Running on one engine

Discussion in 'Powerboats' started by Steve W, Jan 21, 2013.

  1. Steve W
    Joined: Jul 2004
    Posts: 1,806
    Likes: 57, Points: 48, Legacy Rep: 608
    Location: Duluth, Minnesota

    Steve W Senior Member

    I have zero powerboat experience but as i get older, like many i have starting thinking about trawlers, the thing is i have no interest in going fast, after a lifetime of sailboats if i could average 6 knots i would be happy so a single diesel trawler would be fine. However after perusing the adds i see a few such as the Gulfstar 36 that have two smaller diesels, ive always dismissed twins as an uneconomical alternative but ive got to thinking that perhaps its not necessarily so, as an example a marine trader 36 may have a single 6 cyl Ford Leaman of 120 hp while a Gulfstar 36 may have two 4 cyl80hp perkins ( i dont remember exactly what). I guess what im getting at is if the Gulfstar were to cruise in favorable conditions on one engine it would likely be more economical. I know that powercats run on one engine much of the time but i never hear of monohulls doing the same, i dont move in powerboat circles so ive never had the discussions, maybe its common. Any thoughts?

    Steve.
     
  2. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 114, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    Im a sailor, so Ive never operated with two engines.

    Personally I would only choose a motorboat with twin engines for long range cruising, were self sufficiency is critical .

    Coastal cruising with a single engine, good maintenance, a good anchor and proper seamanship seem perfectly logical

    Two engines take up space, adds unnecessary weight and costs more every year you own it. I just did a 250 hour maintenance cycle on a six cylinder diesel...600 euros.

    A 40ft boat with twins doesn't sound attractive to me.

    Id would prefer a top class single screw powerplant , plus a generator for coastal cruising.

    Runnning a twin screw as a single screw means that you are dragging one set of gear and running your single diesel at less than its optimum rpm for fuel consumption.

    Sounds ineffective to me. slow and thirsty
     
  3. Steve W
    Joined: Jul 2004
    Posts: 1,806
    Likes: 57, Points: 48, Legacy Rep: 608
    Location: Duluth, Minnesota

    Steve W Senior Member

    I have always preferred the idea of one engine also for the reasons you state,however when looking at various used boats aome have twins, i would not even entertain a boat with two large engines but two that are smaller than a single may make sense,point taken about dragging the unused prop though, maybe a couple of maxprops? I would think that a single, say 80hp pushing a 36ft trawler (when conditions allow of course) would be a very happy engine working efficiently. Remember im happy with sailboat speeds, S/L 1.1 or 1.2 would be just fine.

    Steve.
     
  4. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 114, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    Thats a problem. When purchasing used, you must purchase what the market offers.

    I suppose the elegant solution is to fit a twin screw with controllable pitch props so that when running single you can eliminate drag and optimize the load on the working engine.

    Problem is those props are eye watering expensive.

    A max prop could be a solution.

    Perhaps you should investigate the AUTOProp. I see a few around but have no experience. Contact the company and see if they have any experience with twin screw trawlers

    http://www.autoprop.info/
     
  5. keysdisease
    Joined: Mar 2006
    Posts: 794
    Likes: 41, Points: 28, Legacy Rep: 324
    Location: South Florida USA

    keysdisease Senior Member

    Limit your search to single engine trawlers, there are plenty out there, you'll be glad you did.

    For all the reasons already mentioned, unless it REALLY makes sense your just better off in a single engine trawler.

    A modern diesel engine properly maintained is extremely reliable.

    I ran a single engine Mainship 34 for 11 years all over Florida and the Bahamas and the only time I ever had any problems it was my own fault (dirty fuel)

    I used to help out in a couple of bareboat sailboat charter operators and believe me nothing takes a beating like boats in that kind of service. The only time the engines didn't run it was operator error.

    Keep the fuel clean, the maintenance on schedule and your Sea Tow membership paid up and you will never look back.

    Steve
     
  6. Submarine Tom

    Submarine Tom Previous Member

    Single is the way to go for all the reasons already given.

    Simple as that.
     
  7. Steve W
    Joined: Jul 2004
    Posts: 1,806
    Likes: 57, Points: 48, Legacy Rep: 608
    Location: Duluth, Minnesota

    Steve W Senior Member

    Thanks guys,as i have already stated, the only reason i would consider twins would be if the boat in question had a pair of engines which,individually,were smaller than a similar single screw would typically use, and i particularly liked the boat, as in the Gulfstar 36 example. What i would like to find out is if people do in fact run on one engine as they do with powercats to improve economy and rebuild intervals, anyone have any actual experience?

