Re: [PSUBS-MAILIST] Intact Surface Stability

["Cliff Redus" <dr_redus@devtex.net>]

Gary
> I have no idea what "Sea State 3" encompasses, but I would think the wave
> height (perhaps wind?).  The height of the hatch above the water would be
> the obvious factor in not taking on water.  But, that is given by ABS, I
> believe.

Table D.1 in the ABS text defines a Sea State of 3 as:
Wind velocity = 16 knots
Average wave height = 2.9 ft
Average 1/10 highest =- 5.8 ft
Significant range of periods = 2.0-8.8 sec
Average period = 4.6 sec
Average wave length = 71 ft
Minimum fetch = 40 nmi ( what is this?)
Minimum duration = 6.6 hrs

Also in ABS Rule 3.19.1a , "the distance from the waterline to the top of
coamings around hatches which may be opened with the unit afloat is to be
not less than 2.5 ft. with the unit upright."

 I would think that the values of, and distances between the CB
> and CG and the "righting" torque they produce would also be a factor.  One
> other factor that might come into this is the rolling Moment of
> Inertia.  To not use dive planes on my sub I have to have the CB and CG
> closer than most.  Thus, the amount of torque to say tilt my sub to 30
> degrees from vertical is considerably less than for most.  However, due to
> the concentration of mass in the hull (18 inch radius), the keel's mass,
> and the sail's mass, my boat takes applied force longer to obtain a
> rotational velocity.  Thus, it does not roll badly in the wake of a
> relatively large wave.  But be careful getting in and out and standing on
> the hatch.  At least get in and out quickly!

I agree, there must be a straight forward dynamic load analysis that one can
make.  I am hoping someone out their that has submitted their boat for ABS
classing will share with us what they submitted.  I am sure this is also in
some marine engineering text.

Cliff

----- Original Message -----
From: "Gary R. Boucher" <protek@shreve.net>
To: <personal_submersibles@psubs.org>
Sent: Tuesday, October 01, 2002 10:08 AM
Subject: Re: [PSUBS-MAILIST] Intact Surface Stability


> Just a thought here...
>
> I have no idea what "Sea State 3" encompasses, but I would think the wave
> height (perhaps wind?).  The height of the hatch above the water would be
> the obvious factor in not taking on water.  But, that is given by ABS, I
> believe.  I would think that the values of, and distances between the CB
> and CG and the "righting" torque they produce would also be a factor.  One
> other factor that might come into this is the rolling Moment of
> Inertia.  To not use dive planes on my sub I have to have the CB and CG
> closer than most.  Thus, the amount of torque to say tilt my sub to 30
> degrees from vertical is considerably less than for most.  However, due to
> the concentration of mass in the hull (18 inch radius), the keel's mass,
> and the sail's mass, my boat takes applied force longer to obtain a
> rotational velocity.  Thus, it does not roll badly in the wake of a
> relatively large wave.  But be careful getting in and out and standing on
> the hatch.  At least get in and out quickly!
>
> I know I am not answering the question.  But, in lieu of any guidance from
> ABS or others with knowledge on this, one might make an intelligent
> argument based on these factors.
>
> Gary Boucher
>
>
>
> At 08:13 PM 9/30/2002, you wrote:
> >ABS Rule 3.19.1a states that "All submersibles are to have at least one
> >hatch.  The unit is to have sufficient intact stability on the surface so
> >that in the worst loading conditions when subjected to a roll expected
under
> >sea state 3 the unit will not take on water through any hatch."
> >
> >Can someone that classed a boat with ABS and met this requirement explain
> >what calculations you can make to meet the roll constraint above?
> >
> >Cliff
>
>