Shaft and Rudder alignment

Bob H. · Post by **Bob H.** » Nov 16th, '12, 18:30

Carl, I was thinking the same thing, Elite marine uses blackfin rudders that hang off the transom, I cant find the pic to see if the shafts are moved back as well. The shafts both being in line or paralell to centerline? How bout changing the toe on the rudders to help merge the thrust and cause the merge & splay like Bruce mentioned. Im going to measure my rudder locations, guess I wont know how it runs till I get her wet...BH

bob lico · Post by **bob lico** » Nov 16th, '12, 19:04

End of shaft to leading edge of rudders 61/2" trust me you can take this to the bank!!!

CaptPatrick · Post by **CaptPatrick** » Nov 16th, '12, 19:15

Bob,

The topic was "Moving the rudders aft"

Image on second page...

Rocket · Post by **Rocket** » Nov 16th, '12, 19:17

Note the anti-cavitation plate on the top of those transom mounted rudders.

JP Dalik · Post by **JP Dalik** » Nov 16th, '12, 21:28

bob lico wrote:End of shaft to leading edge of rudders 61/2" trust me you can take this to the bank!!!

I'm not sure where we are gong here,,, it's confirmed on the OP's boat and another local to me that I have actually tried to steer(with little luck) and couldn't. I see the cavitation plate on top of Carl's and think that may help. With almost half the rudder behind the boat the original design may be failing from blowout on the topside of the rudder and again trying to turn in froth. We are not chasing a ghost here this a real issue. I would bet that if quizzed some other Bahia owners might fess up that rudder reaction vs rudder input is a little light

Tony Meola · Post by **Tony Meola** » Nov 16th, '12, 22:31

JP Dalik wrote: I would bet that if quizzed some other Bahia owners might fess up that rudder reaction vs rudder input is a little light

So the question is, are the Bahia Mar rudders positioned differently on the Bahia Mar than on the Fly Bridge models or is this happening on repowers only when the shafts are redone and maybe cut too short or maybe too long.

Bob H. · Post by **Bob H.** » Nov 18th, '12, 19:04

Thanks Capt Pat thats the shot I had in mind. I checked my rudder position and Ive got 5 1/2" from transom to center of rudder stock. Cant comment on handling due to being stuck in the barn..I hope to heck I dont have this problem..distance from end of shaft is 6 1/2" just enough to clear prop. The angle of the thrust is possibly not hitting enough of the rudder? The transom rudders seem much taller from that pic. BH

Kiffa · Post by **Kiffa** » Nov 19th, '12, 08:39

Neil I am not alone!! Your wake and steering is exactly like mine.
Rocket I measured the distance from the rear of the strut to the stern on the two Sport fish from the 70's along with mine and they are all identical.
I agree with Jp, I don’t think in this case weight distribution has to do with it, and it is more to do with the rudders.
All pictures I have seen of external rudders show them with some sort of cavitation plate, and mine extend beyond the transom.
Bob your rudder location is the same distance as mine. When are you hoping to splash. I think this is the culprit with my boat and I plan on rectifying it sooner rather than later.
Hopefully we can get to the bottom of this before you are ready so you will know how to proceed.
I’ll keep you posted on what I do.

Harry Babb · Post by **Harry Babb** » Nov 19th, '12, 09:51

Of all of the work I did on DeNada.......the steering was the most disappointing.

I removed the Rudder Ports, chucked them in a lathe and took cuts in the ID to "True Up" the worn out of roundness.

I rebedded the Rudder Ports so that they were just slighty off center of the prop shaft.....just so I could remove the shafts without having to drop the rudder.

When rebedding the Ports.....I used a dummy shaft for plumbing the ports in both the fore/aft and the Port/stbd direction.

I made new rudders that I thought would steer better.

My rudder ports are located very close to the Transom and the Tiller Arms extend forward.

At idle she steered.....lets say "Just Ok"........she would steer on one engine if needed

At cruise the steering just did not respond like I expected her to respond.

