prop nut thread

[smj]

Hello, sorry to post this in the Sunrise section as it pertains to a Sunstar 36. We are currently replacing our 3 blade fixed props with Variprop 3 blade feathering. The Variprops come with a custom prop nut. We have gone through 2 pairs of custom nuts of which none were threaded right. We even sent our old nut to Variprop in Germany to have the threads duplicated. Would anyone know what the thread would be in this application. It's a Yanmar 3gm30 with a straight drive1" shaft. I know we are grasping at straws but any help would be appreciated.
Thanks A.J.

[Jadzia]

Hi A.J,
I cannot say what thread you have, but it is quite easy to measure it and then search the internet for a thread sizing website.
With a prop removed you measure the diameter of the shaft across the 'points' of the thread. This is known as the major diameter. Then measure the number of threads per inch (tpi). If there is less than 1" of threaded length, measure half an inch and multiply by two. (Sorry if this sounds patronising). So if, for example the measurements are 22 mm (dia) x 10 tpi your thread would be M22 (Course).

Check the shaft diameter carefully, your 1" could actually be 25mm bearing in mind that 1" = 25.4mm exactly!

By coincidence UNC threads are the same tpi as Metric threads, but as the Variprop is made in Germany I would imagine the threads are metric, either Course or Fine.

Hope this is of some help, good luck with your efforts.

[Jadzia]

Just looked at the Variprop website, and in particular the download of the installation instructions. Page 11 lists all the prop nut sizes, torque settings and threads available. Tells you all you need to know, i.e. Major diameter, thread pitch (from which you can calculate tpi). So you can ignore my previous reply.
Also wondering, how did Variprop know what thread to supply you with in the first place? Did they decide based on your engine/drive installation or did you have to specify?

Enjoy!

[smj]

Hi Jadzia,
Thanks for your reply. We originally sent our original prop nut to the U.S. Variprop dist. and he figured the type thread. When we received them they were wrong. Then we mailed the nut to Variprop in Germany, they duplicated it and it was wrong. We just had a ship repair facility come out and measure our shaft, gauge our threads and order the correct tap and dye. After receiving the tap they realised they had to bore out the nut sent from Germany as it was to small. After retapping the nuts and doing a light filing on the shaft threads they fit like a champ.It was a long process and had us sitting on the hard for an exra 2 weeks so we hope it will be worth the agravation.
A.J

[tuarag]

Hello A.J

Good to here you have resolved the problem. We hope all is well now and that your boat sails better for having folding props. When we bought Jadzia she had 2 bladed props (fixed blades) which we believe to be a vast improvement over the 3 fixed blades we had on our previous boat. As every knot counts I think we shall consider folding props if ever we need to re-prop her.

Fair winds and best wishes for the season.

Sheila & Nigel.