Engine sound insulation

[kevin barber]

Anyone tackled this project?  If so, what insulation did you use, and what areas of the compartment did you cover.  I have been looking at the SPM tiles from sailors solitions..

Not a bad deal for $149,  but what kind of a differnce will it make?

//http://www.sailorssolutions.com/index.asp?page=ProductDetails&Item=SPM18

[Dale Tanski]

Kevin,
Yes and no... but here are a few things to think about.
I have been working on this problem since the moment I heard the engine run, but there is more than meets the ear. There are several problems with reducing the sound levels on a P365, and there is no out of the box solution that will do much of anything.  
First off there are two objectives that I have been addressing.  One is the sound down below deck and the second is the noise you hear in the cockpit while underway. There are several areas that need to be addressed.  For one, the engine does not sit in an enclosed area, and each opening will pipe the sound somewhere else.  There is a huge opening to each of the cockpit lockers and under the cockpit floor, and there is the large opening to the bilge area.  All of these need to be closed off.    I installed an insulated  "firewall" when I replaced my fuel tank, so I have eliminated the migration of sound to under the cockpit floor.  I am working on enclosing each side where my firewall meets the rear bulkhead to close off the cockpit lockers.  I have found that the underside of the bridge deck also needs to be insulated as it acts as a drum transferring sound into the cockpit.  I have made much progress in reducing noise to the cockpit.
The interior problem greatly relies on properly sealing and insulating the engine "box".  Minimizing the noise that is transferred to the cabin via any opening is the goal.  The bilge area is the most difficult to accomplish.  The requirement for the drive shaft makes the bilge section a nightmare.  Installing multiple insulated baffles that the sound must go up and around, only to run into another baffle will help there. This key to solving the problem is just a matter of patients and constant improvements, stopping the transfer of sound where ever it can escape.  The idea is to enclose the sound in an insulated box and let the insulation absorb the noise.  As a side note, as you improve the enclosure around the engine, it is important to ensure proper air flow into and out of the box for proper engine operation and removal of heat.  You may have to add an additional or larger ventilation blower.
This leads us to one last problem... vibration.  The entire boats structure transfers the engine vibrations.  Any panel, bulkhead or surface that is light enough, acts like a loudspeaker and converts the vibration into sound when it vibrates.  Even the standing rigging sings when the engine is running.  This vibration problem will probably be the biggest one to reduce.  I have been looking into better engine mounts to minimize vibration to the main stringers.  This would be the biggest upgrade and yield the most improvement in transferred vibration.
I hope some of this makes sense and helps in your quest for silence.
Dale Tanski

[SV THIRD DAY]

I helps a lot Dale....It moves my Engine Sound lowering project down on my "wish list"....I just have too many other things to worry about that "sound" easier to deal with.

Thanks

[Richard]

Hi Kevin

I have been looking into this.  Seems that part of the noise or vibration on my boat is the engine, and the other part is the drive train.  I have a Westerbeke 40.  To look into this further, I contacted Soundown, that sells insulation.  

http://www.soundown.com

Problem is that the engine compartment would be difficult to really isolate or insulate because of the hoses, etc. going into the forward end of the compartment, and the area under the floorboards (where you access the engine from inside the cabin) would also be tricky.  Not sure how to insulate those areas.  Otherwise, we could just use the lead foam type material that Soundown sells and attach it to the engine side boards and maybe put another board aft of the engine and mount insulation on it too.  Attach under the cockpit floor too, I suppose.

I replaced my engine mounts a few years ago, hoping that this would improve things.  No difference, though someone said I may have used mounts that were too heavy duty.  There are so-called soft mounts, but someone said once that the angle our engines are mounted at precludes this type of mount.  That was probably not true, but I have not checked further.

The other issue is vibration from the drive train.  I have a two-blade prop, and I am told this can create more vibration that a three blade, and also may cause "whip" in the long prop shaft we have.   This may suggest that a mid-shaft bearing is needed.  I replaced my strut and shaft last year, but it did not seem to change the vibration.  A worn cutlass bearing can also cause a problem.  I was very careful with the alignment to the v-drive (prop shaft to v-drive).  If this is off by even a little bit, it can cause vibration.  Someone said that the tolerance (gap between the flanges) should be two thousandths or less!  I think the manual allows three thousandths.

I know I have a problem somewhere because I see the v-drive moving a bit (vibrating) when under power.

This is all I have worked out so far.  I think it would be good to find an expert in drive trains and get them to have them look at things when under power to see where the problems might be, and what the most effective approach would be to reducing the noise and vibration.  My boat is pretty noisy!  Having someone who knows what they are doing look at it might save just spending money on expensive or time consuming fixes that don't work.

What are your thoughts?

[Dale Tanski]

Richard,
The movement of the V-Drive is most likely caused by a bent prop shaft.  The 365 is a problem to pick up as the aft strap tends to get hung on the prop, strut or comes to rest on the shaft itself.  It is difficult to get a stiff strap to slip between the prop blades and the hull.  I would check your shaft carefully.
Dale Tanski

[Randy]

I too would like to reduce engine noise. If you "box in" don't you also reduce air flow and possibly raise engine operating temps?

[Richard]

Thanks for the suggestion about the bent shaft.  However, I would be very surprised if it is bent.  I replaced the original bronze shaft with a new stainless one and must assume that it was straight when new.  The yard that launched the boat afterwards is very careful about placement of the aft lifting strap.

It is possible, of course.  I will check it next time I am at the boat.

However, I have also heard that a two-blade prop can cause whip in the shaft.

