24.5ft NW pilothouse restoration. Corrosion/flooring questions

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tom_northcoast
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24.5ft NW pilothouse restoration. Corrosion/flooring questions

#1

Post by tom_northcoast »

Hi everyone,

First time poster here. I’ve read a lot on these forums, and have found especially helpful the comments of Kevin up in Alaska, learned so much on this forum! 

I have a 24.5ft pilothouse we acquired, and I am in the process of making it my PNW dreamboat. 

The boat was built by northwest welding in Prince Rupert BC, with a build date between 1984-1986. Leo Robinson was the welder, I believe. 

it was initially used as a crew boat for loggers working for Group Mills out of Oona River on Porcher Island. 

it was then purchased by a few fellows who were attempting to run a charter business. Both of them being from out of town, that didn’t take off, and for the last 4 years, the boat has been out of the water at a storage yard. 

the drain plug was left in, all the windows leaked, and the rear deck access ports leaked. The hull was filled with water when we got it. 

the sides are 1/8th, hull looks to be 1/4. Spray foam insulation, with about 1ft overspray on the bottom of the hull.

there is crevice corrosion from the overspray, with only a few nasty looking ones.

there was also all bits of metal in the hull when I took off the wood floors. The angle iron used to hold the floor up also had corrosion as the wet plywood against the aluminum angle iron wasn’t a great idea. Non-SS fasteners we’re also used in some spots for the floor.

there are also corrosion sites running along the channel. I’m guessing this is from dissimilar metals, decades of organic build up (took a lot of dirt, sand, rocks, bits of metal, nails, screws, fishing gear, etc…out of the bottom of the hull). 

the electrical was terrible, I’ve ripped out all the original wiring, and am redoing it all, new, sealed, with starboard backing. 

I would like to hear some of your thoughts about the work so far and the following:

1) should I go back to a wood floor, or aluminum welded right to the sides/angle iron floor supports? (I’m leaning towards aluminum welded deck inside the pilothouse with a few access ports) 

2) the hull is getting “re-skinned” in December with 1/4” aluminum. Going to cost me $7k, but my thought is the boat will be essentially new at that point. And won’t have to worry about the deepest corrosion sites.

3) so far I have power washed inside, vacuumed out all the dirt, disc sanded, and SS wire brushed the hard to reach spots. I would like to aluma brite the inside to etch the aluminum, rinse the hell out of it, and then apply some ACF50 corrosion inhibitor to it 

4) thoughts are not too weld patches over the corrosion that isn’t too deep, don’t want to seal anything off 

5) back of the deck (the self bailing hull part), looks like has some thick coated grease/dirt buildup, was going to spray some acetone back there, power wash, and then maybe alumabrite and rinse, thoughts on how to scour that area clean? 

6) the batteries were initially stored inside the cabin. I’m thinking I’ll get a compartment made against the transom where I can store all the batteries and wires/shut offs. My father in law runs tugs up here, and has always advised against batteries inside the pilothouse as they give off fumes when charging. 

7) there is a few coats of old anti-fouling paint. It’s chipped and missing in many spots. Is there any benefit to keeping this on, or should I sand it off and just acid etch the whole hull? 

again, much enjoyment and knowledge from this forum, thanks all! 
 
 
 
 *The pictures of the rusted up shackles, nails, etc… are some things I pulled out of the bottom of the hull. Had to use an old fishing pole rigged up to grab stuff at the back of the hull I couldn’t reach through deck access ports. 

*the picture of the pitting with the black lighter is the deepest corrosion site. Looks to be about 1/8”. This was also below where they stored the batteries. 
 
