Stainless Steel Thru-Hulls

[merheb]

I was looking for some stainless steel thru-hulls to replace the original plastic ones in a 1996 Seaswirl 2100CC and found some at Walmart of all places at a reasonable price (about $12 for a 5/8"). They are made by a compay called Attwood but the packaging said that they are for above the waterline use only.<br /><br />I'm not sure what that means for my situation... Some of the thru-hulls will be just below the waterline but I trailer the boat (not stored in the water). Is that true for all stainless steel thru-hulls? Is it just for these fittings (Attwood brand)?<br /><br />Thanks,<br />Freddie

 

[Sea Six]

Re: Stainless Steel Thru-Hulls

Curious what drains you have below the water line. Seems like a potential source for water intrusion to me. Mine are all above the water line.

 

[merheb]

Re: Stainless Steel Thru-Hulls

Unfortunately, I have 4 drains that are right at or just below the waterline, depending on loading. I am baffled by that as well since I thought they would be above the waterline (used boat). They are all compartment/livewell drains.<br /><br />Is there a problem with using the stainless steel type in these situations?<br /><br />Thanks,<br />Freddie

 

[Sea Six]

Re: Stainless Steel Thru-Hulls

I suspect Attwood does not want any liability issues just in case the fitting cracks and you take on water. Crack could be due to over tightening the back nut, or corrosion, or any number of issues besides manufacturing defects. Just my guess, who knows. Nylon actually sounds safer to me below the water line.

 

[umblecumbuz]

Re: Stainless Steel Thru-Hulls

Freddie M<br /><br />Stick to plastic and avoid potential corrosion problems. The more wet metal you have on a boat, the more your corrosion problems multiply.<br /><br />Ciao

 

[cuzner]

Re: Stainless Steel Thru-Hulls

Anyone have any idea of where to order online? I've been looking and can't find any<br /><br /> sorry for jumping on your post Freddie<br /><br /> Jim

 

[18rabbit]

Re: Stainless Steel Thru-Hulls

SS thru hulls are fine but there are two issues;<br /><br />(1) any thru hull below the water line must have a seacock value immediately attached inside. Seacock values are usually bronze. This creates dissimilar metals (ss and bronze) in an area of high galvanic potential, so bronze thru hulls are preferred below the waterline. Of course you can throw out the bucks for ss seacocks to fit on ss thru hulls...that no one will ever see.<br /><br />(2) There are two qualities of thru hulls; the plastic and flimsy ss ones are actually intended as thru hull drains for use only above the waterline. They are not designed strong enough for below the waterline mounting…and often have smaller interior flanges. The other kind of thru hull is bigger, beefier, and when properly mounted, will retain a watertight seal against the dynamic water pressures of a boat moving thru water. When a boat occasionally heels over and dips a thru hull drain below the waterline, it does not count...it is still considered above the waterline.<br /><br />Attwood is owned by the Brunswick Group, makers of Bayliners and about 20 other brands of boats. Those ss thru hulls may or may not actually be made by Attwood. They may be repackaged and distributed by Attwood to round out their marine products catalog.<br /><br />If you go with plastic (nylon) thru hull drains, you should paint them to protect them from UV light. Personally, I’d prefer the ss ones. You should have no problems using them as above-the-waterline drains where plastic was originally installed. There are no below-the-waterline plastic thru hulls. If you will be cutting holes and installing new thru hulls, you may want a better understanding of thru hulls before going ahead with the ss thru hulls from Wal-Mart.

 

[merheb]

Re: Stainless Steel Thru-Hulls

18rabbit,<br /><br />The boat has always had plastic thru-hulls. For some reason, they are at or just below the waterline. I trailer this boat and it never sits in the water for longer than a few hours at a time. I know that depending on the loading, those fittings will be below the waterline.<br /><br />I am not drilling any new holes and am only replacing what's been in the boat since 1996. The scuppers are also right at or just below the waterline. There are a total of 5 fitings below the waterline (2 scuppers and 3 drains).<br /><br />In your post, I am confused by this line: "There are no below-the-waterline plastic thru hulls?" Does this apply to boats that sit in the water all the time or to any boat? I do not have a choice and will need to put something and I guess my options are then plastic or bronze.<br /><br />Thanks,<br />Freddie

 

[Sea Six]

Re: Stainless Steel Thru-Hulls

Freddie, check this out:<br /> http://www.westmarine.com/webapp/wc...0001&catalogId=10001&productId=17328&y=5&x=11 <br /><br />Notice these nylon/marelon fittings are considered OK for below the water line. Anything made of generic "plastic" is NOT considered safe below the water line.

 

[umblecumbuz]

Re: Stainless Steel Thru-Hulls

Freddie,<br /><br />Marelon is a well tried and proven plastic through hull material, used both above and below the waterline.<br /><br />It is made from a Dupont patent - a nylon-based material called Zytel - and reinforced with glass fibre. It withstands uv deterioration, large and sudden temperature swings, and can take heavy torque loadings when being tightened.<br /><br />No worries using this for your thru-hulls, and the bonus is that there's no galvanic reaction.<br /><br />Ciao

 

[gutshot grouper]

Re: Stainless Steel Thru-Hulls

Stainless steel is ok if you bond it to your common ground system and protect it all with a sacrificial anode of zinc. Stainless will eat away just as quickly as any other metal if unprotected, I know because I had a zinc collar on my s.s. shaft with a bronze prop and the zinc had eroded away, the shaft looked as if one had taken a quarter inch drill to it in one spot and the keyway had eaten up a bit in one corner. The mfr. who says above waterline only is trying to avoid liability. Gutshot in Raleigh

 

[merheb]

