[Public-list] Longitudinal Center of Gravity
Don Campbell
dk.campbell at sympatico.ca
Tue Sep 27 06:39:13 PDT 2005
John:
I lift annually and use travel lifts to do so, then put the boat on a trailer. The lifting straps aft are at the primary winches which puts them just ahead of the rudder shoe. The straps foreward are 4 inches ahead of the forwardmost chainplate. We do tie the straps on both sides of the boat with dock lines fore to aft from strap to strap at or jsut below the waterline at haulout and below the waterline on launch. Normally we lift with about a 10 - 15 degree angle on the deck plane with the aft end of the boat
higher to lessen the possible slippage on the forward strap. Once you have the straps on either side of the centre of gravity, you will have no trouble lifting. I would think that you will rarely have more than 5500 lbs on one lifting strap, even with non-horizontal lifts and reasonable strap placement. I don't know what you will use for the actual lift, cables or oil hydraulics or a combination of both, but using a single sheave block on the ends of the strap will halve the lift force. (With the travel lifts, we
never come close to its weight limit since the one I prefer to use is a homemade, 60 ton unit, but even the commercial ones at 35 tons are without compromise for lifting. I have also used another homemade one of about 20 tons and both the homemade ones are far more controlled for speed of lift than the commercial ones, and thus, much nicer).
Once on the trailer, I am able to put 10 pads on the hull, 5 a side. They are about 5 feet apart, but not uniform due to the configuration of the hull. The boat sits on a 10 inch wide hickory plank. The biggest danger is in tying the bow down too tightly and breaking the fiberglass. With just 8 of the pads on the hull, I am able to lift the boat off the plank with the screws supporting the pads.
George has a picture of the trailer on the website.
I have also been thinking of making a crane for my workshop, and have felt that I would require about 3000 lbs capacity per corner for an AL30. I have been thinking I could use 4 forklift masts with a good electric hydraulic system, which would allow for independant lifts on each corner as well as a uniform lift on all 4.
Don
JOHN GRAVES wrote:
> Mike,
> I looked at the lines plan on Roger's site and I think the 16' 1" measurement is the Lateral Center of Buoyancy. I'm looking for the Longitudinal Center of Gravity. There are two Centers of Gravity measurements the Verticle Center of Gravity and the Longitudinal Center of Gravity. The centers of gravity are what I am interested in to make the calculations to design the hoist to lift the boat out of the water. Jack probably determined what these centers of gravity measurements were. Do you think you can get these?
> Thanks,
> John
> ----- Original Message -----
> From: Roger L Kingsland<mailto:rkingsland101 at ksba.com>
> To: Alberg 30 Public List -- open to all<mailto:public-list at alberg30.org>
> Sent: Monday, September 26, 2005 3:36 PM
> Subject: Re: [Public-list] (no subject)
>
> John,
>
> I have them posted on this site;
> http://home.att.net/~jinnii/roger/perfect/pi_designs.html<http://home.attnet/~jinnii/roger/perfect/pi_designs.html>
>
> Roger
>
> Roger Kingsland
> Chief Boat Boy, Rubber/Scraper and Check Writer
> Alberg 30 #148, PERFECT intentions
> N40-33.92, W79-51.25
>
> "You don't have to think outside of the box, but it doesn't hurt to peek
> over the edge once in a while."
> Leonardo Da Vinci (or somebody like that)
>
> ----- Original Message -----
> From: "JOHN GRAVES" <jg1111 at msn.com<mailto:jg1111 at msn.com>>
> To: "Alberg 30 Public List -- open to all" <public-list at alberg30.org<mailto:public-list at alberg30.org>>
> Sent: Monday, September 26, 2005 3:17 PM
> Subject: Re: [Public-list] (no subject)
>
> > Mike,
> > Hey, great. Is there any way I could get a copy?
> > John
> > ----- Original Message -----
> > From: Meinhold, Michael J<mailto:MICHAEL.J.MEINHOLD at saic.com<mailto:MICHAEL.J.MEINHOLD at saic.com>>
> > To: Alberg 30 Public List -- open to
> all<mailto:public-list at alberg30.org<mailto:public-list at alberg30.org>>
> > Sent: Monday, September 26, 2005 3:15 PM
> > Subject: RE: [Public-list] (no subject)
> >
> >
> > No problem- I have the lines plan that Jack made and the outboard
> profile
> > from Whitby on the wall in my office - a constant distraction.
> > Mike
> >
> > -----Original Message-----
> > From:
> public-list-bounces at alberg30.org<mailto:public-list-bounces at alberg30.org<mailto:public-list-bounces at alberg30.org<mailto:public-list-bounces at alberg30.org>>
> > [mailto:public-list-bounces at alberg30.org]On Behalf Of JOHN GRAVES
> > Sent: Monday, September 26, 2005 3:12 PM
> > To: Alberg 30 Public List -- open to all
> > Subject: Re: [Public-list] (no subject)
> >
> >
> > Mike,
> > Thanks for the quick reply. I am trying to design a boat lift so I can
> put
> > my Alberg 30 up on the bluff and I am making some calculations to figure
> out
> > the most economical design.
> > Thanks,
> > John
> > ----- Original Message -----
> > From: Meinhold, Michael
> J<mailto:MICHAEL.J.MEINHOLD at saic.com<mailto:MICHAEL.J.MEINHOLD at saic.com<mailto:MICHAEL.J.MEINHOLD at saic.com<mailto:MICHAEL.J.MEINHOLD at saic.com>>>
> > To: Alberg 30 Public List -- open to
> all<mailto:public-list at alberg30.org<mailto:public-list at alberg30.org<mailto:public-list at alberg30.org<mailto:public-list at alberg30.org>>>
> > Sent: Monday, September 26, 2005 3:07 PM
> > Subject: RE: [Public-list] (no subject)
> >
> >
> >
> > I have 16 feet 1 inch aft of the forwardmost portion of the stem - the
> > bow.
> > This is from a hydrostatic analysis by a former Alberg owner (an a
> > neighbor
> > of mine) Jack Hornor.
> >
> > Mike
> > Rinn Duin #272
> >
> > -----Original Message-----
> > From:
> >
> public-list-bounces at alberg30.org<mailto:public-list-bounces at alberg30.org<mai<mailto:public-list-bounces at alberg30.org<mailto:public-list-bounces at alberg30.org<mai>
> lto:public-list-bounces at alberg30.org<mailto:public-list-bounces at alberg30.org<mailto:public-list-bounces at alberg30.org>
> >>
> > [mailto:public-list-bounces at alberg30.org]
> > Sent: Monday, September 26, 2005 2:44 PM
> > To:
> Public-list at alberg30.org<mailto:Public-list at alberg30.org<mailto:Public-list<mailto:Public-list at alberg30.org<mailto:Public-list at alberg30.org<mailto:Public-list>@
> alberg30.org<mailto:Public-list at alberg30.org<mailto:Public-list at alberg30.org>>>
> > Subject: [Public-list] (no subject)
> >
> >
> > Does anyone know exactly where the longitudinal center of gravity is
> > located
> > on an Alberg 30?
> > Thanks,
> > John Graves
> > _______________________________________________
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