Do sterndrives (bellows) sink boats?

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

  1. marshmat
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    marshmat Senior Member

    Must have been a psychotic outboard engine salesman....

    I knew the Merc drives had their weaknesses, but did not realize that sinking from a bad bellows was among them.

    Guess I've been right to have been recommending the Volvo SX over the Alpha to friends looking for these things....

    Still, it is not at all difficult or expensive to come up with a nearly watertight shaft seal. Why would anyone design a sterndrive that does not include a seal in the transom assembly, inboard of the gimbal?
     
  2. CDK
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    CDK retired engineer

    My wife can pretty well take care of herself ( and me, if the need arises). My boat, on the other hand, needs much more attention than I can - or am prepared to- give. Right this moment she - the boat - is swinging wildly at her moorings. It has started to rain unexpectedly and I hear a distant rumble, the cover is rolled up in the cabin but the bilge pump will take care of that.
    My wife came in when the first drops fell and is now frying a nice steak.
    In a few minutes I will eat the steak and we will watch TV together.

    Do not compare a boat with a wife, there are galaxies between them.
     
  3. KnottyBuoyz
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    KnottyBuoyz Provocateur & Raconteur

    Pretty much any penetration of the hull is a potential risk to the boat flooding. Check out what happens when a boat with Z drives runs into skinny water... "scroll down near the bottom"

    http://www.thailandboating.com/page1/page1.html

    Although these are the VP drives I assume the Zeus drives would be just as susceptible to similar damage and flooding under the same circumstances.
     
  4. marshmat
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    marshmat Senior Member

    Good to know, KB. When Volvo and Mercruiser were heckled about "What happens if IPS or Zeus hits a log?", the answer was "the drive leg will shear off and sink, leaving the mount and hull intact." Apparently that's not what happens in reality....
    I have lost count of how many rocks and logs have been hit by outboard legs (and a lonely 1986 OMC Cobra sterndrive) on our lake. It keeps the prop shops happy, but I don't think I've ever seen a leak or any permanent damage caused by such a strike. That Cobra, on an 18' Peterborough runabout, was mounted so solidly you could probably have picked the boat up by the skeg. At last year's boat show, only a handful of sterndrive runabouts had engine/drive installations that looked strong enough to actually trust.
     
  5. Tim.M
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    Tim.M Junior Member

    That's what I'm wondering. Why does the world's most popular sterndrive have the bellows as the sole watertight seal. It would probably cost money to put a standoff box on the drive to move the ujoint aft to allow space for a stuffing-box-like seal at the transom, but it would be easily marketable. Would you like to risk sinking your boat, or pay $250 more for a boat that is safer? I think that would sell at a boat show, at least to the wife :p
     
  6. ben2go
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    ben2go Boat Builder Wanna Be

    Here is my take on things.I have never had a boat sink due to bad bellows.I have had them split from hitting debris under the water.I've never experienced a bad leak that a 500gph bilge pump couldn't easily handle.However,none of the boats were kept in the water and the out drive unit was always covered.I always did the up keep myself and replace the bellows if they became hard or cracked.I check them before entering the water also.So,in my honest opinion,it comes down to inspection and maintaining your vessel.
     
  7. fasteddy106
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    fasteddy106 Junior Member

    ben2go, you hit the barnacle on the crown, we can play "What if all the crabs come out of the ocean at the same time" all day, but the bottom line is the diligence and intelligence of the boat owner. The lazy and the dim get to see Par all the time, the rest get to cruise by him.
     
  8. stormin
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    stormin New Member

    On a fairline Cruiser we have the engine compartment is sealed off with a bulkhead (firewall) and that would stop the rest of the hull filling up and sinking should you have a split bellow, we then have a separate bilge pump in the main hull as well as the enging compartment, this is the only inboard i have owned and would of thought they are all built like that ?
     
  9. ben2go
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    ben2go Boat Builder Wanna Be

    Most of the newer boats are.Some of the older boats only have a bulk head that comes up to the sole(floor) level.Most of the smaller boats I have operated were like this.Most also had automatic bilge pumps.Usually just a bilge pump on float switch.
     
