stabilizers on a 55c

[Paul45c]

Here's a question for your MY guys, since I'm pretty sure I've got the only 55 convertible in captivity with Naiads.

I've painfully refit about every square inch of my '82 55c over the course of about a year and a half -- I mean EVERYTHING. Of course, the running gear got lots of attention from me and I used the same top-tier outfit I used on my old 45c with sterling results (that boat never had a HINT of vibration at any running speeds -- absolutely butter smooth). This one has some noticeable vibration, and I've been chasing my tail on that as well as trying to get it to make its full 2300 rpms. I guess my question is what stabs might have to bear on this problem.

I researched it and found that the boat had originally shipped with 30"x28" Mich Whl 3-blades. The current 12v71 TIs that I have were the basic 650hp models when they shipped. I have the 130 size M15 injectors that my mechanic estimates probably puts me more around 775 hp or thereabouts now.

I've probably reduced (no kidding!) somewhere close to 600 lb. of junk wire that went to nowhere. I have no idea what the POs did with all of it, but it's gone. There were old xducers that weren't used any longer and they and their fairing blocks were removed, thereby streamlining the bottom...including an early-80s Furuno monster ducer about the size of a Manhattan Yellow Pages book. I've never seen a fairing block like it -- it was like an upsdide-down rowboat under the stbd side motor. I'm talking 5 1/2' long by about 2' wide and made of solid teak. There were fairing wedges, I'll call them, placed just ahead of all the direct overboard head thru-hulls in the bow that were designed to create suction, I guess. More streamlining. All-in-all, the bottom's a lot cleaner, now.

While the boat was hauled, the bores through the struts and log were laser-sighted and shown to be dead on. The shafts went out to be proved and trued, and of course the props were tuned. The props were a nightmare of almost infinitely varying pitch and even blade area. They've been brought down to 26.5" pitch from their original 28", and I'm still somewhere around 100 rpms low...only getting 2200.

I've played around with running the stabs in the off position and their centering pins plugged in, running them active, running them on and electronically centered, and running them off and not pinned -- just freely floating in the slipstream. No matter what I do, there's always some amount of vibration (though it does seem to vary at least a little depending on the variables mentioned immediately above). In talking with a local hydraulic shop that's a Naiad installer/servicer, they told me to first run it pinned and off to see if that would make a difference. It seems that gives me my fastest running speeds and rpms, but not much better than having them on and electronically centered...maybe 15 rpms. They next said it was very important to measure the leading and trailing edges of the fins in relation to the keel when they're pinned. It's apparently got to be identical. Both sides measured out to being within 1/4" from the fwd and aft measurements on the fins.

Is there such a thing as a boat that is just not compatible with them? Could they have been installed wrong? Is there something else to check on them?

And, I guess before I got to more trouble running these issues down, what do you suppose my speed penalty with them is? Some have suggested somewhere around 2 kts. on a boat like mine that should cruise along easily at about 20 kts. If it's that much, I'd have to seriously consider dumping them, especially if they make the water flow aft turbulent and cause me other probs in the bargain. My wheels are about 15' aft of the fins.

Sorry to bog you all down in all this data!

 

[SKYCHENEY]

Paul,
I have 4.5 sq ft fins on my boat as does the 60C up here. He has no problems with vibration or reaching max rpms and neither do I. I do, however, get some cavitation in a following sea when running at hull speed.

I had my fins off this winter to put new seals in. When I put them back on, I measured from the keel to the leading and trailing edges as you described. Mine are both almost identical from side to side, but the trailing edges are slightly closer to the keel than the leading edges by maybe 1/4-3/8". I have been told that this pretty much follows the natural flow of the water and they should be setup with a slight toe for that reason.

If you want more info on the 60C with stabilizers, send a PM to Airpilot.

 

[captddis]

Paul,
I remember a 55C that had stabilizers that interupted the water flow to the intakes and would throw a slug of air into the props. I take care of a 61My that has Naiads. I hate using then as when it is rough and the fins are working hard they will cause violent cavitation that causes the whole boat to shudder. Can't say if it is your problem or not but something to consider.
Did you go to 1 piece shafts? PS m15 injectors are comparable to 9215s and put out 115cc.

