310da bravo 3 drive ventilation problem

Discussion in 'Diesel Engines/Drives/Transmissions/Props' started by Big blue, Nov 19, 2017.

  1. Woody

    Woody Well-Known Member

    Nov 20, 2007
    N. Wisconsin/Lk Superior
    2005 420DA
    Cummins 6CTA8.3
    Are your drives and props original spec? What do you normally cruise at, rpm and speed? Can you reach WOT rpm? Are you saying that when this happens at 23-25mph, your drives are trimmed all the way down?

    I'm not sure what kind of performance to expect from this diesel/B3 combination but it sure doesn't sound like slipping clutches or couplers to me.
     
  2. Big blue

    Big blue Member

    32
    Nov 19, 2017
    Cardiff u.k.
    310da sundancer 1998 mercruiser D4.2
    Mercruiser D4.2
    I assume they are the original drives, they are the correct matching ratios, I have changed the props to brand new 4x3 elite series 24p, no real change on this problem from the old 26p 3x3, just better hole shot, which was rubbish on full load before.
    I cruise at 20 knots which is about 23-25mph, around 2700-2800 rpm, and that’s where the problem lies, if I push engines up to 2900-3000 rpm the problem has gone, but I am then doing about 24-25 knots, which is too fast for choppy water( too uncomfortable), she will go up to 3700-3800 rpm and will hit 35 knots which I think is about 40 ish mph.
    Drives are always trimmed in until about 26-28 knots where I trim them out a little,the bow will lift,and it’s great, but I need to be going at lease this speed to trim out as any lower or the bow won’t lift and the props will just lose grip
     
  3. Woody

    Woody Well-Known Member

    Nov 20, 2007
    N. Wisconsin/Lk Superior
    2005 420DA
    Cummins 6CTA8.3
    Looking for info the 1998 parts manual doesn't even list your D4.2B3 option http://www.searay.com/boat_graphics/electronic_brochure/Company1729/1C1_24_74DEIPR3TAP.pdf

    but the 1999 parts manual does http://www.searay.com/boat_graphics/electronic_brochure/Company1729/1C1_24_74DEIPR48C2.pdf

    It shows a 1.81:1 drive with 22 pitch props.

    What you describe is not much different than my '05 280DA, although I could stay on plane a little slower there still was a point that it struggled and couldn't anymore. I'd get prop slippage there too, if the drives were trimmed up at all or the more they were trimmed up the sooner it would happen.

    I'm thinking there's nothing wrong with your boat with the exception being a question on props because the 22p is listed in the parts manual. Maybe talking to a prop shop would help....are your props cupped? maybe more cup? If you have little or no cup, then the adding cup would help in this situation but there's usually a trade off, like maybe slower mph at normal plane speed.

    Maybe you tried this already but....with any boat I've had I've found when conditions get rough, if I drop trim tabs it improves the ride by forcing the bow to cut. I'd drop tabs first at a speed it would take it, then back down on the speed as needed, until you can't. The end result for you might be that your not going any slower but still have some improvement in the ride.

    Even though my 420DA is pretty versatile in rough conditions there's days you just can't get a tolerable ride on plane. Sometimes the waves look about the same to me but the frequency or steepness must be a bit different because I end up with two choices, get off plane or shake the beer cooler until the caps blow off.
     
  4. Big blue

    Big blue Member

    32
    Nov 19, 2017
    Cardiff u.k.
    310da sundancer 1998 mercruiser D4.2
    Mercruiser D4.2
    The 1998 does come with a d4.2 tronic option, I have the original sales brochure for the boat and mercruiser commissioning certificates for the engines dated 1998, the 1999 is a different model with a revised saloon, I have the older model, I have looked at searay specifications for these models on the diesel props, it’s on internet somewhere but it does state that the 1998 has 26p then they revised it twice to a 24p then 22p, not sure if the 22p has the 250hp d tropic motor, but a 22p in my application would give me too much wot.
    I understand that on slow cruise when the wet area of hull increases it can cause issues staying on a plane, but this is different, and the std drive reacts different to the port, to the point it will slip in calm waters at sea too.
    Had some experiences on another boat, sealine s34 with d4.2/b3 and the props dont slip like this,and that boat to didn’t like trim out at low speed.
    Also with the trim tabs, I do use them to slow the boat down in rough sea to keep the revs up, but they ain’t the best, they are a bit too small for the boat
     
  5. techmitch

    techmitch Well-Known Member SILVER Sponsor

    May 1, 2008
    Chesapeake Bay, Middle River/Frog Mortar Creek MD.
    1999 270 DA
    Twin 4.3s W/Alpa I Gen II's
    Possible "Hook" in the hull?
     
  6. Big blue

    Big blue Member

    32
    Nov 19, 2017
    Cardiff u.k.
    310da sundancer 1998 mercruiser D4.2
    Mercruiser D4.2
    I have looked for any hook or rocker in the hull, but everything looks straight, I am going to remove the downscan on next haul out of the water as it will cause some cavitation, it must help a bit even if it isn’t the main cause, shame I couldn’t fit an underwater camera to view what is going on under there
     
  7. Christian Hakansson

    Christian Hakansson New Member

    1
    Jan 11, 2017
    Salt Bay
    Sea Ray 370 Sundancer -90
    Sea Ray 280 Sun Runner -95
    Sea Ray 250 Sundancer -95
    Sea Ray 22 Pachanga -
    Twin 454
    I had the exact same problem on a -95 Sea Ray 280SR. 454 Bravo 3.
    The drive could not be tilted, and in turns the drive would slip, also in mild seas the drive would slip just like you describe. Vibration could occur when slipping.

