Through hull/ seacock replacement

[Hermit Scott]

I have seen the prefered method of replacing through hulls/seacocks, using a flange type sea cock. It looks like once those are installed they are integral with the through hull since the mounting bolts going through the flange are covered up by the mushroom of the through hull.
It seems to me a better idea to have ball valves screwed onto through hulls where you can remove the ball valve and replace it down the road. Except this method seems to be the culprit in broken off through hulls because there isn't enough strength at the base. This is the set up I have in my boat right now.
What causes the through hulls to be weakened over time? Are the flange type ball valves rebuildable while installed in the boat? Are the sizes standard for each application(raw water cooling, inlet for head) or should I go up in size on any of those to aviod any problems down the road? Also is it OK to go through the same hole that the existing through hulls are in now or better to glass those up and drill a new one?
I am going to the boat Thursday to measure all my through hulls/seacocks so I can buy them online any tips on the best deals?

 

[Maine Sail]

I have seen the preferred method of replacing through hulls/seacocks, using a flange type sea cock. It looks like once those are installed they are integral with the through hull since the mounting bolts going through the flange are covered up by the mushroom of the through hull.
It seems to me a better idea to have ball valves screwed onto through hulls where you can remove the ball valve and replace it down the road. Except this method seems to be the culprit in broken off through hulls because there isn't enough strength at the base. This is the set up I have in my boat right now.
What causes the through hulls to be weakened over time? Are the flange type ball valves rebuildable while installed in the boat? Are the sizes standard for each application(raw water cooling, inlet for head) or should I go up in size on any of those to aviod any problems down the road? Also is it OK to go through the same hole that the existing through hulls are in now or better to glass those up and drill a new one?
I am going to the boat Thursday to measure all my through hulls/seacocks so I can buy them online any tips on the best deals?

Scott,

I would use Groco flanged adapter plates for each seacock as it allows a valve change in no time at all even while in the water. Flanged adapters give you the best of both worlds. On the bottom there are NPS threads for the thru-hull to thread into and on top NPT threads for a ball valve to screw onto.

They also through bolt to the hull or if you want you can tap a backing plate, preferably fiberglass if you're going to tap it, and are considerably stronger and thicker in wall section than just a thru-hull. The average wall thickness of an off the shelf bronze thru-hull is barely that of a US penny..

On the left properly matched threads and a flanged adapter. On the right mis-matched threads and a thru-hull and valve:

NPT (tapered threads):

NPSM Straight Threads:

Mismatched Threads = NPS to NPT on Left / NPT to NPT on Right:

The bottom line is this; A Flanged adapter plate, when measured at the NPT threads, is roughly DOUBLE the wall thickness when compared to an off the shelf thru-hull fitting.

Below is how little bronze is between you and the ocean, before any corrosion, when a thru-hull only & valve set up. (actually the penny was a tad thicker at 1.57mm & my measurement for wall thickness of the thru-hull was 1.54mm. The flanged adapter wall thickness was about 3mm!

Thru-hull wall thickness:



Phil should be able to get flanged adapters try here first!!

 

[Bill Roosa]

Flanges

Hi Hermit
I see you are "embracing the horrors" of sailboat ownership with enthusiasm.

What causes the through hulls to be weakened over time?
Corrosion and wear. Corrosion being the primary by far.

Are the flange type ball valves rebuild-able while installed in the boat?
Yes, see Main Sail's post above. Good stuff there.

Are the sizes standard for each application(raw water cooling, inlet for head)
or should I go up in size on any of those to avoid any problems down the road?
If you don't have issues with the current setup you are probably OK on thru-hull diameters. Your engine raw water intake should have a strainer on the outside of the hull to prevent cooling issues.

Also is it OK to go through the same hole that the existing through hulls are in now or better to glass those up and drill a new one?
I'd reuse the existing holes. Fiberglass is pretty good at re-use. You may have to re-glass to have a place to drill through. You will not know till you get the thing out and try to put the new one in.

