Corrosion, Aluminum/Brass/Stainless Steel

[shikeswithcanoe]

Hi all.

Working on my SOF kayak (well, actually thinking about it more than doing it). It occurred to me that I would like to put in some aluminum angle in various places for various reasons. Long term it would probably need to be replaced when the skin is, so it can not be permanent permanent. And, it probably needs to be held in place with screws or bolts.

So, do I need to use brass bolts/screws or stainless steel? For corrosion purposes aluminum ones would probably be best but I doubt I'd find those locally. With two different metals in contact one is going corrode more than the other. I am thinking I would prefer the angle to corrode over the screw/bolt given that at some point when I remove this stuff its going to be the screw/bolt that will be the issue when it comes to removal and not the aluminum angle.

Thanks

 

[Kayak Jack]

Noble metals: http://en.wikipedia.org/wiki/Noble_metals - Noble metals are metals that are resistant to corrosion and oxidation in moist air, unlike most base metals. They tend to be precious, often due to their rarity in the Earth's crust. The noble metals are considered to be (in order of increasing atomic number) ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold.[1]
Other sources include mercury[2][3][4] or even rhenium[5] as a noble metal. On the other hand, titanium, niobium, and tantalum are not included as noble metals despite the fact that they are very resistant to corrosion.
Noble metals should not be confused with precious metals (although many noble metals are precious).


Base metals: http://en.wikipedia.org/wiki/Base_metal - base metals refers to industrial non-ferrous metals excluding precious metals. These include copper, lead, nickel and zinc.[2] The U.S. Customs and Border Protection is more inclusive in its definition. It includes, in addition to the four above, iron and steel, aluminium, tin, tungsten, molybdenum, tantalum, cobalt, bismuth, cadmium, titanium, zirconium, antimony, manganese, beryllium, chromium, germanium, vanadium, gallium, hafnium, indium, niobium, rhenium and thallium.[3]

Shikeswithcanoe, A practical approach may be to isolate the screws from the aluminum with a fiber sleeve and washer set up. Then, keep it dry. Ron Smith may have some information to add; he's pretty knowledgeable about metals.

 

[Kayak Jack]

On thinking some more about this. would lashing provide a sufficiently strong fastening system here? If it works for wood, why wouldn't it work for aluminum?
I've never lashed a frame together before, so am asking why a continuation of the standard procedure wouldn't be satisfactory? Maybe you're seeking more rigidity and less flexibility?

 

[john the pom]

If you used stainless steel angle then you could use stainless steel screws. Try to discern the grade of stainless. Some are more resistant to corrosion than other and it might pay not to mix grade of metal with different grade of screws. Not nearly as important as keeping totally different metals apart.
Know any metalworkers that dabble with stainless? Or a fabrication shop that does. Bear in mind that stainless being so much stronger than aluminium; you could get away with extremely thin SS.
With all the effort we put into boats it might be worth the time and effort to try and get this bit right.
Cheers John.

 

[tx river rat]

John
is dead on stainless can be 3 times as thin for the same strength,so weight difference will be comparable with alum.
If you do use alum there are a couple things you can do to stop corrosion ,one is a fiber or rubber washer between the screws and the angles,you can get these of sheet metal screws used to put sheet metal on building and the screws should be bronze not brass , this has been the metal of choice for boats for several hundred years.
Ron
Just another thought , epoxy cover wood might solve all your problems .
Ron

 

[rpecot]

If at all practical, you want to stay AWAY from using dissimilar metals in contact with one another. You run the risk of creating a galvanic cell. http://en.wikipedia.org/wiki/Galvanic_corrosion

 

[shikeswithcanoe]

Hi guys. Thanks for all the suggestions. I'll keep them in mind and when I finish this thing six years from now I make a command decision.

I figure I should tell you what these metal angles are for. With a skin on frame kayak you can't exactly run some straps on it and pull it really tight to mount on your roof racks. You could break your stringers and or the straps could rub the skin more than you'd like. And when your boat is 17 foot long and the racks are only 3 feet apart that doesnt help much either. We do a fair bit of high speed and distance driving to do our paddling so I want a pretty stout and non damaging way of securing our SOF yaks. Flying boats on the highway could kill someone. And even if it didn't, a flying boat that cost about 1K and took many man hours to make would leave me feeling ill for quite awhile.

So my plan is this. I'll cut and glue up some wood that has the same shape as the cockpit coaming. Put some foam on the flat surface. Then have some vertical pieces that project down (up?) into the cockpit. One in the front, one in rear, two at the widest point on the side, and two along the sides towards the front should restrict the cockpit from sliding or rotating. Now the the foam should do fine for keeping the surface of the cockpit coaming from being damaged. But I need something to keep the inside edges from getting worn. Thats where the pieces of metal come in.

