Repowering? Bigger is better?

[Terra Nova]

Originally Posted by Delancey

...are there...applications where the torque difference matters?...

Depends on how big a difference.

It is possible, in order to meet the letter of ABYC rules, for example, that a manufacturer might limit engine torque so he could use a smaller, cheaper, lighter gear reduction or shaft diameter.

[Stu Jackson]

You're really overthinking this issue between the 35 and 38. Someone on the last page offered his opinion based on a real discussion with his vendor.

Ask the vendor. They'd know best.

[Delancey]

Hey, I'm just asking a question. If what you're saying is that you don't have the answer, then I respect that. Otherwise, what's your point?

I did talk to the vendor, I will talk to him again, and I will probably talk to others. However, in my mind taking to vendors is only one side of the story.

Meanwhile I am here to learn as much as I can about the things I need to know, so sorry to bother you with my minutia.

[Stu Jackson]

Delancey, excuse me, but I did provide a detailed explanation on the previous page. The ONLY point I was making is that what we here are offering are our opinions, and that the vendors, who you have spoken to, will know best. It's good that you have done that.

But given everything here, and all the good input from others, I'm not sure how much more can be offered given your choices.

Eventually, it is, however,

Your boat, your choice.

Good luck, sorry if you misinterpreted my last post.

[Andrew Troup]

In my lifetime, and in parts of the world I've been, the only times I have been able to be certain-sure that vendors were CAPABLE of giving me the "good oil" on their product, it has been because I already knew the subject, and their product, better than the average vendor (but of course, nowhere near as well as this particular vendor)

It's a lot easier to tell if they're WILLING, and motivated by goodwill rather than commercial imperatives, but I think meeting those criteria is not sufficient.

The easiest vendors to dismiss are those who speak with easy certainty about things which are not certain or even knowable. Like,to give one common symptom: leaping to a solution or recommendation with insufficient information.

Unfortunately this is a common malady.

The very best vendors are those who, lacking the product you need, will continue to be energetic in trying to help you find one. To me that's an indication that their name needs to go straight into my contacts list.

[Stu Jackson]

Good point Andrew, and from every boating forum I participate in (and there are many) BETA is extremely good, reliable and trustworthy.

[Panope]

I am not going to weigh in on the merits of having a larger or smaller engine.

Just wanted to point out a common mistake that is made when viewing engine performance curves.

Typically, engine manufacturers give Horsepower, Torque and specific fuel consumption curves based on MAXIMUM LOAD for each R.P.M. This means that the throttle (Diesels don't have a throttle plate but we can use the term for discussion) is kept wide open and the engine speed is reduced by increasing load (with a dynamometer).

The only r.p.m. on the above curves that has ANY relevance to a pleasure boater with a fixed pitch propeller, is the r.p.m. that is achieved when under load (in gear) and at full throttle - usually, red line.

Fortunately, most marine engine manufacturers give a "propeller curve" that is very useful to a typical boater. This curve gives data based on the load of a propeller in water. This curve assumes one has an average boat with an average propeller and is therefore an approximation.

Below is the performance chart that Andrew posted. I suggest that unless one as a way of changing the load on the engine (such as variable pitch propellers, changing gear ratios or engaging additional accessories), that the only curve that is useful is the one at the bottom of the chart.

Steve

[Delancey]

Originally Posted by Stu Jackson

Good luck, sorry if you misinterpreted my last post.

Ha. I've been accused of a lot of things in my life but in so far as I know I have never been accused of thinking too much or too hard so I wasn't quite sure what to make of the comment. No worries here shipmate.

At this point and based on the comments of a few so far, including your own, I want to ask Beta about going to down to a 30, hence my persistence in the weeds.

I have an idea of what he will say, which is that it's a bit on the small side, but I would like to get a couple facts straight and a couple more answers only they can give.

I believe he told me that 32hp should get me to hull speed, if that's the case maybe I can live with being a little short on oomph. What's a couple horses?

