VT 18 Performance Update

[tjsellsfords]

Moved from the second hole to the fourth hole and just took the boat out for a run up the lake. Water was calm, not glassy, but calm. Still have the stock 12.6x19 aluminum 4 blade Spitfire mounted. The boat got on plane much quicker, actually the bow doesn't rise near as much at initial acceleration.

Previously, in the second hole porpoising would start around 40mph gps and maximum speed with bearable porpoising was 44 at 5,400 rpm's.

Tonight I got up to 44 with no porpoising and managed 46 with bearable porpoising at 5,600 rpm's. Trimming back down is necessary in slower turns but not at higher speeds. Water flows just under cavitation plate and all of the prop was in the water at WOT.

I will be changing the prop out but am in no hurry for the extra couple of mph right now.

These numbers are similar to Graham's who moved his from the 2nd to 3rd but he has two different props.

Wes is in the 4th hole and has a Turning Point 13.25x21 stainless 3 blade with his setup and is getting WOT speeds around 50-51 with a light chop. Most dealers are mounting these engine's in the second hole and they really need to be in the 3rd or 4th.

[MattVT18]

Great update, glad those of us with the VT18 are finding some things out the more we use them. I'm probably going to have my engine moved up a hole or two in the very near future. I've ran some numbers on prop slip and such and am finding that all I'm really doing is losing grip the higher I trim. Even though I haven't had the porposing that some have experienced, my boat just "feels" slow. I really don't gain any speed above about 5300 RPMs so I feel like there is more there if the engine started out higher and I wasn't trimming the crap out of it to get more r's. I'd really like to put a 4" jackplate on there so I can really fine tune it, but Crestliner says that a no-no for warranty. All my glass boats had them in the past and even 1/8" made noticeable differences sometimes. Thanks again!

[gatorglenn]

Great update, glad those of us with the VT18 are finding some things out the more we use them. I'm probably going to have my engine moved up a hole or two in the very near future. I've ran some numbers on prop slip and such and am finding that all I'm really doing is losing grip the higher I trim. Even though I haven't had the porposing that some have experienced, my boat just "feels" slow. I really don't gain any speed above about 5300 RPMs so I feel like there is more there if the engine started out higher and I wasn't trimming the crap out of it to get more r's. I'd really like to put a 4" jackplate on there so I can really fine tune it, but Crestliner says that a no-no for warranty. All my glass boats had them in the past and even 1/8" made noticeable differences sometimes. Thanks again!

I wish everyone would read this. Been saying it for ever. Motor height will do more for performance, then trim will ever do.

Ideally you want to trim out to a neutral steering position. Log those rpms. And work on height and prop from there.

[tjsellsfords]

Glenn,

Explain neutral steering position please.

[gatorglenn]

Glenn,

Explain neutral steering position please.

When you first come out of the hole ( when you floor the gas to it) . You will feel torque on the steering to the right. It will stay until you start trimming up. When you trim up( or out ). You will feel that torque start to ease off. When you reach that point, where there is no torque. The steering wheel has equal pressure right and left. Your there (neutral steering). If you keep trimming out more. You will get torque going to the left. At that point your putting the prop in a negative position. Where your rpms will go up, the higher you trim. But your not gaining anymore speed. This is where you'll get a higher prop slip. Trimming more you will feel the boat loose bite, due to cavitation.

So in the neutral steering position. For most boats, it maybe at 1/2 trim or 3/4 trim. Some boats with prop holding problems it can be at 1/4 trim.

Neutral is where the prop will work more efficient. And have the least amount of slip.

Now on 4 blade props the torque isn't near as bad. But it's still there some until the motor is trimmed to the angle that the boat likes.

So with the prop in a neutral steering position. That's where you should achieve proper height and size of prop pitch for rpm range on a given motor.

This will give the boat motor combo its best in, speed, drivability, fuel efficiency, and slip.

[tjsellsfords]

Thank You, I'm learning more all the time thanks to veteran boaters like you on BBC Will I feel it with no feedback steering? I haven't noticed it or maybe I'm just not paying attention

When you first come out of the hole ( when you floor the gas to it) . You will feel torque on the steering to the right. It will stay until you start trimming up. When you trim up( or out ). You will feel that torque start to ease off. When you reach that point, where there is no torque. The steering wheel has equal pressure right and left. Your there (neutral steering). If you keep trimming out more. You will get torque going to the left. At that point your putting the prop in a negative position. Where your rpms will go up, the higher you trim. But your not gaining anymore speed. This is where you'll get a higher prop slip. Trimming more you will feel the boat loose bite, due to cavitation.

So in the neutral steering position. For most boats, it maybe at 1/2 trim or 3/4 trim. Some boats with prop holding problems it can be at 1/4 trim.

Neutral is where the prop will work more efficient. And have the least amount of slip.

Now on 4 blade props the torque isn't near as bad. But it's still there some until the motor is trimmed to the angle that the boat likes.

