Instead of mold release wax???

[Hermit Scott]

I finished the backing plates tonight. That was alot of work! My heart goes out to those that do this for a living. There was a post not too long ago where a guy was asking if $500 was reasonable to replace a through hull. I'm not sure if I would want to do them on someone elses boat for $500 a piece. The 24 oz. mat is harder to wet out than the 6 oz. and it took alot more layers than I thought. I think there is 10 or 12 layers of it to get a 1/2" board, and a few layers of 6 oz. I made enough board for 11 plates 5 in. diameter. It took 1/2" gallon of the polyester resin and 32 square feet of the 24 oz. roving. I am only using 5, the others are for sale for 1 million dollars each.
The backing plates are definitely the worst part about this job. I would recommend buying them some where if you could.
I ended up using wax paper taped to a table. That worked very well. Thanks for that tip Maine.

 

[jibes138]

Why not just use plywood?

Scott,
Why not just use plywood saturated with epoxy to waterprrof it and then saturate the hole for the through hull with epoxy after you bond it in place and cut the hole. Seems like a lot less work and way less cost. You still need to bond them into the hull I take it? It might be cheaper to buy a wrecked boat and cut up the hull to use as backing plates?? You might get one for free if someone wants to get rid of it. Or if you find an abandoned wreck smashed on the rocks. One nice thing in NC there aren't any rocks that I can tell, just clay and sand. You don't get to rocks until somewhere out near Raleigh where you get a hundred feet or so above sea level. That is about 200 miles from the ocean.

 

[Maine Sail]

Scott

It's your first time so it's understandable it took you a while. I can generally lay up a board in about 15 minutes.. For future reference one benefit of epoxy is that it wets out easier. With the right tools it should still wet out quickly. As for buying pre-made stock Garolite G-10 is great stuff...

 

[Hermit Scott]

I am going to epoxy to install them. There was also a 1" crack (smile) in the front and back of the keel joint. I opened them with a thin grinding disc and filled them with 5200. I am going to remove that and epoxy in a larger section. I am sure that won't be the last time I am messing with the keel.
Laying the epoxy went pretty quick, it was cutting the board afterwards that filled my shop with poisonous dust. I tried hole sawing them with a harbor freight hole saw. I bought a set for $5. The 5" saw didn't make it 1/4" through the first hole. I then just used it to make a hole pattern and then ban sawed them.

 

[Hermit Scott]

Jibes-would you rather have fiberglass enforced through hull flanges, or plywood backed ones? They cost less than $50 in materials but about 4 hours of work. When I removed the through hulls, some were plywood backed and one fely pretty soft. It didn't inspire alot of confidence.
What would have made the job better is if didn't trim the edges of the fiberglass board on my radial arm saw. That shot fiberglass dust up in the air all over the shop. Also I would buy really good hole saws. When using the hole saws the dust is really at a minimum. And when they are sharp, they cut right through and save alot of time and effort.

 

[Maine Sail]

I tried hole sawing them with a harbor freight hole saw. I bought a set for $5. The 5" saw didn't make it 1/4" through the first hole. I then just used it to make a hole pattern and then ban sawed them.

With HFT you generally get what you pay for. I suggest Lennox hole saws and have some that go back nearly 20 years that still work fine.

Here is a great tip for using hole saws in fiberglass. DO NOT just try to drill straight through. Wiggling the hole saw from side to side, actually more like a circular motion, as you drill through the fiberglass will expel the chips and dust and also keep the saw cooler.

Tip # 2 rent buy or use a Milwaukee Hole Hawg or similar drill. With a 6" hole saw going through 1/2" glass you can burn out even a heavy duty Porter Cable 1/2" drill in short order (ask me how I know).

If drilling them on a drill press rig your air compressor to blow out the dust as you drill and don't cut it in a continuous motion. The compressed air will also keep the hole saw cooler. Also drill in a cut, lift, cut, lift fashion not one continuous motion... And use the slowest speed your drill press will turn..