The switch from my current engine to the 30 would save me about 240lbs. That's slightly more than half again my current fuel load and could get me half again my current range without affecting my gross, to me that's something worth looking at.

If it means that the best I can make is 6.5 instead of 7.2, then I would at least want to know the move was a step in the right direction as far as optimizing the engine for use as a genny, which is kinda what I am thinking.

Maybe I spend the money I might save buying the smaller engine on some other things, like the 120 amp alternator or some more batteries. Things I am more likely to use more frequently than potential boat-moving-capability that I might not use so much.

So what is the best size engine if you mainly want to use it as a generator anyway?

[Terra Nova]

Originally Posted by cwyckham

...Have you tried saving the existing engine? Is it smoking because it's over-propped? Does it just need a top end overhaul?...

Originally Posted by Delancey

...I have been looking a little bit at repowering...

Why? What problem are you having with it? It can't be just to save some weight?

[Andrew Troup]

Thanks for that, Steve.

I assumed that to be the case (as I couldn't see how else they could measure it) but I failed to follow through the implications that had for the inferences I drew.

My bad.

I'm guessing my argument would only hold (for a fixed pitch) if the comparison was for the same engine fitted to two boats with the same hull, but the first (running at the lower revs), was overpropped to hell, so it would be forced to develop the full hp suggested by the (top) curve at the much reduced revs. The second would have the correct prop to just be able to manage full revs.

So .... it seems to me that the specific fuel consumption for the third case implied by my earlier message, running at lower revs AND lower load (ie with the revs from case 1 but the prop from case 2) , would be likely to be quite a lot worse than predicted by the top curve, because the combustion conditions are optimised for full load.

Does anybody have any leads to reliable data on this question? (ie, specific fuel consumption under reduced load, at various speeds)

[KASHMIR]

I have a 40 LOA 8000kg yacht (Phantom 40). These yachts were built with 60HP engines, my engine needed a rebuild after only 2800hrs because the compression was all over the place (Glazed bores). I could not get maximum horsepower for long because she would overheat. I have a Seahawke Autostream adjustable prop that I adjusted to suit the engine at its redline 4000rpm. Last year I removed the 60hp engine and fitted a Yanmar 3JH5E 37hp. Much smaller and 80kg lighter. After a year of use, all I have noticed is lower fuel consumption, quieter operation, no overheating and less oil leaks (none). I adjusted the prop to suit the new engine and have had to get some push out of some rough situations, she delivers more than adequately.
Go smaller is my vote.

[Delancey]

Originally Posted by Terra Nova

Why? What problem are you having with it? It can't be just to save some weight?

Why? Because it took me like six hours to replace a broken alternator bracket and I build stuff for a living. Because a friend and I beat on the irrevocably seized decompression lever for a half hour before quitting without much more effect than bending the lever arm back and forth a couple times and then straightening it back out. Because I am tired of cleaning oil out of the pan and not being able to tell where the he'll it is coming from. Because, before I got rid of the wheel and replaced it with a tiller, the boat had binnacle mounted engine controls with separate levers and a PO with lubberly ham-hands and as a result the boat is on it's second transmission which doesn't sound so great lately. Because the damn thing takes a good 20 to 30 seconds of glow plugs to get going when it's cold. Because it probably needs a new head gasket, but might need a lot more. Because it would be money well spent for me to take Mack Boring classes and tear the thing apart and rebuild it but I don't believe i have the time or patience knowing how long it took to change the freaking alt bracket. Because one of the engine stringers is cracked which makes me worried about the other one. Because, even though it's a big chunk of change for us kitty wise, repowering means changing something about our home that we feel ashamed of into something we would be proud of. Because it's probably going to have to happen sooner or latter so why not sooner.

Because of all of these things, but maybe most importantly of all, because our engine bums my wife out, which is all the reason I need. It makes her nervous and I can understand why.

Partly it's because she knows less about engines than I do. Partly it's because even she knows our engine is a POS that has a brighter future as a mooring block somewhere in the ooze.

