Motorbox Insulation

[edwin]

I was more concerned with a possible over heating problem due to a reduced air flow.  It seems like Edwin poked a couple of holes in his motor cover on his SLXI because of this reason.

I can't add a picture of my vent modification here, so I've added one in my gallery. I was experiencing vapor lock in the summer when I'd shut the boat down after it had been at operating temps for some time. If it sat for 30 minutes or so when the air temp was 90+, it'd vapor lock.

I put one vent on each side of the motorbox, would just unscrew them on each side and the breeze would do the rest. Never had a problem since.

I finally tracked down the root cause of the problem - the gasoline in the area had just been switched to the new reformulated gas. As soon as they got the mixtures correct, problem solved. FWIW, I haven't removed them in the past 2.5 seasons and no vapor lock.

[onamission]

I did the last boat with the skinned foam that Supra uses. It has a pattern in it like diamond plate witch I though looked cool. I was going to do the new boat in the same material, but Malibu beat me to it and insulate the cover and didn’t charge me or the dealer for it . The only thing that I've noticed between the two is that the cup holders are now cup warmers, but that could be because of having Stewart's metal ones back there instead of the plastic ones. Noise and performance was about the same

[VinRLX]

I would have too, I found it strange enough that I thought I should do it again but, alas it was time to ski and with $3.25/gal gas I don't want to waste any of the precious stuff.

The one thing that I can think of that would explain the difference is IF the whole FIBECs thing actually pressurizes the motorbox.  That seems highly unlikely becuase it's all open and it's a significant volume.

Keep in mind that they were somewhat unscientific readings and I think that the difference of the two falls within the repeatabliity of the test- it was gusting winds.

The other thing is that I didn't notice any sound difference when the cup holders were removed.  That too surprised me.

Hey, if Hank can put plexiglass on his HDS, just to see if it really fills with water, then surely you can burn a few gallons trying to answer the age-old vent question.

Based purely on your unscientific readings, I'd say the motor gets more air through fibecs with the vent covered. Problem would be those who have favorable conditions for vapor-lock. I believe a fair bit of heat escapes from that vent when the boat is off and no blower running.

As for the sound, I wouldn't expect any difference from the driver's seat. Be interesting to get a sound meter reading from the back seat, however.

[skisix@38]

Kinda strange, don't you think? Particularly if you believe the air intake benefits in some way by being that close to an air source.

What prop are you running on that boat?

ACME 515 at 4900 ft elevation

[cgeaves]

Question for any of you who have done this installation. The material from McMaster's is 1" thick and 54" wide and you buy it by the foot. Many of you have said 8' will do the job. Does it ship to you in a sheet that measures 54" x 96"? And which direction did you cut it to get the most of your material? As I have measured my box, 8' seems pretty close. Thanks for any help. Clay

[Jimmy Buffett]

Yes, buy it by the foot, and 8' was plenty for my S LXi. It was in one sheet IIRC. I think I did the middle first since it was the largest continuous portion and then cut the sides next.

[doughickey]

Just some comments based on my classes in Engineering school decades ago.

1/ Re skisix's water tests with vents open & closed.

Some other factors possible. Actual internal engine temps. If your first runs were with a "colder" (internal) engine, then I would expect poorer performance. Engines operate at higher efficiencey when they are in the higher range of their recommended operating temp.

2/ Re foil based vs NON-foil based:

Heat transfers 3 ways. Conduction; Convection: Radiation: That's it. Some examples of each. (Good old planet earth is heated by the sun across 92 million miles via "radiation" only. Homes are usually heated by "forced air" systems = convection. (Actual air movement forced through ductwork). Lastly, conduction is the transfer of heat through materials.... ie heat loss through your home's walls.

So.... what's going on under the motor box. The motor is the heat source. How does the heat get released. Mostly via convection.... or forced air.... via colder air coming through the vents from the front..... and out any openings in the rear. This includes the bilge blower hose and the engine vents near the cup holders. At speed, this should happen via air being rammed into the air inlets...via fibecs ductwork, and released out the rear. At low speed, running the bilge blower would help.

There would also be conduction. This is where the interior surface of the motor box gets heated, and transfers that heat through the fibreglass then through the foam and vinyl on the exterior of the motorbox. I suspect there's not much of this going on.

