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Old 05-01-2017, 04:38 PM   #1
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Twin screw replacement suggestions

If you had a semi/full displacement coastal cruiser between 50-60 ft and the diesels are at the end of their lives, would you overhaul them, or replace them? If replace; what would you recommend for 120-240 HP engines, in the PNW region?

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Old 05-01-2017, 04:47 PM   #2
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John Deere 4045 variant depending on your hp needs.

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Old 05-01-2017, 05:22 PM   #3
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Cummins 6bt 210 hp. Lots of info at or at Tony Athens' site, Seaboard Marine. I repowered with these and have been very happy with them.
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Old 05-01-2017, 05:31 PM   #4
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It depends on money, and what engines are installed now. Most can be rebuilt in place for less than installing new.
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Old 05-01-2017, 05:33 PM   #5
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Depends on the engines. We have a single FL SP135 and looked at rebuilding vs replacement. Rebuilding was ~$15k complete vs ~$40k for a new Luger. The FL is still supported.
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Old 05-01-2017, 05:56 PM   #6
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Hard to beat the Cummins 6BT 5.9 or the 6CT 8.3. Either is a dependable choice. The bigger engine will be working easier at the same hp/torque figures and might yield a smidge better economy. The 6BT has the advantage of having parts available at Autozone or most any Dodge dealer.
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Old 05-01-2017, 06:46 PM   #7
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I repowered my twins, without breaking the bank.

Become a member of Boatdiesel for the most complete information on a large variety of engines. There were even some for sale on that site at reasonable prices when I was doing mine.

What made mine economical was putting in engines of the same make, with the same bolt patterns for engine mounts, exhaust elbows, and transmissions. I was able to avoid also replacing the exhaust from the elbow out, the transmissions, shafts, etc., the water supply, dashboard, engine mounts, etc.

Shortly after I did that, I had a client who tried to repower twins, changing from engines that needed a 3" exhaust on one side of the engines, to 4" lines on the other side, larger shafts, different propellers, engine mounts further apart, laterally, so rebuild the stringers, the list went on.

His cost to repower was over 20 times mine and it took him several months, whereas mine was done in a very short time.
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Old 05-01-2017, 07:10 PM   #8
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To the OP, post what engines are in there now and what the issues are with them.
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Old 05-01-2017, 08:40 PM   #9
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Repowered my boat with a single John Deere 4045TFM75 135 HP. Extremely happy with the choice! Swapped out a low hours Cummins 6CTA 450 HP and about $10K for all the parts and some supplamental labor. 7 Knots at 2 GPH!

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Old 05-02-2017, 07:21 AM   #10
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If available, John Deere 6068TFM75. 6.7 liters, 158 hp, continuous duty. Runs easy and sips.
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Old 05-02-2017, 10:09 AM   #11
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Engine brand is not very important. The best thing about repowering is that you get the chance to decide how much power your boat has. Most trawlers are over powered for what ever reason. The manufacturer probably felt the boat would sell better w a bigger engine or one brand could (or could have been) so popular at the time that any other brand would obviously affect sales. Or multiple power choices would dictate multiple engine brands and that would complicate construction from engine mounts to parts supply. A common problem if the manufacturer chooses a certain engine for a boat an option of more or less power will find that that brand engine dosn't make an engine that would be a good choice for a power option. But dealing w multiple brands is a significant cost problem so an engine of more or less power is chosen to keep the bottom line competitive. Being competitive is very important for a builder.

But you, probably years later can choose any engine you can get your hands on. Some engines are more desireable that others for numerous reasons but the boat owner has a golden opportunity to get things right during a repower. I did a lot of searching and comparing and some research into the question of what power was right for my boat. When it was all said and done I decided the manufacturer or manufacturer/designer was right in the first place. But it's most likely many are not very ideal.

But then I had a problem. My engine of choice had a power lineup such that I would need to be overpowered or underpowered to choose that brand (Isuzu) So I was forced to choose another brand engine (Mitsubishi) to get the ideal power loading. No downside from that decision at all and if I had chosen a different engine (Yanmar, Volvo or whatever) I brobably would have been just as happy. Or if not the difference would be fly stuff in the grand scheme of things.

