I have a 2019 Crestliner VT18 with a 115 Merc Pro XS 19 pitch stainless prop.
The boat starts to porpoise around 42-43 mph.
It will only turn about 5500 rpm
I can throttle it back to 5200 rpm and still run 42 mph
It has 5 mounting holes on the motor.
It is mounted it the second hole from the top. So, I could lower it 1 or raise it up 3.
I installed a hydrofoil and it didn't help at all.
Should I raise the motor a hole or two?
Change props? to what?
115 pro xs.jpg
This is at WOT.
Thats all I can trim it.trim-rpm.jpg
I'm following this. I have a 17' Lowe pad hull aluminum bass boat with a 90 on it (17HP). I love it but it is frustrating from a performance standpoint. It seems aluminum boats just won't handle much trim without bouncing. I can hit about 42 gps speed in my Lowe and I know the engine will turn more and there is more speed to be had but if I trim up just a little the boat handles like a wildcat. I raised my engine a set of bolt holes and it did help some but there is just something about a tin boats design / weight distribution that won't let a prop keep the bow up to get the hull out of the water. When I try to trim the bow up past what it can be then the bouncing starts. I don't know about your 18' Crestliner but looking at my 17' Lowe it is obvious that in order to make for a roomy back deck that the seating is pushed forward to almost middle of the hull. No engine / prop can lift all the driver and passenger weight and hold it up when it is cantilevered out so far from the stern. What seems to be happening in my boat is I trim up and the bow come up and my speed goes up but then the weight falls forward and the bouncing starts. It is a vicious cycle. Now I just get up on pad and trim just a little bit, if I go to far and the bow start bouncing I just bump the trim down and that is the best it will do. Like I said, my rig with a 90 will hit 42 or so but the best I can usually do without all the bouncing is 40. I'm at 5400 - 5500 rpm with a 20P 3 blade Laser II prop. The motor would pull on up to 5800 except for the bouncing. Good luck and please post if you have a breakthrough.
it is frustrating. I had a 2004 Bass Tracker 185. It never had this issue.
I'm trying to line up a friend to come drive it so I can look at the motor and see how deep it's in the water at top speed.
Hopefully I can raise the motor a hole or two and help out. If not I will look at changing props.
I'm just an hour or so south of you. Do you ever fish Weiss or Guntersville?
Raise it a hole. Made a big difference on my vt17.
It probably has one set of trim tabs from the factory. You’re going to need another set.
Your dealer can get them for you. They can be welded on or I’ve seen some people just epoxy them on.
Night and day difference.
Good luck, I used to fish the Big G but not for a number of years. Now I'm pretty much a Chickamauga - Nickajack fisherman. I wouldn't mind getting on Guntersville or Weiss but I never had good luck on the G, just too much good looking stuff to fish and I don't know anything about Weiss. I hope you get your handling / speed problems sorted out. Please follow up to this thread if you do so we can all learn!Originally Posted by danb303
I have some experience with this.
I ran the x7 19p and my rpm's were low. Switched to 17p. Raised it up 3 holes. Boat now runs 48-50 at 6200rpms. You really don't need much trim with some of these aluminum. Slowly bump it up while you are gaining speed.
This was on a 2017 vt18.
do you have the trim tabs on your boat?IMG_2542.JPG
2017 Crestliner VT 18 DX
Mercury 115 ProXS
Motorguide X3 70lb 24V
TP Express Mach 4 13 x 19
"Follow Me," Jesus told them, "and I will make you fish for people!" Mark 1:17
do you have the trim tabs on your boat?IMG_2542.JPGI didn't see them in the picture. If you don't you may be able to raise 2 holes. I raised mine 2 and I think I should have just raised it one. After you raise it you can expect 45-46mph(GPS) 50-51 on the speedometer
Last edited by tjsellsfords; 08-27-2021 at 04:30 PM. Reason: additional info
2017 Crestliner VT 18 DX
Mercury 115 ProXS
Motorguide X3 70lb 24V
TP Express Mach 4 13 x 19
"Follow Me," Jesus told them, "and I will make you fish for people!" Mark 1:17
I used to own a 17’ 6” Triton tin boat, pad hull, with a 90 hp Optimax and having additional cup added to the Laser 2 prop and mounting the motor on the 3rd hole was a good combination. The combo was good for 47 mph in summer and 50 mph in cool weather.
Why does your trim gauge show your trimmed down?
Some owners have used JB Weld and added a bead along the rear edge of the boat. Acts like a trim tab but easy to put on and remove. It will need to be a large bead maybe 4 inches long on each side a few inches from centerline.
