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Seatrial vibration

Discussion in 'Technical Discussion' started by bayoubud, Mar 8, 2017.

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  1. bayoubud

    bayoubud Member

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    We recently surveyed/seatrial a Marlow 65C which had a lot of vibration. The port cutlass bearing was worn enough to warrant replacement and the stb trim tab would actuate down but not return up. They were able to get the tab up to run the seatrial (said boat did not need tabs to run) but did not get the message to the Captain and he trim the tabs down. Of course boat was leaning to port during the run after trying to raise the tabs. I was told two different possibilities for the noticeable shaking vibration, that it could be the underwater exhaust at certain rpm's, and with the stb tab down it would make the stabilizers try to compensate for the leaning to port. The surveyor said he could see the stb engine noticeably moving when this was happening. They are hauling the boat and doing repairs to seatrail again. What bothers me is the comments about exhaust vibration at higher rpm's and saying I would not normally be cruising at that speed anyway. No problems at slow cruise. Anyone experienced a similar situation with a tab down affecting stabilizers or with underwater exhaust vibration??
  2. Kapn

    Kapn New Member

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    This is likely to set off a slew of comments. But I've heard of Marlow vibration issues since their inception. The few that I've ran all vibrated, some owners have spent significant amounts of money at boatyards chasing the issue only to eventually give up. The tab and stabilizers compensating would add to it. There is a reason that no other manufacturers do twin keels in front of the props, clean water flow is important.
  3. olderboater

    olderboater Senior Member

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    This is one reason I advise that you cannot judge any Marlow on the basis of having run an "identical" one, because no two are identical. They constantly have made changes even to existing models, either mad scientist or constant improvement depending on how you feel about them. Therefore, until you sea trial the exact boat, you have no idea. Sometimes you learn as you did this time.
  4. bayoubud

    bayoubud Member

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    Not trying start a controversy, but I have no experience with stabilizers, underwater exhaust, or strut keels. My thought is if some of the exhaust was getting into the props it would cause a pulsating/shaking vibration, not a high pitch vibration. Seemed to be mostly on the stb side. Marlow's are nice boats with some good design features and this was the first time aboard one for us. They claim the keel strut design enhances water flow to the prop. I like the idea for prop protection but have not seen the design other than a metal boat that had metal tubes with supports and a skeg for protection. Also, I had done research on line and did not find many negatives other than mention of vibration on some earlier models plus being wet or not as good of ride vs another brand. Sounds like a problem that may not be fixable. Thanks for your comments about your experience with Marlow's.
  5. bayoubud

    bayoubud Member

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    Thanks ob. Sounds like this is a random problem specific to a hull#?
  6. Capt J

    Capt J Senior Member

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    Ok, I too wouldn't touch a Marlow. I ran a brand new 2014 56' once. It too had times when it had a lot of prop cavitation and vibration. Trim tabs and stabilizers generally do not cause vibration. However underwater exhaust does and it's location. Most Lazzara's have a huge problem with this, and Lazzara has come up with a hull modification called a fence to help a lot with it. Its a combination of too little propeller blade tip/tunnel clearance and location of the underwater exhaust too far forward and close to the props on them. I've seen it on a Lazzara where the cavitation was so bad, it was trying to rip the engines right off of the stringers. I'd go straight to a Fleming and never looked back, as I've run an Offshore in the same size range you're looking at and it too had horrible performance issues.
  7. bayoubud

    bayoubud Member

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    Thanks Capt J, funny I too was thinking if the exhaust dump was too far forward and even a small amount was sucked into the tunnels = cavitation/vibration. Just waiting to hear the results of repairs and new seatrial. Dang, you had performance problems with what size Offshore? One of my favorites, just hardly any 58 0r 62's on the market. Like the Fleming 55 but need more room inside and er. These RHP's are new too me, always had a sportfish.
  8. olderboater

    olderboater Senior Member

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    I wouldn't necessarily say random. It's a not uncommon problem that some Marlow's might have and others might not. I'd assume it until a boat proved me wrong.
  9. olderboater

    olderboater Senior Member

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    Of course a Fleming 55 is small beside a Marlow 65. Now a Fleming 65 will feel better although still won't feel as big. Just one huge difference. The Fleming can cruise the world.
  10. YachtForums

