Volvo MD7A for CD30

[Murray Glue]

Be not afraid of the MD7A. I have had two vessels for 8 years apiece, one with the MD7A and one with a 2002 fresh water cooled. I think that marine engineers are prone to a mindset about Volvo. But as the man said, if the parts are expensive, isnt it great that they dont give trouble very often.

Murray Glue
CD30 107 Dayspring
Nelson
New Zealand

( alas, to be sold tomorrow..is life worth living after a Cape Dory ??)



murray@offshoretechnical.com

[Larry DeMers]

John,

Oh lordy, I completely forgot that dbl. S.S. sink in the galley acting as a sounding board at various frequencies. Nope..your impression seems most correct sofar..too darn hard to isolate that area for sound reduction, and too expensive for the mediocre results you get back. I suspect it would be a war of inches anyway.
I think we will try some insulation on the step and cockpit floor, as those surfaces seem to resonate at a lower frequency..the former due to it's composition and the later due to it's size and unsupported area in the center..it's like a tympany drum skin in a way. But trying to block it all off is a hopeless task me thinks.

Cheers,

Larry

That's interesting engineering jargon regarding the inversion of sound waves and thus cancelling one another.

I remember when I was a kid how my dad's old Mercedes had a resonator after the muffler way back in 1960 and I even recall seeing them on Rovers back then also. Of course autos have been using them for decades since. I suppose some of these newer marine exhaust "mufflers" would be considered more of a resonator than a muffler since the waterlock is the true muffler. Would one work in your 30 with ill effects? I don't know. Space is at a premium in the 30 hull and where you would locate one to be most effective and yet not obtrusive would be a challenge. Perhaps if one was installed as a goosneck riser at the thruhull then it may work. If you attempt to engineer a quieter exhaust let us know the outcome.

I don't think the compression of that mylar/foam laminated lead sound material would make much of a difference in your case. I assume you aren't talking about completely flattening the entire sheet, just where the equipment mounts. The use of risers under the equipment could certainly work but then you have the engine removal conflict you were concerned about before. Always a compromise on board. Let's face it though, the lead in the sheet is the main shield against penetrating sound. The foam and mylar obviously play a role but not as great as the lead. I would just mount the equipment (pumps, valves and filters) right over the sound shield and not be concerned about flattening it.

I think sound shielding the upper teak step above the engine is certainly a sound idea but then you have to contend with the dual sink basin still acting like an amplifier or you would have to completely cover the basins with shielding and then the nexy concern is what about all that area to port of the basins that runs outboard and then around the back of the oven furniture up to the aft end of the setee. It would almost be impractical to correct those design screw ups without tearing the boat apart. In my opinion any attempts you take to sound shield that engine compartment is going to result in mediocre results at best. Just my wooden nickels worth.

I'm going to leave the "quieting testing" to you. I don't have a problem with the Volvo engine sound level in the CD30 with the Volvo. It is much better than many other engines would be in the boat. It would be nice to have a diesel nearly as quiet as an Atomic 4 for example but I don't think it is possible in the CD30 without a tremendous amount of work and expense. Nothing that I am interested in pursuing that is for sure.

Some folks are more sensitive to a boats engine and exhaust noise than others. Just like a car. It would be interesting to hear what others have to say about sound shielding attempts in their 30's.

I agree with you about the rubber component in engine mounts, whether it be a mount in a car, boat, truck .....you name it. Some marine mounts though are made from polymers and urethanes not rubber and so aren't nearly as affected by those situations you mention regarding rubber.

Good luck with the vibrations and noise. You are right, more sailing less engine. That would be the best sound shielding.