Until this post I just figured that the problem was unique to me or DeNada......now I know different

Recently I explained to Capt Pat how my steering was hooked up and he tells me that Bertram tried "Something" for just a couple of years.....and "Something" is shown in the pic below. The purpose of this "Something" is to make the inboard rudder turn at a greater angle than the outboard rudder......if I knew the name of this thing I would call it something besides "Something".

Well I have removed this "Steering Yoke" (somehting) and tossed it......then made a single Tie Rodthat will connect both rudders to the cylinder. Now both rudders turn the same at the same angle.......

Hope to launch again next week.....we'll see if it helps

Do any of you guys have one of these "Somethings" on your 31's??

hb

bob lico · Post by **bob lico** » Nov 19th, '12, 10:37

harry do remember when you drove my boat at green port ? i made you do a lock to lock wot. turn---- crazy, no i made every attempt possible to barrel roll that boat making right angle turns at high speed .the chines cut the water and those huge rudders hold her on track up to 40mph. just like a race car on track you test it under control conditions to know how much you can take her in terrible water condition , pending accident ,large floating debris avoidance. i experimented then finally rip all that oem steering out and went with race car steering in 316 stainless . this is tie rod and drag link with ss. roller bearing on tie rod ends.the drag link is directly connected to a Hy- Drive ss. hydraulic cylinder mounted almost directly parallel . zero play positive steering feels european like Bmw,mercedes. the hard part is easy for you. i made the tie rod out of 11/4" ss bar stock with left thread 1/2" on one end and right thread 1/2" internal on opposite end with rollar bearings you remove bolt from cylinder and can turn rudders inwards or outwards real quick and experiment till it is just right .i will give you specs. if you want. i use the county machine shop engine lathe to make the internal threads in bar stock.

Stephan · Post by **Stephan** » Nov 19th, '12, 11:38

Harry and Gentlemen-
Ever since I took my steering apart for service last winter I've been thinking of potential improvements. I was first motivated by the 3/4" of toe on the rudders which I understand keeps them from chattering at lower speeds but strikes me as a tremendous source of drag and stress at higher speed. I'm not all the way there on my opinion as to what to do with the rudders but am curious if what Bertram tried was Ackermann steering...

I believe tiller offsets are not necessarily a bad thing.
Full presentation at: http://hem.bredband.net/b262106/Boat/TSpeer_acker.pdf

JP Dalik · Post by **JP Dalik** » Nov 19th, '12, 14:02

Any of these affected boats have trim tabs? Wonder if the tabs act as a cavitation plate

Neil does not not sure about Harry

3/4 toe is allot we've done 1/2 max

It was funny I re read the pots and saw that the problem goes away when a little tab is applied. Perhaps it does act to condense the thrust over the rudders and not out the top

Kiffa · Post by **Kiffa** » Nov 19th, '12, 14:43

JP the late 60's Express that my cousin had experienced similar issues to mine but not quite as bad. Her rudders were a few inches further forward but not as far as the others. That boat performed much better when tabs were installed directly over the rudders, even when fully retracted.

Vince Luciani · Post by **Vince Luciani** » Nov 19th, '12, 16:32

OK guys I have been meaning to jump in the post for a while. I have a 1968 Sportfisherman model (with optional bulkhead installed) and I have had less than ideal steering since I have had her. My problem is making "sharp" turns (subjective defination of sharp, let's say speeds say above 18 knots or so). Also, the problem seems to be worse turning to starboard than to port. I have tried many things to fix the problem. I did redo the entire steering system (rudder shelves, re-plumbed rudder ports, etc.) and that improved things, but the problem is still there. I can best describe my condition as the rudders losing their bite when I try to make a sharper turn. I am thinking that this is some sort of cavitation problem. THe boat will turn OK to a point and if I try to turn sharper you can actually feel as though the rudder loses its bite and "slips". At the same time this happens I can feel the release of the pressure against the rudder in my hands on the wheel. I know if I try to turn hard into a stiff wind I have a lot of trouble and need to adjust my engine speeds to better make the turn. I have had the most success with putting alot of weight in the back (big heavy guys sitting on transom), but I have not installed any ballast. I don't really want to go that route. My slow speed steering seems fine. I will be following this discussion anxiously to see what is found. I may also possible be able to contribute some anecdotal information to help brainstorm this problem that I now see some others are having. I can't take any measurements of my rudder settup yet because my boat is still in the water.

