rudder improvement on trawler

[tuna888]

I have a 1977 34 CHB single diesel with a cruising speed of 7 knots. I would like to improve the manuvering ability when trying to dock in a confined space. I would rather not add a bow thruster. I currently have an 16in by 22in aluminum rudder with a 4in hole for shaft removal. To improve rudder efficiency would any of the following help or I am looking for any other suggestions.
1. would putting a zinc in the 4in hole help?
2. I have heard that you can add 2 or 3in to the trailing edge of the rudder and also to put a outward flare or angle on the added on 2 or 3 inches to improve slow speed manuverability. any suggestions?

[PAR]

The rudder is likely not the problem, the hull form is and typical of many displacement powerboats. The hull is designed to carry a substantial burden, which requires depth and this is usually arranged with deadrise, which helps the boat's stability and tracking. All great things when moving forward, but a detraction to steering qualities, especially in reverse. You can try making the cord longer on your rudder, but you'll have very limited returns, particularly against the "prop walk" direction.

[FAST FRED]

The usual "cure " to poor low speed manueverability is two pieces of angle iron.

The pieces are bolted too the rudder with the center corners out.

A series of holes are drilled thru the corners which are then bolted on.
The end result is a square on the trailing edge of the rudder , for the length of the rudder.

It does work , although at the cost of a tiny bit of extra drag at cruise.

Interestingly your Auto Pilot will usually work better.

FF

[tuna888]

Thanks to PAR and FAST FRED for your replies.
1. Do you think adding a zinc in the 4 inch shaft removal hole wil help?
2. It sounds like the 90 degree angle iron is similar to my idea of two 3 inch extension pieces of aluminum at a 45 degree angle but not as radical. Does this sound like a good idea?

[KnottyBuoyz]

If you're willing to invest some cash in improving you rudder you might want to look at "articulated" rudders.

http://www.proboat-digital.com/probo...ge=1&doc_id=-1

There are other resources to look at.

http://www.google.ca/search?hl=en&q=...le+Search&meta=

[Gilbert]

Take a look at www.metalmarinepilot.com
Their site has information on powerboat rudder design. If you send them the required information about your boat they will give you specifications on optimizing your settup. No charge.

[tuna888]

thanks for all the replies and I will spend some time reading then decide which way to go!

[Landlubber]

tuna888,

I am still making these boats in China, the rudder is quite efficient, the hull and keel is what makes "rudder response" slow. The hole in the rudder is to allow the shaft to be removed without the removal of the rudder. It will not affect the performance any better if you filled it.

[charmc]

Tuna888,

I tend to agree with PAR's and Landlubber's comments that changes to the rudder will give only incremental improvements in reverse steering. As the owner of several single screw powerboats over the years, from full keel semi displacement to high speed shallow vee planing hull with very small prop and rudder, I was forced to learn about tight quarters maneuvering. Each of my boats had a flying bridge above a trunk cabin, so, like the typical trawler, there was lots of sail surface for the wind to grab. By all means, look into adding surface area to the rudder, any improvement will help. But steering with the rudder in reverse will never be very effective. If you already use the technique I'm describing below, please don't be offended. I've been amazed at how few people know it.

For me, the biggest improvement came when a veteran commercial boatman took pity on me and taught me to "back and fill", after watching me mess up about 11 approaches to a tiny berth one windy day. That's the technique in which you put the helm hard over in the same direction as reverse prop walk and leave it there. In other words, if the boat walks to port in reverse, put the helm hard over to port, so the stern will go to port in reverse and to starboard in forward. You then steer the boat without touching the wheel, using the gear and throttle levers alone, alternating between forward, reverse, and neutral and "goosing" the throttle for just a moment. The goal is to kick the stern right or left without putting way on. You can spin the boat 360 deg in a bit more than a boat length, and back down accurately wherever you point the stern. Once you've practiced enough to get the feel of the boat, even windy days aren't a problem. It took me hours of practice under different conditions to get confident enough to try it in crowded marinas, but it worked. Surprisingly, there doesn't seem to be much written on the subject in articles and books on boat handling. There is one excellent article here: http://www.his.com/~vann/KrgStuff/360turns.htm .

The article gives an excellent description of the steps to the technique and why it works. My only observation is that you will have to discover for your own boat just how hard to goose the throttle before immediately returning to idle. It will vary for each boat, depending on the wind speed and direction, but the principle in the article is right.

Hope this helps.

[Landlubber]

charmc,

Correct in what you are saying. It is amazing to me how few boat owners can control their vessels, i find sail boats the worse really. So few know today how to sail backwards, how to sail off a mooring and many of the techniques we too for granted as kids. I guess it is "messing about in boats" that gives us these skills.
People should do more of it, messing about in boats. Today for some dumb reason, they think that playing back ups is just showing they do not know what they are doing, whereas in actual fact it is showing that you Do know what you are doing.
The trouble is "We do not know what we do not know"

[Frosty]

You know what? I think you know about what people know. I know that I know .
But if you dont know ,then you don't know is very true. I know this. But you know what--I now know what I didnt know when I knew nothing.

If only I knew then what I know now.

Weld a peice of angle iron to the trailing edge of the rudder, or weld a flat plate to the bottom of it. Putting a zinc in the hole will do nothing.

If you want to get flash you could re design the rudder with an airofoil shape. However all these will do nothing for very slow speed manouvering or docking.

Utilising your prop walk is the best you got.