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Old 18-03-2014, 18:58   #16
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Re: Repowering? Bigger is better?

If your going with a big Alt and will use it's output and refrigeration, go with the bigger motor, the big alt will pull more HP than you might think
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Old 18-03-2014, 19:03   #17
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Re: Repowering? Bigger is better?

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If your going with a big Alt and will use it's output and refrigeration, go with the bigger motor, the big alt will pull more HP than you might think
Does anybody ever put their alternator on a clutch? Also, does anybody happen to know if the Betas will run without power to the lift pump once it gets going?
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Old 18-03-2014, 19:19   #18
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Re: Repowering? Bigger is better?

You could put the Alt on an AC clutch, but wouldn't do much good, better plan is to just not pull as many amps.
Even if an engine would run just fine without a lift pump, over time it could be bad on the fuel injection pump as it could be cavitating without positive pressure on the suck side of the pump.
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Old 18-03-2014, 19:46   #19
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Re: Repowering? Bigger is better?

30-40 diesel horsepower can do an amazing amount of work. It can power off a lee shore or it can run refrigeration, watermaker, generator, alternator(s), pumps, ...

In addition to the high output Balmar that is on Terra Nova I plan to mount a huge alternator I picked up at a boater's swap meet. But there is no plan for a separate generator.
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Old 18-03-2014, 19:53   #20
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Re: Repowering? Bigger is better?

Heres the formula I use when evaluating:

==((((Displacement_LBS)/2240)*75)*(1.4*(((LWL_FT)^0.5)))*0.003)/0.45

which puts you in 32.56 hp…so you can use that to get nearest ngin size
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Old 18-03-2014, 20:17   #21
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Re: Repowering? Bigger is better?

Just a counter point to consider. Our old Swanson used to have a 60 hp. One day the original owner got caught in a bad bit of weather of the coast of Queensland in Australia. He did not have enough power to keep the boat under control and got knocked flat. He subsequently refitted a much bigger engine to the boat.

Neither he nor I will ever know if the bigger engine would have made a difference that time but his feeling (which I agree with) was that it would be better to have some extra power on hand just in case. Conventional wisdom for our boat now reckons at least 75 hp is needed which is interesting as he said up to that point in time the 60hp had seemed adequate.

All this is by way of saying I think a bit of spare power is a good thing provided it does not significantly hider the boat's performance and safety through the weight or physical bulk. I find it hard to imagine the weight saving involved would make that much difference given the probable location of the engine in relation to the waterline and cog but I do not know anything about this particular boat so that's just guessing.

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Old 18-03-2014, 20:25   #22
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Re: Repowering? Bigger is better?

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...

My gut tells me to go smaller if possible and it seems like given some of the responses, smaller might not be unreasonable, but how does alternator size or adding a crash pump factor into the equation? Refrigeration? Obviously they matter, but how much?

...
Per Nigel Calder's, "Marine Diesel Engines," he says, that 130-160 amp alternators are now common on boats and that it takes about 7 HP per 100 amps of alternator output for 12 volts. An engine driven compressor for a fridge is up to 2HP.

Later,
Dan
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Old 18-03-2014, 20:44   #23
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Re: Repowering? Bigger is better?

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Originally Posted by GILow View Post
Just a counter point to consider. Our old Swanson used to have a 60 hp. One day the original owner got caught in a bad bit of weather of the coast of Queensland in Australia. He did not have enough power to keep the boat under control and got knocked flat. He subsequently refitted a much bigger engine to the boat.

...
Can you explain this further? How does an engine keep a boat under control or from being knocked flat?

Wouldn't appropriate sails have done a better job than a larger engine?

60 hp on a 42' boat seems like a lot. 75 hp seems huge! It must spend most of its time at idle.

And boats don't really like weight in their ends. Leads to hobby-horsing. Depends a bit on the boat how close to the transom the engine is, I guess.
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Old 18-03-2014, 20:52   #24
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Re: Repowering? Bigger is better?

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Does anybody ever put their alternator on a clutch? Also, does anybody happen to know if the Betas will run without power to the lift pump once it gets going?
Betas have a mechanical lift pump. You can buy an additional electric one for back-up/bleeding or if you have a keel fuel tank. It costs about $100.

I prefer to fit solar panels and use DC refrigeration (takes about 50 Ah per day). I do have a 100 A Balmar which will in theory suck a few horsepower out if I am at a very low battery state of charge. Mostly, it will produce a lot less than the rated amps, though. And usually I have a few hp to spare anyways as I cruise along under normal circumstances.

If I am at a low state of charge and need the extra hp, my Balmar MC-614 regulator has a "small engine mode." I just flip the switch and the output is halved, halving the drain on engine horsepower.

