Outboard Vs. Inboard Diesel Semidisplacement

Discussion in 'Outboards' started by MihaS, Oct 7, 2016.

  1. ChrisN67
    Joined: Jan 2008
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    Location: Kuwait

    ChrisN67 Senior Member

    Do you have a foundry? Lol, I was talking about the parts. You sound very competent and hands on; but even if we do the work ourselves, we are beholden to the manufacturer.

    Proper preventive maintenance schedule and care will make a big difference in longevity; but diesel engine spares are not as abundant as outboard spares. I keep a complete spare engine just in case.....as I live on Gilligan's Island.

    I rebuilt at least one set of engines, and it is definitely a learning curve (especially the intercooler "cartridge) where you are one misplace oring from a hydraulic lock.

    After the rebuilds were complete we made new engine placards.... what's the point in all that work only to affix the old plate. The old plate was mounted on a secondary placard position on the lower block to maintain compliance with boat registration issues.
     

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  2. mydauphin
    Joined: Apr 2007
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    Location: Florida

    mydauphin Senior Member

    I wish I lived on Gilligans island... but instead I have Detroit 671s, so parts can be hard to find. I buy them in advance. I think I have parts to build 2 more engines. Mechanics for these old beasts are dying off. Anyway, I tell people getting into boating unless your very rich, buy a boat you can do some of the work yourself. There is also a safety factor in bring able to know your engine. Everything you need to know is on youtube. Whatever works best for your boat, and your type of cruising.

    One of my first boats and first boating misstakes, was a very fast boat with twin inboards. I knew how to fix the engines but I didn't realize I didn't fit in the engine compartment. The boat ended up costing me more in maintenance than the cost of the boat.
     
  3. ChrisN67
    Joined: Jan 2008
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    Location: Kuwait

    ChrisN67 Senior Member

    LOL, I have found there are two types of boat ownership schemes; one is an owner with tons of money that knows nothing about the boat and makes critical decisions relating to maintenance and operation. THe other is someone who knows almost all there is to know about boats and does not have the funds to buy a boat that matches his experience.

    Finding a good mechanic is the proverbial needle in the haystack.

    1/3 of the mechanics know what they are doing and try to create issue to make more work
    1/3 barely know what they are doing (1 trick ponies) and create issues to make more work
    1/3 haven't a clue but talk a good game and screw everything up.

    My margin of error is where you find honest mechanics that know what they are doing and charge a fair price for their diligent work.

    That is why I suffered until I took the decision to undertake the hull stretching, painting , electrical and mechanical work myself. I still suffered but at least I got my moneys worth (for every $1 I threw into the ocean I validated $1 disappeared into its depths - not the pocket of an incompetent mechanic.

    THe problem when you operate the boat you work on is that I put on virtually every conceivable bell and whistle such as a water separator bowl purging system for which when the racor separator water presence alarm sounds I only have to press a button; not hang upside down in the hot engine hatch with a cup and channel locks in 125F weather.

    I also installed camera to view drives, anchor locker, under bow pulpit and engine room.

    The gauges indicate above normal engine functions:
    Intercooler In/Out
    Fuel Temp
    EGT/Boost
    CV joint temperature via non contact pyrometer
    Drive qualitative 3 axis vibration sensors

    Ranco Temp sensors for helm and ebox with cooling fans

    36000 BTU Coppernickle heat exchanging radiator in the engine hatch to use sea water to cool the engine hatch. It is controlled also by a Ranco unit.

    and so on....
     

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  4. mydauphin
    Joined: Apr 2007
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    Location: Florida

    mydauphin Senior Member

    ROFL.... yes, I am putting cameras, temperature sensors etc... everywhere myself. Yes, it can get ridiculous. I do enjoy building the boat more than using it.
     
  5. ChrisN67
    Joined: Jan 2008
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    Location: Kuwait

    ChrisN67 Senior Member

    Today a raw water washdown system was installed with a bulkhead hose mount so salt- away can be circulated into the raw water distribution manifold. Salt-Away's active ingredient is inhibited Sulfamic Acid Combined With Corrosion Inhibitor And Wetting Agent.

    I can run the genset, AC circulation pump, raw water pump, toilet, etc with the descaler then fresh water rinse.
     
