Cap off a thru-hull?

[OldDan1943]

One of the first things I did on my AT34 was to replace all the "plastic" hull valves with bronze hull valves. I guess I am just old fashion. Yes, they are all bonded properly and all hull valves are serviced every time I take the boat in for bottom paint.

 

[Steve DAntonio]

I have a thru-hull with a 1.5" tapered cone seacock that is not being used. The seacock is broken so I need to take action and remove it. Is there an obvious reason that I am missing why I shouldn't just remove the seacock and cap the the thru-hull off with a bronze 1.5" pipe cap? I have read where others recommend putting a new seacock in then using a bronze plug on the seacock. What's the difference other than about $150 ? I also do not want to pull thr thru-hull and glass it over permantly. Thanks.

A pipe cap's NPT threads are incompatible with the common through hull's NPS threads. Thread incompatibility is a violation of general engineering practices, as well as common sense (and yet I see it done on a near-weekly basis with through hulls and in line ball valves) and ABYC Standards. Groco and others make thru hulls that include a short section of NPT thread on the inboard end, so if you switched to that you'd technically have thread compatibility, but other reasons to avoid this remain, read on.

Given the choice, I'd much rather have a proper seacock, a purpose made valve, rather than a pipe cap, standing between me and flooding.

And, ABYC Standards call for a seacock on all below the waterline penetrations, with an exception for exhausts and shafts, as well as a few others...

27.5.1 All thru-hull fittings or hull penetrations designed to accept pipes, hoses or valves, terminating below the
maximum heeled waterline, shall be equipped with a seacock to stop the admission of water in the event of failure.
EXCEPTIONS:
1. Boats that conform to the level flotation performance criteria of ABYC H-8, Buoyancy in the Event of
Swamping,
2. Hull penetrations that discharge above the waterline in its static floating position and below the
Maximum Heeled Waterline and meet the requirements of H-27.5.3.
3. Shafting systems.
4. Jet and stern drive propulsion with integral components from intake through the discharge.
5. Inflatable boats that comply with H-28, Inflatable Boats.

 

[Bryant]

Seacock

My boat had multiple thru hulls capped off when I bought it. The first time I hauled it I had every one of them pulled and permanently glassed over. Any other solution is a temporary fix that could possibly fail. My thought process is that I don’t want any more holes under the waterline in my boat than absolutely necessary. My advice is do the same on your next haul out.

 

[FF]

"My thought process is that I don’t want any more holes under the waterline in my boat than absolutely necessary. My advice is do the same on your next haul out."

Depending on the workmanship plugging the holes might be a bit safer than a genuine sea cock , however no one owns a boat forever , and the sea cocks were installed for a purpose, that the next owner might enjoy.

With tapered bronze marine sea cocks , properly thru bolted , there is not any more risk than all the other sea cocks the boat already has.

 

[Steve DAntonio]

My boat had multiple thru hulls capped off when I bought it. The first time I hauled it I had every one of them pulled and permanently glassed over. Any other solution is a temporary fix that could possibly fail. My thought process is that I don’t want any more holes under the waterline in my boat than absolutely necessary. My advice is do the same on your next haul out.

Bryant,

Having dealt with this scenario on many occasions, I must respectfully disagree that this is the preferred, and most reliable approach. Patching holes in FRP bottoms is no small undertaking, the correct scarf ratio, which drives the size of the patch, is 12:1, that's often not done because it makes for a relatively large patch. This also represents a secondary bond, which will never be as strong as the original laminate, and I'd argue not as strong or reliable as a properly-installed, flanged seacock.

 

[bgillroy]

We took Bryant's approach. Removed unused original bronze. Made proper repair with backing. Cut seacocks by 4 (2 BWL). Refit all others in use.

 

[tn6437]

just curious, what was the approximate cost of the work you had done on replacing your thru hull fittings ?

 

[Bryant]

Throughhulls

just curious, what was the approximate cost of the work you had done on replacing your thru hull fittings ?

I don’t remember, I’ll have to look it up. What I do remember is that when I asked the fiberglass tech how much it would be, I didn’t think it was much.

 

[FF]

"Please help me understand how a seacock is any safer than a sealed brass cap?"

If properly installed the seacock will be bolted in place with 3/8 bronze bolts, not just hanging on the threads of the thru hull.

This is done so the thru hull can be easily be removed to inspect it with no harm to the seacock mount or sealing.

 

[Steve DAntonio]

"A sealed brass cap"? Brass, being an alloy of copper and zinc, cannot be used in seawater applications. However, assuming you meant a bronze cap, even that would mean a thru-hull without a valve/seacock, which is verboten, and most thru-hulls are NPS thread, and most pipe caps are NPT thread, and thus incompatible.

The most secure arrangement for a disused seacock is...a sound seacock, which is then fit with a pipe plug, the common NPT threads of each being fully compatible.

FF: While there's nothing wrong with it, seacocks need not be through bolted, there is no requirement in ABYC, ISO or other yacht building standards that requires thru-bolting. Some builders and yards do thru-bolt, however, if they do so, unless the bolts are countersunk into the hull and thus fully encapsulated, they cannot be stainless steel, as they will crevice corrode. Seacock thru-bolts should be bronze. Most seacocks are not thru-bolted and they can do fully comply with ABYC's seacock standard, which includes a 500 lb, 30 sec endurance test.

