How Much Does it Cost to Marinize a Kubota?

Discussion in 'Propulsion' started by CatBuilder, Feb 3, 2012.

  1. CatBuilder

    CatBuilder Previous Member

    I'm trying to decide between and "off the shelf", pre-marinized Kubota (Nanni or Beta), vs. buying a Kubota and marinizing it myself.

    I imagine the steps would be as follows:

    *Fit raw water pump
    *Fit heat exchanger for raw water to coolant cooling
    *Fit exhaust mixer elbow
    *Fit zincs in heat exchanger if not already present

    I am finding that the 20HP engine I'm looking at is $8000 or so at Beta. I'm also seeing the same Kubota runs for about $3000 without marinizing it.

    I've always heard that marinizing your own engine is more expensive than buying a pre-marinized unit.

    So... I'm wondering... does it cost $5000 to marinize a 20HP engine?

    If not, what would you expect it to cost?

    Where do I find the suppliers for the pumps, heat exchangers and mixing elbows?

  2. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Include a Watercooled exhaust manifold . Remember the two pole electric system , gearbox, engine mounts and sub frame .

    I use mostly BOWMAN heat exchangers. Exhaust Water injection is normally home made.

    Kubota is a good engine

    Lister petter builds marine lifeboat might have a look
  3. CatBuilder

    CatBuilder Previous Member

    Thanks, for the input, Michael.

    I believe (but may be saying it incorrectly) that the "mixing elbow" is the water cooled exhaust manifold. Doesn't the water spray directly into there to cool the exhaust? They look like this:


    Check. I will see about the 2 pole electrical system. Wouldn't that just be a matter of using a 2 pole alternator and hooking up the control panel to that ground/earth instead of the rest? Also, engines are a negative ground/earth on all boats, so is there really any difference?

    No gearbox required on this unit. It's to run HVAC pumps. Very small engine.

    Doesn't an engine come with rubber mounts, or do only marine engines come with them?

    Since it is a new boat, there is no worries about an engine bed/frame, since it will be custom built for the engine.

    Am I making any incorrect or bad assumptions above?
  4. groper
    Joined: Jun 2011
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    groper Senior Member

    Id hazard a guess, due to your unique setup you probably could save yourself some money... most boating related products are seen as luxury items and therefore they see it as "if you have a boat you have money to burn" and premium prices are paid for anything with the word "marine" attached to it...

    Whereas the farmer types, are seen as the exact opposite... they are seen as "on the bones of their ***" and the marketing gurus price the products much more competitively it would seem...
  5. eyschulman
    Joined: Jul 2011
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    Location: seattle Wa USA

    eyschulman Senior Member

    If you dry stack and keel cool it can be reasonable and very reliable. Otherwise buy a marine unit.
  6. CatBuilder

    CatBuilder Previous Member

    Ok, dry stack isn't going to fly - charter boat. Has to be quiet. It's also going to run all the time, doing HVAC, watermaker and DC charging duty.

    Keel cooling is probably out, unless it can be recessed into the hull. Can it?

    I have to keep with my "no junk dragging below the boat" rule. :)
  7. groper
    Joined: Jun 2011
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    groper Senior Member

    Theres systems where the heat exchanger is actually embedded in the hull laminate... so no junk slowing you down externally, but you would have to make some changes to your otherwise completed hull shell to install it flush mounted... heres an example of a keel AC condenser -

    you might want to install something like these for your AC systems... and a larger version for the cooling of the engine... perhaps you could make these yourself also... wouldnt seem that difficult to have some bronze cast around some home made copper coils?
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    FAST FRED Senior Member

    "Ok, dry stack isn't going to fly - charter boat. Has to be quiet"

    IS your car loud?

    It probably has a MUFFLER, they are made in many grades (and volume) levels.

    Listen to a Honda 2000 or 3000 running , and understand what can be done.

    For commercial service , 24/7/365 nothing comes close to the reliability of KCDS.

