Rebuild vs Repower

[danderer]

People who want a displacement speed boat don't want a mainship. People who want a mainship aren't looking for forced displacement speeds.

Agreed.

--Former Mainship owner

 

[DavidM]

Where are you guys seeing the Beta 85T propeller power curve. All I see is the WOT power curve. On the Yanmar spec sheet the propeller power curve is the one in blue.

The Beta spec sheet looks like it does give the fuel consumption propeller curve, the lower one on the graph, but not power. Very misleading when you take power from the wot curve and fuel consumption from the propeller curve.

There is no way to figure propeller hp per gph or kW per lph with those curves.

But probably irrelevant given where this thread is going .

David

 

[mvweebles]

Wanna use the N41 as an example? I can guarantee the hull form (prismatic coefficient) is optimized for the speed, and the rudders are matched accordingly. Both Nordhavn and Mainship have very strong resale markets. Putting 85hp engines in a Mainship makes as much sense as putting 370hp engines in a N41. Either would be an unsellable unicorn.

Peter

 

[rslifkin]

The Mainship 430 is more of a planing hull than the other Mainship trawlers, so I'd say it's less of a candidate for de-powering. Even if you go slow most of the time, there are times where more speed/power will be needed to get the best out of that hull. So I wouldn't want to limit it to displacement speeds or just above with tiny engines.

In general, the ideal engine for a boat like the Mainship 430 is something with enough power to comfortably plane the boat, but that's also happy running very lightly loaded and stays efficient when doing so. Whether the original Yanmars achieved that or if something else would be better, I'm not sure. But tiny Betas are likely the wrong answer.

 

[ranger58sb]

> Mac Boring is one outlet to get some numbers from

Thanks. I'll talk to them.

> 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.

If I were in the market for a Mainship, the smaller replacement engines would send me elsewhere. If I were in the market for a normal slow trawler, I probably wouldn't be focused on Mainship first. (We owned a Mainship previously, great boat.)

Do you own this boat now? Or is this a pre-purchase discussion?

I'd be suspicious of the words "some mechanic" and "total rebuild." Perhaps that guy might have thought aftercooler and heat exchanger service, a valve job, and new hoses and belts is a "total rebuild."

In either case, I've read Mack Boring should be your go-to folks for Yanmar diesels.

And in any case, I wouldn't be making a decision without having their guidance first.

-Chris

 

[NEtrawler58]

I also don't think the efficiency gains are going to be as big as originally stated for the same boat speed. But the two big issues that would bother me are resale value and power. You could probably cruise fine with the smaller engines most of the time, but what about a situation that you could use more power? Dealing with large seas and/or a strong wind and current or needing to get out of the way of something quickly, it's good to have power in reserve. The 430 is a big boat. What if you were to lose 1 engine? How well would 1 engine push that boat if you needed it to especially in a challenging situation? And I think resale would take a big hit comparing to similar boats with low hour original engines that are well-maintained.

 

[ofer]

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.

take the fuel efficiency benefit out of your equation. chances are you may not gain any MPG at all. its a lot more complicated than just looking at rpm curves. don't forgot you may have to change gear ratios and props which will further complicate the comparison.

i am not saying don't do it. just saying don't include efficiency on the pro side.

 

[sunchaser]

Apparently, the OP is willing to toss the hit to re-sale out the window, thus what are the tech issues to overcome? He is willing to settle for a displacement speed vessel and not wanting to see the vessel get on a plane.

To accomplish this task all sorts of bits and pieces need to be considered beyond the engines. As noted rudders, shafts, transmissions, mounts and fuel system need redoing.

Given the magnitude of the task, a good cost and details workup will prove surprising, likely more than 2X the cost of the engines and lasting 18 months from the "go" date. Lastly, would a recognized yard tackle this approach?

 

[twistedtree]

If the goal is to get the boat going again, then I would 100% focus on rebuilds. The scope of work will be confined to the engines, and even if one or both turn out to be scrap metal, I'd look for takeouts of like-kind. That way there is no shaft work, no mount or stringer fabrication, no exhaust fabrication, no rewiring, no replacement of instrument and control panels, no pulling new control cables through the boat, no fabrication of control brackets and mounts, etc. etc. etc.. With a repower, the project creep will likely extend into every one of those areas, all at $100/hr or more. Plus you will be dependent on many more people, all of whom are likely overbooked.


As for efficiency gains, DavidM captured it. Any boat's fuel efficiency is determined first and foremost by the running speed. It has an exponential impact, and dwarfs all other factors. Next is the physics of the hull shape. Then last is the engine selection. Changing to different engines will have a relatively small impact on fuel economy, and is a ton of work. Slowing down even 1/2 knot will have a much more significant impact, and is much easier to to. Also, take all manufacturer's performance charts with not one, but two grains of salt. Most are theoretical, not demonstrated, and even the demonstrated ones are usually with a very light boat.



