GB 36 rudder authority

[C lectric]

Some folk have used a welded on piece of angle iron to help with control. THe idea is when you start to turn the angle iron forces the water stream to the side more than just the rudder itself.

Others just enlarge the rudder at the aft end to get a better water grip using a flat piece of steel.

There was a design from a few years ago that has a moveable blade at the tip of the rudder for the same effect as above but it was even more powerfull. However I cannot for the life of me remember the name. Maybe more questions here, at the boat yards, and rudder fabricators may jar some memories.

I don't have a G.B. but do have a single engine with a LARGE rudder. Generally I can get the boat almost anywhere but it has taken practice. Use of the wheel , goosing the engine, including slowing/stopping the boat to get it to sharpen the turn.

In my home slip I back further than my own slip . I watch carefully that I don't get to close to the boats on either side of me. Once far enough in I can go forward at idle, turn into my side slip, crank the wheel to get the stern in and then lots of throttle quickly to stop the boat.

Lines are ready for a quick grab. Bow line brought back to the cockpit and clipped with a CAM CLEAT and the tail draped out of the way on the deck. Cam Cleats are used a lot on sailboats to quickly secure or hold ready a line for near instant use.. These are used when we are approaching a dock. Any other time the line may be in the Cam Cleat but are also tied elsewhere to ensure we don't kick it loose.
Take a look around at what others do to help with docking / undocking.

Good Luck

 

[Caballero II]

If the question is how to modify a rudder to have greater "authority" when the boat is moving backwards, I'm having trouble imagining any modification that will have much effect. When moving astern, it doesn't matter whether or not the propellor is turning. There is no prop wash across the rudder. The maximum achievable water flow across the rudder is the velocity of the water moving at the boat's own velocity through the water.

My experience with a single engine GB 36 is that in stock form, with no thruster or gimmicks, it's a handy boat to maneuver. Regardless of rudder position, it backs straight unless you really get some way on in reverse. But that exercise seems unnecessary. In close quarters (where most slow speed maneuvering happens) it's quick and easy to put the rudder hard over in the direction opposite to that you want to aim the stern toward, goose the throttle in forward just long enough to re-orient the stern, and then resume backing toward your destination. (I guess that's the so-called "back and fill" procedure that the OP refers to). A bow thruster can come in handy to reorient the bow while moving slowly in reverse, and I have run a GB 36 so equipped. It makes the boat a total piece of cake to maneuver.

When it comes to the GB 36 rudder, I'd be averse to messing with success.

Blissboat,

I understand a bow thruster would be an effective solution for slow speed maneuvering, but I am trying to avoid employing that solution, at least for now. But I guess I am not making my point clearly enough. The question is not how to achieve greater steering authority when backing. A GB 36 with a left hand propeller backs slightly to starboard when the prop is turning, no matter where the rudder is positioned. I can live with that. The boat does "back and fill" pretty well, and I use that a lot. However, the question is how to achieve better steering authority when moving forward at very slow docking speeds. Please read my post # 28 again. My second question is, does anyone know of a builder with experience with this type of "fishtail" rudder as described by Dave Gerr in his Boat Systems Manual, preferably on the west coast.

 

[Caballero II]

So, maybe a time for a new thread here, so as to discourage creep, and maybe moved to GB section. Does anyone have any information or where to look for the design or installation of a rudder modification to enhance GB 36 low speed turning? Of the 1,000+ GB's built, and given their poor low speed turning ability, it's hard to believe there aren't some rudder mods out there that have been built. Anyone???

 

[Blissboat]

Does anyone have any information or where to look for the design or installation of a rudder modification to enhance GB 36 low speed turning? Of the 1,000+ GB's built, and given their poor low speed turning ability, it's hard to believe there aren't some rudder mods out there that have been built. Anyone???

One last post from me on this, and then I promise to shut up. Your predicate is that Grand Banks produced thousands of boats characterized by poor maneuverability at low speed. I am unable to agree, both from my own experience with a variety of GBs and the experiences shared with me by others. Put differently, I don't accept your predicate.