 
 
 
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Last edited by tom_northcoast on Mon Feb 07, 2022 9:01 pm, edited 7 times in total.
tom_northcoast
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Re: 24.5ft NW pilothouse restoration. Corrosion/flooring questions

#2

Post by tom_northcoast »

Forgot to mention, the last photo is a bit out of date. It was built with an open transom and had an old Honda 4stroke. Got it running so we could do a bit of running with it, but eventually found a used Yamaha 200 over in Haida Gwaii. Pod and swim grid were put on as well closing in the transom. The run we make to our cabin is quite often done in a large following sea (southeast winds are the norm in the fall/winter and that makes the run back intense), wanted the back closed in. 
 
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Re: 24.5ft NW pilothouse restoration. Corrosion/flooring questions

#3

Post by welder »

:smitty:
 GREAT 1st post and keep them coming.
More will be along soon to help out.
 
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kmorin
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Re: 24.5ft NW pilothouse restoration. Corrosion/flooring questions

#4

Post by kmorin »

tom,
Welcome to the AAB.com Forum and hopefully we'll be able to help your decision making process that enables you to rescue your boat and enjoy her for years to come?

I'm only going to reply to #1 question and will remark about that single item regarding the new deck.

I don't think the new deck is as important as fully understanding point #2!! (!)  the new or replacement deck seems to me, to be below the idea (less in a serial outline of priorities) of 'reskinning' an aluminum hull?

Do you plan to leave the existing hull plating on the bottom?
If yes (?) then you're planning to skin OVER the existing hull bottom plate?
ORRRRRR? are you removing the existing hull plating/skin/panels and REPLACING with new hull panels of 1/4"

VAST difference in theory, plan, practice and end result... so that to me is #1 question to understand?

cheers,
Kevin Morin
Kenai, AK
kmorin
tom_northcoast
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Re: 24.5ft NW pilothouse restoration. Corrosion/flooring questions

#5

Post by tom_northcoast »

Thanks for the reply and the welcome. Just about to head to bed and figured I would reply while I’m thinking about the boat, before I fall asleep and start dreaming of the boat.

So I’m booked in to have the hull work done in December with a local marine welder. The plan is to skin over the existing hull bottom plate. The boat will have the pilothouse removed, the boat flipped over, and then the new plating welded to the existing hull plating.

My thought for this is: the bay where our cabin is empties out at half tide, mostly mud but some gravel and a few rocks, and the boat beaches when the tide is out. Chatham Sound also gets a lot of trees and stumps getting blown out of the skeena river. And I suppose like your area not so far up from us, we don’t have a lot of sand beaches. Tough aluminum boats are a must for this area unless you’re going to avoid land.

I’m also planning on throwing a radar arch/small zodiac up top, so the added weight of new aluminum plating on the bottom of the hull might help offset some added weight on the top of the cabin.

So come the fall when I pull the boat out (after the blacktail rut), the bottom paint will get removed and I’ll clean everything down to bare metal.

Only the decking inside the pilothouse is being replaced. The deck at the stern is aluminum checker plate that is fully welded to the sides. I’ll post some pictures of the back deck in the daytime hours.

I’m booked in for some work at the end of this month, repairing some cracked welds, possibly doing some patches over the deepest pits, and possibly welding in a new floor inside the pilothouse. If time/money permits, then possibly doing a ‘stern locker’ (might not be the right term), but a compartment running along the stern to hold batteries, trim tabs, etc…

I have an idea of where I want this build/restoration to go, but certainly want to plan the steps, do things in the correct order, avoid unnecessary work, etc…

-Tom
Prince Rupert, BC
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Re: 24.5ft NW pilothouse restoration. Corrosion/flooring questions

#6

Post by Chaps »

I'll comment that if the pitting in the bilge adjacent to the black lighter is the worst of it and the bottom is otherwise intact and not beat in from rock groundings I don't see much of a reason to double plate the hull. If the hull is otherwise fair but you are contemplating some tough beachings in the future have your welder put a 6" wide doubler plate down the stem and run it about halfway back on the keel and call it good. That pitting is no big deal on a 1/4" bottom IMO. If they bother you clean them out by whatever means, spackle them with marine epoxy compound sand them fair.
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kmorin
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Re: 24.5ft NW pilothouse restoration. Corrosion/flooring questions

#7

Post by kmorin »

Tom,
I don't recommend the double hull plating for the reason that you'd be creating a 'super cell' of corrosion unless the entire inner area (volume between sheets) was air tested very thoroughly and all 'leakers' TIG floated and retested.

