Is it a bad idea to use a lightweight crankshaft in a offshore boat?
 

I am making a list of parts to build for my engine project.I was looking on awebsite for a crankshaft I do not remember I think it was a callies crank butmaybe wrong.They had a pull down menu showing different options.I do not remember the weights but it was like this

Option #1 65 pound crank

Option #2 52 pound crank

Ultralight crank 46 pound

It was the same part and application but there were options that were ultralight and more $
But I want to know if a lightweight crank is a bad idea in a offshore boat because everything needs to be so heavy duty.Does light weight mean it will be more stressed.It is light but the materials are more like billet I think they don not say more about what they are made of on the lighter versions

Some others will chime in with a more technically correct version, but here's my take (and learned a very expensive lesson because of the following....)

"Lightened" cranks usually mean removing material, mainly drilling lightening holes thru the journals, narrowly missing the oil passages. A boat engine doesn't necessarily benefit from the acceleration a drag auto setup would benefit from with a reduced rotating mass. Realistically, it probably won't affect how the engine produces power fast, or how the rotating mass benefits from a lighter crankshaft, turning faster, "accelerating" the rotating mass "quicker". NOW, one could argue that the reduced rotating mass helps the assembly live longer, or is "easier" on the bearings (physics, right?).

I had an unfortunate mess, in which one of these cranks were used on my assembly. Now, from what I saw there was a flaw in the crank, hole drilled too far off center in order to miss the oil passages. It failed, resulting in trashing a very expensive custom setup, total engine rebuild required after about 15 hours of run time. Machining, new pistons, crank, rods, etc.

I'd like to hear some pro builders chime in on this one.

I'll put my vote towards the solid, "heavy" crank. NO HOLES in mine please.

“We’ve learned over the years that stiffness is much more important than weight,” says Bryant. “Probably less than five percent of the cranks we produce have a target weight to hit. It wasn’t always that way. Fifteen years ago we were making a concerted effort to reduce weight because we thought there was something there. But when the smoke cleared, you were better off to have the stiffness to make more power and be happier in the engine block than something that the driver thought was faster because it revved up quicker.“The trend with the top engine builders now is that stiffer is better than lighter,” continues Bryant. “When you make a crank stiffer you add durability.”

No, not really. IMHO.

My stupid version The first thing I would be concerned about a lightened crank is when I went to get the rotating assembly balanced there would not be enough there for them to do their work. Also lightened cranks are made to allow the motor to spin up faster like for drag racing. I would think the heavier would take longer but once going the there would be more rotating force which is better in a heavy boat.

Anyone ever seen Super Modified's racing in person ? They are nutz ! They are the large go carts with injected big blocks hanging off the side of the 'car.' This is where real light cranks are probably used.

http://s3.racingjunk.com/ui/9/92/36181929-288.jpg

See if this vid posts:

There. Vid link shows.

Gotta a little mag interference

Only if you do not plan to install a Kevlar wrap under your oil pan. Because when it scatters you don't want it to sink the boat too.

ok thank you easy decision.
heavier = no/less problems