Installing larger Seacocks, how to dril the larger hole

[mike_kelly]

MatsuBob,


Thanks for the details. The forespar Marelon 849 instructions state not to use the thru hull nut. It is suppose to thread directly into the flanged seacock.


"You will not be using the thru-hull nut when installing on a flanged seacock. You will need to cut the length of the thru-hull so it engages the seacock by a minimum of 5-6 threads. More is fine but the threads do not need to bottom out in the valve body.
You want to dry-fit first to be sure the valve handle is facing the direction you want and index the head of the thru-hull so you can duplicate this position later. Mark the thru-hull head and the hull on the outside.
Now you’re ready for sealant. You can use an aggressive sealant/adhesive here (like 3M 5200) as you should not need to remove the thru-hull again. Do not use this aggressive sealant on the threads going into the valve however. Use Teflon tape or other removable sealant on the threads to valve connection. Follow all instructions from the sealant manufacturer for proper surface prep and use. Read carefully the cure times required"


The inner surface of the hull is pretty flat but rough. They used a glass fiber that is rough not like roving. So would you sand that smoother?


Most bronze flanged seacocks have you bolt the three flange holes thru the huill but forespar wants you to use downward facing screws or I have seen other instructions that use an upward facing bolt with head between inside hull and lower side of the pad.


I have been sitting on this project for five years because of all these issues.

[MJH]

Originally Posted by mike_kelly

Had gate valves in my little sailboat. Wrestled with removing the thru hulls. Was going to just glass them over but I am just not confident enough to work with fiberglass under the waterline. Tried to get yards to do the work but after years it is just too difficult.



So I decided I could replace the gate valves with seacocks. Like everywhere size of drains could be bigger so went from 1" to 1 1/4". Hence I now need to drill a larger hole and realized that is not easy.


Do I have to fill the existing one inch holes with epoxy just to get soilid surface to guide the hole saw for the larger 1 1/4" hole? Could I glass the pad in and use that as the guide hole for the hole saw?



Extra points question: How critical is the thickness of the pad inside the hull for the seacock to sit on? I have seen 5/8" but not easy to find that around here. I don't feel like laminating up glass pads but I can only find 3/4" pre-made glass pads. It seems too thick though.


Extra Extrapoints: Anybody know if groco's premade pads with work with marelon valve bases? Groco dies not have measurements of the hole spacing between their holes.


Thanks much for any insights.

The previous owner never used a hole saw and left many terrible ugly holes in the boat so I've done a number of these and added to my collection of hole saws. Block the back of the hole with tape, cardboard, etc. and mix a small batch of Durham's water putty (Home Depot) to fill the opening...it sets up like plastic pretty quick depending how thick it is. I will usually also put a blocker on the outside to make sure the stuff doesn't fall out. When dry just drill the new hole.

I originally had this stuff for use around the house for filling knot holes in the siding because you can easily match the color with a water based stain/paint.

~ ~ _/) ~ ~ MJH

[S/V Alchemy]

Originally Posted by bcboomer

Before you buy Marelon, look at Trudesign.

Unlike the marelon they never stick open or closed.

If you've ever had to deal with a stuck marelon valve with a full holding tank and no available pump out you'll understand how important this is.

I just put in four Trudesigns on a standpipe in my steel pilothouse cutter and am quite pleased so far (a month in!). I found they spun on the NPS threads specified pretty easily, whereas I have found the Forespar products can bind a bit. The Trudesigns seem beefier, but cost about 20% less.

[osprey877]

Originally Posted by mike_kelly

MatsuBob,


Thanks for the details. The forespar Marelon 849 instructions state not to use the thru hull nut. It is suppose to thread directly into the flanged seacock.


"You will not be using the thru-hull nut when installing on a flanged seacock. You will need to cut the length of the thru-hull so it engages the seacock by a minimum of 5-6 threads. More is fine but the threads do not need to bottom out in the valve body.
You want to dry-fit first to be sure the valve handle is facing the direction you want and index the head of the thru-hull so you can duplicate this position later. Mark the thru-hull head and the hull on the outside.
Now you’re ready for sealant. You can use an aggressive sealant/adhesive here (like 3M 5200) as you should not need to remove the thru-hull again. Do not use this aggressive sealant on the threads going into the valve however. Use Teflon tape or other removable sealant on the threads to valve connection. Follow all instructions from the sealant manufacturer for proper surface prep and use. Read carefully the cure times required"


The inner surface of the hull is pretty flat but rough. They used a glass fiber that is rough not like roving. So would you sand that smoother?


Most bronze flanged seacocks have you bolt the three flange holes thru the huill but forespar wants you to use downward facing screws or I have seen other instructions that use an upward facing bolt with head between inside hull and lower side of the pad.


I have been sitting on this project for five years because of all these issues.

