Attaching bike fork mounts to swim platform - fastener advice needed

[src]

I plan to attach two bicycle fork mounts to my swim platform, but I want them to be removable in a way that leaves no obstructions/trip points on the platform. Unfortunately I can't find exactly what I'm looking for to fasten them down, so I'm down to plan B. So far here's my plan:

Mount two of these:


Using these (threaded for 1/4x20 bolts):


I plan to drill the mounting holes through the platform, then attach the fasteners from the bottom using 3M 5200. I would prefer to rig up a backing plate as well, but might try to get by with a couple of big washers. With this arrangement, I can just bolt the fork mounts down through the platform, then remove the bolts and fork mounts when I'm done.

My biggest issue is the longevity of the 5200 in this application. As far as I can see, the worst case scenario is that the 5200 fails and I lose the tee-nut when I remove the mount, which would be a temporary but not fatal inconvenience. I would love to find a fastener that has both a top and bottom plate, but although I know I have run across them sometime in my life, I can't find anything like it now. What I remember were essentially two of the items above, one with internal threads and one with external, and they screwed together to clamp whatever material was between them. That would be ideal.

Any advice on this one? Thanks!

 

[JimFromMD]

So taking one step backward, sounds like the goal is to mount the bikes to the swim platform for transport and use while transient at other marinas? I dont have much advice on how to secure the mounts, but as much splashing and backwash that comes up on my platform when dropping off plane, I cant imagine your bike frames/chains/rims lasting too long, especially in salt or brackish water.

I have thought about getting a folding bike or two to transport in the cabin while underway and secure to the platform or pier once at a destination. I couldnt come up with any other approach that seemed feasible besides that other than possibly securing them with a bungy and padding to the gunwhale ralings or further up toward the bow. A lot of the folding bikes come with a zippered storage bag to keep any dirt / grease from getting inside the boat.

 

[src]

I appreciate the input, but right now folding is out of the question - too many $ for something that would be for VERY occasional use. I'm willing to do the maintenance necessary to keep the bikes in good shape, and this is something we only plan to use a few times a year. If we ever do a lot of travelling/transient boating, then we might reconsider, but honestly I could replace the bikes a couple of times for the price of some good folding bikes, and the exposure is really not going to be that bad overall.

 

[St Vitus Dance]

Have you considered one of those hanging tracks like you see on the back of cars that you could rig to hang on transom?

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[src]

Have you considered one of those hanging tracks like you see on the back of cars that you could rig to hang on transom?

Yes, I have. I've had those for cars before, and have never been happy with them. I've used fork mounts on a pickup, and also fork mount roof racks, and just generally feel more comfortable with them.

 

[alwhite00]

Have you considered one of those hanging tracks like you see on the back of cars that you could rig to hang on transom?

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The ones that plug into a receiver hitch - Then you could possible mounr a tube under the platform that wouldn't need to be removed but the bike rack could be.

LK

 

[src]

I appreciate all the suggestions, but I've already settled on the fork mounts. I've considered the various racks (including the one specifically made for boats) and other solutions, and this is the one that's best for me. I just wanted to bounce the physical attachment plan off the group to see if anyone had any suggestions for improvements.

 

[Lazy Daze]

I think your general plan is a good one. But, I would think a little more about reinforcing. The platform is very strong, but I would feel better with a little more "meat" where the fork mounts attach. I would glass-in a piece of 3/4" marine ply (overkill, but I think you'd be hard pressed to find thinner) about 2"-3" larger than the mount in each dimension to the underside. Then, slightly overdrill your hole for the 1/4-20 portion of the t-nut so you can come back and coat the inside edge of the hole with epoxy. Next, you can screw the t-nut to the underside with screws and also use some adhesive sealant, making sure to get some in the screw holes and also between the 1/4-20 part and the hole. I would use Life Calk or 4200 instead of 5200. If the t-nut isn't hollow, drill it out so water drains through. Just for good measure, I'd use a piece of 1/4" starboard between the mount and the platform, cut to the same dimensions as the mount (you can buy this in black).

Be sure to slightly chamfer the top side of the holes you drill through the platform.

What is your plan for keeping the rear tire from bouncing around?

 

[src]

Thanks for the detailed tips. They really improve my idea, and I'll probably do all that once I have the boat hauled for the off season. I've got a trip coming up this week that I'm going to try the version 1.0 out on, and I guess I'll find out how inadequate my idea is then.

Why 4200 instead of 5200? I know that 5200 is forever, and that's pretty much my plan for this. I don't want the t-nut spinning out when I'm bolting things down, and there isn't really enough spacing on the flange to do more than brad them into the bottom (not a great idea, in my mind). I would love to find t-nuts with larger flanges, but so far I've had no luck there.

For the rear tires, I'm just going to bungee them to the platform cutout on the other end for now. I will have to come up with a better long-term solution though. I'll put a brace between the bikes to keep them from flailing around too much, and I'm sure there will be a LOT of tweaks to my plans as I find out what doesn't work as expected.

 

[Lazy Daze]

Permanent is the exact reason I don't like it for this application. The other two will be much more than adequate to do the job - my guess is that your platform is at least 1/2" thick? You can use 1/2" pan head bolts (maybe #8? will fit) which, combined with the adhesive, should be more than adequate. 4200 and Life Calk are close to the strength of 5200. Here's the thing with the 5200 - if it does rip out, it may pull some of the underside of the platform with it.

Here's another idea - find a local welding shop and have them weld a nut (or even just the t-nut) to a piece of SS plate - say 1/8" or 3/16". You could make that plate quite large to spread the load and give more surface area for the adhesive. They'll probably charge you all of about $20 for the labor. Materials - just depends on what they have on hand - hopefully some leftovers.

And another idea for the rear tire... mount the fork mounts opposite of each other - that way you can secure the rear tires to the forks of the other bike. Use a piece of dense foam (wrestling mat) or a type IV throwable device (white cushion) or even some foam noodles in between each.

I'm sure there's still other ideas and no one idea is going to be the best - take the best of each and combine it into what you feel comfortable with.

 

[src]

All good points, thanks!

 

[brewster16]

Hey, i have a suggestion.....for about 5 bucks you get some bungee cords, put your bikes down in the cabin, pad them well, and bungee them snugly to the grab rails in the galley....that's exactly what we do when we travel and works like a charm!

 

[IanBat]

I knew I had seen something on a website, just went to order some fender grips some one else had recomended awhile back on the forum and found it. They do a bike mount

http://www.fendergrip.com/cg.html

 

[Havana Shamrock]

Have you looked at Sea sucker mounts ?

 

[src]

The bow rails are occupied by 2 kayaks, so that's not an option. Sea-Sucker mounts won't work on the swim platform (textured), and I wouldn't trust them without a solid backup attachment.

Again, I don't need alternatives, I was just looking for the best way to do what I described. Although the alternatives are great information for people who are looking for a solution, MY solution is fork mounts on the swim platform.