Marinizing Rotary engine

Discussion in 'DIY Marinizing' started by greendeane, Aug 13, 2008.

  1. pbjosh
    Joined: Jan 2009
    Posts: 3
    Likes: 1, Points: 0, Legacy Rep: 23
    Location: Belingham, WA

    pbjosh New Member

    I signed up just to reply:

    I have 2 marinized 13B motors from a Mazda Cosmo in my 45' Chris Craft. They were done on by the previous owners while the boat was parked in the Columbia River.

    The engines are quite a bit lighter then the original inline straight-6 that was with the boat. The waterline is 3" higher then the boat was orginally with a near half the fuel and full water load. They not only reduced weight by a large amount, they added quite a bit of space to the engine compartment. We are only half joking about adding a jacuzzi.

    The engines from a Cosmo are carburated, in this case with a 390 cfm carb each, giving about 175hp each (over the stock 150hp inlines.) They are ran through a 3:1 gearbox, but I think they places props that are a bit large on, since the engines easily run 6000 rpm (and up to 9000rpm) but with the drive setup, they do not spin more then 3500 rpm (on WOT.) A 5:1 gearbox or a smaller prop will be installed soon. I believe the props are not the 19" that were installed on it.

    The carburator setup is normal, with just K&N air filters. I want to replace the carbs though, they are older and a bit on the worn side.

    The cooling system uses an exhaust manifold built for the engine that does have the cooling water injected into it. Right after the exhaust there is a 3" hose, then the connection to the exhaust lines. There is no abnormal cooling compared to a normal marinized engine, and the engine compartment is far cooler then the one in my bayliner. The motor is cooled through an external heat exchanger. After we replaced the thermostat the engines stayed at 180 no matter what the load. There is an oil cooler, but it is tsmaller than the heat exchanger for the engine. It runs off the same intake line.

    They are VERY smooth, and sound fantastic. There is a deep burble out of the exhaust at the back, while a very interesting whine from the engine compartment. There is almost no vibration from the motors though. There was some in the drive line, but none with the engines. I imagine re-aligning the engine and replacing a motor mount will fix that.

    Performance is a bit spotty, because the gear reduction wasn't enough, or the props are too large. The engine should run at 5000rpm for proper power and for proper lubrication. No, the engines do not need to run 2 stroke oil, they use normal 4 stroke oil.

    The 45' 30,000 semi-displacement hull runs a tad under 20 knots, but very smoothly. While a 15 ton boat shouldn't be moved much by the motors, it is so smooth you would think it was falling down the water.

    If you have any questions feel free to ask. We had to update, clean off and tune them up quite a bit, till we realized the ignition coils were bad. The motors were fine though, and we go just about the same speed at any other Chris of that make.

    Josh
     
    1 person likes this.
  2. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 145, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    Amazing, such small engines in 45' ship reaching almost 20 knots. Someone did a very good job indeed!
    It may well be that 3500 rpm is the point in the curve where the torque is at its maximum. In that case installing more reduction will increase fuel consumption a lot while adding very little to the ship's performance.
     
  3. pbjosh
    Joined: Jan 2009
    Posts: 3
    Likes: 1, Points: 0, Legacy Rep: 23
    Location: Belingham, WA

    pbjosh New Member

    Here is a Torque curve for a marine 13B (mated to a jet drive) from Rotary Power Marine Corporation:

    [​IMG]

    As shown, torque is maximum at 5500-6000 rpm, but not muc more then 350. We were at WOT also - and running rich because the RPM's wouldn't increase.

    Lowering the gearing would increase to torque at the prop, while having the same RPM range at the prop (1100 rpm at the prop or so) and allowing the engines to run at their optimum power.

    Like running a car at the wrong gear. Right now it is like trying to run in 5th while going up hill with a load. Dropping it down to 2nd or 3rd would allow for the boat to go faster, and allow it to run at an optimum rpm for the engines power generation. And save gas.

    But I do think this was geared for lower fuel consumption. And I want to gear it for more control and power.

    3500 rpm at WOT means a cruise at 3200, which on the older 13b's can cause problems with not enough oil lubrication. Part of the problem in RX-7's is that people do not rev them high enough. You should be running 5000 rpm to 6500 in daily driving to keep the apex seals lubed. That is where the engine is designed to run, keep lubed, and have the most horsepower.

    And these have freely zipped to 9,000 rpm without missing a beat. 6500rpm on WOT should be where these engines run to, NOT 3500rpm. Then I can tick back to 3500-4500rpm to cruise. :)

    Josh
     
  4. kistinie
    Joined: Aug 2007
    Posts: 493
    Likes: 8, Points: 0, Legacy Rep: -74
    Location: france

    kistinie Hybrid corsair

    Hi,

    Nice job !

    Do you have pictures of these exchangers and exhausts ?
     
