CONTINUOUSWAVE

FOR READERS WHO HAVE REMOVED THE DECK FROM A 2001 OUTRAGE 21 IN WHICH THE FUEL TANK HAS BECOME LOOSE:

Give me advice based on your experience in removing the deck and repairing the loose fuel tank.

BACK STORY
My particular 2001 OUTRAGE 21 does NOT have the optional fresh water tank installed [aft of] the fuel tank. After more than 20-years, the brackets that hold the 125-gallon under-deck fuel tank on a 2001 OUTRAGE 21 have failed, and the fuel tank is sliding around. [To remedy the problem of the loose fuel tank] I appear to need to take off the deck in order to determine if the cause of the loose tank is from broken brackets or from screw fastener that pulled out [of the hull liner laminate] The deck appears to me to be removable without needing to remove the console.

[I consider this to be a] bad design because the 125-gallon fuel tank is not boxed-in-place, and the weight of 750-lbs of fuel is being held by screw fasteners.

The removable deck covering the fuel tank area has been removed. Taking the boat half-apart was a long and slow day.



A forklift was used to get lifting straps under the deck, and then lifting force was slowly applied to break the deck free from the adhesive holding it down.

To get the deck off took a lot of patience and a lot of wedging.

Removal resulted in only minimal damage to the underside of the deck.

In the illustration below at Figure 2, note where the 90-degree brackets detached from the Florida Marine Tank.



I will hire a welder to reattach the 90-degree brackets to the Florida Marine Tank.

A fiberglass bead or a mini-wall will be added at the aft end of the fuel tank to prevent the fuel tank from sliding aft.



[Moderator's note: I have added figure numbers to the illustrations so that they can be easily identified or made references to. I have also added captions to the photographs to explain (as best as I can intuit what the author intended)) that the illustration was to show. When using illustrations, each illustration should be identified with a figure number in sequence as the illustration appears and given a caption. Providing this information makes reference to the illustrations much simpler, and a good caption adds much more information value to the the illustration. It is also more useful if the illustration appears near on in the text of the post in which the element seen in the illustration is being mentioned. Accordingly I have also moved the location of the illustrations.]

From Figure 2, the shift in the fuel tank towards the stern looks quite significant. That there was enough slack in the fuel filler hose to remain attached (as seen in Figure 1) when the fuel tank shifted is quite fortunate. What was the total distance of the aft displacement as seen in Figure 2?

Also from Figure 2, the amount of adhesive holding down the deck looks quite substantial.

Please elaborate on how the fork lift was used to lift off the deck. You must have been able to pry up one corner to start, I would assume.

ASIDE: The use of just adhesive as a means of fastening the removable deck to the hull liner must have been a new method implemented in the post-Bob-Dougherty era at Boston Whaler. Bob was rather unceremoniously discharged as the head of design at Boston Whaler in early 2000. Replacing Bob was Peter Van Lancker. Van Lancker left Boston Whaler about four or five years later.

rchurchill wrote:I will hire a welder to reattach the 90-degree brackets to the Florida Marine Tank.

You might want to fabricate new brackets, rather than trying to reuse the originals. From what little I know about welding, filling a gap with welding rod material will never be stronger than the original material.

Perhaps you can leave the portion of the original bracket still welded to the tank in place, then make new brackets with perhaps thicker L-channel material, weld the new brackets onto the tank atop the originals, and use more screw fasteners to hold the brackets to the hull liner.

The shift in the fuel tank position was probably about 8 to 10-inches aft.

The fuel filler hose and grounding wire were extremely taught and were literally holding the tank from shifting towards aft even further.

MORE DETAILS ON REMOVING THE DECK



[As seen in Figure 4 above] in addition to adhesive the deck was screwed down with four rows of ten screws along outer edge and into interior structural stringers. The length of the screws was 2.5 to 3-inches.

I started with starboard forward corner with multiple pry bars to get that corner started. That was the most difficult. Minimal damage occurred to the surrounding non-skid deck. Once there was room under that area I put on a strap on the starboard side of the deck section, running from the forward side of the removable deck side through the live well, and then I lifted that corner with forklift, all the while while prying and wedging the deck upward. Once more adhesive released, I moved the lifting strap to go through the live well to the circular deck access ports, and kept lifting. Then I moved the lifting strap again, to pass through the aft hatch. Then I repeated to the process on the port sides.




BRACKETS

I will remove the fuel tank from the 2001 OUTRAGE 21 in a few days, and I will take the tank to a welder.

The plan is to leave in place the remaining section of the original brackets still welded to the fuel tank, and then to weld new, more structurally sound, [extruded] aluminum angled channel (instead of bent aluminum sheet) adjacent to old broken brackets. The welder indicated that using the [extruded] aluminum channel stock instead of bent sheet metal will make a stronger bracket.

HOSES
I will also replace the fuel filler hose and fuel tank vent hose.

These steps seem to be the fastest way to get the boat back in the water.

If the welder knows his craft, the welds will be stronger and longer lasting than the base metal. Most of [the skill in welding] with aluminum is the preparation work.

