2017 glastron gt185 4.3 merc/alpha drive 1.62 14.5 19 prop - porpoise

[baconfudge]

got boat couple weeks ago, been out twice. been reading forums and watching every video i can on porpoise/trim/throttle and new boat owner but family has had bass boats my whole life, been on lakes enough to understand what should be happening and my boat..isn't it.


so stopped or idle, trim all down (tested in driveway motor goes all the way down) i throttle forward quickly to about 75%, rpm will hit 3500ish and bow rises a normal amount and boat planes out, id say 4-6s before bow starts to drop, rpm increase which is normal then the circus starts. boats going around 20-25 mph and i have to pull back on throttle or seemingly break the haul in half. i dont even have a chance to trim up, when ive tested trim up it gets even worse porpoise. ive tried starting at diff trim levels, all it does really is put the bow higher on launch, take longer to plane and when i get there it major porpoise, i can trim back then but doesn't stop it, have to throttle back. only thing im afraid to try is to add more throttle and maybe push thru it and work the trim but it's such bad slamming i dont know if i'd have control of the boat if i pushed the throttle more.

i really want to convey how bad it is, im watching other boats go past on plane with little or no porpoise, im watching these videos on trim they get on plane, more thottle, trim up, get more speed, then the porpoise starts and they trim down a little and it stops, its like a 5-10 degree porpoise, my boat is like 45 degrees, slamming.

so i guess in short, i don't believe it's operator error as far as throttle and trim or water conditions, ive tried different combinations, even ones i know are wrong like launching at 1/2 trim up and it's same results. the only time it runs anywhere close to good is when im barely barely barely on plane and maybe 20mph and really working the throttle to keep it in this very very narrow sweet spot, and trim up, forget it, when i barely get in the sweet spot it i even but up trim barely its slamming time. in that sweet spot i either pull throttle back to much to stop porpoise and come off plane or to much and slamming time.

conditions: somewhat interesting and maybe obvious is trip 1 to lake i had me,gf, parents, daughter and d-bf. about 1300 lbs. with heavy people in chairs and on bench and kids in front it was a struggle to get on plane, to much weight in back, so switched mom and gf and dad to front and could get on plane but it was porpoise but not as bad as trip 2. we did tube and w/ 4 in boat and 2 kids on tube i was running in that sweet spot a little easier and wasnt trying to push the speed plus the turning and working the throttle the slamming wasn't bad. trip 2. just me and gf this is where the porpoise really shines from above 3 paragraph description. we are about 500lb combined, both sitting in chairs.

so..here's what ive learned trying to figure out the issue. please comment and correct me if I'm wrong or totally missing something, i am a new boat owner so just learning as much as i can.

1. i have a 18' boat with a v6 and swim platform creating stern weight which is the cause of the porpoise.

2. the boat isn't loaded down, have some life jackets and the deflated tube under rear bench. a cooler thats maybe 20lbs. then me and the gf.

3. trim tabs can fix porpoise on some boats and really have no negetive effects besides maybe?? lower top end speed, well my top in on slammer jammer is 20mph so not worried about top end speed now.

4. hydrofoil not as good a trim tabs for porpoise, maybe as good for getting boat on plane (getting on plane isn't issue, 220hp merc pushes it up on plane w/ me and gf, it's after on plane is the circus.

5. boat could have some type of hook or eh forget other term but basically the bottom of the boat has some type of defect, i took an old license plate (didnt have ruler) and laid under the boat and put edge along bottom, it was mostly flat but a few places i could rock the plate maybe 1/16" to 1/8", havent found allot of info on what is normal and what is a problem if anybody could explain in terms of testing what is bad id appreciate it as ive read several times that these hooks cause cause the porpoise im seeing.

6. boat could be waterlogged? there is a scale at a pilot gas station up the road, getting app and im going to weigh it to rule that out as causing more stern weight than there should be. its a 2017, its really clean and no water in engine compartment and i got from dealer so im not optimistic that is the cause.