  5. mydauphin
    Joined: Apr 2007
    Posts: 2,166
    Likes: 52, Points: 48, Legacy Rep: 575
    Location: Florida

    mydauphin Senior Member

  6. rasorinc
    Joined: Nov 2007
    Posts: 1,854
    Likes: 70, Points: 48, Legacy Rep: 896
    Location: OREGON

    rasorinc Senior Member

    Here is a company in the US out west in Washington state that converts rotary engines for marine use. The problem I have with rotary engines is they operate at high RPM to generate power so have to be reduced way down with the tranny. Even at moderate speed they are running high rpms and the fuel economy is non-existent. Also, not many people around to repair them. http://www.atkinsrotarymarine.com/
     
  7. kistinie
    Joined: Aug 2007
    Posts: 493
    Likes: 8, Points: 0, Legacy Rep: -74
    Location: france

    kistinie Hybrid corsair

  8. hwbd
    Joined: May 2009
    Posts: 10
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Ireland

    hwbd Junior Member

    I am a big rotary fan and I love the rx7(second and third gen) and the rx8.

    The rennesis engine in the rx8 has come a long way from the rx7 engines but it still requires more oil than a conventional reciprocating engine. It is also worth considering that a decent reciprocating engine will almost always last longer with no major parts replaced than its rotary equivalent. This is part of the nature of a rotary engine similar to a 2 stroke in that respect.
     
  9. powerabout
    Joined: Nov 2007
    Posts: 2,901
    Likes: 61, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    OMC made racing rotary outboards and chain saws ands skidoos
    dropped them all due to what they thought the EPA would do. but that was way back.
    Coolign the engine and the exhaust were the main problems after fixing the mechanical problems
    Sold the technology to a company making VTOL light aircraft
     
  10. MattZ
    Joined: Aug 2005
    Posts: 65
    Likes: 2, Points: 0, Legacy Rep: 21
    Location: British Columbia, Canada

    MattZ Junior Member

    If I'm not mistaken the RX-8 is turbocharged? You might need to look at heat shielding the turbocharger.

    I think the fuel consumption is a tad high on those engines, and the power output is lower than claimed by Mazda. From what I read, Mazda claims 240HP, but enthusiasts have gotten 170HP at the rear wheels in baseline testing.
     
  11. Cheesy
    Joined: Aug 2008
    Posts: 315
    Likes: 12, Points: 0, Legacy Rep: 189
    Location: NZ

    Cheesy Senior Member

    The RX8 is not turbo charged and has a completly different port configuration to the 13b RE or REW engines. As for oil consumption they dont actually use much more than a conventional piston engine. The way the oil injection is set up is a bit of a compromise, a better option is to either remove the oil injection and pre mix with 2 stroke oil or the pum can be modified so it uses oil form an external resivoir, and again 2 stroke oil is a better option than the engine oil. In a marine application a rotary should last as long as any piston engine.

    To pbjosh If you are worried about your engine not getting enough oil you can take the linkage off the oil pump and just wire it to the full throttle position.... it doesnt really make all that much difference, and good luck with getting a 13b to live at 9000rpm
     
  12. jcraig
    Joined: Sep 2009
    Posts: 5
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Alaska

    jcraig Junior Member

    Rotary engines

    Here is a web site where there has been extensive research done as well and possibly down the road a good source for marine and other uses. I have been following these folks for years and am just waiting for the end result of several things that I am considering.
    Also, it is my understanding that these engines can be multi fuel run, ie diesel, rendering them safer than gas in an enclosed bilge.
    I would be interested in the fuel consumption of the 45' boat as well,...
    Jeff:)
     
  13. jcraig
    Joined: Sep 2009
    Posts: 5
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Alaska

    jcraig Junior Member

    Rotary engines

    Here is a web site where there has been extensive research done as well and possibly down the road a good source for marine and other uses. I have been following these folks for years and am just waiting for the end result of several things that I am considering.
    http://www.freedom-motors.com/
    Also, it is my understanding that these engines can be multi fuel run, ie diesel, rendering them safer than gas in an enclosed bilge.
    I would be interested in the fuel consumption of the 45' boat as well,...
    Jeff:)
     
  14. Cheesy
    Joined: Aug 2008
    Posts: 315
    Likes: 12, Points: 0, Legacy Rep: 189
    Location: NZ

    Cheesy Senior Member

    If you want an engine that is actually in production have a look here
    http://www.uavenginesltd.co.uk/
     

  15. jcraig
    Joined: Sep 2009
    Posts: 5
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Alaska

    jcraig Junior Member

    rotary wankle

    Thanks Cheesy, I e-mailed them to inquire. It looks like they mainly service the military, but it doesn't hurt or cost to ask. Is this something that you have looked into as well? Or did you just run across it?
    Thanks again,
    Jeff
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.