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

Discussion in 'Diesel Engines' started by piperca, Apr 1, 2009.

  1. girvin
    Joined: Dec 2009
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    Location: Vancouver Island

    girvin Junior Member

    No I think they are different. they are the high horse higher revving ones used in planing hulls ours is in a 31 ft aluminum covered boat.
     
  2. mark775

    mark775 Guest

    Our local Volvo guy is genius - I'll see if he has an answer...
     
  3. piperca
    Joined: Mar 2008
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    Location: Southern California

    piperca Junior Member

    Wow, I'm surprised how much traffic this thread has got since my last visit!

    As before, I have been wavering back and forth, but have stumbled across a pair of Volvo Penta 41Bs that may be for sale very shortly. They have about 300 hours on them, so they might just fit the bill.

    The mechanic I am using is a certified Volvo Penta guy and has been around this area for years. He swears by these engines and thinks it would be a wise choice, given he's seen a lot of these engines in this specific make boat and feels they give excellent performance/fuel economy.

    Based on this configuration, what would be the best prop selection?

    Twin 41Bs (200hp); 280 outdrives (1.61:1, single prop); boat weight approximately 10,000lbs, loaded. (That's 7,000lbs dry weight, 1,500lbs fuel/water, 1,500lbs gear and persons)

    What kind of cruise, etc, would I see from this setup?

    Also, I have replaced the original tank (140 gallons) with two 82 gallon tanks. I am considerning running the engines off individual tanks. Do I need a separate vent for each tank? When grounding the tanks, can I run the tanks in series or do they need individual grounds? I am using Racor 500MA filters; should a 10 micron element be sufficient at the tank? Any additional input on this subject would be appreciated!
     
  4. BTPost
    Joined: Dec 2009
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    Location: Excursion Inlet, Alaska

    BTPost Junior Member

    For best Design, you should plumb both tanks to feed a separate Fuel Header for each engine, so that if you contaminate one tank, you can still operate on two engines from the other. In commercial vessels, they sometime plumb an Emergency Tank (50USG) into the Return Lines, that then overflows back to the Main Tank. This gives you 50USG, of CLEAN Fuel, that has been thru your Filter System, Injector Pumps, and Injectors, and is KNOWN Good Fuel, that then can be switched into the Engine Fuel Header, should you take any Contaminates into your Main Tanks. Leaves you 50USG to get home on, when ALL Else Fails. 10 micon Racor's will do you fine, for Main Fuel Filters. Just make sure you have two more than you ever figure you will ever need, aboard, at ALL Times, plus a couple of sets of whatever you are using a Secondary Fuel Filters. The old saying,that covers Fuel Systems is: A Prudent Skipper, NEVER runs out of Fuel Filters, NEVER... A little extra piping, NOW, will save you hours of misery, down the road.
     
  5. piperca
    Joined: Mar 2008
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    Location: Southern California

    piperca Junior Member

    I saw the description of that fuel system layout in another thread. One problem I see with my setup is that I do not have room for another 50 gallon tank, or any tank, for that matter. I had thought about running both engines off one tank at a time, but my mechanic brought to my attention the issue of rotating fuel supplies. There is a higher possibility that I'd run the same tank each time I'm out, which might cause fuel problems in the other tank. The other thing he mentioned was separating fuel, air and power to each engine, so, if I did have an issue with one engine, I would always have an engine to get home on ... that made a lot of sense to me.

    The Racors would be mounted directly off the tank and would filter the fuel before the engine-mounted filter unit. I think this would be sufficient filtering, don't you? I did think about doing a double 500MA system, but I think that's a bit overkill.
     
  6. mark775

    mark775 Guest

    There are some fine points with BT's post that I disagree with but will work fine.
    I'd probably just cross the tanks over. I'd also like to see a larger capacity Racor and if you are going to replace anyway, a system like mine is cleaner and has far more capacity.

    Picture 096.jpg

    Mind you this for a single engine.
     
  7. piperca
    Joined: Mar 2008
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    Location: Southern California

    piperca Junior Member

    That is a pretty clean setup!

    The Racor 500MA allows for 60GPH, which I think is plenty for the 41B. That coupled with the engine mounted unit seems plenty, don't you think? I don't know what size Volvo engine you're running, but, by the look of your engine room, I'm sure it is much bigger than a 41B. Wish I had such a space available.

    What do you mean by "cross the tanks over?"
     