7. prop: talk about confusing, i have 3 blade 14.5 x 19, i did notice the little trim fin above the prop isnt there and there is a round plate instead, ive read this doenst affect anything but not sure if glastron comes that way or maybe previous owner took it off to put this prop on and not hit it. so i think i understand the diameter obviously, the 19 how fast it moves forward but the rake seems to be the factor in bow rise or stern rise, i think i have the rake that is stern rise now and its progressive (twisted) fins so i don't know enough about the prop or what props do to know if it's causing or contributing to the porpoise. seems like rake should be a spec but when i did the merc prop finder deal it gave me some prop options (they were x21 and x23 also) but didnt even list a rake spec so i don't even know how to compare mine to another as far as rake.

8. glastron is just a crap boat? i figure every boat manufacturer has some markerting thing, glastron is ssv haul tech that gets on plane quicker, seems great glastron, except when im on plane i rattle my teeth out so is this a glastron issue? not much on glastrons on the google. i was drooling a little at 220hp but maybe thats just to big of a motor for 18' boats?

9. use, id like to put the boat in the water, drive fast and smooth around the lake abit, stop and swim at boaters beach, maybe pull a tube around for abit and have a fun boating day, nothing crazy, i just don't want to porpoise across the lake like im riding over 5' whitecaps. also other boat wake i just thottle down thru them then quick back to plane and try to find sweet spot, there's no running thru even very modest boat wake w/out pretty much a pancake slam.

10. idles fine, have to correct steering whole time in no wake zone but no known issues going slow. boat seems to be level at idle which i find maybe odd id think the stern would be lower w/ all the stern weight. also we anchor at boaters beach, boat seems to be sitting in water level when anchored.

so i guess that's my situation and summary of what i've learned about it, any other info/test/examples would be appreciated.

 

[Rick Stephens]

When I changed my 17 footer from a 4 banger to a V6 it made the trim a lot more sensitive but still manageable in the method you stated - trim up, pick up speed, trim up again until the bow bounces and drop back a little. With the lighter 4 cylinder engine and less power it wasn't nearly as sensitive, as stated.

All along I have had Smart Tabs installed. I keep them at the stiffest settings. Like having shock absorbers. And my bow drops right down and it planes out at a lot lower speeds. Tabs add stern lift. Some props add stern lift.
are designed and known for lift at the stern.

I don't know hull issues at all. Read about them, never seen one that cause issues like this or one that was successfully repaired. Glastron is a good builder. So it ain't that. And I doubt you are water logged, a 2017 designed with a fiberglass tub in a hull if I am not mistaken. Hard to water log that type of structure.

 

[QBhoy]

Can only think you have too many people on the rear seats and a full tank of fuel in the rear too. Shouldn’t porpoise at all with trim all the way down and not being silly with everyone on the back.

 

[baconfudge]

Can only think you have too many people on the rear seats and a full tank of fuel in the rear too. Shouldn’t porpoise at all with trim all the way down and not being silly with everyone on the back.

it's a bench in back, 2 chairs then the bow seating:

trip 1 start: back bench mom:300ish gf: 210 left chair: dad: 300ish driuver: me: 270 bow: daughter: 130 Theboyfriend: 190 definately felt to much weight in back, forgot to mention me and gf put it in lake on trip1 but were only out for about 10min but i did take it up on plane a couple times and had porpoise, then went to dock and got the fam.

so i said to much weight in back, swap

trip 1 swap: bench: daughter/gf passenger mom driver: me bow: bf and dad this seemed most even and was abit better.

trip 2: just me and gf and we were in the chairs all day. all day slamming. never tried to put her in bow.

 

[JASinIL2006]

Assuming you have your prop dialed in (can't help you there; that stuff is confusing), I would consider looking into SmartTabs. They are perfect for this application. They have really great customer service, too. On my boat, they help me get on plane faster and at a lower speed, and they took care of my chinewalking problem, too. They are an excellent addition to a boat that's having porpoising problems.

