37 Sedan- Considering LARGER rudders, thoughts?

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Red5
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37 Sedan- Considering LARGER rudders, thoughts?

Postby Red5 » Tue May 01, 2018 1:42 pm

So I have to change out my port side rudder. Pulling the boat later this week. Changing a couple of through hull fittings, cleaning, new bottom paint, anodes etc. May end up changing both rudders and wanted your opinions.

I drive many 32 foot Marinetes and they feel like Sports cars compared to my 37. My boat is a bit different as I have twin 3208's. But since removing my gen set and going with much smaller fuel tanks I don't draw near as much depth as I used to. But yet still I can barely get out of the marina using just rudders (with both motors running).

I'm very good at driving boats, I've had a Lot of experience. But if I lose one motor I am screwed as far as being able to get into and out of the marina. I've tried many tricks and it doesn't have enough rudder for maneuvering at slow speeds.

My buddy has a 32. We lose a motor often. It's no big deal at all. Just a slight inconvenience.

I want to be able to steer this thing on rudders. How big of a rudder do I need to build? Guessing that I need to keep a certain % of leading edge to trailing edge. Has anyone tried going with a larger rudder on their 37'? Did it help?
37 Sedan Twin CAT 3208's "Under Way is the Only Way".

EWRice
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Re: 37 Sedan- Considering LARGER rudders, thoughts?

Postby EWRice » Tue May 01, 2018 8:08 pm

There are at least 4 boats (not Marinettes) at my marina that have rudder extensions on them for just that reason. My suggestion is look at other boats in your size range with similar draft, deadrise and prop size and see what size rudders they run. You may be surprised what you find. It has always amazed me how many hardware combinations boats can have in the same size range.

You are also correct about keeping the correct ratios of leading and trailing blade area. And if you do add area, add more to the top then the bottom so you don't overstress the stock and log.

Since I have never seen an BigM bigger than 32 out of the water, I would love to know how big your rudders actually are.

Are your 3208s TA or NA?
Good luck!
Muskegon Lake
1972 32' Express flybridge
"AL13"
Twin 318s
On board air & prime 920
1963 Thompson Super Sea Lancer
Graymarine 327
1961 Alumacraft 12'
'55 10hp Johnson

javalin390
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Re: 37 Sedan- Considering LARGER rudders, thoughts?

Postby javalin390 » Tue May 01, 2018 9:27 pm

This subject opens a lot of interesting questions. Was she originally equipped with Cat's? Or was it repowered? If so, were the props specifically designed for the 3208's? Mine is a 37 Sedan with 360 Mopars, it steers beautifully at idle (both engines running) comes up on plane easily, and goes pretty fast (32-38 knots). Torque and horsepower characteristics between gas & diesels are like night and day, thus having the correct pitch on the props is crucial. Might want to talk to one of those shops that specialize in props. Case in point: when I was a kid my father bought a 28 foot fiberglass cabin cruiser with a Merc small block Chevy. She was slow, would never get up on plane and consumed gas in GPM (gallons per minute!!!) After a couple years of this he consulted a prop shop, switched to a higher pitch. Top speed went from 28 to 40 and fuel consumption was nearly cut in half. Dad was just blown away at the difference. Prop pitch determines how much water is pushed rearward in relation as how much is simply slung out the sides centrifugally, at a given RPM. I have a tendency to think you may have a prop issue, not a rudder issue.
Jim Elias
1974 37' SedanFlybridge
Twin 360 Chryslers.
Marblehead, Ohio

Red5
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Re: 37 Sedan- Considering LARGER rudders, thoughts?

Postby Red5 » Tue May 01, 2018 9:47 pm

EWRice wrote:There are at least 4 boats (not Marinettes) at my marina that have rudder extensions on them for just that reason. My suggestion is look at other boats in your size range with similar draft, deadrise and prop size and see what size rudders they run. You may be surprised what you find. It has always amazed me how many hardware combinations boats can have in the same size range.

You are also correct about keeping the correct ratios of leading and trailing blade area. And if you do add area, add more to the top then the bottom so you don't overstress the stock and log.

Since I have never seen an BigM bigger than 32 out of the water, I would love to know how big your rudders actually are.

Are your 3208s TA or NA?
Good luck!



My 3208s are NA the 210 HP models. They weigh a lot and have massive amounts of TQ. Good on fuel. And they are tough motors.
37 Sedan Twin CAT 3208's "Under Way is the Only Way".

Red5
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Re: 37 Sedan- Considering LARGER rudders, thoughts?

Postby Red5 » Tue May 01, 2018 9:52 pm

javalin390 wrote:This subject opens a lot of interesting questions. Was she originally equipped with Cat's? Or was it repowered? If so, were the props specifically designed for the 3208's? Mine is a 37 Sedan with 360 Mopars, it steers beautifully at idle (both engines running) comes up on plane easily, and goes pretty fast (32-38 knots). Torque and horsepower characteristics between gas & diesels are like night and day, thus having the correct pitch on the props is crucial. Might want to talk to one of those shops that specialize in props. Case in point: when I was a kid my father bought a 28 foot fiberglass cabin cruiser with a Merc small block Chevy. She was slow, would never get up on plane and consumed gas in GPM (gallons per minute!!!) After a couple years of this he consulted a prop shop, switched to a higher pitch. Top speed went from 28 to 40 and fuel consumption was nearly cut in half. Dad was just blown away at the difference. Prop pitch determines how much water is pushed rearward in relation as how much is simply slung out the sides centrifugally, at a given RPM. I have a tendency to think you may have a prop issue, not a rudder issue.