This step by step guide walks the installer through a complete seacock installation https://stevedmarineconsulting.com/wp-content/uploads/2020/12/TaskSheet187-Seacocks-FINAL.pdf

 

[Comodave]

I have removed 5 unused through hulls and transducers in my boat. I just glassed the openings closed. It is very easy to do except maybe glassing up on the downside of the hull. Some epoxy will inevitably run down your arm...

 

[ak-guy]

I am guilty of having an unused bronze thru hull with a bronze cap sealed with 5200. I see others mentioning 5200 being permanent and never coming apart. With a little heat that cap would come off just fine.

 

[Comodave]

On metal you can use heat to soften up 5200, on fiberglass not so much. I watched on Ship Shape TV a segment of them trying to get off an outboard bracket that had been stuck on with 5200. They used Debond, hammers, wedges and a lot of time getting it off.

 

[HopCar]

On metal you can use heat to soften up 5200, on fiberglass not so much. I watched on Ship Shape TV a segment of them trying to get off an outboard bracket that had been stuck on with 5200. They used Debond, hammers, wedges and a lot of time getting it off.

I’ve used heat to remove metal fittings glued to fiberglass with 5200. It worked well. Just minor damage to the gelcoat. I’m sure I would have done at least as much damage using other methods.

 

[FF]

Mr D,

The procedure shown uses thru bolts or screws to secure the thru hull to a backing block . While plywood is suggested, ply may not last well if submerged in water .

The use of some other material would not add much to the cost .

"In the locations marked earlier, drill holes for through-bolts or tapping screws that will secure the seacock’s base flange to the backing block and hull.."

We have found using bronze bolts to cause little external drag.

For cored hulls the use of a solid backing plate glued inside is the fastest mounting system, that should still take the 500 lb load.

 

[slowgoesit]

I need to emphasize one point that was made early on by Comodave, and mentioned in passing a few other times. Namely: No matter whether you install a new bronze seacock and cap it off, of if you use a compatible cap on the threaded area after the seacock is removed (and the bronze nut is still holding the through hull in place) you ABSOLUTELY MUST bond the bronze through hull to the boat bonding system!

 

[psneeld]

There is more than one school of thought on bonding....


https://www.westmarine.com/WestAdvisor/Marine-Grounding-Systems



Bonding and Electrolytic Corrosion Due to Hot Marinas

Do not bond any thru-hulls or other immersed metal that can be electrically isolated. Specifically, keep your metal keel/ballast, your metal rudder shaft, your engine/prop, and all thru-hulls electrically isolated, from each other, and from the engine.

 

[diver dave]

True: you cant have electrolysis without an electrical current. And if not bonded, there is no current.
There is a bit more to the story. There can still be galvanic corrosion, not requiring external current, caused by the alloy makeup. For instance, a aluminum alloy that contains copper. It can corrode with no external connection.

 

[psneeld]

True: you cant have electrolysis without an electrical current. And if not bonded, there is no current.
There is a bit more to the story. There can still be galvanic corrosion, not requiring external current, caused by the alloy makeup. For instance, a aluminum alloy that contains copper. It can corrode with no external connection.

I think you will find most recommendations not to bond are for well, made bronze thru hulls with no chance of having current applied and far enough away from other metals/alloys to cause any or any significant galvanic action.


Like all opposing thought or theories....there are levels of exceptions....and possibly much higher reasons to do it one way over the other depending on perceptions.

 

[STB]

I need to emphasize one point that was made early on by Comodave, and mentioned in passing a few other times. Namely: No matter whether you install a new bronze seacock and cap it off, of if you use a compatible cap on the threaded area after the seacock is removed (and the bronze nut is still holding the through hull in place) you ABSOLUTELY MUST bond the bronze through hull to the boat bonding system!

Why?

 

[Steve DAntonio]

Mr D,

The procedure shown uses thru bolts or screws to secure the thru hull to a backing block .

SDA: Thru-bolts OR screws. My point was, through bolts are not mandatory.

While plywood is suggested, ply may not last well if submerged in water .

SDA: If you read the materials list in the article it says,
"backing block material. (GPO-3 or
G10, ¾"/19mm or purpose-made
backing block such as Groco BB
series, or ¾" marine plywood fully
encapsulated in epoxy.)

The use of some other material would not add much to the cost .

SDA: Agreed, I use GPO3 or G10.

"In the locations marked earlier, drill holes for through-bolts or tapping screws that will secure the seacock’s base flange to the backing block and hull.."

We have found using bronze bolts to cause little external drag.

For cored hulls the use of a solid backing plate glued inside is the fastest mounting system, that should still take the 500 lb load.

SDA: Cored hulls must have the core removed where the thru hull passes through the hull, there are no exceptions to that rule. It has less to do with the 500 lb. load and more to do with core saturation, and then loss of structural integrity. Instructions on how to do that here https://stevedmarineconsulting.com/wp-content/uploads/2021/01/TaskSheet189-Closeouts-05.pdf