Aluminum and corrosion

[Clip]

I intend on using aluminum as reinforcing behind the bump rail and on the interior of hull at the deck/hull join, and as a toerail.
What type/grade aluminum should be used?
What metal should the bolts be? Brass?
Are rivets a big no-no for permanent connections?


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[Editor's Additional Note: For clarification, Clip is talking here on the subject of his 27 foot whaler rebuild. He posted on that first here: http://backyardboatbuilding.org.uk/forums/showthread.php?p=30#post30. The link he provides in that post will take you to some really interesting photos of his whaler that I do recommend for a look-see. I've taken the liberty of adding a thumbnailed copy of his already posted pic (above), again for clarification. Click on the thumb to see the full size image.]

[Mike]

Hi Clip

I shy away from using metals, particularly aluminium and rivets. In answer to your query about rivets, I would suggest that there is nothing permanent about a rivet driven through aluminium. And flexing of the hull may cause the rivet holes to enlarge and the aluminium to tear away in time. Having flown aircraft all my life, I am well aware of the properties of aluminium. It can corrode badly with exposure to the marine environment, as anyone who's flown the flying boats will tell you. Why not beef up that hull using some good, solid, hardwoods instead?

Incidentally, I am intrigued by the way you've added an outer hull skin to the accommodation area. Very innovative way of tackling the problem of cold penetration without reducing interior space. You are clearly a lateral thinker. :appl:

Regards

Mike :captain:

[Clip]

The aluminum was to go around the outside of the hull as an 1" wide flange angle facing outward, to help fasten down the deck on the outer edge of the hull, and help support a 2"X 2" rubber bumper that came with the original hull. It will also allow easy attachment of a toe-rail and for some rails. The problem being, that the flotation chambers will have no access after the side deck is in place unless I use screws for everything.

Actually the widening was done:

1/ to provide access around the cabin,

2/ to allow removal of the flotation chambers in the interior bottom portion of the hull, giving a more roomy interior and positive flotation at a higher point on the hull. It also adds 50% more flotation than the originally removed chambers which were saturated anyway. Research of this boat in accidents indicate that after capsizing the hull remains inverted.

3/ to add more beam from the original 6' to 7' 10", though the hull shape will still be tender, since the wetted surface remains the same.

4/ and yes, there will be the insulation.

5/ the last reason was that hull portion above the seating was really lacking in strength and structural support. This was evident when I examined damaged GRP Whalers that had been crushed from lateral loading on their side. So I added a laminated sitka spruce beam under the fiberglass gunwales and the vertical braces used for the widening provided more strength in this area.

I used a polyurethane marine flotation foam that ended up being 4lbs ft3 due to the ambient temperature at the time. It sure stiffened the addition up solid with no drum sound afterward.

[Mike]

Having only fleetingly looked through your photos, Clip, I confess to not having noticed that this hull was GRP. Hence, my suggestion about using hardwood rather than aluminium (or 'aluminum', as you North Americans say :grinning-smiley-003).

We've only ever owned one GRP boat (a kayak), so I am far from knowledgeable in this area and rely heavily on the Gougeon Brothers' book for my own guidance in using epoxy. At heart, I am a wood man, thus a wooden boat man. I simply love working with good wood.

I do like the thinking applied here, though. It is certainly a good plan and I really do look forward to seeing your progress.

One little question, if I may: what is the function of what looks like grab handles below the waterline? Were these boats used to rescue people or as lifeboats in an earlier life? (Oops, that's two questions. Doh! Sorry.)

Regards

Mike

[Clip]

I can certainly understand the preference of wood over GRP when it comes to the work.

The Canadian Navy Whaler was used on their ships as a life saving rescue and odd job boat until inflatable rigid hulls took over in the eighties. They had a motor well for a 20hp outboard, oars, and sail. I suspect the grab handles were there to help hang on to the hull in a turn over event, and even to help right it. Alot can be done with ten lads.

I intend on keeping them and adding twin keels of a total weight of 1200lbs. Ted Brewer from BC has been giving me advice on this. The boat should be a lot more stable afterward.

The name Warshot that I gave her, came from repaired bullet holes that I had found in the bow area under years of paint, she was made in 1964.

[Mike]

Ha ha. Yup, I would agree with you, Clip, on the wood over GRP preference. Epoxy has its uses, for sure, but I am no great fan of the process. It's kinda sticky and messy and I don't enjoy wearing protective gear. Woodworking is almost a cathartic experience. I just love the smell and feel of it.

You really have taken on a huge task here, Clip. Not only are you re-building her but you are also re-designing her, to an extent. With someone as knowledgeable as Ted Brewer helping you out, it seems you will surely succeed. I would suggest he is the best person to consult about the keel bolts and on how to beef up the hull to take the weight of twin 600lb bilge keels. Apparently, the original design did not have bilge keels, so you will certainly need to beef her up to take them.

I tried finding some pics of Canadian Navy Whalers on the Web. There were only a couple there but they show she was a pretty thing in the water when under sail. She looks similar in shape to the old RN whalers, though ours were made of wood and were darned heavy boats to row. I know because I rowed one back in my youth training days (a hundred years ago!! :grandpa:).

This is a really interesting project. Thanks for sharing it with us. We're looking forward to watching the progress. Do feel free to blog 'Warshot' in our Blogs section.

Best wishes

Mike

[Isla]

I intend on using aluminum as reinforcing behind the bump rail and on the interior of hull at the deck/hull join, and as a toerail.
What type/grade aluminum should be used?
What metal should the bolts be? Brass?
Are rivets a big no-no for permanent connections?

Hi Clip,

Plain aluminium is very reactive, especially in salt water. Aluminium manufactured parts for boats are always anodised, that is to say, they undergo a treatment which puts on a surface layer of aluminium hydroxide to inhibit corrosion. I certainly would not use brass or bronze fastenings. There would be an electrolytic reaction with the aluminium causing rapid corrosion, especially with salt water as a catalyst. Best fastenings would be stainless steel. If not anodised the aluminium should be well painted and bedded in a good marine sealant.