Re: Stainless Steel Thru-Hulls

Thanks for the info on the Marelon. I'll check it out at the local West Marine and see if they have it available in the sizes I need.<br /><br />I'll keep you guys posted!<br /><br />Thanks again,<br />Freddie

 

[18rabbit]

Re: Stainless Steel Thru-Hulls

Sea Six and Stillfishing – thanks for the update on the Forespar marelon thru hulls. I didn’t know they made them. I knew Forespar had other plumbing parts available that are made from marelon but they often cost more than their bronze counterparts. Wow! …and the marelon isn’t affected by UV!<br /><br />As far as using them below the waterline, I wouldn’t do it. It has a mushroom head. I prefer the flush mount thru hulls that look like a big countersunk screw head. More work to install but they do not allow debris to smack into it or get hung up on it.<br /><br />Freddie – I looked at pix of Seaswirls online. Not all of them have the waterline marked on the hull. From what I can tell, the thru hulls are basically at the waterline, probably out of the water while underway. They are not considered below the waterline. That is where I would be concerned … the water’s dynamic pressure while underway. Where they are located, they won't see much of that. If Seaswirl installed plastic thru hulls on your boat, you should be ok replacing them with other plastic parts; or you can certainly use marelon thru hulls, or metal ones. Since your boat is trailered and you probably hose it down after each use, you’re not likely to see any issues with corrosion. If you install ss, and get lazy, you may eventually get those little rust streaks down the side of your hull.<br /><br />Why are you replacing them? Were they un-painted plastic parts that degraded in the sun?

 

[merheb]

Re: Stainless Steel Thru-Hulls

18rabbit,<br /><br />I am replacing them because they looked worn and they were the original ones (they were not painted). There were a couple of strainers in the transom that were also badly degraded and were very brittle so I decided to change all the thru-hulls.<br /><br />Along the way, I also found out that some of the hoses connecting the scuppers were badly cracked and that's where water was comning into the hull. This has turned into a bigger job that I was expecting but I want to do it right instead of having to repeat it 2 years down the line.<br /><br />I am planning on using the Marelon fittings. As you mentioned, the fittings are for the most part above water while underway. One thing I noticed is that the scupper flaps get "sucked in" while underway. After stopping, if I don't lean over and pull them out, water starts coming into the deck. I am replacing that scupper with ones where the flaps are more rigid and will prevent this problem.<br /><br />Thanks,<br />Freddie

 

[Northern Eclipse]

Re: Stainless Steel Thru-Hulls

Freddie <br /> Glad to see your paying attention to all the fittings I replaced a drain fitting last summer because it was looking a bit scummy, I was surprized how it almost turned into powder when I removed it,it was very brittle. I remember reading an article once online that was based from an insurance study, it claimed that the number 1 reason pleasure boats sink was from poor quality or broken thru hull fittings and scuppers or scuppers that are at or below the waterline and become plugged with debris such as leaves, which makes me wonder why some boat builders install them the way they do or use them at all, I myself prefer a really big bilge pump. I notice you state the boat is used, do you know if the scuppers are from manufacture or later installed.. have you considered removing and filling the holes, less holes below the waterline the better. Note to Cuzner there is a West Marine store in Midland now its right at hwy12 and King st. Its the old Central Marine Location, They'll have what you need and will save you a ton on shipping.

 

[Ed_McDonnell]

Re: Stainless Steel Thru-Hulls

Stainless steel will corrode when placed below the waterline. That is why the fitting manufacturer recommended that you do not use it there. <br /><br />Also, using plastic thru-hull fittings below the waterline can be dangerous. Crack or damage a plastic fitting and you will sink your boat!<br /><br />Bronze is more expensive, but it is a much better material for fittings below the waterline.

 

[umblecumbuz]

Re: Stainless Steel Thru-Hulls

Taking up Ed-M's comment about stainless underwater, this needs clarifying a bit.<br /><br />There are many stainless fittings underwater on boats, such as props, swim ladders, trim tabs - and these remain healthy for years.<br /><br />The principle is simple - Any metal has the potential to corrode when placed in an electrolyte in proximity to or contact with another dissimilar metal. For example, it is bad practice to use a bronze item underwater if any part of it has been brazed. This is because the brass used in the brazing will corrode faster than the bronze, and the two brazed parts might separate.<br /><br />Similarly, you can kiss bronze goodbye if it's in proximity to - say - 18-8 stainless (passive). The stainless will remain healthy because it corrodes slower than any bronzes.<br /><br />Stainless by itself will probably not corrode if any aluminum parts are also fitted underwater to the same hull, because the aluminum is more anodic. But unless both are protected by a 'weaker' metal - the sacrificial anode - the stainless could have the effect of speeding the corrosion of the aluminum (your prop for instance)<br /><br />Moral is look after your 'zincs' and avoid trouble.

 

[dingbat]

Re: Stainless Steel Thru-Hulls

The reason for the warning is a miss application of the product and not a materials issue. All below the water line applications require the use of a seacock. Since the fitting in question can not be used in conjunction with a seacock you have a miss application of the product and thus the warning. <br /><br />As for the corrosion issue, it’s not the Stainless that is in danger. Stainless is a danger to the other metals on the boat. The SS thru hull would be the last thing to go.

 

[umblecumbuz]

Re: Stainless Steel Thru-Hulls

Quote from dingbat:

Stainless is a danger to the other metals on the boat.

Agree wholeheartedly. This is a mantra that I have been plugging forever! Manufacturers of trim tabs, swimladders, and any other stainless underwater fittings, that do not have provision for their own 'zinc' attachment are either short-sighted, or knowingly passing the potential problem on to other vulnerable components.<br /><br />It is often not a big problem - but it can be. Belt and braces.