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Old 02-27-2013, 08:47 PM   #1
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Rudder Size

We have a 1978 Marine Trader 36. The helm is very slow to respond and then I end up overcorrecting. Even the autopilot has a little trouble keeping a straight course with no zigzaging. I went for a swim today and took a look at the rudder. I measured it. It is 350 square inches which is 2.4 square feet. That seems really small for this size of boat. Anyone know how this compares with your boat?
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Old 02-27-2013, 09:24 PM   #2
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Greetings,
Mr. Ready. I can't for the life of me remember how big the rudders are on MT's I've seen out of the water but a thought comes to mind. Is your steering system tight? Meaning, if you have the chain and rod system, is there any slack in the chains or any slop in the rod/gear joint? If hydraulic, forget I asked...
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Old 02-27-2013, 09:33 PM   #3
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Quote:
Originally Posted by READY2GO View Post
It is 350 square inches which is 2.4 square feet. That seems really small for this size of boat. Anyone know how this compares with your boat?
The stock rudder on my 38' boat is 24" X 16" - 384 sq in.

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Old 02-27-2013, 09:35 PM   #4
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Originally Posted by READY2GO View Post
We have a 1978 Marine Trader 36. The helm is very slow to respond and then I end up overcorrecting. Even the autopilot has a little trouble keeping a straight course with no zigzaging. I went for a swim today and took a look at the rudder. I measured it. It is 350 square inches which is 2.4 square feet. That seems really small for this size of boat. Anyone know how this compares with your boat?
I have a totally different boat that operates both at 7 and 15 knotts. That having been said was very unhappy with rudder response. My prop is 22" in diameter. I built a bigger rudder with better balance that yeilded fantastic results. The twin screw guys around me are amazed with how well it maneuvers. Can even actually back the boat in a straight line with some rudder correction (no small feat for a single screw). My new rudder is 24" x 16.50".

FYI, balance refers to how much rudder is in front of the rudder post as to how much is behind. The more balanced it is, the less effort it takes to turn the rudder under way. My boat doesn't have hydraulic steering, so it makes a big difference. Can now steer the boat underway with a couple of fingers on the wheel.

What is the diameter of your prop?

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Old 02-27-2013, 09:49 PM   #5
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Our steering is hydraulic.
Prop is 23" diameter.
The rudder is 25" tall, 16" long at the top and tappers down to 12" at the bottom. All corners are rounded. It has a hole in it to remove the drive shaft. It appears to be made of 1/4" steel plate. The leading edge of the rudder is about 6" behind the prop. No underwater camera, so no pics.
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Old 02-27-2013, 09:55 PM   #6
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Windmist,
Your rudder is not much larger than mine. How responsive is your steering?
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Old 02-27-2013, 10:08 PM   #7
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Originally Posted by READY2GO View Post
Our steering is hydraulic.
Prop is 23" diameter.
The rudder is 25" tall, 16" long at the top and tappers down to 12" at the bottom. All corners are rounded. It has a hole in it to remove the drive shaft. It appears to be made of 1/4" steel plate. The leading edge of the rudder is about 6" behind the prop. No underwater camera, so no pics.
Hmm, that should be big enough. Might want to check to see if you have any air in your hydraulic steering system.

Have someone turn the wheel from hard over port to hard over starboard and back several times without stopping. If you watch the rudder arm, there shouldn't be any real lag when it changes direction.

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Old 02-27-2013, 11:50 PM   #8
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READY2GO,
This is another one of those times when size matters. Our original rudder on our Willard is large and the steering performance is excellent. We can steer w almost no fwd way and in reverse at 1.5 knots or so. When quartering following seas we have plenty of rudder authority ... enough so that not much deflection is necessary to maintain a reasonably straight course.
So generally speaking if your rudder performance isn't satisfactory just increasing the rudder size will almost always help. However one must have the mechanical authority and strength to handle the increase in size.
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Old 02-28-2013, 05:59 AM   #9
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You may be cruising at a lower speed than the NA contemplated.

IF the steering system is 100% a very simple cure is to modify the ruidder.

1 1/2inch 90deg SS "angle iron" can be bolted to the trailing edge of the rudder to improve low speed steering.

The angle iron is drilled thru the 90deg corners and mounted to create a diamond when bolted in place.

Works great and is low cost low risk modification. Wood works as well.

WE use this on our 50 ft Navy Launch as Unkle Sammy thought 12 GPH at 12K was fine ,

we prefer -3 GPH at 7K till the diesel drops to under $2. a gallon again.
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Old 02-28-2013, 07:38 AM   #10
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Hey Mike...

We had a long discussion regarding this very thing a couple of years ago. Like many, if not all, Taiwanese trawlers of that era, the rudder is insanely small compared to nicer ones like Krogen's and Eagle's. We had my rudder lengthened the first year we owned our boat (1" forward... 4" aft). While it helped the slow speed maneuvering, the cruising speed control showed little improvement.

Recently JD was onboard with me as we delivered our boat to the yard. He was convinced the hydraulic steering needed bleeding. He was right. I now have better control of the steering, but she still wants to wander around the river quite easily. It's just the way it's going to be. In calm conditions, I can get her to stay on a straight course with my hands off the wheel for a minute or two. But whether it's current (not much in the Neuse), wind, or something else, she will eventually find her own way.

The helm is still slow. No two ways about it. I use a simple rule: If you can see the adjustment you make, you've gone too far. It's just something I have gotten used to.

