23' Sceptre I/O - severe wandering at low speeds. Advice needed.

[Handful in NC]

All you wise Seacraft gurus, from whom I have leaned so much, please further enlighten me …

I just refurbished a 77’ 23’ Sceptre I/O. At slower displacement speeds, it wanders the worst of any deep V I/O boat I’ve ever owned. I mean, the Sceptre is all over the place, and so bad that you can’t just leave the wheel alone and let the heading “average out”. The sucker is gonna wear me out trying to keep it pointed anywhere close to the right direction, and something has to be done.

I always thought the tendency for the heading to drift at slow speeds in a deep V was due to weight in the stern (an I/O in this case) and the sharp and deep forward entry of the deep V hull. In simple terms, the back end wants to get in front -kind of like pushing a wheelbarrow, or maybe the way a tail wheel airplane (where the CG is aft of the main wheels) wants to ground loop.

Here’s what I don’t understand. My ’74 23’ Tsunami – an identical boat in every way that has been converted to a 250 Etec on a Hermco bracket and had a pilot house added, wanders just a very little bit- hardly noticeable. The pilot house with its hard top and glass windows has surely moved the CG forward, despite the outboard/bracket. Also, the outboard has less "structure" in the water than the I/O. So shouldn't the tendency for the heading to wander be worse?

I haven't gotten photos of both boats in the water, but the waterline at the stern seems to be about the same.

I’ve heard that lowered tabs will stabilize the Sceptre, but the boat doesn’t have them and doesn’t really need them for my usage.

Any thoughts or comments would be greatly appeciated.


Interesting numbers:
23' Sceptre soft top with 260 hp I/O - tops out at 42 mpg.
23' Tsunami pilothouse with 250 hp Etec on Hermco bracket - tops out at 49 mph.

[McGillicuddy]

No guru but I'll offer a couple of simpleton observations:

Its probably there, but I don't see a zinc trim tab under the blue one's anti-cav plate. I am amazed by the impact the little rudders have on steering and managing steering torque.

A 4 blade prop would likely help also low speed maneuvering.

[dave3fl]

Have you played with the trim at all? My I/O wanders a lot more when it is trimmed up/ out.

Also not sure if it's related or not and it could just be the angle of the pic but your drive looks to be mounted really deep.

[Handful in NC]

Boy, do I feel dumb. I didn't notice the missing trim tab. Surely that would make a difference way out on the outdrive in the prop wash. I've also been having problems with the power steering pump, which is being replaced, and my mechanic just told me the actuator will have play if there is not enough pressure from the pump. I'll try these things first. Thanks for the comments.

[Fr. Frank]

First of all, the Sceptre/Tsunami single stern-drive models DO have the worst steering wander of any boat I've ever driven but one in 45 years of boat operation. (The 23' Martini small-block single Alpha I/O is worse)

Second, the absence of the torque tab will have a slight effect, but only slight.
Drive angle makes a difference, too. At displacement speeds, the deeper the drive, the better.
If you have power steering, check your actuator for play and your pump for fluid.
If manual steering, check the steering head.
4-blade props wander slightly less than 3-blades. (I don't know why)

While on plane, how much wheel turn do you have before the hull responds to the helm?

I used to have a 23' Tsunami w/ 225 Johnson, and it wandered so badly I would not leave the helm while under way.

[McGillicuddy]

There ya go...

[Islandtrader]

If you have power assist steering on your boat then Mercury does not put a zinc torque tab on the out drive. Manual steering yes.

[bigeasy1]

Funny,my 74 Tsunami with a Mercruiser I/O Alpha drive and a 350 engine with power steering doesnt wander even a tiny bit.
Wether i'm under power or at less than displacement speed,it will stay straight as an arrow even with my hands off the wheel.
I even removed the zinc anode rudder when I put the 15-1/2" Mirage prop on it as it didn't clear the prop,and it still runs straight as an arrow.This Alpha drive with power steering came with the rudder anode tourque fin on it.
I may be just lucky or maybe the power steering feature makes it less prone to wander.

I always run it with the outdrive tucked in as deep as possible.When I replaced the transom,in 2009 I got the cut out pattern from Mercruiser.
Maybe that new cut out pattern had a spec for a lower mounting location for the out drive.

One of these days I'll have to put the replacement low profile anode on the outdrive.

[McGillicuddy]

I was hopin' Big John would chime in here, I imagine you guys troll for salmon around 2 knots, no?

Terry, that bit about the absence of a torque tab w/power-assist steering is interesting. I had no idea.

Padre, 23 martini would put the driver in a coma thus the wandering boat

[bigeasy1]

Yeah Gillie our salmon speeds are usually around 2.5-2.8 mph at the probe depending how deep the probe is.
Surface speed can be anywhere from 1.9 to 5 mph on the gps depending on currents.We can be going 5 mph on the surface while the speed of the lure at the down rigger weight probe may only be 2.5 mph.
Now normally I'll troll with the T8 yammy kicker but when it's blowing I'll throw out the bags and troll with the outdrive.I have no wander issues doing that.
We have noticed a huge difference between this boat and my old 22' Trophy.I can leave the wheel on the Tsunami to net a fish and the boat continues on its path amazingly straight.
On the Trophy,if I just let the wheel go for a few seconds,the boat would start turning in large circles.It also was an I/O (OMC Cobra)

These pics show the drive location on the transom.