Screw/Bolt for prop anode R21ec

[Oceanwarryer]

Dove the bottom of my boat last night - changed one of the two anodes on the rudder (they were not the same one as someone had suggest on my parts list. One is half the size of the other at the top upper edge of the rudder.
Changed the bow thruster.

Went to change the prop anode- gone - and all I had was the anode - no screw.

Wondering if anyone has the specifics on that screw/bolt/allen screw

length, size, thread count? I could end up chasing many sticks on this one....I'd like to get it on there ASAP.

thanks
Vince

 

[Cutwater28GG]

i always lose my prop anode first. my divers dream helps protect though. I'd call Andrew and team at the factory for a quick answer on nut dimensions

 

[TBates]

Hello Oceanwarryer,

Here at the factory we've started using a standard hex head 5/16"X18X1 1/4" stainless steel bolt with both a lock and fender washer. I also like to add a little bit of blue Loctite to the threads to make sure it doesn't loosen up.

Please let me know if you have any other questions.

Tim

 

[Red Raven]

Hello Oceanwarryer,

Here at the factory we've started using a standard hex head 5/16"X18X1 1/4" stainless steel bolt with both a lock and fender washer. I also like to add a little bit of blue Loctite to the threads to make sure it doesn't loosen up.

Please let me know if you have any other questions.

Tim

The revised bolt and washer now used by the factory still spins off prematurely maybe even sooner than the cap screw and toothed washer.

Here is my opinion on what is going on after dealing with this for three seasons. The problem is that as the anode corrodes as it gets smaller and shorter making it loose against the bolt and prop castle nut. The lock washer and fender washer have nothing to press against to keep the lock washer compressed when the anode shrinks. The toothed washer is on a surface appears to corrode slower so I think it may actually be better. The anode will still spin off however as it shrinks because the foreword surface of the anode against the castle nut flange corrodes and the anode becomes loose and eventually breaks up and falls off.

The solution (at least the best I have found so far) appears to be lots of locktight on the bolt threads (be sure to let it dry before putting it in the water), a washer (or penny) wedged under the anode against the castle nut to keep it snug even after the end of the anode degrades (this inside surface doesn’t appear to decay as quickly. Thanks to Knotflying for this idea!), and an additional anode(s) on the boat to slow the decay of the prop anode (more zinc equals longer life). I added a divers dream transom zinc and did the above steps and the prop anode now lasts a full season (6 months). If you do use the revised factory system a little paint on the end of the anode under the fender washer appears to slow it’s decay on that surface and helps keep it tight.

 

[Rwnorton]

Agree with Red Raven and others before. I added a divers plate and Locktite. Both help.

 

[rocklobster]

Does the divers plate just mount to the stern or do I also need to bond it to the grounding system? How do you mount your plate?

 

[Red Raven]

The divers dream is mounted on the Starboard side of the transom between the the two starboard swim step stainless supports and bonded to the bonding system. The location is limited by where you can get access inside to drill and install the bolts and bonding wire. Once you get in there you’ll see what is possible.

Use two stainless threaded rods (bolts without heads) so you can attach/remove the bonding wire on the inside as well as the divers dream anode on the outside. Make sure you have the clearance and hole spacing for various anode sizes as they vary. Use length to span (from the inside out) a nut, the bonding wire eye terminal, a nut and washer, the thickness of the hull, a washer and nut, a washer, the anode, a washer, and a locking nut (or just two nuts). I other words, separately secure the bolts to the hull, the bonding wire to the bolts, and the anode to the bolts. My recollection is the bolts were around 3 inches long. Make sure all the hardware is stainless (preferably 316). Fill the holes prior to inserting the bolts with 3M 5200 or equivalent.

Alternative to a divers dream transom anode you can add shaft anodes to each of the swimstep supports under the waterline. The supports are already bonded so this solution is much easier. If I had known about this approach before I would have used it. No holes to drill!