Large areas of the engine compartment for the one-lung Yanmar diesel on our 1977 Hunter 27 have no soundproofing. My project this winter is to reduce the noise when using the iron genny by sticking soundproofing insulation to the cockpit floor, and all the walls of the compartment. I'll also renew the old foam on either side of the enginer, and under the entry step. One specific question - there are some open spaces on the starboard side leading to the cockpit locker, and behind the icebox. Should I mount the insulation on a marine plywood cover for the hole (the largest is about 6" by 18") or just cover it with the foam insulation? In any case, I will leave an opening for air flow, although there are several other air scources for the engine. But I'm also looking for you advice and experience - I have checked the archives, but didn't find much on the subject. Thanks in advance. David Lady Lillie
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bought kits at Defender
I sound proofed my engine using two 1" kits from Defender. Took about three hours. I don't know how to fill holes though. I would not leave any openings though, where air can get in noise gets out. I think you should completely seal the engine compartment. Air will still find it's way in, I can also use my bolwer switch when motoring a long time to reduce heat buildup.
I sound proofed my engine using two 1" kits from Defender. Took about three hours. I don't know how to fill holes though. I would not leave any openings though, where air can get in noise gets out. I think you should completely seal the engine compartment. Air will still find it's way in, I can also use my bolwer switch when motoring a long time to reduce heat buildup.
One of my present projects
I am working on this at present. Look at the link below for more definitive instructions. Also look at "google"-marine noise reduction foam". The bottom line is that you must make the engine compartment airtight. For this reason I have installed an air vent from the engine to the cockpit. I plan on sealing the engine access panels with weatherstriping and uses latches to make strong pressure for closure. I have ordered the diesel noise reduction kit from BOATFIX.COM.(best price)
I am working on this at present. Look at the link below for more definitive instructions. Also look at "google"-marine noise reduction foam". The bottom line is that you must make the engine compartment airtight. For this reason I have installed an air vent from the engine to the cockpit. I plan on sealing the engine access panels with weatherstriping and uses latches to make strong pressure for closure. I have ordered the diesel noise reduction kit from BOATFIX.COM.(best price)
Don't Make "Airtight" Unless...
.... there is a place for air to get to the air intake. Don't rely on cracks or limber holes. The engine air intake must have sufficient air (think displacement x rpm) or it won't run right. Hence preferably cool air vice hot air (can cause overheating). Recommend running a sufficiently large "hose" to the air intake so it can take air from outside the engine room. Since a diesel can run while submerged so long as it gets air the top of the hose should be as high as possible, not in the bilge. Soundproofing studies on single engine aircraft have shown that everything on the firewall must be covered to lower the noise. The light metal firewall transmits the sound and if even just a small area is not covered the db level will not be reduced significantly. It's that last few percent that makes a difference and I think that same principle would apply to an engine room and plywood.
.... there is a place for air to get to the air intake. Don't rely on cracks or limber holes. The engine air intake must have sufficient air (think displacement x rpm) or it won't run right. Hence preferably cool air vice hot air (can cause overheating). Recommend running a sufficiently large "hose" to the air intake so it can take air from outside the engine room. Since a diesel can run while submerged so long as it gets air the top of the hose should be as high as possible, not in the bilge. Soundproofing studies on single engine aircraft have shown that everything on the firewall must be covered to lower the noise. The light metal firewall transmits the sound and if even just a small area is not covered the db level will not be reduced significantly. It's that last few percent that makes a difference and I think that same principle would apply to an engine room and plywood.
Some cut-outs required
I got my rolled sheets of soundproofing from Defender as well, although the shipping cost was pricey because it's heavy. I cut the rectangles and glued (or screwed) them in place and came back a few days later to see where indentations compelled a few cutouts. Really cuts down on the noise. Related web link is nifty. Thanks.
