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Thick steel vibration damper on the 23 Lancer in 1973 and 74

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Paul P
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Thick steel vibration damper on the 23 Lancer in 1973 and 74

Post by Paul P » Tue Mar 13, 2012 5:57 pm

Hi guys,

We think we've decided through a rather unscientific referse engeering discussion, that the very heavy (38 pound) thick steel plate found overlapping the strut support in an unsupported manner is, in fact, a vibration damper intended to deal with the harmonics generated by the prop pocket on this boat. Harmonics can cut steel or bring down a bridge, and I dare say it can cause a shaft to have a conchoidal fracture between the prop and the strut bearing too. I think CC designed this boat and discovered they had some vibration issues, and the "fix" was to leave the hull shape alone and bolt on a 3/4" thick steel plate that extends in an unsupported "tuning fork" manner about a foot on each side of the keel, held down by the four bolts securing the strut itself. There seems to be no other logic why in the heck that plate is there, and now we have found 5 or 6 boats of 1973 and 1974 that have this remedial engineering feature. Chris Smith told me one day they had problems with noise, but I think the noise was more than an inconvenience, I think the high frequency vibration could have been an engineering issue that had to be solved to avoid shaft failure. Comments anyone? Am I totally all wet on this one?

Regards,

Paul
1956 17' CC Sportsman, 300-hp
1957 17' CC Sportsman, 95-hp
1966 20' CC fiberglass Sea Skiff, 210-hp+
1973 23' CC Lancer inboard project, 427/375-hp.
1966 38' CC Commander Express, 427/300-hp(2)

So many boats.........so little time.....but what a way to go!!

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Paul P
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Here are photos of the steel plate

Post by Paul P » Tue Mar 13, 2012 6:09 pm

Here are two photos one from Glenn Feilhauer and the other from Jerry Namken, both avid Chris Craft boaters of the highest order, and a photo from my own 23 Lancer project boat.

Image

Image

Image

You can see from the first and second photos, the plate is unsupported on the ends, and only fastened with the 4 bolts holding the strut. That is some serious vibration being dampened, this plate weighs thirty eight pounds!

regards,

Paul
1956 17' CC Sportsman, 300-hp
1957 17' CC Sportsman, 95-hp
1966 20' CC fiberglass Sea Skiff, 210-hp+
1973 23' CC Lancer inboard project, 427/375-hp.
1966 38' CC Commander Express, 427/300-hp(2)

So many boats.........so little time.....but what a way to go!!

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mfine
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Post by mfine » Tue Mar 13, 2012 6:34 pm

Well the obvious test would be to take it off and see what happens. I would probably do this on someone else's boat however. In warm water. Close to shore. With a quality life jacket on.

FWIW, I don't think that is going to be an effective "vibration dampener" but what all that added mass will probably do is change the resonance frequency outside of the problematic band. A hunk of steel like that wont absorb much vibration and it looks pretty thick to be counting on it to flex. I am sure the shape and material was simply a quick and cheap way to add 38 lbs to the system.

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Paul P
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Post by Paul P » Tue Mar 13, 2012 7:53 pm

Hi Matt, don't ever underestimate the sub micron world. When I was doing first time research on the
Vanderbilt University FEL (Free Electron Laser) facility, we found out that a 60 cycle motor would cause a concrete slab to conform to a sine wave, but only if you could see it in microns. The beam we were working with had a moment arm of 3 microns at 100-feet allowing it to cut the Vanderbilt logo out of a single human cell (of 19 microns). They cut steel with high frequency vibration, and I think we're talking more about metal fatigue than actual "felt" vibration as in a Drivesaver device. It is more up on the higher frequency sound range, rather than the low bass you hear with the gangster speakers in cars these days, way beyond what is felt. Notice how each end is unsupported. The steel has no logical function other than to be sized specifically for a particular harmonic. That's my story and I'm sticking to it.

You know I DO have friends, right?

Image

It will be "interesting" to see how this unfolds, someone has to know for sure.

regards,

Paul
1956 17' CC Sportsman, 300-hp
1957 17' CC Sportsman, 95-hp
1966 20' CC fiberglass Sea Skiff, 210-hp+
1973 23' CC Lancer inboard project, 427/375-hp.
1966 38' CC Commander Express, 427/300-hp(2)

So many boats.........so little time.....but what a way to go!!

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quitchabitchin
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Post by quitchabitchin » Tue Mar 13, 2012 8:04 pm

He is the most interesting man in the world...
FLASH1969 Chris Craft Cavalier Ski-230 HP 327Q

CCABC Board of Directors Member

Wood Commander
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Post by Wood Commander » Tue Mar 13, 2012 8:09 pm

Pretty interesting. What are the powerplants in each boat? Is your boat equipped with a 427 Ford and V-Drive?

I've always found it odd that on Chevy/Chris Craft "Q" engines, (and many other successful marine engines) the factory harmonic balancers were eliminated when the crankshaft snouts were mounted directly to the drive mechanisms without these dampners. I was always told that the theory was that the prop shaft and prop running in the water was thought to be able to telegraph and handle the harmonics for these engines in marine use.