 

[SKYCHENEY]

I get that cavitation and shudder that Dave describes, but only in a very rough following sea. The first time I heard it, I thought I had a loose strut or some major problem. I had every hatch open and was running around with a flashlight looking for a loose rudder or who knows what. Once I figured out what was going on, I just turned the stabs to center. That seems to work best in a following sea anyway.

 

[Airpilot]

My 60C is very smooth at cruise with 650 hp 12-71s. I make full power and always carry a phototac to verify max rpm. I took the boat out last week with Sky in the engine room and made 2330 0n the starboard motor and 2316 on the port motor. This test was done with 1550 gallons of fuel and 500 gallons of water ie I was as heavy as possible. Mark

 

[Nonchalant1]

Have you checked your rudder toe-in? When you are running and can feel some vibration, go open up the rudder control area and listen and look at your rudder arms and cross-arm for small traces of that vibration. I am wondering if incorrect rudder angle (vs each other) could cause some vibration.

Doug Shuman

 

[saltshaker]

Have you checked your rudder toe-in? When you are running and can feel some vibration, go open up the rudder control area and listen and look at your rudder arms and cross-arm for small traces of that vibration. I am wondering if incorrect rudder angle (vs each other) could cause some vibration.

Doug Shuman

Yes it can. I would also check the rudder cutlass bearings and the triangle rudder table bearing for excessive play.

 

[Paul45c]

Wow, lots of good feedback. Thanks, all.

Dave, yes I've gotten that kind of cavitation before -- it would disturb enough water around the port intake that it would overheat that engine very suddenly. We were running brief WOT trials with the mechanic and running gear people on board when suddenly it would disturb flow enough and cause the main engine to suck on a bubble. At that speed, temp would rise really quickly. Never got a real overheat because we were quick enough.

In answer to another question, the cutless bearings in all the struts and rudders were replaced, as were the bushings on the rudder shelf. The posts were inspected and everything repacked w/GFO when we hauled a few months ago. I don't observe any vibration back there from anything connected to rudders.

As to toe-in, I'd asked the running gear people to double check what the yardbirds were doing with reinstalling the rudders with the right toe-in, and wherever they ended up, they all seemed to agree on it being right.

Can anybody say what the speed penalty should be on a convertible like this? Or positive effect it might have on my rpms if I were to dump them?

 

[doc g]

What size are the fins , in square feet ?? I've heard of a few different sizes 4.5, 6.0 and 9.0 . Maybe you could go with a smaller fin and get less drag and cavitation problems .As far as speed penalty ; Naiad says a knot , I've heard more like 2 Kn on the faster boats. Maybe someone put big fins on it to run trawler like speeds and now you are trying to run her like a sporty should be run . I assume that less drag = more rpm also........Pat

 

[Brian Degulis]

What your describing is hydronamics in the flow of water to the props and it's very hard to track down. We,ve had problems like this on large tugs and there are companies that will set up a diver with a weighted platform on the sea floor and actually take a video of what's happening when the boats underway. That's not going to be practical here. I think I would figure out a way to remove just the stabilizer fins and try running it. At least then you will know if they are causing the problem.

You can also ask around try to get some feedback from other owners. The problem with that is always the prospective of the individual. What's vibration to one might be normal operation to another.

Dave our 61 cavitates in a bad following sea with the stabs working or centered. A while back we were returning from Key West with a nasty following sea. One of the boats we were with took a video of us running in it. It was easy to see why there's cavitation depending of which way the bow falls down into the trough the opposite stern quarter at times leaves the water.

Brian

 

[captddis]

Brian,
In the cases I experienced, the cavitation went away when the stabs were centered. Maybe you were in rougher water?

 

[Brian Degulis]

Yes definetly a nasty following sea. In moderate following sea or head sea there is no cavitation with stabs on or centered no diffrence at all. The only diffrence I've ever seen is about a 1/2 Kt reduction in speed when they're working hard. But I think the added stability you get makes for better control and I bet that makes up for the lost speed cause it's easier to stay on course.

Brian

 

[SKYCHENEY]

I like the idea of just pulling the fins and retesting. The fins come off easily as they are just held onto the tapered shaft with one bolt.

I can tell you that the 60C that Airpilot runs has zero vibration. It is very smooth but he only has the 4 1/2 sq ft fins.

