baja27

Steve
Do you know how much a 33 newer style with twin big blocks weight with fuel?
Thanks

302Sport

deadweight would be hull without the power correct???

302Sport

and is it distance moved or distance from COG

nautdesign1

It’s essentially a simple summed Mass X Distance calculation. For round numbers, if:

1) The boat AU weight was say 8,000 pounds;
2) The combined weight of your engines (only) was say 2000lbs;


then movement of your engines 1 inch forward would move the lcg about a quarter of an inch. If you moved them a foot forward your lcg would move about 3 inches forward.

However if:

1) Your current Lcg was say 11 feet from the transom;

and

2) The combined engine center of mass was 5 feet from the transom;

-then 100lbs of additional ballast 30 feet from the transom would have roughly the same effect as moving your engines a foot forward. However as Steve mentioned that’s 100 lbs you don’t need to be carrying around and of course from a dynamic stability perspective this extra mass is also generating a moment of inertia of roughly 35,000 ft/lbs. The large mass of the engines is generating a moment of inertia of only 72,000 ft/lbs due to their proximity to the overall craft lcg so you can see how only 100lbs of ballast right at the bow can generate almost half the moment of inertia of 2000 lbs worth of engines somewhat proximate to the lcg. That’s why you want to keep the bow light and shift your engines to optimize lcg position. This is yet another reason why you see rough water V-hulled race boats with staggered engines-provided of course they have steps…but that’s another conversation for another day…

ND1

302Sport

i got ya.....

sixmassive

http://en.wikipedia.org/wiki/Metacentric_height
there ya go

nautdesign1

Sixmassive -you’re barking up the wrong tree here. Metacentres are generally utilized for stability calcs in the lateral domain (roll stability). 302sports’ issue is not in this “transverse” domain but rather the longitudinal domain –where vcg’s are not the dominant variable or concern.

ND1

delsol

NDI

Can you elaborate on why the v's would have to have steps?

][/QUOTE]This is yet another reason why you see rough water V-hulled race boats with staggered engines-provided of course they have steps…[QUOTE


Thanks, great info on CG -- the term is thrown around all the time -- now it means a litlle more...

sixmassive

i was just giving him something to go on. i know the differnce between longitudinal and transverse stability as i deal with it everyday. Although i havent had to long hand it in a while.
I guess thats what i get for not reading the wikipedia page haha.

nautdesign1

This is yet another reason why you see rough water V-hulled race boats with staggered engines-provided of course they have steps…[QUOTE


Thanks, great info on CG -- the term is thrown around all the time -- now it means a litlle more...[/QUOTE]

For sure,

However as I don’t want to hijack Steve’s excellent and informative thread, I’ll start a new dedicated stepped hull thread. A huge amount of misinformation has been disseminated on this subject over the years hence this is probably the occasion to offer a new perspective. I’ll have time later this week to get this thread started -so if you could give me a few days that would be great.

Thanks,

ND1