24' DYI alloy remodel

[Tfitz]

What size pipe is best to drain the deck of a boat of this size. I don't know too much about the skupper's either. I heard from my neighbor that the ball type work good. I was thinking 3/4 or 1" pipe for the self bailing deck drain. Any opinions on this?

[Tfitz]

I forgot to thank you Kevin for the offer to TIG weld my gas tanks. Shipping is a pain. And I know the work of my welder is good and it's just too easy to let him do it, but I appreciate the offer. Here is a photo of my completely removable floor supports. 12 3/8" SS bolts and no nuts(tapped threads into 1/2" AL). I don't know how you could access the engine for Maintaince with a weld in floor? In just a few minutes I can have my floor and supports removed and out of the way. I have my 3/16" floor plate being bent at a local fab shop now. Trying to figure out my drain. See previous post

[kmorin]

Tfitz, my impression looking at the new framing is that it is inadequate to support the hull. I'd want to see permanent lower cross pieces that has webbing between the hull xverse and the upper welded in xverse to truss that span so the longs on the hull were only supporting the hull for the distance between trussed xverse spans.

Deck drains of 1" presume you're only freeing rain water! But if you get a green one aboard with your unsealed deck this you'll have it in the bilge anyway so the drain will only be emptying the pan depth of the panels you add on the removable deck.

I've built in that configuration before and agree getting to the engine was a "lay on the deck and reach" affair. Most guys plumb the oil pan up to the deck for drainage or use a pump out through the dip stick downcomer. Not much else low on the engine for maintenance, I always relocated oil filter with hose kit, up to manifold cover level, fuel manifold and all other plumbing fittings always located above deck under the engine cover for ease of access. Most engines of this location can be pulled in half an hour with a lift so not much provision to reach below deck.

Cheers,
Kevin Morin
Kenai, AK

[Tfitz]

Kevin thanks for being critical and speaking your mind. That's the kind of direction I need to keep me "off the rocks". But this is not a new build and I know this boat is not structurally well designed but I have to work with what I have. Photo 1 & 2 show the area we are talking about. That's the " hole" where my gas tanks are going. In Photo 4 the cardboard is where I plan to put a 48" tank. And Same on the other side. Photo 3 is the crossmember I installed to strengthen the hull and keel area. I plan to put those cross braces all down the boat at every crossmember. I bet it made that keel / hull area at least 1/3 stronger than original. And the original design stayed intact for 23 years now so I think this plan will still work. Maybe I can look at adding a piece of 1/4" angle at photo 1,2 position to beef up and add to the 3/8" crossmember strength and provide a flat base to support the gas tank. Photo 5 is my new floor pan setting in place and quick / easy removable floor supports. I removed all members in 12 min. I timed it! But it would be unlikely I would need to do That for engine maint. Probably I would just need access to just one side of the engine or the other. I still like my remove the floor idea better than your pull the engine idea... Imagine yourself 80 miles out off the south end of Montague Is trying to pull the engine so you can change the starter??? Photo 6 shows just some of the engine components below my new deck! I would like to see the video on what it takes to pull a boat engine in a half hour? Pull the outdrive, glycol hoses, disconnect electrical, motor mounts, steering, exhaust, engine hoist connection.....ect....yea right. I know my pan style self bailing floor isn't going to do much to protect my from the elusive rogue "green wave" but it my goal is to wash fish parts off deck and overboard instead of in the bilge to get pumped out. And shed rain water water in the harbor without worry about a drained battery. Weld in floor just doesn't work for me and this boat.

[Tfitz]

Just look at the area I have to access the motor with the removal of just 12 bolts! It's like working on an engine mounted in a engine stand! Anyway you look at it... Hard to beat that in my view !!!

[Tfitz]

Kmorin, a piece of 1/4" x 3" angle spanning the areas under the gas tanks would serve two functions. 1. Give the gas tank a flat place to be secured too and 2. Add strength and hull support . The angle in the photo is just a piece if scrap to use as an example (wrong size). 3x3x 1/4 could be cut and fit around the longrens to go all the way to the hull and be welded on both ends to tie into the boat side and keal support angles. I think this would satisfy your concern over inadiquate hull support wouldn't it? Then I could still fit my gas tanks in that spot and only lose about a 1/2" of tank height and not change my ability to remove all floor supports for engine maint access? I think its a win / win solution?? What say U?