I got my rolled sheets of soundproofing from Defender as well, although the shipping cost was pricey because it's heavy. I cut the rectangles and glued (or screwed) them in place and came back a few days later to see where indentations compelled a few cutouts. Really cuts down on the noise. Related web link is nifty. Thanks.
Soundown Insulation
Installed this material (1" foam/lead composite) a few years ago on my 1 lunger Volvo aboard my O'Day 25. Was one of the best upgrades I have done. Brought the noise way, way down from intolerable to we can now sit and converse down below while under power. I had concerns as expressed by John, re provideing air and reducing the heat build up within the compartment due to insulating most of the engine box and floor. So installed a power ventilator in reverse so that cool fresh air was pumped into the engine box (from clamshells vent holes installed just below the hull/deck ). The air exits below a small area left open below the tranny, at the back of the box. This brought the temp of the engine box down from 130 degrees F to about 90 degrees. Don
Installed this material (1" foam/lead composite) a few years ago on my 1 lunger Volvo aboard my O'Day 25. Was one of the best upgrades I have done. Brought the noise way, way down from intolerable to we can now sit and converse down below while under power. I had concerns as expressed by John, re provideing air and reducing the heat build up within the compartment due to insulating most of the engine box and floor. So installed a power ventilator in reverse so that cool fresh air was pumped into the engine box (from clamshells vent holes installed just below the hull/deck ). The air exits below a small area left open below the tranny, at the back of the box. This brought the temp of the engine box down from 130 degrees F to about 90 degrees. Don
Thanks as usual!
A big help! I will buy the marine plywood today to cover the large holes. The planned air entry seems to be from two scoops on the aft end of the deck. The entry for this air to the engine compartment is to the far aft end, and is partially baffled already. I'll report on the results next spring when we launch again! My only question is whether to use 1" or 2" insulation. I'm planning to start with 1 inch from West Marine. David Lady Lillie
A big help! I will buy the marine plywood today to cover the large holes. The planned air entry seems to be from two scoops on the aft end of the deck. The entry for this air to the engine compartment is to the far aft end, and is partially baffled already. I'll report on the results next spring when we launch again! My only question is whether to use 1" or 2" insulation. I'm planning to start with 1 inch from West Marine. David Lady Lillie
Cutting "Trick"
One of the worst parts I've found about installing sound insulation is cutting the stuff. I checked with the manufacturer and they said to use new blades on the sheetrock knife and change very frequently. Another tough install procedure is to attach something that requires a screw through the insulation. What ever it is that turns likes to catch the strings in the insulation and it makes a mess. Never did find a solution for this - just kept working at it. Tried turning the screw backwards x turns and the insulation would grab and then went forward and it undid itself, but it typically took 2x turns forward to get the screw seated!
One of the worst parts I've found about installing sound insulation is cutting the stuff. I checked with the manufacturer and they said to use new blades on the sheetrock knife and change very frequently. Another tough install procedure is to attach something that requires a screw through the insulation. What ever it is that turns likes to catch the strings in the insulation and it makes a mess. Never did find a solution for this - just kept working at it. Tried turning the screw backwards x turns and the insulation would grab and then went forward and it undid itself, but it typically took 2x turns forward to get the screw seated!
Practical Sailor had a review but the 2" Soundown
Will give you the best results. Don's advice about a reverse flow blower is a good idea. I insulated my engine compartment and am very pleased with the results but do have to run the blower anytime the engine is running or it gets too hot. Consider ducting the inlet air hose to the alternator area to cool it while charging the batteries. Best advice is to look at sound panels as vibration decouplers, allowing air passage but no direct transmission of sound waves to any area.
Will give you the best results. Don's advice about a reverse flow blower is a good idea. I insulated my engine compartment and am very pleased with the results but do have to run the blower anytime the engine is running or it gets too hot. Consider ducting the inlet air hose to the alternator area to cool it while charging the batteries. Best advice is to look at sound panels as vibration decouplers, allowing air passage but no direct transmission of sound waves to any area.
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