blade does give more vibration that a hi-5 at idle/trolling speed. But not rattling souning. Just remember those blades are BIG so won't be as smooth at trolling speed as smaller blade prop.

Good luck, water is getting colder now, your speed with go up through the fall

[Minnesota Fats]

You were right - it seems like a great prop so far! I can't wait until I can get it out and get some more hours on it to learn more about it. Interesting to hear you guys both plug the PVS holes. I'm going to try the same next time I have it out and see what it does. I'm hoping I can get it out some night this week and beat on it a little bit. Still need to figure out the hub question, I think I'm going to swing by the dealer tomorrow and look at the parts side by side.

[Minnesota Fats]

Went to the dealer and got an education on the flo torq hubs.

Flo torq 1 - pressed in rubber hub. Prop seats tightly against the thrust washer and is held in place by the nut against the face of the metal insert in the rubber hub.

Flo torq 2 - lightly pressed in delrin hub. the delrin hub is "break away" so if you hit something, it can spin on the delrin and break it, and you aren't out a prop, you just have to replace the hub. And, even with the broken spun hub, you can limp it home. Prop seats against the thrust washer and is held in place by the prop nut against the aft adapter, which seats against the aft race on the prop hub.

Here's where it gets different:

Flo torq 3 - lightly pressed in delrin hub. The delrin hub is two piece and has titanium springs that will bend under torsion - so that there is some free rotational play. This is designed to eliminate the chatter of the prop at idle, when decelerating, and also when shifting into gear. Interestingly, the prop is NOT seated against the thrust washer when the prop is not spinning. The aft adapter is also not seated against the prop. The nut seats the aft adapter against the thrust washer (and therefore, it doesn't slide on the prop shaft), but the prop has some fore/aft free play on the delrin hub. Once the motor is in gear, the prop self seats on the thrust washer.

Flo torq 4 - same as 3, but for higher HP applications

Anyway, he gave me a flo torq 4 in place of my flo torq 2. He said it should eliminate the slight vibration i had at idle before. This has been a fun experiment/learning experience. Thanks for all your advice! I will report back when I get it out later this week.