[Tfitz]

With the 65 gal gas tanks being so heavy in that area I decided to go with 3/8" angle, that's as heavy duty as anything on this boat (Kmorin was right again! ). so I fit the 3 x 3 x 3/8 to span that side of the crossmember. And I think it should give me a good, solid support and bolt in anchor material for my gas tanks. I like it so 3 more to build.

[Tfitz]

Finished welding in my gas tank and 3/8" thick floor supports. It should be a good base for the 65 gal tanks and add strength to the floor crosspeice area. Now I can measure, cut and begin tacking together the ,160" material into two 48" long tanks.

[kmorin]

Tfitz, I'd want to make sure you knew that bilge water or condensate that is trapped between the flat mount and the tank will/can/may/its possible to set up cells that; corrode the tanks. Thick mounts likely won't be pitted badly? but there's no sense in my experience to leave this potential to come true?

I'd recommend using a "floor runner" or carpet runner- this is #1 vinyl #2 has ribs allow drainage paths, #3 cushion the tank from metal to metal #4 and consider primer painting and epoxy strips in way of the mount surfaces on tanks and bedding/mounts - if possible.

We've discussed many times in the past in different conditions- like trailer bunk rot- and seen posts as many folks with metal to metal joints that didn't work well. Even on deck or guard decks where the thin film of water trapped by osmosis becomes acidic- corrosion can begin. Preventable is the best term I can think of.

Cheers,
Kevin Morin
Kenai, AK

[Tfitz]

On my tank measurements I allowed for a 1/4" strip of UHMW plastic material to be 5200 imbedded/glued onto the bottom of my tanks at every support surface. If corrosion happens it will be on the 3/8" support and not the tank. I think that area will be dry 95% of the time anyway. So does this way of supporting the hull and gas tanks get your "blessing" ? Or do you still see the floor support as inadequate? I need to know so I can rid my sleep of caved in hull nightmares and move on to other problems!

[kmorin]

Tfitz, the transverse frames being light where the hull carries both an inboard and internal fuel of decent capacity means the hull (not the metal) the boat hull 'weighs' more than an outboard powered skiff with day tanks. So.... the equal and opposite principle has to come in to your thinking.

If the boat is 'pushing down', then the water is pushing up, what happens? The skin will hold out water if the skin is adequately supported, but if the skin is lightly supported then it will flex upward. What I notice is the longs are shallow, not tall, the xverse frames are well spaced, (more than twice what might be the spacing for this size of frame and hull) and the depth of the xverse elements are not very tall. So.... my vote was to make them trusses. Rigid space frames that transfer the 'up' into out and the metal is great in tension or outward forces.

Ok, you've got the engine and tanks, more mass to support in one since and more wt to float in another; therefore increasing the 'effective UP' force (of course only because of the increased Down).

IF the tanks are well bolted to the mounts, they become support to the floor as added boxes or beams or frames. This will work, but I was noting in one or another picture the flexible frame system you'd shown. I don't think and didn't state that the boat was likely to fold in on itself! I think the failure mode was shown in the last inadequate welds on inadequate frames; cracked or torn out welds due to the frame's ability to hold up the wt.- and an entire structure.

By making trusses of the whole xverse frame this can be eliminated, but if you need the outboard volume for fuel, then... if the tank is rigid, had flanges to bolt in two planes (x,y hopefully z too) or three to the existing structure; they can then contribute to reduce side-to-side flex (which is similar to up and down) or resistance to flex of the two bottom halves from the cabin bulkhead aft to the transom.

NOTE: Why does is seem natural for the cabin bulkhead AND the transom to be stiff enough to keep the boats' shape? For the exact reason of my previous remarks... depth of the rigid structure. Both are just like a trussed frame, admittedly the trussing is flat plate or combinations of plate and framing to keep the plate flat... but the idea remains intact.

What was I observing? The hollow, open and not trussed frames with single pin (read; pivoting) joints of the bolts can all flex up and own, allowing the bottom longs, shallow flat bars, to flex; all without tearing loose the flat bar longs. What will tear loose? well, the joints at the cabin bulkhead or transom or engine timbers or some other joint that is inadequately supported due to flexible framing.

If the tanks are mounted to UHMW strips, then I'd suggest looking at UHMW tape as a solution. ( http://catalog.cshyde.com/viewitems/tap ... c-adhesive ) The idea this area will be dry is not very accurate, just humidity will, via capillary action, enter the joint of metal to metal. Dry 99% of the time won't stop thin film crevice corrosion.