Radiation. If the exterior of the motor box is hotter than surrounding objects (ie: people), they would actually feel the heat. Again, I suspect this is minimal.

So, does using the foil back stuff theoretically make a difference. The engineer in me says yes. Any heat "radiating" from the heated engine and exhaust would be reflected away from the silver backing back into the engine compartment. There would still be convection (air flow), and conduction (heat through the foam and fibreglas and foam and vinyl)...... but, radiation "out" of the would be eliminated. Hence, more heat would stay inside.

So, yes, less heat would find its way to the adhesive attaching the foam to the inside of the motor box.

NET = my vote would be to use the foil backed vs NON-foil backed.

Now, as for the vent holes. When I insulated my box, I left them open. I have no idea how much air actually passes through these holes..... but I assumed they were put there initially for a reason. Since I've added 1" of insulating (sound AND heat insulation by the way) foam to the motor box, that lets LESS heat get transferred through the motor box material by conduction. This would mean my motor box air temps would rise (vs no added insuation.) Since I also used the foil backed stuff, that means I've reduced any heat transfer from the box via radiation". Again this would mean the heat is being more efficiently "trapped" inside the motor box. Sure, I've kept the sound in, but I've kept more heat in as well.

I don't want "vapour lock". I want to ensure I don't restrict any convection (heat transfer via air flow) ..... so I kept the vents open. I also keep my bilge blower on most times when I'm driving..... especially at low speeds.

Does the vent hole let sound out.... yes..... but it's rear facing. When we ski, nobody sits at the back anyway.

No.... I haven't done before/after temp tests on the vinyl motor box surface, or installed thermocouples or temp gauges inside the motor box to prove any of this stuff. Just did what I thought would work.

Net: No vapour lock. Lower sound at idle/low speeds. Worth the work. I'd recommend leaving the rear-facing vents open if possible, and using foil backed.

Edited September 16, 2006 by doughickey

[skisix@38]

I agree with all you have said Doug, I'm an engineer too. I just don't understand the relative impact of those factors. I can say that one year later I've enjoyed the insulation and what it does for the cockpit, and I've not had any trouble whatsoever with the adhesive.

[Deke]

Has anyone considered putting insulation under the flloor board that covers the packing nut and exhaust pipes? I'm doing my 99 Response engine box this spring and may do this too. Since that compartment is wide open to the bottom of the engine box it seems like it might make a difference. Let you know how it works if I do it.

Deke

[WakeGirl]

Has anyone considered putting insulation under the flloor board that covers the packing nut and exhaust pipes? I'm doing my 99 Response engine box this spring and may do this too. Since that compartment is wide open to the bottom of the engine box it seems like it might make a difference. Let you know how it works if I do it.

Deke

The boat that I based that article on already had some deadening material on the bottom of that panel, so for boats in that situation I think that it may be not worth the time or effort to do. If you find that there isn't anything there, then it may well be worth doing. Please let us know how it turns out.

[skisix@38]

Has anyone considered putting insulation under the flloor board that covers the packing nut and exhaust pipes? I'm doing my 99 Response engine box this spring and may do this too. Since that compartment is wide open to the bottom of the engine box it seems like it might make a difference. Let you know how it works if I do it.

Deke

I had some left over insulation and so I put it on the bottom of that panel. It deadens the noise from the tranny a bit as well as the rest of the noise floating up from that. I don't think I would go as far as recommending that some one buy extra insulation to do this job but if you have extra laying around it probabl a good spot for it.

[UWSkier]

Has anyone considered putting insulation under the flloor board that covers the packing nut and exhaust pipes? I'm doing my 99 Response engine box this spring and may do this too. Since that compartment is wide open to the bottom of the engine box it seems like it might make a difference. Let you know how it works if I do it.

Deke

I had some left over insulation and so I put it on the bottom of that panel. It deadens the noise from the tranny a bit as well as the rest of the noise floating up from that. I don't think I would go as far as recommending that some one buy extra insulation to do this job but if you have extra laying around it probabl a good spot for it.

Just thought of something regarding the RPM drop with the cup holders removed. I wonder if having the cup holders removed resulted in a lower air pressure under the motorbox due to vacuum. Theoretically, there should be a vacuum on the back side of the motor box at speed. Maybe removing the cup holders introduced that effect to the engine compartment... Another thing to consider would be the increased turbulence removing them would create...

