Vibration

[Eric]

Hello all,
I have 76 Newport 28 with a A4, which runs great. The only complaint i would have with my A4 would be the noise, both from the engine itself and from the vibration. I just asumed that it was the nature of the beast until i was aboard similar year and size boat which also has an A4, and i was amazed with how quiet it was, and with the little amount of vibration. I am wondering if there are engine mounts that could be replaced, or any modifications that could be done in efforst to reduce the vibration and/or noise that my A4 produces. I have noticed that the prop (12RH6) is a bit rough on the outer edges of both blades...

Thanks in advance
Eric Morin
Saint John, New Brunswick

[Don Moyer]

Eric,

I'm glad you had the opportunity to observe what many of us keep talking about, which is that one of the best features of the Atomic 4 is its smoothness and very low noise level compared to other power options.

I recommend that you have your prop inspected and repaired as necessary and then check your prop shaft alignment before changing your engine mounts. Many of the earlier Atomic 4 powered boats have rail mounted engines with virtually no vibration dampening quality between the engine and rails, and they are not known to have the kind of vibration you're talking about. While the boat is out of the water, I'd also check the condition of your cutlass bearing. If the cutlass bearing has a lot of clearance, this could create quite a stir in connection with an out-of-balance prop.

If the vibration continues after insuring that the prop and associated drive assembly are OK, you could check the rear thrust bearing for excessive wear by pulling up, down, and side to side on the prop shaft just behind the engine output coupling. In fact, since this would have no cost associated with it, you may want to do this check first, although I have to tell you that we hear of very few thrust bearing failures. They are very rugged for the use they are put to.

Please keep in touch. It's very valuable for the rest of us to hear how these exercises turn out.

Don

[Eric_Morin]

Thanks Don!
Someone did mention to me last spring (when the boat was on the hard) that i didnt have much life left in the cutless. I'll start by replacing the cutless, have my prop repaired, and check shaft alignment. I'll post a note to let you know if the above mentioned helped ( Boat will only be back in the water late May or June).

Thanks again!
EM

[Silver Fox]

Serious Vibration Issue

We also had a serious vibration issue.

The engine was smooth in neutral, including at higher RPM's. The engine was also smooth in reverse. But once put into forward gear, it shuddered the boat so much it would knock the folded main off the boom.

It felt like it would shake the boat apart in a matter of minutes.

So we looked at all the options, and here is a short troubleshooting guide that I used to identify the potential problems (I am somewhat of a newbie, and no artist!!):



(Click here if the image is not showing)

It turned out for us that it was our 2 blade FOLDING PROPELLER. Our boat is a 1974 C&C 27 Mk II, and the prop was worn out so that it would not open smoothly - one blade would open first and that was enough to throw the boat around.

We sent the prop to Martec in California, they said it was beyond fixing due to the electrolysis within, so we bought a new prop from them, and it is like a dream!

When the boat is put into forward now it clunks once as the blades open and then torques perfectly, and has only normal vibration. What a relief!!

Hope this helps someone else out there!
Thanks,
Ralph.

[sastanley]

another martec tip

Ralph,

On boats I do not own but have been sailing on many times, I've experienced similar issues with folding (Martec) props. Occasionally, due to barnacle fouling or age (as parts wear) one blade may not open correctly on its own.

I realize you indicate you had a failing propeller, but if you experience this 'phenomenon' in the future with your new prop, usually putting it into reverse, give it a quick throttle up, and then back into forward (allowing time for the engine speed to come down so as not to damage driveline/reversing gear/forward fingers, etc.. related parts) that will snap both prop blades open.

edit - How do you like the Martec with the A-4? My experiences with Martec folding props on similar sized boats have always been with diesels & reduction drive transmissions. I have a Catalina 30 and it is a cruiser, but I'd like to not have to bother aligning my prop behind the keel to minimize drag! We've had extensive discussions in the area of props on this forum, and I am gathering as much data as possible. I'd really like to go folding for the sailing performance, but do not want to lose any motoring performance (already limited with a 10,500+ lbs. boat) if possible.

[Mark Millbauer]

Ralph,
I hope you don't mind but I wanted to jump in and let you know that I am very pleased with the GORI folding prop on my Cat 27. It backs up fine and has plenty of power in forward. 1700 RPM and she is cruising at hull speed. My little brother has a Cat 30 with a Yanmar diesel and he is very impressed with the speed and power that I get with my A4 and the Gori.

Mark
C27 Solution

[Silver Fox]

Folding Propeller

Hi Guys,

Guess I had better first fill in the rest of my propeller story, since it seems to be an area of interest...

The vibration I had was pretty chronic. It would shudder and shake the boat as soon as the engine was put into forward gear. But if you could ride it out, after around 10-15 seconds it would smooth out to only a fraction of what it was before, as by then, the prop had opened fully.

I should mention the folding prop was NOT geared - so the blades opened and closed independently of each other.

The vibration had been there for years according to the PO, who had been conditioned to accept it.

It was too violent for me to put up with, and I figured it would eventually cause more serious problems (engine mounts, strut, cutlass bearing, etc), so I had to address it.

Our 35 yr old prop was clean, and nothing there caused it not to open correctly. The prop did have a couple of dings on the blades, but unlikely to be the cause of the problem. In talking to Gary over at Martec, he told me about the stops, etc and that they could most likely refurbish it. So I sent the prop off to sunny California for a makeover.

When he tested the prop, Gary said it had excessive electrolysis within - which is not visible on the surface, and the prop looked in good condition on the outside. This electrolysis meant the welds to repair the stops, etc, would not "stick". Thus, it was advisable to replace the prop.

I was adamant that I wanted a 2 blade folding prop, as we mostly sail, and can do quite long trips, and I did not like the thought of dragging a fixed blade prop under the boat. We chose Martec as they seemed to have a very good reputation, and are respected by their peers. (Note: Sounds like Gori props are also a good option from Mark's post above).

So we picked the Martec Mark III Eliptical 2-blade folding prop (not geared).
It is an 11" blade, and I would think the A-4 could handle bigger blades (just my opinion, I'm no expert), but we do not have clearance for anything larger.



We are delighted with the prop. It has great torque in forward, very good cruising speed at lower rpm's, goes in reverse acceptably, and most important to us; it opens and closes perfectly every time!!

I don't remember exactly, but we put down something like $600 on the prop (whereas a fixed prop would only be half that price), so it was not inexpensive, but it was worth it to us.

Hope this is of help,
SF.

[Mark S]

We are delighted with the prop. It has great torque in forward, very good cruising speed at lower rpm's, goes in reverse acceptably, and most important to us; it opens and closes perfectly every time!!

Fox, tell us what is your very good cruising speed and at what RPM you maintain it, and what is your maximum RPM. Some of us with longer and heavier boats would like to increase RPM at cruising speed to make better use of our A4s' horsepower, and changing propellers is seen as a good way to do this.

Mark

[Silver Fox]

Performance

Hi Mark,

We can cruise under engine at 6 knots without too much difficulty. Do not have a rpm display, so can't provide specifics...

We are still experimenting, but have noticed the gains in speed drop off over 6.5 to 6.8 knots, when I have gunned the engine in flat seas. It is quite easy to get to those speeds, but much harder to get anything more. That's what I find, but I'm no expert.

Hope this helps...
Thanks,
Ralph.

[rigspelt]

Ralph, I started a new thread based on your last post here, since it we have a C&C 27 II also (very close to your hull number), and I know others are interested in the prop choice/cruising rpm issue:

http://www.moyermarine.com/forums/showthread.php?t=3642