With all that, the ABYC has some standards that make good sense. The chief being that the thru-hull does not break when someone inadvertently sets a 300 lb engine block (or anything weighing 300 lb) on it for 45 seconds. Don't quote me on the numbers. They are close. Don't know where they got there numbers and some of my thru-hulls could not possibly see those kinds of loads but the concept is valid. I try to imagine a worst case scenario where I'm holding an engine block and step on the thru-hull........ Not really concerned that the under-sink thru-hull will see this kind of load but I guess I could drop a big box of WD-40 on it.......
Common sense would seem to be the way to approach this.

 

[Ron20324]

ALL intakes should have an outside strainer on them.

 

[Chuckbear]

ALL intakes should have an outside strainer on them.

That is not necessarily true. Some engine and genset manufacturers as well as Air Conditioning units will have their warranties voided with external strainers in the thru-hulls.

 

[Maine Sail]

Hi Hermit
Your engine raw water intake should have a strainer on the outside of the hull to prevent cooling issues.

ALL intakes should have an outside strainer on them.

There are very differing schools of thought on this and I'll explain my experience.

Exterior screens or strainers are usually fixed in place and are theoretically designed to prevent clogs. Do they work well for this? Sometimes but not always! It all depends on the type of medium that is floating in the water as to how well they work. Up here in the NE we tend to get lots of vertical floating eel grass. External intake screens do virtually nothing to prevent these vertically floating 10-15" long pieces of grass from being sucked into the screen.

The problems arise once they get in there and you can't snake them back out from inside or outside the boat!! I have gone to great lengths to eradicate the problem of intake clogs on my boats and been quite successful comparatively speaking.

When I worked on large yachts we had this happen often to our air conditioning units, generators and other intakes that were screened. It is a bear to clean out and usually required a scuba dive with a coat hanger & knife and one person working the inside at the same time. I have also had these clogs also on my personal boats that had external intake screens. It once took me two hours to partially remove a clog from an intake that had a screen on it, dive poke, pull, poke climb back aboard and work from the inside, dive poke pull etc. etc, for two+ hours and I was solo! Not very safe! If you feel you must use a screen please chose a HINGED screen that can be opened underwater!!

A good basic rule of thumb for external strainers:

1) Never face a scoop strainer forward when installed on an engine or generator on a sailboat. You can FLOOD the engine and fill it with water if the seacock is open under sail.

2) While you are better to face a scoop backwards you can create added vacuum to the raw water intake and may shorten impeller life or compromise the cooling efficiency. I still find facing backwards better than a hydro-locked engine and have not come across a real situation that the added vacuum had any negative effect when impellers were replaced on a regular schedule.

3) ON sailboats use ROUND omni-directional type strainers, preferably with a hinge, if you MUST use one. The round strainers will not force water into a non running engine and create no additional vacuum.

4) If you sail a catamaran or tri and have "scoops" and one engine goes down, or you normally run with only one aux to save fuel, you should ALWAYS close the non-running seacock or you will have a higher risk of flooding the non-operational engine.


So what do I do? My first priority is to make the intake large enough to get any weed or debris through the hose and into the strainer basket. For me this has resulted in 1" ID intakes with smooth radius elbows or sweeps as opposed to 90's. With no screen on the outside I can simply run a snake down through the the intake hose and unclog from the inside. No diving!!

I have had lots of screened intakes clog over the years and the headache that ensues has forced me to find a better way that does not involve diving. External screens are NO guarantee..

With all that, the ABYC has some standards that make good sense. The chief being that the thru-hull does not break when someone inadvertently sets a 300 lb engine block (or anything weighing 300 lb) on it for 45 seconds. Don't quote me on the numbers. They are close. Don't know where they got there numbers and some of my thru-hulls could not possibly see those kinds of loads but the concept is valid. I try to imagine a worst case scenario where I'm holding an engine block and step on the thru-hull........ Not really concerned that the under-sink thru-hull will see this kind of load but I guess I could drop a big box of WD-40 on it.......
Common sense would seem to be the way to approach this.

