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Old 05-10-2021, 03:59 PM   #1
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Outboard power on a pocket trawler

I have been performing a lot of routine maintenance on the VP d4 diesel that powers my boat. The older I get the more I hate contorting myself and scraping up my arms and hands trying to get things done in tiny spaces. It seems that performing PM is an after thought for most marine engines and engine installations. I have it better than most because the engine is coupled to a stern drive and is not buried in the hull. It gets me thinking about outboard power. Modern outboards are incredibly reliable, quiet, and fairly economical. The one thing I can’t get over is how they look hanging so far back on the transom, especially on a traditional pocket trawler like mine. An outboard would free up a ton of cockpit space and save about 900 pounds in weight. Does anybody else think that they have no place on a traditional looking boat? Any opinions would be welcome.
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Old 05-10-2021, 04:04 PM   #2
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I kinda used to be in the same camp as you--OB's only belong on runabouts.

But as I've seen the huge advancements in OB motors I'm starting to rethink my old frame of reference. If I were in the market for a pocket trawler I'd definitely look at having a pair of OB's hanging off the back.
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Old 05-10-2021, 05:03 PM   #3
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We have a Rosborough pocket trawler with an outboard on an extension and it has been great. We opted for an outboard vs diesel I/O for the same reason........space. We got a very usable aft cockpit on a small boat.



To your situation, where you no longer enjoy working on your diesel due to tight space I would urge you to keep your working diesel system and outsource the work at a very small percentage of conversion costs. I am thinking new outboard(s), stern modifications, electrical system, new fuel system and storage tank(s), new control/gauges, adjusting for weight transfer, work to convert the old spaces to new use and current issues of new materials delivery.


So farm out the work at a pittance and keep boating.
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Old 05-10-2021, 05:20 PM   #4
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There is a trend to put outboards into a sort of box enclosure at the stern. You can't really tell it is an outboard powered boat.

Of course this arrangement is not for the braggart who likes to have everyone see four or five merc 400 Bravado engines hanging on his boat.

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Old 05-10-2021, 05:52 PM   #5
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I used to be a diesel purist. But I've come around. I went for a ride recently on an rf246 with a big Honda ob. Nice. Quiet, smooth. And I see outboard Ranger tugs often. They don't look odd.

I agree with Leonard that your money would be better spent on hiring out the nasty stuff. But I think an outboard conversion would be an upgrade.

Great boat BTW. I remember the thread when you found it.
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Old 05-10-2021, 06:14 PM   #6
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I/o are problem childs of the Marine power world..They are prone to the usual problems of hanging an outdrive out the stern..... Diesel or gas power isn't the issue, Its the drive. Go Outboard or straight inboard. That usually means selling current rig and getting the type of power you want.
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Old 05-10-2021, 06:29 PM   #7
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One nice thing about OBs. If they crap out, they are easily replaced without disturbing the interior of the boat.
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Old 05-10-2021, 06:49 PM   #8
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Quote:
Originally Posted by Sweet marie View Post
Does anybody else think that they have no place on a traditional looking boat? Any opinions would be welcome.
Whats not to like? Outboards are clean, quiet, and smooth. Service is available everywhere. No stories about $800 alternators. Easy access OUTSIDE of the boat. No stink or smoke.

We had a D4 and a DPH-A drive in our last boat. The D4 is, at least, designed for marine use and access is reasonable. I loved the performance and efficiency of the D4, but the DPH drives present plenty of maintenance opportunities.

I think Leonard speaks the truth with regard to re powering. Spend the conversion and extra gas money on having the maintenance done. There is not THAT much to do, as long as you keep the drive alive. Once your DPH gives up, you will have around 15K of additional math in the equation. Reach out via PM if you want to chat DPH drives - we had an excellent technician/subject matter expert caring for ours.

That said, I have yet to meet anyone on the docks that is making a profit from their boat. If it blows your horn to re power, you should do it. Keep in mind how it will affect resale value and ongoing insurance costs (switching to gas). And if you do re power, please share before and after performance data.
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Old 05-10-2021, 07:52 PM   #9
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I love the look of outboards on the stern .. fully exposed.

But the big problem for OB’s on trawlers is gear ratio and prop clearance.
Also outboards are seawater cooled. Corrosion isn’t the biggest problem.
Fresh water cooling permits much higher cooling temperatures .. can be above 200 degrees whereas a seawater cooled engine can only run at 120 or 130 degrees. The heat generated by combustion and friction goes largely through the cylinder walls and into the sea (in boats). The higher temps runs best at much leaner ratios. So fuel economy is considerably better w freshwater cooling.

Of course outboards could be made w heat exchangers in the lower unit. But the market will need to bloom for lower speed higher thrust outboards with bigger props. I’d sure like to see it. But for now fuel efficiency will be poor on an OB powered trawler. However if you have or can get a sailboat hull you could convert it and even power it w a small two stroke OB. Sailboats are FAR more efficient than trawlers re power required per ton of boat.
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Old 05-10-2021, 07:57 PM   #10
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Rip that puppy out of there and bolt on an Armstrong bracket. Eh, maybe.

We've discussed doing this to our cat. Our inboards are similarly shoehorned into a tight space. Modern fuel injected outboards are incredibly efficient, quiet, and able.
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Old 05-10-2021, 08:11 PM   #11
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I started a thread on this long ago and feel more strongly now with the advancements that we'll see more outboards on boats under 50'. We've now seen some great performance tests on the Mercury Verado 600, but perhaps even more interesting is the Mercury Sea Pro 500, which is designed as a commercial outboard. They've added Sea Pro versions from 200 to 300 hp which are basically adjusted from the Verado 250 to 400 hp. Then not to be overlooked we have the Mercury two-stroke diesel at 175 hp. Unfortunately it's for light duty.