  8. mark775

    mark775 Guest

    Well, I think that the 41 burns something like 10GPH and flows almost that back to the tank. Multiply that by two and you are looking at 35GPH total flow running thru a filter with 60 GPH flow potential if completely clean. It will work if everything is just so until you replace with common rail engines which flow much higher.
    By cross over I mean connect the tanks so that the fuel levels. It works well this way. I wouldn't use copper lines even tho I did - I just did it because it was always that way and copper was cheap...once. My preferred fuel lines are Swageloks and stainless tubing with a short fire resistant fuel hose to the engine.
    My thots on engine space are that the more pleasant the space is, the more likely you'll want to stay there and do maintenance. The bigger Volvos have a shelf that catches oil when changing filters. That and the plumbed in oil change pump make it a half-hour job on my boat to change oil. Filters almost never need changing as the first one is high capacity "trash" filter, the second, ten micron, the on-engine filter, two, I believe. Only change out a filter when the drag pointer changes position (mine hasn't in three years), drain a bit from the filters each day to see if there is water.
     
  9. piperca
    Joined: Mar 2008
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    Location: Southern California

    piperca Junior Member

    I think maybe I should explain my setup ... I think I did earlier in the thread, but here goes.

    I have a small 28' sportfisher , which has an 8' beam. The original engines were twin VP AQ225Ds (Chevy 305s) attached to VP 280 outdrives. The original fuel tank was 140 gallons.

    I removed the original tank and replaced it with two 82 gallon tanks, one forward of the other, installed along the keel line, forward of the engines. Here's a photo of the bilge area where the engines sit:

    [​IMG]

    Here is the area where the old tank was removed:

    [​IMG]

    Here are the new tanks in place:

    [​IMG]

    This will at least give you an idea of what I'm working with. I think, to keep the fuel level, I would need to run individual tanks to each engine, correct?

    Also, does anyone have input on the prop size I asked about a couple of posts ago?
     
  10. mark775

    mark775 Guest

    Hey, Piperca. I'm sorry, I made an assumption that the tanks were athwarts. Two observations; First, ideally there is air circulating around that tank and it never sits in water. Can you get it up even an inch higher or does this compartment stay completely dry? Second, if there is ever any moisture in that compartment, even condensation, it is not good to have brass in contact with aluminum - the AL is more noble and will rot from electrolosis. I have stainless bushings between my brass and aluminum and it is still the first area to rot on my tanks, albeit it took 31 years and still doesn't leak.
    I think the twin 41 Volvo setup is a good one, BTW. My preference is always for a single so that there can be a nicer space but you are almost already there with the twins. I don't know these engines but they are the ones all the little charter boats here seek - they are considered more reliable than later ones.
     
  11. piperca
    Joined: Mar 2008
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    Location: Southern California

    piperca Junior Member

    Yes, the tanks will be raised to allow air to circulate, I just haven't got around to permanently securing the tanks yet. This area does stay dry all of the time and has excellent ventilation.

    The old tank was of the same construction as the new, in fact they were made by the same company. The old tank was 30 years old and did not show any signs of corrosion around the brass to aluminum union. All of the Skipjacks had the same tank manufacturer and still do. He's been supplying the pickups and immediate fittings for all of these tanks, which are copper pickups with a brass elbow. To tell you the truth, I have never seen any condensation in the bilge of my boat, so maybe this is the reason there isn't any corrosion.
     
  12. mark775

    mark775 Guest

    Great. Keep up the good work and post pics as you go!
     
  13. piperca
    Joined: Mar 2008
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    Location: Southern California

    piperca Junior Member

    Maybe someone would like to give me a suggestion on how to accomplish the following.

    Take a look at this picture and you'll see the bottom of the tank doesn't quite fit the contour of the bottom of the boat.

    [​IMG]

    I would like to shim the underside of the tank, so it has support. I tried using Starboard blocks, adhered using 5200, as in this photograph:

    [​IMG]

    However, the 5200 did not stick to the aluminum. I was thinking about using Alumiprep 33 and Alodine, then painting the bottom of the tank where the shims would be placed. After painting, I would drill several holes or cut grooves in the Starboard blocks then use 5200 to adhere them. The holes or grooves would provide an area for the 5200 to accumulate to hold the Starboard shims in place ... do you think this would work? Does anyone have a better idea.

    I thought of placing a couple of wooden shims along the length of the tank, but attach them to to hull. Glue a rubber strip on top of the shim and then a bead of 5200 between the rubber and the tank ... am I getting closer ... LOL!

    Any suggestions would be greatly appreciated!
     
  14. mark775

    mark775 Guest

    I know you are sick of paying a welder but I would have angle welded on the sides and simply hang them from the stringers. It will be more than strong enuf and there will be no point of water contact.
     

  15. piperca
    Joined: Mar 2008
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    Location: Southern California

    piperca Junior Member

    Do you honestly think that the angle bracket would be strong enough? There would be about 660lbs of fuel in the tank sloshing around. I had thought of that but decided I was asking too much from an angle bracket. I guess I could put something under the tank at the keel and then have brackets on top of the stringers on either side ... what do you think?
     
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