My reason goes like this;  #1 the sheets won't fit one to one perfectly even if this were a new build with 'double hull sheathing'! 

#2 Therefore, some volume of air will exist between the sheets and will be trapped by the welds to install the outer sheet- and some places will require keyholes or 'pocket welds' to attach the new plate in the 'field'.

#3 work will be done in a shop at 60deg F or better (hopefully) and then the boat will be in varying heat until launched at which time the volume in between sheeting will cool by 20-30 degrees (from original shop temp) depending on the time of day and water temps.

#4 This temp raise, while sitting around in the shop or out in the sun, will heat the air inside up to 70-80 degrees while it drops upon launch to 40 or so?   Thus a fairly impressive vacuum and pressure will be expressed into the pits inside the existing hull AND the MIG welds' starts and stops- all of which are potential for leak paths into the volume between the sheets for both the contents of any of your existing pitting sites' contents as well as water.

#5 I can see, in  your photos,  how the bilge water treated the inside of the hull causing pits the contents of which may well be pulled by differential pressure into the new void; that seems like you'd be building in a new source of isolated corrosion cells (the entire new bottom) ?  It seems there is an assumption that the new sheet/plate will eliminate the bottom corrosion risk on the original bottom but I'd argue it will enhance the existing pitting where that pitting can't resist a few inches of vacuum reversed by heated air positive pressure?  I think the cycle of heat from water to trailer or even a hot day on the beach- will insure you have leaks into and out of the void between the sheets.

I don't think that is a wise use of your money for this boat.

I think it might be more cost effective to get a good quality bilge clean up with acid and a thorough rinse then going pit to pit clean up what you can as Chaps has advised.  And as he also mentioned if there is particular area of high corrosion or thinning - consider a 'shoe' or local plate and air test it very carefully after that plate or new box keel shape is added.

A little confused by some remarks vs pics?  Seems like the entire after deck is open- not welded deck? but
tom_northcoast wrote: Tue Feb 08, 2022 1:34 am The deck at the stern is aluminum checker plate that is fully welded to the sides.

 
I'm guessing you mean just at the very stern or engine swim deck is plated?  The pictures seem to show the after deck is all cleaned out and open ?
This area is where the iron/steel/stray metal parts were found in the bilge?  Does the bilge flow common under the cabin sole?  Or is the isolating bulkhead aft the cabin that goes to the hull to isolate the bilge fore and aft?  If the bilge is/was common then pulling the cabin sole and cleaning the whole bilge area looks like its fairly important?

Not some rust looking coloration in the bottom of some pits?  All that needs is water to be reactivated as a galvanic corrosion cell until all the iron is consumed by either rust of reaction to aluminum- which ever comes first!! Pressure washing with regular soap and water- then acid etching and then 'flood rinsing' with a swimming pool of volume of water - dilute and rinse of the acid and oxides that are lifted by the acid- sure would go along way to helping your hull's life.

As to adding a deck over the framed area shown in the photos- yes a welded aluminum deck would help the boat be more seaworthy in regard taking a green one into the cockpit? But unless the bilge is cleaned up you'd just be limiting access to an area of the hull you can see needs maintenance.

As light as the hull is- I'm not sure you need to worry about being boarded by a big offshore wave? Seems like she'd buoy up pretty agilely in a set of waves so just putting in more plywood would be less expensive.  If you'll be doing extensive offshore trips - and fishing from the stern with two or three people aft-plus the engine is now aft the transom with only the center 'pod' or hull extension to float it; maybe adding a welded deck would give you more peace of mind - where the deck washes clean out freeing ports and you have a 'dry bilge'? 