  9. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    You are confusing exhaust water injection with the exhaust manifold.

    The water injection cools the exhaust gas as it enters the aqualift muffler.

    The exhaust manifold is the piece bolted to the side of the engine which collects the red hot exhaust gas from the cylinders. This exhaust manifold must be cooled. On an open workboat its sufficient to insulate this exhaust manifold with packing. In a closed engine room you will have to much heat buildup. A water cooled exhaust manifold would be very challenging to shop build with pipe. Most water cooled manifolds are cast.
  10. dinoa
    Joined: Oct 2007
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    Location: florida

    dinoa Senior Member

    If you want to go cheap get a 3 cylinder Kubota out of a freezer container or freezer truck unit. With dry stack exhaust the whole thing costs about $1500 installed here.

  11. CatBuilder

    CatBuilder Previous Member

    Ah, thank you, Michael.

    All these years, I never really paid attention to the exhaust manifold on any of the diesel I've owned. Never had anything to fix in that area of the mostly Yanmars (and one Perkins) I've owned. Didn't know they had an additional water jacket. Thanks for enlightening me.

    Question about dry exhaust:

    What do you do with the manifold then? I assume since you are still installing the engine in the same space, you need a liquid cooled manifold as well?

    Question about keel cooling:

    Can anyone recommend a setup that will be low (or no) drag?

    Dinoa: Yes, that's exactly the kind of engine I'm looking for, though I'll buy new just so it lasts. It's a brand new boat. I hope to have a few years before the heavy maintenance starts to set in. :) Even brand new, those engines are only $3K.
  12. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Solve the water cooled exhaust manifold problem and keel cooling is an option. I dont know glass boats, but on a metal boat " Skin" cooling is acceptable for small diesel power plants. Skin cooling is simply a water box welded inside the hull that exchanges heat thru the metal hull skin into seawater. Im sure a clever solution could be deployed for a plastic boat.

    With skin or keel cooling you gain still need a seawater pump to cool and silence the exhaust. I dont like a dry exhaust, muffler setup on a yacht. Dry exhaust is for workboats and pickup trucks.

    Personally Id go conventional kubota marinized diesel and leave keel cooling fo refer and ac heat exchangers. Keel cooling is particularly effective with refrigeration...the biggest power consumer on the boat.

    With so many small craft builders going bankrupt there must surely be some marinised diesel for sale cheap. Also look for ship wrecks...remove the marination parts from the seawater, huricane destroyed kubota and transfer to you civilian kubota
  13. Gian Milan

    Gian Milan Previous Member

    Cat, if you want marinizzare a small engine, you need to do three things.

    1) cool oil sump
    2) cooling the coolant of the radiator (which should be removed)
    3) cool the exhaust. this operation drastically reduces the noise.

    The sea water enters by means of a pump, mechanical or electrical.
    first exchanger cools the oil (you need to apply it).

    Then cools the heat exchanger with the liquid cooling.

    Finally, enter the double-wall manifold (it should be applied instead of the old) and from there, going into double-walled exhaust exits from the exhaust.

    The cost of the parts in AISI 316L, does not exceed $ 1000.

    Where is the problem?
  14. CatBuilder

    CatBuilder Previous Member

    The problem is here:

    Where do I buy the correct parts you listed in the States for a Kubota Z602 or D722 engine?

  15. Gian Milan

    Gian Milan Previous Member

    in the U.S. do not know, but from here I can send you a shipping container.
    except pump, no mechanical parts, and are eternal.
    The problem may be the exhaust manifold, but if you have the exact model of engine, this is not a problem.
    I'd take out the cooler oil pan. is a sort of double bottom which applies to the cup.
    Doing it this way, 80% of the heat of the entire engine goes away.
    The noise is much lower of the engine normal.
    I'm at your disposal and if you're really interested I can send you some pictures.
    do u want also price list of the engine?
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