Engine mount stringer build help

Hey guys,

I've got a long laundry list of things to do on my boat. Some of them in progress, some in planning, some in the acquisition of materials.

One of them is as the title states - an engine mount stringer build. The current stringer onboard my boat is totally sound and has no issues. The problem is the engine is new(mid 90's) and the stringers were too wide for the engine mounts to sit on properly.

The solution?
- A steel L bracket bolted into the side of the existing stringer which the mounds can then sit on.

This has lasted atleast 20 years and is a simple solution, and I could be cheap and remove the rusted out L bracket and have someone make a replica - which I may do. If i have new ones made, I will likely go with a bit of a different design and use stainless. I would have the L bracket run to the hull and also go all the way up to the top of the stringer and over the stringer so I could fasten it from the top aswell - think of it as a T bracket welded onto a U bracket

But I want to see what others have to say about how I should go about building up a new section of stringer that could have vertical support as well(instead of relying on lag bolts).

My initial thought was to get some 3/4" marine ply stack them(cut side up) and laminate the faces together and then glass this "new" structure to the existing stringer. I'd use something like a biax 1708 for the glassing/encasing the entire thing onto the existing structure.

Unfortunately, I won't be doing this with much room as I'll be doing it while the engine is in place, so it's going to be a fun crowded project!

Any advice on ideas?

 

I don't know how you would construct new stringers and beds with the drivetrain still in the boat. I'll post a link to a thread we had here back years ago that discussed stringer fabrication. I included some pictures of what I did back then. I never thought of using stainless rather going for 6061 Aluminum angles with backing plates. You can see these in some of the photos in the link.

Stringer And Deck repair https://www.boatdesign.net/threads/stringer-and-deck-repair.29459/

You have to let us know how this comes out and I'd love to see how someone does this with the engine still in the boat.

Regards,

MIA

 

Doing it while the engine still in the boat will be challenging for sure. I'll take a look at the link. I will have to take a look at the idea of using 6061 Aluminum. I was thinking stainless for the purpose of corrosion resistance, but 6061 would also be an option, and it would be cheaper and lighter.



My engine is a Yanmar 4JH2-UTE with a V drive. The "back" of the engine is the first thing you see on it when opening the hatch. This area is going to the "tightest" working area, so I thinking of possibly applying the epoxy via vacuum bagging. I would support the engine by a fender or basket ball or something similar. Still an idea that is in the works in my brain, so it all is preliminary.

 

MIA - Looking through your post, you went with a similar mount design as what my previous owner did, except yours are through bolted. Being this was back in 2009, how are the aluminum mounts holding up?

I'm not sure if the idea of T and U mount idea made sense in my first post, but are you concerned with a failure in bolts causing slippage? Granted you have no plans for crossing oceans, but for someone who will be doing that, I feel like that would make it inherently stronger. I would also consider adding "braces" to the underside of the flange would would give "downward" support to the flange that the engine mounts bolt too.

Going the route of just replacing the brackets would make life MUCH easier as I could do it with the engine in place. I think its "doable" to epoxy in additional structures but it would be more time consuming and more work.

 

I did a complete restoration. Although the post you read was done in 2009, the boat didn't actually launch until 2014. That said, the aluminum beds look like the day they were installed. I've had no issues with alignment whatsoever. I boat in fresh water but don't believe that there would be any problems if I were in salt. If my memory is right I used 3" by 4" angle 3/8" thick. The through bolts are 1/2" stainless steel with nylocks. Through bolting to a backing plate the same size as the aluminum angle spread out the loads across many square inches of area, I think this is why the new beds and stringers are holding up as well as they are. Again, they look like the day they were installed.
You can buy 6061 angle up to 8" and 1/2" thick. I looked up your engine and it's lighter than my Ford V-8 rig. I don't think you would need anything close to 1/2".
The original manufacturer (Silverton) used 1/4" angle iron, set up similarly to what I built, except that instead of using backing plates they used fender washers on the through bolts! Geez. Not even structural washers. These eventually crushed the stringer since the 12 bolts used were bearing on a very small area of the stringers. This allowed the engine to drop over time causing the alignment to get completely out of whack. I built much stronger stringers and used the 6061 for the beds for corrosion resistance.
As long as your stringers are capable of supporting the loads you should be fine with through bolted angles for engine beds, with backing plates of course.

MIA

 

That is great to know! I will have to dig around in my stringers to make sure no rot is present. I am not aware of any but there may be some I am unaware of. The bigger question is will I be able to get backing plates on the backside of the stringer. I am in a sailboat so as usual, space around the engine is limited. I may have to get better at yoga.

Do you have a supplier recommendation for 6061 aluminum? I am located in Seattle, so may ask around to see if anyone in the marina has recommendations on local suppliers, but no opposed to online suppliers either.

Thanks for the advice MIA!

 

I think glass workmanship under and existing engine would be suspect and would never consider it.

The only other comment is nylocks and stainless bolts are sort of well known arch enemies. The bolts are prone to galling in nylocks, so treat them like an already stuck bolt and use lubricants or anti-seize to apply and remove.

Here is a link on nylocks and stainless and galling.

https://www.fastenal.com/content/feds/pdf/Article - Galling.pdf

 

That's pretty ambitious crossing oceans. I'm planning a trip to the Florida Keys next fall. It will be a solo trip but I'll be rarely in the open ocean. Good for you.

Fallguy is telling you something there about trying to work under that engine. The more I think about it the more I don't like it. First it seems to me you could get hurt if anything moved. Second, trying to do fiberglass layups is challenging for an amateur under the best conditions. For me it's like papier mache with toxic chemicals. Can't you find a fork lift or a chain hoist/gantry or something? Maybe work out something with a tree surgeon? You only need to lift a half ton or so, right? If you're doing all this work and going to the expense you'll have much better results if you have room to work. Think about it.
With respect to the aluminum there are numerous internet vendors. I use an outfit called Speedy Metals. I'll plug these guys (if that is allowed) because they have reasonable prices, they have cut everything exactly as I have asked them and have a good selection of product. You may be able to source material locally, as you said.
Fallguy has a point regarding galling. I tried lock washers when I originally installed the engine and they wouldn't hold. So I went to Nylocks with a little Locktite Blue. Seems to work OK.

 

When I was think of the glass work, I had anticipated more room to work with. Now pondering the idea and taking a peak and the area and how I would have to go about it, I think glassing the new members in place would be a GIANT PITA, and as you state MIA - could be dangerous.

I will have to look at pulling the engine if I choose to go this route.

I may choose to go the route of just replacing the steel angle stock with new aluminum. I need to further dig into how they are actually mounted into the stringer. When I finish the current project I'll dive further into it to assess things and go from there.

I appreciate your guys opinions! Helps talking through ideas to find possible issues with what I'm thinking. Being a self taught engineer by trade, the best way for me to figure things out is ponder it for a bit then talk the idea out and get criticism

 

I pulled a couple pics from sbmar.com there’s plenty more good information there.