AT no time do I see the hull caving in, sorry if I've contributed to such a misconception What I see is flexure potential. All that is needed is to put a pair of X (bolt in's) in the areas where there are only vertical single pin joints (...?) . The tanks will do that job if they're bolted inboard low and outboard high, and their vertical walls and baffles both become part of the transverse stiffness you'd be adding. I'd suggest plain old galvanized bolts over SS (if you use SS then take time to passivate them and their nuts). Galvanizing is tin so the galvanic difference is the least compared to aluminum, and they're cheaper too in most cases. If the tanks' are doubled at the bolt points (mount fasteners plates) then odds of having a stress tear due to vibration is reduced.

All engines have harmonics, not all engines are balanced to the point their harmonics won't show up in the odd tank wall. I double all connections after a tank failure due to a diesel that idled at 1250 R. Some how (??) that made the tanks flex/vibrate/tear. The tanks' wall were 0.187" and pressure tested to 5 psi. I've had hundreds of 0.125" tanks for forty (some) years never had a problem, but I double then all- now.

Cheers,
Kevin Morin
Kenai, AK

[Tfitz]

Yes, makes sence to me, I will double all tank bolt down points. I don't see why I can't bolt at X Y and Z on the tank. Good idea! That .160 is pretty stout material and I plan to use .160 baffles so it should be a solid box. I've been avoiding using nuts to keep the taking things apart simple. I've made sure that I have at least 1/2" of aluminum to drill and tap into and used Tefgel on the threads. What's the problem with bedding the UMHW into 5200 glue? I already bought the 5200 and I can buy the UMHW locally? I got my tank material all cut out today but couldn't tack anything together because I ran out of argon :(
All I plan to Mig on these tanks is the double bolt down brackets plates, baffles and tack it all together right? My welder buddy can TIG the rest.

[kmorin]

Tfitz, I see no problem with thick plastic glued to the tanks, just a few thousands of the tape does the same job for a fraction of the cost and effort, just my take on methods. Bolting the 5/32 tanks in well makes the entire area more rigid using the tanks walls and baffles as though you'd welded in full panels to the framing sections and thereby making the framed essentially the 'depth of the tank' solid bulkheads.

MY practice is to MIG then entire tank inside, I usually leave the top off, or if the tank if folded (to reduce welds, stiffen the corner seams in bends, and simplify construction) then you could only get a one sided weld on the last panel- top or end. That last weld is where I stress the importance of good keyhole weld (the weld is often done with a gapped fit to enhance the keyhole penetration) but the entire body of the tank as a 'box' I weld inside with MIG including baffles, filler downcomers, pick up pipes, interior "furniture" of all types, baffles and all other parts.

When done inside first..... the MIG welds usually have some bulge or sag through outside the edge-to-edge plate seams. This is dressed back to the original V fillet using a carbide saw blade or other tool to cut out the drooped outward weld, and the back weld from the outside it TIG. This method usually gives a good reliable tank that takes a pressure test easily. I'd pressure test at 3 psi minimum (80" water roughly) and as high as 5 psig (140" water) but the tanks' panels may start to bulge a bit above that pressure of 700 lb. per square foot!

Once a preset regulator was connected to a small day tank of 1/8" and the shop hand didn't notice the screw handle on the regulator was twisted nearly all the way in. The setting was probably 50 or more psig. The tank blew up like a round sided box the seam that failed was along one side where the MIG gun back weld was at a very poor angle, but the failure points were at the HAZ lines- just outside the welds. It didn't so much blow up explosively as bulge and expand then let air out the torn side seam. But the pressure test will allow any cold laps, pin holes or other pressure flaws to be fused. Small couple gallon tank didn't take long to fail but a big tank will take some time, if you use a plastic tube manometer it acts like a PSV and that is one reason its considered a good solution to this type of pressuring up a tank. Small size, but still test level accurate pressure indicators are not common. Most are small gauges are not accurate enough to do reliable testing so the manometer solves both the accuracy and pressure relief safety.

I've had poor long term performance from tapping aluminum. I've done it, its been functional and then created huge headaches after a few years, so I've gone away from that practice and I've used Tef-gel, liquid thread pastes of a half dozen brands and types, passivated SS bolts, galvanized bolts, thread inserts, O-ring sealed bolt heads ( http://sealingscrews.com/ ) and some even 5200 to seal the entire thread and head area..... Not the best joint for threads in a boat in my experience.