And if for any reason you want some form of hydrid electric, sell your boat and get an engineered package like a Greenline. Just be sure you fully understand what you get and what you don't get. It's not like an electric car.


Now all this assumed your goal is to get the boat running so you can use it. If instead you are looking for a fun project, then by all means do whichever would be the most fun.

 

[NEtrawler58]

If I were in the market for a Mainship, the smaller replacement engines would send me elsewhere. If I were in the market for a normal slow trawler, I probably wouldn't be focused on Mainship first. (We owned a Mainship previously, great boat.)

Do you own this boat now? Or is this a pre-purchase discussion?

I'd be suspicious of the words "some mechanic" and "total rebuild." Perhaps that guy might have thought aftercooler and heat exchanger service, a valve job, and new hoses and belts is a "total rebuild."

In either case, I've read Mack Boring should be your go-to folks for Yanmar diesels.

And in any case, I wouldn't be making a decision without having their guidance first.

-Chris

+1 on Mack Boring. Not sure where the OP is located but I have found MB to be very responsive and helpful both by phone and email.

 

[ksanders]

If, and this is a big If resale value is taken out of consideration, there is a decent argument for smaller engines.

My 2011 repower is a pretty good example.

I had tired 330 HP cummins 6BTA engines. I seriously considered putting in the 210HP cummins re power engines.

Why????

Engine simplicity is the main reason. The 210HP version is a simple turbocharged engine, where the same block at 330HP is seawater aftercooled.

I went with the 330 engines and am glad, but I seriously considered just dropping in a pair of those bulletproof low output engines.

 

[Solly]

With all the variables involved does anybody think the printed mpg, gph, ratings are anywhere near accurate ??? Maybe under ideal conditions.

To me it takes a certain amount of power (fuel) to move a boat at a set speed. As long as the engine size isn't way out of line you should get about the same fuel burn regardless of size.

If I wanted to go slow, at an efficient engine rpm for the Yanmar's, I'd swap out the props for something with less pitch. Then if it didn't work out you could put the original props back on.

 

[rslifkin]

If I wanted to go slow, at an efficient engine rpm for the Yanmar's, I'd swap out the props for something with less pitch. Then if it didn't work out you could put the original props back on.

De-pitching the props to get higher RPM but still with very light load will increase pumping and friction losses in the engine, typically leading to worse efficiency, not better.

 

[Comodave]

If you are looking for efficiency at slow speeds you typically want to increase the pitch of the props. However you run the risk of overloading the engines at higher RPMs.

 

[jgtrucking]

If you want a traditional trawler, why not sell and buy one. Many advantages that come with the speec limit besides fuel burn... you would be giving those up.

 

[NEtrawler58]

If you want a traditional trawler, why not sell and buy one. Many advantages that come with the speec limit besides fuel burn... you would be giving those up.

Just curious what you see as the advantages to a full displacement trawler compared to something like a fast trawler that can cruise much faster if desired? What is given up?

 

[Slowmo]

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.

I wondered the same thing. What would cause both engines to fail and at what hours? Is there something to learn there? Anyway, other's have pointed out the weakness in just looking at the OEM f/c charts. Real world fuel consumption tends to be affected by many factors independent of the engine itself. This is seen in the on-road experience where theoretical improvements from engines have not necessarily translated to like sized real world improvements. A lot of this is because even if an engine is more efficient, it is just one part of the system.

 

[Waterant]

If you want a traditional trawler, why not sell and buy one. Many advantages that come with the speec limit besides fuel burn... you would be giving those up.

I had enough of messing around with the boats from the 80s while younger than 20 years "traditional" trawlers are out of my budget, especially after the recent price jump.

Imagine:
The convenience of a great layout and low maintenance of not having any outside wood of 43' Mainship and fuel efficiency of small Betamarines 85hp!
it's a poor man's Nordhavn!

If seriously, after reading all the comments (thank you!), the rebuild will be my plan A unless the rebuild quote from a pro shop will be much more than replacing it with Betas. (Did I tell you those Yanmars have only 280 hours on them? ... do not beat me too hard.)


if the price of diesel keeps going up, putting much smaller engines is still something to consider if the timeline and resale value are not the problems.
I think the argument that a large engine is as much efficient as a small engine at a slow speed is not entirely correct.

The difference is negligible at the same power output but the actual power required to move the boat at that speed is very small. maybe a large 370 Hp motor simply can not give you that little power even at the idle speed so this is where the much lower consumption comes from.

