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raw water pickup removing

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paw2000

Contributing Member
Hi, making progress on my refit and trying to do some plumbing updates. The boat has 2 raw water pickups, look like 1.5in size. The outside has a strainer (rivets to the thru hull fitting) as it comes thru the hull, it has a wood backing plate and the seacock attached to it. The seacock has a flange for 2 (screws?) to the backing plate. It had only 1 screw holding it. How is the thru hull fitting attached to the seacock? Is it threaded into the seacock? I'm thinking either when the boat was made they tightened the seacock onto the thru hull and just used screws into the backing plate to keep it from turning. The backing plate is painted the same color as the bilges so it appears original.

I rather not use a sawzall to remove the seacock, as I know these can be serviced. I'm going to replace them and the backing board, but would like to save the old and either resell to someone looking for parts.

I'll take a picture of what I have.
 
As a reference, check out the Buck Algonquin pages . You will likely find your combination there and it can help you formulate a plan for repair, renovation or redesign
 
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paw2000 said:
The outside has a strainer (rivets to the thru hull fitting)
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Rivets are new to me. Most of the integral strainers are simply castings with the thruhull. Unless you are talking about the large, seperate perforated strainer that is external and not attached to the thruhull.

paw2000 said:
The seacock has a flange for 2 (screws?) to the backing plate. It had only 1 screw holding it. How is the thru hull fitting attached to the seacock? Is it threaded into the seacock?
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The best way is to use a couple of flat head silicon bronze 1/4 x 20 screws. The screw goes thru the hull, the flat head is flush to the external hull surface. The seacock gets fastened over the backing plate with 4200 and uses the 1/4 x 20 nuts and bonding wire.


THe actual thruhull is a straight thread, and simply screws into the seacock. The seacock should not depend on the thruhull for attachment to the hull.


paw2000 said:
I rather not use a sawzall to remove the seacock, as I know these can be serviced. I'm going to replace them and the backing board, but would like to save the old and either resell to someone looking for parts.
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THe thruhull unscrews, it may not be easy. THere is a special tool for this, although i've use things like broken files for the purpose. I tend not to use plywood for the backing plate. Delrin is the best choice, in my opinion, although rarely used.
 
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thru hulls should match the rest of the intake if only the engines are on the circuit (way it should be) and they should be 1.25" ID. Like DD said, the thru hulls are straight thread (no taper).

I, too, doubt there are rivets. If you are on the outside and have the scoop-strainer over the thru hull, what may look like two rivet heads are likely screws, with filler or bottom paint filling the slots. scrape and pick at it - you're like to find them.

I like DD's delrin backing plate concept; when I redid mine, we used oak encapsulated in epoxy, after removing the foam core (OEM mistake).
 
Having little knowledge of this material I did try to look up a few things and this caught my eye coupled with several other notes about extruded Delrin with fibers or not ...

"In general, acetals do not perform as well in abrasive wear applications as nylons. Compensation for moisture related growth generally allows Nylatron® nylons to be used for wet, abrasive applications. If your application requires dimensional consistency in an abrasive, high humidity or submerged environment, Ertalyte® PET-P will often offer improved performance."

Is there a recommended TYPE of Delrin to use? I used plywood soaked with Dr. Rots wood treatment, kind of like Mark's encapsulation. I have had very good success with their products
 
