My experience removing the fuel tank access hatch to add sound insulation

[Bruce]

First I obtained Robertson FA5515 #4 Robertson bits.



Then I grabbed a 1/4" impact and was able to remove 8 of the 14 bolts but it would not budge the other 6. So I switched to a 1/2" impact.



It turned all of the remaining bolts but I broke off 3 of them. All 6 seemed to bend as they came out. I believe they were in at an angle, were screwed through metal they had cut threads into and were installed using something like 5200. The successful removals were using very short bursts of the impact.



I thought I would be able to use vice grips to
remove the three that had broken. The vice grips spun on the threads. Then I drilled the bolts and tried a screw extractor. The extractor bit but I could not get the bolt to spin. I tried vice grips and a crescent wrench on the extractor. The tools spun on the extractor.

So I moved on to drilling the bolts out. I found that even after removing one side of the bolt from the threads they still would not spin. I managed to flatten one side of the bolt and tried to spin it with vice grips. Everything above the threads broke off without ever spinning.

Two of the three bolts that had broken off were at the front and protruded into the ski locker. I decided to use a washer and nut in the ski locker to secure those. A lot of work with drill bits and punches was required to remove the portion of those bolts that was protruding into the ski locker.

The third was toward the back. I simply drilled a 9/32" hole where it had been and re threaded it with a new 5/16" bolt.

Here is what I recovered of the front two bolts.



Then I covered the entire bottom of the hatch with dynamat extreme.



Then I replaced the bulb seal with 5 x 3/4" strips of dynamat.

I used 4 pieces of dynamat extreme.



I reinstalled using 12 x 1.5" 5/16th 18 pitch threaded stainless bolts, 2 x 2" bolts, 4 washers, 2 lock washers and 2 nuts. I purchased these at Lowes. I reused 12 of the factory plastic washers. I placed a large amount of anti-seize on each bolt. I used hand tools to install the bolts. The factory bolts were 2" in length. The 1.5" bolts seem to hold sufficiently and the 2" bolts that were in stock had too short of a threaded section. I will monitor this and replace the bolts if needed. The stainless bolts at lowes were $0.70 each.



The hex bolts do not stick up any further than factory and did not change the walking comfort.

We have not tested sufficiently to make a call on the noise reduction.

 

[KXCam22]

That's exactly what I did. Great that you documented it. My bolts all came out easily by hand. I am a pessimist but I do think there is a sound reduction. Cam.

 

[ArmyChief]

What....no before and after SPL meter readings?
I'm shocked at your lack of scientific data @Bruce

Keep us posted

 

[graham cormack]

im curious as to why you were addind sound proofing to the hatch there - does it make a lot if difference?

i like your deck mats too, really smart i might go and have a look on ebay for some!

 

[Bruce]

I think it did make a big difference in noise in the boat. Unfortunately I do not have numbers to confirm. The theory is that the floor panel vibrates.

The 1.5" stainless bolts held up fine to this years very rough Bimini crossing.

The flooring is from http://JetBoatPilot.com. It would be great if you knew someone vacationing in the U.S. that could bring some home to you in an extra suitcase.

 

[graham cormack]

thanks Bruce, I might be visiting the states myself next summer so I may well wait till then and get a set of mats when im over!