Hi John,

The rubber in the mounts tends to harden over time, and environment, and that allows in a variable that is particular to the location of the boat, and also maintenance habits of the operator. Things like spilled oil accumulating on the rubber will effect it over time. But so will the presence of Ozone or gases if concentrated and the exposure is for a long period.
I am always needling at different aspects of my boat, to improve or understand the aspect. THe noise/vibration is not excessive on DLM, especially now that I am routing the exhaust thru a right-angle exhaust tube into the water after it leaves the thru hull at the transom. That removes the base-beat from the helm area, and makes listening to the radio at normal volumes possible now. But a series muffler in place of the water muffler I added (not the water-lift muffler of course) might be able to provide an inverted resonance to the engine beat, which will cancel it. This is what is used on Honda cars for instance. They use a resonator behind the muffler, which produces a peak due to resonance at some frequency that is likely to be the average operating rpm's frequency, and inverts it. You hear the original beat note as well as the inverted note of the same frequency and they cancel -mostly, leaving quiet. Even the mike on my Standard VHf radio uses active noise cancelation technology (same description as above for mufflers). So the theory is sound (hah!~), but as you wisely mention..that space is not made for this kind of work at all..way too open.

The sound absorbing material I was thinking about would be above the engine and on the sides of the engine, which would absorb much of the radiated sound..leaving that great hole behind the engine to echo it all back to you. One thing I learned years ago building speaker cabinets..it does not take a lot of insulation to effect echos in the cabinet..it just has to be placed in the perfect location to do the absorbing over the frequencies encountered. Bose stereos get tremendous audio from their tiny speakers becasue they have modeled this phenomena, and understand it better than most anyone.
I do think there is progress to be made in quieting our boats engine noise..but there is a lot of testing to undergo to find the right combo of materials and placement.

You are right..with the stuff I have hanging on the starboard wall of the engine room, I have literally no room to spare, and worry that any absortive material I put there will be compressed into insignificance by the stuff mounted there; water filter, two fuel filters (a Racor FG500 water sep/filter with 10micron element, and a Fram Black Beauty water sep/ with 1 micron element), 3 two-way fuel selectors (to steer the fuel to the scrubber or to the engine), and a diesel fuel pump for scrubbing the fuel when needed.
Maybe I should try remounting this stuff on a 1/4 ply that was itself mounted on standoffs, thru the sound deadening material, not compressing that material. ahh, another project.

Tnx for the comments..

Larry

Hi Ya Larry,

You pose some good questions. Regarding the mounts that were used in our CD30's with the MD7B they are a typical generic mount used by many different manufacturers. I'm not certain who the original manufacturer is of those mounts but they are readily available at just about every engine distributor. You can get them mailorder from Hamilton, and I think even Defender sells them and I believe Boat US also carries them in their engine parts stores. I have not seen anyone with the Volvo use a substitute mount. I have seen other mounts used as replacements with other engines. I note one case inparticular where the Vetus Hydro Damper "Mitsteun" mounts were used on a 20HP Yanmar and they made a big difference over the stock Yanmar mount. I've also seen them used on a Westerbeke, Bukh, BMW (Renault)and a couple others but I never witnessed the results obtained on those engines. With that said I've heard only good reports from engine mechanics about their use on the smaller diesels such as what are found in the CD's. Those mounts are a very interesting and unique design and you can find a link to them below. If I were in need of replacing the mounts on my Volvo that is mount I would employ.

Globe makes a nice mount also but the concept is different. They use two different hardnesses of plastic to absorb vibration and movement potential. They are a pretty clean design without that metal *cup* component that is on the generic mounts at the base of the mounting stud. You know the spot that collects all the dirt and moisture and starts to corrode or rust on the original mounts. these Globe mounts have a good reputation but I have never used them.

PYI makes a mount also that is supposed to be pretty good but like the Globe I have never used it. Two other manufacturers are AquaDrive and Treleburg, the later makes a "cushyfloat" mount that you might want to check out. I'm not sure how that works.

I haven't seen the latest Yanmar mount you are refering to. It wouldn't surprise me one bit if it were one of the mounts I've already mentioned. It seems they (engine manufacturers) just source those mounts out, they don't make them. That is why for years different engines all came with similar or exactly the same mounts.

Zeida just replaced the rear mounts on her CD33. She obtained them from the Universal distributor in Miami and they were just a generic mount, nothing unique to Universal. They appear to be the same mount used on the MD7B. Probably made by Sundown or a similar company.