As for boxing in the engine, I would think that the water cooling would be the main source of heat dissipation, no matter how hot the air is around the engine (within reason).  But many boats have enclosed engine compartments and blower fans presumable remove the heat and supply fresh air.  I would have to check with a mechanic on my assumptions!

[Dale Tanski]

Richard,

I am in agreement on the heat buildup in an enclosed box statement.  As long as you have adequate air in and out via the ventilation blower system, temperature should not be a problem.  When I get to that point I will consider installing a smaller blower to supply air.

I have never heard of o two blade prop causing shaft wobble but I guess anything is possible.  I have the stock factory three blade unit. If I disconnect my prop shaft at the flange my V-Drive does not wobble at all with the input shaft spinning.  When connected it wobbles at the same point of rotation with each rotation.  I have yet to put a dial indicator on it to determine the amount of deflection (bend) but judging by the observed deflection it must be in the 50 to 60 thousand range. As soon as it warms up a bit I am planning to pull it and make a new one.  

Dale Tanski

[JRICH526]

I have a 2 blade prop on TNT and the prop shaft has no vibration whatsoever.
There are a couple of causes one of which is the bent prop shaft.
The other is the shaft alignment to the v-drive.
The v-drive is mounted in slotted holes that allow for minor adjustments. There should be no more than .003 clearance at any point around the 2 mating flanges. If this is off it will create quite a vibration.

[Richard]

That is good information about the two-blade prop.  The boatyard installed a brand new stainless shaft last year, and I really doubt that it is bent, but it could be I guess.  I carefully aligned it with the v-drive flange.  Someone told me the tolerance should actually be 2 thousandths!

I will try turning the shaft and checking for run out, and also checking the alignment again.  It would be nice if it were only the alignment!!

What instrument or tool do you use to measure run out?

Do you get some vibration in the boat from the prop anyway?

[Richard]

Jerry

I also have a cutter and would like to get your email if I could to stay in touch.

Please send a message to rchrdm(at)earthlink(dot)net


Admin email edit to avoid email spam

[Dale Tanski]

Hey Guys,
One other thing to consider... We started out talking noise and with that subject came the vibration aspect.  A rotating propeller can cause significant propeller induced noise as each blade passes close by the hull.  The noise comes from the high/low pressure pulses of each blade as it the hull and the associated cavitation caused by those pressure changes.  Cavitation is nothing more than the tiny bubbles but apparently when these bubbles form and collapse noise is generated.  

I have an old Penn Yan Tunnel drive inboard powerboat, and at low RPM's the noise generated by the prop is impressive.  You can hear each individual blade as it passes by the hull.  The situation/problem is so great that the boat came from the factory with a bronze cavitation liner or sleeve in the prop tunnel to protect the hull from erosion.

Apparently the more blades you have, the smaller each pressure pulse and the less noise generated.  Maybe this may have something to do with shaft wobble and two blade props as well.

Dale Tanski

[JRICH526]

I know sometimes one subject leads to another altogether in the discussion. But I love this site because somebody out there with another Peason has probably experienced an issue one of us may be having and it sure helps to eiminate added expense and down time trying one thing or another until we finally hit. Kudos to Rich Boren and those  who keep this site alive and well
I don't think there is any way to completely remove all vibration. And the same goes for engine noise I won't even attempt to deminish it. It makes it more special when we can turn off the old iron wind and sail these things.
I still get my share of vibrations even with a true running shaft. I just had TNT in the boat yard and had the shaft checked and v-drive aligned and it eliminated a big part of my vibration problems.
 
Here is the official way to check shaft aligment from Walter. I have the RV-20 model but this goes for RV-10-20-30-40-&48
-Many good installations are ruined by improper propeller shaft flange alignment. Accurate alignment will ensure a smooth operating drive train and eliminate many problems that arise due to misalignment. Final alignment should not be attempted until the boat has been allowed to "settle"in the water. Adjust v-drive until the pilot diameters of the gear shaft flange and the propeller shaft flange engage freely.Butt the flange faces together. Without rotating either flange, check with a feeler gauge in at least four places If the maximum feeler gauge that can slip between the flange faces at any point is .003 the unit is properly aligned.If a thicker gage can be inserted at any point, the V-Drive must be readjustd until proper alignment is obtained. Turn the propeller shaft flange 1/4 turn without moving the gear shaft flange. Try inseting the .003 feeler gauge as described above.The gap will not change if the propeller shaft is straight. if it increases, the shaft or flange is bent and must be removed and straightened. Rotate the propeller shaft flange in two more 1/4 turn increments and repeat the procedure. The pilot diameters must be rechecked to ensure that they still engage freely. Tighten the nuts on the mounting brackets and the locking nuts on the adjusting screws. Remove the set screws from the brackets(none on the RV-10 or Rv-20, spot drill and securley tighten. Recheck the flange alignment to make sure the V-Drive didn't move out of alignment. Secure the two flanges together with heat treated bolts and high collared lockwashers.

[kevin barber]

Last week I decided to pull the trigger and buy the engine room insulation.  I went ahead and bought the SPM from sailors solutions, and so far I am very happy with the results!  The major issue with Pan Dragon was the engine noise down in the cabin, so I only insulated the forward sections of the engine compartment.   I can now carry on a conversation down below without having to yell.

[Trinity]

That's a well organized, clean engine compartment there Kevin.  Glad to hear the sound level improved, I'm planning on some insulation too.  Have you noticed any change in the running temp of the engine post-installation?
Regards,
Marc