Do sterndrives (bellows) sink boats?

Discussion in 'Powerboats' started by Tim.M, Apr 17, 2009.

  1. Tim.M
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    Tim.M Junior Member

    I'm looking at a couple boats, one with outboard and the other stern drive. I can't help shaking the fear that cutting two big holes in the transom for the sterndrive with only rubber bellows to keep the water out is a bad idea... Do failed sterndrive bellows or gaskets sink many boats?
     
  2. KnottyBuoyz
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    KnottyBuoyz Provocateur & Raconteur

    Volvo Penta's, no, Merc outdrives, yes. OMC's, I don't know.
     
  3. Tim.M
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    Tim.M Junior Member

    Thanks KnottyBuoyz,

    Do the Volvo Pentas have a backup gasket or something more like a stuffing box, or how do they not have the same weakness as the mercs?

    Are there stats on how many boats sink because the merc bellows fail?
     
  4. KnottyBuoyz
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    I don't know if the VP's have a gasket but the drive shaft fits tight into a bearing. If the bellows splits etc. it'll drip but definitely not enough to sink a boat. Ours is a 290DP and we split the bellows year before last. We had about a half cup of water in the boat after a week sitting like that. My buddy had his boat sunk when a muskrat chewed up the bellows on his merc bravo outdrive.

    I don't know of any agencies that track those types of statistics. You might want to contact your insurance agent, they might be able to find out.
     
  5. PAR
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    PAR Yacht Designer/Builder

    Leaking bellows have sunk many an I/O equipped craft. Keep it serviced and it's not a problem.
     
  6. Tim.M
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    Tim.M Junior Member

    Does this mean that the symptom that almost always leads to failure is obvious to the eye, as in small cracking of the rubber always showing before it splits catastrophiclly? Or that the bellows are best replaced every x-years regardless of whether they show any symptoms?
     
  7. PAR
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    PAR Yacht Designer/Builder

    Bellows have a replacement cycle just like oil filters. If they are used frequently (the boat) it will live longer. If the boat sits idle for long amounts of time, it will dry rot and split, crack, etc. much faster.

    On boats with I/O assemblies, 70% of the reported sinkings, were a result of some sort of bellows issue.
     
  8. Tim.M
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    Tim.M Junior Member

    Wow - 70%! I expected it to be something but not that high.

    Are most "sinkings due to sterndrive" while the boat is sitting at anchor, buoy, or dock?

    Do most boats have enough of a hole behind them when underway that they won't sink if the bellows crack from steering/trimming under power?
     
  9. KnottyBuoyz
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    Like Par said, the likelihood of a boat sinking due to negligence is high. This includes good bilge pumping arrangement w/adequate battery capacity. Water ingress into the hull by any means is a threat and bellows aren't the only route. Any thru-hull fitting is a risk especially if they're not installed, maintained or operated properly.

    Again, I don't know of anybody that gathers these types of statistics other than maybe the insurance industry. I work for the Cdn. Coast Guard and I know we don't have those stats.

    Sterndrive equipment has been around a long time now. They're for the most part efficient and reliable and safe if as has been said if they're maintained properly. I can personally attest to the high cost of repairs if bellows aren't changed as recommended by the manufacturer having lost the use of our boat for a season the year before last when the bellows broke after only 3 years use in fresh water.

    Personally I wouldn't sweat it too much. If it was really such a big problem nowbody would own them right?
     
  10. marshmat
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    marshmat Senior Member

    Good point about the bilge pump capacity, Rick (KB). I am always surprised, at the boat shows, how few manufacturers fit adequate pump capacity as standard. The little 800 or 1000 gph pump that is usually standard equipment on 18' bowriders can only handle the equivalent of a couple of garden hoses, and would be completely overwhelmed if the bellows of a Merc Alpha were to fail. (Indeed, I've seen a few that were too small even to keep up with a missing drain plug.)
     
  11. PAR
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    The USCG and the insurance industry do keep these figures. I got mine from a report made in 2003 by the USCG. The insurance industry figures are higher in regard to I/O bellow sinkings.

    I change bellows all the time. In fact I wouldn't let a guy leave here a few weeks ago unless I changed out both his OMC bellows (plus the other work) or he was taking it directly to some one who would change out the bellows (I know everyone locally and would have checked). He was pissy until I told him what would happen and the statistics for I/O's. What is it about Bayliner owners anyway . . .
     
  12. rasorinc
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    rasorinc Senior Member

    Do you guys recommend any product to apply to the rubber to keep it plyable and crack resistant??? Or just cover it from the sun and weather when not in use? thanks
     
  13. PAR
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    PAR Yacht Designer/Builder

    The bellows rubber can get quite hot, causing it to take a set. Some chemicals can soften the bellows to a degree, but frankly, if you're at the point where you need to think about this as part of your maintenance, then it's time to change out the bellows.

    The common problem is the boat gets used, run hard, the drive is lifted to it's full up position, then it's parked for months, even years before it's used again. The hot rubber take the set of it's last position (up) and maybe has some dry rot or UV degradation. The drive is lowered and because it's "hardened" into an up position, it pulls the top lip out of the groove and the boat leaks. You don't notice the leak, because the engine sits in a well, aft of the attention of the driver, but eventually the battery shorts, you lose speed from the stern dragging or something, you turn around to see water well over the sole and the butt of the boat way lower then it should be. At this point you're screwed unless you happen to be carrying a Honda 5 HP with an attached pump.
     
  14. rasorinc
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    rasorinc Senior Member

    Thanks Par I tried to post but told I have to spread it around first. Stan
     

  15. fasteddy106
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    fasteddy106 Junior Member

    Hi Guys, great to be here!

    I've had an OMC for the last 8 years and never had a problem with the transom seal other than the real p.i.a. it is to change it for p.m. You need three hands and a whole lot patience. The gasket is pretty durable but cleaning and inspection is of course needed. Barnacles can cause some damage as the gasket flexes so keep it clean. Other than a puncture by a sharp object there is really nothing to worry about. I've seen more boats get in trouble from bad bilge pumps than transom seals.
     
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