    YachtForums Publisher/Admin

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  11. bayoubud

    bayoubud Member

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    Good comments and advice, no way will I chase a vibration on a boat for sale, did that once. Was gawking at a Fleming 65 at Bradenton a few weeks ago, wow! Makes a 55 look small.
  12. Pascal

    Pascal Senior Member

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    I ve been running an 84 lazzara for about 6 months now, with the fences, and cavitation or exhaust gases aren't an issue as long as you don't jam the engine control forward. On sea trial the rent a cap hired by the seller did just that and indeed the vibration was horrendous. With the C32s the boat gets in plane at 1500rpm / 17kts and 38% load so i usually add 100rpm every second from 1000 to 1500. 5 second total... common sense

    It s like getting into a high performance car, putting the pedal to the metal in first and wondering why the tires are spinning...
  13. olderboater

    olderboater Senior Member

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    Good analogy.

    It's a characteristic you've learned to live with, to work around. Now, I don't think the Marlow solution is necessarily as simple.
  14. bayoubud

    bayoubud Member

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    That is some good speed @1500 on a 84. I can imagine those C32's are digging hard when accelerating fast. I do remember the capt going full throttle from about 1800. Not sure if that created the problem. The boat was 100 rpm from turning the 2300rpm by cat specs. Are the fences you mentioned similar to the faring buildup on the leading edge of a bow thruster opening?
  15. Capt J

    Capt J Senior Member

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    Yes they're a 2" thick and deep lip they glass halfway around the center side of the exhaust opening and then run back the edge a few feet. Quite honestly I would be looking for another boat. I would be buying a boat with majoring engineering issues from the builder and also poor business ethics from same builder. A 64' Hatteras MY is another option, they're fast some cruise at 28 knots but you can dial them back to 20 knots at 100 gph, or 10-11 knots at 15 gph or so. A lot less exterior maintenance than a Marlow or Fleming. The Offshore I ran was right around the same size as the Marlow you seatrialed.
  16. bayoubud

    bayoubud Member

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    We did look at a 63 Hat with 3412's had a great er. My last boat was a Hat sf with 3412's, great engines but was wanting inline 6's, speed is not a priority now. Did not like some things but overall a nice rig. You are right, much less maintenance, which has been a concern being a owner operator. I won't go into details but there are more issues with this boat from lack of use and deferred maintenance. Reviewing the maintenance records over the last 5 years got my attention, they are high maintenance boats. Everyone I have dealt with has been professional, answered all my questions, good to work with, and would hesitate to work with them again. There are a couple of other boats on my radar.
  17. Capt J

    Capt J Senior Member

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    Some 63' Hatteras MY's were built with C18's. I ran one with them, it still cruised at 24 knots and burned 75 gph.
  18. Pascal

    Pascal Senior Member

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    IMG_4421.JPG IMG_4422.JPG

    Here are some pics of the fence on the 84. I may be able to accelerate faster but never do because of passengers and stuff around the boat. I just don't see the need to jam the engine controls forward and stress the drivetrain for no reason.

    Boats are all about compromises... while the hatt capt J mentioned handles rough water better, in calm seas we burn 70gph at 20kts instead of 100... and the boat is bigger. Fast cruise is 26kts on 110gph and top speed is 32. And all that with no trim tabs...

    Back to the original question, vibration can be tough and expensive to trace...the things you mentioned like bad cutless, inop trim tabs are warning signs of neglect... big red flags
  19. bayoubud

    bayoubud Member

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    A Hat 63 with C18's would be a good setup. Have not seen one listed.
  20. bayoubud

    bayoubud Member

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    Pascal, your 84 has good performance and fuel burn. Thanks for those pics, never seen that fix. Interesting. Sounds like it cured your exhaust problem. Is this a common problem with underwater exhaust?

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