Boat "snakes" at low speed

[Roughasguts]

Cool the plot thickens, so now i'm wondering if you should look at the trim tab,(zinc anode) on the leg of your outboard.
Cause the leg is just a Symetrical aerofoil wing shape, so once it gets some sort of deflection, (maybe trim tab out a tad) then the leg skeg Etc will try and corect the mis aligment and in doing so will over compensate until the leg trys to compensate in the other direction. (kind of like a dutch Roll the boeing 727 Gets with the ailerons)
So maybe when your out next, take your spanner and adjust the trim tab and see what differance you can make, even let it flap around to start with.

I know this is only part of it, as were not taking gyroscopic, blade, and torque effect in to consideration yet.

[banshee]

My 500 explorer/115 Merc does it between 4-6 knots,it doesn't worry me at all as the only time I pick up on it is first thing of a morning in the go slow areas before I head to sea,I think it can be exagerated greatly by over correcting in an attempt to keep the boat dead straight.If it is a design fault or the like it is something I'm quite happy to live with and a small price to pay for a boat that has so many attributes.

[death_ship]

It is normal at low speeds ( 6knots) my haines and the 680 i go in often both do it at 6 knots, even after replacing motor, if its doing it when on the plane there is definitely something wrong, maybe steering problem.

[Roughasguts]

Geeez, i'm really curious about this. So what does it exactly do.
does the boat turn (yaw) or does it roll first, get to a certain roll angle then drop as if to fall of the Vee, then continue to go the other way.

[banshee]

Mine just changes direction ever so gently,the boat remains stable and rock solid,no lurching rolling etc,then the slightest of corrections with the wheel(and I mean moving my hand about a quarter of an inch with the wheel) will have it wander off in the other direction while the boat remains perfectly level (relative to the trim),the whole thing is so subtle in mine that no one else is aware off it,earlier on when I was over correcting it was noticed by a few of the deckies that used to come with me.

[Cheech]

Only when going through 6kn restrictions. Otherwise I am up on the plane and do not have it happen.

[Owen]

Sounds like you're using the steering system out of my old FC holden

It'd be interesting to see a pic from the side of the boat(s) at this speed.
I was out at the dam the other day and saw a 4-5m tinnie trolling around with a very pronounced nose down attitude. Couldn't see what was in the boat, but there was two blokes in it in the rear half, which made me wonder how much weight must be down the front to offset the motor plus the two guys
I suppose a long boat (relative to width) would be somewhat less bouyant at the front?

[Roughasguts]

Thanks cheech & Banshee, bloody hell, so you guy's got foils on your motor or anything like that. I guess you both have 3 bladed props, I wonder if that and the slow idling power setting has any thing to do with it.

Something like the power stroke working better on the down going blade, then a few seconds later the power stroke working better on the up going blade, and that somewhat altering the thrust line when going slow.

Wonder if a 4 bladed prop would do it as much or at all.

[explorer500]

Hi again,

Thanks a lot to everyone for their replies. I had the boat out again on Saturday and experimented with the motor trim and boat speed.

Banshee, I also find that a small pre-correction once you get the feel of the weaving seems to keep it more or less on course.

I did find that if I trimmed my motor up to 6 or 7 on the trim-o-meter (courtesy of Yamaha!) the weaving was noticeably less. I just need to remember to trim down before taking off.

RAG - no foils on the boat - not sure if a 4-blader would be different. I also tried experimenting with the fin anode, with no results.

When I get some time, I'll take some photos of the motor setup from back and side - just to see whether others think it is in the right spot.

Cheers,
Mark.

[MyEscape]

Mark,

I have an identical boat, except a 115 Merc on it, brand new still under 10 hours on it. I haven't had a problem similar to your yet however where we launch from in Gladstone the under 6 knots area is not a long area to travel so perhaps I just haven't noticed it yet.

Nice boat though aren't they.

Steve

[explorer500]

Steve, you are right - they are a great boat!

Makes me want the 6.25 for the extra room, though. Oh well, maybe next year...

Mark

[Daisy]

Hi Mark
Sounds like a classic case of nose walking, goes good on the hop and then gets pushed around at lower speeds weaving back and forth as you compensate as you should. NoelM is on the moneywith more weight astern. As for Roughasguts I reckon less fuel on the way home might be the answer (wild stab in the dark) I hope this helps or I could be full of crap. Let us Know how you go.
Cheers Mick Day

[kingtin]

Never had it happen to me with a rig with an outboard, and I've had 6.

The moment I got the Whittley with the Mercruiser it was a bloody nightmare, snaking all over the place at 6 knots. I figured that stern drives were just oversensitive, I was "oversteering" and I would have put up with it. Now, 18 months later, I manage to steer ok although all the kids and deckie have problems. I figure that 'cause I'm the one who does most of the driving then perhaps I have just subconsciously learned a new skill and that some engines/boats simply behave differently. If it was a fault, or un-natural, then I reckon one wouldn't be able to compensate, unless my brain's as un-natural as my rig

kev