Vince

Vince Luciani · Post by **Vince Luciani** » Nov 19th, '12, 16:57

No trim tabs on mine.

Sean B · Post by **Sean B** » Nov 19th, '12, 23:51

This thread has me interested mainly because I took some ship's design classes while I was a marine engineering major in college, and amazingly I actually remember some of it.

I think what you're describing is the rudders sucking in air from the trailing edge of the hull. As I recall, the further aft the rudders are, the more this has a tendency to happen. The fast flow of water on all the rudder surfaces has to be contained or the rudders quit working. The boat's hull normally does this, but having rudders so far aft that their trailing edge is behind the transom allows the water flow to escape (up) right where it needs to be contained. Rudders create a lot of forces when you turn them, and that water wants the easiest way out - which is up. Having your water flow escape like this basically means you're also sucking in air to replace it.

I remember all this because I remember the interesting lecture about why an outboard hanging off the back of the boat hull cannot work right configured as a fixed prop + moving rudder. To get good steering from an outboard, the prop itself has to turn.

I believe that the answer may be an extension off the bottom of the hull directly over the rudders. Wide enough trim tabs centered right over the rudders. I don't think the tabs should need to be deployed to keep the rudders working, they just need to be there, and to be wide enough (don't know how wide though).

Carl · Post by **Carl** » Nov 20th, '12, 07:15

Sean, that is some real interesting information.

Tabs act as a cavitation plate...huh.
So slight tab would works, or possibly a cavitation plate brazed to existing rudder or move the whole enchilada forward to clean water may be possible solutions???...ooch... on that last choice.

Harry Babb · Post by **Harry Babb** » Nov 20th, '12, 08:22

Carl wrote: or move the whole enchilada forward to clean water may be possible solutions

Upon reconsideration........I'm GOOD! ! ! !

hb

Carl · Post by **Carl** » Nov 20th, '12, 14:48

Harry Babb wrote: Upon reconsideration........I'm GOOD! ! ! !

hb

Come on Harry, don't you think it's about time you did some work to that boat of yours...

Bob H. · Post by **Bob H.** » Nov 20th, '12, 19:01

Ive found the same info surfing the web on rudder design and position, go fast boats do hang the rudders way off the back but most of the boat is out of the water. I wonder how that bahi mar Elite marine rehabed with those transom rudders performed? Im with harry on moving the rudders forward..OUCH...that was the very first project I completed WAAAAAAAAAAY back when...Ill get used to long slow turns...LOL..BH

JH_B28 · Post by **JH_B28** » Nov 21st, '12, 08:12

I have a friend whose 4 years into his B31 rebuild. Reman 6BTA 370's mounted 6" further aft. His rudders had to be moved to allow the proper spacing between the shaft & rudder. I guess he is going to have the same problem you guys mentioned because most of the rudder area is behind the transom.

Here's a picture I took a couple of weekends ago:

Guess we'll have to wait for a sea trial to know.

Bob H. · Post by **Bob H.** » Nov 21st, '12, 18:47

Ive also found that the rake of the rudder leaning back like in the pic posted by JH above will raise the bow leaning the lower end of the rudder forward towards the bow will lower the nose. In the pic the prop does seem to be "aligned" or the rudder in the thrust wash of the prop. Sea trial will answer all...BH

Capt.Frank · Post by **Capt.Frank** » Nov 21st, '12, 23:07

Why were the struts and rudders moved back?

In Memory Walter K · Post by **In Memory Walter K** » Nov 22nd, '12, 09:54

Good question. Strikes me as a performance problem in the making.