The ABYC standard is 500 pounds static load at the inner most hard fitting, or furthest hard point from the hull, which is usually a hose barb. The longer or taller your group of fittings, like if you added a tee after the seacock for two intakes off one seacock, the more leverage you'll have at the inner most hard plumbed item.. I actually broke a thru-hull on my C-30 with a spare alternator in rough weather and this is what forced me into gaining a better understanding of thru-hull penetrations.. Early Catalina's did not even use thru-hulls they used threaded pipe that was simply glassed into the hull. By now I would imagine most have been converted as they usually leaked after only a short while..

 

[Ron20324]

We don't get much floating weed in the Chesapeake Bay, but I've certainly seen horror pictures of other cruising grounds. Going from Key West to the Dry Totugas on my first offshore I was surprised at how much weed was floating around. I like the idea of the hinged one, but can't say that I've seen one. Maybe I'll keep an eye out.

 

[Roger Long]

External intake screens do virtually nothing to prevent these vertically floating 10-15" long pieces of grass from being sucked into the screen.

Having an externally fixed screen strainer, and being naturally curious, my ears certainly perk up.

Were your strainers mounted so that the slots were forward or aft? I started to put mine in with the slots forward for scoop effect and the boatyard guy said, no, other way round, at least on sailboats and slower powerboats. I've never had a clog and very little shows up in my stainer.

From the front, all you see is smooth bronze. For anything to go it, it has to turn the sharp corner. This doesn't seem to be problem for water flow as the water is mostly being sucked from the still boundary layer aft of the strainer.

 

[Maine Sail]

Having an externally fixed screen strainer, and being naturally curious, my ears certainly perk up.

Were your strainers mounted so that the slots were forward or aft? I started to put mine in with the slots forward for scoop effect and the boatyard guy said, no, other way round, at least on sailboats and slower powerboats. I've never had a clog and very little shows up in my stainer.

From the front, all you see is smooth bronze. For anything to go it, it has to turn the sharp corner. This doesn't seem to be problem for water flow as the water is mostly being sucked from the still boundary layer aft of the strainer.

They faced aft as they should on slow speed vessels.. I also had a round one with holes in it but no hinge unfortunately it tends to be cumulative and builds up over time. Eel grass has a way of getting in there especially at anchor if running the engine to charge or cool engine driven refrigeration.

Personally I much prefer the safety aspect and ability to snake the intake from inside the vessel rather than having to dive..

Here is a hinged intake screen..

Photo courtesy of West Marine

 

[Stu Jackson]

In addition to snaking, there is the idea of using the dinghy foot pump to try to force whatever might be in there out. We don't have the heavy eel grass and it may not work for that, but it has worked for us in SF Bay. Since our rw intake strainer is on top of the thru hull valve, we disconnected the hose from the intake to the rw pump and blew thru there. Worked great, just another little trick for your arsenal. We've discouraged what I term "thru hull cover plates" because sometimes they create more problems than they can fix. I agree with Maine Sail and don't understand why you'd want to install yet another source of potential blockage, especially to your critical rw intake.

 

[Maine Sail]

You know..

You know you have a large photo database when you can dig up pictures of eel grass..

 

[Ron20324]

[qI agree with Maine Sail and don't understand why you'd want to install yet another source of potential blockage, especially to your critical rw intake.[/quote]

We all have our theories.

Different strainers for different brainers.

 

[Hermit Scott]

I didn't see the adapter flange before on your pbase site mainesail. How long ago did you add that?
So along with occasionally unclogging the through hulls, I read that the seacocks are supposed to be lubricated. Why don't seacocks have a grease fitting? Since they don't have a grease fitting, how and with what do you lubricate them?

 

[jlp]

This thruhull/seacock thread combined with twisting the handle off of one Marelon seacock last year prompted me to spend time yesterday attempting to lubricate the Marelon seacocks on DejaVu.

Forespar data recommends lubricating the seacocks twice yearly....not easy when the boat is hauled every 2 -3 years. Having replaced stuffing box packing and depth/speed/ transducers as well as the the broken seacock while the boat is in the water with no difficulty I thought I'd have little problem. Remove hoses, unscrew seacock, quickly replace with appropriate pipe cap, relax, lubricate seacock, replace. An easy afternoon project....