Passivated SS 316, into coarse threaded tapped recesses, with lots of TefGel with annual removal and replacement after cleaning all tapped holes and all threads and redoing the process has shown to have promise but... lots and LOTs and PLENTY of other installations have shown problems.

Cheers,
Kevin Morin
Kenai, AK

[Tfitz]

Mig welding the all seams sounds like great practice. It is a treat to weld on new material after spending the majority of my time welding to old oxidized AL. So maybe tonight I can get the tanks tacked together and take measurements to have my baffles bent. My TIG welder buddy told me to make the baffles with flanges so they are less Likely to tear out from flexing. The flange allows for a little flex instead of a direct weld connection to the tank wall. Then I plan to just cut the corners out of the baffles to let the fluid to flow and equalize between the 3 compartments (two baffles for each 48" tank). Do U concur?

[kmorin]

Tfitz, in my experience if your tank walls are 0.160" 5/32" 50 series there is not going to be enough flex to risk tear out, but in the 0.100" and thinner tanks I do agree flanged baffles provide some flexure that may be important to those designs.

I'll estimate for the sake of conversation that since 1976 I've built (exact number) "quite a few" tanks using thicknesses from 0.060" to 3/8" rolled plate for a pressure vessel with domed ends. In that time I have not flanged any baffles on tanks 1/8" thick or heavier. If I were putting a single baffle in a 4'-0" tanks' run.. OK then I'd likely flange that single baffle since the number of baffles is wholly inadequate to support the side walls adequately and it will flex.

I use the idea of making my tanks somewhat more rigid, in other words in a 4' tank I'd put at least three if not four baffles and they would be T type butted to the inside and welded from both sides if possible? I'd stitch those double sided welds, in my idea of tank building from both sides if at all possible? My idea of tank design is very similar to my idea of concrete side walk casing- not very flexible.

I use the size of the fuel fill down comer (area of pipe) to make a decision on the baffles (1/2 per side) area of cutouts or corner miters. It seems to me that one section would flow to the next easily if the total area (and therefore related volume) of the fill downcomer were equal to the lower cutouts added together? Just my idea of tank construction but has seemed to work so far.

Wave Effect, Surface Effect, fuel movement in a tank is a pretty potent force so I put more baffles that perhaps are needed? I'd say that two baffles in 4' feet would be wider baffle spaces than I'd leave.



here is a tank without top, and the tank will be suspended on plastic boat, plastic encased timbers as extensions of the engine timbers- SO... the bottom is supported by the welded in baffles and that also reduces gasoline movement when the tank is less than half full- most of the time. All baffles/honeycomb grids are straight butts to their relative sides and the entire tank is 0.160".



the beginning of this set of tanks using the bottom as a tack up base along with the main and secondary baffles interlocking.



final view of all 'furniture' installed and MIG welded ready for the top panels- this image may not show that the average size of unsupported panel is less than 10" square? (meaning dim of sides of panel not area) ALL sides except top.



One big concern to me it decent MIG inside the tank. So I built 1/2 of one set of baffles in two stages vertically. This allowed the gun to reach in without degrading the angles of the gas cup to metal putting down the lower baffles' double sided beads. Working in a tank with different MIG torches sure has made me design and build differently over time. I helped a friend work on tanks in his shop where he used a pistol grip style 1lb. gun and the torch was so large we had to make the entire baffle system different than I show here.

So if you want my opinion on tanks, tank bottoms if they're suspended, tanks' end plates if they're larger than 100"^2 or tank stiffness- think concrete sidewalks, that's my rule of thumb. I regularly put X braces on end panels of tanks that don't need them, I regularly end up with quite of bit of time filling with acid, sloshing with acetone to get the soot out, and rinsing obsessively before the pressure test. But I have not had any tanks back in the last plural decades either.

Of course, this opinion is just my own, I'm sure I could easily be declared to overbuild, but I have come to my tanks' scantlings by personal errors in the first year of four decades welding tanks; I find that I'm very comfortable with my cast concrete version of a welded metal tank.

You may notice all the mill scale was removed from the material before the tanks was built? Also, the tanks were etched with acid solution after work was done. THEN a couple of separate rinses with acetone insured the weld soot was gone... and when they went in service? They were fine.

Have I failed to do each and every single step listed. Yes, I have.
Did I get those tanks back, yes I did.
Did those tanks cost me twice or four times what I was paid to do them, yes they did.
Am I overreacting to tank construction? not in my view.