I'm not saying my decisions are better than those who center all their power needs and heavy weather thinking around a large engine. I'm just saying that's not what fits my way of cruising or my thoughts about fossil fuels and self-sufficiency. I'd rather use as much renewable as possible (and I have a small fuel tank).
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Old 18-03-2014, 21:00   #25
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Re: Repowering? Bigger is better?

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Betas have a mechanical lift pump. You can buy an additional electric one for back-up/bleeding or if you have a keel fuel tank. It costs about $100.

I prefer to fit solar panels and use DC refrigeration (takes about 50 Ah per day). I do have a 100 A Balmar which will in theory suck a few horsepower out if I am at a very low battery state of charge. Mostly, it will produce a lot less than the rated amps, though. And usually I have a few hp to spare anyways as I cruise along under normal circumstances.

If I am at a low state of charge and need the extra hp, my Balmar MC-614 regulator has a "small engine mode." I just flip the switch and the output is halved, halving the drain on engine horsepower.

I'm not saying my decisions are better than those who center all their power needs and heavy weather thinking around a large engine. I'm just saying that's not what fits my way of cruising or my thoughts about fossil fuels and self-sufficiency. I'd rather use as much renewable as possible (and I have a small fuel tank).
So, in other words, you would rather spend the weight on a larger house battery bank than spend it on a larger engine?
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Old 18-03-2014, 21:09   #26
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Re: Repowering? Bigger is better?

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Originally Posted by cwyckham View Post
Can you explain this further? How does an engine keep a boat under control or from being knocked flat?

Wouldn't appropriate sails have done a better job than a larger engine?

60 hp on a 42' boat seems like a lot. 75 hp seems huge! It must spend most of its time at idle.

And boats don't really like weight in their ends. Leads to hobby-horsing. Depends a bit on the boat how close to the transom the engine is, I guess.
Well, I wasn't there, so I am a little unclear on the sequence of events, but I gather he did not have enough power to keep the nose pointed into the wind. I asssume he got side on to the waves and got rolled. This from a guy who knew his stuff too, twenty years travelling the South Pacific, 42,000 miles on this boat alone, and he drives ships for a living. I trust he knew what he was doing. I don't know how he was rigged when it happened, but I do know he had good sails at the time. (They don't look quite so good 20 years later though...)

Anyway, as a result of this we now have 96HP Nissan ED33, and it is NEVER idling. I use a good half throttle or more to get to 5.6 knots, full throttle I get to about 7.5 knots. The engine is pretty well midships, and being a truck engine, the weight is not too bad and it is all well below the waterline so it is probably not doing much harm to our ride. Also, a 96HP truck engine is really about 82HP the way it has been setup for marine use, we are not propped for peak revs, but peak torque instead.

The few S42 owners I have spoken to think at least 75HP is good and a bit more HP is even better. We have a lot of freeboard, and weigh in at nearly 17 tons.

Matt
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Old 18-03-2014, 21:10   #27
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Re: Repowering? Bigger is better?

Im confused what you think you will get from this upgrade? Less stress?

More RPMS won't add anything.
Your WL is your max speed.
Added weight detriment.
Larger prop higher proportion to torque. You won't anything out of it.

The largest issues I have found are boat manufacturers under power their boats to save $$$

Using figures, go for the next higher ngin in the series provided by manufacturer of choice. But don't go lower, and don't go too high.
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Old 18-03-2014, 21:41   #28
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Re: Repowering? Bigger is better?

G'Day Delancy,

Re the alternator load issue:

1. I am pretty suspicious of the "7 hp per 100 amp" figure. We run a 150 A Balmar, usually at around 80 A and 13+ volts driving it with a single 13 mm V-belt. That belt would be VERY hard pressed to pass more than 3-4 hp, especially with the small diameter pulley involved. After all, 7HP is around 5,000 watts, and 100 amps at ~13 volts is but 1300 watts... you work it out!

2. In the unlikely event that the alternator did add excessive load, a simple switch in the field circuit of the alternator will completely disable it, dropping the load to zero.

So, I think that you can drop that worry from your worry list!

Cheers,

Jim
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Old 18-03-2014, 21:43   #29
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Re: Repowering? Bigger is better?

With the right sort of regulator, you can dial back the alternator demand on those rare occasions when you need every bit of urge for forward progress.

Marine diesels don't just perform better at 80% full load than 60%, they last longer. Significantly longer.

If it was me I would definitely go smaller.
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Old 18-03-2014, 21:56   #30
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Re: Repowering? Bigger is better?

If I have my history correct the boat was originally spec'd engine was a 40hp Universal but at some point they made the switch to the 44hp, but I am not sure why the change was made.

Whether it was the result of a real or perceive deficiency, or a marketing strategy I couldn't say. In lieu of any other significant considerations my inclination is to go smaller over bigger.
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