However, I am willing to take you at your word that your particular GB is hard to maneuver at low speeds. I am reminded of a longtime former TF member (now sadly passed) who had a 40' DeFever with a single 210 hp Cummins. Frustrated by his boat's dissatisfying rudder responsiveness, during haulout he began measuring and comparing its rudder shape and dimensions to those of similar boats, including other DeFevers. It took no time to discover that his particular single-shaft DeFever had been fitted with a rudder intended for twin-shaft DeFevers. IOW, it had always been too small for the boat. Presumably it was a builder's error, and the owner corrected it easily by replacing his rudder with the correct item.

It's hard for me to imagine the "old" American Marine yard making such a boneheaded mistake, but at your next haul out, maybe look into that as a possible reason for your frustration. Whatever you do, good luck. Boat handling should be fun and satisfying.

 

[CharlieO.]

I was also wondering if you have taken a look at how far your rudder swings before hitting the stops.

 

[Caballero II]

One last post from me on this, and then I promise to shut up. Your predicate is that Grand Banks produced thousands of boats characterized by poor maneuverability at low speed. I am unable to agree, both from my own experience with a variety of GBs and the experiences shared with me by others. Put differently, I don't accept your predicate.

However, I am willing to take you at your word that your particular GB is hard to maneuver at low speeds. I am reminded of a longtime former TF member (now sadly passed) who had a 40' DeFever with a single 210 hp Cummins. Frustrated by his boat's dissatisfying rudder responsiveness, during haulout he began measuring and comparing its rudder shape and dimensions to those of similar boats, including other DeFevers. It took no time to discover that his particular single-shaft DeFever had been fitted with a rudder intended for twin-shaft DeFevers. IOW, it had always been too small for the boat. Presumably it was a builder's error, and the owner corrected it easily by replacing his rudder with the correct item.

It's hard for me to imagine the "old" American Marine yard making such a boneheaded mistake, but at your next haul out, maybe look into that as a possible reason for your frustration. Whatever you do, good luck. Boat handling should be fun and satisfying.

Boy, oh Boy, Blissboat. I hope you will keep your promise. I have a stock rudder on the GB 36. It isn't as good as I would like at low speeds, and I have been commercial boating all my life from a very young age, and I am 73 years. What I am saying is at my present location it is not performing as well as I would like given the crosswinds I have and the narrow channel. Don't mistake. I always get it in the slip, and I know the tricks. What I am now asking most specifically is "has anyone done any rudder improvement modifications to make the boat more responsive at minimal docking speeds". Period. I am looking for an improvement, not denigrating the boat. Maybe you could consider accepting that "predicate"?

 

[Caballero II]

I was also wondering if you have taken a look at how far your rudder swings before hitting the stops.

I have not, but it seems to be a standard model quadrant. As I look into this exercise, I will definitely look into that. From my reading, anything much over 35 degrees is not helpful, unless a modification of the rudder has been performed, which might make increase rudder angles useful.

 

[SteveK]

@Caballero II

I do a lot of reading here. I have not come across rudder modifications that made such a difference that others copied, only one here and there. I have seen many with this concern get thrusters. Following their success many follow.​

 

[Caballero II]

@Caballero II

I do a lot of reading here. I have not come across rudder modifications that made such a difference that others copied, only one here and there. I have seen many with this concern get thrusters. Following their success many follow.​

Fair enough. I remain surprised, and Dave Gerr's comments to me on the subject say differently, though I am sure the improvement seen is subjective, and likely in the eye of the beholder. His comments to me would carry a lot more weight, could they be corroborated. That's all I'm looking for here.

 

[rslifkin]

I have not, but it seems to be a standard model quadrant. As I look into this exercise, I will definitely look into that. From my reading, anything much over 35 degrees is not helpful, unless a modification of the rudder has been performed, which might make increase rudder angles useful.

Going past 35 degrees may be helpful in close quarters at low speeds, especially if the rudder has some balance area forward of the rudder post. My factory setup swings about 45 degrees either side and will turn very tightly in forward idle.

Going past 45 degrees or so is unlikely to help as the water would need to change angle too sharply and you might start getting flow deflecting off both sides of the rudder. So to get more effect than you get at about 45 degrees, it's time for either a bigger rudder or one with a modified profile to get more effect (the movable trailing edge flap would help here, as you could have the main rudder turned, say, 40 degrees and then the flap turned 20 degrees beyond that to increase the angle of the water coming off the rudder).