Line Cutters for Shafting

[Pitou]

Curious as to who is using what, if anything, and what your thoughts and experiences are.

I was fortunate to come across a pair of two inch shaft compatible Spurs Marine cutters this past spring and was able to make one good set and had it refurbished by Spurs Marine. The tough side of it is that the shaft strut needs to come off to be drilled and tapped to accept the holding block for the stationary cutter and I'm just out of time in order to get into the water for the short New England Season.

I've been checking out Shaft Shark (1 piece & 2 piece) along with the ones manufactured by Evolution which seem similar, but are pricier. I am considering this type as a solution. Anyone have any experience with these types of cutters, any others or for that matter the Spurs Marine choppers?

[Tree]

Kevin,

I know its the wrong side of the water but have a look at http://www.ropestripper.com/products.php

This is what i have on mine - similar to the Spurs Marine cutter but with teeth and they are ultra sharp - extreme care needs to be taken when handling them!

Also, Robin is a lovely chap to deal with - or certainly was when I fitted mine almost five years ago and his knowledge of propulsion is second to none, in fact I believe he played a large part in the design of our nuclear submarine fleets propellers.

cheers

Lee

[jleonard]

I had Spurs on my Mainship 34 and I know they work. I cut 3 lines over the years I had them and there was never a trace of line or damage left behind.
There was always an audible "Thud" when the buoy hit the bottom of the hull as the line was cut.
I now have a cutting disc on my Albin like the shaft shark but not serated and I don't know how effective it is because fortunately I haven't run over anything yet
But I KNOW that Spurs work.
Hope this helps

I did NOT remove my strut to drill/tap for my spurs installation. I drilled carefully and used a "bottoming tap" ( flat end) and never touched the shaft.
Easy peazy. You can do it

[RobS]

Even if you had the time to pull the strut or cutlass housing I agree with Jay, not needed, mark your drill bit with blue tape for the depth you need and drill carefully and use a bottoming tap.

[Tree]

I’d like to add that if you do drill your housing, when you tap it use a spiral point machine tap first - don’t bother with a hand tap as they are a misery to use. Once most of the thread is cut then use a second tap (flat bottom) to get the depth and full thread engagement. I only know this because it’s what I do for a living! Make sure you use lots of cutting fluid on the tap because the base material has a habit of “gripping” on the drill and tap causing them to snatch and that’s when you start to break HSS bits in holes and that’s when it becomes a right PITA to remove.

[Pitou]

Okay boys, thanks very much for the guidance and renewed confidence about drilling with the housing in place.

I had no idea about the bottoming tap which is why I thought that I needed to pull the strut/cutlass housing. By using a regular tap there was no way that I was going to get the bite that I need to attach the holding block. Now that I know about this type of tap, I'm back in and will let you know how I make out.

Headed to Bar Harbor in Maine this summer and the waters are littered with lobster buoys. Not looking to hit anything, but it sure would be nice to know that I've got a little help from below.

Thanks for jumping on my post. All of your help is very much appreciated.

[jleonard]

If you have trouble sourcing a bottoming tap you can grind off the point on a standard tap to accomplish what you need to do. Just be smart about the grinding i.e. Use plenty of quenching water and don't let the tap get blue.

[Pitou]

If you have trouble sourcing a bottoming tap you can grind off the point on a standard tap to accomplish what you need to do. Just be smart about the grinding i.e. Use plenty of quenching water and don't let the tap get blue.

I was thinking about grinding just as you described, but got lucky and found a bottom tap locally just up the road 15 minutes from the house at a chandlery/machine shop on the waterfront in Gloucester. On my way to pick it up now. Hope they have what they say they do ...

[DougSea]

They (whoever "they" are) say you should try and learn something new every day.

Bottoming Tap - never heard of such a thing. How did I get this far in life without that knowledge?! Would have made any number of projects easier!!

Thank Jay and Rob! (And Tree and Kevin)

[Tree]

They (whoever "they" are) say you should try and learn something new every day.

Bottoming Tap - never heard of such a thing. How did I get this far in life without that knowledge?! Would have made any number of projects easier!!

Thank Jay and Rob! (And Tree and Kevin)

In the old days ( and today for that matter) taps came as a set of three. First, second and plug the plug being the tap that removed the lead from the other taps at the bottom of the hole.

Grinding taps is something we do quite often even though in a precision industry it isn't good practice as it can and will lead to an oversize thread - the go gauge goes in but so does the no go! Thats where ball bearings come into play but thats another story for another day

[jleonard]

Ball bearings???
You know that's cheating.
Don't ask how I know

[Tree]

Ball bearings???
You know that's cheating.
Don't ask how I know

[Pitou]

Thanks for all of the help and direction and here's the follow up ..

I mounted the holding block last Monday for the Spurs Line Cutter and launched on Saturday. Was a bit concerned with all of the new hardware that I'd have a vibration or even worse ... lose a knot or two. Neither occurred.

Used a punch, small drill bit then 1/4" bit before using the 5/16 - 18 starter tap and then finished with the bottoming tap:

.3125 - 18 thread.jpg

Had to cut of 1 thread of each holding block bolt length to fit / apply red loc-tite & lock washer:

2 inch Spurs.jpg

Filled extra shaft length with zinc anodes:

2 Anodes for Filler.jpg

[DougSea]

No vibration, no performance loss, and more peace of mind...nice!

[RobS]

Nicely done, a tedious one no doubt ....... that was not a job for a yard monkey...
Quite the prop overhang, it's normally not much more than a shaft diameter, is that the way Albin set her up? Can't see the top of the prop, maybe Albin needed to gain so "tip to hull" clearance..or maybe was there a drivesaver added?