    Steve.
     
  8. keysdisease
    Joined: Mar 2006
    Posts: 794
    Likes: 41, Points: 28, Legacy Rep: 324
    Location: South Florida USA

    keysdisease Senior Member

    No, I don't. But I have run many a boat with twins and even if the economy numbers for fuel consumption worked out for what you are trying to do (I doubt it would) I still wouldn't consider the tradeoffs worth it.

    Most twin engined trawlers with two engines are designed to run on two engines. This usually means smallish rudders which on a boat to boat basis may or may not be able to handle the asymmetric power. Even if the boat would track straight on one engine a wake or wind change from the wrong direction may put you in a turn you may not be able to get out of, and you may as well forget an autopilot on one engine.

    Just the space loss in the engine room and the doubled maintenance costs are a good enough reason not to go there.

    Steve
     
  9. Frosty

    Frosty Previous Member

    I have a power cat and no power cats do not run on one engine , mine will do kind of but the rudder is way over so how much power waisted is that . One 24 inch prop dragging and 2 rudders way over.

    Servicing is a pain , when you changed oil and anodes your do it all again twice.

    Single engine single rudder. And you can still spin them in a little over their own length if you know how to do it.
     
  10. Steve W
    Joined: Jul 2004
    Posts: 1,806
    Likes: 57, Points: 48, Legacy Rep: 608
    Location: Duluth, Minnesota

    Steve W Senior Member

    Frosty, many well designed displacement powercats do in fact run on one engine on ocean passages, alternating to keep the hours even, i used to own a sailing cat with one outboard on the stbd transom and it tracked just fine without excessive helm but of course it didnt have the drag of running gear on the other side as well as having decent sized rudders, planing powercats probably dont run on one engine and i doubt if planing monohull powerboats do either but i have absolutly zero interest in these types of boats. This purpose of this thread is to try to see if anyone here has actual experience with a twin screw displacement trawler in the mid 30ft size range who may have real opinions not based on speculation, i can speculate as well as the next guy.

    Steve.
     
  11. Frosty

    Frosty Previous Member

    Steve in your op you said you knew that power cats can run one engine. I thought I would let you know that my Australian Seawind 44 foot 500HP twin does not... I dont plane all the time,-- Its not speculation.

    My 40 foot Grand banks I had in Hong Kong had twin Lehmans 120HP each. It was very economical but some one with more experience will be along soon.
     
  12. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 114, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    There is one of those Grand Banks in the harbour. Looks like 40 ft and you can tell that its owner loves it...perfectly maintanned. I have a feeling its a very good design.
    The other design that I often see very well maintained is the Fisher 37 canoe stern motorsailor.
     
  13. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 145, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    In almost 50 years of boating, I've experienced everything from fishing nets in a prop to an exploded V-8 engine with less than 100 running hours and once hit a submerged rock in very bad weather, turning a 3 blade prop into a 2 blade one.

    So I would never consider a single engine boat.

    I have cruised for weeks on a single engine because of fuel economy, alternating between port and starboard engine each day and must admit it is no fun at all, so after I found out that the savings are only marginal I changed habits and used both engines at near idle rpm. But if the unexpected happens it is good that there it still one engine that will take you home.
     
  14. Landlubber
    Joined: Jun 2007
    Posts: 2,640
    Likes: 123, Points: 0, Legacy Rep: 1802
    Location: Brisbane

    Landlubber Senior Member

    Single engine, but slow revving.

    Think of all the sea trawlers that leave port, basically every one here is single engine.

    Straight shaft if possible, dry exhaust, KISS.
     

  15. johneck
    Joined: Nov 2011
    Posts: 233
    Likes: 12, Points: 18, Legacy Rep: 117
    Location: New England

    johneck Senior Member

    The other issue with the twin is that there is additional drag from the second shaft, struts and rudder. The twin props are also likely smaller in diameter than a single prop so also not as efficient.

    If you do get a twin, it is probably best to run with both turning. The drag of a trailed locked or freewheeling propeller is probably 30-40% of the drag of the whole boat. Feathering the propellers would reduce this of course, but unless you have a controllable pitch propeller, they will not be a s efficient as a fixed pitch prop.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.