GB Stringers

[Scoid]

I’ve decided to mount my new strainer on a board and attach that board to the main starboard stringer on my fiberglass GB32.

I know the stringers are foam filled but they must be pretty strong to hold the weight of the motor.

I’d like to attach the mounting board for the strainer with an L bracket using screws or lag bolts going down thru the top of the stringer. Bedded in of course.

Is this ok or a bad idea????

Someone has already used lag bolts to secure a mounting plate for a watermaker , and, I’m guessing the motor mounts attach somehow.

Anybody got any knowledge about mounting things to the stringers???

 

[SteveK]

bedded, sealed from water, go for it

 

[Comodave]

That should hold a strainer just fine.

 

[Choices]

The motor mounts are drilled into a bedded steel plate. Might want to miss that.

 

[Greg QS]

Why use wood. Use starboard and 5200 to the stringer and use minimal screws to attach it.

 

[PM]

Through bolt it and bed it well.

pete

 

[Scoid]

The motor mounts are drilled into a bedded steel plate. Might want to miss that.

Does that plate run the entire length of the stringer?

Thanks!

 

[Scoid]

Why use wood. Use starboard and 5200 to the stringer and use minimal screws to attach it.

There are two mounting attachments for the Groco ARG. One at the top and another near the bottom that uses a Zip Tie. There has to be somewhere to mount the lower mount, otherwise I would just mount it to the L-Bracket.

 

[Scoid]

Here are some pics to show what I'm planning to do. The main question I have is, is it OK to mount the L bracket to the top of the stringer using screws or lag bolts?

I had to use a different board for demonstration in the last few pics because the other one still has wet paint.

 

[Bacchus]

James
My $0.02 from the photo and looking up the Groco mtg pieces & instructions
The top of the stringer appears to be an added (& bedded? ) piece of something and not just the layed up stringer? Is that Alum? Starboard? What are the fasteners for the horizontal gray board in the foreground? I would duplicate them for mtg the angle.
If so several (4) shorter screws or threaded bolts into that piece probably better than a larger/ longer lag bolt into stringer core
I see the board is helpful to mount the lower bracket but it also provides the opportunity as Pete mentioned to bed the board using 5200 for added stability.
View attachment 133295

 

[Choices]

Not sure. Someone told me it is 3/8"+. Would assume it runs at least as long as the engine.

 

[Scoid]

James
My $0.02 from the photo and looking up the Groco mtg pieces & instructions
The top of the stringer appears to be an added (& bedded? ) piece of something and not just the layed up stringer? Is that Alum? Starboard? What are the fasteners for the horizontal gray board in the foreground? I would duplicate them for mtg the angle.
If so several (4) shorter screws or threaded bolts into that piece probably better than a larger/ longer lag bolt into stringer core
I see the board is helpful to mount the lower bracket but it also provides the opportunity as Pete mentioned to bed the board using 5200 for added stability.
View attachment 133295

Talked to Oxford. There is either steel or copper under that top piece. It can be drilled and tapped. The top piece looks like aluminum but I’m not sure. Anyone know more about the stringer construction?

 

[Comodave]

Why use wood. Use starboard and 5200 to the stringer and use minimal screws to attach it.

5200 probably will not stick to Starboard. Elastomeric caulk will but it isn’t structural.

 

[Scoid]

5200 probably will not stick to Starboard. Elastomeric caulk will but it isn’t structural.

Right. I need something like 5200, permanent adhesive that remains flexible, but made for bonding aluminum.

Anyone got any suggestions???

 

[Scoid]

For anyone who's interested,

First, I removed one of the bolts that holds the motor mounts onto the stringer. As advised by John Shannahan of Oxford, there is metal that is drilled and tapped for the mounting bolt embedded in the stringer about 3/4" down. The metal itself is about 1" thick! Can't tell if it's copper or steel but my guess is steel.

Then, I drilled a test hole down thru the top of the stringer. The light grey metal cap on the stringer is Aluminum and probably 1/4" thick. Next is fiberglass 1/2" thick. Below that I ran into hard metal at 3/4" and stopped drilling. This was halfway between the forward and aft motor mounts, so it likely runs the length of the stringer where the motor is.

Now we know how 1988 GB stringers are made. Yay!!!

 

[mvweebles]

Through bolt it and bed it well.

pete

Yep. All the talk of 5200 and such is distraction. Solid Lumber will last longer than plywood. Starboard would be fine - even though nothing will stick to it, doesn't matter as caulk is being used as a sealant, nothing structural.

In my opinion, y'all are over thinking this one.

Peter

 

[Scoid]

Yep. All the talk of 5200 and such is distraction. Solid Lumber will last longer than plywood. Starboard would be fine - even though nothing will stick to it, doesn't matter as caulk is being used as a sealant, nothing structural.

In my opinion, y'all are over thinking this one.

Peter

I'm using solid 3/4" red oak.

 

[mvweebles]

I'm using solid 3/4" red oak.

As long as you're over 40 years old or so and you don't sink the boat, should be fine on your lifetime.

Seriously, this one is simple. Not sure you need the chunk of angle iron, but since you've got it, use it.

Good luck. Glad to see you replaced the old one.

Peter

 

[Comodave]

Right. I need something like 5200, permanent adhesive that remains flexible, but made for bonding aluminum.

Anyone got any suggestions???

5200 will bond aluminum and then almost never come off. If you have 1/4” aluminum cap why not just drill and tap it. That should be strong enough to hold a strainer.

 

[Scoid]

5200 will bond aluminum and then almost never come off. If you have 1/4” aluminum cap why not just drill and tap it. That should be strong enough to hold a strainer.

Good point. I’m really considering that. What do you think would hold better, a 10-24 bolt or a 5/16 lag screw. Should be 6 threads in a 1/4” of 10-24 but 5/16 lag screw has some pretty large threads. 5/16 lag screw 2.25 threads in 1/4”.

Another thing to consider is dissimilar metals. Which thread is going to hold up better to this kind of corrosion?

 

[Comodave]

If you are going into aluminum I wouldn’t use lag screws. How many bolts hold the strainer on?

 

[Scoid]

If you are going into aluminum I wouldn’t use lag screws. How many bolts hold the strainer on?

Three wood screws. Good point.

 

[Comodave]

3 10x24 bolts should hold a strainer well. But if you are concerned get a scrap piece of 1/4” aluminum and do a test and see if you can rip it off. I doubt it.

 

[Scoid]

If anyone is interested, here's what I did to solve the problem.

https://www.trawlerforum.com/forums/s15/air-entering-raw-water-strainer-65729-3.html

See post #57

One correction for this thread. The aluminum cap on top of the main stringer is about 1/8" thick on the top and 1/4" thick on the sides.

 

[SteveK]

If anyone is interested, here's what I did to solve the problem.

https://www.trawlerforum.com/forums/s15/air-entering-raw-water-strainer-65729-3.html

See post #57

One correction for this thread. The aluminum cap on top of the main stringer is about 1/8" thick on the top and 1/4" thick on the sides.

Looks good and you are pleased.

Tip: See post #57. Click on the 57 in the post and then copy the link.
https://www.trawlerforum.com/forums/showpost.php?p=1135095&postcount=57