25hp Mercury EFI Prop???

Discussion in 'Prop Shop' started by Rbeasley, Jun 11, 2009.

  1. Rbeasley

    Rbeasley I Love microskiff.com!

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    Hey guys I hate to do this on my first post, but this forum is what I was looking for. I have spent countless hours searching for info about props with these smaller engines. I think my wife is getting suspicious! Finally a site where you don't have to have twin 225's to find info.

    Here is my deal. I have a 1995 Scout 141 Sportfish. The boat and engine weigh approximately 475 pounds. In addition I have a CMC tilt plate. The engine is a 2007 mercury 25hp EFI 4 stroke. I am guessing with two people aboard along with gas, anchors, cooler, ect the weight is around 1300 to 1400 pounds

    The cavitation plate is approximately 1" above the bottom of the hull. With the heavy 4 stroke, and several inch setback of the CMC tilt the boat is stern heavy. If me and my wife are sitting at the bench seat behind the wheel the boat will not plane and the rpm's will not crack 4500. If one of us goes forward the bow will come down, and the boat will plane off. RPM's around 5200. Recommended is 5000 to 6000. The gear ration is 1.92 to 1.

    Running in the busy waterway we are constantly having to slow down, and one of us has to go forward to plane off. It gets kinda old.

    The prop is a 9.75" x 11 pitch. The engine is set on the lowest manual tilt pin location. It still seems if I could get a little more negative tilt it may plane out on its own.

    My thoughts are 9.75" x 9.5 pitch prop, transom wedges, and or smart tabs. The reason I posted here is with all the talk of cupping, rake, and other things I don't quite understand I wonder if I need to find the proper prop. I suspect the boat is somewhat underpowered, but I really am not looking to go that fast. I am more interested in it being able to plane off at slower speeds.

    Thanks in advance, and I will update if you guys are interested.

    Richard
     
  2. mark_gardner

    mark_gardner I Love microskiff.com!

    sounds like you need to decrease your pitch and maybe install a hydrofoil or some tabs. i had the same motor with a 12 pitch proip and always felt that the motor had more to offer if i would have just changed pro but decided to sell it instead :-/
     

  3. iMacattack

    iMacattack busy, too busy

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    Welcome to the forum... Gin and Tonic Please...  ;D

    You don't have to have twin 225's here, just trip 25's...

    [​IMG]

    ;D

    I think the first thing you should consider is balance... Can you put any permanent weight forward... Fuel Tank, Batteries etc.

    Second you need less pitch. Now here comes the fun part. Hope you like test and tune? Your thought on a 9.75 X 9.5 might not be too far off, but another thing to consider is material. A SS (stainless steel) prop will perform better than an aluminum.

    Before you try a bat wing mounted to your motor I would recommend a set of tabs. Bennett, Lenco and Minn Kota all have a form of powered tabs. If your not ready for this move Smart Tabs would be the next obvious choice.

    I would start with the transfer of weight first. Then move to the items that will cost you some coin.

    Cheers
    Capt. Jan
     
  4. Brett

    Brett > PRO STAFF <

    Looks like you've defined the problem quite well.

    1) Stern heavy... shift the load to balance the boat.
    2) Change of pitch will up your rpm's, allow a better hole shot.
    3) Trim tabs will solve the rest.

    What do you need us for? ;)

    btw, welcome aboard.
     
  5. noeettica

    noeettica Well-Known Member

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    Welcome :)

    9.75 x 10 ?

    Or Try Ron He can assist you ...
     
  6. Rbeasley

    Rbeasley I Love microskiff.com!

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    Thanks for the replies guys!

    Of course I like to tune and tinker. That's a good thing if you own a boat. I have been told BOAT = Break Out Another Thousand.

    I will update with changes and outcome.

    Thanks,
    Richard
     
  7. TomFL

    TomFL Well-Known Member

    I have the same motor, albeit on an LT25 gheenoe hull.

    Two words:

    Doel Fin

    [​IMG]

    Will solve your issues for $35. Half the price of a new prop. Trust me when I tell you 1.5" of pitch change on this motor is a huge difference; I had a test I posted here a long time ago on this motor and the Doel-fin setup. The boat is much, much quicker to plane (less than half the time), no bow rise, will stay on plane at a lower speed, rides nicer at any speed, and is slightly faster with the doel-fin. Plus, unlike tabs and trim plates or jackplates there is never any fiddling. Just bolt it on and forget it.

    Granted, even I'll agree you'll be able to fine-tune a hull better with trim/tilt and a jackplate vs the doel-fin, but on a small hull like this, what are you realistically going to pick up, like 1 mph? And what is the $$ outlay to do so vs the doel-fin???

