Crestliner VT18 performance...

[ReefOctopus]

Good morning,

I recently changed props to the spitfire x7 19p and raised the motor one hole ( i can still go up 2- Merc pro xs 115).

The porpoising issue is completely gone, running about 44 mph (gps) with 2 full sized adults and gear.

Wondering why I am only seeing about 5200 RPM's on my stock tach... I know they are not the most accurate but I am no where near the peak performance for that motor. Is this bad for motor? Should I go up another hole? Prop change?

[Grahamb]

I tried the same prop on my VT18 with ProXS 115. I couldn't get it to spin any faster and was advised to go back to my original prop.

[BBW]

what was your original prop, i am having same problem , dealer said try a 17 pitch, going to take mine back to water tomorrow and run solo , i was running sat with 500 lbs people talon and full tank gas and fishing gear may be the load that is keeping it from turning , best i got sat was 5200 rpms 44 mph, after 44 boat would start to porpoise , any other vt18 owners out there with 115 pro sx 4 strokes that may help please let us know.

[Grahamb]

what was your original prop, i am having same problem , dealer said try a 17 pitch, going to take mine back to water tomorrow and run solo , i was running sat with 500 lbs people talon and full tank gas and fishing gear may be the load that is keeping it from turning , best i got sat was 5200 rpms 44 mph, after 44 boat would start to porpoise

BlackMax 17p

I still have porpoising if I trim up past a certain point.

[BBW]

grahamb- what speed and rpms are you running with black max 17

[ReefOctopus]

Mine came with the black max as well. Terrible handling and porpoising (not sure if that was prop related). I couldn't spin the black max past 5200 either.

The spitfire is great, except I can't seem to turn it. Will it hurt the motor by not reaching 6K+?

[Grahamb]

Here's what I wrote about it two years ago after taking it to the dealer -

So I tried out the boat this weekend. I got it back from the dealer with the 17p Black Max on it, motor raised to the third hole from the top, and transom wedges added.

It feels happiest around 42-44, above that there is still some bounce. I've had it as high as 45 while still riding smoothly, so after more time in the seat I hope to be able to replicate that more. At 46 it's bouncing, but it felt like a smoother bounce than before and wasn't scary. I kept trimming and got it up to 48-49, but it felt like it wanted to fly at that speed.

At the beginning of last season I also put a hydrofoil on it but it made no difference.

[ReefOctopus]

Here's what I wrote about it two years ago after taking it to the dealer -



At the beginning of last season I also put a hydrofoil on it but it made no difference.

I am not trying to squeeze every MPH out of the boat I just want the boat to perform reasonably. Honestly Im ok with 44-46 mph. I just don't want any damage to the motor if it can't turn at optimal RPM.

If that makes sense. I do run a decently heavy boat with 2 guys jammed packed with gear. Maybe thats why I can't spin it to 6k+?

2 guys ~ 500 lbs plus gear

[Tim Kelly]

Have you tried trimming up in little bumps? I remember reading a post, I think from T-Mac, about his experience getting the best out of the Lund mod v. He found bumping the trim in little steps allowed you to trim it further than moving the trim smoothly up. Pretty sure I remember that right.

[ReefOctopus]

Have you tried trimming up in little bumps? I remember reading a post, I think from T-Mac, about his experience getting the best out of the Lund mod v. He found bumping the trim in little steps allowed you to trim it further than moving the trim smoothly up. Pretty sure I remember that right.

I have tried that, doesn't seem to make a big difference if any. I am more concerned if I am doing any damage to the motor by not reaching optimal RPM's under WOT. Might just be a load/ weight issue? IDK at this point. I think I will try raising the motor up one hole.

[GeauxTide]

My 19" spins my Opti ProXS 5600 (46mph), but I'm at hole #3. The 4 blades can run closer to the surface. Now, you're sitting 1100rpm down from the 6300 WOT of the 4s ProXS. WOT range for that motor is 5300-6300, but I would not be comfortable with any thing short of 500rpm difference. Hearing nothing about hole shot/handling, bring motor to hole #3 and try'er again. If you're not turning 5800, then it's a 17". Really surprised that your 1126# hull won't spin the 19. The lower unit of the 2s and 4s are the same, unless you have a CT Motor.