Can others label this as "more than needed"????- it's not in my boats, but I freely admit others' are welcome to assign this as overbuilt.

you asked ( )

Cheers,
Kevin Morin
Kenai, AK

[Tfitz]

I am certainly not going to argue much about gas tank construction when getting advice from a guy who has built them for 4 decades! I will do it just like you say. At least 3 maybe 4 baffles per tank. Stitched, T welded, both sides if possible. No flanges. Flangless is good! That means I won't need to take the baffles someplace to have them bent. I'm still going to need one top flange for the key hole weld. right ? But I can probably just bend that one in my 6" bench vise. After spending so much time welding on old oxidized material it's a treat to weld on new. You forget my miller 30A spool gun has a flexable tip that I really find functional and can get into tight spots at the correct angle. I was going to start to tack the tanks together tonight but instead I will spend my time mechanically removing ALL millscale first!!!!! Today I picked up a 2'x4' sheet of 1/8" UHMW for $40. Add a tube of 5200 and I'm around $55 to insulate the tank bottoms from AL to AL contact. I think my way is cheaper than your tape way when you include shipping

[kmorin]

Tfitz,

depending on the baffles' stiffness you can make a key hole weld of the edge of a piece of plate backing the keyhole weld. That is a 5/32" baffle behind a pair of 1/4" holes drilled 1/2" apart is "doable" weld wise: with the one condition that the sides of the keyhole (5/8" long and 1/4" wide) REALLY REALLY should be beveled outward and upward.

Otherwise, the welder will say things about your Mom that are not true. The frustration is with AC TIG that the arc is stabilized at each of the AC's sine wave swing through zero voltage by a 'miniature lightening' arc that is generated like continuous static electricity- at a very high frequency. That is HiFreq that ruins radio reception and will try to avoid 'going down a hole'. So if the weld keyhole is straight sided the HiFreq will wander to the upper lip edges and it makes welding to the sheet edge of a baffle frustrating- hence the sailor like language by the welder about your Mom.

If you take your cone shaped carbide burr after you've make the two drilled holes and connected them with the jig saw, and make the sides slope outward on the top surface.... by about 20 degs or so... this will allow the welder to reach to the bottom of the weld hole, light up on the baffle's top edge and close with the sides of the keyhole. You can MIG tack these keyholes to the baffle edges and skip plate or bends.

OR>>> you may want more flat support on the top surface and then I'd say using angle scraps is about as easy as any way to get a surface to weld the top down onto. But the keyhole shape is still best done (for AC TIG) as I've described. If you use a backer you can just drill a hole and make it conic with the burr, but the shoulders of the keyhole being leaned outward so the AC arc HiFreq is not 'pulled' to the first grounded edge.... well you'll have a happy welder.

Sounds like a good buy on the plastic sheet! Cutting money without cutting corners is good building.

Tank welding can be pretty recreational because its usually bench work so you can roll them around to get the most comfortable position- unlike trying to roll the whole boat to do the same.

One thing to consider and anyone reading may want to store this away for future reference. It doesn't get much press but of the many tanks I've repaired, most were corroded inside out. The inside of the tank had water collect from #1 condensate ambient humidity, #2 water in the marine gas supply, #3 left over water when cleaning or testing the tanks.

Dead Horse time.

Water on aluminum gives up any oxygen to the aluminum, and becomes DE-aerated so slightly acidic. Then, being under gas or diesel, there's no real source for more oxygen so the acidic water begins to corrode the aluminum. There are only a couple of choices in tank design to preserve your work. One choice is to put a draw tube into the lowest possible point of the tank so the water bottoms are picked up entirely and collect in the filters and this does work reliably if you design the tanks to do that.

Another way is to make a low point sump and install a separate tank bottoms draw tube that is pumped by hand with a bulb so the water bottoms are taken off the bottom of the tank and are not free to pollute the gas or filter OR to damage the tank.



this 1-1/2" deep piece of 3" sched. 80 pipe has a 1/2" plate bottom and forms a water bottoms sump in this flat bottom tank. Due to regular motion the water will collect in this low point by just trailering motions and by moving in the water.