Yamaha hasn't caught up yet but they do have a 425 hp offshore model which is very impressive.

We're seeing more boats every day sold with outboards and some are large. Interestingly, Sea Ray no longer offers a Diesel Sundancer above 32' but they do offer a Sundancer 370 with triple Verado 300's.
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Old 05-11-2021, 12:57 PM   #12
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I appreciate the feedback. There are some factors that would affect my final decision. From what I have seen a used, lower hour d4 seems to command north of $15k. This would offset a large portion of the cost of a 200hp outboard. In terms of the necessary modifications to the boat and installation of the motor, I would do that all myself. The only thing I would not do if it was necessary for the warranty would be to hang the actual outboard on the bracket. I have found a hydraulic bracket that protrudes 17”. This combined with a small 10” deep well would be a good compromise on how far back the outboard sits while still providing much more cockpit space. The hydraulic bracket also pulls the engine completely out of the water making it nice for when we slip the boat in the summer. Suzuki makes a 200 hp outboard with double gear reduction which has a final ratio of 2.5 - 1. This would swing a larger diameter prop. However the Merc 200 has a much larger displacement for the same horsepower. I would have to choose between the two. In terms of weight the original boat was designed for a d3 but because the builder got a great deal on a d4 at a boat show and he went with that motor instead. The stern of the boat rest well below its original designed water line. An outboard and bracket would weigh very close to what a d3 would have. I am considering a 200hp outboard because right now I can cruise at 15-16 knots burning about 3-4gph. This equates to roughly 75hp. A 200hp outboard would be running at about a 40 percent load which should help it live a long life. The boat is so easily driven that with the current 225hp motor I can do 31 knots. Way more than enough speed for me. I do have a couple of unresolved concerns. One is the ability to produce hot water with the engine, and the second is the fact that I have a below deck Webasto diesel heater. I do not know if the heater presents a risk if I switch to gasoline. I would also like to be able to produce hot water while underway without the use of an inverter. Sorry this went a little long.
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Old 05-11-2021, 01:18 PM   #13
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Personal preface, diesel.

If you go with gas, enjoy.
Most big outboards can come equipped with larger generators to charge the batteries and house loads.
I am not sure if and how they could support an A/C. You will need a rather large inverter. I would put a "soft start" on the A/C.... Kinder to the A/C especially if you have 2 A/Cs.

Please post a pic of the 4d boat with the outboard(s). Means nothing to me without a picture.
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Old 05-11-2021, 01:53 PM   #14
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Re: 12v Marine AC systems “mabrustore.com”, there’s also many designed for the sleeping cabs of large trucks due to all the recent “anti idling” laws.
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Old 05-11-2021, 02:32 PM   #15
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I have owned a tiny trawler- an outboard powered Atlas Pompano 23, a gas inboard powered Cape Dory 28, and various 34' diesel inboard powered trawlers

30' and under seems to be a good break point to consider gas and particularly inboard power. The gas powered Cape Dory would have been a nicer boat with a 300 hp outboard hanging off its stern rather than its Chrysler inboard gasser and even nicer than the 200 hp diesel powered version.

Yes raw water cooling of today's outboards does cause a bit of an efficiency hit, but adding fresh water cooling would significantly add to the weight and complexity.

Outboards and their I/O drive cousins inherently don't last as long as straight diesel engines. Sea water corrosion eats them up particularly, the I/Os that sit in the water all of the time.

The Rosborough 246 and Atlas Acadia 25 outboard powered small trawlers are particularly well suited to outboards. MJM made a very nice outboard powered 29Z, but their bigger boats with outboards seem more like runabout fun boats rather than a trawler/cruiser.

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Old 05-11-2021, 09:03 PM   #16
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I always thought the Cape Dory 28 would make a great trailerable trawler with an outboard and a shaved down keel. Great looking boats. I think they are 9-6 wide which is doable. I towed a 29’x10’ Phoenix for a few years and it was never an issue.
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Old 05-12-2021, 05:39 PM   #17
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Need to consider what removing a lot of weight from the middle and hanging it on the aft end will do the the structure, ride, and handling of your boat. Your boat is built for all that weight to be in the middle, not at the back.

It might not make a noticeable difference, but it could. It is something you should keep in mind.
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Old 05-12-2021, 07:25 PM   #18
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ssobol,
A lot of guys like big engines .. OB or IB. And those that do will suffer the end result that you predicted. But if you power for rather slow planing speeds the engine may not be too much weight aft. And w OB extensions the weight is way far aft. But if the OB is smallish and the extension short good balance could be had.

If I was converting a 20 - 25’ boat to OB power I’d forget all about those extensions and mount the engine on the transom .. for all the world to see. Meaning I don’t like OB’s in boxes. OR extend the whole boat at the stern or a bit fwd. Then there is hull volume to support the engine and possibly fuel.
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Old 05-12-2021, 08:55 PM   #19
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I prefer not to have gasoline on board. And prefer most boat weight in midship.
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Old 05-12-2021, 09:47 PM   #20
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Get too much weight concentrated amidships and you’ll have a hyper pitching boat. But on the bright side turning will also be quick.

But it’s difficult to do so it seldom happens. My boat has two 50 gallons of domestic water in the lazerette. Not ideal but it dosn’t seem to be a problem either. And there’s also lead ballast in the laz. There’s only so much room in a boat. But designers do their best. And sometimes ya just gotta buck up and put it where you don’t want it to be. We’d like to have that 100gal of water amidships but there’s 100gal of fuel there. And close to 1000lbs of engine and trans + batteries and a tank for black water and another for domestic hot water. All this in the middle of a 30’ boat.

So your notion of all a boat’s weight in the middle is not going to happen.
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