Bolt anchors for under deck ladder installation

[danielm300]

I'm replacing my single step swim ladder on my 1988 Sea Ray Seville with a 3 step ladder. The existing ladder uses 1/4-20 machine bolts into some kind of insert. The swim platform is 1/2" fiberglass over 1/2" plywood. This is a blind installation as I can't get to the back of the material. My question is what kind of bolt anchors/ inserts are best for this type of application?

 

[JASinIL2006]

I wouldn't be surprised if you have T-nuts holding the machine bolts (see pic below). These of course, require access from the inside of the boat, as do most solutions. You could use some sort of really hefty toggle bolt, but they normally require a very large hole, which is not ideal for swim ladder. Pictures of your swim platform and ladder would help us figure out what might work.

Can you replace the bolts and just use whatever fastener is holding them now, or are you concerned the fasteners will drop out when you pull the bolts? Again, pics might help us know what you're seeing.

 

[dingbat]

There are literally 100 of inserts that fit the description. Need a picture to narrow down the options.

Here is a large selection of styles and materials

https://www.mcmaster.com/blind-nuts/

 

[danielm300]

Here are pictures of the installation location. The new ladder requires 4 bolts. I thought about going all the way through to the top of the platform and using some type of carriage bolt but that installation wouldn't be as clean as the original.

 

[dingbat]

Here are pictures of the installation location. The new ladder requires 4 bolts. I thought about going all the way through to the top of the platform and using some type of carriage bolt but that installation wouldn't be as clean as the original.

Need a good picture of the insert to tell what kind of insert...screw-in, expansion, etc. Can match up with link above

Need to use stainless...”plated” steel will rust even in fresh water.

https://www.mcmaster.com/blind-nuts/stainless-steel-tapping-inserts-for-hardwood/

Coat hole with marine epoxy before installing insert.

 

[danielm300]

Thanks for the responses. Unfortunately I cant see the inserts. It even looks like the bolts shred off when removing. I like the idea of an insert with marine epoxy. With the large number of different types of anchors out there I was overwhelmed. I'll look at the hardwood blind nuts

 

[AShipShow]

Can you drill a hole the entire way through and thru bolt it?

 

[danielm300]

We've been studying that option. The issue is finding a flat enough bolt head so we won't stub toes, knees, etc. or using some type of open weave utility mat that would be thick enough to cover the bolts. We're looking at having to use fender washers to spread the load and prevent pull-thru.