The same sump from the bottom of the tank. There is a dedicated draw tube of 3/8" pipe that is welded to the tank top and 1/2" coupler and to the bottom of this cup with a 45 cut in the tube end. This insures that any water bottoms in this tank are #1 in a very thick walled sump #2 at the pump out site below the tank bottom and #3 if regular maintenance is done this method provides a longer lasting tank that is reliable, and if bad gas is taken on... it shows up very quickly in this water bottoms sump pump out.

My intention is to help you decide to handle tank water bottoms by one or the other methods while the tanks are not built. Then either method, both work well, can be included in your design. Since the boat will be down by the stern more often than not.... I'd put the both the fuel draw AND any provision for a sump aft both trailing and running will be bow up, draining the bottoms to the stern.

Cheers,
Kevin Morin
Kenai, AK

[Tfitz]

I have both tanks tacked into shape and all baffles and end pieces cut and fit and mill scale removed. 12" spacing on the baffles seems about enough to me. Besides, I was down to just a few scraps left over from 2 ea 4' x 10' sheets of .160. I even had to splice one baffle to have enough finish. The tanks are ready but I won't be doing any welding tommorrow. We're headed south to Denali Park to do some mountain sking in this beautiful weather were having. It will be a nice change after spending so much of my winter inside my shop.

[kmorin]

Tfitz, I hope the skiing is good, and the weather better? Its been nice here since July... global warming ?

I guess the corners are not clipped or mitered in the pic of the baffles -yet? Don't forget, the center of the baffles can be cut out too, surface effect (waves in tanks) won't go through a baffle and continue a wave so the middle 50% can be cut out without any problems.

As to making baffles, I usually use scrap/offcuts/left over edges. When building you end up with some sheet edge slender pieces that are too narrow to do much and so they often end up sold for scrap. But.. if they're cut into the side pieces of a baffle, they work GREAT to use up that metal, conserve on what can be some large areas of plate and will work just as well as whole pieces. By using the strips with the flat (original sheet sides or edges) as the edge welded to the inner tank sides you'll conserve the left overs, have straight edge baffles and all you have to do is use vise grips to overlap the pieces to make a reasonable baffle plate with a whole in the center.

I think the tank prep will serve you well, and the tanks won't be 'rotting out' from water bottoms and mill scale- looks good from my view point.

Hope the time on Denali is safe, fun and a relief from the shop.

Cheers,
Kevin Morin

[Tfitz]

My son and I had a great time in the mountains. We skied up to the ridge behind the tree in the first photo. You can see Mt McKinley in the second photo. Perfect weather. Not so perfect snow for skiing but fun anyway. I spent all day today welding on one tank! And I'm still not done!! When I was cutting out those holes in the baffles I was wondering why I was doing it? To reduce weight? But as I welding I realized they were pretty helpful being there for access to weld easier. I think this box is strong enough to hold concrete!

[Tfitz]

Kevin, I think I built the tanks like you described. I still need to weld in a 1.5" coupling for the filler hose before I take the tanks to the TIG welder. I had to order couplings, no one stocks them in Fairbanks. I'm pretty tight for space on top of the tank for the hose fittings. I didn't plan it right and it's going to be close. I need find some compact 90 deg fittings to make it work or I will have a raised bump in my floor! My new trim tabs arrived and I don't like how they recommend to install them. The directions call for drilling holes through the transome behind where the trim tabs mount, then run the cable out the hole to plug into the the back of the unit. The thing I don't like is they seal the hole and cable with a rubber grommet clamp fitting. I don't like wet rubber against my aluminum hull!!. I've already fixed too many problems related to that and I don't want to go down that path anymore. Any ideas?

[kmorin]

Tfitz, I'd have had a tendency to put all the tank fittings along the outboard edge so their connections rose vertically from the fitting in the tank. Then I usually run pipes to the fill down comer so it leads to within one diameter of the bottom, even if it had to penetrate a baffle. The draw tube from the lower inboard after corner would also work well by running up to the top of the tank outboard. Last, the vent fitting along that edge allows the slop jar/vent can/charcoal filter (whatever overflow and fume provisions you're providing) could be installed near the deck fill fitting but under that guard deck.

I'm not sure I understand the fill, draw and vent locations that I see in the tanks but I do see your requirement for the short radius 90's !! a St El fitting is only so tight a radius, 1.5D ?? so it does look pretty tight. I don't see the gain from having fittings in the middle of the tank instead of along one edge?- outboard?