Also, I know that on cruisers, in around 1956 or so, Chris Craft started adding a third layer of thicker inner planking in the area of several frames forward of the transom, possibly for vibration and other issues.
Bret

1953 35' Commander "Adonis III"

1970 23' lancer project

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quitchabitchin
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Post by quitchabitchin » Tue Mar 13, 2012 8:14 pm

The most interesting thing to me is that both of these boats have mufflers.
FLASH1969 Chris Craft Cavalier Ski-230 HP 327Q

CCABC Board of Directors Member

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Paul P
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Post by Paul P » Wed Mar 14, 2012 7:56 am

quitchabitchin wrote:The most interesting thing to me is that both of these boats have mufflers.
The rubber mufflers are the ones that came on my project boat, note how the pipes leading from the motor are bigger than the ones going through the transom. When the decision was made to repower this boat with a 427 motor those pipes were changed to 4" diameter through the transom and no mufflers. Back to the harmonic tuning fork situation, having a couple rubber water filled mufflers sitting on the harmonic device would probably render it ineffective.



You know.........I don't often go boating in a Lancer, but when I do......I take along a 38 pound steel plate. Stay thirsty my friends.

regards,
Paul
1956 17' CC Sportsman, 300-hp
1957 17' CC Sportsman, 95-hp
1966 20' CC fiberglass Sea Skiff, 210-hp+
1973 23' CC Lancer inboard project, 427/375-hp.
1966 38' CC Commander Express, 427/300-hp(2)

So many boats.........so little time.....but what a way to go!!

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Paul P
Posts: 622
Joined: Mon Oct 30, 2006 1:48 pm
Location: Nashville, Tennessee, Cumberland River and Lake system
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Post by Paul P » Wed Mar 14, 2012 8:17 am

Wood Commander wrote:Pretty interesting. What are the powerplants in each boat? Is your boat equipped with a 427 Ford and V-Drive?

I've always found it odd that on Chevy/Chris Craft "Q" engines, (and many other successful marine engines) the factory harmonic balancers were eliminated when the crankshaft snouts were mounted directly to the drive mechanisms without these dampners. I was always told that the theory was that the prop shaft and prop running in the water was thought to be able to telegraph and handle the harmonics for these engines in marine use.

Also, I know that on cruisers, in around 1956 or so, Chris Craft started adding a third layer of thicker inner planking in the area of several frames forward of the transom, possibly for vibration and other issues.
The flywheel forward 283 setup (now deceptively a 327 block with high performance cam and intake) on my 1956 17' Sportsman has no harmonic balancer. They just did without. The 427 motors are internally balanced, but the other motors in the FE engine series such as the 428 are externally balanced.

The particular 23 Lancer I am working on came without a motor and I happened to have a pair of 427 motors sitting in my shop. Upon looking at things closely I decided to shed off as much iron as I could to lighten the motor which I did, and now it weighs about the same as a small block Chevy. The heavy brass circulation pump was removed, 80 pound iron intake was swapped for a 25 pound Performer RPM, the iron exhaust logs and risers were replaced with aluminum. The sea water pump now cools everything in similar manner to the INTERCEPTOR version of this same motor as used in Century boats. Here is a photo of the engine being prepped, as you can see I rather strayed from original details on this one.

Image

The installation is in a standard inboard 23 Lancer. Power is "over 300".

Back to the steel plate: I plan to keep the steel damper plate but since the prop is much higher pitched to work with the extra power we'll just have to see how it goes with the vibration harmonics. Maybe I can get someone from NASA who is no longer working on a moon or shuttle project to figure out what thickness and length the new piece of steel needs to be!

Regards,

Paul
1956 17' CC Sportsman, 300-hp
1957 17' CC Sportsman, 95-hp
1966 20' CC fiberglass Sea Skiff, 210-hp+
1973 23' CC Lancer inboard project, 427/375-hp.
1966 38' CC Commander Express, 427/300-hp(2)

So many boats.........so little time.....but what a way to go!!

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mfine
Posts: 1405
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Location: Pittsford and Penn Yan NY

Post by mfine » Wed Mar 14, 2012 9:27 am

I stand by my analysis. That steel is there for added mass, not its own harmonic vibration properties. The frequency that the "wings" would vibrate at would require more precision in mounting to make sure you got wave cancellation and not reinforcement and the effective frequency band would be extremely narrow. On the other hand, as added mass to the system, there is little need for precision. Just bolt it in place, the resonant frequency of that portion of the hull changes dramatically, no matter how much hull to hull variation there is, and there is far more inertial resistance to any flexing. Voila, problem solved with a big hunk of stock steel and four bolts.

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Paul P
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Post by Paul P » Wed Mar 14, 2012 12:59 pm

I think we're actually saying the same thing. What does mass do?

Otherwise if we're not saying the same thing, then we're saying something different and I take issue with it, whatever it is, lol.

best,

Paul
1956 17' CC Sportsman, 300-hp
1957 17' CC Sportsman, 95-hp
1966 20' CC fiberglass Sea Skiff, 210-hp+
1973 23' CC Lancer inboard project, 427/375-hp.
1966 38' CC Commander Express, 427/300-hp(2)

So many boats.........so little time.....but what a way to go!!

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