And some more work, but no official final results before you get too excited.
I've been debating for quite a while to try and "soundproof" my 165. I haven't found anybody else who's done it so I recently decided to pull the trigger. Again, I have NO RESULTS yet... so all of this is not knowing how much of an improvement it will have in the end. But I will report back in the spring when we don't have 2+ ft of ice on the water.
First of all, I debated doing this last summer. So I took my phone, mounted it in its usual "place" which on the left of the steering wheel on a mount glued to the dash. I used an app called Physics Toolbox Sensor Suite on Android. It allows you to record decibel levels. Is this accurate? meh... but good enough. Not spending a fortune on a decibel meter.
I proceeded to perform various tests, see the graph for the details. Each test lasted about 50 seconds, thus giving me 10 seconds to switch to the next test. Note that it was pretty windy that day, so the ambient noise levels varied quite a bit. At the end of the test, the wind was a little quieter, so that ambient noise level is probably more accurate. While running, the phone is behind the dash, so wind noise should be a little minimized. For those that aren't aware, 3 decibels is equal to a DOUBLING of noise. So going from 90 to 93, you've doubled the noise levels. From 93 to 96, you've doubled again (i.e. 4X the noise of 90 decibels). So "small changes of 3db" is quite significant.
Now enter winter. I now store my boat inside my own garage (the beauty of a small boat I suppose). I decided I was going to finally install soundproofing. After a bunch of research in dynamat and all kinds of other soundproofing materials, I opted for something called Technicon FB1.
TECHNICON #FB1, SOUND REDUCTION INSULATION. The Chandlery Online Note that I live in Ottawa, Canada. This store is local so I was able to pick up the material at the store. It's about 1" thick with a vinyl layer in the middle that is quite heavy. The idea is the weighted layer absorbs low frequencies (i.e. vibrations) while the foam absorbs high frequencies. The aluminum foil of course if for engine heat. I calculated that I would need 3 of these sheets (54"X32" each). I was correct. Had some waste of course, but in the end, needed three of those sheets and I've got about 1/3 of a sheet leftover to do this job.
To glue it, it was recommended I use a spray adhesive called 3M Super 77. This worked very well. Bought a big can of it and ended up having JUST the right amount to do the job while spraying both the foam AND the fiberglass on the boat (applying it to both surfaces helps adhesion and makes it quite a bit stronger).
First, disconnect the gas springs so you can open the hatch completely. I leaned it against my garage wall while I worked. I then proceeded to remove blower pipes, my custom cup holder drainage pipes and cup holders. Next, clean the surface well. Then, go at it! It takes a lot of work and patience (about 9h straight... I'm a little OCD... so yeah). It's also extremely uncomfortable. You can remove the hatch completely, that would help. But I didn't feel like doing that and didn't have the space to do it either. I stood inside the engine bay while working and straddled the engine. Careful not to damage anything.
I would eyeball each piece (I thought about a cardboard template... but decided that it would be more work to do that than to just eyeball each piece), cut with heavy duty scissors (the mass loaded vinyl in the middle is quite tough to cut) and fit/trim until the piece maximized the area to cover well. Once I had this, I would step off the boat, go onto my cardboard covered area, spray the adhesive on the foam and then on the boat. Follow the instructions by waiting a few minutes until it was very tacky (adhesive shouldn't transfer onto your knuckle when touching it). Then I would install the piece CAREFULLY. What I learned was that once it was in contact, it's NOT COMING OFF! lol It sticks incredibly well.... great! But tricky to install, especially around rounded corners. So patience as you're working. Make sure to apply lots of pressure everywhere to get good adhesion. Piece by piece, I managed to cover the whole hatch. Careful around the perimeter, if you go too far, you may have trouble closing the hatch. You can always trim afterwords if needed.
Once all of this was done, I then used mylar tape to cover every spot where two pieces met. Also, have to cut out a few holes for pipes, zip tie, ventilation, etc. Don't forget these.
I then did the back of the seating area behind the storage bag. Removed the storage bag (easy), I then cut a single, rectangular piece to fit that area as best as I could. I then did the adhesive once again, but this time, I punctured the soundproofing with the extra long storage bag bolts (why are these so long anyways? Worked in my favour... but weird.). This "hangs" the soundproofing quite well. Apply pressure to glue it everywhere. I then installed nuts and washers using those same bolts to secure it further. Then reinstalled the storage bag.
Finally, I got a hold of some old pillows (5 in total). I put them in heavy duty garbage bags and squished them under the seats between the gas tank and the fiberglass (3 of them). I also put one in between the fiberglass inside the gunwales. The plan is to test with and without the pillows to see if that makes any difference at all. If it doesn't, I'll remove them. If it does, then I'm probably going to get better bags than garbage bags since garbage bags puncture easily with exposed, non-rolled fiberglass. I don't want the pillows to get wet. Alternatively, find some more foam and stuff it in there. But foam isn't cheap as I've discovered and I don't want to invest in more foam when pillows can achieve something similar.
When all of this was done, I discovered that my gas springs weren't strong enough to lift the hatch by itself (it used to, although very slowly and sometimes wouldn't depending on outside air temperature). So I replaced the two springs with stronger ones (90 OEM to 120lbs each... this is frankly too much. If I had to buy those again, I'd buy no more than 110lbs). It now pops up REALLY fast lol Video:
https://photos.app.goo.gl/vcrfYweHiCcrvsue8 The reason I saw these are too strong, I noticed that the top brackets on the top of the springs was bending outwards a bit. My gas spring would pop off when it was bent too far out. So I flopped the ball joint around towards the inside of the boat, thus counter acting the bending action and now keeping the brackets straight. This worked wonderfully and didn't take much work.
I'm very curious to see how much of a difference this will all make. I somehow suspect that the phone won't measure a big difference, partially because wind dominates a lot of the noise at speed but partially because I think a lot of the noise comes from low frequencies (like vibrations) and I don't think the phone can pick this up very well. Every person that has done soundproofing (including manufacturers) thinks it makes a pretty big difference obviously, but nobody seems to be able to quantify it since it's so unique for each boat. I suspect I'll see the biggest difference at idle or slow speeds. But at high speed, I suspect the engine noise will still be drowned out by wind noise anyways. We'll see....
My plan is to do the same tests this spring and rebuild that chart. I'll report back whenever that is... probably late May if this damn cold weather goes away (-13C today 8.6F).
Hopefully other boat owners and specifically 165 owners will find this useful or at least entertaining (Why did this idiot do all of this? Won't make a lick of a difference!). lol
Sorry for the long post, but I got frustrated finding incomplete details from all kinds of forums on this type of work. People aren't specific and I feel so frustrated when I'm trying to understand things.
But also you can see those lights in the dark when backing it up at night time (which I keep having to do for random reasons).
. I'm dying to know if the sound level from the engine went down. Thats a big downside with 165, its a fairly loud noise from the engine. 