Not sure I've addressed all the original questions but the big one to me seems to be the idea of doubling the hull plating?

Cheers,
Kevin Morin
Kenai, AK
 
kmorin
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Re: 24.5ft NW pilothouse restoration. Corrosion/flooring questions

#8

Post by kmorin »

Tom,
i'd like to remark about using embossed plate/tread plate/diamond tread and my experiences with it.  First is the alloy- usually 6061 or 3000 series and very rarely 5000 series - so its brittle in the sense that as sheet it will crack if something heavy and sharp it dropped on it- like a 2x6 end wise- will dent the deck much more than a flexible alloy like 5052 or 5086 (or 5083).  Not a big deal but something to be aware of.

Next is the corrosion resistance of 6061 - is lower than 5000 series in the same application and that is the space under the deck and on top of deck frames- this is almost always keyhole welded (pocket welds/recess welds) to attache to the frames- so water wills stand in this space and bedding is hardly applicable since its a welded joint.  So, I've pulled lots of old diamond tread deck plates to find the tops of the framing nearly pitted out- due to capillary action pulling in bilge vapors/water/mist and that creating crevice corrosion cells.  IF the bilge is nice and tight- and air tested - then vented via a riser/gooseneck/Ptrap tube- AND it gets dried out periodically- less of a problem long term.

A better alloy for the deck would be smooth 5000 with a traction coating you can renew over time.

In my experience with beach skiffs (set net skiffs here in the Cook Inlet in S.Central AK) diamond tread plate is not a good choice for any part of the beached skiff.  Extra-Tuff's always carry beach sand in the treads of the soles.  Even if you're 'religious' about rinsing before  you step on deck- odds are you'll have plenty of sand on the deck every time you board her while she's beached?  Then unless you rinse that immediately(?) you will begin to 'sand' off the tread embossed 'diamonds' and they will become rounded - not sharp.

Then in one or two seasons you'll have the deck wet, land a salmon or flat fish and the rounded over diamonds will act like you're walking on marbles coated with fish slime! which you will be!  I built a net skiff with an entire bottom (deck was bottom) and within two seasons they were already coating the bottom with 'wing walk' - trowel on mastic that has sand in it- to keep from busting their stern falling in the boat!

So, my view of embossed plate is not favorable; the idea it will provide a good traction is short lived in my experience as I've seen it rounded/sanded by normal beaching and climbing in and out in Extr-Tuff's.  I now use any regular epoxy paint system - abrade (sand blasting is best but rotary will help if not blasting), etch, Allodyne (chromium oxide), primer and paint. IN the last top coat of paint I just use white 'filter sand' or silica and make a paste of the paint mixed with sand and trowel than onto the deck in taped off sections- not all the way to the sides or transom by 2-3";    or....I use 3M (tm) traction tape in strips which holds up well and is replaceable pretty easily w a heat gun to pull up the old and a linoleum roller to put down on torch heated decks wiped with acetone to make sure the surface is clean and grease free - warming helps to make the adhesive backing stick - I've used this in net skiffs that had bilge water all day and those strips stay put even underwater.

Tom,  just some notes about my poor experiences with 6061-T6 embossed plate - traction plate/tread plate/diamond plate- and what I've learned when you walk on that material in sandy boots.  I'd prefer plywood soaked in epoxy with some traction coating over diamond plate- personal preference.  Look around and see if there are any skiffs in your harbor that had embossed plate decks? Maybe you can see what I'm talking about those skiffs are regularly beached?  If a boat is used dock to dock- out and back- this wouldn't be as much a problem looking to become dangerous.

Cheers,
Kevin Morin
Kenai, AK
 
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Re: 24.5ft NW pilothouse restoration. Corrosion/flooring questions

#9

Post by tom_northcoast »

Hi Kevin,

Thank you for the reply. I have added a few more pictures to show the deck from the stern up into the bow.