Capt.Frank · Post by **Capt.Frank** » Nov 22nd, '12, 10:54

Ya, The engines shaft angle doesn't look like it was changed much. So I don't understand why you would move the struts back 6-12"?

bob lico · Post by **bob lico** » Nov 22nd, '12, 11:31

Do not put this boat in the water! You completely missed the hold idea of balance versus running gear.number one pull out those shafts that will definitely fail between forward hub of prop and rear of struct.never more than a inch with 370hp.next move rudders back to a point where the leading edge off those very nice rudders are 6" from end off shaft. Promise me ever go hard abound and bend shaft and you make that rudder dead center of shaft for maximum turning ability.completely remove shaft log with just a slot in bottom where shaft log went. Now put tape measure thou struct to output flange off zf gears to 6" off rudder now cut shaft and make new key way in gear end of shaft.. Follow capt. Patrick instruction on new fiberglass shaft log this is a must due to set back of engine. Where ever the shaft log ends up that your angle. Do exactly what I said with no deviationnomatter what and the boat will steer perfectly. Right now that boat will go straight down in the bow no matter what you do even with a elephant sitting on the transom.you cannot " just" push the engine back! The motor must go lower and new shaft angle by way of fog shaft log.

Vince Luciani · Post by **Vince Luciani** » Nov 25th, '12, 20:10

OK guys I pulled the boat today and took some pictures. You can see that my rudders do extend past the transom. Also, my shafts are slightly offset to allow removal without pulling the rudders. This was the stock setup for my boat. Even though I have repowered I made no changes to the running gear except going to 1 ½ inch diameter shafts.

I certainly can understand how it would be easier to cavitate with the rudders extending past the transom. I am now wondering if there is anything that can be done to improve things short of relocating the rudders, shafts, etc. How about anticavitation plate welded onto the top of the rudders?

Kiffa · Post by **Kiffa** » Nov 26th, '12, 08:48

Vince the Express here that had the steering issue put trim tabs directly above the rudders that helped quite a bit even when they were fully retracted.

JH_B28 · Post by **JH_B28** » Nov 26th, '12, 09:41

Capt Frank.: I believe the owner wanted more space in the cabin, so he moved the rear bulkheads 6" to the stern. I don't agree with his decision, but its his boat.

Bob, I'll be sure to give the owner your instructions. I believe that they were still in the alignment phase when i took the picture, so there is nothing permanent yet. Also, those aren't the props that they are going to use. I think they are using them for temporary alignment or something like that. The boat is being done by Jimenez Boatworks here in PR. They have done some pretty good B31's in the past, so I hope they know what they are doing.

Thanks!

George,

JH_B28 · Post by **JH_B28** » Nov 26th, '12, 09:46

Forgot to mention,

I think they reduced the shaft angle to 12 degrees.

jspiezio · Post by **jspiezio** » Nov 26th, '12, 10:13

http://bertram31.com/newbb/viewtopic.ph ... ilit=elite" onclick="window.open(this.href);return false;

There are a few good shots of the transom rudders and running gear on that thread. The boat runs great, super fast, super efficient, and super stable. The entire drive train has been shifted aft and the shaft angle has been reduced as well.

There are traditional trim tabs mounted above the rudders. The pics below show the swim platform installed, this actually helps as a sort of guard, keeping lines away from the rudders and tabs.

http://bertram31.com/newbb/viewtopic.ph ... ilit=elite" onclick="window.open(this.href);return false;

Stephan · Post by **Stephan** » Nov 26th, '12, 16:05

I believe my gear is as delivered from the factory. 1972 FBC with gas engines.
The center of the rudder shaft to the intersection of the transom is approx. 8 inches.
The tip of the prop shaft to the leading edge of the rudder is approximately 9 inches.

I do not have the sort of "flat wake" in the other post above and do not have trim tabs. I believe I have good steering authority.
There are shots at 4:50, 7:00 and 7:30 showing the wake..

Hope this is useful.
Stephan

mike ohlstein · Post by **mike ohlstein** » Nov 26th, '12, 19:22

Nice looking boat.