I could be wrong but I don't think so. As far as I know there are no bad engines. Bad power loading yes but most all engines are just about as good as others available IMO. Some places a V type engine could be too wide and exhaust outlet or engine mount location could be an issue. Due to different heights of propeller shaft output locations on gears some engines could be undesirable due to incompatible bell housing/transmission bolt patterns ect. This variable could cause the necessity of mounting an engine several inches higher than the original boat design. And changing the propeller shaft location on an existing boat is at least a dark horse.

I thought engine shopping was fun and a learning experience. Go for it.

There's a tendency on forums and groups of a common activity like camping, auto sports, mountian climbing and boating that to equip oneself w the best equipment is the best thing to. "The best stuff".. (It was even a movie I think) and the consensus of the group is often thought of as best for making those decisions. Clearly the easiest route but not the best for many reasons IMO. Anyone's environment is different or very different from the next guy so different decisions and solutions will be good or even required for the best outcome.

North Western Washington State USA
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Old 05-02-2017, 05:36 PM   #12
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Eric: I agree with you for the most part but what would you recommend in 120-240 hp for replacement in the PNW region? Just asking?
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Old 05-02-2017, 06:09 PM   #13
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Depends what you have now. If you have something awful, poor parts availability/cost, or other major negatives, changing might be worthwhile, especially if you see yourself as a long term owner.
Otherwise, changing engines for different engine make/model would be my last choice. Before I went there, I`d look at rebuilding what you have, even getting replacement identical engines from somewhere. It`s not so much the engines themselves, it`s the beds, mounts, electrics, panels, exhaust systems, water supply, etc etc, that make change complex and expensive.
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Old 05-02-2017, 06:28 PM   #14
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First thing I would do is all the research I could afford time wise to know how much power my boat requires. I would find an engine that pushes my boat at the normal cruising speed using about 55 to 65% of its max power. Because of my good experience w them I'd see what Yukon Engines has in Ballard. Their main line is Isuzu and Mitsubishi. But they have other brands.

The first Yukon engine I saw was in 1972 in the Queen Charolette Is. I man I knew was building a boat to use in the BC fisheries patrol. It was a 6 cyl Klassen (now Yukon). They have been marineizing engines since before then mostly for the fishing industry. So they are basically industrial products and the've been servicing the fishing fleet in remote places in both Canada and Alaska. You can get on the VHF and have parts flown out to you on bush planes or use more common shipping but they are very good at that.

Most folks here seem to think you need service that completely attached to the originally purchased product but I think not. You need quick and good advice from the original source but there are mechanics everywhere so most service on the go would be provided by a shop or mechanic where you have the trouble. So the main service from the source of the engine should be parts and the knowledge and experience to get the right part to you wherever you are.

If you PM me I will tell you what engine suppliers to avoid. But if they had the right engine I'd still buy it from them .. but seek services elsewhere.

My engine searches were over 10 years ago so I'm out of the loop as to where to go and what brand to seek. As I've said earlier I think the most important thing to get right is an engine that is rated as close to the power requirement that you have. And the engine should cruise at less than 75% load and over 50% load. Perfect for a FD boat would be about exactly 4 1/2 hp per ton of displacement. But there are more easily driven FD boats that only need 3hp per ton and some that may need a tad over 5. W/O getting a degree in engineering the best learning tool is lots of observations of many boats and calculations that you can do to arrive at the power you need.
For your boat I'd start comparing the KK42 to the Nordhavn 46. I'm not sure but I'll bet 85 to 100hp would work well. Just an off the cuff guess but comparing what the N46 does w 100hp and comparing the resistance of both hulls w real world weights a lot could be learned.
Also read Voyaging Under Power and compare your boat w more similar boats. And then find other boats to compare with. Try to identify the overpowered boats and some dock talk won't hurt if you can stay objective. Lots of what you hear won't be but in time you'll be able to quickly identify the real stuff.

North Western Washington State USA
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Old 05-04-2017, 05:37 AM   #15
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First find out what the boat displaces, to decide on HP required.
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Old 05-04-2017, 08:35 AM   #16
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Originally Posted by LeoKa View Post
If you had a semi/full displacement coastal cruiser between 50-60 ft and the diesels are at the end of their lives, would you overhaul them, or replace them? If replace; what would you recommend for 120-240 HP engines, in the PNW region?
Pardon my question, but do you own a boat now with twin diesels? If so, please provide details.

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