  10. CDK
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    CDK retired engineer

    My boat also has a bulkhead, so during the event the carpet in the cabin stayed dry. Just the engine bay flooded and that was damage enough.
    Had nobody noticed how low the stern was in the water, eventually the water would have started to flow over the top of the bulkhead to the compartment where the fuel tank is and from there to the cabin.
    There was an automatic bilge pump and two large batteries to feed it. the plastic pump body was distorted and the motor burnt out. It seems that a bilge pump is not designed to run for a long time: it may have a duty cycle of only 20%. It is also possible that a small object got into the pump cavity and blocked the impeller.

    It is too easy to point the finger at the owner and accuse him of neglect.
     
  11. Boston

    Boston Previous Member

    there is a thread in here somewhere that is about a couple who designed and built there own 80' motor cruiser
    in the pictures of there newest build they clearly depict a double compartment for the stern drive that would act as a one seal protecting another
    Ill try to go find it but the name of the thread escapes me at the moment
     
  12. Stutts
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    Stutts Junior Member

    http://www.yachtsurvey.com/GoodGrief.JPG

    Stern drives are a dog of a thing and very expensive to maintain and need a lot of maintenance, especially if they are sitting in salt water. The one in the photo above had oysters growing on the drive legs. They would have to be replaced at $10,000 or about half the cost of the boat.

    Most manufacturers recommend sterndrive/drive unit maintenance every 50 hours. To most boaters this equates to once per season and that includes an expensive stern leg drive alignment that should be done EVERY year... $$$. The only advantage of the stern drive is if the boat is doing a lot of miles per year and the saving on fuel over an outboard is worth taking into account re- service costs. They can sink your bank account long before they sink the boat.

    Anyone who had a look here would never buy a stern drive:
    http://www.yachtsurvey.com/SternDrive.htm unless they had money to burn and that's what they do best. For a good mechanic these boats can often be bought at bargain prices, as apart from selling to the unwary who have done no homework. These boats can be very hard to sell and often go cheap and that's what sucks in the mug buyers.
     
  13. Landlubber
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    Landlubber Senior Member

    Often the bellows on moored boats are left to get covered in barnacles, they love to cut holes in the bellows, but please, keep us in business and buy one....I do not know of any shippy that has not had good work from I/O legs!

    They would have to be the best money makers ever invented. Oh yeah, also the exhaust elbows are good at that, sorry, forgot about them, they are also good for a few quid.
     
  14. powerabout
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    powerabout Senior Member

    stern drives boats are kept in rack storage in the US..thats the answer
    PS
    dont forget the shift cable bellows will also sink a Merc
     

  15. marshmat
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    marshmat Senior Member

    There are a lot of valid points here regarding the vulnerabilities of sterndrive legs.

    However, we cannot forget the advantages that they do offer. For one thing, freshwater boaters don't really have to worry about the saltwater corrosion issue. And there are a lot of freshwater boats in the 16 to 30 foot range, with decades-old sterndrives, that are working just fine.

    Another big factor- and one that is important on more remote lakes- is the question of repairs. There are only a handful of sterndrive legs on the market, and they are not redesigned very often. And there are only a handful of engine blocks that are used with them. Apart from an ECU and fuel injectors, most of these engines have changed little over the years, and can be repaired by almost any engine mechanic. The leg itself, apart from the bellows and transom seal, is essentially the same as an outboard lower unit, and (once out of warranty) can be repaired by any mechanic familiar with outboards.

    Outboard engine product lineups, on the other hand, tend to be frequently redesigned, and if you don't have a local service centre for the brand you own, getting parts out in the boonies for a 20 year old motor can be a real pain. This seems to be especially true when direct-injection systems or computer controls are involved- these get redesigned for each model every few years, and the old ones become scarce and pricey. In saltwater, obviously, the ability to tip the outboard clear of the sea when docked is a big plus, but we freshwater types don't care about that.

    I'm not saying that sterndrives are the be-all and end-all. But they do have numerous benefits that, for many of us, outweigh the potential downsides. Especially with drives like the Volvo SX that appear not to have the sinking-from-cracked-bellows flaw.
     
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