Rebuild vs Repower

I need your opinion on something:

I've got 2002 Mainship 430 with twin Yanmar 6LYA 370 Hp engines.
Engines do not run and there is a good possibility they need a full rebuild - I do not have all the details yet and evaluating my options for the worse case.

A full rebuild of those engines will be around $60k
Removing them and putting in brand new Beta 80T engines will be around $60k
* If I'm off in those numbers, let's say the cost of the project will be the same, whatever it will be.

Pros for replacing Yanmars with Betas are:

- much simpler and smaller engines - I like working on the engines and being able to fix everything myself is a big plus. those Yanmars seem to be much more complex and not much space in the engine room to work around them.

- triple fuel efficiency and the range - I like to go slow and far so fuel efficiency is much more important to me than having the ability to run at 20knots from time to time. I know Yanmars can be run at 1200RPM but this is not good for them and they still use 10 mpg at 7-8 knots.

- I want to finish my Great Loop and 5500 miles at 1 mpg with Yanmars vs 3 mpg (or possibly better) with 80T Betas @$6 per gallon will be $33,000 vs $11,000 for fuel.
So, it's like $10k savings in fuel cost every year (I like to go far and see new places every season) which is 60-90 nights at decent marinas every year.


Cons of replacing Yanmars with Betas are:

- Possible loss of boat value, because those were built as "fast trawlers" (if there is such a thing), and a lot of potential buyers, want the ability to run at 20 knots when needed.

- Wrong weight distribution which will probably require adding extra ballast or tankage because of the difference in weight of smaller motors vs larger ones.

- The whole engines replacement project will take much longer with lots of challenges to overcome.


Did I miss something?
What would you do?

What are the specs on the Beta engines? I’m not familiar with them.
Normally I would say go new because a rebuild CAN be a crapshoot (even from.a good shop). But I don’t know the Beta and personally I have my doubts about being 3 times more efficient. And that seems to be what you are banking on

I would expect the Betas to lower resale value only because it would make marketing the boat weird. The Betas are good engines but most people shopping for Mainship 430's have already selected that model and expect it to be similarly equipped to other 430's. There are certainly trawler shoppers who are happy with displacement only, but your boat wouldn't be on their radar because that model is known to be a semi-displacement boat.

I would expect that any fuel savings would be well surpassed by resale loss.

The Yanmar 370's are well regarded engines, seems odd that a full rebuild is required for both, did it sink?

Would it make sense to consider replacing with a lower powered Yanmar ? That may save some complication ( and cost ) as all your engine controls, transmission bolt patterns, exhaust location etc. are more likely to be compatible.

If you go with the Betas, will you be able to use the same transmissions ?

Have you gotten firm bids on the replacement costs? These type of projects can spiral out of control as far as cost and time goes. If you were putting the same engines back in it would be a fairly simple job, but with different engines everything changes. Transmissions, motor mounts, exhaust, wiring, gauges, controls, etc and more will all have to change and some of it custom made. Think long and hard. Good luck with whatever way you go. Keep us informed and we WILL need photos along the way.

Rebuild.
If the manufacture thought 80 hp engines in there were a good idea they would have put them in. Seriously doubt if you'll see that much increase in mpg. Props will probably need to be changed.
If you have to, rebuild and sell, then get what you want.

> What are the specs on the Beta engines?

Those are based on Kubota engines. https://betamarineusa.com/portfolio/beta-85t/
Because those are only 80-85 hp, they will be in the perfect working range for 8 knots hull speed vs idle RPM of 370 hp engines.

> Would it make sense to consider replacing with a lower powered Yanmar ?

As I know, the cost of new Yanmars will be much higher even if I go with smaller engines.

> If you go with the Betas, will you be able to use the same transmissions?

The quote I've got for new Betas includes transmissions but they said i may be able to use the existing ones.
Betas are marketed specifically for repowering and come with custom engine mounts to fit the existing beds.
In any case, I will probably will need new props for Betas because all the power/toque/RPM curves are different.

> I would expect that any fuel savings would be well surpassed by resale loss.

yes, this might be the biggest issue with repowering to the smaller engines but on the other hand, there are a lot of Mainship owners who always go slow. plus higher diesel prices may push even more people away from running fast so why not go slow even more efficiently than running 2x 400 hp engines at idle speeds?
And the living space and accommodations of Mainship are much better than my former "true" trawler (Defever 41) with a small single-engine.


> The Yanmar 370's are well regarded engines, seems odd that a full rebuild is required for both, did it sink?