 

[Scott Danforth]

it's a bench in back, 2 chairs then the bow seating:

trip 1 start: back bench mom:300ish gf: 210 left chair: dad: 300ish driuver: me: 270 bow: daughter: 130 Theboyfriend: 190 definately felt to much weight in back, forgot to mention me and gf put it in lake on trip1 but were only out for about 10min but i did take it up on plane a couple times and had porpoise, then went to dock and got the fam.

so i said to much weight in back, swap

trip 1 swap: bench: daughter/gf passenger mom driver: me bow: bf and dad this seemed most even and was abit better.

trip 2: just me and gf and we were in the chairs all day. all day slamming. never tried to put her in bow.

just an FYI, your glastron rating is for 8 people (at about 150# a piece) or a total weight of 1200#. your a bit over-loaded with the people listed, and most of them are in the stern of the boat.

that would account for some of it. not sure how big a pad your boat has, have you tried moving the beer cooler to the front to help balance on the pad when you are on plane?

could also have the wrong style of prop on the boat - a bow lifting prop maybe

or the hull could have a rocker.....

here is how I have always operated any boat with PTT....... from a dead stop, trim all the way in......... and mash the throttle, as the boat starts to climb out of the hole, my thumb is raising the drive until it starts to porpoise, then bump it down a bit..... the only difference between a boat with 500hp and one with 140hp is how quickly it comes out of the hole and how fast Im normally cruising.

on my old 3.0 powered avanti, I didnt have enough motor to get on plane quickly and up on the pad, so we normally would normally load people in the bow to help balance vs being perpetually stuck in the hole.

 

[baconfudge]

here is the prop, im pretty uneducated on how to identify what this one is doing or what one would be a helpful replacement if one even would be.

 

[Cortes100]

just an FYI, your glastron rating is for 8 people (at about 150# a piece) or a total weight of 1200#. your a bit over-loaded with the people listed, and most of them are in the stern of the boat.
.

My guess is weight is causing the problem. I have the same boat but with the Merc 4.5L. Running by myself or 4 adults, boat rides great. On a nice cruise speed (lets say 25-30mph) on a calm day, I've fooled around with the trim. Can see the water spray move back + forth while I'm adjusting the trim. Also the bow lift is very minimal, actually don't even notice it cause it only lasts for a second.
In the couple years we've owned it, I've only gone out once with 6 adults. Tried 4 people onboard, pulling 2 single tubes. Also pulled 2 skiers (to see if boat could do it), and never had any issues with porpoise.

Does the boat have this problem when there's only 2 of you onboard?

 

[baconfudge]

Does the boat have this problem when there's only 2 of you onboard?

yes, the major problem is when only two of us were in it, the best it ran was w/ my dad in the bow facing aft and 2 kids on tube, i was going slower on plane and turning allot and using throttle so it wasn't as bad, two of us, right after it gets on plane, nose just starts porpoising extremely bad, i dont trim up at all and it goes right into porpoise, if i try to trim up as the nose is coming down and boats coming up on plane it just porpoises even faster, its almost like i need more down trim to get it to run flat but i have no more, its max down trim all day running cause any up trim just exacerbates the problem.

 

[Bondo]

Ayuh,...... Welcome Aboard,..... You need to examine the runnin' surface of the hull,..... the boat's Bottom,....

I suspect it's got a rocker near the back,......

Crawl under it with a 6' straight edge,.... The aft 4' should be straight,.....

 

[baconfudge]

are these rockers? i can see light, the picture w/ numbers down is port to starboard along back edge left of drain plug.

the other two pics are bow to after on each side, one is flush, is this a problem?


*edit* i totally screwed this up huh? you said 6', i dont know that i have something 6' long thats straight? what do you use? like a 2x4?

how big exactly is a rocker? like 1/16" or like 1"? how much would the 6' straight edge be away from boat to be an issue? I'm looking up and down this and i dont see any dips or bulges.

 

[Bondo]

Ayuh,...... Check it parallel to the keel line, not side to side,.....

I use a straight piece of aluminum or steel,....

A hog is when you see light in the center of yer straight edge, which usually causes the hull to plow, 'n not get up,'n run on-plane,.....

A rocker is when yer straight edge rocks, front to back on a hump in the center,...... porpoising if the usual results,....

As I said, the last aft 4' of the hull should be flat, true, 'n straight,.....