Cheers,
Del

[Stu Jackson]

Originally Posted by Delancey

So what is the best size engine if you mainly want to use it as a generator anyway?

WADR, the consensus is that that is the very worst thing you can use an engine for. Solar is the answer for providing adequate charge to your house bank. An engine will usually get a bank up to 80% SOC and then there is a steadily diminishing law of return on power and input because of declining battery acceptance. And, even if you're going to a smaller engine, you'll most likely still be able to use a 100 A alternator (based on my first post of this subject).

If you motor as little as you say you plan to, then, yes, you'll get something out of the alternator, but please don't think of it as a power generator. It'll get the initial bulk charge in, but go back and read the small engine mode and amp manager discussions: initial startup because of overnight depleted batteries puts a large load on an alternator, and most of us have found that for the first hour or so one needs to cut back with either of these features to keep from overheating. And, if you install the alternator temperature sensor (which is just an automatic small engine mode uses the same external regulator connections) the regulator will do this automatically anyway. Welcome to Balmar, download the MC-614 regulator manual.

[Delancey]

Originally Posted by Stu Jackson

WADR, the consensus is that that is the very worst thing you can use an engine for

I am not disputing this, but how do most liveaboard cruisers really use their engines?

My guess is "well I usually run the engine for about an hour in the morning to charge up the batteries and pull down the icebox" has to add up and that in the end it might account for as much or more much engine hours as actually using the thing to get you somewhere. I mean, how much time to does it take to slip a mooring and clear the breakwater, 15 minutes?

Part of the reason I am interested in saving weight where I can is because I would like to build my electrical system around a very lavish house bank which I hope to draw on modestly and mostly charge with wind and solar.

I'd like to improve the boat's performance where possible and the last thing I want to do is impinge on it, so in my mind any loss in engine is a gain in amp hours and a decision I don't have to think very hard about.

I must say I am very interested in Andrew's plan, very smart for so many reasons. I wonder if he would like to expand a little bit on how he intends to integrate it with with electrical system?


Also, for what it's worth, I don't think it is so much about how much or how little I intend to motor as at what speed am I willing to do it at. This is the thing I really have to think longest and hardest about. I have spent plenty of time in boats that couldn't do better than five knots and never had any safety concerns because of it.

Can I live with a 30hp? Can I live with 6 knots instead of 7? I think people with smaller boats do it all the time. Can I get a fancy folding variable pitch prop for the money I save that will make the boat a better sailboat?

What's a fancy prop cost? Can you get one for $2k or will I have money left over for more batteries?

[cwyckham]

Originally Posted by Delancey

I am not disputing this, but how do most liveaboard cruisers really use their engines?

My guess is "well I usually run the engine for about an hour in the morning to charge up the batteries and pull down the icebox" has to add up and that in the end it might account for as much or more much engine hours as actually using the thing to get you somewhere. I mean, how much time to does it take to slip a mooring and clear the breakwater, 15 minutes?

Part of the reason I am interested in saving weight where I can is because I would like to build my electrical system around a very lavish house bank which I hope to draw on modestly and mostly charge with wind and solar.

I'd like to improve the boat's performance where possible and the last thing I want to do is impinge on it, so in my mind any loss in engine is a gain in amp hours and a decision I don't have to think very hard about.

I must say I am very interested in Andrew's plan, very smart for so many reasons. I wonder if he would like to expand a little bit on how he intends to integrate it with with electrical system?

Very eloquent description of why you want a new engine. Works for me. I'm making a similar decision and mine isn't as bad as yours.

As far as the "typical cruiser," there is no such thing. A cruiser with a boat set up with adequate solar will not turn the engine on daily to draw down the fridge or charge the batteries, though. That's what the panels are for.

If you set the boat up as you are describing, the 100A alternator that is standard on the Beta will be more than adequate and you won't need to run the engine to charge the batteries unless you have a fault in the solar system or a very long stretch of bad weather (even with cloud, you get a lot of power from solar, though).