.
I used stainless Tee nuts set into the plywood pad before attaching it to the hull. You can dry assemble the pad with the tee nuts and the marelon seacock to make sure the bolts you use are the correct size. The base to hull fit is not that critical, just make sure you have plenty of whatever sealant you are using so that the joint is waterproof. The forespar instructions say to fit the thruhull fitting first, then screw the seacock onto it from the inside. I didn’t have room to turn the seacock so had to thread the mushroom thruhull into the fixed seacock. It worked fine, no leaks. The only complaint I had about the forespar system is that they don’t make a tee or cross fitting that fit into the seacock valve, only a straight or elbow, which means only one use per seacock unless you splice into the Bose upstream somewhere. The Groco bronze fittings include tee and crosses, so you can have multiple uses for one seacock. My forward head thruhull has the toilet supply, sink drain and deck wash supply on it. Difficult to plumb with marelon but simple in bronze.

[CarinaPDX]

I have used the two concentric hole saw method on several occasions and recommend it as well.

Even the best plywood backing plates, sealed with epoxy, can deteriorate with time. I strongly recommend using G-10/FR-4 composite sheet, cut out in "donuts" with two hole saws. This will be a permanent, very strong solution. It will have a very flat, smooth surface so no need for smoothing.

Greg

[mike_kelly]

i REALLY APPRECIATE ALL THE ADVISE. It really helps to get the broad spectrum of options.



It is not real easy to find pre-made frp online except in large sheets. I do like the idea of the durability.


I thought about the Tee nuts myself and it would be slick and seems better than using wood screws as Forespar specifies.


The Trudesign are not cheaper than I get Forespar, I am a very very good shopper. I got my new Forespar 849 1 1/4" seacock for $75 each.

[Yellowjacket]

I used a large half-round file with just a little bit of elbow grease. Kept fitting the new water speed indicator to find the high spots. Took less than a half hour. The new indicator fit almost perfectly, and with a good cleaning and ring of 4200, formed a perfect seal.

[mike_kelly]

Yellowjacket, That sounds like the judicious persons choice. Although laying on my back with my arms stretched up to reach the opening is going to require some ibuprohen.



I finally found some .625 G10 Phenolic 6"x12" sheets for $20. Six inches is close for the 849 seacocks but I think it is enough spacing around the seacock flange.



So reckoning day is near.

[Yellowjacket]

Originally Posted by mike_kelly

Yellowjacket, That sounds like the judicious persons choice. Although laying on my back with my arms stretched up to reach the opening is going to require some ibuprohen.

It was a friend's boat, so I put away the Dremel and the grinding wheels he bought for his electric drill, because I prefer making catasrphic mistakes slowly.

The first thing I did was draw a circle with a sharpie around the new fitting. I had a good file with large, sharp teeth and was surprised at how straightforward it was. I was also able to work from the inside, so the fiberglass fell down and out, away from me. A bit of boat yoga, and stretching afterwards.

While probably not necessary on a solid core boat, I also put a skin of epoxy around the freshly chafed hole.

[CarinaPDX]

Phenolic should be fine, but for custom G-10 sizes look here: https://www.professionalplastics.com/G-10--FR4


Greg

[mike_kelly]

Yellowjacket, Unfortunately I will have to work with the crap falling in my face. I'll have to use a face shield.


CarinaPDX, They are 3x more expensive. Too rich for my budget.

[stormalong]

The way I make backing plates for through hulls is to use two layers of plywood. First layer is 1/4 thick, second is 1/2 or at least as thick as the nut. Cut pieces large enough to put screws through the mounting flange of the seacock into the plywood. For easy alignment drill a pilot hole through both pieces while they are clamped together. Drill a hole in the thin piece to pass the tailpiece through. Drill a hole in the thick piece large enough to clear the O.D. of the nut. Epoxy the two together and paint with epoxy.

When all cured secure the tailpiece to the hull with lots of your favorite caulk and fill any gap between the backing plate and the hull with caulk. Draw down the nut. Here is an important tip: No need to torque the nut too tight. Only tight enough to align everything and get the tailpiece flange fairly solid against the hull. The caulk is what makes it watertight, not torque. When that has all cured thread on the seacock with some teflon tape on the tailpiece, then drill pilot holes in the plywood and screw the seacock flange to the plywood.

Another tip: Spray the caulk with water to accelerate the cure.

I have done several seacocks this way with no problems.

[mlydon]

Groco make g10 backing plates sized to fit their seasick flange holes, with inserts already installed.

https://www.wholesalemarine.com/groc...BoC58gQAvD_BwE

Compass marine has an excellent howto on how to make your own, AND excellent installation instructions

Matt

[mike_kelly]

Stormalong, If the adhesive is what is holding the thruhull in why do you use a nut on the tailpiece vs the way Forespar does it?


mlydon, Yes I would use those Groco pads if they gave the hole to spacing spec.There is no way to determine f they would fit the Forespar flanged Seacocks.


Now that I found the G10 material cheap enough I think I will just go G10. Makes sense over plywood given the longer lifespan. I am not into doing this stuff over and over again. You can get in a loop of doing mods and repairs and all of a sudden you are back doing the same repair again with no break or time when things all are ok at the same time.

[mlydon]

Do check out the compass marine site. One of his tips is to use bronze carriage bolts (the shaft part only) and epoxying them into the backing block.

Matt