So with the prop in a neutral steering position. That's where you should achieve proper height and size of prop pitch for rpm range on a given motor.

This will give the boat motor combo its best in, speed, drivability, fuel efficiency, and slip.

[gatorglenn]

Thank You, I'm learning more all the time thanks to veteran boaters like you on BBC Will I feel it with no feedback steering? I haven't noticed it or maybe I'm just not paying attention

It won't never as bad with that system. But it's there some. Most boats, if you can level the bottom of the boat. And level the cav plate with it. Mark that spot on the trim gauge. If no gauge. Use a mark that you can see from the seat looking back at the motor, like this. See the white tape with two marks on it. When timed down to get on plane. It can't be seen. But trimming up to where the first mark is flush with the mount bracket. Is level, and the 2nd mark ( one on the bottom) is the highest trim before leaving that neutral running. That's where the bow has lifted, and the boat frees up. And steering is still neutral. Pass that point, and your just getting into more prop slip. Are if you look back and your rooster tail is more then 2' high you have passed it.

[tjsellsfords]

Gotcha I do have a trim gauge.

[Grahamb]

This weekend I was out and there was a stiff wind at my back and decent chop. The stars aligned and I guess the chop offset the porpoise and I could continue trimming much higher than I ever could before. Sustained over 49 with a blip to 49.9 on the gps. It felt glorious.

[tjsellsfords]

I'll be changing props out some time soon. Considering a 3 blade SS 21p, which one are you using? Glad I didn't buy the X7

Did you read what Glenn explained about neutral steering position earlier in this thread?

This weekend I was out and there was a stiff wind at my back and decent chop. The stars aligned and I guess the chop offset the porpoise and I could continue trimming much higher than I ever could before. Sustained over 49 with a blip to 49.9 on the gps. It felt glorious.

[MattVT18]

Grahamb - was that with the motor in the 3rd hole and the 17P BlackMax?

[Grahamb]

Grahamb - was that with the motor in the 3rd hole and the 17P BlackMax?

Yes, but please don't think that's the norm. it's a noteworthy story because it was a one off.

[starfox101]

I must have one strange boat! I don't have a rooster tail, The more I trim, the faster she goes. Last time I really tested, I will get 42 on gps jumping out of the water "proposing" I can get "neutral steering " way before max RPM. I am cheating because I put a jack plate on it. The 42 MPH was without jack plate, 41 maybe with jack plate but without proposing.

[tjsellsfords]

I think 41 without porpoising is good with the 75. You could probably get more with a different prop if you wanted it. I'm not the one to ask though I'm still in the learning curve.

I must have one strange boat! I don't have a rooster tail, The more I trim, the faster she goes. Last time I really tested, I will get 42 on gps jumping out of the water "proposing" I can get "neutral steering " way before max RPM. I am cheating because I put a jack plate on it. The 42 MPH was without jack plate, 41 maybe with jack plate but without proposing.

[gatorglenn]

I must have one strange boat! I don't have a rooster tail, The more I trim, the faster she goes. Last time I really tested, I will get 42 on gps jumping out of the water "proposing" I can get "neutral steering " way before max RPM. I am cheating because I put a jack plate on it. The 42 MPH was without jack plate, 41 maybe with jack plate but without proposing.

That's because your motor is to low. If you were to trim out to a neutral steering. And work on there with height to get those RPMs up your speed will definitely go up maybe more than what you're seeing now. You're just trimming out to cleaner water. If you can trim all the way out and you don't lose any speed from ventilation your motor is actually too low.

[MattVT18]

Yes, but please don't think that's the norm. it's a noteworthy story because it was a one off.

The prop?

[Grahamb]

The prop?

The overall performance isn't usually that high. 49.9mph was a one time thing.

[MattVT18]

The overall performance isn't usually that high. 49.9mph was a one time thing.

Gotcha, thanks.

[MattVT18]

I've been able to get my rig on the water a few times since my last comment. I've really paid attention to where "neutral steering" is on my trim gauge. It's actually a pretty small amount of trim required to get there on my boat. Glenn - any idea how much of an increase in RPMs per hole to expect? Also, would you recommend raising the motor or changing the prop first? I'm going to move to a SS prop, just don't know which one yet. Like I said before, I've only had a fixed height engine on one other boat and it was already tweaked when I got it. The 20P Laser II seems to be a really solid performer on the Ranger RT188s but a 21P 3 blade is not out of the question. Really just with Crestliner would just say a jackplate was ok and I'd be done with it...

[tjsellsfords]

Matt,
See what Glenn says but I think I've read other threads that it's about 50 rpm's per hole. I think I went up a little over 100-150 with 2 holes. The last two times out I had a slight chop in the water and I got 45 mph with no porpoising against the wind, empty livewell, gas tank was between 1/4 and 1/2 full, by myself. Going back with the wind I had fish in the live well and still got 45. I'm may experiment by putting a sand bag in the front and see if I can see another mph without porpoising. I'm happy for now but I will likely buy a SS prop next year.