Lennox Hole Saws (LINK)

Milwaukee Hole Hawg (LINK)

 

[jibes138]

Seems like a lot of time and expense

Wouldn't it just be easier to use square backing plates instead o this hole saw business? Then you could use a band saw, or circular saw. Sealed plywood should be fine for this job, or plywood with a layer of glass, easy to wet out, inexpensive. Imagine your entire deck is filled with that or balsa. Also the original equipment is what 25 or 30 years old and wasn't sealed most likely and lasted this long. No question your repair is better but is the time effort and cost worth the trouble? My plywood coated with epoxy dinghy is about 10 years old and still going strong.
Regarding Lennox. I grew up about a mile from the factory in East Longmeadow Ma. It is actually American Saw and Mfg. Co. and one of their brand names was Lennox. They used to hacksaw a car in half to show how good the blades were. This was a great privately owned company that was exporting tools all over the world, imagine an american manufacturing company as an exporter of world class products. The company was sold to Newell Rubbermaid a few years back and now the sign on the building reads "LENNOX."
My favorite watering hole was next door to the plant, 25 cent beers, and you could get those pickled eggs in a jar and play the bowling machine, the kind with a puck. Ah the good old days.

 

[Hermit Scott]

I'm sure alot of people use plywood as backing plates. As long as you have no leaks you won't have any problems. With fiberglass and resin coating the plywood, even if you had a leak and the wood rotted, you may never know because the glass is so strong. For example, the keel stub in my C30 is plywood. It may be rotted out but there is alot of fiberglass around it so it's hard to tell. If I had a choice, I would have no plywood below the water line. When my training as a Sailboat Jedi is complete, in a few years I will drop the keel and take a look at the keel bolts and replace the plywood with fiberglass.
As far as the round shape instead of a square shape...I thought about doing triangle shapes with rounded corners, the same shape as the adapter plate flanges. I wouldn't use a shape with sharp corners. Cast shapes have a greater tendancy to start to crack at those corners. It seems intuitive to me to make them round instead of something with sharp corners. I don't regret spending the time building them though. Each new thing I learn to do expands my possibilities to the types of things I can build.
I finished a new prototype last week. We were trying to figure out how to vacuum form an ABS cover for it. The draws were too deep and would have to be injection molded, which cost 10s of thousands for a mold. Which you don't do for a prototype. Now I realize I could have made it from fiberglass, but I have a show in march so no itme. But now that's a possibility where before I wouldn't have considered it.

 

[sailingdog]

Square backing plates can cause stress lines at their edges, far more readily than a round backing plate will—especially at the corners. Also, it is often easier to seat and place a round backing plate than it is a square one.

Wouldn't it just be easier to use square backing plates instead o this hole saw business? Then you could use a band saw, or circular saw. Sealed plywood should be fine for this job, or plywood with a layer of glass, easy to wet out, inexpensive. Imagine your entire deck is filled with that or balsa. Also the original equipment is what 25 or 30 years old and wasn't sealed most likely and lasted this long. No question your repair is better but is the time effort and cost worth the trouble? My plywood coated with epoxy dinghy is about 10 years old and still going strong.
Regarding Lennox. I grew up about a mile from the factory in East Longmeadow Ma. It is actually American Saw and Mfg. Co. and one of their brand names was Lennox. They used to hacksaw a car in half to show how good the blades were. This was a great privately owned company that was exporting tools all over the world, imagine an american manufacturing company as an exporter of world class products. The company was sold to Newell Rubbermaid a few years back and now the sign on the building reads "LENNOX."
My favorite watering hole was next door to the plant, 25 cent beers, and you could get those pickled eggs in a jar and play the bowling machine, the kind with a puck. Ah the good old days.