Then, this wooden mounting thingy will have some other pieces of wood cut and shaped so it sits properly on the roof racks. Anyway thats the plan. Thought you guys might be interested. I have also come up with a nice way of having stout attachments for the bow and stern lines for tying the boat as well. We know somebody that did not use bow and stern tie down lines when transporting their boats (they were just secured to the roof rack. They got in the turbulence of a semi truck on the interstate. The boats along WITH the rack got ripped right off the roof of their vehicle :shock:


Maybe I can write up my plan for the bow and stern lines sometime in the near future.

 

[oldsparkey]

Anyone who has transported a boat on there roof rack knows what you are saying about the 18 wheelers or large trucks when they pass , either direction.
Now add to that a good cross wind and things get really interesting. We have open areas down here and on the interstates or even back roads when that cross wind hits you and a 18 wheeler passes you a boat will dance around on that rack.

A buddy of mine was in a hurry and only used the straps on the canoe and not any bow or stern lines. A 18 wheeler passed him and he found his canoe hanging off the back of his truck and partly cross ways to the cab. It did not get loose enough to come off but it sure scared him. He said there was also a good cross wind that day. Not a good thing when you are going several hundred miles for a paddling and camping trip.

The bow and stern lines are nothing more then an insurance policy in case the main lines ( straps ) over the boat come loose. Whatever you do just have them snug and not tight enough to actually bend the boat down on the stern or bow , that can destroy a boat really fast.

 

[Kayak Jack]

RE: Tying down bow & stern lines. Under my hood, and under others that I've looked at, there are a couple of points up forward, near the front corners, where some bolts or strong screws hold something to something else. Find two strong ones that are closest to your front corners. Measure from each screw to the outside edge of the joint between fender and hood. Do it for both sides if they are not symmetrical.

Double that length, and add 12". (EXAMPLE: Distance from screw to fender = 10" Get a piece of nylon web strap 20"+12" = 32" long for that strap, and the necessary length for the other strap too. This should be more than needed.) Get some nylon web strapping, 3/8" to 1/2" wide. Get enough for both sides of your hood, and maybe a few inches extra.

Using scrap wood as a work base, cut your straps to the length you've calculated. Double the strap over into a loop, with the two ends together. Using a sharp, 1/8" drill, carefully drill a hole into both ends, about 3/4" in from the ends. Using a lighter or wooden match, carefully seal the ends and frizzies around edges of the holes.

Use star lock washers (these will bite into the strap when the screw/bolt is tightened, so position the sharpest edges to the inside directly into the nylon strapping material), one on each outside surface of the doubled straps. Put the screw/bolt down through the washers/straps/washer assembly. You may have to go to the hardware and buy a longer screw or bolt to have sufficient length to remount these back under your hood.

Install the straps back in the original holes, with the loops hanging out sideways and exposed when the hood is closed and securely latched. Now you have an anchor point for your bow lines. When not in use, fold the straps back inside, and close the hood as before. Also, make sure the straps don't interfere with anything when folded in and the hood is closed. Inspect the attach points for proper security each time you mount a boat. Retighten and/or repair as required to ensure your boat is strongly anchored.

To tie down your skin on stick boat, have you considered a plywood cradle to set it down into? I'm not familiar with the curvature and cross sectional configuration of your boat, so it is possible that a simple, flat piece of plywood with foam shaped to fit your boat may suffice. If you're not comfortable with that, a shallow vee of plywood lined with foam may do better. To secure the bottom cradle, you could either attach a couple of slats or cut notches. These would line up with the crossbars of your car rack, so the cradle would remain aligned fore and aft and not be able to rotate on the rack under side pressure from wind.

I'm pretty sure that some other ideas are floating around too.

 

[john the pom]

John thinks lotsa people tie their boats down too tightly. Have seen plastic boats deformed by combination of tight straps and hot sun. There is being secure and being tight. Since I read of a bloke whose kayak and front roof rack left the vehicle because of a BB truck. I add an extra strap that runs over the boat. around the roof rack and through the doors, meeting in the middle inside the car. Yep itsa bit of a nuisance in the cab but I feel happier with it being there.
Cheers John.

 

[Kayak Jack]

Some roof racks are glued on! Meaning that the strength of the bond between paint and metal is part of the fastening system. WTH thought THAT one up?
For what it's worth, I saw a station wagon in a parking lot near a canoe put-in, with the rack sawed off. Evidently he had the boat cable locked to the rack, and the thief had a hack saw and time. Buggar scratched the paint on the car too - thoughtless!