Here is the thread from 2010 I started about it: Boating Straight

Hope it helps.
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Old 02-28-2013, 09:56 AM   #11
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FF is right on here as these semi-disp trawlers will go well over hull speed as semi-disp hulls do and can even go faster w more power. Above hull speed a big rudder causes too much drag and since these boats have the hull lines to go faster smaller rudders are appropriate. And the tendency for builders, owners and even NAs at times to over power the small rudders seem even more appropriate. But when the semi-disp trawler is run as slow as a FD hull then the rudders are too small. Since the rudders are designed for higher speeds, stress and loads increasing the size should not overpower the rudders as long as FD speeds are maintained.
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Old 02-28-2013, 12:03 PM   #12
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Quote:
Originally Posted by READY2GO View Post
We have a 1978 Marine Trader 36. The helm is very slow to respond and then I end up overcorrecting. Even the autopilot has a little trouble keeping a straight course with no zigzaging. I went for a swim today and took a look at the rudder. I measured it. It is 350 square inches which is 2.4 square feet. That seems really small for this size of boat. Anyone know how this compares with your boat?
Are you talking "play" in the helm or unresponsiveness under way?
There was a ton of play in my MT steering system due to loose connections and a rotten pillow block with rusted out bolts. Never could get my steering cables to stay tight until a surveyor caught it.
There are a ton of connections in.these systems and they all contribute to the generally sloppy helm response. Luckily they go so slow that you have time to correct.
It takes about 3 to 5 seconds for these boats to respond so if it can't wait then don't bother correcting.
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Old 02-28-2013, 03:07 PM   #13
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Thanks all for your replies.

Thanks Tom for the link to the other thread. I read the entire thread and one thing stands out to me. If I turn the wheel hard to one side and hold it, after a few seconds it will turn a little more and keep turning in little increments. It will never stop and stay stopped. Does this mean there is an internal valve leaking somewhere?
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Old 02-28-2013, 03:32 PM   #14
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Greetings,
"It will never stop and stay stopped." Ahhh....the plot thickens.
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Old 02-28-2013, 03:36 PM   #15
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Thanks all for your replies.

Thanks Tom for the link to the other thread. I read the entire thread and one thing stands out to me. If I turn the wheel hard to one side and hold it, after a few seconds it will turn a little more and keep turning in little increments. It will never stop and stay stopped. Does this mean there is an internal valve leaking somewhere?
Nope. You have air in your hydraulic steering. I talked to Teleflex last month. They told me that when the air is out, the steering has a definite end to the turning.
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Old 02-28-2013, 03:42 PM   #16
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Greetings,
Mr. T. GOOD information! This may also firm up the steering as well then?
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Old 02-28-2013, 06:57 PM   #17
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The rudder on my 40' Marine Trader is 18" front to rear and 29" high. 4 inches of the 18 are in front of the rudder post. I have a 26"d by 19"p prop. It is tender, you must have a steady hand not to over correct.
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Old 02-28-2013, 09:20 PM   #18
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By far the best general-purpose reference for this type of question is The Nature of Boats by Dave Gerr. For a semi-displacement hull, his formula is 0.045 * Waterline Length * Hull Draft (not including keel).

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Old 02-28-2013, 11:34 PM   #19
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Nope. You have air in your hydraulic steering. I talked to Teleflex last month. They told me that when the air is out, the steering has a definite end to the turning.
I totally agree with TOM.B's statement & suspect that many owners think they have all the air out but they really don't!

When I bought my boat 6.5 years ago, the steering was so sloppy that the owner (very nervous) came down in his price so much it almost scared me off. He acknowledged the steering problem and stated he had made many attempts to bleed the system. When I ask him how he did it, he pulled an eye dropper out of a drawer and said that he fills through the fitting that's In front of the helm while turning the helm from side to side. (Obviously thinking that the system bleeds itself if a continuous supply of steering fluid is available.) Of course, he was dead wrong! We were on the sea trial when the steering problem became apparent and after his explanation I told him not to worry about it as I would correct it.

After the official closing of the deal, I contacted SeaTec Marine in San Diego and Craig Lamb (Owner) sent his mechanic (Wade) to my slip to have a look. Wade attached 2 pieces of clear tubing to opposite sides of the hydraulic ram, removed the filler plug at the helm and mounted an open bottle of steering fluid, upside down, at the helm filler port. (He had cobbled up a fitment just for this purpose that he gave to me. ) He instructed me to turn the helm from stop to stop while he cracked the bleeder screws (one on each side) at the ram. We did this procedure for about 5 minutes per side, until only clear fluid ran into the bucket and there were no bubbles apparent in the clear tubing. He tightend the bleeder screws, checked the operation of the helm against the rudder indicator, shook my hand and left. That was 6.5 years ago and I haven't had a problem since. Wade has fixed a windlass & bow thruster problem since then and they have stayed fixed.

There is absolutely no substitute for knowledge and I have found that doing business with SeaTec Marine is money well spent. I have no monetary interest in the company...I'm just a happy customer.
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Old 03-01-2013, 12:19 AM   #20
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When I put hydraulic steering on Willy I plumbed it to be basically self bleeding. The Hoses ran fwd from the slave cylinder at the rudder and down about 18". Any air from the low spot (about 2.5' fwd of the slave cylinder) would readily migrate to the cylinder and could be bleed off. Fwd of the low spot the hoses gradually rose all the way to the helm pump. Nowhere from the low spot to the helm is there any flat spot or down turning to the hoses. Any air in the fwd part of the plumbing gradually migrates to the helm pump. There's a short hose above the helm pump that serves as a surge tank and bleeder vent.

I bled some air after installation and a few bubbles a few weeks later and haven't seen a bubble since. That's been 7 years ago.

I have a large slave cylinder and a Capilano pump. The hoses are large dia industrial (orange) hoses usually used on front end loaders ect. The system has performed flawlessly and there's been no change in fluid level. When I get Willy dialed in on a straight course my steering corrections when it's calm amounts to 1/8 to 1/4" at the helm. Don't know what air in the lines feels like.
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