two engines or one plus kicker

Discussion in 'Outboards' started by arthor, Nov 15, 2009.

  1. arthor
    Joined: Apr 2008
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    Location: UK Yorkshire

    arthor Junior Member

    Hello all,

    I am intending to build a cruiser in the 28'-30' region. The ultimate aim is to take her out into coastal waters, across the English Channel up in to the Baltic and Norwegian fjords. She will also spend a good deal of time on rivers/canals. As you can imagine, this gives me quite a wide range of power requirements. I have spoken to the designer and it can be built with engine beds for a sterndrive to be dropped in later but there is nothing to say I can't start off with an outboard well. I have pondered the benefits of outboard versus inboard and to be honest, for simplicity, interior space reasons and initial outlay, I quite like the idea of outboard power. (why is there so much panic about the dangers of petrol when we quite happily drive around in potential firebombs anyway??). It is semi displacement and the designer says 25 HP would happily get me home in an emergency.

    If I was going to spend my time blasting about at sea then engine choice would be easier but I will be bimbling about at low speed a lot of the time and just want the power on tap if I need it or want it. I have heard and read that outboards don't like low speed operation. Is this the case? Is it possible to change gearing or props to offset this?
    Would my best layout be something like a 200hp and a 25 aux or would a twin 90/115 layout be my best option?
    I was thinking that the 25 could also be my river engine but maybe a slightly bigger one would be better. Perhaps a 200/40 hp layout??

    Are most big/little layouts rigged up so that both are hooked up to steering and throttle regardless of whether they are tilted up or running?

    regards

    arthor
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    The steering will be together, but the throttles and shifters separate. If you need 25 HP minimum, a bit extra wouldn't hurt, say 40. Usually you tilt the motor not in use.
     
  3. apex1

    apex1 Guest

    Think about a inboard Diesel and a Controllable Pitch Propeller and the problem is fixed! Low speed, low consumption on rivers (without killing the engine), higher speed, power when demand at sea!

    Regards
    Richard
     
  4. arthor
    Joined: Apr 2008
    Posts: 46
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    Location: UK Yorkshire

    arthor Junior Member

    thanks

    Thanks for those replies gents.

    The main reason for the little engine was as an auxiliary. I just thought that running it on rivers would avoid the scenario where a spare engine gets ignored until you need it, at which point it sulks and refuses to go.
    I also figure that it seems daft to have two fuels on. So a big and little outboard seemed to be a fine idea. If I have already put the beds in for an inboard then I have the option of changing later. I anticipate that I would have to get into the realms of a lot of big power usgae to justify the expense of a diesel outdrive set up. Even then, unless I go for a twin, I would still need aux power, ie the little outboard.
    I am still pondering the question of whether outboards like low revs working and whether a change of gearing or prop is possible to offset this.

    thanks again

    arthor
     
  5. apex1

    apex1 Guest

    Understand, sorry no clue about outboards! But I, for example, am fine with one engine only.

    Regards
    Richard
     
  6. tonyr
    Joined: Oct 2003
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    Location: Gagetown, N.B., Canada

    tonyr Junior Member

    Low speed outboards.

    I built a 24 foot lobster-style boat 4 years ago, and have run it at displacement speeds (say < 6 knots) since then using a single 50 h.p. high thrust Yamaha outboard . Rev speeds typically run in the 1400 to 2200 range, with 1800 typical. The WOT speed quoted for the engine by Yamaha is in the 5000 rpm range.

    So essentially I have been running the unit at very slow speeds for years, with NO adverse affects at all. Maintenance has been as specified (oil changes, plugs, grease etc.).

    It really does seem that if you are running a modern computer controlled, fuel injected gas engine that it will not foul up at extended low revs like a Diesel might.

    For what it is worth, but I hope this helps.

    Regards, Tony.

    PS I use a 2.5 h.p. on a towed 10 foot hard dinghy as my get-you-home device. If I was running at sea regularly instead of mostly inland, I would go with two 25 h.p. engines instead of a single bigger one. If the latest Yamaha 25 h.p. high thrust had been available four years ago, that would have been plenty of power for my application, and more economical too.
     
  7. apex1

    apex1 Guest

    You´re dead right tony,
    the outboard (4stroke) does´nt do wrong with low revving for years. The Diesel gets killed after a while.

    so you did something like this?[​IMG]

    Regards
    Richard
     
  8. tonyr
    Joined: Oct 2003
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    Location: Gagetown, N.B., Canada

    tonyr Junior Member

    Richard, yes, it looks quite familiar. I even ballasted mine (650 pounds) to get more of a shippy feel to it.

    Tony.
     
