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Old 10-12-2011, 08:16 PM   #1
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Moving from Sail to a Trawler

I have two questions as I am looking at several trawlers for purchase.* First , is two engines , like two ford lehman 120's better than one in a 43 ft. boat.* It seems that one will move the boat at approx the same knots.* I am being told that they will burn about 2.5 per hour, per engine. Is this true for a 43 footer?*

I like the two engines but dont want to burn more than 5 gallons per mile.

*

Second, Is a three blade prop better or worse than a four blade. It seems more are moving to a 4 blade. Is there because of fuel economy.

We* will be liveaboards in St lucia area. same as before , but with a trawler.
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Old 10-12-2011, 08:38 PM   #2
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RE: Moving from Sail to a Trawler

At 8 knots with a 43 ft boat you should burn around 4 gph total *+/- with twin 120 Lehmans.

A 4 blade prop with less pitch vs a 3 blade prop with more pitch are apples to apples. The idea is to get the motor to full RPM and working at it's rated HP. A prop calculator will usually give both 3 and 4 blade choices.
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Old 10-12-2011, 08:51 PM   #3
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Moving from Sail to a Trawler

Well, you will stir up a hornet's nest now..... :-) The two-vs-one argument is endless and unwinnable. They both have their advantages and disadvantages. On top of this will be personal preferences.

We have a GB36 with two FL120s. Together they burn about 5 gph at the rpm we run (1650). That gives us a cruise speed of about 8 knots.* If we had one FL120 we could still run at 8 knots no problem but the one engine would have to work harder to do it.* So it would burn more fuel than either one of the engines in the twin.* Which is why given the same boat and the same engines and props, the two engines in the twin will not burn twice as much fuel as the single.* They will burn more, but not twice as much.

We used to charter a GB36 with one engine. We fly floatplanes with one engine, we drive narrowboats in the UK with one engine. All our cars have one engine. When we decided to purchase a boat of our own we didn't care if it had one engine or two. As it happened, the boat that best fit our requirements and our boating budget had two engines. Now, thirteen years later, we would never buy a single engine boat. Partly because I like running engines--- I'd have three of them if they'd fit. Partly because we like the redundency--- we've needed the spare engine four times so far, three due to cooling issues, one due to a fuel transfer mistake on my part.

But the main reason a single engine boat will never be in our future is that my wife--- who has no problems flying into the remotest parts of the Coast Range in BC in a floatplane not only powered by one engine but an engine built during WWII to boot, is far more comfortable, confident, and relaxed with two engines under the floor instead of just one. And I don't care how much economic sense it makes to run one engine, it will always be trumped by what makes my boating partner the happiest.

So if it was me-- -which it isn't--- I would want two engines in that 40-something foot boat your are contemplating. Whether you burn 5 gph in that boat with 2 FL120s, that will depend on the rpm you run at. I can tell you an FL120 is happiest between about 1600 and 1800 rpm. Get down below 1500 rpm and you may have trouble keeping the cylinder temps where they should be.

Your prop question is easy. The fewer blades a propeller has the more efficient it will be. A one-bladed prop would be the most efficient but it would be a bitch to balance :-) However, the more blades a prop has, the smoother it will run (or the less vibration it will produce, however you want to look at it). So it depends on what your priorites are. Our boat was shipped from the factory with three-bladed props. A previous owner installed four-bladed props. We were going to switch back to three-blades but given the cost (about $1700 or so per prop at the time) and the fact that the prop shop was able to completely rework and re-pitch (down) our four-bladed props for about $350 per prop, we elected to stay with the four bladed props.


