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07-31-2004, 08:31 PM
I had to make boat prop nuts over the weekend and I could not find any info on them in "The Bible" (aka Machinery's)
Where would I find this info.
Need Distance across flats,flange size,thickness,etc for various shaft sizes.
ps:I walked around the yard and took some notes on the boats that were up to get some info.,but I was hoping for a "standard"

07-31-2004, 09:01 PM
Motor,dunno if there are any,most I see are either standard nuts or flanged castle.Some of the newer stuff around use ny-locs.As for personal favorites I like the flanged castle nuts,no need for a washer,just tighten and cotter.

07-31-2004, 09:07 PM
The ones I made over the weekend were large 2.5-6 tpi,One flange type and one jam type.(yes double nutted)Can get rough here off Newfoundland.It's were the Titanic sank!!
Copied a similar shaft of a boat that was also up,but had her nuts intact.
ps Hope the arm is feeling ok

Forrest Addy
07-31-2004, 09:38 PM

Prop nuts are typically heavy hex castellated nuts. Bronze or navy brass back when I was making them. A heavy hex nut is a nut made on the next larger nominal sized hex stock.

Example a standard ANSI B18.2.2 3/4" nut would be 1 1/8" AF X 41/64" long. A 3/4" heavy pattern nut would be 1 1/4" AF and 47/64" long including the castellation.

Some castellated nuts are longer than standard. If you use a standard castellated nut on a prop sfaft made for the long nuts the cotter pin will barely engage. and if the shaft was drill to suit a standard nut and you have a long one, get out the rat tail file.

Heavy hex nuts are in my handbook. Real marine supply houses and boat yards stock them.

[This message has been edited by Forrest Addy (edited 07-31-2004).]

John Garner
07-31-2004, 10:57 PM
motorworks --

A rule of thumb from the late 1800's still works well in the absence of a Standard: The across-flats dimension of a standard nut should be 1 1/2 times the Major Diameter, a heavy nut should be 1 1/2 times the Major Diameter PLUS 1/8 inch. (if you do the rule-of-thumb arithmetic for a 3/4 inch Major Diameter thread, you'll find that the across-flats dimensions match the ANSI Standard dimensions that Forrest Addy cited).

A second old-time rule of thumb for nut thickness is that the thickness of the nut should be equal to the Major Diameter of the screwthread. (This rule of thumb would produce a slightly thicker nut than either of the ANSI Standard nuts that Forrest mentions.)

Do keep in mind that rules-of-thumb such as these are NOT accepted by the Standards organizations (ANSI, SAE, ISO, and so forth), and none of us would want to rationalize their use in testimony before the legislature or courts.


08-01-2004, 08:02 AM
Motor,arm is fine.Like Forrest said the heavy series nuts work good,always good to have extra meat around the shaft.

Just one word of caution,don't over torque the nut when installing a prop,I have seen them pop off the threaded section before.The way I always do it is to warm the bore up about 200*f and slide it onto the cold shaft,then suck the nut home before the hub cools down,this way you get a tight fit on the taper and don't have to put soo much stress on the threads.

BTW,it don't take much to hold a prop on,last one I did was for a 67' sail boat,had this $$$$$$ Italian vari-pitch prop,on a 1-3/4 aqua-met shaft,the whole thing relied on this dinky little bronze spanner nut,it was threaded 1"-8tpi.Customer took the boat out for the first time and grounded it not 500 yards from the slip,not knowing any better he "porposed" the boat off the bottom with the throttle,95hp diesil and a 2.5:1 reduction wrapping on that dinky little shaft and nut,but it stayed on even though he was turning up oysters http://bbs.homeshopmachinist.net//biggrin.gif

08-01-2004, 08:22 AM
Thanks for all the help guys
Found a site below with some specs.
I am going to keep notes so that the ones from my shop will be some what consistent.


ps Home shop is always a great source of info.