The boat took some water because of the clogged drains and failed bilge bumps but the water did not reach the engine blocks. also, the engines were not winterized properly at some point so some parts of the raw water system may have to be replaced. I really hope there will be no need for a full rebuild but preparing for the worse case.

Comments in bold below:

QUOTE=Waterant;1089357]I need your opinion on something:

I've got 2002 Mainship 430 with twin Yanmar 6LYA 370 Hp engines.
Engines do not run and there is a good possibility they need a full rebuild - I do not have all the details yet and evaluating my options for the worse case.

A full rebuild of those engines will be around $60k
Removing them and putting in brand new Beta 80T (Don't see an 80T, 85T yes) engines will be around $60k
* If I'm off in those numbers, let's say the cost of the project will be the same, whatever it will be.

Pros for replacing Yanmars with Betas are:

- much simpler and smaller engines - I like working on the engines and being able to fix everything myself is a big plus. those Yanmars seem to be much more complex and not much space in the engine room to work around them

The Yanmar does have a turbocharger and an after cooler and the after cooler needs a full service job every 3-5 years depending on what kind of water you cruise in. Took me about a day plus $100 in valves. Otherwise I don't see much different than the Beta.

- triple fuel efficiency and the range No, No and No. I ran my Yanmar 370 at 1,400 rpm and it burned 2 gph making 30 hp each. A pair of Betas will do maybe 10-15% better at that power level - I like to go slow and so fuel efficiency is much more important to me than having the ability to run at 20knots from time to time. I know Yanmars can be run at 1200RPM but this is not good for them and they still use 10 mpg at 7-8 knots. 1,400 rpm is about as slow as I would run them. Run them up to 2,500 for 5 minutes every eight hours to blow out accumulated carbon
- I want to finish my Great Loop and 5500 miles at 1 mpg with Yanmars vs 3 mpg (or possibly better) with 80T Betas @$6 per gallon will be $33,000 vs $11,000 for fuel. No, see above. You might save $2,000.
So, it's like $10k savings in fuel cost every year (I like to go far and see new places every season) which is 60-90 nights at decent marinas every year.


Cons of replacing Yanmars with Betas are:

- Possible loss of boat value, because those were built as "fast trawlers" (if there is such a thing), and a lot of potential buyers, want the ability to run at 20 knots when needed. Big loss of value. I wouldn't buy that boat with those engines. Not many would either. At best you would get the normal market value less the cost of replacing the Betas with Yanmars.

- Wrong weight distribution which will probably require adding extra ballast or tankage because of the difference in weight of smaller motors vs larger ones.

- The whole engines replacement project will take much longer with lots of challenges to overcome.

Did I miss something?
What would you do?[/QUOTE]

You have totally mis calculated the efficiency of the Yanmar vs the Beta at low power output. Yes it does take more power to move the internals of a 5 liter engine vs a 3 liter one, but no where near the numbers you are figuring. That plus loss of resale value makes it an unwise move to replace the Yanmars with Betas.

I am attaching the data sheet for the Yanmar 370. Compare its fuel consumption at 40 hp with the Beta. There isn't that much difference.

And finally what makes you think that the Yanmars are trash. It takes something catastrophic like loss of oil pressure while running hard and seizing up to completely trash an engine that young. Even a severe overheating shouldn't cost more than $10 grand to fix.

David

What if you just rebuilt one Yanmar and ran on one engine all the time ? That would get the engine RPM up into your desired range but still allow you the fuel savings and slow speed you are after ?

I know it's not an ideal solution but if it can cut a $60k repair bill in half, it might be worth considering.

> If the manufacture thought 80 hp engines in there were a good idea they would have put them in.

Possibly but that was in 2002 when the diesel was $1.5 per gallon (remember those good old days?)
and Mainship got bankrupt a bit later, so they may not be right after all.


> Seriously doubt if you'll see that much increase in mpg.

here is my logic:

from what i could find, 1700 RPM is what the owners of Mainship 430 with the same Yanmars are running to get the fuel efficiency at 8 knots

Yanmar 6LYA at 1700 RPM processes 50 kW of power @ 3 gph of diesel consumption
https://www.trawlerforum.com/forums/attachment.php?attachmentid=114476&d=1613510108

Beta 85T processes the same 50 kW of power at 1900 RPM @ 5 Lph or 1.3 gph of diesel consumption
https://betamarineusa.com/wp-content/uploads/2020/10/B85T-HE-Power-Graph.pdf
and I still have 20% of power in reserve to compensate for the wind and current and still maintain the hull speed.

so, I'm looking at the total of 6 gph vs 2.6 gph for the same 50 kW of output power.
yes, props will have to be replaced but getting more than doable efficiently may be worth the trouble.