    BATWING to the rescue.......!!

    -T
     
  8. Rbeasley

    Rbeasley I Love microskiff.com!

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    I promised to update, and I think I went overboard. I found a great deal on a brand new 40hp.

    I have a contest going on the general discussion. Guess my speed and win a tach harness.

    Thanks guys!
    Richard
     
  9. TomFL

    TomFL Well-Known Member

    Same two words. Now more than before!

    -T
     
  10. Rbeasley

    Rbeasley I Love microskiff.com!

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    Re: 25hp Mercury EFI Prop???Slight Update

    Tom it will be a cold day in you know where before I install a fin on my motor. Just not a fan of them. No offense meant. I appreciate all replies.

    Further testing with the 40hp. I raised the engine one notch and it is hard to tell if any difference was made. Boat was still porpoising badly.

    The cheapest fix of the century. Two sand bags, 100 pounds total in the bow anchor locker did wonders. Of course that is temporary. The boat slowed some, but the riding attitude changed for the better. Planes at a slower speed. The titanic sized wake is gone. The boat was a very hard ride, and now it feels like I am lounging in a lazyboy. Much better, but still will not take trim before porpoising starts.

    I will run it again this week with the battery moved under the console, and one bag of dirt removed. There was a slight hook at the stern that I sanded off. I have a feeling it has much to do with the porpoising.

    I think I need a prop with more stern lift. Does anyone here know the rake or stern lifting characteristics of a Mercury Blackmax 10.25" x 14 3 blade aluminum prop?

    Thanks guys!

    Richard
     
  11. Brett

    Brett > PRO STAFF <

    Electric trim tabs.... ;) ;D
     
  12. TomFL

    TomFL Well-Known Member

    Re: 25hp Mercury EFI Prop???Slight Update

    No worries about the doel-fin, some people don't like the way they look. Some couldn't care as long as it solves their issues, and that's my position on it.

    As far as your setup, I highlighted something in your post above that makes me wonder if you're making your problem worse. You say you raised the outboard one notch on the pin, which would raise the bow and effectively make the porpoising worse.

    That may be a typo, but if you have been raising the pin one notch at a time, you're going the wrong way to solve a porpoising issue.

    Keep us posted

    -T
     
  13. Rbeasley

    Rbeasley I Love microskiff.com!

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    When I say I raised the engine I mean height not tilt pin. The engine has power tilt, so there are no tilt pins. The AC plate was below the bottom of the hull, lowest setting, so I raised it one bolt hole.

    Richard
     
  14. rkmurphy

    rkmurphy Well-Known Member

    Cav plate level with bottom and motor tilted to where it is level. That's where mine works best...I was lucky and had it right first try.
     
  15. Rbeasley

    Rbeasley I Love microskiff.com!

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    Re: 25hp Mercury EFI Prop??? Update

    Well since I last ran the boat I have done some work on the bottom including sanding off a hook at the transom, and a small bulge further forward. I also moved the battery under the center console. I removed the 100 pounds of sand from the anchor locker. Today was the first run.

    It is a completely different ride. It is much softer, and the porpoising is almost gone. At high speed it goes away unless you start giving it trim.

    Went back to the dock and added 50 pounds of sand, and ran it again. I didn't notice too much difference except it seems to have slowed the boat down a fraction, and the boat will now take a few bumps of trim. Still more work to do. The chine walking is history. It may have been the boat wanting to ride on the hump.

    I don't know if the tach is correct, but it show 6500 rpms at approximately 3/4 throttle. I think the rev limiter is 6300 rpms, so I suspect the tach is wrong.

    I know the paddle wheel speedo is wrong It was showing 60mph!!! I think the boat was running 40 to 42 or so.

    I will continue with the updates until you guys get bored.

    Going really work on the bottom this winter. Next move is another battery under the center console a little farther forward and a battery switch.

    Richard
     
  16. TomFL

    TomFL Well-Known Member

    Glad to see it's working out for you. That's what tweaking is all about.

    Keep us updated!

    -T
     
  17. mark_gardner

    mark_gardner I Love microskiff.com!

    you really should reconsider the hydrofoil idea, i have used them thru the years on various small boats like the ones we're dealing with and they have always improved the ride one way or another
     
  18. Rbeasley

    Rbeasley I Love microskiff.com!

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    Yea but repairing the underlying problem also works. The boat is running very well without a fin. The hook removal solved the porpoising. The hump removal solved the instability, and the weight shift has improved the ride. Just a little more weight up front, and blueprinting the bottom and it will be even better, and probably more stable than just adding a fin.

    Richard