Edited October 31, 2008 by WakeGirl

[SAG JUNKY]

Do you Have to use the retainer hardware or just the adhesive, and if so can you get them as the Overtons kit does not come with them.

[WakeGirl]

Do you Have to use the retainer hardware or just the adhesive, and if so can you get them as the Overtons kit does not come with them.

I don't think that you have to as long as you're good with the spray adhesive. The retainers just give a little insurance. I have no idea where you'd get something like that.

[GrahamH]

I am thinking of using the 1" Skinned Foam from McMaster Carr. The article hear says to use Aluminum Tape. If I am not using foil backed foam, am I better to use the Polyethylene Foam Tape from McMaster Carr? What width do you recommend? Thanks.

[hiexpo]

I just bought this stuff called the insulator from napa auto parts and it is double foil backed, no raw insulation to deal with and it is used in aircraft applications, but ok for boats to. It cost me 101.00 for two 4 by 6 pieces. Got the tape and glue and insulation pins from a hvac wholesaler and a great deal. I am in this about 150. also with left over materials and this has made so much differance. Thanx for the idea all.

[sportster]

I just bought this stuff called the insulator from napa auto parts and it is double foil backed, no raw insulation to deal with and it is used in aircraft applications, but ok for boats to. It cost me 101.00 for two 4 by 6 pieces. Got the tape and glue and insulation pins from a hvac wholesaler and a great deal. I am in this about 150. also with left over materials and this has made so much differance. Thanx for the idea all.

i work for napa thought only had it 1x1 pieces can you give me bk #

[DIE2SURF]

For Sale: Set of 17 Pins and locking washers for motorbox insulation mod. (can use 3 pins on each side, 3 on front, 3 on back, and 5 on top). Since they only come in 100 quantity, I bought them for my motorbox and have been selling the remainder to anyone who wants them. (Sold)

I also have approximately a 40 yard roll of 3" diameter aluminum tape (I used approx 20 yards).

Aluminum Tape part # and description

http://www.mcmaster.com/#7631A33

$20 for the aluminum tape shipped (it cost me $30 shipped)

I'm not trying to make a bunch of $, just trying to allow others to save $ who want the pins/tape but don't want to pay $55 for a huge, unnecessary quantity.

PM if interested.

Edited May 12, 2009 by DIE2SURF

[medicdiver]

I have many of the pins left as well. Just bought them do do my insulation on my motorbox.

[davemac]

just finished insulating mine tonight (w/ the adhesive backed foil faced & supplemented support w/ about 14 "pins"). One tip to throw into this thread... when you measure the long piece (that goes front to back), add a few inches. Once you start the actual install, the "scrunching" of the material reduces the length. You can always trim later if need be.

Edited May 15, 2009 by davemac

[DONTW8]

I lined mine with the B-Quiet material. Took it out for the first time Sunday. I really think it made a difference. One thing I know is that the noise seems to be a lower pitch.

[smooth as glass]

I always assumed the cup warmer vent was for venting a hot engine while at rest. I put a piece of foam across it to minimize engine noise while underway, allowing airflow to continue. FWIW...

[Michigan boarder]

I just did mine today, turned out great. I used 3M adhesive #74 and 1" foil faced foam, part numbers 7610A15 and 5692T35 respectively, from McMaster-Carr. With that adhesive you don't need the pins, the glue is plenty. It is tough stuff and the foam will have to separate before it comes off. Cleaned the engine box surface with Xylene before spraying the glue. Also, I didn't use the tape. If you are careful with your cuts, you can miter in the 3 pieces together, so the seam is almost undetectable. I ordered 11' of the material, and it comes in 54" width. I could have gotten by with 9'. I also had enough left over to do the panel in the back above the exhaust.

[ed obermeier]

I lined mine with the B-Quiet material. Took it out for the first time Sunday. I really think it made a difference. One thing I know is that the noise seems to be a lower pitch.

Ordered the B-Quiet material Saturday, should be here in a day or two. As soon as I get the boat home from storage that will be my first project. Got the thicker version, it's gotta make a difference. Thanks for the info on it Dontw8.

Ed

[Woodski]

Has anybody gotten a weight for the amount of insulation used for the motor box? Any comments on how much noise was suppressed?