  9. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    Most outboards don't really mind being run at lower RPM. They tend to be happiest around 1/2 to 3/4 throttle, but modern 4-stroke or 2-stroke DI types will loaf along near idle quite nicely. The older, carburetor-type 2-strokes often don't handle low revs as well, though.

    I have a suspicion, Arthor, that your boat is a little too large and heavy for efficient operation with outboards- you might not be able to swing a large enough diameter prop at low enough RPM. Without more data on the boat, it's hard to say.

    By far the biggest killer of outboard engines is dirty/wet fuel, which usually kills twin engines within a minute or so of each other. Twins (or a kicker) as a "get home" backup only works if they have independent fuel systems, filters and tanks. Catastrophic mechanical failure of the engine itself is, by comparison, quite rare.

    Being in England, you probably see quite a difference in price (and perhaps more importantly, waterside availability) between petrol and diesel fuels, which certainly strengthens the case for a single inboard diesel despite its greater up-front cost. However, your use profile would leave the diesel underloaded a lot of the time.... hence Richard's suggestion of a CPP system.
     
    1 person likes this.
  10. apex1

    apex1 Guest

    We do´nt ballast, there is a Diesel in her.[​IMG]
     
  11. mark775

    mark775 Guest

    You designed and built these beautiful craft, Richard? What is the notch in the transom?
    I just clicked on your profile and I think the answer to the first question is "yes". Right up my alley, your work.
    Oh, to the thread...I concur with Richard on that, as well - the single diesel inboard can be trusted with no need for a kicker. My personal (single engine) boat since 1984 with about 4,000 days on her has not failed to find the barn under her own power.
     
  12. apex1

    apex1 Guest

    Too many flowers Mark.

    Build yes, though not with my own hands. Design, no, we have NA´s and designers engaged to do the "paperwork", before the shipwrights get their hands dirty.

    Nice to hear you enyoyed the Gallery.

    The notch is the step from the "swim platform". There will be a door to close that.

    Regards
    Richard
     
  13. arthor
    Joined: Apr 2008
    Posts: 46
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    Location: UK Yorkshire

    arthor Junior Member

    thanks again

    Many thanks again gents. Much food for thought.
    The main points I have from this are that a decent modern outboard will quite happily run at low revs for some of the time.
    People tend to regard a diesel as the engine of choice for a boat in the 28-30 foot range.
    It was my intention to have seperate fuel tanks and try to fill up at different pumps.
    I was intending that the 40hp would run me quite happily up and down rivers and probably quite high revs and the bigger engine would be for coastal work when it would also be running at quite high revs. It would be on low revs when used on the river as I would be going slow but would mainly be used just to keep it "on the go" if we went a long time without going offshore. Each would be a spare for each other with both being the ideal engine for its prime use. Lots of 30' grp cruisers (and even bigger) only have 40-60 hp outboards over here. There is one parked up next dor at our marina.
    Your points are taken regarding the diesel but if they don't like low revs either, I will still be best of getting a little outboard.
    We went down to our current boat last weekend and it started when we got there but we were delayed getting on the river. Went to start it an hour later and it wouldn't start (inboard diesel). It turned out to be an electrical fault and I finally got it fixed the next day. Glad it didn't happen upstream as we don't have a little outboard on. I reckon you can now understand my paranoia.

    thanks again gents

    arthor
     
  14. Willallison
    Joined: Oct 2001
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    Location: Australia

    Willallison Senior Member

    Arthor - can you give us a little more info on the boat you are intending to build? The weight, in particular.
    The idea of allowing for an inboard for later installation seems like a rather odd solution to me. Are you suddenly going to change your cruising habits down the track, whereby the 'current' set up is no longer a sensible approach? Also, one advantage of an outboard installation is that the cockpit sole can be lower, lowering everything else in the process. With an outboard (or 2) on a pod, you can gain a great deal of additional cockpit space (though the pro's and cons of pod installations are somewhat complicated too...).

    As others have said, modern outboards - whether direct injection 2-strokes, or 4-strokes - are quite happy pottering along slowly all day long. Furthermore, they don't spit half the fuel out the exhaust like the old ones used to, so are pretty economical at low revs too.
    It's impossible to make a sensible call one way or the other without a great deal more info.... if you can give it to us, we'll enjoy helping you to make the decision though!
     

  15. Willallison
    Joined: Oct 2001
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    Location: Australia

    Willallison Senior Member

    Oh - one other thing.
    A single engine is pretty much always the most efficient solution. Commercial vessels, large and small, manage to safely ply the oceans of the world with just one day in, day out.
    However, the single / twin engine debate is (generally) an emotional one. If you are not going to be comfortable setting off with only one propulsion source on board, then it's best to eliminate it as an option and move on to finding the best alternative
     
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