-- Edited by Marin on Wednesday 12th of October 2011 08:56:31 PM
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Old 10-12-2011, 09:33 PM   #4
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RE: Moving from Sail to a Trawler

Thanks for the info, I had only one engine on my sailboat for the past 6 years , and I think I would like the way two engines work a boat. So am leaning that way, but the fuel use is a factor, but if the stats are as you stated, then I would be ok with 2. I am used to a displacement hull , so that very important to be comforable. I am looking at an Albin 43 and 49, and a GB 43, plus some custom boats. This will be our last boat we hope, so we are being careful.
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Old 10-12-2011, 10:02 PM   #5
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RE: Moving from Sail to a Trawler

There is no GB43 so I assume you mean a GB42. If a displacement hull is what you're after, a GB isn't one. All GBs except the very latest models have semi-planing hulls and as such they have the roll characteristics of the typical, nearly-flat after section, hard-chine hull many trawler-style boats have. The roll is best described as a "snap-back" roll which a lot of people find very uncomfortable in a beam or quartering sea. As opposed to the perhaps farther but smoother roll characterisics of a displacement hull.

Two engines certainly offer some maneuvering advantages but I don't believe there is any maneuver you can do with a twin that you can't do with a single. The techniques will be different, but the end results will be the same. We prefer a twin primarily for the redundancy of systems. Plus, as I said, I just like operating engines. But if maneuvering was our sole criteria in determining how many engines our boat had, we'd probably get a single with a bow thruster if the boat we wanted was available in that configuration (it isn't).
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Old 10-12-2011, 10:18 PM   #6
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RE: Moving from Sail to a Trawler

yes, 42 GB, Which trawlers have the best displacement hulls, Albin? etc. I do agree with the single engine , I had that down to a science on my 51 sailboat, but the prop was more center mounted , thus going astern was also easier. Also, I dont mind 7 to 10 knots, as that is what I am used to . Thanks for the good info.
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Old 10-12-2011, 10:24 PM   #7
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Moving from Sail to a Trawler

GW,

You should have a list of givens and druthers.**Givens are constraints such*as financial resources available for boat, draft limitations of your waters, etcetera.

Druthers are important wants.* For example, my druthers were 360-degree view from helm position, 360-degree decks and safety railings, keel-protected rudder and propeller, etcetera.

Two versus one engine weren't a consideration for me because two engines are not generally available in the boat size I was considering.* Dual engines provide redundancy, increased maneuverability, and more likely the ability to exceed hull speed, while a single engine costs less to acquire and maintain and the boat is more likely to have a keel protecting the rudder and propeller.

PS -- I'm a former sailboater too.


-- Edited by markpierce on Wednesday 12th of October 2011 10:31:57 PM
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Old 10-12-2011, 10:26 PM   #8
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RE: Moving from Sail to a Trawler

Quote:
GW wrote:
Which trawlers have the best displacement hulls, Albin? etc.
You might get your best answer to that question from someone like Eric Henning.* My knowledge of hull design and characteristics goes no farther than the verys*simple*basics.* Eric, on the other hand, has a wealth of knowledge about hull configurations and attributes.
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Old 10-12-2011, 10:45 PM   #9
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Moving from Sail to a Trawler

Grand Banks made several models, now discontinued, of Eastbay 43s. However, that is probably not the type of boat you're looking for. You can check them out on the Grand Banks web site.

-- Edited by Giggitoni on Wednesday 12th of October 2011 10:48:29 PM
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Old 10-12-2011, 10:45 PM   #10
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RE: Moving from Sail to a Trawler

That keel and protected prop is very important, yes making a list would be important. Thanks, guys. I am looking at a 38 this weekend with a bow thruster, single engine. Will let you know how it comes out.
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Old 10-13-2011, 04:01 AM   #11
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Moving from Sail to a Trawler

Due to what is known as induced drag fewer prop blades is more efficient than more.

IF the prop can absorb the power, which with a displacement trawler is seldom a problem.

Twin engines will allow perhaps 5% better in slip manuvering , at a fuel cost of perhaps 15% extra when cruising.

This will be added to the hull drag ,(another 15%) if the boat was plaining or semi plaining , but run at displacement* speeds.