The boat never hit the water as a gas boat. Went from the factory straight to Whayne Supply where she was fitted with her power plants. I agree that this may also be a prop pitch/diameter issues but I feel that the size/ratio of the rudders have more to do with it than anything else.

32-38 KNOTS is FLYING! Wow! I spend most of my time going about 6-7 knots, just above idle. This way I average about 3.2 MPG. :)

I've owned the boat (and or family) since about 1986. I've had a Lot of variation when dealing with prop sizes and types. Pretty sure that I am dealing with inadequate rudders. (but I could be wrong)
37 Sedan Twin CAT 3208's "Under Way is the Only Way".

EWRice
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Re: 37 Sedan- Considering LARGER rudders, thoughts?

Postby EWRice » Wed May 02, 2018 11:31 am

First off, I can close my eyes and hear the sweet sound of those Cat V8s idling. Makes me smile. I bet they fire and idle quicker than you can let off the key.

As far as the prop affecting steering, you would have to substantially increase diameter to affect steering. Almost to the point of longer struts and steeper shaft angle. If this was done from the factory and they used the same size rudders as the gas engines, then I can see where this could be a problem. Pitch should have little affect on steering, only thrust at a given shaft rpm.
What size props are you running?
Muskegon Lake
1972 32' Express flybridge
"AL13"
Twin 318s
On board air & prime 920
1963 Thompson Super Sea Lancer
Graymarine 327
1961 Alumacraft 12'
'55 10hp Johnson

Red5
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Re: 37 Sedan- Considering LARGER rudders, thoughts?

Postby Red5 » Fri May 04, 2018 11:55 pm

EWRice wrote:First off, I can close my eyes and hear the sweet sound of those Cat V8s idling. Makes me smile. I bet they fire and idle quicker than you can let off the key.

As far as the prop affecting steering, you would have to substantially increase diameter to affect steering. Almost to the point of longer struts and steeper shaft angle. If this was done from the factory and they used the same size rudders as the gas engines, then I can see where this could be a problem. Pitch should have little affect on steering, only thrust at a given shaft rpm.
What size props are you running?



They do sound sweet. And you are also correct in that they fire up immediately. Even in the cold months.

I run a 1 3/8 shaft and I currently run 19 / 21 three blades (My spare set of props) I also have 20 / 19 Nibral DQX 4 blades. (One of them :roll: )

I've tried many different prop sizes and I am telling you all that this is a rudder issue.

I found a 37 aft cabin that is being parted out. How the heck do you get to the rudders in that thing? The stern was full of water so i didn't mess with it much.
37 Sedan Twin CAT 3208's "Under Way is the Only Way".

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Re: 37 Sedan- Considering LARGER rudders, thoughts?

Postby Fastjeff » Sat May 05, 2018 7:34 am

IF you build large rudders, which I think is a good idea, be sure to copy and enlarge the shape of the present ones.

The amount of metal on each side of the post determines the balance and is CRITICAL to proper steering feel.

Jeff
"We live at the bottom of an ocean of air, not at the top." General Marvage Slatington

Red5
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Re: 37 Sedan- Considering LARGER rudders, thoughts?

Postby Red5 » Mon May 07, 2018 8:09 pm

Fastjeff wrote:IF you build large rudders, which I think is a good idea, be sure to copy and enlarge the shape of the present ones.

The amount of metal on each side of the post determines the balance and is CRITICAL to proper steering feel.

Jeff



Jeff,

I am very glad that you remain active on this board. You always give good advice. Thank you.

Roger Brown was nice enough to upload a design of rudders for his 37. But the design goes against what you just said. I've spent my day beating my rudder with various sized hammers and trying to get that arm off of the rudder. I'm close, but my puller quit working right as I got it almost off. Left it soaking in penetrating oil over night.

Once the rudder comes out I will be able to tell if it is something that is savable or a definite replacement. If I have to design a new one I'm wondering if I would have to do both? This is not a fast boat. And the starboard rudder seems just fine.

My goal is to be able to steer the boat on one motor. I agree that the amount added to the leading edge and the trailing edge has to be in proportion to one another but I don't know if the should be equal. Seems to me the if the widest part of the existing rudder was 11 1/2 with only 2 3/4 on the leading edge that one would use that same ration when adding to the existing rudder.
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37 Sedan Twin CAT 3208's "Under Way is the Only Way".

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Busia
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Re: 37 Sedan- Considering LARGER rudders, thoughts?

Postby Busia » Mon May 07, 2018 11:18 pm

The balanced rudder takes most of the work out of steering. If it was not balanced (like some early airplanes were built) you have to do all the work, and the rudder would want to go back to center. What you want to do is keep the ratio of the area's the same. So much in front of the centerline to so much behind the centerline. I would not change only one rudder. That would make it handle differently depending which engine was running.
BUSIA
located in Ketchikan, Alaska. Gods country
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