> If you have to, rebuild and sell, then get what you want.

Good option, but I want a low-maintenance boat with no wood outside with the layout of Mainship 430 and the range of a Selene. Putting small diesels into Mainship 430 will get me very close to my perfect boat for way less than the cost for Selene 43.
I do understand that repowering will take a lot longer with lots of issues to resolve so it's not an easy decision.

DavidM said:

No, No and No. I ran my Yanmar 370 at 1,400 rpm and it burned 2 gph making 30 hp each. A pair of Betas will do maybe 10-15% better at that power level

Click to expand...

I was writing my assumptions at the same time you sent this.

on the power graph, there is no 1400 RPM for Yanmar but looks like the data is almost the same as for 1700 RPM (the lowest on the graph)

Yanmar 6LYA at 1700 RPM processes 50 kW of power using 3 gph of diesel
https://www.trawlerforum.com/forums/attachment.php?attachmentid=114476&d=1613510108

Beta 85T produces the same 50 kW of power at 1900 RPM using 5 Lph or 1.3 gph of diesel
https://betamarineusa.com/wp-content/uploads/2020/10/B85T-HE-Power-Graph.pdf

so, I'm looking at the total of 6 gph vs 2.6 gph for the same 50 kW of output power.

maybe I'm missing something but those are the numbers I see on those graphs and do not have any reason not to believe them.

DavidM said:

And finally what makes you think that the Yanmars are trash. It takes something catastrophic like loss of oil pressure while running hard and seizing up to completely trash an engine that young. Even a severe overheating shouldn't cost more than $10 grand to fix.

Click to expand...

I should know more next week but for now, I'm assuming a full rebuild at the estimate I've got so far and I'm evaluating my options.
if the problem will cost $10k to fix, I'll be the happiest boat owner of the month.

> What if you just rebuilt one Yanmar and ran on one engine all the time ?
> That would get the engine RPM up into your desired range but still allow you
> the fuel savings and slow speed you are after ?

my OCD (or whatever this condition is called) will drive me crazy very fast if i have only half of something working while another half is broken

I think DavidM pretty much hit the nail on the head. The thermal efficiency differences between the two engines simply can't be as big as you assumed. Just from a pure engineering view the difference of 10-15% is about what you should expect.

Rebuilding guarantees you that you won't have any difference in fitment, weight, or performance. Changing the engine you will find lots of things need changing to adapt to the new engine which will cost you more in the end. My only hesitation is why the Yanmars died in the first place, 2002 isn't old for a boat.

I would not just do one engine. The boat will be a PITA to handle. And if you get into challenging conditions it could be even worse. And the resale value will be in the dumper.

Slowmo said:

Just from a pure engineering view the difference of 10-15% is about what you should expect.

Click to expand...

I would expect as much if someone ask me without any data but looking at the power charts of both engines for the same 50 kW output you can see a huge difference in consumption. I do not think Beta would publish deceiving information.
or maybe I'm missing something on the chart but it seems to be 5 Lph or 1.3 gph for 50 kW of power at 1900 RPM on Beta 85T vs 3 gph at 1700 RPM for the same 50 kW on Yanmar 6LYA.

Slowmo said:

My only hesitation is why the Yanmars died in the first place, 2002 isn't old for a boat.

Click to expand...

This is a $60000+ question but I do not have enough details right now to ask for help in that direction.

When comparing power curves, it appears you’re using max power on the Beta curve and propeller power on the Yanmar curve. If you look at max power on the Yanmar curve it’s actually producing 125kw at 1700. And using the propeller curve on the Beta requires 2200 rpms and 9lph to achieve 50kw output.

kchace said:

When comparing power curves, it appears you’re using max power on the Beta curve and propeller power on the Yanmar curve. If you look at max power on the Yanmar curve it’s actually producing 125kw at 1700. And using the propeller curve on the Beta requires 2200 rpms and 9lph to achieve 50kw output.

Click to expand...

thanks. i suspected I was missing something there. 4.6 gph is still better than 6 gph (25% more efficient?) but not as sexy as 2.6 vs 6.

Have you looked into remanufactured Yanmar engines? I was curious if they were available since I used remanned Cummins on my repower and they turned out fine, including a new-engine warranty. Remanned Yanmars are available from MECO, macdonaldequipment.com. I know nothing about their prices or real-world experience with these engines, only that they are being advertised by MECO.

