Glasswork

[Meriachee]

After installing the back winches on the 270, I find that the lines aft of the EZGlide cars touch on the stb side and rub on the port side. I made a couple of mounts for foot blocks, and while the port one through bolted nicely through the lazarette, The Stb one will not through bolt without the boltheads being in the aft berth.
Here's the question: If I grind away the gelcoat, would a nice coat of epoxy be sufficient to hold the base if the block was attached with screws that penetrated the core? The block isn't very large, about 2" wide and 3" long, and the sheet loads could be quite high given that we're talking close to a 90 degree bend.
Any input welcome. Glasswork is easy, calculating shear factors is way beyond me.

 

[RonM]

Securing foot blocks

After installing the back winches on the 270, I find that the lines aft of the EZGlide cars touch on the stb side and rub on the port side. I made a couple of mounts for foot blocks, and while the port one through bolted nicely through the lazarette, The Stb one will not through bolt without the boltheads being in the aft berth.
Here's the question: If I grind away the gelcoat, would a nice coat of epoxy be sufficient to hold the base if the block was attached with screws that penetrated the core? The block isn't very large, about 2" wide and 3" long, and the sheet loads could be quite high given that we're talking close to a 90 degree bend.
Any input welcome. Glasswork is easy, calculating shear factors is way beyond me.

I'm not ready to tackle the shear factors either. However, I'm a firm believer in backing plates behind anything that suppose to hold a line. That includes the correct sized bolt, nut and plate. You might get away with attaching your foot block with screws only, but I'd never want to rely on it holding, especially when things head south and you absolutely, positively require it to hold. Yes, the glasswork is relatively easy, but I'd find a way of securing the block properly.

 

[CloudDiver]

Let me just say your molds and glass work are PRO level, I admire that greatly. Keep that mold because those risers could be useful to anyone using the same block on any boat, let alone to other 270 owners.

I would say that epoxy thickened with colloidal silica is extremely strong, but you'd have to get the numbers from WEST Systems on what the sheer strength would be. I'm willing to bet that with two stainless screws through the block and into the deck core (which will give you great clamping force when applying epoxy) that it would be plenty strong enough. Then again I have no idea what the sheet loads are... In any case You are always safer through bolting with a backing plate, so it begs the question; what would be wrong with the backing plate and nuts being in the aft berth?

 

[centerline]

backing plates and nuts are a MUST... screws into the core will be torn out, and if you have ever seen a block break or what the bight of a line under tension can do when it comes suddenly free, you will know why it needs to be thru bolted.

its not exactly a shear load as the pulling power of the line will want to peel the block up, not slide it across the surface... and depending on load angles, more so sometimes than others.... shear loading does not take this tensile load factor into account.

for the bedding, butyl tape or 4200, but to attempt to adhere it with epoxy is only setting yourself up for disaster...it may hold forever with a light load, but not when the load is the highest and can do the most damage... I can vision a broken leg or arm... possibly much worse depending on who and how their body part is situated when it comes loose.... and at the very least a mess that has to be cleaned up so that on the second attempt to get it right, it can be done correctly by thru bolting with a backing plate.

anyone who would underestimate and doubt the power of a bight of line under tension is a very foolish person.

 

[Meriachee]

The headroom in the alcove of the back berth is less than minimal on a 270, and while a backing plate, washers and nuts don't take up a lot of space, having tested the clearance, I can say that there will very likely be some impact damage at some point, and I'm not looking forward to the resulting pain.
While I do absolutely subscribe to the "do it right" plan, in this case, there is personal logic for deviating, but only if the solution is reasonably robust. Anything can, and will break if subjected to enough force, and my concern here is that the base of the block is not overly large, and does not provide a very large surface area.
Maybe the approach should be to make some kind of cover for the interior hardware that would lessen the possibility of poking holes in the head.

 

[justsomeguy]

snip-
Maybe the approach should be to make some kind of cover for the interior hardware that would lessen the possibility of poking holes in the head.

 

[Jackdaw]

Remember that if you epoxy it:

The deck is NOT a monolithic structure. Gellcoat is attached to the fiberglass, and holds to it at about 400 PSI. Depending on the direction/strength of the load it would be possible to see the part pulling off, taking only the gellcoat with it.

 

[centerline]

The headroom in the alcove of the back berth is less than minimal on a 270, and while a backing plate, washers and nuts don't take up a lot of space, having tested the clearance Maybe the approach should be to make some kind of cover for the interior hardware that would lessen the possibility of poking holes in the head.

I would assume you are using #10 hardware to attach the block.... if you thru bolt it, you can very easily break off any extra length of bolt that sticks past the nut with a pair of pliers.. then spray glue a piece of foam or other material over the installed backing plate....

an option is to leave the hardware long and get some 3/16 fuel line and slide onto the bolts, one end of it on one bolt, and then cut to length so the other end can be slid on to the other bolt... this creates a soft loop that your head will feel so you have the opportunity to duck before you get to the more solid bolts... at least it wont poke a hole in your head
this will usually prevent any issues of severe contact.

 

[Meriachee]

Jack,
Not even I am dumb enough to glass to the gelcoat. The gel would be removed and the surfaces prepped accordingly, providing some tooth for the epoxy to have as much surface area as possible. My concern is that very bond, we'd still be attaching to an existing, layer of epoxy that is very well set up.
I am digging into the West docs, I guess it's time to add scientist to the fabricator role. Where's Christopher Lloyd when you need him?

 

[Meriachee]

After all the research and questions and hand wringing about glassed on parts exploding the first time they got loaded up, I measured today and find that the area behind the valance where the berth lights are mounted on the Stb side is just wide enough to allow through bolting and backing plates. None of the parts in the berth will be impact obstacles, or even seen under the valance cover. Woo hoo.
The project can be completed now.

Here's the port side block installed on the dirty boat. That's what you get for going to the coast for a week. A spider infested, bug splattered mess. Tomorrow, we clean. Today, we sail!

 

[centerline]

After all the research and questions and hand wringing about glassed on parts exploding the first time they got loaded up, I measured today and find that the area behind the valance where the berth lights are mounted on the Stb side is just wide enough to allow through bolting and backing plates. None of the parts in the berth will be impact obstacles, or even seen under the valance cover. Woo hoo.
The project can be completed now.

Here's the port side block installed on the dirty boat. That's what you get for going to the coast for a week. A spider infested, bug splattered mess. Tomorrow, we clean. Today, we sail!

theres ALWAYS a way, but sometimes one just has to look harder to find it..

 

[PineyWoods]

Remember that if you epoxy it:

The deck is NOT a monolithic structure. Gellcoat is attached to the fiberglass, and holds to it at about 400 PSI. Depending on the direction/strength of the load it would be possible to see the part pulling off, taking only the gellcoat with it.

Even with the gelcoat ground off and with the ideal epoxy bonding silica/microfiber mixture, all the stress will be taken by the perhaps 1/8" thick deck chopper-gun low tensile strength fiberglass layup.

If this were much thicker, and an epoxy layup, I'd have no qualms over the 5-6 sq inches of contact area shearing or pulling free. Tapped-in fasteners will be stressed in straight shear only, and should be solid if epoxy-coated at installation.

Pete