Personaly with the Volvo MD7B in our CD30 I see no need to go to a more cushy mount. The engine is so smooth the way it is I just don't see what could be gained to justify the expense and labor. That heavy flywheel on the Volvos makes a huge difference in why they are so smooth. It puzzles me why you are mentioning vibration with your boat. Of course at certain rpm's there may be an attenuation of a little vibration but nothing that I would consider a problem or annoying for a diesel. Our last boat had a 3GM30 Yanmar and that baby would really shake things up, I hated it, I'm glad it is gone. The Volvos don't even come close to that kind of annoyance.

I imagine the Vetus mount would be helpful in further reducing any existing vibration you may be having based on the results I have witnessed from using them. The caveat being that I don't know if the mounting holes would line up with the bed holes. I've never checked it out with the CD30. I believe they would because of the generic mount used in the CD30.

No I do not think the mounts are too soft. The mounts will only let the engine move so far off centers, period. The Volvo is heavy so it's movement tendency will be less than say a Yanmar, Universal, etc.,. No matter what mount is used any engine is going to experience maximum movement in a fore/aft direction due to forces from the prop. As you know all mounts will allow for this to occur to a degree. I don't know how one would do a comparison to determine that motion allowance in any given mount. Manufacturers of mounts don't make those specs readily available. It's just more of a judgement call based on the mount design. One thing is for certain if a mount is allowed too much lateral flex it is going to seperate or break down. Thinking about that while looking at the design of the Hyro damper mount you can see how the mount can probably withstand more allowance of movement without sustaining damage. No intact mount is going to move so far as to allow misalignment or damages to occur to a drivetrain.

Your muffler question is sure a wide open question. I think only Volvo could answer the back pressure question. I would never make an assumption on whether or not that little engine can handle an additional sound muffler in series with the waterlock. It is common in larger boats but not common in smaller boats. The general design of the additional sound muffler would certainly be the biggest factor. You could probably do it but it would take some careful planning and consultation with Volvo. I don't think the Volvo is that noisey for a diesel. The quieter you can make any diesel the better but is it necessary?

Sure I think there is plenty of room in the engine compartment for a lead sound sheet deadener. I know from your posts you must have a lot of stuff in that engine compartment so perhaps you are too crowded to fit it in but that would be hard to imagine. It compresses a lot under mounted hardware and equipment. I see absolutely no reason why sound deadening material would restrict engine removal. The wood trim around the engine compartment would be far more of an issue and that is not a problem.

You know you have to consider the benefits you can expect from investing in sound deadening material. The problem in the 30 or probably any other model as well is that you would have to also install the material to all the areas under the cockpit as well which could be a miserable task. Even if you did that it is still wide open at the aft end of the hull under the cockpit sole. You would have to close that off also which would truly be miserable work. Then you would still have noise radiating up between the aft galley bulkhead and the bridgedeck riser which would compromise all your efforts. I say leave it all alone. Maybe only add some deadening sheeting to benefit the cabin interior from noise and maybe the icebox from some heat.

Only two tricks Larry and you have addressed them both: sound deadening and mounts. It's just how much you want to invest in $$$ and time to try and gain some improvement. One simple fact.....the boat just wasn't designed to allow good sound proofing. The mounts are an experimental issue but the Vetus is the way I would go. Consider yourself lucky you have the Volvo or these issues would be much worse.

Vetus mount link below:

demers@sgi.com

[Olli Wendelin]

Whats the problem? My engine sounds great when I wear my Mickey Mouse Ears (Sound Suppressors). Easy to install, low cost, and distinctive appearance.

As I recall the Volvo is a two cylinder. My Yanmar YSB12 single cylinder shakes and roars. Not too bad in the cockpit, but the cabin gets a bit loud. Doesn't help that the aft bulkhead isn't actually connected to the deck, there is a 2" air gap with a baffle in front.

Olli Wendelin
BLUE MOON
Charleston, SC



wendelin@spawar.navy.mil