 

[jibes138]

Laying up sheets

Scott, why not make a mold for your backing plates? Insert glass, then use resin transfer molding to wet them out? You pull a vacuum on the mold and suck resin in the opposite side of the mold. Out pops a backing plate with some trimming of the resin. The mold would be extremely simple and you could sell these things on e-bay (the backing plates). Soon you will be sailing in a Perinni Navi with a crew and captain. The Catalina could be up on deck to use as a dinghy in port.
Sailing dog, why not just use stainless steel for these backing plates? To me neither plywood nor FRP is particularly strong in compression yet this is being use to strengthen a compression joint. Seems like stainless steel would be a lot better. Understand your comment about stress concentrations but seems like the risk would be extremely low. What are they doing on new production boats?

 

[sailingdog]

Sailing dog, why not just use stainless steel for these backing plates? To me neither plywood nor FRP is particularly strong in compression yet this is being use to strengthen a compression joint. Seems like stainless steel would be a lot better.

I prefer aluminum to stainless steel since it is lighter and much easier to work with.

Understand your comment about stress concentrations but seems like the risk would be extremely low. What are they doing on new production boats?

Depends on the manufacturer... some high-end ones use stainless steel or aluminum, in some cases embedding the backing plate into the laminate and drilling and tapping it instead of using nuts. Lower end manufacturers often use solid fiberglass or add marine plywood to high stress areas.

 

[Maine Sail]

Stainless steel..

What are they doing on new production boats?

IMHO the question is not and should not be what are the "low cost" builders doing but what are the high quality builders doing? Morris & Hinckley as well as many other high end builders use solid GRP. The backing plate is not so much for compression as it is to evenly distribute side loads and to minimize any hull flexing. Using stainless or aluminum can lead to dissimilar metals galvanic corrosion and it would have to be rather thick to aid in stiffening the hull any. Stainless is also a bear to work with and bonds rather poorly with marine adhesives. As for wood, even epoxy coated, I have seen very, very few wood backing plates that I could actually, or would actually, re-use and very few that did not exibit moisture.

Another shortcoming of wood is the expansion contraction coefficients compared to fiberglass. In the winter it can shrink and dry out considerably and in the summer swell considerably. Over time this can lead to flexing of the seacock and a failure of the sealant..

Being from Maine, a mecca of high quality builders and multiple boat building schools, I can tell you for a fact that my own boat yard as well as many others use solid glass backing plates when doing repair work so this is not out of the ordinary for high quality yards to do. Of course lots of yards are simply not high quality yards. Many employ $8.00 per hour hacks that were working at the car wash just last week.

These are some of the boards my boatyard lays up and a box of scraps..

Scraps & Leftovers:

 

[jibes138]

How much larger than the flange?

How large a FRP disc do you recommend as a backing plate?

 

[Hermit Scott]

Having a metal backing plate is like having no backing plate at all. Putting a 1/2" thick metal backing plate is the same as getting a flanged adapter that is 1/2" thicker on the bottom.

 

[jibes138]

The assumption is the backing plate is considerably larger

A backing plate is used to spread the loads over a larger area so it is assumed any backing plate will be much larger than the item being supported. The question is how large is large enough? Let's assume the failure mode is to pull the flanged adapter straight through the hull in shear. The larger the backing plate the more shear area available to resist the force.

 

[Hermit Scott]

I am ready to fix the backing plates tomorrow(sunday) to the hull. I bought a new drill, all the apropriate hole saws, epoxy, sikiflex, bronze hardware. I also picked up a can of short hair bondo polyester resin, and I have most of a can of long hair polyester resin.
The epoxy takes days to fully cure. The polyester bondo hair cures in 30 minutes or something like that. Is it worth turning it into a 2 day event to use epoxy instead of the hair polyester? If I use epoxy, all I have available for tomorrow is 24 oz. roving, can I cut that and unravel it and stir in into epoxy to make a suitable mixture for fixing these plates? What is the best way to do it with epoxy? Do I need to keep pressure on these plates to get them to adhere properly?
With the materials I have available, please give me a short detailed instruction of what and how I should do this.
I have long hair bondo polyester, short hair polyester, 1/2 gal. polyester resin in a can,
one gal.epoxy, 24. oz roving. I think I can get chopped matt from the yard tomorrow.