Aluminum oxidizes quite rapidly and welding oxidized aluminum requires way more heat than you want to introduce

Clean aluminum surfaces are a necessity on both sides and a dedicated stainless brush or sander is the preferred tool to prep the metal before welding.

Another tidbit is preheating the weld area before welding takes place will greatly improve the weld quality and makes welding easier. Ask about itm and if the welder doesn't know about preheating go elsewhere.

Mahalo for the comments on welding. Much appreciated.

I believe that the aluminum L-channel stock is actually extruded, which means the aluminum alloy used is more malleable. The much thicker material should be stronger, and certainly the L-channel should not tend to fracture at the 90-degree bend as there is a nice fillet incorporated in the extrusion.

I assume the fuel tank is held in place vertically by sitting on the bottom of the fuel tank cavity molded into the hull liner, so the tank weight will not be exerting much downward force on the bracket--although perhaps some upward forces at times, again due to boat movement. The other force on the bracket is a shear force, resulting from the tank wanting to move forward or aft from the boat motion.

As for welding the L-channel onto the fuel tank, to know the aluminum alloy of the tank--which might be indicated on the label from FMT--and the alloy of the L-channel would be interesting. If the two aluminum parts are the same alloy, I would assume there would not be any problem welding them. If the two are made from different alloys of aluminum, I don't know if there would be a problem welding them. I would ask the welder about that.

A cursory look at welding dissimilar aluminum alloys indicates there could be a problem related to thermal conductivity, that is, the ability of the different alloys to conduct heat, which could cause one alloy to heat at a different rate than the other alloy.

I suspect that perhaps the reason the original tank fabricator made the L-brackets from bent aluminum sheet stock was to be have the brackets be the same aluminum alloy as the fuel tank itself to promote good welding. Or, perhaps it was just a convenience, as the fabricator would already have plenty of that aluminum sheet on hand from which to make to make a small bracket.

Welding aluminum already requires more craft in the process than typical with welding steel, so a good aluminum welder should know about any problem with alloy mixing, or at least I would hope he does.

MOVING BRACKET LOCATION ON TANK

I would assume that the area in the hull liner where the screw fasteners for the brackets on the fuel tank were placed was reinforced with embedded material to give the screw fasteners a strong purchase. This seems to be confirmed in the outcome that the bracket failed at the bend line before the screw fasteners sheared out of the hull liner.

If you move the location of the L-brackets on the fuel tank, the new location may or may not have any embedded material under the the fiberglass laminate to hold a screw fastener. Or, perhaps, that entire length of the upper edge of the fuel tank cavity already has reinforcement material as it might be accepting the screw fasteners that hold down the deck.

jimh wrote:If you move the location of the L-brackets on the fuel tank, the new location may or may not have any embedded material under the the fiberglass laminate to hold a screw fastener.

You are spot on. Thanks for this tip.

Looking at the wood locating diagram (attached below), the 3/8-inch phenolic board is placed only where the fuel tank brackets were screwed in. This makes the option of simply welding new brackets aft of the sheared-off brackets not a viable option unless I provide additional structural support at new location.

I believe it will be easier to work with a welder to get a new bracket welded on top of the old one.

Q1: [between trying to add reinforcement in a new area and welding replacement brackets atop the original brackets] which would you do?

jimh wrote:I would assume that the area in the hull liner where the screw fasteners for the brackets on the fuel tank were placed was reinforced with embedded material to give the screw fasteners a strong purchase.

Before I opened up the deck I expected to see the fuel tank bracket screws pulled out of hull of the boat, but as pointed out, they are secure with the backing, and the aluminum was the weak link.

rchurchill wrote:Before I opened up the deck I expected to see the fuel tank bracket screws pulled out of hull of the boat, but as pointed out, they are secure with the backing and it was the aluminum that was the weakest link.

As shown in the wood locating diagram for the 21 OUTRAGE, the reinforcement material used to retain the fuel tank brackets was phenolic. Typically phenolic material can be tapped to hold a machine screw (as opposed to a self-tapping sheet metal or wood screw). I suspect that the fasteners holding the brackets to the sidewalls of the fuel tank cavity may be machine screws, which probably accounts for the strength of their purchase onto the backing material.

Q2: have you removed those screw fasteners yet?

[The fasteners that held the fuel tank retaining brackets to the hull liner were] 1.5-inch-long self-tapping screws [of unspecified diameter or size].



{Moderator's note: I reworked illustration to remove a very large amount of background material, to reorient the image to be more horizontal, to reduce the number of pixels by 84-percent, and to reduce the file size by 95-percent. There really is not a particularly urgent need to illustrate a 1.5-inch self-tapping screw with a 105,000-kiloByte image, but the image included the broken aluminum bracket, which was much more interesting.]

ROGER on the use of a self-tapping screw to fasten to phenolic instead of tapping the phenolic and using a machine screw. Perhaps that represents another change in engineering in the Van Lancker era from the Dougherty era of Boston Whaler boat design.