Ant, some thoughts:

Not all "rebuilders" are created equal. Is the rebuild you're contemplating being quoted by a recognized Yanmar dealer that can offer a full warranty? Where is the vessel located? If not done already and you're on the East Coast, Mac Boring is one outlet to get some numbers from. As mentioned by others, some luck may be in your favor provided the motors didn't swallow water and then sit.

A removal rebuild offers the opportunity to make the ER a showpiece. David Marchand knows Yanmars pretty well, listen to him carefully if you choose the rebuild route. Also check into boatdiesel for some detailed Q&A.

What exactly is wrong with the Yanmars? Has a professional said they BOTH need to be rebuilt?
If it were me, I would fix both engines, sell the boat and buy what you really want.

My 2 cents for what it is Worth

That boat would be more attractive to me with the smaller motors. Although I question the fact that the cost will be similar between new and rebuilt .of course I am aware of the high prices yamar charges for parts. Of course with new motors be moving away from those issues
If your numbers are correct I would be in favor of the smaller motors

> Have you looked into remanufactured Yanmar engines?

Not yet. I did not think rebuilding the existing yanmars could be more expensive than replacing them with rebuilt engines of the same Hp.

my question is more about putting smaller engines to get better range and economy compared to the old engines if the price of the project is the same (hypothetically).

> Mac Boring is one outlet to get some numbers from

Thanks. I'll talk to them.

> A removal rebuild offers the opportunity to make the ER a showpiece.

Oh, that would be awesome. I checked a few posts about people removing the engines and refreshed ERs look like a sparkling mechanical haven.

> What exactly is wrong with the Yanmars? Has a professional said they BOTH need to be rebuilt?

PO had some mechanic look at them and said they both need a rebuild. I'm assuming this is true for now until i get more details. I had an older version of this engine on my Defever and it's hard to imagine a total distraction.

> That boat would be more attractive to me with the smaller motors.

Yes! Thanks, motion30
I knew I'm not alone in thinking not all boaters want/need 700+HP in a 43' boat

This is one of those nutsy threads. People who want a displacement speed boat don't want a mainship. People who want a mainship aren't looking for forced displacement speeds. Not only will resale be low, but the boat will languish racking up expenses.

There are few things in life worse than a planing boat that won't get up on step. I once helped a guy with the sea trial of a Bayliner 32xx. Nice boat and if ever there was a cabin cruiser that cried out for gassers, this was it. The guy really, really wanted diesels so he finds a rare example with small Hinos. She failed first sea trial due to messy bottom and we try again a week later. As long as the broker would stand at the bow, she'd sorta get on plane. Small rudders meant she was a dog at displacement speeds. The boat would push hard and burn a ton of fuel, but just couldn't make it over the hump. He bought it anyway.

Good luck. Sounds like OP has fallen in love with the idea. But make no mistake, this is a bad idea on at least a couple levels. Repower, small engines.

Where are buyers like this when Im selling?

Peter

mvweebles said:

Sounds like OP has fallen in love with the idea. But make no mistake, this is a bad idea on at least a couple levels. Repower, small engines.

Click to expand...

Nope, not in love. Just doing my research and crowd-thinking because members here have much more experience than I do.

My other idea was to put 2 electric motors with a large generator plus a tesla battery and a load of solar panels. A quick search showed this will be more expensive and not even that fuel-efficient because of the loss of energy on the conversion from diesel to electricity and from electricity to torque. and solar panels which could fit on the available space will not help much except for some short trips around the marina.

Having a crazy idea and doing a crazy thing are not the same.
I'm not the first one with the dilemma to rebuild or repower and all the comments and opinions may help others in the same situation in the future to make the decision.
I'm grateful to everyone who commented

Having just purchased(early 2021) a 2001 Mainship with a Yanmar 6LP-STE 300hp, I looked at and researched a lot of boats for many years leading up to this purchase.

I had no illusion that this would ever be a fast boat and it “kinda” planes but we run at 8kts, 9.5 is high cruise. “Planing” is 12-13 kts. and is just really a huge wall of water being pushed and smoke and the cool sound of the turbo at wot. We don’t do that haha.

That being said if I were shopping again and came across my same boat with an 80hp Hino, I’d probably pass, or want a lot off asking price compared to what I bought. And yes I know I don’t need 300hp to go 8kts.

I am no expert, fairly handy and do a lot of my own work, but I’d be a bit scared of an under power re-power. If I was in love, I’d want a lot off just to deal with potential future problems.

I boat where currents aren’t a big deal, but I like knowing I can juice my Yanmar if needed and there is some extra HP there.

If you do proceed with the under power re-power, do it knowing and not caring you will take a hit when you sell, and you will scare many buyers away, you just have to accept that.