The aft deck is welded to the sides and only accessible through the two deck covers. The deck inside the pilot house is open. Though previously closed in with plywood. 

the aft deck is not truly sealed as it not sealed from midships forward. I’ve added a picture of the aft deck as seen from inside the pilot house. Of note, is the overspray of foam on the sides, but also on the bottom. It looks like this continues to the stern of the boat. Hard to tell as I can’t get back there. This overspray was initially thought the hull inside the pilothouse throughout the boat going out to the first piece of channel, about a foot from the funnels. I have no idea how the foam got all the way back there as the sealed portion in the stern wasn’t foamed in. 

im going to try tonight to get my disc sander back there attached to a bit of 2x4.

I hadn’t considered the idea of a super cell of corrosion! Skinning on additional plates isn’t unheard of here, one of my buddies has a boat that was ‘skinned over’. It was actually the welder that thought of that idea. Initially we had thought the hull to be a lot thinner. But when i was going through the boat, I found an old crack that was drilled out and patched from the bottom. I stuck a piece of thin rod down the drill hole (I circled the two drill holes along the patch), and the rid goes down to about 1/4” to the top of the patch. 

From what you have described, it would NOT be a good idea to skin over the boat. Given that was the major piece of work to do, I would rather not undertake that project if it wouldn’t be good for the boat. 

So that leads me to another question, given the aft deck is going to not get near as good of a scour as the bow half, and it appears there’s foam overspray further than I can reach down the aft deck. Will that pose any problems for acid etching the boat with some aluma brite? I am worried some of the acid could leach into the foam and would then hasten any potential corrosion underneath that overspray. 

or is this a case where I’m going to have to bite the bullet, take off the deck, proper clean, and then have the aft deck welded in. I find the self bailing very helpful as I leave the boat at the marina for summer! 

Best,

Tom
Prince Rupert, BC
 
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kmorin
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Re: 24.5ft NW pilothouse restoration. Corrosion/flooring questions

#10

Post by kmorin »

Tom, the new photos really help put the photos above into a better location reference!  Now I can see that a shot from on deck into the cabin sole framing wasn't looking aft!  Now that you show the after deck from above; the below deck image makes complete sense- but I'd not been able to infer correctly, those locations.

First, I'm not sure if over-spray that is sticking fast to the aluminum, and is above the level of the bilge water hasn't proven its adhesion to the metal?  If sprayed foam would adhere perfectly- or extremely well- then the crevice cells wouldn't from since that 'glue like ' grip on the metal would exclude any water- which is the catalytic agent needed for the crevice corrosion cell- also when a poultice type cell is formed.

That said, cleaning up the over-sprayed areas would only be critical i they're fomenting corrosion?  So clean under what ever location of this coating can be reached and look at the underlying metal?  If its clean- non water has gotten between the foam and metal?  Then taking up the back deck is less important.  However is the foam comes off easily and there is any white chalking or pitting where it was on the hull?  THEN taking up the deck and cleaning to bare hull metal is more important.

I suspect your hull's bilge has been a "galvanic soup" for some time? This is implied by the iron/steel and other metals you've taken out of the bilge. That has likely been the source of the wide spread pitting shown?

As to leaving the overspray and etching?  since the original hull didn't get cleaned of mill scale- the acid will have a layer to 'attack' or 'dissolve' since the foam is actually attached to mill scale.  The mill scale adjacent to the edges of any over-spray patches will get lifted by the acid, when you rinse this will dilute and flow away so there's no 'acid' left;  but the edges or seal of the foam to metal will have been lifted to some degree- even if only for a fraction of an inch? This will probably allow further water (if the bilge level gets to this edge) to work on the edge of the mill scale remaining and begin a crevice corrosion site?

If I were remodeling for the longest use of the hull- I'd say pull the deck and get down to clean parent metal everywhere.

In regard the acid effecting the foam- test a small patch to see what happens?  Hope this helps to address your questions?

Cheers,
Kevin Morin
Kenai, AK

 
 
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