    This was really annoying. I noticed when i measured the keel to cavitation plate, i had like 1" rising of the drive.
    That will be totaly OK in B1 configuration.
    Also the 280SR is a little bit bow heavy with single engine, this cause the drive to ventilate with a B3.

    Ended up buying one of these drive spacers, i think i put a 1.5 inch spacer on it.
    Ventilation GONE.

    http://www.lathammarine.com/bravo-bravo-spacers.htm#1.

    // Chris
     
  8. techmitch

    techmitch Well-Known Member SILVER Sponsor

    May 1, 2008
    Chesapeake Bay, Middle River/Frog Mortar Creek MD.
    1999 270 DA
    Twin 4.3s W/Alpa I Gen II's
    Interesting, never saw/heard of these before. Good first post, welcome to CSR.
     
  9. Big blue

    Big blue Member

    32
    Nov 19, 2017
    Cardiff u.k.
    310da sundancer 1998 mercruiser D4.2
    Mercruiser D4.2
    Thanks Chris, never seen these spacers, there is a lot of info around about correcting ventilation problems with mounting heights of outboards, but with stern drive it’s a bit difficult, but this spacer is the answer, I understand on a single drive the cavitation plate is supposed to be level with the bottom of keel, I take it on the twin setup the centreline of the cavitation plate is supposed to be inline or below the hull, I need to check this too when boat comes out, I think the drives are too high, but not by much, maybe 1/2”.
    Waiting for weather to warm up a little and will be pulling boat out and trying a few good suggestions that I have from this site so far
     
  10. Big blue

    Big blue Member

    32
    Nov 19, 2017
    Cardiff u.k.
    310da sundancer 1998 mercruiser D4.2
    Mercruiser D4.2
    8B2A2E52-DC9F-4520-8AAA-BCCACB3B1407.jpeg 03D1AA81-8C5B-4F5E-8EDF-6345FED55B8E.jpeg 477748B3-17ED-45AD-889F-8213B830DF16.jpeg Update of progress so far
    Boat is out of the water and a few points raised are being assessed, so far removed the downscan as it was inline with the starboard drive, the cavitation plate is in line with the hull, but only just,still worried about the bearing carrier corrosion, not sure if this can cause cavitation,few photos added 78038FB7-9791-4CBF-9E06-B3E380E75ACD.jpeg
     
  11. Bt Doctur

    Bt Doctur Well-Known Member

    Aug 21, 2010
    New Jersey
    Ex SRV 240 Weekender twin
    in between
    I see 2 possable issues, The cavitation plate is above the water line and the transducer right inline with the prop.Any shart turns will expose the prop to air.
     
  12. Big blue

    Big blue Member

    32
    Nov 19, 2017
    Cardiff u.k.
    310da sundancer 1998 mercruiser D4.2
    Mercruiser D4.2
    BD1A40C9-7117-446D-9DCE-0735FA9DA80A.jpeg D2556C8E-3811-406E-9D80-090583825297.jpeg I was a bit concerned about the cavitation plate being too high, I have removed the transducer, and fitted a flush blank instead, what’s your thoughts on the bearing carrier with a chunk missing, I have attached a photo of the prop installed and there is a small hole between gear case and hub, I have inserted a small screwdriver in the gap to illustrate
     
  13. WasteKnot

    WasteKnot New Member

    2
    Aug 18, 2015
    Holland, MI
    340 Sundancer 2006, purchased 03/2018
    Mercruiser 496 Sterndrives
    Did you ever get this issue resolved? I bought a 2006 340 Sundancer this year with 496’s and Bravo 3 sterndrives. I inherited the same problem - what I thought from the beginning was cavitation during acceleration and at cruising speed in anything but perfectly calm seas (Great Lakes). Below 3000 rpm I’m losing ground on plane.

    I just replaced the props from the original 3x3 26p to Hill Marine 4x4 at the same pitch (per their website). Much improved the cavitation, especially in waves, but it still happens during acceleration, plus I lost 300 rpm in WOT. I am planning to exchange the 26p with 24p, which should fix the rpm issue. Wondering if the cavitation with 24p will be better or worse.

    The engines only have 290 hours and drives looked good. I am curious about the spacer suggestion - I have not considered that, but plan to research it. I do have a factory installed bow and stern thruster, but nothing else protruding from the hull. Stern thruster is not below the transom. Curious what the minimum should be for the cavitation plate to be below the hull line.
     
  14. WasteKnot

    WasteKnot New Member

    2
    Aug 18, 2015
    Holland, MI
    340 Sundancer 2006, purchased 03/2018
    Mercruiser 496 Sterndrives
    I’ll correct myself - I believe the props are ventilating, not necessarily cavitating.
     
  15. Big blue

    Big blue Member

    32
    Nov 19, 2017
    Cardiff u.k.
    310da sundancer 1998 mercruiser D4.2
    Mercruiser D4.2
    Hi
    I have improved the problem a little on that the starboard engine doesn’t cavitation as much as the port by removing the transducer, but in rough water below 20 knots they cavitation, or like you say, they may be ventilating, but not sure as yet, I have tried to resolve this with changing the props to 4x3 later design units with no change on the matter, my only assumption is that the drives are not low enough in the water, but this involves fitting extensions which are costly, are your drives aligned straight or are they a little toe out, I measured the props 1/2” closer together than the front of the drive casing, as this seems to make a big difference from toe straight
     

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