The trade off between 2 totally exposed props or one well protected for the advantage of a get home engine , must be considered in light of reports that most engine failures are fuel related.

Since you are paying for fuel, the speeds of your sail boat (hull speed) will be expensive.

Figure best fuel consumption will be at .9 to 1.1 times the Sq Rt of the LWL, not 1.34.

If trawler crawling is your speed the handicap of twin engine and semi plaining hull should not be a big problem.

Yes ,a boat that might burn 3gph to cruise 6.5k (40ft LWL) may require 4gph , but it is still affordable.

Try cruising at 12K -14K, where many semi plaining boats top out and its 1nm/gallon, but what a breeze!


-- Edited by FF on Thursday 13th of October 2011 04:04:23 AM
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Old 10-13-2011, 06:52 AM   #12
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RE: Moving from Sail to a Trawler

Like Marin said single vs twin is a personal preference, there is no right answer for everyone, if there was then thats what everyone would have.

But it is important to weight the advantages of each and make an informed decision.

Twins: more maintenance, higher fuel costs, safety in numbers, both above and below the water line, easier to maneuver when docking.

Singles: opposite of the above.

If you want a planning hull, most are twins, but not all.

I was out the other day on my twin going 18 kts and noticed the tranny pressure fluctuating and higher than normal. Shut it down and returned home single, but restarted to dock. Can't do that on a single-would have to consider calling for a tow.

Another consideration; When not in a rush I cruise single engine at 7 kts and burn slightly less than 3 gph. Pretty close to what you single guys get.

But there are other considerations beside engine configuration. I've been in 4-5 seas and though not confortable, safe. No way would I consider being out in seas above this though.
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Old 10-13-2011, 08:07 AM   #13
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RE: Moving from Sail to a Trawler

For me the advantage of the protected prop is the deciding factor, A single engine and bow thruster works for me BTW I have seen some Very large trawlers with singles but believe most have some sort of emergency power,
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Old 10-13-2011, 08:40 AM   #14
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RE: Moving from Sail to a Trawler

GW, I sent you a pm ref St Lucia...thx
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Old 10-13-2011, 09:12 AM   #15
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RE: Moving from Sail to a Trawler

As mentioned by Motion, a single prop is protected by ??? from ???**This implies twin props are not.*I struggle with this logic. With*line cutters, twins and singles are equally protected from pot ropes and fishing lines. With a deep keel twin (not a Bayliner or Carver) the props are protected from ??? and in the case of some twins double keels are utilized for prop protection. I daresay a vigilant twin operator is better protected than a non-vigilant single operator. Therein lies the crux, attentiveness.
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Old 10-13-2011, 09:15 AM   #16
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RE: Moving from Sail to a Trawler

Thank you Marin. Four blade or 3 blade dos'nt make enough difference to talk about on most boats but 3 is more efficient. The shape of the blade tips will have a bigger influence. *FF good post BUT, "speeds" are not expensive. I reread that Fred and think I see what you mean now. Too many people don't realize that running 1 to 1 1/2 knots below hull speed is what full displacement boats are designed to do *...hull speed is their TOP speed unless over powered and most yachts are.*And twin engines CAN be more efficient.*Figure 3 to 5hp per ton of displacement. And I think Fred is right that propeller protection gained from a single screw is over sold. If you lived in an area w almost all sand or mud bottoms and had little propeller fouling flotsam adrift the advantages of get home power w the twin would be FAR more advantageous than propeller protection afforded by the single. Here in Alaska the abundance of both large amounts of kelp and very few soft bottoms that you may run into (mostly rocks) one would think the single would be best BUT Alaska is a very unpopulated place and in case of trouble there is no vessel assist. The CG is wonderful but mostly you're on your own and so in view of that I'd say twins would be better here. Lots of variables on that one but wherever you are on that one I would'nt consider it a deal breaker. UNLESS you are looking at a typical trawler that has twice the power in most boats w twins as singles. Manufacturers were very stuck on 120hp Lehmans (British Fords) so you (unfortunately) get an slightly under powered boat or an overpowered boat. So if you're concerned about fuel consumption don't look at any twins in this category. If you find a twin that is powered properly it is in my opinion the best boat but there are very few. Also very scarce are full displacement boats that have powered performance characteristics mostly like your sailboats. Fisher's and Willard's come to mind especially Willard's as I have one (in avatar). I'm going to predict that the same thing will happen to you as happened to me in that fuel consumption will not be as big an issue as time passes. I was keen on getting a 1gph boat when I was shopping for Willy but now I'd buy a boat without reservation that burned 2 to 2.5 times as much. Many things enter into that but most of us think we'll use our boats more than we actually end up doing. Post the boats you're serious about and if I'm around I'll probably PM you if I think you're look'in at a boat that's not good for you or just not good.*
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Old 10-13-2011, 11:45 AM   #17
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RE: Moving from Sail to a Trawler

