transom strength for shaft to outdrive swap

Discussion in 'Sterndrives' started by arthor, Oct 26, 2009.

  1. arthor
    Joined: Apr 2008
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    arthor Junior Member

    Greetings all.

    I have a fjord 27 with a very tired old 6 cyl volvo 106hp on a shaft. I am looking to clear more space in the cockpit area and also up the power. These boats are reknowned for their strength and other examples have been fitted with up to 200hp.

    Streamenvironmental here in the UK do marinising kits for peugot 1.9l (90-115hp) turbo diesels with an adaptor plate for volvo 270/280 drives.This is quite a common engine over here and I thought it would solve the power increase and space problem all in one. It would also ease my paranoia about only having one engine. I see it as giving me some problems to overcome

    1) Weight distribution - At the minute a gert water tank sits in the aft cabin and that could be moved forward along with batteries etc.

    2) Beefing up the transom - To what extent would this need to be done? The engines themselves sit on their mounts and surely only the drives hang off the transon.

    3) I know I will have to put two holes in the transom but to what extent do you think I would need to involve "professionals" in order to ensure a successful survey and renewed BSS Cert?

    4) Once the other engine etc is removed, I think I should be able to cut/grind off the skeg and then glass over any redundant through hull openings. Would I also need to fit short skegs for the outdrives?

    Your views on this, probably insane, scheme would be appreciated.

    thanks arthor
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Giving advice helps with dwgs, to scratch n sniff!
     
  3. arthor
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    arthor Junior Member

    Not sure what that means??
     
  4. marshmat
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    marshmat Senior Member

    It might mean that:

    1) AH has been giving advice five times a day all weekend (I've been hassling him a lot in the last day or so) and is probably now getting tired;

    2) It is very difficult to make a reasonable assessment of your situation without some design data to start from. For example, we can't even guess at how much weight needs to be shifted around without having seen the boat. Nor can anyone advise what to do about your skeg, without seeing it.
     
  5. arthor
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    arthor Junior Member

    Thanks for that reply. Understandable if someone has been answering daft questions like mine all week. I will try to come up with some more info and leave it a few days before posting.

    thanks again
     
  6. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    The transom needs to be somewhat connected to the stringers. That is where the thrust will be made. You need someone on site to inspect the boat.
     
  7. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Matt

    As always, spot on:
    "..It is very difficult to make a reasonable assessment of your situation without some design data to start from. For example, we can't even guess at how much weight needs to be shifted around without having seen the boat. Nor can anyone advise what to do about your skeg, without seeing it..."

    I, like many on here, are more than happy to provide advice/guidance. But unless there is some info/dwg/data etc, without the ability of having ESP, makes the task somewhat difficult at best.

    Time zones, often cause a delay in replies too :p
     
  8. CDK
    Joined: Aug 2007
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    CDK retired engineer

    If I remember correctly, the Fjord 27 originated from the 70s-80s and was fitted with both stern drives and prop shafts, although the majority had a prop shaft. But it can also be that the ones with stern drives are younger.

    It certainly has a 2" thick transom, so strength can be no problem.
    Of course the weight distribution changes: the stern will be approx 3" deeper in the water once you complete the transformation.
    But is it worth all the trouble? These boat have a market value between 10 and 15.000 euro, perhaps a bit more when traded in. The conversion is a major operation that will use up all your spare time for at least a year.

    I did incredibly expensive conversions on my Draco twincab that I would probably not have done had I known the implications.
     
  9. gonzo
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    gonzo Senior Member

    If you want to shift the engine aft, a Vee drive would do that with less complications.
     
  10. arthor
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    arthor Junior Member

    thanks

    thanks for that input from all of you.
    I know all the logic for just getting rid when I'm ready and getting something else.
    My wife has declared that she likes it as it is and would rather we got something else when we outgrow her. I guess that puts that to bed then.
    Thing is, this seems to have rekindled my boatbuilding bug that I'd thought buying a boat would cure.

    thanks again
     
  11. gonzo
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    gonzo Senior Member

    The boss has spoken
     
  12. Frosty

    Frosty Previous Member

    Where are you Arthor? Hull, Scarborough?
     
  13. jakeeeef
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    jakeeeef Senior Member

    What's a vee drive?! Sorry about the daft question, i'm a sailor.
    It's not by chance like a stern drive but doesnt have to be close coupled to the engine is it? if it is, thats what I need!

    While we're at it could someone pls give me a definition of the differences between a z drive, a vee drive and a stern drive, as I'm quite new to inboards and becoming confused.
     
  14. jakeeeef
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    jakeeeef Senior Member

    All sorted, I've found out what a vee drive is http://www.glen-l.com/inboard-hdw/hdw-description.html here. Useful diagram. Not at all what I thought it was and I guess it's pretty rare.

    i've found out what a z drive is too from wikipedia. I think this phrase might be commonly misused as it is nothing like what I thought it was and has not very much to do with small planing speedboats I have heard it used in the context of.
     

  15. marshmat
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    marshmat Senior Member

    V-drive gearboxes aren't the most common sight, but are far from rare- they've long been a popular choice for light, high-speed boats and have recently become quite popular on the wakeboard scene.

    In some places, the terms Z-drive, I/O, outdrive and sterndrive are used interchangeably.
    You'll also come across S-drive, or saildrive, a fixed leg used for auxiliary power on sailboats.
    Rotating drive pods sticking straight out the bottom of the hull can be called Z-drives, azipods, main thrusters, or several proprietary brand names (Zeus, IPS).

    Confused yet? :D
     
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