  6. kireodkaneo
    Joined: Apr 2017
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    Location: Ohrid.Macedonia

    kireodkaneo Junior Member

    same problem

    Hello to everyone.

    I have a semi displacement steel hull and weights about 14000 lbs.Using a marinized Mercedes motor that has aout 80 hp, and its reduced 2,97 : 1.
    The propeller is not calculated well so my top speed is 7 .5 knots.

    Anyway i am thinking to use outboards (twin or one).I have a reasons for that.
    1.in our lake we don't have marina, so pulling the boat out is a risk, and expensive operation.
    2.i want to reduce the draft of the boat (1.2 meters).
    3.go faster when needed to go safe shore.
    etc.

    I plan to use 2 outboards with 80 - 115 hp. What will i get?
    in addition here are some pictures.
    thx
     

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  7. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    What are the dimensions of it , and particularly the width from chine to chine ? Would you expect to drop about 2000 lbs taking out the diesel and drive train ? What plans do you have for the skeg ? Remove completely or modify ?
     
  8. ChrisN67
    Joined: Jan 2008
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    Location: Kuwait

    ChrisN67 Senior Member

    My guess is 8-10 knts cruise; 12 knts max
     
  9. kireodkaneo
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    Location: Ohrid.Macedonia

    kireodkaneo Junior Member

    The LWL is about 34', and from chine to chine is about 9.3',i expect to drop 2000 lbs, but outborards would be about 700 lbs.i plan to modify the skeg and reduce it.

    My biggest fear is when going downwind with waves in the stern, the outboards will be in the air, and loose the cooling.(that happened to me with the backup motor).I hope the weight of the outboards at the stern will make it heavy enough to stay in water.

    And my question is ..Is it going to plan?! i know the best answer would be a test
     
  10. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    You needn't worry about outboard motor propellors being "in the air", in my opinion, fitted correctly it will not be an issue. What is an issue is that outboards are not ideal for slower boats, as it is difficult to get the right propellor size. You partially offset that be using twins. It is possible to get engines in the hp range you mention, that swing the biggest diameter outboard propellors, and are able to do so because they employ higher reduction ratios. I am not quite as pessimistic as ChrisN67, you might be able to cruise at mid teens mph, but you have a pretty hefty boat that won't be planing as the typical boater understands the term. The underwater shape of your boat does lend itself to significant increases in speed beyond "hull speed" though, but at the expense of greater fuel use. You will certainly get a significant reduction in draft from outboards, though. At the end of the day, unless you are doing a lot of miles, the extra fuel may not be a deterrent. But "normal" outboards would be useless, you need the ones with the right gearbox/prop, and with four-stroke power the fuel consumption will only be semi-horrid, where in the past it would have been a killer with twins ( always use more fuel with twins)
     
  11. kireodkaneo
    Joined: Apr 2017
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    Location: Ohrid.Macedonia

    kireodkaneo Junior Member

    TNX a lot. I wouldn't change inboard with outboard for my boat, if that isn't necessary.
    Buying a new inboard with every other needs its a lot for me and i have to import it from other country and pay a lot of additional taxes. So outboard is better option for me.I will look for long shaft and big foot outboards with largest props that can feet.i will try to calculate the props and ask from another opinion from the seller.i hope i will do something.
     
  12. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    You can get a good selection of props, a five-blader may be better for the purpose, be guided by a prop man on that score. And certainly you should be using 25" shaft.
     
  13. ChrisN67
    Joined: Jan 2008
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    Location: Kuwait

    ChrisN67 Senior Member

    You have a non standard application. SHaft length of the outboard will be installation specific with the longest being preferable. The Cavitation plate should be no more than 1" below the hull bottom and certainly not above it. I assume you are using a bracket (i.e. Armstrong)
     

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  14. ChrisN67
    Joined: Jan 2008
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    Location: Kuwait

    ChrisN67 Senior Member

    What type on inboard is it?
     

  15. kireodkaneo
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    Location: Ohrid.Macedonia

    kireodkaneo Junior Member

    At the moment is Mercedes d300 barely 80 hp, it's a car motor adjusted with Borg Warner 2.98 : 1 reduction, and the prop is not calculated well.
     
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