[FloridaFlyer]

My 19" spins my Opti ProXS 5600 (46mph), but I'm at hole #3. The 4 blades can run closer to the surface. Now, you're sitting 1100rpm down from the 6300 WOT of the 4s ProXS. WOT range for that motor is 5300-6300, but I would not be comfortable with any thing short of 500rpm difference. Hearing nothing about hole shot/handling, bring motor to hole #3 and try'er again. If you're not turning 5800, then it's a 17". Really surprised that your 1126# hull won't spin the 19. The lower unit of the 2s and 4s are the same, unless you have a CT Motor.

Did you run the motor before you raised it to the third hole? Did things change? Exactly what would a person expect to see going from the second hole to the third hole? Would it improve handling noticeably or would the RPMs increase much or would speed increase a little? What happens differently from being in the second hole and moving the motor up one hole?

Thank you for the info...

To the original poster.... You really really need to get the RPMs up some at WOT for the long term health of the motor is what my mechanic told me. They need to run more at the top of the acceptable range than at the bottom is what he said.

[ReefOctopus]

I have tried that, doesn't seem to make a big difference if any. I am more concerned if I am doing any damage to the motor by not reaching optimal RPM's under WOT. Might just be a load/ weight issue? IDK at this point. I think I will try raising the motor up one hole.

When you say hole #3, what do you mean?

Currently I can go up 2 or down 2. I have 5 total so I am in hole #3. Originally I raised it 1 and it made a big difference. Increased RPM's, handling, etc. I also changed the prop from the black max to the spitfirex7 at the time of the hole change.

[Grahamb]

I am not trying to squeeze every MPH out of the boat I just want the boat to perform reasonably. Honestly Im ok with 44-46 mph. I just don't want any damage to the motor if it can't turn at optimal RPM.

If that makes sense. I do run a decently heavy boat with 2 guys jammed packed with gear. Maybe thats why I can't spin it to 6k+?

2 guys ~ 500 lbs plus gear

I had someone tell me that this isn't good for the motor. You should post it over in the Mercury forum. I think there are some experts there who could weigh in.

[GeauxTide]

Did you run the motor before you raised it to the third hole? Did things change? Exactly what would a person expect to see going from the second hole to the third hole? Would it improve handling noticeably or would the RPMs increase much or would speed increase a little? What happens differently from being in the second hole and moving the motor up one hole?

FlaFlyer: My RPMs were 5400 at hole #2. Hole shot on an X7 isn't great at any level, but it's acceptable. At hole #3, the handling and turning were dramatically improved and I gained 200rpm.

[BBW]

ok guyes i ran today without my 275 lb buddy and 30 lbs less gas <305 lbs> turned 5600 and 51 mph gps ,when i ran sat with the extra weight i ran 5200 and 44 it seems the vt 18 is very sensitive to the weight, now i am wondering if i need to try the 17 pitch i still have 700 rpms to the 6300 limit if my gauge is correct, only thing don"t know what it will do to hole shot and speed, my hole shot is great handling is good and speed is ok at 51

[Tim Kelly]

51 is very impressive. I imagine a 17p would work well for you, especially when you have your buddy with you.

[fishon396]

Never hurts to have a spare prop or props for different situations.

[Wil Holmes]

You may greatly benefit having a Mercury mobile Vessel view to receive accurate RPMs and everything the motor is doing. Personally seems strange that the motor needs running hard to maintain its health. I would think that would be opposite. Motor is running good if you are seeing 51 by yourself, is that GPS speed?

[Great Scott]

Dont carry a yrs supply of tackle for a one day trip.
Same for fuel. If the most you have used in a trip is 1/2
take, fill to that level. All boats have load limitations and
a balance point. It is just as bad or maybe even worse
to lug a motor than it is over revving it. Lugging causes
a lot of excess heat build up in your engine, and can lead
to premature failure.
Always prop to as close to max RPM that your engine will turn.
It will in most cases require 2 props. One for light loads or winter
temps. The other for hot weather or heavier loads.LDS