Alignment seems variable.

[unbusted67]

Motoring down the icw you have a lot of time to listen to your engine and I've noticed that it seems like at times it is more aligned than others without any drastic shifts in boat condition ie groundings, taking on fuel/water, or days of hard sailing. For example yesterday the engine/shaft was bumping around a bit at 2300 rpm, then this morning, smoother than it's ever been at the same rpm, now this afternoon, it's a little rough again. Am I going nuts?


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[a64pilot]

No, your not. And it may be things other than alignment, it may be simple harmonics. Everything has it's own natural resonance frequency sometime it's pretty narrow band, so even if you think your at the exact same RPM, you may be just enough different to get into one of those resonance freqs.
Ever run a multi engine? Remember how very little RPM difference it took for them to sound out of phase?

[GrowleyMonster]

What he said.

It doesn't take much to change the resonant vibration frequency for the hull or a piece of equipment. Simply standing in a different spot can change the vibration or noise level a small amount. Aluminum fuel tanks with flat, unsupported top or sides can contribute a certain feel or sound that varies with fuel level, and water or sewage tanks, too. The wind in the rigging. Reefer cycling on or off. Changing load on the engine by adding or shutting down an electrical load. Alternator belts can oscillate and their resonant frequencies can change due to load, tempersture, etc. If it is minor, it's probably nothing to be concerned about. As for the shaft alignment, you could check that by resting the palm of your hand on it as it turns. If it doesn't displace your hand up and down, you don't have an alignment problem. There is actually considerable wiggle room, literally, for very minor shaft alignment issues in small sailboats.

[zeehag]

yes.
you own a boat.
you are nutzzzzz.
as well as what others have already stated.. is all good.. make sure your stuff is aligned correctly and you are good and no vibration and then go for it.. should be good-- we have these ears that "hallucinate" when we go sailing and motorsailing..... use that to your advantage...

[unbusted67]

I've been driving myself and my wife nuts with this the entire trip. I'm convinced the thing is out of alignment. She says it's just the way engines sound. I've aligned it twice myself and it looks spot on. I don't know. I've checked the cutlass bearing and it looks great. It's hard for me to say if it's really even vibrating that much. It's just bothering me, you know. I am insane. Hahah


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[Cheechako]

One thing to keep in mind.... there were many times when I was going down the ICW that I discovered I was "plowing"..... and the engine sounded different when I was... I discovered it by looking behind me and seeing a plume of stirred up mud in the wash behind the boat!


And Zee is right.... I hear all kinds of funny engine noises from time to time.. and start questioning... "is that a new sound?"... sometime it IS a new sound so pay attention!

Once during a haul out I spent time cleaning up the rusty engine coupling, painted it, new stuffing , everything looked wonderful when I launched. Shortly after that, I started hearing rattling in the engine room. Finally it got really loud. I discovered that those new bolts I put in the coupling had fallen out! (2 of the 4) Lesson learned! NEVER USE NYLOK NUTS ON A COUPLING!

[unbusted67]

Actually as I've discussed in another thread, I think we are really trimmed wrong. Our bow is down and I can't figure out why since I think all of our weight is in the stern.

Could an over pitched prop be contributing? I suspect our prop is over pitched because it is really challenging to reach full rpm. Maybe that is adding to the vibration?


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[zeehag]

Originally Posted by unbusted67

I've been driving myself and my wife nuts with this the entire trip. I'm convinced the thing is out of alignment. She says it's just the way engines sound. I've aligned it twice myself and it looks spot on. I don't know. I've checked the cutlass bearing and it looks great. It's hard for me to say if it's really even vibrating that much. It's just bothering me, you know. I am insane. Hahah


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if your packing gland isnt pissing like 3 crack kids after 4 cases of beer each , then you are still in good alignment.
dont worry about your alignment if your engine mounts are good.
you will hear all kinds of stuff to worry about, even tho it isnt wrong nor bad... we dream up stuff to suit our personal fear needs... you dont want engine to quit in wrong place...
but most of the noises we hear or think we do arent really bad sounds --not until the song drastically changes. you will know that time, and you will have advance warning for the problem as it progresses.
in cars when ye have these thoughts we merely turn radio up louder--is more difficult in boats...
if you feel the glitch with feet on deck, then be concerned.
ears can be misguided if used alone to diagnose problems that have yet to show up. use smell and referrred sensation thru feet to more accurately guide your ears when trying to determine the problem,....and guages

and listen to wifee--she sounds smart... goood lady.

as for prop--you want to record the rpm and boat speed at the rpm and include max rpm and boat speed when you take the info to a prop shop for consultation.


.

[Blue Stocking]

Originally Posted by Cheechako

One thing to keep in mind.... there were many times when I was going down the ICW that I discovered I was "plowing"..... and the engine sounded different when I was... I discovered it by looking behind me and seeing a plume of stirred up mud in the wash behind the boat!


And Zee is right.... I hear all kinds of funny engine noises from time to time.. and start questioning... "is that a new sound?"... sometime it IS a new sound so pay attention!

Once during a haul out I spent time cleaning up the rusty engine coupling, painted it, new stuffing , everything looked wonderful when I launched. Shortly after that, I started hearing rattling in the engine room. Finally it got really loud. I discovered that those new bolts I put in the coupling had fallen out! (2 of the 4) Lesson learned! NEVER USE NYLOK NUTS ON A COUPLING!

2nd that last piece of advice. Saw a fishing boat with twin Kermath diesels, 3 bolt metal-to-metal couplings, figure-eighted 1 pair of couplings, and lifted one of the engines up into the cockpit when the shaft coupling hit the bottom of the boat. Not Pretty.

[unbusted67]

Originally Posted by Cheechako

NEVER USE NYLOK NUTS ON A COUPLING!

Well yeah! The vibration I am referring to is felt through the deck it is slight but feels like an egg beater at higher rpms. This is all made more confusing by the fact that my tac is off as noticed by a mechanic who then was kind enough not to adjust it for me. So maybe I'm just cranking the rpms too high and don't know it. I am up to about 6.5 knots through the water before the vibration starts it's an35 foot boat with a 40hp engine. I've been in boats with bad cutlass bearings and really bad alignment and it's not that bad. But still noticeable. I should mention I've recently aligned it myself and was within .004" when I reattached the coupling. I should also mention I was thoroughly bloody and covered in oil etc.

This summer, a fellow cape who will go unnamed drove over a mooring pennant in a twin screw boat. At which point the twins decided they wanted to be Siamese ripping the strut right out of the bottom of the boat and sinking it! How's that for strut sadness.


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