So many people talk about fuel use, but when considering dockage, insurance, maintenance, depreciation and everything else fuel use is a small part of the typical boaters total expense for a year. If you are doing the Loop, ot lots of long distances than it is a big factor, but look at all of the 10 to 15 year old boats on the market with less than 2000 hours. Two smaller engines or one larger engine used over 3 years to 15 years will have a small difference in total dollars spent on fuel compared to all of the other expenses.
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Old 10-13-2011, 12:18 PM   #18
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RE: Moving from Sail to a Trawler

Tom's point about attentiveness being a greater factor in fouling props and rudders than how many of them you have is well taken. While this is a fairly meaningless statistic since the sample is so small, I have met more boaters with single engine boats up here (including sailboats) that have fouled their one prop on something than I have boaters with twin engine boats who have fouled either of their props or rudders on something. This doesn't necessarily mean the single-engine drivers were less attentive, just that a single engine boat can snag stuff as readily as a twin if everything lines up right. Perhaps in a place like the ICW and east coast waters where there are apparently highly mobile sand and mud bars scuttling about all the time a single with a protected prop and rudder would be beneficial as from what I gather going aground in these waters is an hourly occurrence :-) But out here, unless you whack into a rock or reef, the things you have to be concerned about are floating, either on the surface or just under it.

Which is why, even though I have been mocked on this forum for the practice, when we are running in water or light conditions that make it difficult to see debris on the water, both my wife and I man the helm together, one to steer and look out for stuff and the other to look out for stuff. Given that she often sees things I miss has prevented many log-deadhead-eelgrass/kelp mat-lumber-crab pot float encounters. All the people we know who have fouled a prop or rudder on floating debris were unaware of its presence until they hit it.
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Old 10-13-2011, 12:51 PM   #19
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RE: Moving from Sail to a Trawler

No mocking from me on two sets of eyes Marin. My wife's eyes and attention span are very good so she does most of the helming on the longer jaunts. While she is manning the helm, I am either looking forward, goofing off playing with the chartplotters or going into the ER (a standup one) since my male attention span is handicapped. As a compliment, to her a log is anything that is bigger than a 2X4.
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Old 10-13-2011, 12:57 PM   #20
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RE: Moving from Sail to a Trawler

Yes, * I consider myself very vigilant and with both of us looking we hit a log. BOOM and I was sure from the sound of it we had been holed but we did'nt take any water and found no marks on the bottom at the next haulout. And Tucker *..very good point but that varies a lot depending on what boat and what income the skipper has and what stage of life the boat is in. We have low income and low fuel burn but lots of yachts are bought new that burn 10gph and with the cost of a new boat it's obvious the new boat owner has enough money that the 10gph is fly stuff but 25years and 3 owners down the channel 10gph is BIG money. However, I knew a guy w a 50' Canoe Cove w twin Detroit's and figured out his total cost and fuel came in at 2%. Like you say it can be very small even though it seems large.
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