Not so easy....it seems Catalina decided to place the galley seacock so close to the water lift muffler box that it impossible to unscrew it without first removing the muffler assembly. Not a trivial task.
(see pic)

Having considered replacing all of the “plastic”thruhulls and seacocks with bronze I stopped by one of the best boat yards in the area to see what it might cost. Not cheap, estimated $500/thruhull. Because it is almost impossible to simply remove existing thru hull (bedded with 5200) they usually use a large hole saw to remove existing thruhull and backing plate, leaving a 4” - 6” hole which needs to be reglassed/finished before drilling a new hole and installing bronze thruhull......$2000 to replace 4 Marelon thruhulls/seacocks.

Think I'll ignore it all for awhile and go sailing.

Jeff
Portland, OR
DejaVu, C30 MKIII, TRBS

 

[Maine Sail]

I stopped by one of the best boat yards in the area to see what it might cost. Not cheap, estimated $500/thruhull. Because it is almost impossible to simply remove existing thru hull (bedded with 5200) they usually use a large hole saw to remove existing thruhull and backing plate, leaving a 4” - 6” hole which needs to be reglassed/finished before drilling a new hole and installing bronze thruhull......$2000 to replace 4 Marelon thruhulls/seacocks.

Jim,

You might try another "one of the best boat yards". Any boat yard that uses that method to remove a thru-hull should NOT even be in business! Sorry to be so blunt but they are NOT the best nor anywhere close to it if that is their strategy for dealing with 5200. If that is how they operate FIND ANOTHER YARD that has more tools than just a 3lb. sledge hammer in the tool kit & Darrel & Darrel on the time clock...

That is the most asinine thing I've herd from a boat yard in years.. I can assure you removing thru-hulls bedded with 5200 is a royal PITA but having done well over 100 I can assure you that they DO come out and you DO NOT need to damage the surrounding hull..

Why pay hacks like that to destroy your boat when you can the job your self, with better finally quality, for the cost of supplies and a weekend of your time??

As for lubing Marelon a little Morey's Red waterproof grease on a flux or acid brush goes a long way! Just put on your wet suit, grab the flux brush, stick it in the grease, dive under the boat (the grease is waterproof), stick the brush up into the seacock and slather the ball. Now go back into the cabin & pull the hose and do the same. Re-attach the hose and exercise the valve about 20 times and you're good to go...

Are yards this bad? We generally have very good yards up here in Maine but then again we have three or four boat building schools pumping out educated and skilled craftsmen?? What's up with a 4-6" hole to remove a frigging thru-hull?? Clowns!!!!!

 

[Hermit Scott]

Update

I removed all the seacocks but one. I need to go back with a pipe wrench for one of them. The engine intake and marine AC have plywood as a reinforcement plate with mushroom heads on the outside. The sink drain and both head through hulls appear to not have mushroom heads, one of the pictures shows the outside waste through hull with no mushrom head. What is the deal with that? Is it a flush type head? Inside there is glass molded around them that looks like it is from the factory! The inlet for the head has JB Weld all around it. The ones with mushroom heads will come out easily, how do I go about removing the others?
On a side note here, I found out my keel stub is probably made of plywood and may be wet, if a PO didn't have it replaced. I was going to drill into the bilge to check it but there was water in it when I got there. I vacumed it out and dried it but I didn't have epoxy with me and didn't want to leave a hole that water could leak into. So is there any way to check the keel bolts for corrosion with out dropping the keel? Are the keel bolts sealed in any way like with 5200? Because a bilge is made to hold water but if water leaks past the bolts then the plywood(if it's there) will definitely be wet.
I Started on Fastnet Force10. I had tears in my eyes when that guy died on Grimalkin and told the one guy left on the boat to tell his wife that he loved her. I couldn't believe those 3 guys took the life raft and left them for dead! I would leave a dead body but I would die myself before I could leave someone behind like that while they are still breathing.

 

[Maine Sail]

The sink drain and both head through hulls appear to not have mushroom heads, one of the pictures shows the outside waste through hull with no mushrom head. What is the deal with that? Is it a flush type head? Inside there is glass molded around them that looks like it is from the factory!

