Forum Newbie - Boat Handling Safety Issue

**Old Bass Tard** · 05-02-2019, 07:07 AM

Hello all. I'm Mike, aka Old Bass Tard. First time on the forum and I have a boat handling problem that I'm hoping you folks might be able to help me with.

I have a 2008 Triton 18 Explorer Bass Boat with a new, as of last fall, 2018 Mercury Pro XS 115 hp Four Stroke. Model: 1117F131D w/Standard 14x29 2.07:1 gear case. Previous engine was a 2005 Mercury 115 hp ELPTO 2-Stroke.

I have Cable steering that was installed about a year ago, and I ran it for several months with old engine and didn't notice any problem.

The Prop is a Laser II 48-16990 20P and the motor is set 5.25 inches below pad. No jack plate and we had to lower the engine that much (One hole left) to reduce the prop blowout at WOT, 52 mph. The Prop, after trying several, was the one that we found that provides the manufacturers recommended 6300 RPMS.

Side Note: after talking with Mercury, I was told that "These four-stroke engines like to sit much lower in the water than a two-stroke, so you will likely need to drop the engine as low as possible. This should help with the issue of blowing out, and may help with the handling of the boat as well."

Here's the issue: (Never had this with the old engine)

When I throttle up towards top speed, and reach around 42-45 mph, the back of the boat kicks out drastically, just for a second, but a scary one.

By "kicks-out", I mean, picture sitting in a swivel chair with someone in front of you holding the arms of the chair and then they quickly and somewhat violently jerk/swivel the chair 1/8 turn to the right.

I've been operating all kinds of boats since the 60’s and never seen anything like it.

The kick out is controllable, so far, and once it passes that point the boat straightens out. After that, the only thing I notice is that the boat is a bit more skittish then it was with the old engine, but I figure that’s the new norm since the new engine runs the boat several MPH faster than the old 2 Stroke 115 hp and its now sitting higher up on pad than before. (WOT is now 51 to 52 mph.) "Skiddish" is also better than Chine walking I guess.

During all this I’ve been very careful passing this kick–out point because I’m a bit worried about whether there’s a safety issue or not. I don't want to get thrown from the boat if it suddenly digs in and "hooks". (Yes I do wear a kill switch cord and a PFD, regular, not auto inflate. Old school and I don't trust that they'll work when I need it too)

So here I am. Not quite sure of the cause but I don’t want to leave things as they are because there seems to be a safety issue with the kick-out. I'm at a loss to explain the exact cause.

Other than doing the Hydraulic steering upgrade which I'm probably going to do, and adding the Jack-plate to get the motor into cleaner water, I don't know what else will help. BTW, It didn’t do this "kick-out" thing with the old engine.

Any ideas?

Thanks in advance

**XstreamVking** · 05-02-2019, 10:54 AM

What kind of trim are you using when the boat kicks? negative, positive nuetral?

**Old Bass Tard** · 05-02-2019, 06:54 PM

At that point, I'm probably feeding in a little up trim in increments as speed increases from a starting point of down trim at take off.

**XstreamVking** · 05-03-2019, 01:47 PM

Lower it down all the way and see if it changes. Sounds like it is lifting on the bullet getting a ton of stern lift.

**90VIPER** · 05-03-2019, 06:52 PM

Sounds like the boat is jumping up on the pad or the lifting strakes and it upsets the boat. My Concord will do this if I accelerate and trim gradually. I've heard the foustrokes have soft engine mounts which doesn't help either.

**home made tunnel** · 05-03-2019, 07:28 PM

My 115 Pro XS four stroke has very soft mounts. I've been looking for solid mounts, but nobody makes them yet. May have to see a machinist about that in the future.
The soft mounts are probably contributing to the problem as the prop unloads and blows out. I'm amazed that 5"+ below the pad you're getting blowout at any kind of speed though.

**WillySteve** · 05-03-2019, 10:00 PM

Originally Posted by home made tunnel

I'm amazed that 5"+ below the pad you're getting blowout at any kind of speed though.

