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Old 03-23-2016, 03:43 AM   #1
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Outboard Powered Trawlers

Hi
Would a pair of 150 HP mercury sea pro 4 stroke outboards with the lowest pitch highest diameter props be able to safely power a 10 tonne semi displacement trawler (Grand Banks 40 style ) in strong currents?

Currently powered by a pair of 40 year old 120 hp ford lehmans
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Old 03-23-2016, 04:03 AM   #2
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The only thing that comes to mind is WHY ????????
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Old 03-23-2016, 05:01 AM   #3
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I've been considering replacing my old tired engine s for the past 3 years and love the idea of of brand new outboards. They can be lifted up when not in use. And have minimal maintenance.
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Old 03-23-2016, 05:15 AM   #4
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I've been considering replacing my old tired engine s for the past 3 years and love the idea of of brand new outboards. They can be lifted up when not in use. And have minimal maintenance.
Outboards produce about 12hp/gal , diesels 20hp/gal.

A catamaran on outboards can equal the mpg of a trawler on diesels, so if you want to convert a big heavy boat to ob's you better have lots of cash for fuel.

Of course you could make an argument for some very cheap V8 gas engines on shafts. I'm no expert on these engines but you can buy them brand new for a few thousand $ and maybe swop over the marinising gear off an old scrapped one.
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Old 03-23-2016, 08:07 AM   #5
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You could definitely push the boat with them. The speed or current limitation would be tough to determine. There will be a point when the lack of propeller diameter limits out increased speed. If you could find out what the biggest diameter propeller was for the outboards and see if you could borrow something comparable to try on your existing engines, that might give you an idea of limitations.

Seems like an expensive experiment. Then there is the question of trim when you remove all that weight from the low center of the boat and add 1,000+ pounds to the transom.

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Old 03-23-2016, 09:02 AM   #6
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Thank you for the reply. I'm ok with the increased fuel consumption as I forsee that I would only be travelling a maximum of 300 miles a year for the next ten years or s
o. As long as it's not over the top. Also I'm willing to bear with the cost of the conversion. The only issue is the current which in the area can be quite strong. Your suggestion is good. But unlikely to find a similar prop to fit.
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Old 03-23-2016, 09:14 AM   #7
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Do you see a lot of new trawlers offered with outboards for power? Do you see any?


Do you think there might be a reason?


Have you considered the true cost of this conversion? Not just the engines but the steering, gauges and controls. The fuel tank(s) and system? Replacing everything electric near the fuel tanks with ignition protected devices?


Have you considered that this boat will be very hard to sell when the time comes?


BTW: Outboards do require maintenance and some requires being out of the water. And how many hours do you think the outboards will run before they have to be replaced? Compare that to your diesel engines.


You can rebuild or replace your existing engines for less than the cost of installing outboards and you will have a far better boat when you're done. And one that you can sell when the time comes.
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Old 03-23-2016, 09:25 AM   #8
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Then there's the Neander Shark 50hp diesel outboards distributed by Yanmar;

Yanmar re-enters 50hp Diesel outboard market with Neander!!!!
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Old 03-23-2016, 09:36 AM   #9
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You probably could go with a pair of 90's and still do displacement speeds with ease. Handling won't be as good, outboard props (exhaust through prop) are not so good in reverse. Had a house boat next to me for a number of years, he made a really nice bracket for the outboards, but when he was backing in looked like the water was boiling and alot of revving. Final note, resale would be in the toilet.
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Old 03-23-2016, 09:46 AM   #10
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Then there's the Neander Shark 50hp diesel outboards distributed by Yanmar;

Yanmar re-enters 50hp Diesel outboard market with Neander!!!!

Are they available in North America?
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Old 03-23-2016, 10:14 AM   #11
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Are they available in North America?
Quote from article linked in thread above;

Quote:
Marking its return to the diesel outboards market, engineering company Yanmar Marine International (YMI) has agreed exclusive distribution rights with German outboard manufacturer NEANDER Shark. YMI, whose headquarters are in the Netherlands, is to distribute NEANDER Shark outboards worldwide through its extensive network with access to more than 130 countries.