If you check N41 sea trial data (it was not on smooth water and the boat was pretty loaded), they got 2 mpg at 7.4 knots with 46% of power from Betas 85T:

Dropbox - File Deleted - Simplify your life
Nordhavn 41 - Nordhavn Yachts"]Nordhavn 41 - Nordhavn Yachts

while Mainship sea trial at the lower speed barely gives you 1 mpg:
Dropbox - File Deleted - Simplify your life
https://dicksimonyachts.com/blog/boat-reviews-brochures/mainship-430-trawler-review-simple-pleasures

plus the gearbox and prop are configured for slow speeds while with a larger engine we are trying to do what they were not designed to do.
I do not think the hull shape makes much difference at those speeds.
and do not forget, N41 is 43300 LBS while Mainship is only 36000 LBS

 

[Slowmo]

If the price of fuel keeps going up sailboats and single engine trawlers will go up in popularity! I'm kind of shocked that your Yanmars only made 280 hours. In automotive terms that's like 15000 miles. What happened?

You are correct, hull shape makes the biggest difference. Most of our 'trawlers' are semi-planing hulls with hard chines (turbulence), flat lifting surfaces aft, and very beamy. I've had a full displacement round bilged trawler and yes fuel consumption could be very low. Some builders started moving that way in the 1970s with the energy crisis but then oil prices dropped and speed returned as the driving force. I suspect it will be the same this time, builders will introduce more efficient but slower boats. Greenline is a good example of what might be to come.

 

[Waterant]

I'm kind of shocked that your Yanmars only made 280 hours. In automotive terms that's like 15000 miles. What happened?

The only information i have right now is that the engines were not winterized properly at some point and do not start. someone told the previous owner they require a full rebuild. i'm planning to finalize the sale in a couple of days and will start by calling Mack Boring guys.

 

[pacopico]

If you are looking to sell the Yanmar's I am interested!

 

[Waterant]

If you are looking to sell the Yanmar's I am interested!

sure, let you know

 

[rgano]

SO, the engines were not well winterized. What does that have to do with the block which has oil and antifreeze as the internal liquids? Was the raw water cooling system full of brackish or freshwater and froze? Has anybody with knowledge of these engines had a look?

Let's say the raw water cooling system is trashed. That's VERY far from an "engine rebuild" in costs from simply correcting the raw water cooling issues. Your repower vs rebuild calculation may be extremely off. You seem biased toward the Betas which is maybe clouding the obvious and far cheaper soluton of fixing what is there.

I am not super knowledgeable of the impact of EPA regs on your Yanmars, but if my 315 HP Yanmar 6LPA-STP were to go south, I understand that rebuilding it is not economically feasible. In order to replace it I would have to provide proof that I am replacing like for like in order to import this non-EPA compliant engine for replacement because apparently you cannot just go buy and imprt one because you want one. Swapping what is generally a desireable engine for Betas would forever eliminate the ability to put Yanmars back in there, IF they suffer from this tree-hugger regulation issue.

 

[sean9c]

In my area rebuilding is pretty rare anymore. The cost of parts and especially labor make it too expensive. Engines are just pulled and replaced

 

[Waterant]

Swapping what is generally a desireable engine for Betas would forever eliminate the ability to put Yanmars back in there.

good point. i was wondering why Beta could not quote me 115T engines and the largest they could do is 85T (which are still large enough for this boat).

Let's say the raw water cooling system is trashed. That's VERY far from an "engine rebuild" in costs from simply correcting the raw water cooling issues. Your repower vs rebuild calculation may be extremely off.

yes, this would make my day (well more like my year)
I'm not crazy enough to do a $60k engine replacement instead of $10k repairs.

 

[Benthic2]

Are you purchasing a boat without knowing for certain that you might need to spend $60k to be operational ?

Your tolerance for uncertainty is considerably greater than mine.

 

[Waterant]

Are you purchasing a boat without knowing for certain that you might need to spend $60k to be operational ?
Your tolerance for uncertainty is considerably greater than mine.

I'm buying it assuming i will have to spend $60k on repairing the engines so spending less will make me a happy boater.

 

[SteveK]

Reading al these posts I conclude that the engines should be repaired. Rebuilt seems to be a stretch if indeed they did not get drowned. The extent of Freeze damage will determine if they are boat anchors or viable blocks with externals that can be replaced easily and cheaply relative to replacement or total rebuild

 

[Waterant]

The extent of Freeze damage will determine if they are boat anchors or viable blocks with externals that can be replaced easily and cheaply relative to replacement or total rebuild

right. I'm eager to find out myself soon.

 

[BruceK]

I'm buying it assuming i will have to spend $60k on repairing the engines so spending less will make me a happy boater.

You are, wisely and prudently, making a "worst case" assumption/provision. With remarkably low engine hours, let`s hope it turns out way less than 60K!
I tend to agree on keeping the Yanmars if it makes economic sense, considering repair cost, value retained, resaleability, etc. Hope it turns out well.
I would probably have bought a 395 if the water tankage wasn`t so miserable and there was someplace to add tankage(there wasn`t).