I do not have facts, but I find it difficult to believe a re-power is the same cost as rebuilding. But, I just sold a used truck and paid less for the new same model truck, so these days logic is out the window.

It is an interesting idea, I like hearing your logic and will be very interested is what you find for costs and eventually decide on.

mncruiser

That's a good point. On my last trip going against St Lawrence river I did wish I had more power a couple of times. My Defever 41 had a single 170hp Yanmar in it which is be approximate the same weight pushed by the same HP as two 85hp Betas. But maybe 1987 engine with 4000 hours did not produce all the power it was rated at.

By the way, I just find out a new NORDHAVN 41 has Betamarine 85T x 2 - exactly the same engines I'm considering. And Nordhavn is the gold standard in lthe ong distance trawlers.

So, maybe it's not such a bad idea after all.

That is interesting - a much heavier NORDHAVN 41 with approximately the same LOL of 40' and 2x Beta 85T engines gets 2 mpg or 3.7 gph at 7.5 knots
https://nordhavn.com/models/n41/

From the sea trial data I found for Mainship 430, the best it can get with 2x370 HP engines is 1 mpg

So, it seems like repowering to smaller Betas can give me efficiency and range I'm looking for after all. And the option to rebuild Yanmars, sell this boat and get the boat I want does not work because even older N40 is 3 times the price of Mainship.

mncruiser, what mpg do you get in your Mainship with Yanmars?

Waterant said:

That is interesting - a much heavier NORDHAVN 41 with approximately the same LOL of 40' and 2x Beta 85T engines gets 2 mpg or 3.7 gph at 7.5 knots
https://nordhavn.com/models/n41/

From the sea trial data I found for Mainship 430, the best it can get with 2x370 HP engines is 1 mpg

So, it seems like repowering to smaller Betas can give me efficiency and range I'm looking for after all. And the option to rebuild Yanmars, sell this boat and get the boat I want does not work because even older N40 is 3 times the price of Mainship.

mncruiser, what mpg do you get in your Mainship with Yanmars?

Click to expand...

I just have a single 300. I have a floscan that I’m assuming is accurate. I don’t really track the fuel consumption well, so these are memory from last season, the first season. I might be remembering it wrong but here goes.

Delivery from Lake Michigan to Lake Superior, we were in a hurry, so high cruise around 9.5-9.8 kts. I think that was around 7-8 gph.

When I slow down to around 8.5,I think I’m burning 4-5 gph. If I slow to 7.5, I think I’m down to 2-3 gph. We usually are going 8 to 8.5. The times I remember going very slow the floscan was saying .9 gph at 3-4 kts.

Non-boaters ask me a lot now how I will deal with fuel prices. My response is that if I decide to care, I’ll go 7 instead of 8 kts. That will cover the fuel costs.

The truth is, I don’t care because the fuel is the least of my concerns where we boat. We are seasonal Lake Superior boaters, mainly long weekends. I don’t burn enough fuel to care compared to a lot of you.

I will track it better this next season just to have a good reference.

Ant
When you mentioned twin Betas the N41 popped up in my mind. If you are serious about a Beta repower find the right group to do it. Personally I don't see it as a bad move, different but so you've got an 8 knot boat, we "all" do too.

The N41 fuel/power/speed curves would give you a pretty good idea as to what to expect from your vessel. I doubt you'd be burning more than 3.0 to 3.5 gph at 7-8 knots. It would be interesting to work up a repower bill of materials and assess availability of the individual parts and pieces. These are trying times for accessing new stuff.

With all that's been said, I think the OP is opting for the twin Betas, all things considered. He likes everything about the boat, except the engine problem, so if the Betas achieve his desires, so be it. He has certainly put a lot of thought and research into this.

"

I'd say go w/ the Betas, realizing all that has been said here, knowing full well the hit to the sale price of the boat. This will be the cost of his enjoyment, so if he accepts this, who's to say, "Nay?" One answer to the sale price question is never to sell the boat. The longer he enjoys it, the less hit of the expense over the years, and he does have what he wants.



Instead of selling it, if it comes to that, perhaps donate it to a charity, school, etc., and help w/ his tax deductions. Yes, there'll be a loss, but as I say (and I think the OP knows and accepts this), it's the cost of his enjoyment.

I guess it depends on whether or not this will be a long term last boat for you so you don’t need to care about resale value. However we have bought 5 “last” boats. We are on #24 right now but 5 boats ago we said it would be our last…. How did that work out for us? But not everyone is like us. Some may say last boat and actually stick to it. Good luck.