GB 36 rudder authority

[Caballero II]

I have a single screw GB 36, with a Lehman 120 hp. I'm happy with it and do the best I can with the tools at hand, which are what I can do with propeller "walk" and "back and fill" when maneuvering in tight spaces. But, is there a well accepted rudder modification which allows more rudder authority at low speeds while docking, and/or allowing some reverse control? It doesn't matter where I put the rudder in reverse, the boat backs to starboard. "Back and fill" is about all I've got to pivot the boat. I'm looking for a tried and true rudder modification that would improve low speed maneuvering.

 

[SteveK]

The rudders on my twins GB36 were small and only have affect at speeds higher than docking.
Many DIY mods seen over the years, however I do not know of any rudder mods to make a signifcant difference at slow movement. Thrusters?

 

[mvweebles]

There are two possible modifications. A fishtail trailing edge of the rudder; and an articulated rudder.

Schilling rudder - Wikipedia

en.m.wikipedia.org

https://www.passagemaker.com/technical/steve-zimmerman-right-stuff-articulated-rudder-trawler

I don't know whether the GB36 single's rudder would accommodate either or both - requires a skeg.

Thruster would be cheaper and more effective. And would also have a modicum of resale improvement.

Peter

 

[Jaep]

I have a single screw GB 36, with a Lehman 120 hp. I'm happy with it and do the best I can with the tools at hand, which are what I can do with propeller "walk" and "back and fill" when maneuvering in tight spaces. But, is there a well accepted rudder modification which allows more rudder authority at low speeds while docking, and/or allowing some reverse control? It doesn't matter where I put the rudder in reverse, the boat backs to starboard. "Back and fill" is about all I've got to pivot the boat. I'm looking for a tried and true rudder modification that would improve low speed maneuvering.

On my smaller 50’ single screw commercial fishing vessel I made the rudder as large as possible. I also welded a tapered plate both sides on the aft part of the rudder, top to bottom. Not sure of angle, enough so flow would hit it and add more force. I will try to add a pic.

 

[rslifkin]

The biggest thing that will add more rudder authority in reverse is a bigger rudder (most likely requiring beefed up mounting). Chances are, the current rudder will steer some in reverse, but only at higher speeds than you'd want while docking.

To get more than a small improvement there you'd probably be getting up towards a sailboat sized rudder. And the amount of keel a GB36 has will also limit how tightly it'll want to turn with the limited turning force available in reverse (even with a big rudder).

 

[Bmarler]

Different boats will just have different backing characteristics. I have a good friend who says that no matter where the rudder is pointed his boat backs straight. He wishes it backed to one side or the other so he could count on that for docking.
Be careful what you wish for.

 

[Choices]

I have a GB36 single. We have a bow thruster and it makes a tremendous difference. Can't imagine how nice a stern thruster would be.

An articulating rudder would help a lot.

Boat does prop walk but your really need perfect conditions.

 

[Caballero II]

The rudders on my twins GB36 were small and only have affect at speeds higher than docking.
Many DIY mods seen over the years, however I do not know of any rudder mods to make a signifcant difference at slow movement. Thrusters?

You hit it on the head. The tiny rudders on these boat require a fair amount of prop wash to have any authority, too much for docking speeds. I've tried to avoid thrusters (cheaters) because they're not sexy and I hate the way they sound. However, I must admit that they probably are likely the best answer.

 

[CharlieO.]

I can back straight with my wheel turned all the way to port, I can back slightly to starboard with my wheel centered, I can back around a corner to the starboard with my wheel turned all the way to starboard.
No backing to port at all for us.

 

[dhays]

There have been some past threads on this topic, if I have some time I will try searching for them.

I feel your pain. Coming from sailboats that had rudders that actually worked, it was a tough transition to a power boat. The articulating rudders apparently can make a difference at slow speed and I think would be very nice to have.

Articulating rudder 101

I need a lesson on articulating rudders! I saw a boat for sale where the owner claims he spent 7k on it and it works better then a stern thruster?? Can y'all elaborate on this? I'm trying to learn. Never really knew what the pros or cons where on this, for in all my boating years, I never really...

www.trawlerforum.com

 

[Comodave]

Look at SideShift thrusters. They are relatively inexpensive, about $5K, and are simple to install. No holes below the waterline. Ours work very well. We have bow and stern.