I know that a lot of people don't do it, but I strongly recommend a safety line on the anchor. If that thing winds up bouncing out of its chock on a nasty day, it'll be in your prop before you notice it.

AndreF · Post by **AndreF** » Nov 26th, '12, 22:21

At the worst possible time..........

Rawleigh · Post by **Rawleigh** » Nov 27th, '12, 09:31

I have two SS eyes screwed to the deck below mine with heavy twine tied to them to tie my anchor down in the chock with. I have never had a problem with that setup, but I am not out in the ocean taking blue water over the bow often either.

Stephan · Post by **Stephan** » Nov 27th, '12, 10:57

mike ohlstein wrote:Nice looking boat.

I know that a lot of people don't do it, but I strongly recommend a safety line on the anchor. If that thing winds up bouncing out of its chock on a nasty day, it'll be in your prop before you notice it.

Thanks for this good advice. I will heed it.

Stephan

Carl · Post by **Carl** » Nov 27th, '12, 15:36

Stephan wrote: Thanks for this good advice. I will heed it.

Stephan

I prefer a Bun-Gee cord over anchor mounted to a low deck clip then tie off line to a cleat.

PeterPalmieri · Post by **PeterPalmieri** » Nov 27th, '12, 21:50

When we redid my bow I wound up not storin the anchor on the deck but I believe perko makes an anchor chock with a screw built into it that secures it in place. I think fortress provides a link from their site to it.

bob lico · Post by **bob lico** » Dec 2nd, '12, 08:39

vince the rudder is radius at the bottom leading edge where you 90% of the thrust is . some day think about purchasing capt. patrick rudders and with your set up every thing else is correct. here is the set up on phoenix .

bob lico · Post by **bob lico** » Dec 3rd, '12, 08:36

Answer to all e- mail -------- yes the entire circumference of each blade is pitched . The radical rake and shape of the blade are obvious . These props drive a 14,250 lbs 31 FBC 39 mph with OEM 315 hp cummins and cruise at 30 knt. All day at 15 percent off the pin.

Vince Luciani · Post by **Vince Luciani** » Dec 3rd, '12, 11:28

Bob,

I can certainly see how there is more rudder below the centerline of the shaft in your setup. It makes sense to me that there should be some rudder suface at that point. I now see that surface area of the rudder alone is not the critical variable. The shape of the rudder is just as important. I guess I need to look into pruchasing some new rudders!

Vince

bob lico · Post by **bob lico** » Dec 4th, '12, 09:19

Vince there will be a dramatic change in low speed stering . Especially convinent in and around docking area,trolling.

Kiffa · Post by **Kiffa** » Dec 19th, '12, 12:06

Hi Everyone,

Well I bit the bullet and pulled back ashore to move the rudders forward!!
It took a day and a half and we hit the water yesterday.
The boat is now a different machine. The real effectiveness of Capt Pat's rudders can now be seen, the boat steers twice as well and I no longer have the problem at any speed.
For the first time in her life my boat now runs the way I am sure Bertram wanted her to run.
If anyone who has this issue on their boat gets a chance to move the ruder forward I recommend doing so.
I left enough clearance between the end of the shaft and the leading edge of my rudder to remove the props, this still left the trailing edge under the hull.

CaptPatrick · Post by **CaptPatrick** » Dec 19th, '12, 12:20

Chris,

Glad to hear that the problem was solved! Hopefully, others will benefit from this exercise...

Rocket · Post by **Rocket** » Dec 19th, '12, 12:49

Fantastic, I am happy for you that the fix worked! What is the distance from the rudder post to the transom now?

Bob H. · Post by **Bob H.** » Dec 19th, '12, 19:30

Chris, Glad to hear ya got it all worked out...bad news for me..Ill take a wait and see approach..gotta get her floating..BH

Kiffa · Post by **Kiffa** » Dec 20th, '12, 07:32

The distance from rudder post to transom is 12".
I agree Bob put her in and try her out first. Makes no sense trying to fix something that may not need fixing in the first place.