 

[Ross Macdonald]

For what it's worth we have a 60 C EB and have the 650 HP 12 V 71s. We have 9 sq. ft. fins and we don't seem to have any vibration. They cost about a knot or two at the top end, but the boat is slow anyway. We are in the middle of a 3,000 mile trip from San Diego to Ixtapa and back and the stabilizers have really made for a smoother ride. In big following seas down the outside of Baja the boat would track fairly straight, but with the amt. of weight up high with the enclosed bridge, we prefer to leave the stabs on. Hope this helps. When we make the long bash uphill from Cabo San Lucas to San Diego the stabs don't affect performance. Having said all this, we always travel at 10-11 knots. Ross

 

[Paul45c]

Interesting. I just got back from a seatrial with the local installer here in Lauderdale. First, he didn't see any problem at all with the function of the units, so that's ruled out. FWIW, he didn't seem to feel I had any excessive vibration, either. Maybe I'm just fussy.

BUT...he was absolutely amazed that I had the 6 1/2 sq. ft fins on my 55. Depending on how much I care about stability at very slow trolling speeds, he suggests I can even do the 3 or 3 1/2 sq. ft. fins and get very satisfactory performance. He says there's also no question that they'll have much less effect on water flow under the boat and going back to the wheels. At the most he'd suggest the 4 1/2 fins, but not the ones I have. His chart told him that's more what you'd put on a 75' + vessel.

Anyway, he's checking with Naiad directly tomorrow, so we'll know their firm recommendation. His book told him that the small 3 1/2's are good for cruising speeds 18 kts. and above, so that should be right where I live. I like the idea of a smaller fin. The boat's plenty stable with all that beam and keel, anyway, and it's not a MY...I'd sooner trade perhaps a little stabilization for more speed and rpms any day.

I'll let you all know what I learn.

 

[SKYCHENEY]

I'd say go with the 4 1/2 sq ft fins. That 60C of Airpilots has that size and it seems to perform well. He does have a bit more roll at hull speed than I do, but they work great when cruising on plane.

I also have the 4 1/2 sq ft fins, but my boat is shorter, has less beam, and a higher center of gravity than either the 55C or the 60C. So, for me, that size fins works well at all speeds.

 

[Ross Macdonald]

Great point on fin size. When we looked at other 60 C EB boats before buying this one 7 yrs. ago, there were some without fins and we did the same thing and spec'd out putting in Naiads. Our dealer in San Diego said the boat should have 5 sq. ft. fins. But the PO of our boat, for some reason, got talked into 9 sq. ft. We also don't (and wish I did) have Naiads. The PO installed Wesmars and we had an unbelieveable number of problems with them and very poor factory tech support. We were lucky to find an independent guy in our area who, after about 4k solved all the problems. I would definitely go with Naiads. Cost a bit more but well worth it. I've also found that if we slow to 7-8 kts. the fins don't work as well as about 10-11 kts. All of this though is a non issue with the new technology on fin reaction time..ross

 

[Paul45c]

The Naiad installer came back with some info for me. First, like what was said here, he recommends just taking the fins off in the water. He's going to lend me the puller, and yes, he says it's quite easy. That will hopefully be very telling in terms of running dynamics.

The Naiad factory rep he spoke to recommends the 4 1/2 sq. ft fins. They say on my boat that it should reach full stabilization at around 11.5 kts with that size. With the 3's, it doesn't reach full until around 19 kts.

That's quite a difference. There's also some difference in cost. I was BLOWN AWAY by costs on these darned fins. $2200 ea. for the 3's, $3200 for the 4 1/2's!

I'm going to guess that this installer's answer would be that it wouldn't matter materially, but I'm wondering if any of you would have a good guess as to what speed penalty I'd suffer going with the 4 1/2's vs. the 3's. I honestly care more about speed and efficiency than stabilization. It's luxury enough having stabs at all on a sportfish, by my reckoning.

 

[REBrueckner]

Speed comments:

"what speed penalty I'd suffer going with the 4 1/2's vs. the 3's. I honestly care more about speed and efficiency than stabilization."

If you currently incur a 2 knot estimated speed penality with your current 6.5 fins, I'd take the ratio of fin areas for a smaller size and estimate a speed change using that as an increase in speed indicator. The only better estimate would be actual trial run data from Niad on a similar hull at similar speeds. As a further refinement, check the change in speed w/o any fins at all on your own boat and use that in your estimate.

4.5/6.5 is about 0.7 so maybe you'd get back 30% of your two knot loss; 3/6.5 is about .5 so maybe you'd pick up 50% or so of two knots or maybe one knot...