I know it's traditional and somewhat "satisfying looking" to use backing plates under seacocks. With solid FRP hull construction of good quality (decent thickness), one could argue that backing plates are not necessary at all. I must confess at this point that my current boat did not use backing plates under any of the seacocks, since 1973. There has been no observable water seepage under the bronze. But, we are talking about at least a solid inch of glass at these points. Perhaps a review of why there ever were backing plates used at all is in order. AND, these are just my observations and informed reasoning, I have by no means looked at all the various possible failure modes. If I was dealing with a wood hull, a cored hull, a metal hull, a "thin" FRP hull, or a hull that made the seacock sit "non-level" with the hull, I'd go for a backing material. Otherwise, why not seal directly against the hull? THere is no issue with galvanics, caulk sealing, hull compression, or stability when the seacock is right against the hull. You will reduce the sealing joints by half.
If your installation did demand a plate, you would want one that did not rot, did not compress (much), and would not split. I've had solid teak planks split; that's a bad failure here, so thats out. If you pick a solid piece of wood, pick a strong one, probably not too thick, maybe MM's oak is OK. Plywood has a big advantage there, it won't split. It's easy to find. Low viscosity epoxy is great for soaking into any wood that is picked. BUt, I'm not sure any of the wood solutions will give a routine 30 to 40 year service life.
Enter plastics. From what I read, almost any plastic has many orders of magnitude less moisture migration than most any wood. Aren't we tallking about 10% moisture vs .005% or less? A lot of plastics won't take sealants well. PE (starboard) is tolerant of attack, but the sealant won't stick. So, they are out. Rigid PVC will crack if stressed enough, that's out. For common stuff, filled nylon, poly carbonate and acetal (Delrin) would seem to be good choices. Poly carb could be attacked by some sealants, so watch out there. I'm left with Delrin. Strong, tough, resistant to sealants, drills and works a bit like metal, but easier. Comes in black, won't show oil!
 
Dave....

Great write up! You seemed to have logically sorted it out and systematically ranked them in usable order. I did notice by googling Delrin to find a supplier, several "structural grades" for lack of a word, are available. The claim there was that some contain fibers which in my head translates to higher strengths.

When I replaced the shims in my engine mounts, I thought of using TREX decking material, machined to the correct size. Made a few up....so easy. Then the comments flew about compaction, impaction, durability, water resistance etc. Got me worried enough that I switched over to plywood as I found out the FIBERS in TREX are wood.... who knew. Jeff had said, they lasted 30 years so far ?

I think Delrin is great stuff but I was just wondering IF a specific type may be better than another . Quite likely a call to their tech dept will decide that one.
 
And ask for some samples; many will send them for little or nothing.

One note on cored hulls. Ours was 'thru hulled' without the shop having a good idea of what they were doing. They went stright thru the skins and core and did a 'traditional install'. come haul out time, guess what - liquid drips from the hull. turns out the core was pretty wet.

The fix was to remove the water and then the core around the seacocks. a solid filler was then put in (FRP) then the inner skin resealed. Afterwards, the seacocks were reinstalled.

with 20/20 hindsight, I should have used DD approach. But we were trying to stay on schedule and the materials were readily available so we kept with 'tradition'.
 
knuckle47 said:
Having little knowledge of this material I did try to look up a few things and this caught my eye coupled with several other notes about extruded Delrin with fibers or not ...

"In general, acetals do not perform as well in abrasive wear applications as nylons. Compensation for moisture related growth generally allows Nylatron® nylons to be used for wet, abrasive applications. If your application requires dimensional consistency in an abrasive, high humidity or submerged environment, Ertalyte® PET-P will often offer improved performance."

Is there a recommended TYPE of Delrin to use?
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I'm no expert on making or even specing Delrin. I thought it was usually cast into sheets from pellets, like a polycarbonate. At my work, it's used for a lot of test fixture pieces, being machined on the same mills as steel/aluminum. It certainly passes the "hit it with a big hammer" test! Sheets will ultimately dent, but not crack. It's about as tough as an unfilled plastic resin can be. I don't put the abrasive properties high on the must-have list. Although, they do machine this stuff into gears!
One thing though, don't expect compression to "align" the seacock to the hull, like plywood. If you need to make up something of a wedge, mill it or maybe sand it to the correct angle.
 
Airmar, who makes our transducer, has an excellent instruction sheet regarding the installation of thru hull items into cored hulls and angled areas. A peek at their PDF may also help to grasp the concept.

Dave, that's why I would had thought the TREX stuff would have been ok for those shims... but the posts when on and on about compression and strength....I went to the plywood, even though I'd smacked those TREX shims plenty of times with the BFH.
 
knuckle47 said:
Airmar, who makes our transducer, has an excellent instruction sheet regarding the installation of thru hull items into cored hulls and angled areas. A peek at their PDF may also help to grasp the concept.
.
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YES! Been there, done that. Used a large band saw with a tilt table here to cut an Airmar high speed fairing for my B256 'ducer. Still have all my fingers!
 
I use the table saw with tilt blade to cut the fairing blocks. The band saw blade always seems to bend a little and not get a good cut.
 
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