MacGregorSailors.com

I am not sure what kind of plates are on other Macs, but assume most have stainless steel plates that are used to attach the rudder support plates to the transom.

On my 2008 26M I noticed that the starboard side plate was missing one of four stainless steel bolt heads. It was the upper left when looking at the plate from the rear of the boat.

Upon inspection of the bolt which I removed from inside the boat, it appeared the portion of the bolt just below the head had corrosion which probably caused fatigue then broke the head off. The entire plate is loose and not secured tight against the transom. I am guessing the other 3 bolts have similar corrosion which is providing some "slop" between the bolt head bottom and the plate.

I am going to replace all 4 of the bolts, nuts and washers.

Here are my questions.

1. Has anyone else observed this corrosion of the bolts?

2. I am assuming Macgregor used 316 Stainless Steel bolts and nuts. Anyone know differently?

3. Has anyone used a non metallic spacer between the plate and bolt to eliminate electrical transfer between the two? What material did you use?

4. Any other thoughts on how to reduce corrosion at this area?

Thanks, Ed

Stainless does that when exposed to salt/water and deprived of oxygen. A buddy of mine almost trashed a Boston Whaler when his lifting eye gave way due to similar corrosion - all hidden inside the hull penetration.

You might want to replace all of your rudder fasteners while you’re at it (or at least inspect them all).

Make sure the hole is good and dry and bed it liberally with 3M 4200 or similar.

I highly doubt they are type 316. Nothing in these boats is 316

Ix

Ok. Here is what I have found to date.

Jimmyt you are correct. When stainless steel is exposed to saltwater which is a mix of chlorides and sodium and oxygen is not present, corrosion will be sped up.

The void beneath the hex head and the plate will create an area for this corrosion to happen. I believe that is why my 2008 rudder plate bolt heads are deteriorating to the point where one bolt head has broken off and others are loose.

The 1/4" x 1" bolts with coarse threads (#20) will be replaced with new locking nuts and washers.

Home Depot and West Marine stainless steel bolts and nuts are 304 grade alloy. Ok for marine conditions, but will show pitting over time.

316 Grade stainless alloy has more molybdenum in the alloy making it superior for corrosion resistance. This is especially needed when the metals will be submersed in saltwater and be subject to both galvanic corrosion and or electrolysis.

I am going with grade 316 stainless bolts, lock nuts and washers. Searched around and found that boltdepot.com has 8 of each for a total cost of $5.60.
The shipping cost is minimal at $4.95 for a grand total of $10.94. A small price to pay to make it the best. I only like to make repairs once.

The bolts and nuts will be installed with a sufficient amount of 3M 4200 sealant from the base of the hex head, through the transom to where the bolt exits inside of the boat. I will pay attention to the area directly behind the plate where the holes are drilled, filling that void with 4200 sealant to remove that void where water will get in over time.

I asked in a different post what type of stainless was used in the construction of the Mac 26 boats. I got one response that indicates he feels that most is probably 304 grade stainless.

Is it possible Macgregor went cheap to save one dollar and used 304 grade below the waterline?

Hope this helps,

Ed

Update.

As stated, I just bought the boat and am in the process of refurbishing the hull and attachments from the waterline down. I have not put it in water yet.

Previous owner indicated that the boat was sitting in S Florida saltwater for 6 months prior to me buying it. Based upon the barnacle growth over previously applied antifouling paint that seemed to be a good estimate of how how long the boat was sitting recently in saltwater.

I pulled the bolts out of all of the two rudder plates mounted on the transom today. 8 in total. Every one of the bolts had extensive corrosion from the head of the bolt to where the locking nut was attached. Most of the nuts turned but when I put a little side force on them, the bolt broke off. Not good for bolts only being on there 16 years. If I where to have used the rudders down in sailing mode, I am sure the rudders would have fallen off very quickly.

Has anyone experienced dramatic corrosion on their rudder plate bolts?

Is it possible there could be damage to the transom itself? How could I check?

Thanks,

Ed

Hi The Islander

Sorry to hear of your corrosion problem.
It isn’t that MacGregor went cheap in as much as 304 and 308 are the common SST materials for bolts as it’s generally stronger and less galling than 316 or 316L.

Note: Nearly everything corrodes eventually… it’s the nature of things.

When going to 316 bolts and nuts be careful to avoid galling. A little bar soap in the bolt threads at assembly helps prevent that.

Best Regards,
Over Easy

Appreciate the heads up on use of 316L Stainless Steel. I did not know it existed. I just found out it has a slightly lower concentration of carbon making it slightly better against corrosion.

I just got my bolts from Ma. today. The hardware is all 316 SS. They were actually cheaper than what West Marine and Home Depot 304 SS hardware were asking. The manufacturer suggested lubrication on the bolts when tightening to prevent galling.

Thanks Over Easy!