Remember when I said; "Early Catalina's did not even use thru-hulls they used threaded pipe that was simply glassed into the hull. By now I would imagine most have been converted as they usually leaked after only a short while..". I think you found one!

 

[Paul F]

Cost of Bronze thru hull install

In the process of replacing the exhaust elbow I was cleaning up the rusted out pieces, etc. and decided to remove the raw water intake hoses to gain better access. In trying to remove the hose from the ball valve fixture the fitting broke off. Knowing the ball valve was old I figured to replace it. In attempting to take it off, the thru hull stated to leak. The boat is a 1980 and a broken thru hull at this stage is expected. Called a scuba diver who has done work for me before. He will install a bronze thru hull with ball valve or seacock for $260. Now, I admit he is very reasonable but the earlier post of $500 per installation is crazy.

 

[Maine Sail]

In trying to remove the hose from the ball valve fixture the fitting broke off. Knowing the ball valve was old I figured to replace it. In attempting to take it off, the thru hull stated to leak. The boat is a 1980 and a broken thru hull at this stage is expected. Called a scuba diver who has done work for me before. He will install a bronze thru hull with ball valve or seacock for $60. Now, I admit he is very reasonable but the earlier post of $500 per installation is crazy.

Are you going to do this in the water? What will you use to seal the thru-hull fitting?

$500.00 is really not that crazy when you add up the man hours involved in installing a proper seacock. Proper seacocks are through bolted to the hull and have a large flange which makes them much stronger. As you've experienced a ball valve simply threaded onto a thru-hull is not a very robust installation.

In most proper seacock installations the process is as follows. I have left out the time it takes to look for tools walk back and forth to the shop etc. etc. and also the cost of materials and haul out..

Remove hose -3-10 minutes depending upon location
Remove old ball valve - 3-10 minutes depending upon location
Remove old backing plate - 20-60 minutes
Clean hull of marine sealant - 30-120 minutes
Fabricate new backing plate / fiberglass - 1 hour
Clean exterior of hull for mushroom head - 15-30 minutes
Drill center hole for-thru hull in backing plate - 5 minutes
Wax thru-hull to prevent epoxy sticking to it - 5 minutes
Rough hull and backing plate with 60 grit - 10 minutes
Wipe backing plate and hull with acetone or de-waxer - 5-10 minutes
Mix thickened epoxy - 5-10 minutes
Apply epoxy to hull and backing plate - 2-4 minutes
Clean tools of epoxy - 5-10 minutes
Insert thru-hull and tighten to squish out epoxy - 15-20 minutes
Fair joit around backing plate - 15-20 minutes
Mark thru-hull for depth of fit and cut thru-hull - 20-30 minutes
Install thru-hull into seacock and make tight - 5-10 minutes
Mark backing plate and drill holes through hull - 20-40 minutes
Countersink exterior of hull where through bolts are - 5-10 minutes
Remove seacock -5 minutes
Apply marine sealant and re-install with through bolts - 20-30 minutes
Clean up marine sealant 5-15 minutes
Mix epoxy and fill exterior screw holes - 15-20 minutes
Sand screw holes - 5-10 minutes
Mix epoxy and fairing filler and hit the holes again - 15-20 minutes
Sand and fair screw head holes - 5-10 minutes
Mix barrier coat and apply to seal hull around seacock - 15-20 minutes
Re-apply bottom paint to affected areas - 5-10 minutes
Connect hoses and make final inspection 10-15 minutes

On the high end of these time estimates this is about 500+ minutes of time or 8+ hours at about $80.00 per hour. 8 X 80.00 = $640.00

Granted I used the high side of all these time estimates but $500.00 for a proper seacock with a flange would not be all that unreasonable.. Of course the $500 per estimate above included a 6" hole cut into the hull....

 

[Paul F]

In water thru hull replacement

Yes, we are changing the thru hull in the water. This same diver changed out my stern tube, pulling the prop shaft, etc. in the water three years ago so I trust he will do a good job. I will post photos of the completed work after Wed. We are changing it out Wed. afternoon. I assume he will use 5200 to seal the thru hull but will let you know when it is finished, what was used and how it went.