Yes, there's a reason. Because the sub is hydrobatic, when the sub is at a 90 degree roll the drop weight will exert a bending moment. So I made it stubby. The maximum diameter is 1.5", and its set in an insert that is 3" in diameter. The difference between the diameters of the shaft and the hole is only 2 thousandths of an inch, so that the O rings cannot extrude and so the insert will help the shaft resist the bending moment. And the reason I said "maximum diameter" is that there is a 1" section on the shaft too, to prevent the ambient pressure from shooting it into the boat after releasing the drop weight, or when the sub is inverted. Sorry for writing a book on such a small topic... Alec -----Original Message----- From: Brian Cox [mailto:ojaibees@ojai.net] Sent: Fri 2/27/2004 5:40 PM To: personal_submersibles@psubs.org Cc: Subject: Re: [PSUBS-MAILIST] thru hull fittings Thanks Alec, I read a few posts back that your drop weight shaft was like 2" or something, it seamed rather large was there some reason for that? Brian ----- Original Message ----- From: "Alec Smyth" <Asmyth@changepoint.com> To: <personal_submersibles@psubs.org> Sent: Friday, February 27, 2004 1:28 PM Subject: RE: [PSUBS-MAILIST] thru hull fittings > With a 1.25" insert, you have added much more reinforcement than the material you removed with a 0.5" shaft hole. If I remember right, the rule of thumb is that you should add twice as much as the hole removed. So it should be sufficient. > > Alec > > -----Original Message----- > From: Brian Cox [mailto:ojaibees@ojai.net] > Sent: Fri 2/27/2004 3:51 PM > To: Personal_Submersibles@psubs.org > Cc: > Subject: [PSUBS-MAILIST] thru hull fittings > > > Hi All, I am in the process of machining thru hull fittings (316L ss) that will have 1/2" shafts running through them to turn valves, turn rudders, and other functions as well, drop weight, and possibly move trim ballast ;-) . The fittings that I am machining at the moment are 1 1/4" od with the 1/2" id ( for the shaft) is that 1 1/4" a big enough chunk of steel to be welded through 1/4" A516 70 or should that OD be larger for some reason? > > Thank You > > Brian Cox > >
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