27' Magnum Weight & C / G ???

[FLYWITHME]

Does anyone know what the empty weight is of a 27' Magnum.

I'm repowering my 74 with a single Ilmore MV10-625 and an Arneson SD. I also need to know where the centre of gravity is to make sure it's balanced right, so it doesn't plow. I plan on moving the fuel tanks from under the cuddy...to under the cockpit. Any advice would be greatly appreciated

I've posted this question before, but no one seems to know much about old Mag's....how about you ? Thank's, Tony

[Pat McPherson]

There is a fellow that goes by "tripps" here on OSO that repowered a 27' Magnum with a single 598 and speedmaster.
Hunt him down, he my be able to help you...

[FLYWITHME]

Thank's...Pat.! HAVE A HAPPY HOLIDAY !!!!

Tony

[tj309]

I dont know much about your boat but determining a rough CG is easy. If you trailer your boat and it tows nicely the CG is about 18" infront of the front tires.

[FLYWITHME]

That's probably almost right...but it isn't exact. I thought somebody that is installing a single might know the exact C of G., as it will be of the upmost importance to keep the boat from plowing...with so much less weight in the stern. But..as it seems nobody wants to devulge this information. Anybody that is installing a single has to know this....to properly set the C of G so that the boat doesn't plow. It's call'd "lifting the bow". If you don't balance the boat right...it will plow.

An old magnum...with a single... will plow..unless you re-distribute the weight properly. That means moving a lot of things...to balance it. Otherwise...it won't ride properly or run fast. To me...it seems like everybody...doesn't want to tell you diddily sh*t. If you are really smart..and you know what you're talking about... spill the bean's bro...tell me what you really know, with experience. Mathamaticians wanted!!! I'm sure there's some smart people out there..show yourself!

Get with the program

[Rik]

My 2 cents.

Get the boat to balance roughly 6' 9" from the stern.

[FLYWITHME]

Rik

Just where did you come up with that dimension? Maybee I'm missing something. Is there a rule of thumb...or formula for finding the C of G...or are you just trying to be funny.

It's an exact science in airplanes...and can be calculated within 1/16th of an inch. And if you're wrong...you're usually dead. I don't mean you're in trouble if you're out that little...but too many pilots...don't take the time to calculate it...when going on trips...with extra baggage and more passengers that they usually don't have on board.

So much for airplanes. Let's make it simple. I just want to know...if any owners of 27' Magnums...know what the empty weight of their boat is...and if they know where the C of G is. I would say...most don't!!! And the reason they don't know where the C of G is...is because they don't care to know. Unless you're someone like me that's puting a single in a Magnum...it really is not important. BUT...to me it is...because it will ride entirely different without all that extra weight. My question is...does anybody know the real answer...and can they back it up???

[Bosco]

How about some common sence information. Your boat was built back in the 1970's ?
Most boats can be weighed by foot length. Your boat at 27' by 150 lbs per foot = 4050 lbs. Heavy by today's standards with special core materials and less resin use.
With twin small blocks that boat was burning fuel at approximatley 7000 lbs.
Obviousley, again common sence dictates the center of gravity will differ on what you decide to rig the boat with. Twin vs single, equipment placement etc.
I would suggest you begin by finding the vessel only C.G. and build on that with your engine selection, drive selection, steering etc.
From there you can use tank placement, batteries, and equipment to put it were you need it. Better to error with weight aft so you could always add balast to the nose easily with small bags of lead shot.
Have the stripped boat lifted at your local marina with one strap to find its true C.G. and go from there. No guess work involved, mark the hull and go to work!

Bosco

[audacity]

make it complicated and yes; center of gravity, center of thrust, and center of pressure (also center of lift on a cat)and their relationship matter.

make it simple (for this app.); move it all as far backward as it can go. the reason being is you can always add a little weight to the very front of the boat to dial it in vs. adding loads of it to the rear....you'll also benefit from a more ideal moment of inertia set-up as well.

ps...never lift a boat with one strap! they can and will slip off!LOL....we always calculate it...but you can set the boat on a 2x4 using 2 straps, front and rear.

[ThirdBird]

Originally Posted by FLYWITHME

Rik

Just where did you come up with that dimension? Maybee I'm missing something. Is there a rule of thumb...or formula for finding the C of G...or are you just trying to be funny.

It's an exact science in airplanes...and can be calculated within 1/16th of an inch. And if you're wrong...you're usually dead. I don't mean you're in trouble if you're out that little...but too many pilots...don't take the time to calculate it...when going on trips...with extra baggage and more passengers that they usually don't have on board.

So much for airplanes. Let's make it simple. I just want to know...if any owners of 27' Magnums...know what the empty weight of their boat is...and if they know where the C of G is. I would say...most don't!!! And the reason they don't know where the C of G is...is because they don't care to know. Unless you're someone like me that's puting a single in a Magnum...it really is not important. BUT...to me it is...because it will ride entirely different without all that extra weight. My question is...does anybody know the real answer...and can they back it up???

You're getting kind of edgy there Flyman!!!!!!

Relax a little, this place has answers but you won't get them by pissing in people's faces.

First thing I'd do is call Magnum. I know, I know, the current Magnum factory didn't design or build your boat. But, they might have obtained that info from "The Don".

Next, post this thread in the Magnum Forum. If no luck there, there is another site that deals only with old Cigs and Mags. I think it's called "Thunderboat Row" or some such name. Ask in the Magnum forum, they'll know.

If all that fails, take the advice above. You'd have to drastically alter the CG before you start "plowing". As the guys said above, err to the aft.