 

[baconfudge]

best i had was a long piece of cardboard lid, i crawled all around under the boat looking at different angles, i dont see anything wrong w/ the bottom.

learned something else today that the front wheel needs to be up higher for the boat to drain out transom plug. i took plug out saturday when we got home and hardly any water came out, was like, nice no water. then tonight i opened the ski locker and it was full of gunk and maybe a gallon of water, took hose and got most of it cleaned out but no water came out of boat so i figured it was down where that drain plug drains it. when i was getting out of boat it occurred to me water runs downhill, cranked front wheel up and took out plug, and all the water from locker and hose came out so there's that, crank the wheel up so the boat is angled back. i put noodles and this hook pole in locker, i think dealership said that was self draining in the locker but i stock my finger in the hole, its jsut feels like a tube to me. pretty sure it should have a plug in it to keep water from coming into the locker.


i got a response from nautica on the trim tabs, of course nothing is just easy so my swim platform is going to block the top bracket if i put them on outside (position1) in pic, so im going to be in position2, these are like $140 and i see no negetive affect of having them on the boat.

my plan tomorrow is to call the dealership that sold the boat to original owner, maybe they have some insight. then going to talk to dealership i got boat from tomorrow and have the trim tabs installed (if you knew my luck you'd understand why im not drilling holes in boat). anyway nautica says its same same in either position, anybody have experience w/ these inside or outside making a difference?

going w/ the self adjusting ones. SX9510-60

 

[Scott06]

Try a prop with more stern lift like a Michigan vortex 4 blade 18” pitch. That And or the trim tabs To offset tail weight from swim platform.

i got a bunch of stern lift with this prop on my sea ray 170.

 

[Rick Stephens]

I went outboard as far as I could. The boat will be more stable from rocking if the stance is wider. Also, because I fish with my wife who is half my weight, I can adjust the port tab to be less stiff and the boat rides level. You can also see I had to cut a notch out of the step to clear the mount.

 

[baconfudge]

rick, did you have porpoise issue before you installed them? see you have 4 blade also, always had that or try different ones? i dont think i can cut my swim platform, ill ask dealer what he thinks to get them farther out if possible. i know the manual says dont mount to hte bottom of swim platform so thats not an option for me.

 

[Rick Stephens]

I installed the Smart Tabs when I had the 4 cyl engine. Things did get nose light when I installed the V6. Still, if I left the drive all the way down, the boat would plow through the water without a touch of porpoising even without the tabs. So I don’t have anywhere near the issues you have.I have run the boat for a day with the shocks disconnected from the tabs when one of them failed and made the boat tip over to one side. No issue without the tabs, just lost all the advantages.

You can probably have them build an aluminum bracket that goes around the swim platform mount. A bridge. Attach the tab shock mount to the bridge a little further away from the transom. Would work fine.

 

[baconfudge]

thanks for suggestions, took the boat back to dealership today, their service techs are going to look it over and hopefully go put it on the water. ill update w/ their results.

 

[QBhoy]

Hi
i think with the people listed above, then you might find that would be part of the issue...but if it’s happening with just two onboard and sitting at the helm area of the boat, that’s not normal or your fault.
The only thing I’m wondering around now is if you are using the trim gauge as a reference and not the actual position of the outdrive and looking to see what’s happening out the back of the boat. In all the boats I’ve ever had, I’m not sure I’ve ever used or looked at the trim gauge on the dash...simply because I’d think that most guys that have had boats for years usually pay no attention to them at all and prefer to use feel and visual reference to control and adjust the trim and attitude of a boat. All I’d say is that I usually hold the trim button Down until I hear the note of the trim pump change with it venting pressure at its lower limit. Get up on plane then trim up until the boat settles at its happy cruising speed with least load on the engine...all the while looking out the back to see the shape and form of the prop wash too. That and as earlier suggested, trimming up until the point of porpoise...then a nudge down until it settles well. All about the feel, sound and visuals really. Don’t pay too much attention to the trim gauge at all would be my advice.
just thought I’d throw this in there. Forgive me if it’s not relevant and you are already aware of this

 

[Bondo]

cranked front wheel up and took out plug, and all the water from locker and hose came out so there's that, crank the wheel up so the boat is angled back. i put noodles and this hook pole in locker, i think dealership said that was self draining in the locker but i stock my finger in the hole, its jsut feels like a tube to me. pretty sure it should have a plug in it to keep water from coming into the locker.

Ayuh,...... Drainage holes should be allowed to drain,.....

The transom plug, should be Out, anytime the boat is on it's wagon, Period,....