GB 46 classic - rudder response

[Chris Foster]

We bought our GB 46 Thea about two years ago. We love everything about it but the handling.

She has terrible rudder response. A following sea is miserable, and even routine steering seems a handful.

I just ran a 42 for a day trip a couple of weeks ago, and there was a world of difference. One spoke of wheel turn produced a nice steady turn, and centering the wheel brought her right back to straight. The 46 seems to be all over the place in comparison.

I've done a basic check of the steering system. The rudder position appears to follow the helm as expected.

The rudders seem really small for this size of boat, but I have to believe the 42 is similar, and I can't believe 4 feet of boat should make such a difference.

Only thing that I can even guess at is rudder rigging. Perhaps they are supposed to be set up with a bit of "toe in" or "toe out" (to use an automotive term).

Any guesses if this is the nature of the beast, or is there something else to investigate?

 

[Comodave]

If it is hydraulic steering maybe there is air in the system? Most trawlers don’t handle well in a following sea.

 

[Chris Foster]

Yeah, I thought about air in the system, but I would expect that would give a dead zone where the wheel moves but the rudder position doesn't change. That doesn't seem to be the case.

Yes to the following seas being a handful in any trawler. But I noticed such an extreme difference in the rudder responsiveness in the 42 versus my 46 that I have to believe the 42 would be a lot easier to steer with the waves behind.

So still a mystery.

 

[DavidM]

A little toe out (the trailing edges of the rudders are closer together than the leading edges, will help with the dead spot. But that is a tiny part of your problem.

I suspect you have hydraulic steering, not cable. But in both cases you can speed up the action by moving the hydraulic cylinder (or the cable attachment point) closer to the rudder post.

The other way if it is hydraulic is to replace the helm pump with one that pumps more volume per rotation. That will also speed up the action, probably more so.

How many turns lock to lock is your helm. As I recall two turns is about right.

David

 

[SteveK]

A little toe out (the trailing edges of the rudders are closer together than the leading edges, will help with the dead spot. But that is a tiny part of your problem.

I suspect you have hydraulic steering, not cable. But in both cases you can speed up the action by moving the hydraulic cylinder (or the cable attachment point) closer to the rudder post.

The other way if it is hydraulic is to replace the helm pump with one that pumps more volume per rotation. That will also speed up the action, probably more so.

How many turns lock to lock is your helm. As I recall two turns is about right.

David

David, I know this in the opposite direction. The forward edge is toe in, the trailing is toe out.
So I searched online and actually found that toe out instructions were given to imagine a person sitting on the swim grid facing aft and toes out.

Ackermann’s Angle

 

[La Mer]

We bought our GB 46 Thea about two years ago. We love everything about it but the handling.

She has terrible rudder response. A following sea is miserable, and even routine steering seems a handful.

I just ran a 42 for a day trip a couple of weeks ago, and there was a world of difference. One spoke of wheel turn produced a nice steady turn, and centering the wheel brought her right back to straight. The 46 seems to be all over the place in comparison.

I've done a basic check of the steering system. The rudder position appears to follow the helm as expected.

The rudders seem really small for this size of boat, but I have to believe the 42 is similar, and I can't believe 4 feet of boat should make such a difference.

Only thing that I can even guess at is rudder rigging. Perhaps they are supposed to be set up with a bit of "toe in" or "toe out" (to use an automotive term).

Any guesses if this is the nature of the beast, or is there something else to investigate?

Grand Banks 42 uses a system of sprockets, pulleys, stainless steel cable, and chain for steering , nothing hydraulic there ;


So your rudder is stiff or short to move ; Pretty sure that your steering issue seems to be seizure of one or both of the shafts of your rudders ; The holder corroded and squeezed the bearing tight on the shaft ; behave that progressively it may lock up completely ;


Disconnect the hydraulic pomp then try to move the rudders with a 1 meter tiller arm ;
If a bearing is seized, the rudder will be difficult to move ; there a stuffing box where the shaft enters the hull ; the only way should be to dismantle the shaft , pull it out , clean everything and replace stuffing box ;


This happened to a friend of mine , take a look at the pics

 

[Steve1.0]

Chris, my 46 also seems sluggish to turn. I have cable steering and all works smoothly and as it should. The rudders just seem too small and not very well shaped as far as hydrodynamics. They seem to have an over stretched oval shape, with the trailing edge having the same radius as the leading edge. Not a very effective foil IMO.

I recall a post on the GBOF of a member making new larger rudders of metal to correct this. I've been kicking that idea around as well.

 

[IWAB]

GB Rudder Size

I’ve often questioned my rudder size on my 79’ EU GB. Recently I viewed on an old website reference to “GB approved larger SS rudders”. Has anyone else ever seen this information? How to get design etc.?

The photo is the larger GB rudder. Will try to attach my current rudder size.

 

[hmason]

If you have Capillano hydraulic steering (which was the case on my GB 46) there is an adjustment knob just below the helm wheel shaft. IIRC tightening the knob decreases the turns lock to lock. The best I could get was 3 1/2 turns lock to lock.

 

[DennisB1]

Chris
Do you have a picture side view of your rudders and prop (w/dia) it would help understand your rudder/steering.

I have a GB49 classic 1990 which has grease fitting in each rudder shaft housing.

Boat steers reasonable well with both engines operational. Rudders are too small for easy steering with one engine. At idle speed it is both rudders, engine or bow thruster to make tight turns. I will try to load a side view of my rudders this evening.

Dennis

 

[Pete Meisinger]

It seems like you will have to get your boat up on the hard to actually watch the rudder action while someone works the wheel. Your rudders may actually be pointed in opposing directions causing you to have to oversteer.

You don't see it much anymore but on a lot of older boats you could see rudder modifications just walking a boat yard. Often on working or commercial boats.

One final point, or question. Do you feel your load is pretty evenly distributed fore to aft? If you have a lot of extra weight in the bow it can contribute to lots of steerage issues. A simple test is to see if you are plowing a lot of water at cruising speed.

pete

 

[North Baltic sea]

Chris
Do you have a picture side view of your rudders and prop (w/dia) it would help understand your rudder/steering.

I have a GB49 classic 1990 which has grease fitting in each rudder shaft housing.

Boat steers reasonable well with both engines operational. Rudders are too small for easy steering with one engine. At idle speed it is both rudders, engine or bow thruster to make tight turns. I will try to load a side view of my rudders this evening.

Dennis

Hi, remember you have twins to give you the power to turn tight without a bow thruster.

 

[sunchaser]

Chris
The Northwest Exploration group out of Bellingham are quite familiar with GBs. I'd guess every issue known to have arisen on GBs they've dealt with. Although they may be busy cruising in AK it would still be worthwhile to stop in and start a dialogue.

 

[Choices]

The Copano helm has knob under it. Turning the knob increases pump flow per revolution.

It can get pretty sensitive. I like it, some don't. Makes docking a single a little easier.

 

[Steve1.0]

Hi, remember you have twins to give you the power to turn tight without a bow thruster.

And thank goodness for them. I guess thats why on the single screw boat the rudder resembles a barn door.
It's not a mechanical issue.
More speed thru the water (if safe) helps with following seas.