I second that!!!
OK, looking at things logically, the boat doesn't care if it's a 2 or 4 stroke engine. All it sees is the horsepower, (if any), weight difference and propeller size and style.
Were it mine I would start at a known good engine height, same as the old 2 stroke if it ran well there. I would also stay with the same style prop that you had since your hull liked it. From there change the pitch, depending on what's needed for your redline and raise or lower the engine in 1/2" increments until you find a sweet spot, then fine tune from there. Remember that in most cases, raising the engine close to the surface will also increase the wot rpm's a bit but at those low settings you refer to I doubt you'll see a change!
I might also mention, I don't even run my pontoon engine that deep in the water?

**WavetoWave** · 05-04-2019, 12:55 PM

Originally Posted by WillySteve

I second that!!!
OK, looking at things logically, the boat doesn't care if it's a 2 or 4 stroke engine. All it sees is the horsepower, (if any), weight difference and propeller size and style.
Were it mine I would start at a known good engine height, same as the old 2 stroke if it ran well there. I would also stay with the same style prop that you had since your hull liked it. From there change the pitch, depending on what's needed for your redline and raise or lower the engine in 1/2" increments until you find a sweet spot, then fine tune from there. Remember that in most cases, raising the engine close to the surface will also increase the wot rpm's a bit but at those low settings you refer to I doubt you'll see a change!
I might also mention, I don't even run my pontoon engine that deep in the water?

This exactly. 2 stroke and 4 stroke is irrelevant. You're running it way too low.

**XstreamVking** · 05-04-2019, 01:16 PM

SOOO... after talking with Mercury, I was told that "These four-stroke engines like to sit much lower in the water than a two-stroke, so you will likely need to drop the engine as low as possible. This should help with the issue of blowing out, and may help with the handling of the boat as well."

THe lowers are very different, and merc knows it.....

**WillySteve** · 05-04-2019, 03:40 PM

I ask the question about engine height and driveability as to 2 vs 4 strokes on a Bullet forum for the guys who have gone to the merc 4's from 2's. Keep in mind these are 300-400 hp mercs and most have Sporty gearcases...here are answers I received:

*It’s 100% been dependent on the prop. I’ve ran anywhere from the heights the old sporty likes to as high as I can get my plate. Best way I can describe handling is I can remember the first day I drove it, and even though the motor was higher than previous setup it felt more stable than ever in my opinion.

*I’m running 3/4” below the pad. Same as my old motor.

*About 1in higher handling is much more difficult with the 4 stroke torque on the wheel modifying the skeg can help though.

*I drove a pair of V8s on Xb21’s and honestly I don’t know what the motor height was and they felt essentially the same as my 2 stroke....main things I noticed was I like the sound but love the automatic shifting.

*Depends on which 4 stroke your referring to! Sportmaster or Torquemaster?

**XstreamVking** · 05-04-2019, 04:06 PM

This guys boat tops out at 50. This is not a candidate for a surfacing lower. This type of boat needs the lower in the water for proper operation. jm2cts...

**WavetoWave** · 05-04-2019, 04:59 PM

Originally Posted by XstreamVking

SOOO... after talking with Mercury, I was told that "These four-stroke engines like to sit much lower in the water than a two-stroke, so you will likely need to drop the engine as low as possible. This should help with the issue of blowing out, and may help with the handling of the boat as well."

THe lowers are very different, and merc knows it.....

No, the gear case is the same. Running it that low is causing his issue.

**XstreamVking** · 05-04-2019, 05:15 PM

Ahhh, the propshaft center 5'' below the bottom is not that deep for a low speed boat. But you guys take over here and figure it out...

**WillySteve** · 05-04-2019, 05:17 PM

My point was to see if ANY others were having to lower their mota when switching over. I will agree it should be "in the water" and not surfaced but 5 inches seems like it would be making more problems than curing. One thing I can't understand is How can the prop blowout at 5 1/2" ptp....there has to be an underlying problem here we're not seeing?? The Wrong prop on the right boat will cause all kinds of weird things to happen!!!
We're it mine I'd be looking for a 4 blade and then go from there!

**WavetoWave** · 05-04-2019, 05:23 PM

Originally Posted by WillySteve

My point was to see if ANY others were having to lower their mota when switching over. I will agree it should be "in the water" and not surfaced but 5 inches seems like it would be making more problems than curing. One thing I can't understand is How can the prop blowout at 5 1/2" ptp....there has to be an underlying problem here we're not seeing?? The Wrong prop on the right boat will cause all kinds of weird things to happen!!!
We're it mine I'd be looking for a 4 blade and then go from there!

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