If the tops are not welded yet, my take is that it worth the time to move the fittings, add the piping, and patch the top - all of the work will be air tested so a little extra welding seems worth the price to replan, remodel and rebuild? AT least the fill would move pretty easily, the small diameter draw and vent may not be as much a fitting problem? If you left them and moved the draw adding the downcomer so there's not blow back and the vent works- its only one patch per tank and a much easier fill hose routing.

If I understand the trim tab install, the entire block you show will be screwed to the transom and there is a connection to the center for the electrical? I guess the choices I see are to weld a doubler to the hull as a sacrificial surface, tapped to take the fittings fasteners with one hole in through for the cable and packing gland inside to make is safe?

Another choice is to make a stand off with a bottom plate extension deep enough of far enough aft to allow all the connections to mount to the extended 'box'. I'd still tend to rig a welded on gland for the cable to penetrate but then any place a below the waterline through hull is mounted I prefer packing glands or flanges that allow thicker materials.

I've mounted the plane style tabs and their oil hoses could be sealed with bulkhead fittings, most electrical through hulls I've done are not below the waterline the packing gland type fittings needed I'd make of threaded aluminum pipe smooth end to the hull or a flanged mounted packing -like shaft seal even though it may be considered overkill on an electrical cable?

Cheers,
Kevin Morin
Kenai, AK

[Tfitz]

I think our logic is close enough to where I don't think I need to change anything. My filler neck location is the black circle far left looking towards the bow. You can see the fill cap hole location outside the boat, port side deck. I have not installed the fitting / coupling for the filler down pipe yet because I'm waiting for the mail ordered couplings to arrive.
The 3/4" vent is located far right, across from the fill pipe. My theory is I will be standing close the boat edge holding the fill nozzel and the boat will be slightly listing to that side making that vent location the high point.
The 1 1/2" fitting bottom left is the stern end of the tank and will be for my vertical slider fuel sending unit.
The 1/2" fitting bottom right will be my fuel pick up tube. That will be the lowest point in the tank and will hopefully keep the moisture out as per your instructions.
I have 2.5" of space on top of the tank, and the bottom of the floor/deck for fittings. I think it will work, just barely, but it will be close mostly by luck not design! Where can I find a 1.5 D SS 316 90? Or what do you recommend?
The second photo is the stern of my neighbors boat that was factory set up for this style trim tabs. They made a open pipe that terminates on a backplate bracket held abot an inch off the stern then penetrates the stern and the pipe 90's up inside the boat an extends above water line. So you have a 1" pipe for each trim tab and just feed the cable down the pipe no seal necessary. What do you think of this? What alloy pipe can you bend and is corrosion resistant enough for salt water? Only thing available in Fairbanks is 6063 pipe.

[kmorin]

Tfitz, replying to the P-trap or Riser seals of 6063. It is generally accepted that 6063 is has too much copper alloy fraction for any immersion at all. 6061 will bend if done properly and while it has some copper in the mix it won't 'Swiss cheese' in a season- like 6063 underwater.

The key bending 6061 pipe without cracking is; the bending die's interior surfaces need to be #1 sanded to 120-180 grit smooth & #2 must be lubricated for EACH bend, & #3 the pipe must be bent to large enough radius. If you measure the cable end plug's dia., you can decide if you can flatten the bent piece any- and still expect to get the fitting around the bend.

I'd probably go with a gland type seal for through hulls below the waterline. A riser seems somewhat more work and still has to have hull seal weld at the lower end, so the gland fitting remains my personal choice.

The boxes to extend the mounts so the fasteners are not through-hulls looks about what I was suggesting, but the 6063 riser is not really a good idea in my experience.

I'll review the tank post and try to reply.

Cheers,
Kevin Morin
Kenai, AK

[Tfitz]

The seal method would certainly be the easiest and cheapest thing to do and if you don't think corrosion will happen then that's what I'll do. I will take a better look at the seal they provide and decide which way to go. Maybe I will order a stick of 1" 6061 and see if I can even successfully bend it.
I had another idea on the "not enough room for fittings" problem on top of my gas tank... What if I cut a nipple the length needed to extend 1 1/2" NPT threads just above the tank top and allow enough room to TIG weld it AND long enough to go to one pipe width away from the bottom. Forget the coupling. Only use the piece of threaded pipe then screw a 1 1/2" 90 onto the pipe end and a 1 1/2" hose nipple into it. As Long as the 1 1/2" 90 is around 2" that may be my shortest option. I think I will get the 1 1/2" SS 316 90's ordered from buyfittingsonline first thing tomorrow