So I guess you'd have to contact your nearest Yanmar dealer.
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Old 03-23-2016, 10:55 AM   #12
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Outboards have small propellers intended for more speed. You can install OB power but it or they will be seriously lacking in thrust.

You'll buck the currents better w a straight shaft and an inboard.
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Old 03-23-2016, 11:29 AM   #13
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Ian,


Your Lehmans may be "old" but why do you say they are tired? Those engines will run almost forever if they are properly maintained. Perhaps you are the one that's tired - of diesel maintenance. Or do you just want a change? I'm not being critical, just curious. At the end of the day, it's your wallet.


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Old 03-23-2016, 12:11 PM   #14
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I would be concerned about keeping the props in the water in extreme conditions.
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Old 03-23-2016, 12:17 PM   #15
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Thank u for all the advice. Let me explain: My engines are in pieces. I don't have any gauges. My steering hydraulics leak. My impellers keep getting eaten up. Oil leaks into the billiage. The list goes on. I've reached a stage where I've lost confidence in the mechanicals. I have to send a diver down prior to going out as rubbish keeps getting caught in my running gear. And I can't find a disciplined competent mechanic that can sort all my problems out at a reasonable cost. I myself don't have much time to spend repairing my boat and would prefer to be out in the water than in the engine room.

Thus my question is whether a pair of brand new 150hp Mercury outboards would be able to power the boat with decent speed against strong currents of around 5 knots at times.
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Old 03-23-2016, 12:25 PM   #16
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Current 150 hp outboards by Mercury have 1.92:1 gear ratios. The new sea pro WOT is around 5000. 500 rpm less than the standard model. I'm thinking about finding the lowest pitch prop maximum diameter that the outboards can handle and adding prop guards knort nozzel to increase thrust. Would anyone have any experience on such installations?
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Old 03-23-2016, 12:27 PM   #17
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David, you're rignt about the ford lehmans they do take a lot of abuse. And are solid engines.
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Old 03-23-2016, 12:41 PM   #18
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I'm not convinced of the economics of the situation - a pair of OBS plus rigging/gauges/etc is going to be north of 40k. Surely you could get your old ford lehman's up and running and make the necessary improvements to the running gear. Another option is to replace the lehmans with gas inboards which could be had for less than 5k a piece. YOU MUST ensure all your ER equipment is ignition protected but even still we aren't likely talking about much more cash. The only way I can see OBs being a good option is if you are going for the floating condo thing and really just need to move it a short distance every once in a while in which case I would get a single OB with basic controls (think the console out of a console Dinghy), throw a removable gas tank on the aft deck and get it done but I can't see investing all that cash into a pair of OBs for this use.
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Old 03-23-2016, 12:43 PM   #19
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Ahh...you are in Malaysia which means the costs may be totally different. However, that also means you can probably buy diesel outboards which aren't tier 4 compliant here in the US. Worth considering, you'll have more torque for steerage, won't need to deal with fuel storage, and won't lose as much efficiency - plus isn't diesel significantly cheaper that gasoline there?
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Old 03-23-2016, 01:29 PM   #20
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Great Harbour is in the process of designing a transportable trawler powered by outboards. The initial design is based on using dual Suzuki DF60's. They expect a speed of 14-15 knots with a burn of 3 GPH or less. The boat is projected to be 35' long with a beam of 10'4" and a displacement of 7,000 lbs or so (I am betting it will be closer to 9,000). Your boat is larger and much heavier and you are looking at much larger engines.

Despite what others have said, I find a lot to like with your idea. There is a lot of gutting that can be done to the ER if you go with outboards. You can remove two engines, transmissions, shafts and shaft logs, rudders, cooling and exhaust components, seacocks, hydraulic steering, etc.

However, there are some issues you need to think about. You will need to remove or at least significantly modify your swim platform. To mount the outboards might require some beef up of the transom. Then there is the issue of power. Do you have a diesel generator? Do you plan to keep it? If so, then you will need to keep both diesel and gas on board. You might also want to think about your fuel tanks. If 30-40 years old they might need replacing prior to using gasoline in them.

If you are having a hard time finding skilled labor to work on your boat, what make you think you can find a suitable crew to convert it from diesel to gas?

I don't envy your problem.
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