RT188
I LIKE boats...BUT I LOVE PLANES
Oh yeah.... I love the RT188 too.
Have more experience with this issue than I'd like to admit. Owned a 2014 Lowe 18HP Pad Hull with a 115 Opti ProXs. With factory tabs, it wouldn't porpoise, but it would not lift the hull past the console. Tried a 6" TH Marine JP, which gave me 46, but squirrely. Changed prop to X7 SS 19" and boat was rock solid, but lost the 2mph from the 20" Laser II. Still wouldn't lift the hull. In 2017, I got a Ranger RT188, also with a 115 Opti ProXS, mounted at hole #3. Now, I added a port console, which added 125# to the weight, so 45mph light was it. Handling is magnificent. I absolutely agree that it's easy to over trim a semi-vee hull. I only trim mine until I see the water break behind the seats. Semi-vees don't have any lifting surface like the Trackers that have an inset step to give some measure.
Last edited by GeauxTide; 09-07-2021 at 10:28 AM.
2015 Ranger RT188 DC; BassCat Storage Box; Mercury Optimax 115ProXS;
19" Spitfire X7; Vessel View Mobile; Minn Kota Ultrex 80; GForce Handle;
TM Eliminator; Helix 7 G2N SI Combo F/R; HydroWave KVD; BBT 4" Angled Bow Mount; Durasafe Locks for Electronics and Ultrex;
Twist Step Boarding Ladder; EZEE Step ES1; BAC RAC Rod Storage; Motor Mate Transom Saver
I have a lot of issues like this with my Triton, no tabs of any kind. When I’m alone it’s not bad, but when I add a person, gear, livewell full it gets bad. All of this points to the motor being too low. The cavitation plate is underwater at wot so the motor keeps trying to do its job but can’t and the boat porpoises...it’s a cycle that once started is hard to get it to stop.
My ptp measurement is close to 6”, too low. I really want to add a 4” jackplate to fix this issue. I trim very slowly now, just a tap at a time until it gets right to the point of starting to porpoise, then back off a touch. It’s an aluminum boat thing.
2006 Triton SP-185, 2006 Evinrude Etec 90, PowerTech NRS3, Garmin Echomap Plus 73CV & 93SV
I wanted to emphasize this because I know people here that have fixed boats with this and it is cheap to try and experiment to see if it helps...maybe $20 in JB Weld and can easily be removed afterwards....and you can do it at home and see what difference it makes. It is very surprising what a little tab in the very rear does.
The tab has to be a little fat and build it up a little maybe 3/8 inch or so and 3 to 4 inches long on each side maybe a foot or so from the centerline and a couple of inches from the edge of the transom.
See what it does. I think you will be surprised. It can easily be removed with a sander or oscillating tool.
By the way, the Crestliner hull is VERY SIMILAR to the Ranger RT hull. They are almost identical. The early RT 188 hulls had a problem with some of them porpoises. They added the little trim tabs to the transom area for a fix. You can find a lot of information on this along with pictures on this forum. The jp or something else might also help but these trim tabs do the trick a lot cheaper unless you want the jp for other reasons.
Last edited by FloridaFlyer; 09-07-2021 at 09:48 AM.
RT188
I LIKE boats...BUT I LOVE PLANES
Oh yeah.... I love the RT188 too.
^^^^ this... if you want an inexpensive fix.
RT188
I LIKE boats...BUT I LOVE PLANES
Oh yeah.... I love the RT188 too.
I've got a 18 and 17.5 foot Crestliner. One is a flat bottom rig with a 90hp Mercury and the 17.5 is a Fishhawk deep V with a 115 Mercury. They both would porpoise at different speeds and depending on waves. I installed a Hydro shield on the flat bottom rig and it sat higher in the water, the boat could run at a low speed of 16 mph with no porpoising and none at any other speed. I was actually shocked it worked so well. I saw them on a FB add and said for the small price I'll give it a try. I added one to my deep V and it will plane perfectly at 15 mph and zero porpoising at all. It actually improved the hole shot a lot. The back end of the boat sat higher in the water and the boat will tuen on a dime. This isn't a plug for them at all but I'm so impressed I'm thinking about trying it on my 21 foot Ranger with a 250 mercury. It has a bad porpoise at slower speeds. It will stop the porpoising I believe on any boat and improve handling. 2 buddies of mine tried them on a 18 and 19 foot Nitro with 200 Mercurys and both were very happy. https://www.hydro-shield.com/
i owned a vt 18 never achieved max rpm with out porpoising, I just ran mine until porpoising started and then trimmed down, most people including myself try to get more out of these hulls than it is capable of doing
That's all I can trim it without porpoising
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