Help me make the decision ... twin or single diesel?

Yes, the angle will be strong enuf - just use 1/4" four by four angle on the thwarts of the tank (or go full length). They will stiffen it and it's not going anywhere (I see you were cautious on the fore and aft baffles so I will assume that there is one running the other way, too). I have a twenty gallon tank for my Espar hanging by three 1.5" tabs of 1/4" angle. It doesn't even wiggle. Granted, 82 gallons is a long way from twenty but I have seen this done many times and consider it preferred to any other method. Even in a wet environment, the SS lagbolts can be moved over a few inches when they rot the aluminum out after 15 years.
Just out of curiosity, you said you used 5200 on the Starboard but it looks like silicone - you must have used denatured alcohol to neaten it up - how did you know to do that?

 

I actually used acetone.

I cleaned the tanks with the acetone, then applied a coat of 5200 to the underside of the Starboard block and affixed it to the tank. Once the the 5200 squeezed out the sides of the block, I removed as much as I could by mechanical means, then used an acetone soaked cloth to clean and tidy the 5200.

 

piperca, When i put new tanks in a boat i like to foam them in to support them. For drainage run lengths of pvc pipe under tanks fore and aft, Hang the tanks temperaraly with some pvc straps. Build temperary bulkheads from cardboard or luan fore and aft ends to keep foam contained around tanks. Or you could build a permenant bulkhead on aft side of tank witch would help support the tank from move aft and then use that bulkhead to mount your filters on or anythingelse you may need to mount. Keep your drain pipes out the ends, Use coast guard approved 2-part foam found at Boat fiberglass supply shop it comes in a few densities or pound weight i use 4-lb on mine any lighter will crush over time. even adds some floatation, stiffness, vibration and sound deadening to the boat. Do not use lighter floatation foam for tank setting. you want the stuctural 4 lb or more. If you are concerned of ever removing or moisture you can rap tanks in plastic or viscuine before you pour. This is a closed cell foam i am refering to. when you remove the temp. bulkheads you can glass or epoxy around your drain pipes if you feel it is needed to make more water tight. When the foam is hard you can form it to any shape with knives and sander, Just depends on how fancy you want to get. This is common practice in a lot of boats. You do not want your tanks rubbing the inside of your hull. Bad news there. The foam will support the whole tank bottoms and sides up to the top of your stringers. Are your tanks mounted forward of midships? they will take a beating. And they are large heavy hammers pounding on your boat. if you plan on planning this boat at a cruise speed.This is one reason most planning boats have tanks mounted midships or aft.There are several different way's of doing this. This is just one way to foam tanks. PVC pipe is easy and cheap way, you can take fiberglass pipe cut in half and glass to the boat under tanks then glass ends to permenant bulkheads. just depends on how fancy you want to get. $$ Good luck. Ken

 

No...

 

Have u ever looked at an engine mfg called Steyr ,,, high revolution diesel with small footprint and weight to power ratios are awesome... Many people are switching from mercruisers gas to this diesel with great performance success and not a total retrofit to install... just food for thought

 

Ken, I have considered foaming the tanks and my mechanic thinks I am a fool to not do it, since the area the tanks are housed is always dry. He thinks that corrosion would occur after another 30 years, if at all! If I am to do the foam method, I will run drainage under the tank.

Gruenemachine, yes I've heard of Steyr, but I am not considering them at this time. Funds and application are both issues, but thanks for the information.

Mark, what do you mean by "No..."? Foam?

 

Just my opinion. I have seen a lot of damage due to this. I can see an application - boats that are thrashed hard and you want the tank and foam to be part of the structure but my life is centered around making things last for the long haul and if any moisture gets in there, EVER, the whole mess turns to mush. I just don't see a reason to do it other than it is easy and looks very stout until it comes apart and the tank leaks into the foam.

 

Concur Mark.

No foam under tanks! The "dry areas" are not always as dry as we like them. And proper access is one of the "secrets" of your boats bristol shape.

Regards
Richard

 

Okay, I've heard this time again and I understand where some might be coming from; however, I am considering using foam. The original tank had 30 years of use and the only reason I replaced it was due to it probably being time. The tank didn't show any signs of corrosion.

The way I am intending on using the foam is on the sides and partially across the bottom. IF water was to get under the foam, it would be able to escape at the underside of the tank. As I mentioned before, I am also considering painting the area that will be foamed. What do you think? I will try to post a drawing of what I am considering.

Update: Here is what I am considering ... comments, please!



The yellow being the foam, black the boat and grey the tank.

 

Perfect moisture trap, congratulations! That is exactly the way the industry does it (or did at least) in mass products, where nobody asks for service life.

Listen to Marks comments, he knows from (painful) first hand experience what serves him well.

Regards
Richard

 

Thanks for the sarcasm, it was helpful!

If you look, the foam is only along the sides and part of the underside of the tank. The area of the keel and a portion of the underside is free of any foam (white area on drawing).

I was offering this for constructive criticism, since I thought leaving the underside free of foam would eliminate the chance of moisture entrapment. Also, as I mentioned in a prior post, I was going to treat the underside and sides of the tank with Alumiprep 33 and Alodine, finishing it off with an epoxy paint. Surely this would eliminate the possibility of corrosion.

I have spoken to the tank manufacturer and a few local marine shops and they all concur that hanging the tanks from the stringers without additional support is a bad idea. The possibility of the tank twisting and weakening the welds is their main concern; therefore, I need to find some way to support the tanks from below. Does anyone have any ideas?

 

Do what you were going to do anyway.

 

Mark, I understand the issue with foam, but I am trying to come to some compromise here. I am throwing out these thoughts and ideas for feedback, not because I am set in my ways and am going to do what I intended, anyway.

If you would like to comment on what I proposed and provide me reasons that certain things might be an issue, I think that would be very helpful.

Update: I did some surfing and read a very interesting post on another site. Here is part of a response that hits on what my concerns are ... and the concerns of some of the people I have spoken to ... good read!

"I’m still stuck on the material fatigue issue. Devil’s advocate here, I’d make the remark that I’d rather have a ¼” thick tank wall, foamed in, with an effective epoxy barrier coat, and try and manage the failure mode of corrosion, then to try and intermittently support an aluminum tank with the risk (however low) of catastrophic fatigue failure. When you mount an aluminum tank what is the fatigue life in cycles? You have localized stress concentrations that may be above the endurance limit of the material. How do you know with unknown load conditions and unknown material properties (in the vicinity of the welds)?

Note that a corrosion failure will likely be a pinhole leak, and may (hopefully) get noticed by smell before you get 600 gallons of fuel in the bilge. Not so a fatigue failure, when it goes, it goes-all of it.

How many “conventionally” mounted aluminum tanks with perfect drainage, no standing water and no corrosion fail from fatigue? I don’t know. How many T-Tops fail in the same way? That I do know-a lot.

All the speculation and worst case scenario stuff aside, and moving past bias and preference, is there any engineering reason why a properly mounted thick wall tank, coated with a non-permeable epoxy based coating (like coal tar epoxy), foamed into place with no standing water allowed , would EVER fail? If so, what is that reason?"

 

Well,

when you really coat it with Ep (that would be one primer film and one thick film layer at least) and have some space between the foam sheets, as you describe it, that could work well.

Regards
Richard

 

Richard, that was might thought. My only concern is that I've never worked with the chemicals mentioned and believe there is a trick behind using them. I'm led to believe that improper application can lead to corrosion issues, so I am researching this to make sure I am not headed for disaster.

Has anyone worked with Alumiprep 33 and Alodine? What might be the complications of an improper application? What, if any, are the tricks to applying these chemicals?