Early 80s H36 Strut

[chichiflys]

Good afternoon all,
We're in the midst of some winter projects, one of which is replacing the now 42+ year old prop shaft strut. Living in Maryland we are lucky in that Miller's Island Propellor shop in Baltimore still carries the struts. In case anyone has done research and found the information on SBO's website to be confusing, fear not, it is confusing and incorrect.

I went to the shop today in Baltimore and the foreman concluded that model H-34 (to the left of my pink strut) is the proper model number (not H-33 which is to the right) to be used to replace the stock version (at least that is the case for an early 80's H36 sailboat, ours is an '82). The dimensions on the website (including those from Dahler Marine which was the OEM supplier) are incorrect. Here is a snap shot of my old and completely galvanically compromised strut compared to the H-33 and H-34 models. Note the new versions are in an "un-processed" condition, they still need to be cleaned up quite a bit. Hope this helps.

Cheers,
Marc

 

[Ralph Johnstone]

Here is a snap shot of my old and completely galvanically compromised strut

It doesn't look too healthy.

Any chance you could scrape the surface of your old strut to a few 0.001" and show us what it looks like under the pink skin ? It would be interesting to see how deep the dezincification goes.

Thanks if you would.

 

[heritage]

Good information. You might want to do what I did and fit a small mushroom zinc on your new strut.

 

[chichiflys]

I can certainly grind down some of the strut when I get it back, but the pink is pretty deep. You can kind of see it on the picture, I sanded a small area on the flat part....but I'll inquire about attaching a small zinc to the strut.

As an alternative I was planning to bond one of the strut mounting bolts inside the boat to the engine using some heavy gauge wire...was going to add the shaft log as well to that "circuit" - its my understanding that should then be able to protect the strut and shaft log using the zincs that are on the prop shaft....but if I can safely attached a zinc to the strut without compromising it's strength that may be easier?

 

[heritage]

No problems with my strut with a hole drilled in the fattest part of the strut. It's had zincs for about 3 years. But it probably does sap a little strength from it, but not nearly as much as dezincification. On my boat I connected one of the strut bolts with a copper wire to the bronze shaft log, to protect it.

 

[dlochner]

If an appropriate new strut is not on the shelf, the old strut can be used to make a mold and a new strut cast. I used Mystic River Foundry in Mystic Connecticut many years ago. Be forewarned it can be rather expensive to go this route.

 

[Davidasailor26]

I can certainly grind down some of the strut when I get it back, but the pink is pretty deep. You can kind of see it on the picture, I sanded a small area on the flat part....but I'll inquire about attaching a small zinc to the strut.

As an alternative I was planning to bond one of the strut mounting bolts inside the boat to the engine using some heavy gauge wire...was going to add the shaft log as well to that "circuit" - its my understanding that should then be able to protect the strut and shaft log using the zincs that are on the prop shaft....but if I can safely attached a zinc to the strut without compromising it's strength that may be easier?

Yes, you should get some protection that way, but it may not be perfect. For a zinc to protect a metal they need to be in the same electrolyte and electrically connected. Certainly the strut and prop zinc are in the same electrolyte. The electrical path is the somewhat iffy one. The prop zinc’s electrical path is good up to the transmission output shaft. The problem is that the transmission’s lubricated gears don’t make an ideal electrical path to the rest of the engine where your strut bonding wire would be connected.

 

[rardiH36]

I don't log on to the forum very much these days. Except yesterday. And observed this current thread. Just in case you have not discovered in the archives just yet, I went through a similar experience about a decade ago. Here is the link to my recount I posted at the time. Read through it. Possibly may give you some ideas.
Pink Strut Blues - Ideas For Replacement

 

[heritage]

Yes, you should get some protection that way, but it may not be perfect. For a zinc to protect a metal they need to be in the same electrolyte and electrically connected. Certainly the strut and prop zinc are in the same electrolyte. The electrical path is the somewhat iffy one. The prop zinc’s electrical path is good up to the transmission output shaft. The problem is that the transmission’s lubricated gears don’t make an ideal electrical path to the rest of the engine where your strut bonding wire would be connected.

My thinking is that with the shaft log bonded to the strut, the electrolyte continuity would be through the exterior bolt heads that secure the shaft log.

 

[chichiflys]

Good evening Rardi! Yes I most certainly referenced your posting from several year ago. In fact I printed it out. It sure seems that you had the H-33 strut (slightly shorter) and mine is the H-34. What is even more confusing is the tech at Miller's Island Prop mentioned that the specs on Dahmer's website are incorrect. So when I first got there I asked for an H-33 model (as the website measurements of the H-33 more closely matched the measurements to the strut on our boat, although not quite exactly), but the H-33 clearly wasn't close to the dimensions on my strut when we compared them side to side. The angles between the two are also different....Hopefully when they are done cleaning up the cast piece, installing the bearing, and drilling the holes it'll mach up pretty close with the old one, as I dont want to do a lot of re-alignment....

Side note - I noticed you have a wire connected to a bolt for the strut - do you have a whole-boat bonding system or is that wire connected to the engine block? I was thinking of connecting the strut to the shaft log to the engine block to help reduce galvanic corrosion of the those two pieces by using the anodes on the prop shaft, but it may be futile...Referencing Davidsailor26's post above.

 

[rardiH36]

Side note - I noticed you have a wire connected to a bolt for the strut - do you have a whole-boat bonding system or is that wire connected to the engine block? I was thinking of connecting the strut to the shaft log to the engine block to help reduce galvanic corrosion of the those two pieces by using the anodes on the prop shaft, but it may be futile...Referencing Davidsailor26's post above.

You are observant to notice the wire from my pictures!

When I went to install my new strut, I saw that Hunter had originally affixed a bonding wire to one of the strut attachment bolts. The wire had long since broken away. I debated whether to do it again. From one perspective, the strut is electrically isolated from the shaft and all else since the cutlass bearing is rubber. As such the strut may not be subject to galvanic corrosion. Still on my 44 year old boat are the original bronze thru-hulls. Never bonded. I check them at each haul-out by gouging them with a sharp screw driver. As of my last haul-out three years ago, the metal was still gold-yellow. No pink.

But ultimately I decided to again run a grounding wire to the engine block. I was aware of losing some electrical conductivity because of the gear/lube interface. However I have a shaft grounding brush installed. A wire from that is connected to the engine block. I also use a fish anode hanging over the side at all times when at berth. The fish anode is wired to the shaft brush. So the strut is protected by both the prop shaft zinc and the hanging zinc. At least that is the plan!

 

[chichiflys]

Ah, all makes sense! I was looking at shaft grounding brushes as well the other day as a work around. But considering we got 40 years out of this strut gives me some confidence that I'll get to enjoy this for some time still.