From your original post:

It's incomprehensible to me that you added about 250 HP (total, both engines), had to reduce prop pitch and are still under rated RPM. Was a tower added after delivery by Hatteras?? Perhaps owners who have boats close to yours will comment, but I'd expect that 250 HP to have increased your speed about a knot, maybe at most two, maybe RPM by a hundred or so.
Is it possible your bottom is water soaked? (sorry to bring THAT up!!)
Did you verify the original speed and RPM with Hatteras??

That means any speed increase from the larger injectors was likely offset by the drag of the big Niads.

Also, several years ago there was a thread here on Sam's about calculating speed changes on Hatts with changes in HP. There were a number of examples posted which would enable you to calculate an approximate speed change related to your increase in HP and compare that my guess of 1 to 2 knots. Anybody keep a refernce to that thread it??

Found one to get you started: http://www.samsmarine.com/forums/showthread.php?t=2555&highlight=speed+change

Also, you did not say your props were actually computer scanned. I assume that has been done; if not, it might reveal a flaw in the traditional prop tuning you had done. Such scanning might give you a small improvement in speed...maybe 1% or 2%. (Anyone have typical data ??) Locally here in NY my mechanic has had props returned after regular refit,not computer scanning, and after exhaustive checks with continued vibration, returned them to find they were NOT correctly set up. That should NOT happen with computer scanning IF its done right.

Fairing blocks: With the exception of the one monster you mentioned, I doubt fairing blocks would make any difference in speed. Removing the ones forward of intakes could possibly change turbulance a tiny bit, but not enough to make any difference. Keep in mind Ray Hunt type planing boats used running strakes for many years and that area is many,many times what you faced.

I assume all your engine mounts are ok?

When I bought my 1972 48 YF, 8V71TI's, some years ago, I noticed a bit of vibration: by running one engine underway at higher RPM, maybe 1500 to 1800 RPM, with the other engine in neutral, it was immediately apparent it was my stbd engine causing the vibration...turned out the back of the engine alignment was low relative to the shaft....maybe you can isolate whatever you feel to port vs starboard...if not, it's NOT an engine drive train issue.

 

[Paul45c]

Rob, thanks for all you put into that post. I appreciate it.

The side which generated the most vibrations was stbd, and prior to alignment, the coupler/shaft was found to be too low. That was adjusted and rechecked in the water. In the process of doing that, the mounts were all gone over, and in some places some bolts and shims replaced/adjusted. As recent as a month and a half ago it was dial-indicated while I was watching. You also don't preceive any hop at all in the shafts when the boat is trucking along.

We once again checked everything connected to rudders while the boat was doing a fast cruise just last week, and nothing was vibrating back there. I didn't think it would after the work done on rudders.

My prop guy does a totally manual process where he scribes them and lays them out by hand in a really painstaking method. The running gear subcontractor that referred him to me originally years ago explained that his is the only true way of getting the right setup from root to tip and everything in between. When I explained that maybe we should send these wheels out to another shop he told me I'd just be wasting my time, and that the shops reliant on computer methods just compare root and tip measurements and anything variable or out in between likely wouldn't even get picked up. He also said that they don't do any hammer work, but rather just turn the root of the blade red-hot and do a quick tool bend. It's quick production work and it's fine if you're not too fussy, is what I was told. It's not S2 conditioning. I'm no prop guy and don't want to be, but I've heard too many locals in the boat industry around here say that if High Seas said to use this guy on props, use that guy. They know what they're talking about.

With all that being said, if it didn't do pretty much the same thing with 2 completely different sets of wheels, I think I'd still spend the money and have another shop look at the wheels, but there you have it. And this same combo of High Seas and Preferred Propeller had my old 45c dialed PERFECTLY. Not a hint of any vibration at any speed. I used to get comments on it regularly by inboard boaters that knew what to look for.

I've got one fin off and once I've got a good high tide tomorrow AM I hope to have the other off. That should tell me plenty. Tell you what, you end up standing on that cheater bar every bit as much as you do on a prop nut! I was using a 4 footer, and I was happy for every inch. It's just tough to get any decent leverage in 6' depth when doing it.

I'll let you all know how the 1st check ride w/no fins goes. I'm hoping for smooth sailing and lots of rpms. It makes sense -- these 6 1/2's are some big honking fins.